DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

BUIXETTN" 373

THE SMOKELESS COMBUSTION OF COAL 

IN BOILER PLANTS

t

WITH A CHAPTER ON CENTRAL HEATING PLANTS

BY

D. T. RANDALL AND H. W. WEEKS

.WASHINGTON

G O V K K N M E N T P li I N T ING O !<' I1 ' I C E

1909

CONTENTS.

Page.

Introduction............................................................... 5

The problem and its solution............................................ 5

Investigation of industrial plants....................................... 5

Scope and purpose................................................ 5

Summary of conclusions............................................ (i

Personnel......................................................... 7

Method of collecting data.......................................... 7

Sizes of coal....................................................... 7

iDefinition of boiler horsepower...................................... 8

Determination of total heating surface............................... '9

Tests by the Geological Survey......................'................... 9

General statement.................................................. 9

Summary of conclusions............................................ 10

Representative boiler plants burning coal without smoke..................... 11

General statement...................................................... 11

Plants with mechanical stokers ................'.......................... 12

Overfeed stokers.................................................. 12

Chain grates......:................. ^......................... 12

Front-feed stokers.............................................. 34

Side-feed stokers................................................ 48

Underfeed stokers.................................................. 77

Smoke prevention at boiler plants with great variations of load....... 99

Hand-fired furnaces................................................... 99

Smoke observations at Geological Survey fuel-testing plants.................. 139

Tests at Norfolk, Va.................................................... 139

Hand-fired tests................................................... 139

Tests with mechanical stoker....................................... 143

Tests at St. Louis, Mo................................................. 144

Comparison of methods of supplying air for combustion....................... 167

Methods compared.................................................... 167

Relation of efficiency to-capacity with air admitted through grates and by

automatic devices ................................................... 168

Comparison of results from different coals with varied air admission....... 169

Relation of efficiency to capacity with varied air admission.............. 170

Conclusions........................................................... 171

Influence of volatile matter in fuel on the smoke problem.................... 172

Horsepower from different coals............................................. 173

Central heating stations..................................................... 175

General conclusions on smoke abatement. .................................. 184

Bibliography............................................................. 185

Survey publications on coal and fuel testing............................ 185

Miscellaneous publications on smoke abatement. ....... ^................ 186

Index.................................................................... 187

3
ILLUSTRATIONS.

Page. 

FIGURE 1. Chain-grate stoker and Babcock & Wilcox boiler, with uptake in

rear.......................................................... 13

2. Chain-grate stoker and Stirling boiler..................:......... 14

3. Chain-grate stoker and Babcock & Wilcox boiler, with uptake in

front.......................................................... 15

4. Chain-grate stoker and return tubular boiler....................... 16

5. Front-feed stoker and Babcock & Wilcox boiler, usual setting...... 34

6. Front-feed stoker and Cahall boiler.............................. 35

7. Front-feed stoker and Heine boiler............................... 36

8. Front-feed stoker and Stirling boiler ............................. 37

9. Front-feed stoker and return tubular boiler........................ 38

10. Side-feed stoker in Dutch oven and Babcock & Wilcox boiler...... 49

11. Side-feed stoker in Dutch oven and Cahall boiler................... 50

12. Side-feed stoker and Heine boiler................................ 51

13. Side-feed stoker in Dutch oven and Stirling boiler .................. 51

14. Side-feed stoker and Stirling boiler.............................. 52

15. Side-feed stoker and return tubular boiler, elevation.............. 53

16. Side-feed stoker and return tubular boiler, cross section............. 54

17. Underfeed stoker and Babcock & Wilcox boiler.................... 78

18. Underfeed stoker and Heine boiler.............................. 78

19. Underfeed stoker and Stirling boiler.............................. 79

20. Underfeed stoker and return tubular boiler, elevation............. 80

21. Underfeed stoker and return tubular boiler, cross section........... 81

22. Underfeed stoker, plan.......................................... 82

23. Underfeed stoker and Scotch marine boiler....................... 83

24. Load and boiler-service chart of large power plant.................. 100

. 25. Automatic steam and air admission device and water-tube boiler... 103

26. Automatic steam and air admission device and re turn tubular boiler. 104

27. A. hand-fired furnace and Babcock & Wilcox boiler................ 105

28. Down-draft furnace and Heine boiler............... ............. 105

29. A hand-fired furnace and Babcock & Wilcox boiler, elevation ...... 106

30. A hand-fired furnace, plan...................................... 106

31. A hand-fired furnace, cross section................................ 107

32. A hand-fired furnace and Scotch marine boiler, elevation .......... 119

33. A hand-fired furnace, cross section............................... 120

34. A hand-fired furnace and return tubular boiler.......... '. ........ 121

35. A hand-fired furnace and retunrtubular boiler, elevation........... 122

36. A hand-fired furnace, plan....................................... 123

37. A hand-fired furnace and return tubular boiler, cross section....... 124

38. Elevation and plan of setting of hand-fired Heine boiler............ 140

39. Cross section of setting and plan of bridge wall of hand-fired Heine

boiler........................................................ 141

40. Proportion of smoke-producing compounds given off at different

temperatures by several coals................................. 174

4
THE SMOKELESS COMBUSTION OF COAL IN 

BOILER PLANTS.

By D. T. RANDALL and H. W. WEEKS.

NOTE.

The drawings used as a basis for figure 1. (p. 13) and figure 3 (p. 15) of this 

report were supplied by Mr. A. Beraent, of Chicago, and'are slightly modified 

from the form in which they appeared in the Peabody Atlas, edited by Mr. 

Bement and published (Chicago, 1906) by the Peabody Coal Company.

The title line under figure 3, page 15, should read as follows: "FIGURE 3. 

Chain-grate stoker serving a tile-roof furnace designed by A. Bement, with a 

Babcock & Wilcox boiler."

Figure 27, page 105, represents a Dorrance furnace.

The drawings used as a basis for figures 29 and 30 (p. 106) and figure 31 

(p. 107) were reproduced from the Peabody Atlas.

For the drawings used as a basis for other illustrations in this report the 

authors are indebted to the kindness of the Westinghouse Machine Company, 

the Underfeed Stoker Company of America, the Green Engineering Company, 

the Murphy Iron Works, the Water Arch Furnace Company, the Detroit Stoker 

and Foundry Company, Charles J. Dorrance, the Burke Furnace Company, 

James McMillaii & Co., G. S. Calder, and the Hawley Down Draft Furnace 

Company.

tionable. Proper equipment, efficient labor, and intelligent supervision are the necessary factors.

INVESTIGATION OF INDUSTRIAL PLANTS. 

SCOPE AND PURPOSE.

In the investigation of industrial establishments a study was made 

of the conditions in thirteen of the larger cities in Illinois, Indiana, 

Kentucky, Maryland, Michigan, Missouri, New York, Ohio, and Pennsylvania, between 400 and 500 plants being inspected. Sufficient 

information was collected to make the data from 284 plants of value

5
6 SMOKELESS COMBUSTION OF COAL.

for this report. In nearly every city visited coal was supplied from 

points both in and out of the State, so that although but nine States 

were visited, the facts ascertained apply to coals from a greater 

number.

The main purpose of the inspection was to obtain a better knowledge 

as to the influence on smoke production of furnace design and of the 

conditions under which combustion takes place.

SUMMARY OF CONCLUSIONS.

The results of this investigation are set forth in detail on later pages 

of this volume. The general conclusions to be drawn can be summarized in a few paragraphs.

Smoke prevention is possible. There are many types of furnaces 

and stokers that are operated smokelessly.

Any one kind of apparatus is effective only if so set under boilers 

that the principles of combustion are respected. The value to the 

average purchaser of a manufacturer's requirement on this point 

lies in the fact that he is thus reasonably certain of good installation. 

A good stoker or furnace poorly set is of less value than a poor stoker 

or furnace well set. Good installation of furnace equipment is necessary for smoke prevention.

Stokers or furnaces must be set so that combustion will be complete 

before the gases strike the heating surface of the^boiler. When partly 

burned gases at a temperature of, say, 2,500° F., strike the tubes of a 

boiler at, say, 350° F., combustion is necessarily hindered and may be 

entirely arrested. The length of time required for the gases to pass 

from the coal to the heating surface probably averages considerably 

less than one second, a fact which shows that the gases and air must 

, be intimately mixed when large volumes of gas are distilled, as at 

times of hand firing, or the gas must be distilled uniformly, as in a 

mechanical stoker. By adding mixing structures to a mechanical 

stoker equipment both the amount of air required for combustion and 

the distance from the grates to the heating surface may be reduced 

for the same capacity developed. The necessary air supply can also 

be reduced by increasing the rate of combustion.

No one type of stoker is equally valuable for burning all kinds of 

coal. The plant which has an equipment properly designed to burn 

the cheapest coal available will evaporate water at the least cost.'

Although hand-fired furnaces can be operated without objectionable smoke, the fireman is so variable a factor that the ultimate solution of the problem depends on the mechanical stoker in other 

words, the personal element must be eliminated. There is no handfired furnace from which, under average conditions, as good results 

can be obtained as from many different patterns of mechanical stoker, 

and of two equipments the one which will require the less attention
INVESTIGATION OF INDUSTRIAL PLANTS. 7

from the fireman gives the better results. The most economical 

hand-fired plants are those that approach most nearly to the continuous feed of the mechanical stoker.

The small plant is no longer dependent on hand-fired furnaces, as 

certain types of mechanical stokers can be installed under a guaranty 

of high economy, with reduction of labor for the fireman.

In short, smoke prevention is both possible and economical.

PERSONNEL.

This investigation was carried out under the direction of D. T. 

Randall, L. F. Beers and H. W. Weeks procuring most of the data. 

Mr. Weeks has also prepared a large portion of the report. In the 

collection of the information much assistance was given by the city 

smoke inspectors, by manufacturers of boiler-room equipment, and 

by the owners of the plants visited, and to them especial thanks are 

hereby extended for their active cooperation.

METHOD OF COLLECTING DATA.

On entering a city a list was obtained of the plants where mechanical stokers or special devices for hand-fired furnaces were in operation without smoke. Smoke observations were taken on the stacks 

at these plants, or records at the smoke inspector's office were reviewed 

to determine the plants to be visited. The stack was always watched 

at times when the plant was running under average conditions, and 

always without the knowledge of the engineer or fireman. The 

length of the observations varied from one hour to ten hours, although 

a one-hour record determined whether a stack was good or bad. The 

observer usually checked this record by watching the stack during 

several shorter periods while he was in the city.

During the visit to each plant an attempt was made to obtain data 

enough so that the furnace and boiler setting could be duplicated. 

All information except that in regard to drafts and furnace measurements was supplied by the manager or the engineer in charge of the 

plant. The engineer usually knew the approximate amount of coal 

burned per day on heavy and light loads and the number of boilers 

used to carry the load. Draft readings were taken to obtain the 

drop in draft through the boiler and to learn the effective draft which 

burned the coal. Special notice was taken of the methods of operation to determine whether in case the plant was duplicated the same 

results could be expected if it was operated by the average fireman.

SIZES OF COAL.

The size of the coal which was being burned at the various plants 

inspected is stated in the tables as run-of-mine, sized egg or nut, and 

screenings, except for the Illinois plants, where the sizes are given
8 SMOKELESS COMBUSTION OF COAL. 

as Nos. 1, 2, 3, 4, or 5. The standard for sizing coal is not uniform 

over the whole State of Illinois, but in Williamson County washed 

coal is passed over screens with round openings and is sized and numbered as follows:

No. 1, coal passing through 3-inch screen and over If-inch screen. 

No. 2, coal passing through If-inch screen and over 1-inch screen. 

No. 3, coal passing through 1-inch screen and over |-inch screen. 

No. 4, coal passing through f-inch' screen and over J-inch screen. 

No. 5, coal passing through |-inch screen.

About half the washeries in Illinois size coal according to the above 

scheme.

DEFINITION OF BOILER HORSEPOWER.

To determine the percentage of the rated capacity being developed 

it was necessary to assume the amount of coal each plant burned per 

boiler horsepower per hour. To a mechanical engineer the term 

"boiler horsepower" suggests two things a measure of the rate of 

work and a measure of the capacity of the boiler.

Rate of work. The measure of the rate of work of a boiler is based 

on an arbitrary unit of an evaporation of 30 pounds of water per 

hour from a feed-water temperation of 100° F. into steam at 70 

pounds gage pressure. This unit is termed a boiler horsepower, and 

was suggested as of possible value at a time when a good engine had 

a water rate of about 30 pounds per hour. It became so widely 

used that in 1885 it was adopted by the American Society of Mechanical Engineers as a standard for conducting steam-boiler trials. The 

revised code of the society defines it as follows: "The unit of commercial horsepower developed by a boiler shall be taken as 34^ units 

of evaporation per hour that is, 34* pounds of water evaporated 

per hour from a feed-water temperature of 212° F. into dry steam 

of the same temperature. This standard is equivalent to 33,137 

British thermal units per hour. It is also practically-equivalent to 

an evaporation of 30 pounds of water from a feed-water temperature 

of 100° F. into steam at 70 pounds gage pressure." The unit of 

evaporation is thus equivalent to 965.7 British thermal units.

Capacity of boilers. The measure of the capacity or rating of a 

boiler is variable,"there being no standard. Under a proper method 

of rating the proposed rated capacity should be attained when using 

average coal, giving average attention to firing, and using only part of 

the available draft, yet obtaining good economy. T.o rate all boilers, 

whether of the water-tube or fire-tube type or a combination of the 

two, on the basis of 10 square feet of heating surface per boiler 

horsepower is becoming a general practice, as this method comes 

within the required conditions.
TESTS BY THE GEOLOGICAL SURVEY. 9 

DETERMINATION OF TOTAL HEATING SURFACE.

The determination of the total heating. surface with sufficient 

accuracy for ordinary purposes is not difficult. A short approximate 

method for any boiler is to figure the heating surface in the tubes 

and divide it by 0.85 for a return tubular boiler or by 0.90 for a 

water-tube boiler. In case the return tubular boiler has an arch 

over the top for gas passage, giving a so-called third return, it is 

necessary to add from 100 to 200 square feet to the result to obtain 

the total heating surface.

This short method may be proved by two examples, as follows:

(1) Take a return tubular boiler which is 18 feet long and 6 feet 

in diameter, with 72 4-inch tubes. According to Kent, the square 

feet per foot length for a 4-inch tube = 1.047; then 

1.047 X18 X72 = 1,357 square feet in tubes. 

.3.1416X6X18 = 339 square feet in shell.

(3.1416 X9) -(72X3.1416 X0.172) X2 = 44 square feet in tube 

sheets.

339 Hence the total effective heating surf ace = 1357+ ^- +44 = 1570;

1 357 but '-n = 0.863 + , hence approximately 85 per cent of the total 1 ,o i (J

effective heating surface of a return tubular boiler is in the tubes.

(2) Take a Heine water-tube boiler having 116 tubes 3$ inches 

in diameter and 18 feet long and a 42-inch drum 21 feet 6 inches 

long. According to Kent, the square feet per foot length for a 3^-inch 

tube = 0.916; then 0.916x18x116 = 1,912 square feet in tubes. The 

approximate dimensions of the water legs are 6 feet 6 inches by 4 

feet = 26 square feet; the tube area in water legs = 8 square feet; and 

the heating surface in water legs = (26 X 2) (8 X 2) = 36 square

f 4. rm, ff .- u * f i 3.1416X3.6X21.5 reet. The effective heating suri ace m drum= - ^-- =

£

118 square feet. Thus, the total effective heating surface = 

1,912 + 36 + 118 = 2,066 square feet; but ^| = 0 - 925 + > lience

approximately 92 per cent of the total effective heating surface of 

a Heine water-tube boiler is in the tubes. In other types of watertube boilers the ratio was found to be lower; but 90 per cent may 

be assumed as a fair average ratio.

TESTS BY THE GEOLOGICAL SURVEY. 

GENERAL STATEMENT.

During 1904 to 1906 coals from all parts of the, United States were 

burned at the government fuel-testing plant at St. Louis, in furnaces 

which were in the main of the same design. Most of the tests a

a For descriptions of the plant and tests see Bull. U.S. Geol. Survey Nos. 201, 290, 323, and 332.
10 SMOKELESS COMBUSTION OF COAL.

were made on a hand-fired furnace under a Heine water-tube boiler. 

The lower row of tubes of the boiler supported a tile roof for the 

furnace, giving the gases from the coal a travel of about 12 feet before 

coming into contact with the boiler surface. This furnace is more 

favorable to complete combustion than those installed in the average 

plant. A number of coals were burned in this furnace with little or no 

smoke, but many coals could not be burned without making smoke 

that would violate a reasonable city ordinance when the boiler was 

run at or above its rated capacity. Boilers having furnaces installed 

under less favorable conditions will give off more smoke.

In 1907 the steaming section of the St. Louis plant was moved to 

Norfolk, Va., where subsequent tests of this nature have been made. 

The plant at Norfolk was equipped with two furnaces one fired by 

hand and the other by a mechanical stoker. Both were operated 

under Heine boilers.

In the course of the steaming tests at St. Louis and Norfolk some 

special smoke tests were made and the influence of various factors 

in smoke production was noted. As the tests were made as far as 

possible under standard conditions, with a minimum of variation in 

boiler-room labor, the results bring out the importance of other factors such as character of fuel and furnace design. /

SUMMARY OF CONCLUSIONS.

A detailed discussion of these tests, with numerous tables, is 

presented on pages 139-167 of this volume. A brief summary of the 

general conclusions is as follows:

A well-designed and operated furnace will burn many coals without smoke up to a certain number of. pounds per hour, the rate varying with different coals, depending on their chemical composition. 

If more than this amount is burned, the efficiency will decrease and 

smoke will be made, owing to the lack of furnace capacity to supply 

air and mix gases.

High volatile matter in the coal gives low efficiency, and vice versa. 

The highest efficiency was obtained when the furnace was run at 

low capacity. When the furnace was forced the efficiency decreased.

With a hand-fired furnace the best results were obtained when 

firing was done most frequently, with the smallest charge.

Small sizes of coal burned with less smoke than large sizes, but 

developed lower capacities.

Peat, lignite, and subbituminous coal burned readily in the type 

of tile-roofed furnace used and developed the rated capacity with 

practically no smoke.

Coals which smoked badly gave efficiencies 3 to 5 per cent lower 

than the coals burning with little smoke.

Briquets were found to be an excellent form for using slack coal 

in a hand-fired plant. They can be burned at a fairly rapid rate
PLANTS BURNING COAL WITHOUT SMOKE. 11

of combustion with good efficiency and with practically no smoke. 

High-volatile coals when briquetted are perhaps as valuable as lowvolatile coals when not briquetted.

A comparison of tests on the same coal washed and unwashed 

showed that under the same conditions the washed coal burned 

much more rapidly than the raw coal, thus developing high rated 

capacities. In the average hand-fired furnace washed coal burns 

with lower efficiency and makes more smoke than raw coal. However, washed coal offers a means of running at high capacity, with 

good efficiency, in a well-designed furnace.

Forced draft did not burn coal any more efficiently than natural 

draft. It supplied enough air for high rates of co.mbustion, but as 

the capacity of the boiler increased the efficiency decreased and the 

percentage of black smoke increased.

Most coals that do not clinker excessively can be burned with l

to 5 per cent greater efficiency and with a smaller percentage of 

black smoke on a rocking grate than on a flat grate.

Air admitted freely at firing and for a short period thereafter 

increases efficiency and reduces smoke.

As the CO in the flue gas increases the black smoke increases; the 

percentage of CO in the flue gas is therefore, in general, a good guide 

to efficient operation. However, owing to the difficulty of determining this factor, combustion can not be°regulated by it.

The simplest guide to good operation is pounds of coal burned per 

square, foot of grate surface per hour.

REPRESENTATIVE BOILER PLANTS BURNING COAL 

WITHOUT SMOKE.

GENERAL STATEMENT.

Bulletin 334, the preliminary report on smokeless combustion, 

takes up information collected and conclusions reached while assembling the data summarized in the present report and sets forth many 

facts of general interest that are not discussed in the following pages. 

This paper deals especially with the equipment of particular boiler 

plants which were found to be burning coal without smoke, and with 

the essentials of good furnace design. A brief summary of the general 

conclusions is presented on pages 171-172. The details on which 

these conclusions are based are set forth in the following pages.

For the sake of clearness the important features of the equipment 

of the boiler plants visited are stated in tabular form.

Although there were very few plants at which' all the items covered 

by the tables could be ascertained, the more essential details those 

bearing directly on the subject of smoke prevention were obtained 

at nearly every plant. The density of the smoke is stated on a 

percentage basis, 0 meaning a clean stack and 100 per cent meaning 

dense black smoke.
12 SMOKELESS COMBUSTION OP COAL.

In the tables the furnace dimensions are checked by letters from A 

to H, which refer to the dimensions indicated by the corresponding 

letters on the illustrations showing typical installations of furnaces 

under boilers of various types. These illustrations are intended to 

show especially the average and the minimum travel of the gases 

from the fire to the first cooling surface in the boiler, the height of the 

furnace, and the length of the coking arch.

In the- illustrations some makes of boilers appear more frequently 

than others. This does not imply any preference for certain models. 

Boilers of widely differing patterns have shown equal efficiency in 

steaming trials, and it is coming to be a general belief that among the 

types of boilers ordinarily used at power plants peculiarities of tube 

arrangement count for less than proper furnace design. This report 

of what has been done to effect smokeless combustion emphasizes the 

importance of furnace design and management and makes no comparisons between boilers. The illustrations show details of furnace 

construction and the importance of certain features.

For convenience of treatment the following order is adopted in 

discussing the equipment of the various plants:

Mechanical stoker plants, 

(a) Overfeed stokers.

1. Chain grates.

2. Front feed.

3. Side feed. 

(6) Underfeed stokers.

Hand-fired plants.

(a) Furnaces under water-tube boilers. 

(6) Furnaces under return tubular

boilers. 

" 1. Down-draft furnaces.

2. Furnaces using steam, jets.

3. Furnaces with miscellaneous 

equipment.

PLANTS WITH MECHANICAL STOKERS.

The use of mechanical devices for firing coal reduces labor in the 

boiler ropm, but the main object of mechanical stoking is to feed a 

steady, regulated supply of coal and air to the furnace. The advantages of feeding a fire steadily were seen in the early days of 

steam engineering, but defects in design or faulty installation and 

management kept mechanical stokers from coming into general use. 

Within the last decade, However, their use has greatly increased. 

They are of two general types overfeed and underfeed.

OVERFEED STOKERS. 

CHAIN GRATES.

GENERAL DISCUSSION.

The earliest mechanical stoker was of the treadmill type, so called 

because the arrangement of the grate bars as a traveling belt resembled 

the apron of a treadmill. It was patented in England as far back as 

1841. Improved in details of construction, this.type, under the 

name chain grate, has come into extensive use in this country. The 

coal is fed from a hopper, which extends the entire width of the grate
PLANTS WITH MECHANICAL STOKERS. 13

and has a plate at the back for regulating the depth of the bed of 

coal, to a continuously revolving grate, the top of which is made to 

move from front to rear by power applied to the front or rear sprocket 

shaft. As usually installed, the surface of the grate is horizontal, but 

occasionally chain grates are given a slight incline. Back of the 

hopper and extending over the whole width of the grate is a fire-brick 

arch. The length of this arch differs in plants equipped by different 

makers, but the present tendency is to lengthen the arch and to proportion its length and slope to the grade of coal to be used.

In operation, coal from the hopper begins to ignite as it passes 

under the arch and the grates carry the burning coal toward the bridge

FIGURE 1. Chain-grate stoker and Babcock & Wilcox boiler with uptake in rear.

wall at a rate which permits complete combustion before the chain 

passes the rear sprocket and the refuse falls into the ash pit below.

The majority of the stokers of this type are particularly adapted to 

a free-burning coal high, in volatile matter, such as is mined in the 

central and western fields, and give less satisfaction with the higher 

fixed carbon coking coals of the Appalachian field. As they can burn 

the poorest grades of noncoking coal with complete combustion, 

they offer a valuable means of producing cheap power. At all the 

plants visited where these stokers were in use small coal was burned.

As has been said, the chief difference at present among chain grates 

as put in by the various makers is in the length of the fire-brick arch.

In many water-tube boilers this arch is made short, and the gases 

of combustion-are led to the tubes by the shortest path. A furnace 

and boiler with stoker thus set are shown ,in figure 1. In this setting
14 SMOKELESS COMBUSTION OF COAL.

the distance of travel for the gases from the grates to the tube heating 

surface, indicated by the line B, is reduced to a minimum and the 

average distance from the fire to the first cooling surface encountered 

(A) approaches a minimum.

This type of installation is common in the Middle West, where a 

higher proportion of chain grates is in use than in any other section 

of the United States, but the short arch and the brief travel of the 

gases to the first tube heating surface are features unfavorable to 

smokeless combustion.

A water-tube boiler of another make with furnace fed by chain 

grates is shown in figure 2.

FIGURE 2. Chain-grate stoker and Stirling boiler.-

A method of setting designed to lengthen the travel of the combustible gases from the bed of coal and allow them to mix and be 

completely burned before entering the boiler is shown by figure 3. 

Here the type of boiler illustrated by figure 1 is baffled, so that the 

uptake is'in front; the fire-brick arch over the grates is.no longer 

than in the other furnace, but it is supplemented by the bottom 

baffling made of C tile supported by the water tubes, so that the 

least distance from grates to tube heating surface is three times as 

long as in the mounting shown in figure 1. The bottom baffling,
PLANTS WITH MECHANICAL STOKERS. 15

though it can not, on account of its construction, become as hot as 

the ignition arch, has slight chilling effect, and there is ample opportunity for complete combustion before the gases reach the first cooling 

surface.

Comparatively few chain-grate stokers were found under tubular 

boilers. An example of the usual setting is given in figure 4. Here, 

while the ignition arch is short and the shell of the boiler has a cooling 

effect, the average distance from the grates to the beginning of the 

tube heating surface is so long that smokeless combustion can be

FIGURE 3. Chain-grate stoker and Babcock & Wilcox boiler with uptake in front.

obtained with ordinary care in operation. In the journey from the 

grate to the rear of the boiler the cooling effect of the boiler shell, 

though not negligible, is much less than it is often thought to be, 

inasmuch as the area exposed is not more than that of eight or nine 

tubes.

DETAILED DESCRIPTION OF PLANTS.

"In the course of the field investigation 57 plants, ranging from 300 

to 9,600 rated boiler horsepower, at which chain grates were installed 

were visited. The detailed information collected regarding these 

plants is presented in Table 5 (pp. 19-32), but some of the more 

important facts to be gained from a study of that table are summarized here.
16 SMOKELESS COMBUSTION OF COAL.

The coals used, all small sizes, came from five different States and 

the average depth of fire in burning them ranged from 4.5 to 6 inches.

The kind of coal and the depth of fire are given in Table 1, which 

incidentally shows that the chain-grate stoker has been found to work 

remarkably well with Illinois coals.
PLANTS WITH MECHANICAL STOKEES. 17 

TABLE 1. Kind of coal and depth of fire at plants with chain grates.

Kind of coal.

Illinois.......................

Number 

of 

plants, a

21

8

8

Average 

depth of 

tore.

' Inches. 

5

5

4

Kind of coal.

Ohio.........................

Number 

of 

plants.o

6

6

10

Average 

depth of 

lire.

Inches. 

5

4.5

6

a Two plants burned both Indiana and Illinois coal.

Forty of these plants maintained uniform loads; the remainder 

had to carry variable loads. At 18 per cent of the plants the stokers 

were under boiler units of 200 horsepower or less and at 69 per cent 

they were under units of 300 horsepower or less. The average boiler 

horsepower developed, the boiler being rated on 10 square feet of 

heating surface per horsepower, ranged from 23 to 158, the average 

being 93. The ratio of square feet of heating surface to square feet 

of grate surface varied from 33 to 1 to 88 to 1, the average ratio being 

50 to 1.

The height of the ignition arch at the front of the furnace ranged 

from 0.9 to 1.1 feet, and the height above the grate at the rear of the 

arch from 1.3 to 2.2 feet. In 16 plants out of 46 the forward ends of 

the stokers were some distance in front of the boiler. The average 

height of the ignition arches above the grates is given in Table 2.

TABLE 2. Average height of arch at front and rear at plants with chain grates.

 Type of boiler.

Stirling ........................................................

At front of furnace.

Average 

height 

of arch.

Feet. 

1.1 

1.1 

1.1 

.9 

1 

1.1

Number 

of plants 

at which 

measured.

6 

13 

6 

16 

3 

5

At rear of furnace.

Average 

height 

of arch.

Feet. 

1.7 

1.5 

1.6 

1.5 

1.3 

2.2

Number 

of plants 

at which 

measured.

6 

13 

5 

14 

3 

6

The coal as received burned per square foot of grate per hour of 

average heavy load ranged from 11.4 to 39 pounds, the average 

being 23.3 pounds.

Table 3 presents in more impressive form some of the particulars 

recapitulated above. It was compiled to show that with chain-grate 

stokers installed under 10 types of boilers (five different makes of 

water-tube boilers are included under "Miscellaneous") which were 

run. at about their full capacity, at no plant was there any serious 

emission of smoke, combustion being practically smokeless. As

74897 Bull. 373 09 2
18 SMOKELESS COMBUSTION OF COAL.

bearing on the proper length of travel of the burning gases for coals 

from different States, the least and average distances from grates to 

tube heating surface are given.

TABLE 3. Summary of various observations at plants with chain grates.

Type of boiler.

Aultman & Taylor. 

Babcock & Wilcox.

Stirling..............

Miscellaneous watertube.

Kind of coal.

Illinois, Ohio, and 

. Pennsylvania. 

Illinois, Kentucky, 

Ohio, and Pennsylvania.

Illinois, Indiana, Kentucky, and Ohio. 

Indiana, Kentucky, 

and Pennsylvania. 

Illinois, Kentucky, 

Pennsylvania, and 

Indiana.

Number of 

plants.

7 

12

7 

18

5 

8

Furnace 

draft.

Inch of 

water. 

0.23

 .21

.22 

.19

.20 

.15

Coal 

burned 

per 

square 

foot of 

grate surface per 

hour, 

average 

heavy 

load.

Pounds. 

19.4

24.0

21.2 

23.5

20.2 

24.9

Percentage of 

rated 

boiler horsepower developed, 

average 

heavy 

load. a

83

88

113 

94

104 

108

Distance 

from grates 

to tube 

heating 

surface.

Average.

Feet. 

5.2

5.2

8.4 

7.0

8.3 

19.0

Minimum.

Feet. 

3.2

3.3

6.4 

4.9

5.5 

14.7

Black 

smoke.

Per ct. 

4.4

2.7

0.5 

5.4

7.5 

2.8

a Boiler rated on 10 square feet of heating surface perhorsepower.

The draft measurements at the plants with chain grates are summarized in Table 4.

TABLE 4. Summary of draft measurements at plants luith chain grates.

Type of boiler. Measurement taken at 

Base of stack. .....................................

Furnace ..........................................

Furnace ..........................................

Number 

of plants 

at which 

taken.

5

6

3

12

5

5

2

4

18

17

7

G

4

2

8

4

3

Average 

draft 

(inch of 

water).

0.23

.46

.71

.21

.34

.57

.22

.58

.77

.19

.47

.96

.20

.41

.60

.15

.43

.81

Average furnace draft, 54 plants, 0.19 inch of water; range, 0.07 to 0.45 inch. Average draft at rear of boiler, 40 plants, 0.43 inch of water; range, 0.11 to 0.94 inch. Average draft at front tube sheet, 4 plants, 0.43 inch of water; range, 0.25 to 0.61 inch. 

Average draft at base of stack, 24 plants, 0.77 inch of water; range, 0.26 to 1.30 inch. 

These figures show approximate average drafts as follows: Furnace, 0.20 inch of water; 

rear of boiler, 0.45 inch; base of stack, 0.80 inch. These results give a drop in draft 

through the boiler of 0.25 inch of water and a drop from boiler to stack of 0.35 inch.
TABLE 5. Details of observations at plants with c

No. of 

plant.

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39

State.

Ohio..................

.....do................

.....do................

.....do................

.....do................

.....do................ 

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

Illinois. ...............

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

Kentucky.............

Kind of stoker.

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Babcock & Wilcox; Green. .

.....do......................

.....do......................

McKenzie bar. ..............

American

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Green.......................

Total 

builder's 

rated 

horsepower.

700 

1,100 

1,000 

825 

500 

600 

600 

1,440

500 

655 

595 

450 

3,600 

2,184 

1,200 

500 

310 

300 

2,700

1,000 

750 

600 

1,260

1,800 

. 1,500 

1,050

800 

800 

608 

600 

600 

400 

1,520

675 

495 

201 

620

Commercial name.

 Pittsburg No. S. ........

.....do..................

Washed................. 

.....do..................

Duquoin; Springfield . . .

Wher

Ohio......

Ladd, 111

Carterville, 

.....do.... .

Belmont Co

Monongahel

.....do.....

Williamson 

counties, 1

Carterville, 

.....do....

.....do....

.....do....

Indiana; Illi

.....do.....

.....do....

.....do....

Western Ke
TABLE 5. Details of observations at plants with chain 

No. of 

plant.

40

42

40

AC.

47

AQ

49

^

51

CO

CO

S4

55

56

57

State.

Ohio..................

.....do................

.....do................

......do................

.....do................

Kind of stoker.

.....do......................

Green

.....do......................

.....do......................

.....do......................

.....do......................

S. andS....................

.....do......................

Total

rated 

horsepower.

300

3,400

1,170

9, COO

1,000

924

400

350

1,000

1,584

1,400

750

w>

300

300

600

4,000

400

Commercial name.

.....do..................

.....do..................

.....do..................

Whe

.....do...

.....do...

.....do...

Collinsville

.....do...
TABLE 5. Details of observations at plants with chain gra

No. of 

plant.

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 24' 

25 

26 

27 

28 

29

Load.

Requirement.

Power and light. ............

.....do.......... ...........

.....do......................

.....do......................

.....do......................

Power and heat .............

.....do......................

.....do.. ....................

.....do.............*.........

Power and light. . ...........

.....do.....................

.....do......................

.....do.....................

Nature.

Uniform.-. ............. 

.....do.................

....do.................

....do.................

.....do.................

......do1 .................

Variable...............

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Character.

.....do......................

.....do......................

.....do......................

Office building ..............

... .do... ............:......

.....do......................

.....do......................

.....do......................

Department store. ..........

Factory. ....................

Packing house ..............

Average lo

Heavy.

Hours 

per 

day 

load 

is on 

plant.

24 

24 

10

24 

24

24 

9 

10 

5 

24 

10 

10 

24 

24 

10 

10 

24 

9 

14 

11 

24 

8.5 

12 

10 

10 

24 

11 

14

Coal 

burned 

per 

day 

(short 

tons).

16 

17. 

21 

30 

27

24 

40 

32 

3.5 

32 

7.5 

7.3 

50 

58.6 

13.3 

10.4 

18 

7.5 

112 

50 

25 

20 

6 

35 

15 

110 

25 

38

Ho

p

d

lo

is 

pla

2

2

2

2

' Boiler rated on 10 square feet of heating surface pe
TABLE 5. Details of observations at plants with chain g

No. of 

plant.

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

50 

' 57

Load.

Requirement.

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do. .....................

.....do......................

.....do......................

Nature.

»

.....do.................

.....do.................

.....do.................

.....do.................

.....do.:...............

.....do.................

.....do..................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Character.

Shops and car heating. . .....

Packing house ..............

Office building. . ............

Packing house ..............

Factory. ....................

Mill.........................

Brewery ....................

Depot.......................

Mill. ........................

.....do......................

Store building. ..............

Commercial .................

Mill.........................

. . . ..do......................

Mill.........................

Factory. ....................

Shops.......................

Pumping station. ...........

Office building ..............

Refrigeration ...............

Factory. .....................

Laundry. ..................'.

School building. ............

Ice plant. ...................

Waterworks. . ...............

Foundry and ironworks.. . . .

Average l

Heavy.

Hours 

per 

day 

load 

is on 

plant.

24 

24 

12 

24 

12 

10 

24 

24 

24 

24 

11.5 

24 

12 

24 

10 

24 

24 

24 

24 

24

24 

10 

11.5 

20 

24 

24

Coal 

burned 

per 

day 

(short 

tons).

50 

25 

10 

25 

10 

60 

26 

18 

7.5 

40 

3.5 

116 

24 

350 

22 

65 

23 

25 

48 

35

30 

16.5 

4.5 

7 

29.5 

151

H

l

i

p
TABLE 5. Details of observations at plants with chain g

No. of 

plant.

1 

2

3 

4 

. 5 

6 

7 

8 

9 

10

11

12

13 

14 

15 

16

17 

18 

19

20

21

22 

23

24 

25 

26 

27

Thickness 

of 

'fire 

(inches).

3 

4.5

4-4.5 

3-4 

4 

6-7 

4-5 

6 

4-10 

3.5-4

3-5

4-4.5

4-8 

4-6 

4-5

4-5

3 

4-S 

3-5

6-8

3-6

5-7 

4

4 

6 

4-5 

6.5

Boilers. 

Type.

Aultman & Taylor water-tube. . 

...:.do... .......................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Babcock & Wilcox water-tube.. 

.....do..........................

.....do..........................

Babcock & Wilcox; Henry \rogt

Babcock & Wilcox water-tube. . 

.....do..........................

.....do..........................

. ..do..........................

fBabcoek & Wilcox; Stirling 

\ water- tube.

.....do..........................

.....do..........................

.....do..........................

Mohr and Heine water-tube. . . .

.....do..........................

.....do..........................

Size.

168 4" tubes; 2 48" x 20i' drums .............

126 4" x 18' tubes. ...........................

126 4" x 18' tubes. ...........................

126 4" x 18' tubes. ...........................

144 4" x 18' tubes, 2 36" x 20.2' drums .......

126 4" x 18' tubes, 2 36" drums ..............

Babcock <fe Wilcox, C3 4" x 18' tubes; 1 drum.

1-126 4" x IS' tubas, 2-72 4" x IS' drums ..... 

72 4" x 18' tubes. ............................

140 4" x IS' tubes. ...........................

\192 4" x 18' tubes. ...........................

142 4" x IS' tubes. ...........................

72 4" x 18' tubes. ............................

72 4" x IS' tubes. ............................

138 34." x IS' tubes, 1 48" x 20f drum ........

Mohr, 140 34" x 18' tubes; Heine, 138 34" x IS' 

tubes. 

138 34" x 20' tubes. ..........................

278 34" x IS' tubes, 2 42" drums. ............

223 3 J" tubes, 3 42" x lOjV drums ...........

192 3i" tubes, 342"xlO' drums. .....:......

Number 

installed.

2

4

4 

3 

2 

2 

2 

6 

3 

2

4

3

3 

12

S

3

2 

2 

2

S

5

4 

3

2 

3 

6 

6

Nu

Ave

hea

loa
TABLE 5. Details of observations at plants with chain g

No. of 

plant.

28 

29 

30 

31 

32 

33 

34

35

38 

37 

38 

39 

40

41

42

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55

56 

57

Thickness 

of 

fire 

(inches).

4 

6-8 

3 

4-6 

3-3.5 

4-6 

3-5

4-4.5

4 

4.5 

5.5 

3.5-4 

4.5

4.5

4.5-5

7 

3-5 

3 

3.5-4 

3 

4 

8 

5-6 

6 4 ' 

4-6 

4-5 

3.5

4

7

Boilers.

Type.

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

..:..do..........................

.....do..........................

.....do..........................

.....do..........................

.....do...........................

Heine and Stirling water-tube..

.....do..........................

.....do..........................

Cahall horizontal water-tube. . . .

.....do..........................

.....do..........................

.....do..........................

^Return tubular and Bronson 

\ special fire-tube.

i 

Size.

220 3"-87" x 16' tubes, 4 30" x 12' drums ..... 

102 3J"-72" x 18' tubes, 16 4" water tubes. . . . 

72" x 20'-84 4" tubes, 16 4" water tubes ..... 

72" x 18', 72 4" tubes ........................

72" x 18', 27 6" tubes ........................

72"xl8', 72 4" tubes........................

|lO 84"x 18', 176 3", 6 90" x 18', 184 3", and 13 4". 

72" x 16', 70 4" tubes ........................

Number 

installed.

3

2 

4 

2 

2 

3 

1

5

3 

3 

1 

2 

2

8

4

24 

4 

3 

1 

1 

4 

6 

4 

3 

2 

2 

2 

4

16 

4

N

Av

he

lo

Va

Usually.
TABLE 5. Details of observations at plants with chain g

No. of 

plant.

1 

2 

3 

4 

5 

6 

7 

S 

9 

10 

11 

12 

13 

14 

15 

16 

17 

IS 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

Furnaces.

Number.

2 

4 

4 

3 

2 

2 

2- 

6 

3 

2 

4 

3 

3 

12 

8 

3 

2 

2 

2 

10 

5 

4 

3 

2 

3 

6 

5 

3 

2 

4 

2

Kind.

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.:...............................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do....................:...;........

.....do.................................

.....do.................................

.....do.................................

Tile roof ...............................

Plain ..................................

:....do.................................

.....do..................................

.....do.................................

.....do.................................

.....do................................

.....do.................................

Grate area per 

boiler (square 

feet).

54.4 

67, 28 

45.5 

59.5 

52 

58.5 

72, 25 

58.5 

63 

54 

31.5, 36 

IS, 45 

IS, 19. S 

50.4 

59.4 

63.8, 81 

67.3 

28, 25. 3 

28 

72, 76. 5, 94. 5 

88, 93. 5, 71. 5 

50 

76.5, 72 

54 

90 

63 

63 

, 67.5 

94.5 

54 

67.5

Distance from grates to 

tube heating surfa'ee.

Average (A).

5.5 

4.0 

6.0 

4.5 

6.0

4.2 

6.5 

5.25 

65.1, 

5.0 

4.5 

4.0 

6.0 

66, S 

6.0 

5.5, 4.5 

5.0 

<=6. 7, 4.3, 6.8 

18.0 

5.3 

4. 0, 16. 0 

11.5 

4.3 

8.7 

7.3 

7.3

6.5 

6.7

Minimum 

(B).

2.5 

2.5 

4.0 

2.5 

4.3

3.3 

4.0 

3.8 

63.75, 

2.5 

3.0 

3.5 

3.5 

3.5 

3.5 

3. 0, 2. 0 

3.5 

e 4. 0,3.3, 4. i 

14.0 

 4.0 

3.25, 13.5 

7.0 

3.6 

6.0 

5.6 

5.0

4.5 

4.5

Width 

furnace 

aS, 

63

c3.0, 

67.5

 =8.0,8.5

S.O, 8.5

S. 5

First dimension applies to large boiler. 6 First dimension applies to Babcock & Wilcox b
TABLE 5. Details of observations at plants with chain 

No. of 

plant.

32 

33 

34 

35 

36 

37 

38 

 39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

56 

57

Furnaces.

Number.

2 

3 

' 1 

5 

3 

3 

1 

2 

2 

8 

4 

24 

4 

3 

1 

1 

4 

6 

4 

. 3 

2 

2 

2 

4 

16 

4

Kind.

Plain ..................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do.............. . . ..............

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do .................................

Plain..................................

Tile roof. ..............................

.....do ................................

Plain ..........:........................

.....do .................................

.....do.................................

Plain and tile -roof .....................

Plain..................................

Grate area per 

boiler (square 

feet).

54 

45 

90 

74.4 

68.9 

33.2 

56 

74.3 

39.1 

81 

67. 5, 54 

84 

49 

68 

90 

72 

42 

51.6 

67.5 

54 

54 

36 

36 

36 

42 

31.5

Distance from grates to 

tube heating surface.

Average (A).

as

6.7 

8.2 

6.8 

6.25 

6.0 

6.5 

6.0 

6.0 

«3.0, 7.5 

'8.5 

8.0 

10.0 

4.1

10.5 

8.5 

17.5 

7.5 

6.5 

17.0 

5.0 

18.0 

c21, 22 

18.5

Minimum 

(B).

4.3 

4.7 

5.5 

5.8 

.4.6 

4.4 

4.5 

4.2 

6.'0 

02.5, 4.5 

4.0 

5.7 

6.0 

3.9

6.5 

5.5 

13.0 

3.5 

2.5 

14.0 

4.1 

13.5 

«16, 17 

14.5

Widt

furnace 

67.5

a First dimension applies to Heine boiler. 6 First dimension applies to large boiler. 
TABLE 5. Details of observations at plants with chain gr

No. of 

plant.

1 

2 

3 

4

5 

6

7

8 

9

10 

11 

12 

13 

14 

15 

Iti 

17 

18 

19 

20

21 

22 

23

24 

25

 o

Draft.

Kind.

Chimney. .

....do.....

....do.....

....do..... 

....do.....

....do.....

....do.....

....do.....

....do..... 

....do.....

....do..... 

....do.....

....do.....

....do.....

Induced... 

Chimney. . 

....do..... 

....do.....

Chimney. . 

....do..... 

....do.....

....do..... 

....do.....

....do.....

Readings (inches of water).

Furnace.

0.26 

. 23- . 27 

. 13- . 15 

. 12- . 23

. 25- . 27 

.30

. 15- . 36 

.40

.13 

. 03- . 11 

. 09- . 17 

. 18- . 30 

. 10- . 20 

. IS- . 36

. 19- . 70 

. 06- . 07 

.12 

. 17- . 25 

. IS- . 32

. 21- . 23 

.18 

Very low.

.24 

.20

.12

Rear of boiler.

0. 40-0. 48 

. 45- . 73 

.25 

. 19- . 30

.54- .£3 

.48- .58

. 55

. 35- . 48 

.75

.24 

. 08- . 14 

. 14- . 18 

. 25- . 36 

. 16- . 33

. 45-1. 10 

. 12- . 15 

. 19- . 21 

. 28- . 37

. 74- . 78

Front 

tube 

sheet.

Breeching.

* 0. 82

..........

-

.73

. 47- . 62

1.30

.45 

.23

- ' .80

. 36-. . 78

i

.40 

Combustion 

chamber, .31. 

Lower, .40; upper, .50.

%

Near stack 

2.00

.60

.92

.es

Base 

of

stack.

0.85

.eo

.67

.32

.97

.60

.42

.52

.80

.eo

.63

1.04

Conditions under which 

readings were taken.

Draft varied by thickness of 

fire.

Dampers open; rear IV of 

grate bare. 

Damper open; rear half of 

grate bare.

Dampers partly closed; thin 

fire. 

Dampers open; thin fire. ....

Dampers open ; economizer 

in use.

Dampers open; rear onethird of grates bare.

Dampers one-half open; rear 

of grates bare. 

Damper open ; rear one- third 

of grates bare.
TABLE 5. Details of observations at plants with chain g

No.of 

plant.

27 

28 

29 

30 

31 

32 

33 

34

35 

36

37 

38 

39 

40 

41 

42

43

44 

45 

46 

47 

48

Draft.

Kind.

Chimney.. 

....do.....

....do..... 

.....do..... 

'....do..... 

....do.....

....do.....

....do..... 

....do.....

Induced...

Chimney.. 

....do..... 

....do.....

....do.....

....do.....

....do..... 

....do..... 

....do.....

....do..... 

....do..... 

....do..... 

....do.....

Readings (inches of water).

Furnace.

0. 18-0. 32 

. 17- . 18 

. 17- . 18 

. 04- . 17 

.28, .29 

. 08- . 10 

.14- .17 

.11

.23- .32 

.09- .15

.27 

. 36- . 35 

.11 

.13 

.18 

. 14- . 23

. 19- . 25 

. 31- . 44

.11- . 14 

.09 

 . 12 

. 17- - 26

Rear of boiler.

Lower rear, 

0. 48-0. 64. 

Lower rear, 

.38- .41. 

Lower rear, 

 33- . 38. 

Lower rear, 

. 16- . 40. 

Lower, .48; upper, . 90. 

Lower rear, . 25

Lower, .27- .28; 

upper, .48- .66 

Lower, .32; upper, . 63. 

Lower rear, . 58 

Lower rear, 

.31- .33. 

. 56- . 61 

Lower rear, . 56 

Lower rear, . 52 

.47

Lower rear, 

. 80-1. 08. 

Lower rear, 

. 65- . 77.

.58- .67 

.36 

.30

Front 

tube 

sheet.

Breeching.

.52

.85

.72

.97

.72

.70

. 34- . 90

.70

Base 

of 

stack.

.84

.68

1.12

.90 

.78

1.10 

1.30

.94

26

Conditions under which 

readings were taken.

Dampers open; rear of grates 

bare.

Thin fife; running conditions

Damper open; rear half of 

grate bare.

Damper open; rear one-third 

of grates bare.

.....do...............I......

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................
49

50

51

19

53

54

55

56

57

....do.....

....do.....

....do.....

....do.....

....do.....

.25

. 10- . 13

.12

.17

.10

. 20- . 30

. 12- . 13

. 10- . 18

. 18- . 20

.35

chamber,. 14-.26

0.52

.25

. 45- . 77

.20- .45

.80

1.20

.86

1. 10-1. 50

.56

.62

.55

1.25

.63

third of grates bare.

Several. 6 Various lengths. 
TABLE 5. Details of observations at plants with chain g

No. of 

plant.

1

2 

3

4

5

6

7

8 

9

10 

11

12

13 

14

15 

16

17

18

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet).

5

9 

4

10

10

6 

0

28 

22

16. 

17

13

13 

0

90 

3

0 

13

Size 

(feet).

4x7

9 x 5J 

6x 12

0

Place at which 

measurement 

was taken.

.....do...........

Number 

of elbows 

between 

boilers 

and 

stack.

0

0 

1

0

1

0 

0

0 

0

1 

3

1

2 

0

0

2

0 

1

Stack.

Height 

(feet).

125

216 

150

175

125

175 

135

185 

275

116

85

110

90 

2(fo

200 

95

110 

100

Size 

(feet).

a5.4

0.5 

8.0

6.0

a 5.0

a5.5 

aS.O

8.0 

8.0

o2.5 

3.8 x 3.S

a 4. 5

11

9.0 

5.0

a 4. 6

Area 

(square 

feet).

23.0

33.2 

50.25

28.3

19.6

23.7 

50.25

50.25 

50.25

4.9 

14.7

15.9

95.0

63.6 

19.6

12.56

Ignition arch.

Length 

(feet).

4.5 

3.5

3.5

5.0 

3.0

6.5

4.0 

4.0

3.0

3.5

5.0 

3, 3.5

3.0 

3.5

Style.

Sprung..

Sprung. .

Flat.....

...do..... 

Sprung. .

Usual

per 

Coal ru

wide 

Range 

An 

thro

from 

Coal a

cons

Usuall

When 

smo

bad 

Stack 

Before 

the 

On he

On ac

heav

cons

Coal a

2 pe

rated 

Stack 

Coal a

cent

stack

Coal a

Babco

grate

and 
23

24

25

28

29

30

31

32

33

34

35

38

?8

1?06

11

154

?28S003

30 

310s

22 004

7x9

Ai -v *\1

7x9

SJxll

4x8

00

o5i o4"0

4x6 00

....do..........

.....do..........

Near stack. ..... 

.....do..........

Near stack......

11001

2 0100

0 000

1 1010001

108 

119 

200

150

150

115 

200

225

185

150

140 

110

125

130

125 

11.0 

135

40 

136

110

125 

125

a4.0 

10 

9.0

7.0

3. 25 x 6

a4.0 

9.0

9.0

9.5

6.0

10.0 

4.0

05.0

2.5x2.5

a 5. 5 

3.8x3.8 

4.0

a 4.0 

a6.0

a 3. 5

a 4. 5 

a 4.0

12.56 

78.5 

63.6

38.5

19.5

12.56 

63.6

63.6

70.6

28. 3

78. 5 

12. 56

19.6

6.3

23.7 

14.4 

12.56

12.56 

28.3

9.6

15.9 

12.56

63.6

38.5 

19.5

12.56 

63.6

63.6

70.6

28.3

12. 56

19.6

6.3

23.7

14.4

12.56

12.56 

28.3

9.6

15.9 

12.56

3.6

4.0 

f Mohr, 4.0

3.5 

4.0

3.5

3.5

3.5

3.6

4.0 

3.5

3.0

3.5 

3.5

Sprung..

Flat.....

Flat.....

Sprung. . 

Flat.....

Sprung..

Flat..... 

Sprung..

Boilers h

Dampe

20 per 

U tile on 

inches 

not inc

each bo

burnin

C tile on 

vertica

'C tile on 

Coal as f

5 feet o

is so co

This sta

minute

Coal as 

baffled 

boiler 

at ratin

Dry coal 

cent o

on ma

Two sim

runs f

many 

contin

Coal is w

of boil

Two sim

of dam

Coal we

Separate 

someti

usuall

plant 

Speed of 

Stack so

load a

suffici

Stack re

tion o

nearly 

Two sim

Plant u

about 

3 Diameter. 
TABLE 5. Details of observations at plants with chain 

No. of 

plant.

41

42 

43 

44

45 

46

47 

'48

49 

50

51

52 

53

54

55 

56

57

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet).

7

12 

20 

0

0 

12

12 

0

15 

80

24

34 

18

30

0 

50

7

Size 

(feet).

0 

0

8 xlO 

7Jx 5|

5 x 3£

4x4 

o4

3Jx 7

Place at which 

measurement 

was taken.

.....do..........

.....do..........

.....do..........

.....do..........

Number 

of elbows 

between 

boilers 

and 

stack.

0

0 

2 

0

0 

2

1 

0

0 

2

2

2 

1

1

0

2

0

Stack.

Height 

(feet).

208

171 

220 

90

125 

125

125 

90

203 

325

125

125 

125

35

110 

250

100

Size 

(feet).

11

7.0 

14 

3.0

4.5 

o4.5

o4.5 

3.2

9.0

7.7

»5.0

a6.0 

a4.5

o4.0

05.0 

11 .

4.5x4.5

Area 

(square 

feet).

95.0

38.5 

153.9 

7.06

15.9 

15.9

15.9

7.85

63.6 

47

19.6

28.3 

23.7

12.66

19.6 

95.0

20.25

Ignition arch.

Length 

(feet).

3.0

3.5 

3.6 

3.0

4.0 

5.0

2.8 

1.3

4.0

40 

4.0

4.0

40 

3.3,5.0

5.75

Style.

Sprung. .

Flat....' 

...do....

Flat..... 

...do....

Sprung. . 

...do....

...do....

Coal 

per 

of 

tim

Usua

All fl

Four 

tro

pos

 Thre

Stack 

bla

Stack 

Co

Coal 

cen

. Fo

Draf

bei

U til

aut

C tile 

Large 

ope

dam

Fired 

con

Large 

Coal 

kee

Boile

o Diameter.
PLANTS WITH MECHANICAL STOKERS. 33

SUMMARY.

The chain-grate stoker was found in plants carrying uniform loads 

and in plants where loads were extremely variable. With a uniform 

load and a proper setting there should never be any smoke with this 

equipment, but when a variable load is carried a faulty method of 

operation may cause the emission of dense smoke. In a chaingrate plant having a variable load, with the fire carried up to the 

water back, a sudden release of load will require a reduction of 

draft. Too often the damper is nearly closed, so that the coal on 

the grate and the fresh coal fed to hold the fire are burned with a 

imited air supply, causing the stack to smoke badly.

Plants equipped with the chain grate 'can be made to carry a very 

variable load with good results by changing the thickness of the fire, 

the speed of the grate, and the position of the damper to suit the load. 

The draft should not be reduced below a certain value, which can be 

determined for each plant by gradually closing the damper and 

watching the stack. In a plant where the maximum variations of 

load are nearly the same, it might be necessary to vary only the speed 

of the grate and the position of the damper. The damper regulator 

is often the cause of a smoky stack, because it is usually set to choke 

off the entire draft, a condition which is never necessary.

Both the speed of a chain grate and the slope of the ignition arch 

are important. Too often the grate is run so fast that volatile 

matter is being driven from the coal as far back as the center of the 

grate;'usually in this case there is not only a loss from incomplete 

combustion of the gases but also losses from unconsumed carbon 

in the ash and from injury to the grate. Live coals in the ash pit 

will not only warp a grate but gradually burn it up. The grate should 

not be run so fast that it will be hot when reentering the furnace. 

In one plant where a high draft was carried a sloping arch was removed 

and an arch built parallel to the grate. With the sloping arch the 

stack smoked, but with the flat arch it was entirely clean.

With chain-grate equipment a plant may run very inefficiently 

if the fire is carried only on the front half of the grate, as sometimes 

happens. When coal is burned in this way with a proper setting, it 

is because the fireman finds it the easiest way to carry a variable load 

and have a clean stack, demanding less of his attention in operation.

At some plants the boiler is forced by firing considerable coal 

through the inspection door. Although the desired result is accomplished by this practice, the plant becomes the equivalent of a handfired plant and the stack will invariably smoke badly. 

74897 Bull. 373 09 3
34 SMOKELESS COMBUSTION OF COAL.

FRONT-FEED STOKERS.

GENERAL DISCUSSION.

Inclined-grate stokers were patented years ago. As'a result of the 

competition between different makers and the consequent improvement in details of construction, the present types have been evolved. 

They have been installed at many places and handle a great variety 

of coals. All those in extensive use have grates with mechanically

FIGURE 5. Front-feed stoker and Babcock & Wilcox boiler, usual setting. 1, Air space; steam jets

enter furnace at this point.

operated grate bars. From the difference in position of the hopper 

supplying the grates, these stokers are conveniently divided into two 

classes front feed and side feed.

In the front-feed type the hopper is in front of the boiler, extending 

from side to side. Immediately back of it is sprung a coking arch, 

usually short. A reciprocating pusher feeds the coal to a dead 

plate beneath the front of the arch, where it begins to ignite. The 

construction and movement of the grate bars, which cause the burning 

coal to move down the grate, vary in different makes of this type.

These stokers can force a fire quickly and are often given severe 

treatment, but tests have shown that with the average setting, in
PLANTS WITH MECHANICAL STOKERS. 35

FIGURE 6. Front-feed stoker and Cahall boiler. 1, Air space; steam jets enter furnace at this point.
36 SMOKELESS COMBUSTION OF COAL.

which the grates are placed close 1 to the heating surface, more than 

average attention is required to keep down smoke;' consequently 

such stokers should be so set that when the fireman pushes green 

coal down the grate there is sufficient space for the combustion of the 

gases before they strike the tube heating surface. Failure to provide 

such space usually results in a smoky stack.

To intensify the combustion most stokers of this type are frequently set with an air space at the front of the ignition arch, through 

which steam jets enter the furnace. The accompanying illustrations 

show some boilers having stokers set in this manner. Figure 5

FIGURE 7. Front-feed stoker and Heine boiler. X, Point at which air and steam jets enter; Y, C tile 

on lower row of tubes, forming a tile-roof furnace.

represents a Babcock & Wilcox boiler with stack at the rear and 

baffled so that the gases from the burning coal travel but a short 

distance before they strike the bottom water tubes.

Figure 6 shows a stoker of the same make as installed at a plant 

having Cahall water-tube boilers. Here the fire-brick arch back of 

the hopper covers a larger proportion of the length of the grate than 

in the setting illustrated by figure 5, and as the boilers are vertical 

the furnace is in a Dutch oven the arch of which covers the space 

between the ignition arch and the front tubes of the boiler. The 

travel of the gases to the first heating surface is much lengthened in 

this setting and ample space is provided for combustion when forcing 

the fire,
PLANTS WITH MECHANICAL STOKERS. 37

A Heine water-tube boiler, with uptake in'the rear and a furnace 

fired by a stoker of the front-feed type, are shown in figure 7. In 

this installation the bottom baffling of tile on the water tubes lengthens 

the course taken by the gases in reaching the first heating surface. 

Ample space is provided for complete combustion when the boiler 

is carrying heavy loads. ;

FIGURE S. Front-feed stoker and Stirling boiler. 1, Air space; steam jets enter furnace at this point.

Figure 8 shows the usual methods of placing a front overfeed 

stoker beneath the arch that is part of the regular setting of the 

Stirling boiler. Figure 9 represents a similar stoker, with longer 

ignition arch, under a return tubular boiler.

DETAILED DESCRIPTION OF PLANTS.

Detailed information was collected at 32 plants, ranging in size 

from 200 to 2,500 rated boiler horsepower, where front overfeed 

stokers were used. This information is presented in condensed form
38 SMOKELESS COMBUSTION OF COAL.

in Table 9 (pp. 40-47), in which the same order of particulars is 

followed as in Table 5. In Table 9 the grate area of the front overfeed stokers includes the area of both the sloping grates and the 

dump grates.

FIGURE 9. Front-feed stoker and return tubular boiler. X, Point at which air and steam jets enter.

The different plants burned various sizes of coal, but at 11 plants 

the stokers were handling run of mine. The depth of fire ranged 

from 3.5 to 7 inches. The source of the coal and the depth of the fire 

are summarized in the following table:

TABLE 6. Kind of coal and depth of fire at plants with front overfeed stokers.

Kind of coal.

Kentucky .....................

Ohio..........................

Number

ofplants.

10

3

2

8

1

Average 

depth of

lire.

Indies. 

4

4

3.5

4

Kind of coal.

West Virginia

Number 

ofplants.

4

1

9

1

Average 

depth of 

fire.

Inches.

4.5

7

At 40 per cent of the plants the stokers were under boiler units of 

200 horsepower or less, and at 4 plants the stokers were in a Dutch 

oven, this setting having been installed at two plants because the 

boilers were of a vertical water-tube type. At 6 of the plants visited the boilers had a variable load and at 2.6 a uniform load. The 

least ratio of heating surface to grate surface that was determined was 

28.4 to 1 and the highest 58.3 to 1, the average being 40 to 1. The 

coal as received burned per square foot of grate surface per hour averaged 15.6 pounds; the smallest consumption of coal per'square foot 

of grate surface per hour was 6.4 pounds, the largest 34.7 pounds.
PLANTS WITH MECHANICAL STOKERS. 39

The percentage of the rated boiler horsepower developed on mean, 

heavy load (the boiler being rated on 10 square feet of heating surface 

per horsepower) averaged 84, the lowest and highest values being 55 

and 111 per cent, respectively. The percentage of boiler horsepower 

developed by different makes of boilers, the coal consumption, and 

the least and average distances from the grate to the tube heating 

surface have been summarized for ready reference in Table 7.

. TABLE 7. Summary of various observations at plants with front overfeed stokers.

Type of boiler.

Babeock & Wilcox. . .

Stirling..............

Miscellaneous wati> 

tube.

Return tubular.

Kind of coal.

Illinois, Maryland, 

Virginia and West 

 Virginia. 

Illinois, Kentucky, 

and West Virginia. 

Illinois, Indiana, 

Maryland, and 

Pennsylvania. 

Indiana, Kentucky, 

Maryland, and 

Pennsylvania. 

Illinois, Maryland, 

and Ohio.

Number of

plants.

9

4 

5

7 

7

Furnace 

draft.

Inch of 

water. 

0.31

.22 

.24

.32 

.21

Coal 

burned 

per 

square 

foot of 

grate surface per 

hour, 

average 

heavy 

load.

Pounds. 

10.8

12.4 

14.5

19.7 

13.2

Percentage of 

rated 

boiler horsepower developed, 

average 

heavy 

loacl.o

87

81 

80

91

78

Distance 

from grates 

to tube 

heating surface.

Average.

Feet. 

6.3

5.0 

7.1

7.2 

17.6

Minimum.

Feet. 

5.8

5.0 

7.1

5.7 

15.6

Black 

smoke.

Pcr,t. 

7.5

14.1 

5.6

7.7 

5.2

« Boiler rated on 10 square feet of heating surface per horsepower.

The average drafts, as determined at the furnace front, at the 

rear of the boiler, and at the base of the stack, are given in the following table:

TABLE 8. Summary of draft measurements at plants with front overfeed stokers.

Type of boiler.

Stirling..................................

Measurement taken at 

Base of stack .........................

Number of 

plants at 

which 

taken.

8

5

6

3

4

3

4

7

3

6

4

4

Average 

draft 

(inch of 

water).

O qi

Vi

.87

.22

.48

.76

.24

V)

09

 .21

.54

.66

OO

.43

.76

Range of furnace draft, 29 plants, 0.09 to 0.62 inch; average, 0.26 inch. Range of 

draft at rear of boiler, water tube, 17 plants, 0.25 to 0.74 inch; average, 0.44 inch. 

Range of draft at base of stack, 20 plants, 0.38 to 1.30 inches; average, 0.76 inch. Average drop of draft from furnace to rear of boiler in water-tube boilers, 0.16 inch. Average drop from furnace to front tube sheet in return tubular boilers, 0.33 inch.
TABLE 9. Details of observations at plants with fron

No. of 

plant.

.58

. 59

60

, 01

02

03

04

65

66

07

-68

69

70

71

72

73

74

75

76

77

78

79 ' 80

81

82

83

84

85

86

87

88

89

State.

.....do.;.:.:.:...:....

.....do...:.....:.:....

.....do...........:....

Missouri . ......... : . .

Ohio.....:.........:..

.....do...:............

Ohio.....:........:...

.....do................

.....do................

.....do................

.....do................

.....do................

Ohio...................

Indiana. ..............

.....do............... .

Ohio.............. .

Indiana..... ........

.....do.... ............

Maryland .............

Pennsylvania. ........

New York............

Maryland .............

Kind of stoker.

.....do.. ....................

.....do......................

.....do......................

.....do......... ............

.....do......................

.....do.:....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do:.....................

.....do......................

.....do......................

.....do......................

.....d3. .....................

.'... .do...... ................

.....do......................

.....do......................

.....do......................

.....do......................

.....do...... ..... ...

.....do......................

.....do......................

.....do......................

.....do.....'.................

.....do. .....................

....do......................

.....do..........:...........

Total

rated , 

horsepower.

1,200

300

1,400

800

800

700

750

2,700

600

500

300

i snn

230

750

630

500

375

330

crm

480

500

260

TOO

500

1,740

450

300

200

2,800

800

Commercial name.

.....do..................

.....do..................

.....do..................

.....do..................

Belleville.. .............

Belleville...............

.....do..................

Georees Creek

Wh

Ladd, 11

.....do...

.....do...

West Virgi

.....do...

^Vest Virgi

.....do... ..

.....do...

.....do...

Collinsville

.....do...

.-...do...
TABLE 9. Details of observations at plants with front overfee

No. of 

plant.

58 

 59 

-60 

61 

 62

. : 63

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

75 

76 

77 

78 

79 

80 

81 

82 

83 

84 

85 

86 

87 

88 

89

Load.

Requirement.

i 

.....do..............:.-......

.....do.......................

.....do......................

.....do......................

.....do......................

.....do..........'............

.....do...................... 

.....do......................

.....do......................

.....do......................

.....do......................

.....do.'. ....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Nature.

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Uniform ............... 

......do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Variable ...............

.....do.................

Character.

Office building. . ............

.....do......................

Rolling mill. ...........:....

.....do......................

Office building. . ......... .-.-.

Mill.........................

.....do......................

Rolling mill. ................

Office building ..............

Average l

Heavy.

Hours 

per day 

load is 

on 

plant.

24 

10 

24 

7.5 

3.5 

8 

12 

24 

12 

10 

10 

24 

14 

10 

12 

10 

24 

10 

11 

24 

12 

10 

8 

6.25 

24 

10 

24 

24 

8 

24 

12 

24

Coal 

burned 

per day 

(short 

tons).

60 

7.5 

50 

4.6 

4.5 

9 

12 

125 

7.5 

8.5 

5.75 

71 

2.5 

8 

4.3 

4 

8.25 

5 

6.5 

20 

5.5 

6.5 

. 9 

4.5 

82 

11 

12 

28 

3.4 

100 

17 

26

H

p

lo

p

Boiler rated on 10 square feet of heating surface per ho
TABLE 9. Details of observations at plants with front overfe

No. of 

plant.

58 

59 

60 

61 

62

63. 

64 

65 

66

67 

68

69 

70 

71

72 

73 

74 

75 

76 

77

78 

79 

80

81 

82

Stoking.

Thickness of 

fire 

(inches).

3 -4 

2.5-3 

3 -4

7 

6

3

5

3.5 

3 -4

2

2.5 

4 

5 

5

4 -5

4 

3 -4

Frequency of cleaning 

 fire.

8 times in 24 hours .... 

2 to 3 times in 10 hours.

3 times in 12 hours. . . . 

5 times in 10 hours. . . .

2 times in 10 hours .... 

2 times in 12 hours. . . .

2 times in 12 hours ....

Boile

Type.

Babcock & Wilcox 

water-tube. 

Standard; Babcock & 

Wilcox. 

Babcock & Wilcox 

water-tube. 

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

O'Brien and Heine 

water-tube.

.....do.................

Bronson special firetube.

.....do.................

.....do.................

.....do.................

.....do................

.....do.................

Stirling water-tube. . . . 

.:... do. ................

.....do.................

.....do.................

.....do.................

Size.

140 4" x 18' tubes, 2 36" drums. .

168 4" x 18' tubes, 2 42" x 20TV 

drums. 

108 4" x 18' tubes, 2 36" x 18' 

drums. 

108 4" x 18' tubes, 2 36" x 18' 

drums. 

162 4" x 18' tubes.. . ...........

126 4" x 18' tubes, 2 30" drums. . 

1264" x 18' tubes. .............

168 4" x 16' tubes, 2 30" x 16' 

drums.

85 3i" x 18' tubes, 78 3J x 18' 

drums. 

140 3i" Ji 18' tubes. . ...........

53 3i" x 16' tubes..............

84" x 18', 150 3i", 18 4" x 18' 

water tubes.

72" x 20', 70 4" tubes. .........

66" x 18', 54 4" tubes. . ........

66" x!6', 54 4" tubes. .........

72" x 18', 744" tubes...........

4 60" x 16', 46 4", 2 60" x 16', 

544". 

192 3J" tubes..................

198 3i" tubes, 3 36" drums ..... 

259 3J" tubes, 2 42" x 12Ty 

drums.

Number installed.

4 

2 

4 

4 

4

2 

3 

10 

2

2 

2

6 

2 

2

6 

2 

3 

3 

4 

6

2 

1 

2

1 

5

Num

to 

Aver

age 

heav

load

1
S3

84 

So

86

87 

88 

89

3 -4

3 -4 

3

4 -0 

4

2 times in 10 hours .... 

4 times in 24 hours. . . .

2 to 3 times in 24 hours. 

4 times in 24 hours .... 

.....do.................

Wickes vertical 

water-tube. 

Atlas water- tube ...... 

Henry Vogt watertube. 

Cahall vertical watertube.

Standard water-tube..

112 4" tubes....... ............

108 4" x IS' tubes. .............

2

3 

3

1

S 

4 

4

o!25° F. at boiler. 
TABLE 9. Details of observations at plants with front overf

No. of 

plant.

58 

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

75 

76 

 77 

78 

79 

SO 

81 

82 

83 

84 

85 

86 

87 

88 

89

Furnaces.

Number.

4 

2 

4 

4 

4 

2 

3 

10 

2 

' 2 

2 

6 

2 

2 

6 

2 

3 

3 

4 

6 

2 

1 

2 

2 

5 

2 

3 

3 

1 

8 

4 

4

Kind.

Plain..................................

Plain ..................................

.....do.................................

.....do.................................

.....do.................................

.....do.................................

.....do........ ............. .... ....

.....do.................................

Tile roof ...............................

Plain ....... . ... ...........

.....do...............:...........,....

.....do.,. ............;..................

Tile roof .... ...........

Plain............... ........... .....

.....do.................................

.....do.................................

.....do........ ............... . .

.....do.................................

.....do.................................

.....do.................;...............

.....do........................... ....

.....do.................................

.....do...... . ....

.....do............................ .....

Dutch oven ............................

Plain ..................................

.....do.................................

Dutch oven ....................... .....

.....do ................................

Plain ..................................

.....do .................................

Grate area per 

boiler (square 

feet).

64 

42. 5, 39. 5 

60 

56.3 

57 

76 

60 

72 

72 

72.25 

55. 25, 42. 25

73 

28.6 

68 

37.5 

48 

37.5 

37.5 

45 

27.5 

76 

75 

76 

117 

76, 104. 5 

55 

34.64 

« 48 

49 

83 

52. 5, 59. 5 

57

Distance from grates to 

tube heating surface.

Average (A).

9.5

5.5 

5.5 

5.5 

6

5.5

6 

4 

8 

15 

18.5

18 

19

7 

7.25 

7.25 

66.5,7.5

10.5

7 

4

Minimum 

(B).

5

7

5.5 

5.5 

5.5 

6

5.5

6 

4 

5.5 

13 

15.5

17 

17

7 

7.25 

7.25 

66, 7

8 

5 

4

Widt

furnace 

5. 

68

8. 

"First dimension applies to O'Brien boiler. 6 Fir
TABLE 9. Details of observations at plants with front overfe

No. of 

plant.

58

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74

75 

76 

77 

78 

79 

80

81

82 

83 

84 

85 

.86 

87 

SS 

 89

Draft.

Kind.

Chimney.. 

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do...... 

...do...... 

...do......

...do...... 

...do......

...do......

Chimney ; 

induced. 

Chimney..

Chimney.. 

...do......

...do......

...do...... 

...do......

...do......

...do...... 

...do...... 

...do......

...do......

...do......

...do......

Readings (inches of water).

Furnace.

0. 30-0. 33 

. 12- . 24

.19- .21 

. 17- . 22

. 50- . 57

.20 

.25 

-IS- .22

.30 

.16 

.30 

.09

.20

. 05- . 07

.16 

.25 

. 21- . 33

.28

.10- .40 

.20 

.20- .25 

.26 

.28 

. 26- . 40

Rear of boiler.

0.64 

.36

.25 

0. 25- . 32

.25 

.44 

.50 

.35- .40 

.60

.64 

Lower rear, . 47 

Lower rear, . 41- . 4S 

/Lower, .45 

\Upper, .CO 

Upper rear, . 50- .f.O 

Lower rear, . 2d 

.39- .41 

.74 

Lower rear, . 30

Front 

tube 

sheet.

«0. 40 

' .60

.38

.44

. 15- . 17

}.........

..........

Breeching.

1.14

.52 

.70 

.32 

.32

1.10 

. SO- . 90

.40- .45 

.90

. 55 

.45- .95

.64

.71

1.15

1.10

Base 

of 

stack.

0.65 

.70 

.60

1.25 

1.10 

.90 

.64

.54

1.10

.70

.47 

.SO

.64

.65 

.80-1.0

.38

.75- .85

1.30

Conditions under which 

readings were taken.

Damper and poke-hole 

doors open.

.....do.................

.....do.................

.....do.................

.....do.................

.....do:...............

.....do... .............

.....do................

a Several. 6 Various lengths. <= Front wa
TABLE 9. Details of observations at plants with front over

No. of 

plant.

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

Length 

from, 

stack to 

nearest 

boiler 

(feet).

10

5

0

0

5

6

' 30

8.5

12

40

3

55

12

0

17

45

20

2

19

0

6

0

Size 

(feet).

5x5

7x17.5

3.5x4

5 x 3. 5

a 5

6

 o

0

Breeching.

Place at which 

measurement was 

taken.

.....do............

Number 

of elbows 

between 

boiler and 

stack.

> 0

0

0

0

0

0

1

0

1

1

4

1

0

2

3

0

3

0

0

0

Height

(feet).

150

150

125

200

260

90

140

175

125

78

128

30

100

105

9G

Stack.

Size 

(feet).

«6

06

06

06

a 12

a 4. 3

o5

o5

o3.5

a 7

o3

o5

3x2

04

»5

04

Area 

(square 

feet).

15

28.3

28.3

28.3

28.3

19 6

113.1

12.56

14.7

19.6

19.6

9.7

38.5

7.06

19.6

6

19 6

12.56

19 6

12.56

Length of 

coking arch 

(feet).

2.4

3

.

3

3

2.8

2.2

3

3

2

9 ";

2.7

stea

bad

use

tinu

blac

stea

blac

rest

blac

two

Som

clea

Two 
81

82

83

84

85

86

87

88

89

0069

4008

11

0

82' 0

0001000096

f 120

\ 110 

105

-130

50

120

130

150

a 4

" 5

«5

04

04

5x5

a 6

12.56

19.6

8.8 

19.6

23.7

19.6

.12.56

12.56

25

28.3

1.75

\r. ......... 3

2.5

2.75 3

Stack 

(Three 

i. stac

l foot 

Three 

dam

dam

Coal r

was 

half 

acro

han

firs

a Diameter.
48 SMOKELESS COMBUSTION OF COAL.

SUMMARY.

A review of the remarks in the preceding table shows that with 

the front overfeed type of mechanical stoker, success in smoke abatement has been attained by one of three methods the continuous use 

of steam jets, a generous admission of air, or careful operation.

SIDE-FEED STOKERS. 

GENERAL DISCUSSION.

Like the front feed, the side-feed stoker has beeri in use for many 

years, the first American patent for this type having been taken out 

in 1878. Several firms now make such stokers, which differ chiefly 

in the manner of feeding coal and getting rid of clinkers and ash. In 

all the coal is fed from two magazines, one at each side of the boiler. 

At the bottom of each magazine is a flat built-up iron and steel plate 

called the coking plate; beneath this is an air duct and on it rests 

the coal-feeding mechanism. Over this feeding device is a heavy 

casting, the arch plate, on which rests a fire-brick arch extending 

over the whole grate area and having along the upper side an air duct 

connected with the fire space by small openings in the skew-backs 

supporting the arch. These openings are designed to admit hot air 

above the coal at a point where the volatile hydrocarbons are given 

off. The movable grate bars and a clinker-breaking 'device at the 

bottom of the V-shaped space between the grates are actuated by a 

small engine that forms part of the equipment.

Stokers of the side overfeed type are characterized by large coking 

space per foot of grate area and an ample combustion chamber. 

They have been installed at both large and small plants, and are 

successfully carrying both uniform and variable loads. In the field 

investigation here reported no other type of stoker was found doing 

as well under so great a variety of conditions. Its chief defect seems 

to lie in the devices for getting rid of the ash. Though supposedly 

automatic, they often^require the service of a fireman. This introduces an element of varying value in the operation of the plant.

The two makes of this stoker that are most used formerly differed 

in arch construction, one having only side arches over the coking 

plates. As now installed, the arch in both makes extends over the 

grate area and the two styles differ merely in the devices for distributing coal to the grate and for getting rid of refuse. One employs 

for coal distribution a shaft rotating through a small arc to move 

stoker boxes on the coking plates; as the boxes work forward, they 

push coal toward the edge of the plates. Between the lower ends of 

the grates and supported by a bearing shaft is a hollow iron bar with 

projections on its surface; this bar, when rotated, grinds up the 

clinker. The other make feeds the coal by a screw and has heavy iron
PLANTS WITH MECHANICAL STOKEES. 49

disks actuated by a reciprocating bar for crushing clinker. Both 

these stokers are frequently set in Dutch ovens.

AAAAA "AAAAAA "

Figure 10 shows the stoker first mentioned in a Dutch oven having 

a chamber above the arch for heating the air admitted over the coal, 

74897 Bull. 373 09 4
50 SMOKELESS COMBUSTION OF COAL.

FIGURE 11. Side-feed stoker in Dutch oven and Cahall boiler.
PLANTS WITH MECHANICAL STOKEBS. 51

as set at a battery of Babcock & Wilcox boilers. This setting, with 

its ample combustion chamber and fairly long travel from the grates

FIGURE 12. Side-feed stoker and Heine boiler. 1, C tile on lower row of tubes, forming a tile-roof furnace

FIGURE 13. Side-feed stoker in Dutch oven and Stirling boiler.

to the tube heating surface, allows nearly perfect combustion of the 

hydrocarbons from the bed of coal.
52 SMOKELESS COMBUSTION OF COAL.

The other make of stoker as installed under a Cahall boiler is shown 

in figure 11. As the boiler is vertical, the stoker is placed in a Dutch 

oven. In this setting also, the combustion chamber is large enough 

to permit thorough mixing of the gases from the burning coal and a 

moderately long travel from the grates to the first row of water tubes.

A side-feed stoker set in a Dutch oven under a Heine boiler is 

shown in figure 12.- The ignition arch extends over the grates, and by 

baffling the bottom row of tubes the space between the back of the

FIGURE 14. Side-feed stoker and Stirling boiler. 1, Continuous screw for distributing coal.

arch and the rear end of the baffling becomes a tile-roofed furnace. 

The gases are given a long journey from fire to heating surface, and 

the construction insures a smokeless fire under heavy loads and forced 

feed.

The chief difference in the two patterns of side-feed stokers under 

discussion are shown in the accompanying illustration of these stokers 

under Stirling boilers. Figure 13 shows the stoker first mentioned 

set in a Dutch oven. The feeding device is not shown, but the 

rotating clinker bar is. In figure 14 the screw for feeding coal and the
Ai

CO

/ HI c~- 

FIGURE -15. Side-feed stoker and return tubular boiler, 
54 SMOKELESS COMBUSTION OF COAL.

device for crushing clinker, the special features of the other make of 

stoker, are evident. One stoker is set in a. Dutch oven; the other is 

placed beneath the arch that is a characteristic feature of the Stirlinoboiler. Both installations exhibit 

a meritorious feature of the side-feed 

stoker the large 

combustion space 

over the grates.

The fact that a 

large number of the 

plants visited have 

a side-feed stoker 

under a return tubular boiler indicates that this type 

has given satisfaction when used with 

tubular boilers. 

Details of a sample 

installation, showing the particular 

features of the sidefeed type that have 

been mentioned in 

this discussion, are 

presented in figures 

15 and 16, which 

represent sections 

through the stoker 

and boiler. Figure 

15 shows the high 

arch over the grates 

and the long distance from grates to tube heating surface. The situation of the coal magazines, of the hot-air ducts above the arch, and 

of the air passages under the coking plates, as well as the ample size 

of the combustion chamber, are made plain by figure 16.

DETAILED DESCRIPTION OF PLANTS.

In all, 76 plants with side-feed stokers were visited; at 44 the 

stokers were installed under return tubular boilers, at 30 under watertube boilers, and at 2 under boilers of both types. The plants ranged 

in size from 50 to 6,750 horsepower. The coal used came from Illinois, Indiana, Kentucky, Ohio, Pennsylvania, and West Virginia,

FIGURE 10. Side-feed stoker and return tubular boiler, cross section. 

1, Coal magazines; 2, hot-air ducts; 3, air-admission openings under coking plates.
PLANTS WITH MECHANICAL STOKERS. 55

and ranged from slack to run of mine. Eleven plants were burning 

slack. The other 65 used small nut or nut and slack.

Plants with water-tube boilers. At the 30 plants where stokers of 

this type were installed under water-tube boilers alone the kind of 

coal used and the depth of fire were as follows:

TABLE 10. Kind of coal and depth of fire at plants with side overfeed stokers under watertube boilers.

Kind of coal.

Ohio...........................

Number 

of 

plants."

6

1

1

7

Average 

depth of 

lire.

Inches. 

5

6

7

5

Kind of coal.

Number 

of 

plants.**

7

 4

5

Average 

depth of 

fire.

Inches. 

5

5

6

a One plant used both Ohio and Pennsylvania coal.

At 35 per cent of the plants with side-feed stokers under water-tube 

boilers the boiler .units were 200 horsepower or less. The coal as 

received burned per square foot of grate per hour ranged from 10 to 

41 pounds. The percentage of the rated horsepower developed on 

average heavy load (the boiler being'rated on the basis of 10 square 

feet of heating surface per horsepower) ranged from 37 to 189. 

These and other details are summarized in the subjoined table.

TABLE 11. Summary of various observations at plants with side overfeed stokers under

ivater-tube boilers.

Type of boiler.

Babcock <fc Wilcox.

Stirling............

Miscellaneous

water tube.

'

Kind of coal.

Illinois, Ohio, and

West Virginia.

Illinois, Ohio,

Pennsylvania,

and West Virginia. 

Illinois, Indiana,

Kentucky, Ohio,

and Pennsylvania.

Number of 

plants.

8

9

15

Furnace 

draft 

(inch 

of 

water).

0.24

.36

.22

Cotil

burned

sq uare 

foot of 

grate 

surface 

per hour, 

average 

heavy

load.

Pounds.

22.6

23.1

23.7

Boiler horsepower developed, 

average 

heavy 

load, (a.)

91

85

81

Distance

from grate 

to tubeheating 

surface.

Average.

Feet.

8.5

9.4

7.9

Minimum.

Feet.

5.7

6.5

5.5

Distance 

from 

front of 

furnace 

to front 

of 

boiler.

Feet.

(6)6.9

4.1

(c)4.1

Black 

smoke.

Per ct.

5.2

2.8

6.0

a Boiler rated on 10 square feet of heating surface per horsepower. 

t> From 7 plants. 

c From 13 plants.

The average ratio of heating surface to grate surface at these plants 

was 59.1 to 1, the range being from 33 to 1 to 72 to 1. The grate 

area of this type of stoker was taken to be equal to the distance
56 SMOKELESS COMBUSTION OF COAL.

between the coking plates multiplied by the distance from the front 

of the furnace to the rear of the grates.

Natural draft, supplied by a chimney, was used at most of the 

plants. The furnace draft varied from 0.10 to 0.35 inch of water, 

but most of the readings were between 0.15 and 0.25 inch. The 

draft measurements are summarized below:

TABLE 12. Summary of draft measurements at plants with side overfeed stackers under

water-tube boilers.

Type of boiler.

Stirling. ..................................

Measurement taken at 

Number of 

plants at 

which 

taken.

7

7

2

8

7

5

12

7

8

Average 

draft 

(inch of 

water).

0.24A"*

.58

OR

.47

Q1

.22

.51

.07

Furnace draft, 27 plants, 0.10 to 0. 53 inch water; average 0. 27 inch. Draft at rear 

of boiler, 21 plants, 0.18 to 0. 90 inch; average, 0. 47 inch. Draft at base of stack, 15 

plants, 0.18 to 1.10 inches; average, 0. 71 inch. The approximate average drafts were 

as follows: Furnace, 0.25 inch; rear of boiler, 0.50 inch; base of stack, 0.75 inch. 

These figures show a draft drop of 0, 25 inch of water through the furnace and of 0. 25 

inch from boiler to stack.

Details of the observations at plants with side-feed stokers under 

water-tube boilers are given in Table 13.
TABLE 13. Details of observations at plants loith side overfeetf stok

No. of 

plant.

90

91

92

93

94

95

90

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

State.

Illinois................

.....do................

Ohio ..................

Ohio ..................

.....do................

Ohio..................

.....do.............:..

.....do................

.....do................

Ohio..................

.....do................

.....do................

.....do................

Ohio..................

.....do................

.....do................

Ohio..................

Kentucky-.. ..........

Kind of stoker.

.....do......................

.....do:.....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do. .....................

.....do......................

.....do......................

.....do............'..........

.....do......................

.:...do......................

.....do......................

.....do......................

......do......................

.....do......................

.....do......................

Model.......................

.....do. .....................

Total

rated 

horsepower.

5,040

500

500

200

1,200

500

458

. 2, 000

400

1,200

500

41*3

1,200

. 306

600

200

400

GOO

1,000

250

400

1,200

350

200

1,200

300

600

6,750

300

Commercial name.

.....do..................

.....do..................

.....do..................

.....do..................

Where 

.....do.....

.....do.....

.....do.....

.....do.....

.....do..:..

.....do.....

.....do.....

.....do.....

.....do.....

.....do.....
TABLE 13. Details of observations at plants with side overfeed stokers und

No. of 

plant.

90 

91 

92 

93 

94 

95 

96 

97 

98 

99 

100 

101 

102 

103 

104 

105 

106 

107 

108 

109 

110 

111 

112 

113 

114 

115 

116 

117 

118 

119

Load.

Requirement.

.....do....................... 

.....do.......................

Power

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

Nature.

.....do..................

Uniform .........*...... 

.....do.......:..........

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

.....do.. ................

.....do..................

.....do......... .........

.....do...................

.....dD.. ................

.....do..................

Character.

. ....do...................

Municipal waterworks...

. ....do...................

.....do...................

Office building..........

Hotel ...................

Hotel ...................

Hotel ...................

Average load

Heavy.

Hours 

per day 

load 

is on 

plant.

24 

24 

24 

10 

24 

10 

10. 25 

11 

9 

14 - 

10 

10 

10.5

24 

5 

24 

11 

24 

12 

14 

24 

12 

10 

10 

10.5 

24 

24 

11 

. 8 

10.5

Coal 

burned 

per day 

(short 

tons).

150-200 

12 

19 

4.7 

60 

2.6 

6.5 

70 

6 

15.3 

7.3 

7 

15.5 

10 

6 

7 

6.75 

20 

14 

7.75 

- 11.5 

24 

19 

8.7 

3.5 

20 

8.8 

7 

80 

5

Hou

per d

load 

is o

plan

24 

24 

24 

10 

24 

14

12 

 9 

18 

10 

10 

10

24 

19

11 

24 

12

12 

10 

10

24

8 

10

Boiler rated on 10 square feet of heating surface per hors
TABLE 13. Details of observations at plants with side overfeed stokers und

No. of 

plant.

90 

91 

92 

93 

94

95 

96

97 

98 

99 

100 

101 

102 

103 

104 

105 

106 

107 

108

109 

110 

111 

112 

113 

114 

115 

116 

117

118 

119

Stoking.

Thickness of 

fire 

(inches).

6 

3.5-4

4 

3-6

4-6 

( b)

6-8 

4-6

5-6 

5-6 

4 

6 

4-6 

4-6 

4 

3-4 

3-6

6 

6-8

5

5-6 

4-6

4-5 

4-6

6-10

Frequency of cleaning 

fire.

.....do................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do..................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do................

.....do.................

.....do.................

2 times in 12 hours ....

.....do.................

Boilers.

Type.

Babcock & Wilcox. . . . 

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Aultman & Taylor. . . .

Heine; Stirling ........

MoNaull. .............

Atlas..................

Size.

198 4" tubes, 3 "S"x 20i' drums 

90 4" x 18' tubes, 2 30" drums. 

Small boiler, 72 4" x 18' tubes. 

1084" x 18' tubes..............

154 4" x 18' tubes, 1 42" x 20J' 

drum.

1-126 4" x IS' tubes, 1-108 4" 

x 18'. 

2-181 3J" tubes, 3-403 3J" tubes 

181 3J" tubes, 3 36" drums .....

1Q9 ^1" tnhipQ

144 4" x 18' tubes, 2 36" drums. 

113 3i" x 16' tubes, 2 30" x 16' 

drums.

2-67 3i" x 18' tubes, 1-138 4" x 

18' drums. 

192 4" x 18' tubes..............

Number 

installed.

12 

2 

3 

1 

4

2 

2

5 

2 

4 

2 

1 

4 

1 

3 

2 

2 

2 

4

2 

2 

6 

6 

1 

2 

3 

2 

3

15 

2

Numb

to ca

Average 

heavy 

load.

( 6 )

2

1 

4

1 

2

4 

1 

3 

2 

1 

3 

1 

2 

2 

1 

1 

2.5

2 

1 

6 

4 

1 

2 

2 

1 

2

12 

2

o Boiler rated on 10 square feet of heating surface per horsepower. 
TABLE 13. Details of observations at plants with side overfeed stokers unde

* No. of plant.

90.............................................

91

92.;...........................................

93 ..............................................

94 ... I.........................................

95.............................................

96.............................................

97

98.............................................

99.............................................

100.............................................

101.............................................

102 .............................................

103.............................................

104.............................................

105.............................................

106.............................................

107.............................................

108.............................................

109 .............................................

110.............................................

Ill .............................................

112 .............................................

113.............................................

114. .................. .....4...... .............

115 .............................................

116 .............................................

117... ...........................................

118...... .......................................

119.............................................

Furnaces.

Number.

24 

2 

3 

1 

4 

2 

2 

8 

2 

8 

2 

1 

4 

1 

3 

2 

2 

2 

8 

2 

2 

8 

6 

4 

2 

3 

2 

3 

15 

 2

Grate area 

per boiler 

(square feet).

70 

35 

36,25 

42 

56 

42 

42,36 

38.5,77 

39 

50 

42 

64 

48 

49 

36 

24 

35 

49 

30 

30 

25.7 

42,63 

36 

100 

20 

59.5 

26.5 

25,49 

56 

23.2

Dim

Distance from grates to 

tube heating surface.

Average (A).

10 

9 

8,8.5 

9.5 

8.5 

8 

"8,7 

14 

7.5 

11 

7 

7 

8 

14.5 

8.5 

9.5 

5.5 

20 

9

69,6.5 

9 

8

10.5

67.5,8 

9 

3.5

Minimum 

(B).

6.5 

5.5 

5.5 

6.5 

5.5 

6 

o5.5,4.5 

10.5 

4.5 

9 

3.5 

3.5 

5 

11 

6 

6.5 

3.5 

16.5 

6.5

6" 7, 3 

6

4.75 

7.5

5.5

--6 --- 

3

Width of 

furnace (C

5 

5 

5,6 

7 

8 

7 

6 

5.6 

6.5 

5 

7 

8 

8 

7 

6 

4 6.7

7 

3 

5 

4.7 

66,7 

6 

5 

4 

7 

4.4 

65,7 

8 

5.2

First dimension applies to small boiler. 6 
TABLE 13. Details of observations at plants with side overfeed stokers 

No. of 

plant.

90 

91

92 

93 

94

95 

96

97 

98 

99 

100 

101 

102 

103 

104 

105 

106 

107 

108 

109 

110 

111 

112 

113 

114 

115 

116 

117 

118 

119

Draft.

Kind.

Chimney.- 

...do.'..'..

'...do......

...do......

...do......

...do......

...do......

...do...... 

...do......

...do...... 

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do...... 

...do...... 

...do......

...do....... 

...do......

...do......

....do......

...do......

...do...... 

...do......

...do......

...do.. .... 

...do......

Readings (inches of water).

Furnace.

0.18-0.27 

.18

.17- .19 

.09- .12 

.25- .30

.37 

.37, .42

.20

.18^ .24 

.18- .28

.18- .36 

.11- .18 

.53 

.15 

.10

.12 

.08- .17

.34 

.12- .30

.14- .25

.12- .15

.13- .15

.30- .48 

.18 

.20- .30 

.20- .29 

.22- .26

Rear of boiler.

.50

.31- .40 

.16- .19 

.44- .45

.50

.55, .58 

Lower rear, . 35

.32- .38

Lower rear, .34- .58 

Lower rear, .40- .60 

Lower rear, . 60

Lower rear, .45

.90

.39- .45

.53- .67 

.43 

.30- .40 

.25- .56 

.39- .49

Breeching.

.70- .75

.22- .34

.90 

. 75

.90 

.43 

1.26

.t>4 

.65- .74

.26- .34

Base of 

stack.

0.56

.60 

' .75

.54

.76

.90

1.10

.55-. 60 

.18

.65 

1.10 

.70 

.65 

. 92-1

Conditions under which readings 

were taken.

Ash-pit doors open, dust doors 

cracked.

Ash arid dust-pit doors open; 

damper partly closed. 

Damper and ash-pit doors open. . . 

Dampers open; ash-pit doors 

cracked.

.....do............... ........... 

.....do............................

Damper and ash-pit doors open . . 

Several. 
TABLE 13. Details of observations at plants with side overfeed stoker

No. of 

plant.

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

Length 

from 

stack to 

nearest 

boiler 

(feet).

4

5

0

50

35

26

3

4n

12

9

0

0

15

35

3

10

11

20

11

Size 

(feet).

0

0

0

4x4

10x4

Breeching.

Place at which 

measurement was 

taken.

-

.....do............

Number 

of elbows 

between 

boilers 

and 

stack.

0

1

0

4

0

1

1

1

0

1

0

0

0

1

0

0

0

1

0

Height 

(feet).

203

110

105

71

150

165

122

305

195

140

108

152

1 wi

125

80

252

127

305

Stack.

Size 

(feet).

a 16

a5

4x4

3x3

ol2

"5.5

o5.5

613x6

05

6x6

«2.5

a3

08

«4

2x2

04

a6

Area 

. (square 

feet).

201

19.6

16

9

113.5

23.7

23.7

70.3

19.6

36

4.9

.06

33.2

K.f\ 94

12.56

4

12.56

28.3

38.5

pressure regula

with storage ba

considerably, 10 

heavy load.

horsepower the 

Run with dust-

too large for ligh

pit doors closed

account of these 

draft reduced to 

Murphy and Sti

some readings 10 

feet.

and 100 per cent 

has to be poked 

chamber, also 1

cross the tubes f

on lower row of 
109

110

112

113

114

115

116

118

119

18

18

2208

1120

12

0

10200012I

125

125

110

66

125

lye

105

120

9V>

95

04

a 7.1

04

05

o7 '

o3.5

12.56

40

12.56

19.6

38.5

. 9.6

19 6

201

11.1

stoker per Hein

of Heine boiler. 

as under Heine 

is baffled like H

damper.

o Diameter. 
64 SMOKELESS COMBUSTION OF COAL.

Plants with return tubular boilers. Side overfeed stokers were installed under return tubular boilers at 48 plants, with rated boiler 

capacity varying from 50 to 180 horsepower. At two of these 

plants the stokers were set in a Dutch oven. The kinds of coal 

burned and the thickness of fire were as follows:

TABLE 14. Kind of coal and depth of fire at plants, with side overfeed stokers under

return tubular boilers.

Kind of coal.

Ohio..........................

Number 

of plants.

7

3

5

6

Average 

depth of 

fire.

Inches. 

5

4

4

5

Kind of coal. 'Number 

of plants.

11

8

S

Average 

depth of 

fire.

Inches.

0

5

Other details given in Table 15 regarding the setting and operation 

of side-feed stokers at these plants may be briefly summarized thus:

Draft through fire, 0.17 inch; coal as received burned per square feet of grate surface 

per hour, average heavy load, 20.6 pounds; percentage of rated boiler horsepower 

developed, average heavy load (boiler rated on 10 square feet of heating surface per 

^horsepower), 90; average distance from grates to tube heating surface, 14.5 feet; average vertical distance from clinker grinder to coking arch, 3.75 feet; per cent of black 

smoke, 5.6. Approximate draft averages gave a furnace draft of 0.15 inch and a drop 

through the boiler of 0.25 inch. The drop from the boiler to the stack averaged 0.20 

inch.

Details of the observations at plants with side-feed stokers under 

return tubular boilers are given in Table 15
TABLE 15. Details of observations at plants with side overfeed stoker

No. of 

plant.

120

121

199

19^

124

1OC

19A

197

129

130

131

1 39

IQO

134

135

1 Qft

-lOQ

140

141

I/O

143

' 145

146

147

148

i *in

151

1 *\9

1^3

154 

155

156

State.

.....do.................

....do.................

....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Ohio. .................

.....do.................

.....do.................

.....do.................

.....do.................

Michigan.............. 

Ohio..................

Michigan. .. ...........

Kind of stoker.

.....do."...'....-........-.....

.....do.......................

....do........................

.....do..... ..................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.....--.-......-...--..

.....do.....-...----...-......

.....do.......................

.....do...... .................

.....dO..-...-...--.......-...

.....do.......................

.....do.......................

..:.. do...... .................

.....do.......................

.....do......-.--..-.-.--..-...

.....do.......................

.....do.....--....-...--.--.-.

.....do.......--.-..-....-....

Detroit..... .................

Detroit ......................

Total

rated 

horsepower.

640

360

320

9^n

400

1Q =

onn

100

600

600

500

450

Ofin

874

600

405

320

onn

300

Of\fl

900

150

50

1,000

790

750

445

350

or\n

250

Commercial name.

.....do...................

.....do...................

.....do...................

Reynoldsville.

.....do. ..................

.....do...................

Pittsburg No. 8; Thacker.

Red Jacket. . .....'.......

Where 

.....do.....

.....do......

.....do......

.....do.....

.....do......

. ....do..... .

Ohio......

.... .do...... 

Pittsburg, P

.....do.....

.....do.....

.....do.....

... ..do. .....

.....do.....

.... .do. .....

.....do.....

.....do.....

.....do.....

.....do.....

Ohio; West 

.....do......

fed 

c
TABLE 15. Details of observations at plants with side overfeed stokers unde

No. of 

plant.

157

158

159

ICO

161

102

163

164

165

State.

Ohio..................

Ohio..................

.....do.................

Kind of stoker.

.....do.......................

.....do.......................

.....do.......................

.....do.......................

Total

rated 

horsepower.

140

1,000

450

250

200

ISO

179

150

Commercial name.

Whe
TABLE 15. Details of observations at plants with side overfeed stokers unde

No. of 

plant.

120 

121 

122 

123 

124 

125 

126 

127 

128 

129 

130 

131 

132 

133 

134 

135 

136 

137 

138 

139 

140 

141 

142 

143 

144 

145 

146 

147 

148

Load.

Requirement.

.....do..................'....

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do.......................

.....do......................

Power......................

Nature.

.....do.................

.....do. ................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Uniform ...............

Character.

.....do......................

.....do......................

Store and office building. . . .

.....do......................

Mill.........................

Factorv .....................

Average 

Heavy.

Hours 

per day 

load 

is on 

plant.

11 

IS 

18 

24 

9 

17 

IS 

9.5 

24 

24 

24 

10 

11 

9.5 

14 

17 

12 

12 

10 

12 

24 

11 

18 

12 

11 

10 

24 

12 

10

Coal 

burned 

per day 

(short 

tons).

33 

16 

10 

14 

7 

6 

8 

11 

10 

20 

20 

3 

1.6 

2.5 

8 

11.6 

10 

S 

4.4 

15 

10.3 

6.7 

7 

10 

10 

5.5 

6 

5.5 

2.S

p

Boiler rated on 10 square feet of heating surface per 
TABLE 15. Details of observations at plants with side overfeed stokers und

No. of 

plant.

149 

150 

151 

152 

153 

154 

155 

156 

157 

158 

159 

160 

161 

162 

163 

164 

165

Load.

Requirement.

.....do......................

.....do.................:....

.....do......................

.....do......................

.....do......................

Nature.

.....do.................

.....do.................

.....do............:....

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Character.

Hotel .......................

Mill .........................

Office building ..............

.....do......................

Mill.........................

.....do......................

. ' Averag

Heavy.

Hours 

per day 

load 

is on 

plant.

11 

11 

10 

16 

10 

13 

24 

10 

24 

12 

24 

14.5 

24 

10.5 

9.5 

13.5 

10

Coal 

burned 

per day 

(short 

tons).

2 

12.9 

9 

8 

13.4 

4.5 

8.5 

. 2.6 

2 

28 

30 

3.5 

6.7 

3.4 

3 

5 

4

a Boiler rated on 10 square feet of heating surface per h
TABLE 15. Details of observations at plants with side overfeed stokers under 

No. of 

plant.

120 

121

122 

123 

124 

125 

126

127

128 

129 

130 

131 

132 

133 

134 

135 

136 

137

138 

139

140 

141

142 

143 

144 

145

Stoking.

Thickness of 

fire 

(inches).

4 

3-4

3-6 

4-5 

6 

3-4 

5

4

3

4 

3 

4 

4-6 

5

4 

4 

5

5-6 

4-5

4 

4-6

6-7 

4 

4-6 

3-5

Frequency of 

cleaning fire.

3 times in 24 hours ....

.....do................

3 to 4 times in 24 hours.

.....do................

.....do................

.....do................

.....do..'. .............

.....do................

.....do................

.....do................

.....do................

.....do................

......do................

.....do................

.....do................

.....do................

.....do................

.....do................

Boilers

Type

.....do................

.....do................

.....do................

.....do................

,.... do.. ..............

.....do................

.....do................

.....do................

.....do................

.....do................

.....do....:...........

.....do................

.....do................

.....do................

.....do. ...............

.....do................

.....do................

.....do................

(2 return tubular. ......

.....do................

.....do................

.....do................

Size.

1 48" x 14', 32 3J" tubes; 6 

48" x 16', 32 3J" tubes; 2 42" 

x 16', 28 3i" tubes.

1 66" x 16', 54 4" tubes; 1 60" 

x IS', 42 4" tubes. 

3 66" x 16', 64 4" tubes; 1 66" 

x 14', 72 3*" tubes.

72"xl8' 72 4" tubes..........

66" x IS' 56 4" tubes. . ........

3 60" x 16', 48 4" tubes; 1 72" 

x IS', 90 3i" tubes.

2 60" x 18', 72 4" tubes; 1 90 

4" x 16' tubes; 1 10S 4" x 16' 

tubes; 1 120 4" x 16' tubes.

3 60" x IS', 36 4£" tubes; 1 72" 

x IS', 60 4i" tubes.

62" x 16'.............. ........

60" x 16'. 44 4" tubes. .........

Number installed.

9 

9

4 

4 

2 

3 

2

4

3 

3 

3

2 

1 

1 

4 

3 

4 

4

3

> 

4 

4

3 

4 

2 

3

Num

to c

Average 

heavy 

load.

2 

2 

 2 

2 

4

3 

2 

2 

2

2 

3 

4
TABLE 15. Details of observations at plants with side overfeed stokers unde

No. of 

plant.

146 

147 

148 

149 

150

151

152 

153

154 

155

156 

157 

158

159 

160

161 

162 

163

164 

165

Stoking.

Thickness of 

fire 

(inches).

6 

4 

3-4 

(a) 

8-10

6-8

6 

3-4

3-5

4-5 

5-6 

6

4 

4

6 

6

4-6 

4

Frequency of 

cleaning fire.

.....do................

.....do................

3 to 4 times hi 11 hours.

Once in ten hours ..... 

6 times in 24 hours ....

.....do................

.....do................

.....do................

.....do................

.....do.. ..............

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

Boiler

Type.

.....do................

.....do................

.....do................

.....do................

Return tubular; Heine 

water-tube.

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do............... .

.....do..:.............

.....do................

Size.

72" x 16', 92 3£" tubes ........

72" x IS'

60" x 16', 36 4|" tubes .........

60" x 16', 18 6" tubes. ........

4 72" x 16', 84 4" tubes; 4 72" x 

16', 72 4" tubes. 

1 72" x 18', 70 4" tubes; 1 113 

3£" x 16'; 2 87 3i" x 16'. 

72"xl6', 70 4" tubes..........

4 60" x 16', 44 4" tubes; 1 72" 

x 18', 45 5" tubes. 

78" x 18', 82 4" tubes. .........

1 72" x 18', 72 4" tubes; 1 72" 

x 18', 92 3£" tubes. 

72" x 16', 70 4" tubes. .........

2 72" x 20', 60 4" tubes; 3 72" 

x 20', 60 4V tubes. 

78" x 20', 86" 4" tubes. ........

1 72" x 18', 94 4" tubes; 1 60" 

x 16', 47 4" tubes. 

72" x 16', 84 3}" tubes. ........

60" x 18', 36 4i" tubes. ........

1 72" x 18', 45 5" tubes: 1 54" 

x 14', 42 3i" tubes. 

60" x 16', 46 4" tubes. .........

Number installed.

2 

2 

2

1

8

4

5 

5

2 

2

2 

2 

5

3

2

2 

2 

2

2 

1

Num

to 

Aver

age 

heav

load

a Variable.
TABLE 15. Details of observations at plants with side overfeed stokers under 

No. of plant.

120 .............................................

121 .............................................

122 .............................................

1 93

124 .............................................

125 .............................................

126 .............................................

131

133 .............................................

134 .............................................

136 -..........-.......-......-...........-----..

138 .............................................

i qo

140 .............................................

142 .............................................

1 d^

145 .............................................

1 452

149

150 .............................................

Furn

Number.

9 

9 

4 

4 

2

3 

2 

4 

3 

3 

3 

2 

1 

1 

4 

9 

4 

4 

3 

5 

4 

4 

3 

4 

2 

3 

2 

2

9

1

S

Grate area 

per boiler 

(square, 

feet).

33 

14 ^ 

IS 

24 

33 

20 

30 

25 

16 

22.5 

20.3 

21.8 

29.3 

25 

33 

36 

22 

20, 30 

25 

36, 45 

24.75 

22.5, 27 

25 

25 

33 

25 

36 

33 

20 

22.5 

33, 27.5

Distance from grates to 

tube heating surface.

Average 

(A).

21 

16, 18 

16 

17 

17.5 

16 

15, 17 

15.5, 13.5 

20 

IS 

IS 

IS 

IS 

17 

17.5 

19.5 

17.5 

15, 17 

17.5 

lo, 8 

IS 

IS 

17 

15 

17.5 

15.5 

15 

17 

15.5 

15.5 

16, 13

Minimum. 

(B).

18 

14, 16 

14 

14 

14.5 

13.5 

12, 14 

13, 11 

IS 

15.5 

15.5 

16 

15 

15 

14.5 

17 

15. 5 

13, 14.5 

15.5 

12.5, 5 

15.5 

15.5, 15 

15 

13 

14.5 

13.5 

12 

14 

13 

13.5 

15.5, 12

Width 

of furna

(C).
TABLE 15. Details of observations at plants with side overfeed stokers und

No. of plant.

151..............................................

153..............................................

154. .............................................

155 ..............................................

156..............................................

157:.............................................

158. .............................................

159. .............................................

160. ..............................................

161..............................................

162..............................................

163.........................:....................

164 .............................................

165..............................................

Fu

Number.

4 

5 

5 

2 

2 

2 

2 

5 

3 

2 

2 

2 

2 

2 

1

Grate area 

per boiler 

(square 

feet).

30-39, 33

25 

25, 30 

29.4 

25 

22 

13.5 

30, 36 

33 

33, 25 

25 

22.5 

25, 15 

17.7 

36

Distance from grates to 

tube heating surface.

Average 

(A).

6, 6, 16 

15.5 

16, 18 

17 

17.5 

16 

18 

26, 26.5 

19.5 

17, 16 

15 

18.5 

20.5 

15 

17

Minimum 

(B).

4.5, 4.5, 13. 5 

13 

13.5, 15 

15 

15.5 

14 

16 

23.5 

16.5 

14 

13 ' 

16 

19, 18 

13 

15

Wid

of fur

(C

6, 

5.
TABLE 15. Details of observations at plants with side overfeed stokers unde

No. of 

plant.

120

121 

122

123 

124

125 

126

127 

128

129 

130 

131 

132 

133

134 

135 

136 

137 

138 

139 

140

141 

142

Draft.

Kind.

Chimney..

...do...... 

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

,..do......

..do......

...do......

...do:.....

...do......

...do......

...do......

...do......

...do......

...do......

...do......

Readings (inches of water).

Furnace.

0. 08-0. 12

. 08- . 12 

. 08- . 12

.07- .08

.3Q 

. 10 -. 12

.22 

.11- .14

. 16- . IS

.36 

.10- .13

.25 

.09 

.18

. 20- . 27

.28- .37

. 07- . 11

.10- .16

.06- .08

.09- .15 

.33- .34

.23- .24

. 10- . 12

Rear of boiler.

' a. o. 22

.12- .22

Front 

tube 

sheet.

0. 38-0. 48

. 34- . 35

. 46- . 48

. 63- . 65

.37

.41

. 38- . 45 

.09- .19

Breeching.

0. 31-0. 68

. 52- . 68 

.85

.58 

.46

.46

.28

.46- .48

.36 

.35

.50- .65

.92 

.84

.42

.55 

.37

Base of 

stack.

0.64

. 48-. 52

1.10

.90

.50

Conditions under which 

readings were taken.

Furnace doors cracked; pit 

doors and dampers open. 

Dust pit and dampers open. . 

Dampers and ash-pit doors 

open; thin fire. 

Dampers and ash-pit doors 

open. 

Dampers partly closed; thin 

fire; dust doors threefourths open. 

Dampers and pit doors open. 

Damper and ash-pit doors 

open. 

Dampers open; ash and dustpit doors closed. 

Dampers and pit doors 

open; thin fire.

' Dampers open; thin fire. . . .

.....do......................

Damper and ash pit doors 

open.

Dampers open; ash-pit doors 

cracked.

.....do......................

<J Combustion chamber. 6 Several. 
TABLE 15. Details of observations at plants with side overfeed stokers und

No. of 

plant.

143 

144

145 

146 

147

148

149 

150 

151 

152 

153

154 

155 

156 

157

158 

159

160 

161 

162 

1631 

164

165

Draft.

Kind.

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do...... 

...do......

...do......

...do......

...do......

...do......

...do...... 

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

Readings (inches of water).

Furnace.

0. 12-0. 14

. 12- . 15

. 10- . 15

.OS 

. 16- . 18

. 08- . 16

.10 

.12 

.10- .12

.10- .16

.17 

.24- .29

.17- .20

.18

. 35- . 40 

.13- .15

.10- .32

. 16- . 19

.25- .27

. 12- . 15

.27- .30

.22

Rear of boiler.

a 0. 36-0. 40

d.20 

.25

d.45

Front 

tube 

sheet.

0. 20-0. 27

.16

.32

.33

.30

.43

Breeching.

6. 67^6. 75 

. 30- . 55

.85 

.32

. 38- . 40

.50 

. 85- . 95

.42- .45

.53 

.45 

. 47- . 50

.GO

Base of

stack.

0.58 

. 60-. 65

.47

.40 

.90

.55 

.56

.65 

.54

.62 

.75

. 47-. 50 

.76

Conditions under which 

readings were taken.

Ash-pit doors and dampers 

open. 

Average conditions; dampers partly closed.

Ash-pit doors and damper 

open. 

Damper and dust-pit doors 

open.

.....do... ...................

Dampers open; thin fire; ashpit doors cracked.

Damper and ash-pit doors 

open.

Thin fire; dampers partly 

closed.

Dampers and ash-pit doors 

open.

a Upper rear. & Several. c Various le
TABLE 15. Details of observations at plants with side overfeed stokers under 

No. of 

plant.

120 

121 

122 

123 

124

125 

126

127 

128 

129 

130 

131 

132 

133 

134 

135 

136 

137 

138 

139 

140 

141 

142 

143

144 

145 

146 

147

148

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet).

16 

15 

30 

0

47

48 

0.15

15 

15 

9 

3 

11 

11 

28 

12 

IS 

40 

20

7 

6 

8 

6 

0

26 

15 

50 

0

3

Size 

(feet).

6x5

4x4

4x3.5 

3. 5 x 4

0

0 

..........

Place at which 

measurement 

was taken.

45' from stack...

Number 

of elbows 

between 

boilers 

and 

stack.

1 

1 

1 

1

1

1 

1, 2

1 

1 

1 

0 

0 

0 

1 

0 

1 

1 

1 

2 

0 

2 

1 

1 

0

1 

1 

3 

0

0

Stack.

Height 

(feet).

185 

230 

ICO 

150 

125

180 

100, 90

90 

*90 

120 

100 

100 

53 

85 

220- 

220 

135 

140 

88 

138 

150 

100 

175 

100

100 

90 

120 

100

115

Size 

(feet).

a 10 

6x6 

4x4 

o5.3 

5x5

o3.5 

a3,2.2x2. 7

3.7x3.7

°5 

a4.3 

a 4. 3 

a 2. 5 

4x4 

a 4. 3 

06.0 

o5 

3.5x3.5 

a 4. 6 

"6.5 

a 4. 5 

05

06 

4x4

o3 

o5

Area 

(square 

feet).

78.5 

36 

16 

22.2 

25

9.6 

7.06,5.8

13.4

19.6 

14.7 

14.76 

4.9 

16 

15.7 

33.2 

19.6 

12.3 

16.5 

33.2 

15.9 

19.6

28.3 

1C

7.06 

19.6

7.06

Smokes considerably. 

Shavings fed continu

ulator on main dam

Plant has damper reg

keeping smoke dow

smaller than No. 3 is 

Smoke due to poking 

Smokes continuously, 

Smokes continuously, 

Plant has automatic r

Boilers arched over to

Smokes continuously, 

Boilers arched over to

Boilers arched over to

Boilers arched over to

Readings include som

passage.

Fires have to be poked 

Stack rests on rear of b

Boilers arched over 

Boilers arched over t

varied from 0.1 7 to 0

a Diameter.
TABLE 15. Details of observations at plants with side overfeed stokers unde

No. of 

plant.

149 

150

151 

152 

153

154 

155

156 

157 

158 

159 

160

161 

162 

163

164 

165

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet).

5 

4

17 

4 

4

28 

9

23 

8 

6 

4 

5

15 

6 

3

18 

0

Size 

(feet).

Place at which 

measurement 

was taken.

Number 

of elbows 

between 

boilers 

and 

stack.

0 

0

3 

0 

1

1 

0

2 

0 

0 

2 

2

. 1 

0 

1

0 

0

Stack.

Height 

(feet).

100 

165

158 

150 

103

100 

100

110 

149 

ICO 

150 

120

100 

90 

90

100 

100

Size 

(feet).

3x3 

"5

4x5 

«5

a4

2. 7x 4 

a4

2x3.4 

a 2. 5 

a6 

a6 

a 3. 2

a4

"3.5

o2.5 

4x4

Area 

(square 

feet).

9 

19.6

20 

19.6 

12.56

10.7 

12. 56

6.7 

4.9 

28.3 

28.3 

7.85

12.56

9.6

4.9 

16

Smoke observations 

Boilers arched over t

per cent black read

None of the observati

Observations include 

Coal does not work 

fifteen minutes, cau

Stack generally good

Observations have b

attached to main d

One side of each stoke

Boilers arched over to

Do. 

A J-inch steam jet e

ously. Observatio

regulator on main 

' Boiler arched over to

Usually a very good 

over top for gas pa

Stack smokes occasio

Boilers arched over t

a Diameter.
PLANTS WITH MECHANICAL STOKERS. 77

SUMMARY.

The importance of installing -the side-feed stoker with an arch 

over the entire grate can not be too strongly urged. At nearly every 

plant observed where this stoker had been installed with a short 

ignition arch only, trouble was experienced in keeping down smoke.

Some of the stacks having this stoker under them smoked badly 

because the fireman took advantage of the opening into the furnace 

and fired a part of the coal by hand.

There was some trouble in maintaining a. uniform feed of coal, at a 

few- of the plants visited. This seemed to happen when very fine 

coal was supplied. .With this stoker as ordinarily set, a banked fire 

can be maintained and the boiler thrown into service with only a 

small amount of smoke. The stoker has the valuable feature of a 

large coking plate area.

UNDERFEED STOKERS.

GENERAL DISCUSSION.

Stokers of the underfeed type differ radically from those described 

in the preceding pages. The fresh coal is forced into a horizontal 

retort, beneath that which has already ignited, and burns in a long 

heap that forms in the middle of the furnace. The unburned refuse 

is largely fused to a clinker, which slides down the sides of the heap 

and is hooked out by hand through the front of the furnace. The 

method of burning compels the use of mechanical draft, a fan being 

employed to force air through openings in tuyere blocks along the 

sides of the retort, at the level where the volatile hydrocarbons from the 

heap of burning coal are given off. Two makes of this stoker that have 

been put to the test of use under average power-plant conditions 

differ chiefly in the feeding mechanism and the device for handling 

the partly burned coal after it leaves the retort. In one pattern the 

coal is forced in continuously by a cone-shaped screw driven by a 

small steam engine, and the partly'burned coal falls on a flat grate 

through which air is drawn by a chimney. In the other pattern the 

coal is pushed beneath the burning heap in large charges, and the 

partly burned coal that rolls down the sides of the heap falls on a dead 

plate, where combustion is completed by the excess air that enters 

through tuyere openings. This method of burning coal has proved 

to be the better, and the plan of using air from the tuyeres for complete combustion has been generally adopted as correct. The newer 

models of underfeed stokers are always installed with automatic control for coal and air.

In all underfeed stokers the air and the distilled gases are intimately 

mixed and intensely heated by rising through the incandescent coal, 

so that combustion is complete within a very short distance from the
78 SMOKELESS COMBUSTION OF COAL.

FIGUKE 17. Underfeed stoker and Babcock & Wilcox boiler.

. FIGURE IS. Underfeed stoker and Heine boiler. 1, C tile on lower row of tubes, fonning a tile-roof furnace.
PLANTS WITH MECHANICAL STOKEES. 79

retort. Hence the combustion space required over the fuel bed is 

less than with any other type. By reason of its compactness and the 

small combustion space it demands, the underfeed stoker sometimes 

O 

gives good 

O 

results when installed in the 36-inch corrugated 

tJ

flue of an

internally fired boiler.

The customary method of placing this stoker under a Babcock & 

Wilcox boiler with uptake in the rear is shown by figure 17. In the 

setting of the Heine boiler (fig. 18) the C .tile on the lower stow of 

water tubes make a tile roof for the furnace. This increases the travel 

of the gases from the fire and permits complete combustion of the

FIGURE 19. Underfeed stoker and Stirling boiler.

carbon before the gases are chilled by contact with the tubes. In the 

regular setting of the Stirling boiler (fig. 19) the stoker is placed under 

the fire-brick arch. The construction of one of the makes of underfeed stokers is shown by figure 20, an elevation of a stoker under a 

return tubular boiler; figure 21, a cross section through boiler and 

stoker; figure 22, a plan of the stoker.

Attention has been called to the compactness' of the underfeed 

stoker and the small amount of space required above the grate. An 

illustration showing such a stoker set in the corrugated flue of a 

Scotch boiler is given in figure 23.
FIGUKE 20. Underfeed stoker and return tubular b
PLANTS WITH MECHANICAL. STOKERS. 81

Having the advantage of positive draft, the underfeed stoker allows 

a plant to be run without regard to weather conditions that may make 

the attainment of high draft by a stack impossible. The effects of 

weather changes on furnace draft are considerable and are very noticeable at plants which require all the available draft to carry their loads. 

Another valuable feature of this stoker is the ease and economy with 

which a variable load may be carried. The change from he'avy to

oooooo oooooo 

oooooooooooo 

oooooo oooooo 

oooooooooooo 

oooooooooooo

FIGURE 21. Underfeed stoker and return tubular boiler, cross section. 1, Dead plates; 2, retort; 3, tuy6re 

blocks; 4, air chamber; 5, space through which air passes before entering retort.

light coal charges or vice versa can be made without loss, because 

when the fuel supply is altered the air supply is at once regulated to 

the amount of coal being burned.

It sometimes happens that, to meet the competition of other types, 

a single underfeed stoker is installed under a boiler unit as large as 

200 horsepower. It is easy to show that such overloading of a stoker 

is not good business economy, particularly in localities where poor 

coal is supplied. On the assumption of an average ratio of heating

' 74897 Bull. 373 09 6
82 SMOKELESS COMBUSTION OF COAL.

surface to grate surface of 50 to 1, a 200-horsepower boiler should 

have 40 square feet of grate. Now while it is possible to burn, say 

30 pounds of average coal per square foot of grate surface per hour, 

or 1,200 pounds of coal per hour for a 200-horsepower boiler, it is not

FIGURE 22. Plan of underfeed stoker.

considered good practice to try to burn over 700 to 800 pounds of 

coal per stoker per hour with an underfeed stoker, as heavier feeding 

gives questionable results.' The consequence of trying to feed 4,200 

pounds of dirty coal per hour with one stoker of this type i§ evident.
PLANTS WITH MECHANICAL STOKERS. 83
84 SMOKELESS COMBUSTION OF COAL.

It is the general opinion that it is harder to keep down smoke at 

the small hand-fired return tubular, boiler plant than anywhere else, 

but the underfeed stoker has replaced many hand-fired furnaces at 

such plants. The only variable element in the operation of this stoker, 

once it is correctly installed, is the cleaning of fires, l?ut if the fireman 

is careful to burn clown the fires before breaking them, up there will 

be no necessity of making smoke.

DETAILED DESCRIPTION OF PLANTS.

The underfeed type of stoker was found at 48 different plants in 

eight different States, the size of the plants ranging from 75 to 3,500 

rated boiler horsepower. These plants burned coal from Illinois, 

Indiana, Kentucky, Ohio, Pennsylvania, and West Virginia, the cost 

of which.ranged from $1.03 to $2.75 per ton, the conditions at the 

different plants varying widely. The size of the boiler units ranged 

from 50 to 500 horsepower; at 33 plants the units were 200 horsepower or less, and with two exceptions one stoker per boiler was 

installed at these plants. All but five of- the plants had automatic 

regulators for coal or air. But two of these stokers were set in a 

Dutch oven; this setting was used because the boilers were of the 

vertical type.

Plants with water-tube boilers. Underfeed stokers were found under 

water-tube boilers at 22 plants, at 4 of which the fuel was run-of-mine 

coal. At 13 plants the load carried was uniform, and at 9 it was 

variable. The thickness of fire ranged from 8 to 18 inches. The 

kind of coal burned is stated in the following summary:

Kind of coal burned at plants with underfeed stokers under water-tube boilers. 

Number of 

plants, a.

Illinois.......................................................... 5

Indiana......................................................... 1

Kentucky...................................................... 1

Ohio........................................................... 7

Pennsylvania................................................... 8

- West Virginia.................................................... 1

Some averages of the observations at these plants are given below:

Difference of draft between ash pit and furnace, 3 inches of water.

Coal as received burned per stoker per hour, average heavy load, 560 pounds; 

extremes, 330 and 1,060 pounds.

Percentage of rated boiler horsepower developed average heavy load (boiler rated on 

10 square .feet of heating surface per horsepower), 92; extremes, 58 and 146.

Average distance from grate to heating surface (dead plates to shell), 4.9 feet; 

extremes, 3 and 7.5 feet.

a One plant burned both Ohio and Pennsylvania coal.
PLANTS WITH MECHANICAL STOKERS. 85

Least distance from grate to heating surface (dead plates to shell),.3.8 feet; extremes, 

2 and 5.3 feet. 

Smoke, black, 2.4 per cent. 

Average draft conditions: Pressure in ash pit, 17 plants, 2.45 inches of water; range,

I to 4 inches. Draft in furnace, 19 plants, 0.33 inch; range, 0.01 to 1 inch. Draft in 

rear of boiler, 13 plants, 0.48 inch; range, 0.17 to 1.07 inches. Draft at base of stack,

II plants, 0.80 inch; range, 0.24 to 1.50 inches. The approximate pressure and drafts 

deduced from these readings are as follows: Pressure in ash pit, 2.50 inches of water; 

draft in furnace, 0.35 inch; draft at rear of boiler, 0.50 inch; draft at base of stack, 

0.80 inch. This gives a drop of about 3 inches through the fuel bed, of about 0.15 inch 

through the boiler, and of 0.30 inch from the boiler to the stack.

Details of the observations at plants with underfeed stokers under 

water-tube boilers are given in Table 16.
TABLE 16. Details of observations at plants with underfeed sto

No of 

plant.

166

168

169

170

171

172

174

1 7^

176

177

178

179

181

182

1 QQ

1 fid

185

186

187

State.

.....do................

.....do................

.....do................

.....do................

.....do................

Ohio..................

.....do................

New York

.....do................

Kind of stoker. 

.\

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do.... ................. .

.....do......................

.....do......................

.....do......................

.....do.... ..................

.....do......................

.....do......................

.....do......................

.... .do... ...................

Total

rated 

horsepower.

3,500

2,000

2,000

1,875

400

230

728

909

COO

300

300

200

200

1,400

800

720

700

000

320

300

276

275

Commercial name.

.....do..................

.....do..................

Pittsburg No. 8.........

burg; Reynoldsville.

Thacker. ...............

W

Illinoi

.....do.

.....do.

.....do.

Ohio..

.....do.

.....do.

.....do.

.....do.

.....do.

.....do.

.....do..

.....do.

.....do.

West Vi
TABLE 16. Details of observations at plants urith underfeed stokers und

No. of 

plant.

166 

167 

168 

169 

170 

171 

172 

173 

174 

175 

176 

177 

178 

179 

180 

181 

182 

183 

184 

185 

186 

187

Load.

Requirement.

Power

.....do......................

.....do......................

.....do......................

..... do. .....................

.....do......................

.....do......................

.....do......................

Nature.

.....do....................

.....do....................

.....do...................

......do....................

.....do....................

.....do... .................

.....do....................

.....do....................

.....do....................

.....do...................

.....do....................

.....do...................

Character.

.....do. .....................

.....do......................

.....do......................

.....do.....................

.....do.....................

Hotel.. ....................

Av

Heavy.

Hours 

per day 

load is 

on plant.

20 

20 

20

8 

24

9.5 

10 

10 

10 

10 

24 

24 

24 

10 

16 

12 

9 

24 

24 

10 

10

Co

burn

per 

(sh

ton

I

a. Boiler rated on 10 square feet of heating surface per h
TABLE 16. Details of observations at plants with underfeed stokers u

No. of 

plant.

166 

167 

168 

169 

- 170 

171

172

173 

174 

175

176 

177

- - 178 

179

ISO

181 

182 

183

' 184 

185 

186

187

Stoking.

Method.

Automatic... . 

.....do........

.....do........

.....do........ 

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........ 

.....do........

.....do........

.... :do.-. -.-:.. :

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

/H a n d -o p - 

\ erated.

.Thickness of 

fire 

(inches).

14 

14 

14 

Variable.

Variable. 

12-15

12-15

12-15

Variable. 

15-18

15 

8-15

} 12-15

Frequency of 

cleaning fire.

5 times in 20 hours. 

.....do............

.....do............

3 times in 24 hours . 

6 times in 24 hours . 

4 times in 24 hours.

Once in 9 hours....

4 times in 24 hours. 

Once every 4 hours 

2 times in 10 hours .

.....do............

2 times in 8 hours . . 

2 to 3 times in 24 

hours. 

2 times in 10 hours .

3 times in 9 hours .

3 to 6 times in 24 

hours. 

3 to 4 times in 24 

hours. 

2 times in 10 hours.

fl to 2 times in 10 

\ hours.

Type.

.....do.........

.....do.........

Scotch marine. 

Babcock & 

Wilcox.

.....do.........

Park .....'.....

Wickes vertical. 

.....do.........

Scotch marine . McNaull.......

Edgemoor.....

Gill..!........

Babcock & 

Wilcox. 

.....do.........

Babcock & 

Wilcox. 

Wood horizontal.

Size.

.....do........................

286 3J" tubes, 3 36" x 14' drums

54 4" x 16' tubes, 1 36" drum. . .

Two, 176 34" tubes; one, 280 

3J" tubes 3 36" drums each.

131 4" x 18' tubes, 3 35" x 20' 

drums. 

140 4" x 18' tubes between 

water legs.

144 4" x 18' tubes, 1 42" drum.

72 4" x 16' tubes...............

64 4" x 16' tubes, 1 36" drum . . 

}...............................

Num

ber i

stalle

: 

: 

10° to 24° F. superheat.
TABLE 16. Details of observations at plants with underfeed stokers u

No. of plant.

166.........................................................

167 .........................................................

168 .........................................................

169.........................................................

170 .........................................................

171 .........................................................

172 .........................................................

173.........................................................

174.........................................................

175.........................................................

176 ........................................................

177 ...............................I.........................

178.........................................................

179.........................................................

180 .....................:...................................

181 .........................................................

182 .........................................................

183.........................................................

184.........................................................

185.........................................................

186......................:..................................

187.........................................................

t Kind.

Plain..........

.....do..........

.....do..........

.....do..........

Corrugated flue.

.....do..........

.....do..........

.....do..........

Dutch oven .... 

.....do..........

Corrugated flue. 

Plain'. .........

.....do........./

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

Number of 

stokers per 

boiler.

3 

3 

3 

3 

2

1 

(a) 

2 

2 

2 

2 

1 

2 

2 

2 

1 

2 

2 

1 

1 

1 

1

Distance from 

tube heating 

Average (A).

4.5 

4.5 

4.5 

7.5 

10 

4.5

7.5 

5 

6 

6 

11 

4.3 

4.75 

-.---. - 4.8 

3.5 

7 

4 

3.5 

3.5 

4 

3 

a Two on 328 horsepower; one on 200 horsep
TABLE 16. Details of observations at plants with underfeed stokers u

No. of 

plant.

166 

167 

168 

169

170 

171

172

173 

174 

175 

176 

177 

178 

179 

180

181 

182 

183

184 

185 

186 

187

Draft and pressure.

Kind.

Chimney and forced.

.....do...............

.....do...............

Induced and forced . . 

Chimney and forced .

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

.....do...............

Readings (inches of water).

Pressure 

in 

ash pit.

3.6 

2.8 

3

0. 90-1. 13 

2.25

2 

1 

2 

2 

.25

4 

2.1

2.3

2-3 

1.5 

3-3.2

2 

2 

3.5

Draft.

Furnace.

0.28 

.33 

34 

0. 86-l! 02

.35 

.32

. 32-. 35

. 20-. 30 

.48 

.20 

.23 

. 17-. 25

.32 

. 25-. 55

. 43-. 66 

.44 

. 10-. 17

. 28-. 50 

.12 

 .15 

0-.02

Rear 

of 

boiler.

0.48 

.53 

.54 

a.98-1. 16

.39 

a. 40-. 42

&. 33-. 40

o.28 

o.50

. 55-. 78

a.60 

. 34-. 44

.19

14- 19

Front 

tube 

sheet.

0.70

.70

Breeching.

.50

0. 52-. 56

.90

.80

Base 

of 

stack.

1.50

.57 

.70

.64

.88

1

Q9

.9-1 

1

.24

.40

90

Conditions under 

readings were ta

Dampers open, fan 

at maximum spee

Average conditions; 

partly closed. 

Average conditions; 

doors cracked.

Average running co

Damper open; fan 

at average speed.

Damper one-half op

nace doors cracked 

o Lower rear boiler. * Upper rear boiler. 
TABLE 16. Details of observations at plants with underfeed stokers un

No. of 

plant.

166 

167 

168 

169

170 

171

172 

173 

174 

175 

176 

177 

178 

179

ISO 

181 

182 

183

184 

185 

186

187

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet). t

0 

8 

0 

32

28 

4

30 

80 

0 

8 

3 

8 

15 

23

24 

28 

10 

0

25 

105 

3

65

Size 

(feet).

4x4

»70

Place at which 

measurement 

was taken.

50 feet from stack. .

Number 

of elbows 

between 

boilers 

and 

stack.

0 

0 

0 

2

1 

1

1 

2 

0 

2

0 

2

1 

8

1 

 1 

0 

0

1 

2

2

4

Stack.

Height 

(feet).

80 

158 

80 

330

37 

85

123 

165 

120 

80 

80 

200 

162 

150

135 

200 

125 

120

145 

. 150 

58

175

Size 

(feet).

a 4. 5 

«6. 4 

a6 

a8

o4 

3. 3 x 3. 3

a 6. 2 

«5 

.6 x6 

4 .x4 

aS.S 

2. 5 x 2. 5 

a6 

6 x6

«6 

a5 

06 

04

<*5 

«3 

«3

a6

Area 

(square 

feet).

15.9 

32.3 

2S.3 

50.25

12.-56 

11.1

29.86 

19.6 

36 

16 

11.6 

6.3 

28.3 

36

28.3 

19.6 

28.3 

12.56

19.6 

7.06 

7.06

28.3

Seven stacks, each 

Two stacks, each o

Coal varies from 11

to 12 per cent mo

With damper part

smoke produced 

taken while clea

fire.

Coal as fired runs a

Stack on rear of bo

Stack smokes abou

Do.

Boiler baffled verti

Boilers baffled ver

smokes 10 to 40 p

Observations inclu

Coal as received ru

Coal runs about S 

running at abou

Boiler baffled verti

Coal as received ru

Cleaned fire durin

stoker per hour, 

a Diameter. 
92 SMOKELESS COMBUSTION OF COAL.

Plants with return tubular boilers. Underfeed stokers were installed 

under return tubular boilers at 26 plants. The fires carried ranged 

in thickness from 12 to 18 inches. Four of the plants burned runof-mine coal. Seventeen carried a uniform load, and 9 a variable 

load. The kinds of coal burned were as follows:

Kind of coal burned at plants ivith underfeed stokers under return tubular, boilers.

Number of 

plants.a

Illinois.......................................................... 1

Indiana......................................................... 4

Kentucky....................................................... 1

Ohio............................................................ 3

Pennsylvania.................................................... 8

West Virginia.......................................:........... 4

Miscellaneous................................"................... 7

Various particulars regarding these plants are condensed in the 

following statement:

Coal as received burned per stoker per hour, average heavy load, 513 pounds; range, 

225 to 750 pounds.

Percentage of rated boiler horsepower developed, average heavy load (boiler rated on 

10 square feet of heating surface per horsepower), 74; range, 57 to 135.

Average distance from grates to shell, 2.8 feet; range, 2 to-3.75 feet.

Smoke, black, 2.6 per cent.

Approximate average pressure in ash pit, 1.75 inches.

Approximate average draft in furnace, 0.20 inch; at front tube sheets, 0.30 inch; at 

base of stack, 0.50 inch. This gives an average drop of 2 inches between the ash pit 

and the furnace, 0.10 inch through the boiler, and 0.20 inch from the boiler to the 

stack.

Details of the observations at plants with underfeed stokers under 

return tubular boilers are given in Table 17.

a Two plants burned both Ohio and West Virginia coal.
TABLE 17. Details of observations at plants with underfeed stokers u

No. of 

plant.

188

189

190

191

192

193

194

195

196

198

199

200

201

202

203

204

205

206

207

208

209

210

211

213

State.

Illinois................

.....do................

.....do................

.....do................

Ohio..................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

.....do................

Illinois. ...............

Kind of stoker.

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Total

builder's 

rated 

horsepower.

200

S

CAft

?nn

125

530

300

9nn

200

1 V»

1,104

860

800

736

625

260

i zf\

500

500

375

300

o=n

Commercial name.

Washed.................

.....do..................

.....do..................

.....do..................

.....do..................

.....do..................

Where min

.....do...........

.....do...........

.....do...........

Ohio............

Ohio; West Virgi

.....do..........

.....do..........

.....do...........

.-...do..........

.....do..........

.....do..........
TABLE 17. Details of observations at plants voith underfeed stokers under 

No. of 

plant.

188 

189 

190 

191 

192 

193 

194 

195 

196 

197 

198 

199 

200 

201 

202 

203 

204 

205 

206 

207 

208 

209 

210 

211 

212 

213

Load.

Requirement.

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Heat........................

.....do......................

.....do......................

Nature.

.....do....................

.....do....................

.....do....................

Uniform. .................

.....do....................

.....do....................

.....do....................

.....do....................

.....do....................

.....do....................

.....do...................

.....do....................

Character.

Oil refiner y .................

Salt works ..................

Hospital....................

.....do......................

.....do......................

A

Heavy.

Hours 

per day 

load is 

on plant.

8 

17 

10 

11 

11 

18 

24 

10 

12 

10 

14 

24 

24 

14 

24 

12 

10 

12 

24 

24 

24 

 24 

24 

12 

24 

9

Co

burn

per d

(sh

ton

5

. 

5

2

3

2

2

2

^Boiler rated on 10 square feet of heating surface per h
TABLE 17. Details of observations at plants with underfeed stokers under 

INo.of 

plant.

188 

189 

190 

191

192 

193 

194

195 

196 

197 

198

199 

200 

201 

202 

203

204 

205 

206 

207

208

209 

210 

211 

212 

213

Stoking.

Method.

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

Hand operated..

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

.....do..........

Hand operated.. 

.....do..........

.....do..........

.....do..........

.....do..........

Thickness of 

fire 

(inches).

-

12-15

15 

12-15

15-18 

12-16 

12-15 

15-18

15-18 

15

i2-is

12

12-15 

12 

15-18

Frequency of cleaning 

fire.

1 to 2 times in 8 hours . .

4 times in 10 hours. . . . 

2 times in 11 hours. . ..

.....do................

4 times in 24 hours ....

Once in 14 hours ......

4 to 6 times in 24 hours. 

4 times in 24 hours. . . . 

3 to 4 times in 24 hours. 

4 to 6 times in 24 hours. 

6 times in 12 hours. . . .

Every 4 to 6 hours. . . . 

3 times in 24^hours ....

4 to 6 times in 24 hours. 

6 times in 24 hours ....

S times in 24 hours ....

2 times in 12 hours ....

2 times in 9 hours .....

Size.

60" x 16', 42 41" tubes .......

72" x 18', 135 3" tubes. ...........

66" x 16', 64 4" tubes.. .......:....

1 60" x 14', 60 3" tubes; 1 60" x 

16', 52 4" tubes. 

72" x 16', 84 4" tubes .............

48" x 16', 36 3J" tubes. . ..........

2 72" x 16', 724" tubes; 2 78" x 18', 

84 4" tubes. 

72" x 18', 100 3J" tubes. ..........

72" x 16', 84 4" tubes..............

60" x 16', 72 3i" tubes.. . ..........

1 66" x 18', 544" tubes; 1 66" x 16", 

54 4" tubes. 

78" x 18', 154 3" tubes.. :..........

84" x 18', 1044" tubes............

78" x IS', 104 4" tubes.. . ..........

78" x 18', 154 3" tubes.. . ..........

4 72" x 17', 100 3£" tubes; 1 72" 

x 15', 94 4" .tubes. 

72" x 16', 724" tubes..............

3 72" x 18', 72 4" tubes; 1 tiO" x 

18', 54 4" tubes. 

1 72" x 16', 72 4" tubes; 2 72" x 16', 

90 3" tubes; 1 72" x 16', 92 3" 

tubes. 

72" x 16', 92 3" tubes.. ............

.....do............................

72" x 20', 47 5" tubes. ............

60" x IS', 44 4" tubes. ............

Number installed.

2 

20 

7 

2

1 

2 

4

2 

2 

2 

2

b 

4 

4 

4 

5

4 

3 

2 

4

4

4 

3 

2 

2 

1

Num

c

Avera

heav

load
TABLE 17. Details of observations at plants with underfeed stokers under 

No. of 

plant.

188 

189 

190 

191 

192 

193 

194 

195 

196 

197 

198 

'199 

200 

201 

202 

203 

204 

205 

206 

207 

208 

209 

210 

211 

212 

213

Furnaces.

Kind.

Plain ........................ ...."....................................

.... .do ................................................................

.....do ................................................................

.....do ................................................................

.... .do ...................................................................

.....do..................................................................

.....do............................................:....................

.... .do .................................................................

.....do..................................................................

.....do.................................................................

.....do.................................................................

.....do.................................................................

.... .do ................................................................

.....do.................................................................

.....do..................................................................

.....do.................................................................

.....do..............................................................;..

.....do.................................................................

.... .do .................................................................

.....do....................................'.............................

Plain .................................................. ^ ...............

Plain ..................................................................

.....do.................................................................

.... .do .................................................................

Number of 

stokers per 

boiler.

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1

Distance from gr

tube heating su

Average 

(A).

15.5 

15.5 

15 

13,15 

15 

16 

15, 17 . 

16.5 

15 

15 

17,15 

17 

17 

17 

17 

16,13 

15 

17 

18 

17 

19.5 

20 

14. 5, 19. 5 

17 

19 

16.5

Mi

1
TABLE 17. Details of observations at plants ivith underfeed stokers under 

No. of 

plant.

188

189 

190

191 

192 

193

194 

195 

196 

197 

198

199 

200 

201 

' 202 

203 

204 

205 

206 

207 

208 

209 

210 

211 

212

213

Draft and pressure.

Kind.

Chimney and 

forced. 

.....do........

.....do........

.....do........

.....do........

.....do......... 

.....do.........

.....do........

.....do........

.....do........

.....do.........

.....do......... 

.....do........

.....do........

.....do.........

.....do.........

.....do.........

.....do........

.....do.........

.....do.........

.....do........

.....do.........

.....do........

.....do.........

.....do........:

Readings (inches of water).

Pressure in 

ash pit.

2.5 -3

1. 40, 1. 50

2.55 

1.25

1.5

.75 

1.45 

1.70

2 

2.5 -3 

1.5 

1.5 

1 

2 

1. 25-1. 50 

.90-1.10 

2.25

.5 

1.6-2.1 

1.4 

2. 5-2. 75

Draft.

Furnace.

0.12-0.14

.04- .20

.29- .30

.36 

. 13- . 20

. 20- . 46 

.21- .22

.22- .28 

.28- .29 

. 39- . 41

.10- .13 

+ .28 to -.06 

.50 

. 16- . 24 

+ .04 to -.02 

.06- .16 

. 15- . IS 

.12 

. 10- . 15 

.02- .12

.08- .13 

0- .08 

.46- .55 

-.17

Rear 

of 

boiler.

Front tube 

sheet.

0.40

.40 

0. 2C- . 36

.32- .37

.17- .24

+ .30-to-.04

.50 

.25- .28

+ .12 to -.04

.17- .18

.11- .20

.46- .55

Breeching.

aO.52

.27

0. 2S-. <6

.54

.30 

.34 

. 1C-. 22

.16-. 22

.30

1

Base of 

stack.

0.60 

.40

.70 

50

Conditions under 

which readings 

were taken.

Average condition

dampers open. 

Dampers wide ope

Average condition

dampers open.

.....do............

Fan running at ma

imum speed.

54

.90 

.30

.50

.35

.40 

.40 

.44

.65

.37

Average condition

damper open.

I::::::::::::::::::

One boiler in serv

ice; damper ope

Near stack. >> Several. r Various l
TABLE 17. Details of observations at plants with imderfeed stokers unde

No. of 

plant

188 

189 

190 

191 

192 

193

194 

195 

196 

197 

198 

199 

200 

201 

202 

203 

204 

205 

206

207 

208

209 

210 

211 

212 

213

Breeching.

Length 

from 

stack to 

nearest 

boiler 

(feet).

15 

15 

0 

8 

0 

5

9 

24 

17 

31 

30 

6 

70 

13 

5 

32 

5 

6 

16

13 

0

16 

9 

45 

'0 

2

Size 

(feet).

3.5 x 3.5

Place at which 

measurement was 

taken.

Number 

of elbows 

between 

boilers 

and 

stack.

0 

2 

0 

1 

0 

1

1 

1 

0 

2 

1 

0 

3 

0 

0 

1 

2 

0 

1

1 

0

1 

1 

2 

1 

1

Stack.

Height 

(feet).

110 

200 

85 

140 

65 

80

95 

SO 

80 

97 

130 

100 

150 

200 

70 

90 

65 

75 

 100

125 

100

75

75 

120 

75 

55

Size 

(feet).

a3.25 

a8 

a5.5 

a3.1 

a3

.05.5 

a 3. 5 

a 4. 25 

4x4 

a3.5 

7.5 x 7.5 

06 

a4 

5x5 

a6.5 

3x3 

3x3 

5x5

a 4. 5 

a4

a4 

04 

5x5 

a 3. 3 

2.5 x 2.5

Area 

(square 

(feet).

10.5 

50.3 

23.7 

7.45 

7.07

23.8 

9.6 

14.1 

16 

9.6 

56.25 

28.3 

12.56 

25 

33.2 

9 

9 

25

15.9 

12.56

12.56 

12.56 

25 

8.7 

5

Observations incl

Distance to heatin

Large combustion 

pit was measure

Boilers arched ov

Some smoke when 

Large combustion 

Boilers arched ov

Cleaned fire durin

Boilers arched ove

Two similar stack

Coal not well bu

light load. Fire 

observation. S

Boilers arched ove

No smoke except 

(or lower) smok

Do. 

Each furnace gives 

Burned 728 pound

Some smoke wh

oDiameter.
PLANTS WITH MECHANICAL STOKERS. 99

SUMMARY.

The underfeed stoker affords a means of increasing both the economy and capacity of plants which by gradual growth have added so 

many boilers to a single stack that the draft capacity of the stack has 

been exceeded, and natural draft does not supply the necessary amount 

of air to permit the required amount of coal to be burned with high 

efficiency.

A very much smaller stack will suffice with the underfeed stoker 

than with some other devices, as it is only necessary to have enough 

stack draft to carry away the gases of combustion, all the air necessary for burning the coal being forced through the foe.

It will be seen that this stoker is meeting with most success in districts where low-ash coal is used.

The notes show that the greatest difficulty in keeping down smoke 

came when cleaning fires, but in general at the plants visited there was

little trouble on this account.

In this stoker the ash accumulates at either side of the -retort. 

The furnace temperature is so high that most of the ash fuses and 

is pulled out of the furnace in large pieces. Both for this reason 

and to permit complete combustion of the fuel it is advisable to have 

the dead plate on which the clinkers accumulate of sufficient width 

to permit cleam'ng foes without breaking up the fuel bed.

SMOKE PREVENTION AT BOILER PLANTS WITH GREAT VARIATIONS OF

LOAD.

The data already presented show that bitumnious coals high in 

volatile matter can be burned without smoke. Smokeless combustion at large plants carrying loads that fluctuate widely, where boilers 

over banked fires must be put in service quickly and foes forced to 

the capacity of the units, is no less possible. The accompanying load 

diagram (fig. 24) shows the variations in boiler horsepower in service 

and in power output at a plant of about 10,000 horsepower. The 

sudden increase in output and in boilers in service between 5.30 and 

8.30 a. m. and the heavy peak load in the'early evening are strikingly 

brought out. Yet the stacks at this plant, though frequently watched 

at the time of peak load, were quite clean. No better demonstration 

than this of what can be done by proper equipment, efficient labor, 

and intelligent supervision could be given.

HAND-FIRED FURNACES.

GENERAL STATEMENT.

None of the problems of combustion have received more experimental treatment than the burning of coal in hand-foed furnaces. 

Hundreds of devices for smokeless combustion have been patented,
100 SMOKELESS COMBUSTION OF COAL.

but almost without exception they have proved failures. This record 

may be explained by the fact that many of the patentees have been 

unfamiliar with all the difficulties to be overcome, or have begun at 

the wrong end. Numerous patents cover such processes as causing 

the waste gases to reenter the furnace, and schemes for collecting 

and burning the soot are legion. So many -manufacturers who have 

been looking for some cheap addition to a poorly constructed furnace

 Total kilowatt output

 Rated boiler horsepower in service

5A..M. . 0 3RM. 8 12

FIGURE 24. Load and boiler-service chart of large power plant with mechanical stokers. The total 

rated boiler horsepower used to supply the demand for power varied from about 2,000 to 12,000. This 

plant is absolutely smokeless.

to make it smokeless have experienced inevitable failure that the 

work of educating the public to rid cities of the smoke nuisance has 

been hard, long, and only partly successful.

The total number of steam plants having boilers fired by hand is 

far greater than the total of plants with mechanical stokers, but if 

the comparison is based on total horsepower developed the figures 

show less difference. Particularly is this true in sections of the Middle 

West, where mechanical stokers are generally used at large plants.
HAND-FIKED FURNACES. ' 101

As a general rule hand-fired plants do not have proper furnaces, and 

methods of operation are far from conducive to good combustion. 

Coal is usually,fired in large quantities, and little opportunity is given 

for the air and gases to mix before the heating surface is reached and 

combustion is arrested. In all the hand-fired plants visited success 

in smoke prevention has been obtained chiefly by careful firing. The 

coal was thrown on often in small quantities; the fire was kept clean, 

enough ash to prevent the passage of air through the fire never being 

allowed to collect on the grate; and more air was supplied at firing 

than after the volatile matter had been distilled. Even with such 

precautions the plants might have made objectionable smoke at times 

but for the fact that usually some method was employed -for mixing 

the gases and air before they reached the heating surface.

COKING FURNACE.

One pattern of furnace that requires less attention from the fireman 

and less care in operating than the usual hand-fired types was found 

at several plants. This is known as the coking furnace, which in its 

earliest form was the invention of James Watt. With this furnace 

large charges of coal may be fired at one time. The coal is shoveled 

or fed from magazines to a dead plate at the mouth of the furnace, 

where the volatile compounds distill, and the coal is later pushed 

back. Unfortunately, in the model of this furnace generally used 

the magazines are open after the coal on the dead plate has burned 

down, so that the coal is consumed with a large excess of air.

STEAM JETS.

A clean stack with hand firing is not as good evidence of efficient 

operation as it is with almost any type of mechanical stoker, because 

of the special devices used with hand-fired boilers to prevent smoke. 

Steam jets are the most common of such devices. Usually they are 

not automatic, and at many plants they are allowed to run longer 

than is necessary or else are not used at all. Any steam jet that 

will so mix the gases and air at the times of greatest need, when coal 

is fired, as to prevent smoke will, if allowed to run continuously, 

probably waste more of the energy in the coal than it will save. At 

the same time a steam and air admission device allows a regulation 

which, if properly made, will keep a stack clean and save coal.

The steam jet is found in an improperly designed furnace or in one 

where the air supply is too small. It is an expensive device, all 

conditions being considered. The only purpose it can serve is to mix 

the air and gases.intimately and prevent the combustible gases from 

coming too quickly into contact with the heating surface. The 

claims sometimes made that the use of a steam jet will increase the 

thermal value of the fuel are erroneous.
102 SMOKELESS COMBUSTION OF COAL.

It takes the same amount of heat to dissociate a pound of steam 

into hydrogen and oxygen as is given off when a pound of steam is 

formed by the union of hydrogen and oxygen. Moreover, the fact 

must not be overlooked that to burn hydrogen in the average furnace 

is extremely difficult, and therefore if some steam were dissociated by 

a jet it is probable that part of the hydrogen would escape to the 

stack unburned. The same quantity of oxygen that is formed by the 

dissociation of a pound of steam would be required to burn enough 

hydrogen to form another pound of steam, therefore there would be 

no oxygen available from dissociation to burn the coal.

In a water-gas plant, sometimes cited by makers of steam-jet 

attachments, the heat required to dissociate the steam is supplied by 

the coke and is later utilized when the gas is burned. The process is 

as follows: Air is blown through the fuel bed until combustion is 

fairly well started. The air is then shut off and steam is blown 

through; this is dissociated, the fuel loses its heat and if the operation 

continues too long the fire goes out; but after a certain length of time 

the steam is turned off and air is passed through until the fuel bed is 

in condition to give up more heat. Then steam is turned on again 

and the process repeated. After several hours of operation several 

thousand cubic feet of gas have been formed from the union of the 

dissociated oxygen of the steam with the glowing carbon of the coke, 

but there has been no gain in thermal units.

Another fact to be remembered in using steam jets is that all steam 

entering the furnace must be heated to stack temperature, and the 

heat required for this is supplied from the coal.

As most air is required in a furnace at the moment of firing fresh 

coal, and the requirement diminishes as the volatile matter in the 

coal is distilled, steam jets need close regulation for good economy.

To make this regulation independent of the fireman several devices 

for automatically turning the steam on and off have been patented. 

Figure 25 illustrates one of these devices at a furnace under a watertube boiler, and figure 26 gives a section through a return tubular 

boiler with similar equipment. Opening the furnace door turns on the 

steam, and a dash pot suitably connected shuts off the jets after a 

short interval.

MIXING DEVICES.

There is no question as to the value of mixing the air and gases in 

a hand-fired furnace, and if the mixing could be done by some 

effective arrangement of fire-brick piers the losses resulting from the 

use of steam jets would be avoided, but to build arches and piers 

that will stand the intense heat from intimate mixing and combustion 

has proved a difficult matter. Moreover, the piers and arches take
HAND-FIBED FURNACES. 103

up room and diminishing the space in a furnace will usually reduce 

the available furnace draft, so that less coal can be burned even 

though there is more perfect combustion. The easiest and most 

nearly perfect solution of the problem is a mechanical stoker properly 

set under the boiler.

DETAILED DESCRIPTION OF PLANTS.

During the field investigations 71 hand-fired plants run without the 

emission of dense smoke were visited. The types of boilers installed 

at these plants were as follows: Return tubular, 44; water-tube, 22;

FIGURE 25. Automatic stearn and air admission device and water-tube boiler, l, Dash pot used to control 

length of time steam jets are in operation; 2, air admission through furnace doors.

Scotch marine, 5. Tables 20 to 25 give all the essential data that 

could be collected regarding these plants.

Plants witli water-tube and Scotch marine toilers. Hand-fired 

furnaces operated under water-tube or Scotch marine boilers were 

found at 27 plants. These furnaces were of the following patterns: 

Plain, Dutch oven, Burke, Dorrance, down-draft, Puddington, and 

twin arch. Brief descriptions of three of these, including the downdraft pattern, are appended, and some of the others are described 

in the discussion of hand-fired furnaces with return tubular boilers 

(pp. 117-124).
104 SMOKELESS COMBUSTION OF COAL.

One of these furnaces is virtually a Dutch oven with a long, 

rearward-sloping arch that entirely covers the grate and projects into

the space back of the bridge wall. The grate also has a rearward 

slope. The accompanying illustration (fig. 27) of one of these furnaces
HAND-FIRED FURNACES. 105

under a Babcock & Wilcox boiler shows how the travel of the burning 

gases is lengthened.

The distinguishing feature of the down-draft furnace is an upper 

grate, which may be formed of tubes through which water circulates,

FIGURE 27. A hand-fired furnace and Babcock & Wilcox boiler.

connected to headers and supported by lugs. The fresh coal is thrown 

on this grate, whence, after partial burning, it falls to a grate of ordinary construction a foot or more below, where combustion is comFIGURE 28. Down-draft furnace and Heine boiler. 1, Water-tube grate; 2, C tile on lower row of tubes,

forming a'.tile-roof furnace.

pleted by the excess of air drawn through the upper and lower 

grates. The air and the distilled gases from the fresh coal are heated 

and intimately mixed in passing through the fuel bed, facilitating
106 SMOKELESS COMBUSTION OF COAL.

combustion in the space between the grates. One of these furnaces 

under a horizontally baffled Heine boiler is represented in figure 28.

The third furnace has back of the bridge a fire-brick wall with 

two arched openings at its base separated by a projecting angle. The

FIGUKE 29. A hand-fired furnace and Babcock & Wilcox boiler, elevation. X-X', Line of sectional plan,

figure 30.

long minimum distance from grate to first tube heating surface is 

shown by figure 29. The plan of the furnace (fig. 30) and the cross 

section (fig. 31) show the construction of the mixing wall.

y 

FIGURE 30. A hand-fired furnace, plan along line X-X', figure 29. y-y', Line of cross section, figure 31.

These 27 plants ranged in size from 75 to 1,500 horsepower. Seven 

were equipped with steam-jet devices. Ten had a variable load and 

17 a uniform load. At 9 plants the coal supplied was either run-ofmine, egg, or lump. The coal as fired burned per square foot of grate
HAND-FIRED FURNACES. 107

surface per hour varied from 10.8 to 40.4 pounds and averaged 23.9 

pounds. The average ratio of heating surface to grate surface was 

49.6 to 1, the lowest being 26 to 1 and the 

highest 73 to 1. Thirty-five per cent of 

the furnaces were installed under boiler 

units of 150 horsepower or less and 50 per 

cent under units of 200 horsepower or less. 

Forty-four per cent of the plants had either 

rocking or dumping grates. All plants except one with induced and one with forced 

draft ran on natural draft. Thirteen of the 

plants were fired by the spreading method, 8 

by the alternate method, and 3 by the coking method. The kind of coal used and 

the average depth of fire are summarized in the following table:

TABLE 18. Kind of coal and depth of fire at plants with hand-fired furnaces under coalertube and Scotch marine boilers.

FIGURE 31. A hand-fired furnace, 

cross section along lino y-y', figure 30. 

1, Openings in mixing structures.

 Kind of coal.

Illinois.......................

Indiana......................

Ohio.........................

Number 

ofplants.

14

2

2

1

Average 

depth of 

fire. '

Inches.

7

S

15

Kind of coal. Number 

ofplants.

1

Average 

depth of 

fire.

Inches. 

11

7

Details regarding type of furnace, kind of coal, amount consumed, 

draft, furnace setting, etc., are summarized below:

TABLE 19. Summary of various observations at plants with hand-fired furnaces under 

water-tube and Scotch marine boilers.

Type of boiler.

B a b c o c k &

Wilcox.

Heine..........

Scotch marine. .

Miscellaneous..

Kitad of furnace

and number of 

plants.a

Dutch oven 2,

plain 1, twin

arch 1.

Dorrance 1 , Hawley 3, Puddington 1.

Burke 2, Hawley

1, plain 2.

Dorrance 3, Dutch

oven 1, Hawley

3, plain 4, Burke

2. twin arch 1.

Kind of coal.

Illinois and West

Virginia.

Illinois, Maryland,

Ohio, and West

Virginia.

Illinois and Indiana.

Illinois, Indiana,

Maryland,

Pennsylvan ia,

and West Virginia.

2 o

e3

P*H

Inch

water.

0.24

.41

.21

.30

Is

 o

2* .

03 intl § &!

f o> 

*3£ ft* Ea 

v%£ 2 a

es&P 03 c3 ^&s

§ O 03

O

Lbs.

20.5

30. 5

19.7

24.5

U » .S'O

2 8, " 0«.

 o'ffl'g *s;° 2^~

"S * s

a) v

<c fefi I'&i

a^2

QJ £H (D S ° S- 55 fl «

PH

107

303

84

104

Distance

from grates 

to tubeheating 

surface.

0)

20>t><)

JP/.

11

S . (\ U

4.2

9.4

g

|'3

S

j-r

8

r>. 2

3.0

7.2

t-< 

5

o|

+» 2 c-0

0 "S

J- O 

+s

II

o qj-w

o a> C o

*" H

.22

ft

7'V.

4.8

0.

4.3

2.9

5 

ca 02 r; o B"S

gg

AM

03.9 O-S

C C3 

ca a)

tn"^ 

^ *

"O o

«-g

.2 fc e«

03 O

( "*"

JF/:

3. 1

2.0

1.7

2.9

1o

^ 

SC3

5

P.c<.

4.5

4.3

4.0

4.5

« One plant has both Hawley and plain furnaces.

b Boiler rated on 10 square feet of heating surface per horsepower.
108 SMOKELESS COMBUSTION OP COAL.

The draft observations may be briefly summarized thus:

Average furnace draft, 25 plants, 0.29 inch of water; least, 0.07- inch; most, 0.60 

inch. Average draft at rear of boiler, 11 plants, 0.54 inch, least, 0.32 inch; most, 0.70 

inch. Average draft at base of stack, 19 plants, 0.75 inch, least, 0.50 inch; most, 1 

inch. From these readings were deduced the following approximate'draft averages: 

Approximate average draft in furnace, 0.30 inch of water; at rear of boiler, 0.55 inch, 

at base of stack, 0.75 inch. This gives an average drop of 0.25 inch of water through 

the boiler and of 0.20 inch from the boiler to the base of the stack.

Details of the observations at plants with hand-fired furnaces under 

water-tube and Scotch marine boilers are given in Table 20.
TABLE 20. Details of observations at plants with hand-fired furnaces unde

No. of 

plant.

214 

215 

216 

217 

218 

219 

220 

221 

222 

223 

224 

225 

226 

227 

228 

229 

230 

231 

232 

233 

234 

235 

236 

237 

238 

239 

240

State.

.....do....-.--.-.......

.....do.................

.....do.................

.....do....--.-.-...-...

.....do........----.-...

.....do........--.-...-.

.....do.....--.---.--.-.

Illinois................

.....do.................

.....do...----..-.......

.....do.................

. ....do. ....... .........

Device used to facilitate combustion.

HI

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do.......................

.....do. ...............:......

.....do.......................

.....do.......................

.....do.......................

.....do.......................

Steam jet ...................

Total 

builder s 

rated 

horsepower.

450 

825 

100 

80 

900 

424 

325 

500 

200

711 

200 

1,500 

500 

900 

900 

600 

540 

500 

450

856 

200 

75 

765 

600 

150

Commercial name.

.....do...................

Block...................

Georges Creek.. .........

Whe

Carterville, 

West Virgin

Ohio.....

.....do....

Carterville. 

.....do....

Carterville, 

.....do....

.....do....

.....do....

.....do....

.....do....

.....do....

Mary land ..
TABLE 20. Details of observations at plants with hand-fired furnaces under wate

No. of 

plant.

214 

215 

216 

217 

218 

219 

220 

221 

222 

223 

224 

225 

226 

227 

228 

229 

230 

231 

232 

233 

.234 

235 

236 

237 

238 

239 

240

Load.

Requirement.

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Nature.

..... do... ..............

. ....do.. .......... .....

.-...do.................

.....do........--.--....

.....do. ................

.....do. ... .............

.---.do.................

.....do.................

. -...do......... ...... ..

.... .do..... ............

.....do.................

.....do... ..............

...-.do.................

Character.

Offices and manufacturing. . 

Office building........ ......

Hotel.......................

Hotel.......................

Hotel.......................

I*rintinK office

Hotel.......................

Averag

Heavy.

Hours 

per day 

load is 

on 

plant.

10 

12

9

C

12 

24 

12 

17 

12 

17 

24 

24 

11 

24 

12 

8 

u 17 

24 

10 

10 

10.5 

18 

11 

12 

10 

17 

17 

11

Coal 

burned 

per day 

(short 

tons).

11 

10 

1.9

2 

19 

6.2 

15 

7.5 

4.3 

20 

22 

3.5 

GO 

4.9 

12.5 

12 

12 

5 

8.8 

6 

1C 

18 

6.5 

3 

14 

20 

2.5

t Boiler rated on 10 square feet of heating surface per h
TABLE 20. Details of observations at plants ^uith hand-fired furnaces under rooter

No. of 

plant.

214

215 

216 

217 

218

219 

220 

221

222 

223

224 

225 

226 

227 

228 

229 

230 

231

Stoking.

Method of 

firing.

Alternate. . . . 

.....do.......

Spreading . . .

Alternate. . . . 

Spreading . . . 

.....do.......

.....do.......

.....do.......

Coking......

Spreading. ..

Spreading..; 

.....do ......

Alternate.... 

Spreading... 

.....do.......

Alternate....

Frequency 

of 

firing 

(minutes).

CO

15 

7-12

(»)

( 6 ) 

15

(6 )

20 

(*)

(6 ) 

( 6 ) 

18-25 

12 

4-6 

15-30 

( 6 ) 

5-7

Coal 

fired at 

each 

firing per 

boiler 

(pounds).

75-90

65 

60-90

45 

250-400 

150-180 

(")

270-370 

( 6 )

60

(») 

350-400

50-70 

150 

.400-500 

40-60

Thickness of 

fire 

(inches).

10-12

S-10 

4-6 

6-8 

0-8

(6) . 

3-4 

6-8

( 6 ) 

6-S 

( 6 ) 

8 

5-6 

6 

10 

<=S 

6-S

Frequency of 

cleaning fire.

Once in 10 hours..

Type.

Babcock & Wilcox 

water-tube. 

.....do........ ..

.................... .....do...........:

...... .... . ....do. ...... ...

3 times in 24 hours .

2 to 3 times in 12 

hours. 

3 to 4 times in 17 

hours.

3 times in 24 hours 

.....do.............

Once in 11 hours. . 

6 times in 24 hours.

Once in S hours ... 

2 times in 12 hours . 

3 times in 24 hours. 

Once in 8 hours. ...

Heine water-tube. 

.....do............

.....do............

.....do............

.....do............

Scotch marine.....

Inverted Scotch 

marine. 

Scotch marine.....

.....do............

.....do............

Cahall horizontal 

water-tube. 

O'Brien watertube. 

Cahall horizontal 

water-tube. 

Detroit water-tube

Size.

84 4" x 16' tubes . .

120 4" x 18' tubes-. 

54 4" x IS' tubes. .. 

32 4" x 14' tubes... 

170 3i"x IS' tubes, 

2 36" drums. 

54 zy x IS' tubes. 

1 36" drum. 

176 4" x IS' tubes. .

116 3V x 19' tubes, 

1 40" drum. 

58 3i" x IS' tubes.. 

84 4" tubes, 9iV x 

IS' shell. 

94 3" tubes, 94" 

shell. 

44 3.V" x 15' tubes, 

78"" shell. 

13S 4" x 12' tubes, 

10' shell. 

2 3S" flues, 2 42" 

flues. 

160 4" x IS', 2 42" 

drums. 

140x18' tubes.....

162 4" x IS', 120 4" 

xlS'. 

96 4" tubes, 1 30" 

drum.

»Boilerrated on 10 square feet of heating surface per horsepower. 6 V
TABLE 20. Details of observations at plants with hand-fired furnaces under wate

No. of 

plant.

232

233

234

235

236

237

238

239

240

Stoking.

Method of 

firing.

Spreading...

Alternate....

.....do.......

.....do.......

Coking......

.....do.......

Spreading . . .

Frequency 

of 

firing 

(minutes).

20

(a}

10-15

(a)

(a)

(a)

8-12

10

Coal 

fired at 

each 

firing per 

boiler

(pounds.)

100

30-35

60-75

AZ*

(a)

(a)

120-150

50-90

Thickness of 

fire 

(inches).

11

3-4

A C

(a)

14-16

9 I9

5-6

Frequency of 

cleaning fire.

2 times in 10 hours .

.....do............

.....do............

hours.

2 times in 11 hours .

Type.

,

O'Brien watertube.

lor water- tube.

lor water-tube.

tube.

tube.

Stirling water-tube

Size.

113 3 £"x 18' tube

72 4" x 18' tubes

1 36" drum

36" drums.

140 4" x 16' tubes

a Variable.
TABLE 20. Details of observations at plants with hand-fired furnaces under water-t

No. of 

plant.

214 

215 

216 

217 

218 

219 

220 

221 

222 

223 

224 

225 

226 

227 

22S

229

230 

231 

232 

233 

234 

235 

236 

237 

23S 

239 

240

Furnaces.

Number.

3 

3 

1 

2 

6 

4 

1 

2 

2 

3 

6 

2 

12 

4 

6 

/2 

U 

2 

3 

2 

3 

3 

4 

2 

1 

3 

4 

1

Kind of furnace.

.....do.............................

Hawley ............................

.....do.............................

.....do.............................

do

Kind of grate.

Flat...............................

Flat...............................

.....do.............................

Flat...............................

Flat......................:........

.....do.............................

.....do.............................

.....do.............................

.....do.. ...........................

Flat...............................

Flat. . ....... ...............

Grate area 

per boiler a 

(square feet).

36 

48.75 

23 

20 

45.6 

28.2 

48 

39

48 

36 

 23. G 

40 

38 

46

55

59,G1.5 

33.25 

52 

25 

27.5 

36,47 

27 

21.3 

75, 41. 25 

53.5 

35.75

Distance 

tube-he

Averag

(A).

17 

8.

7.

10 

12 

3 

9 

9 

8.

1.

7.

4 

61.

12

17

11 

9 

11

9 

11

4.

2.

5

uw

1

a In down-draft furnaces, area of upper grate only. 6 First dimension applies to small boi
TABLE 20. Details of observations at plants with hand-fired furnaces under water-

No. of 

plant.

214

215

216

217 

218 

219 

220 

221

222 

223 

224 

225

226

227 

228 

229 

230 

231 

232 

233 

234

235 

236 

237

238 

239 

240

Draft.

Kind.

Chimney.... 

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do......

.....do...... 

.....do......

Induce'd..... 

Chimney....

Chimney....

Readings (inches of water).

Furnace.

0.38

.18

.16 

0.50- .53 

.26- .38

.16 

.50

.55

.16 

. 22- . 48

. 04- . 09 

. 25- . 40

. 11- . 17

.27 

.29

.23 

.54 

.36 

.12

. 24- . 25 

. 11- . 12

.09

.60 

. 22- . 44

.35

Rear of 

boiler.

0. 46-0. 50

.32

0 .78

.43

.68 

.54

.60 

.66 

.47

.56 

. 46- . 47

c.45

. 32- . 45

Front 

tube 

sheet.

0. 37-0. 40

Breeching.

0.72 

.75

1.46 

0.56- .84

1.45 

.95

.96

.74 

.56- .64

.94

.76

.90 

.92 

.60

Base of

stack.

0.78

.55 

.55

.51

1

.50

.90

0. 75- . 85 

.85

.76 

.78

1

Conditions under which readings were taken.

Damper open, door in base 

of stack cracked.

Damper open, ash-pit doors 

three-quarters closed.

Damper and ash-pit doors 

open.

Door at base of stack open. . .

Damper and ash-pit doors 

open. 

Dampers open; ash-pit doors 

cracked.

Door in base of stack open . .

Dampers and ash-pit doors 

open.

Fan running at average 

speed.

N

b

o

v

o Several. 6 Various lengths. 
TABLE 20. Details of observations at plants with hand-fired furnaces under water-t

No. of 

plant.

214

215

216

217

218

219

220

221

222

223

Length 

from 

stack to 

nearest 

boiler 

(feet).

8

11

0

10

32

22

0

40

12

28

Size 

(feet).

3. 5 x6

A........

4.6x6

0

4x6

Breeching.

Place at which 

measurement was 

taken.

Number of 

elbows 

between 

boilers and 

- stack.

2

0

0

0

1

2

0

1

1

1

Height 

(feet).

130

270

90

100

235

108

100

152

306

Stack.

Size (leet).

04

o4.4

3x3

"3

o4.25

04

a4.5

Area 

(square 

feet).

12.56

14.7

.9

28.3

7.06

14.2

12.56

15.9

23.7

firing. Mu

Two boilers 

good with 

10, 20, and 

J-inch ste

Automatic 

nace. Succ

black for o

closed, but 

Device in s

usually bur

surface figu

checker wo

entering th

automatic b

firing. Ash

smoked 20 

firing. Dry 

in coal as r

furnace, als

ash pit to f

admissions 

sionally on 

for one-half 

24£-inch ste

matic; in u

several 10, 

damper.

10,800.

Diameter.
TABLE 20. Details of observations at plants with hand-fired furnaces under water-

No. of 

plant.

224

225

227

228

OOA

231

232

234

oqc

237

238

239

04O

Length 

from 

stack to 

nearest 

boiler 

(feet).

10

7

20

18

15

17

12

3

50

7

70

12

18

9

15

10

Size 

'(feet).

4x7

63

fl 3. 5x11

3. 5x9

3x0

3x8

2.5x3

a

Breeching.

Place at 'which 

measurement was 

taken.

.....do............

}..............:....

.....do............

.....do..:.........

.....do............

Oval.

Number of 

elbows 

between 

boilers and 

stack.

1

2

2

3

1

0

1

1

0

1

1

1

1

1

1

1

1

Height ' 

(feet).

250

135

80

200 200'

150

279

110

200

225

105

210

125

140

125

Stack.

Size (feet).

a4 x 6

4 x 1.9

64.2

65

64.5

65.5

64

4x4

64. 7

9x9

64

62.1

65

3. 2 x 3. 1

Area 

(square 

feet).

20.50

. 7.6

13.6

19.6

15.9

23.7

23.8

12. 56

16'

17.1

81

12.56

3.4

19. fl

10

Plant usua

ing metho

kept filled

cleaning fi

Water- tube 

Total length 

Boilers baffl

combustio

inch of wa

sionally sm

closed. F

Considerab

Fired by spr

Lower row 

boilers. F

bish burne

wide open

Automatic s

across fron

opens and 

and one to 

to one min

cally. Sta

minous co

ously. Tw
HAND-FIRED FURNACES. ' 117

Plants with return tubular boilers. The size of the 44 plants having 

hand-fired furnaces under return tubular boilers varied widely, the 

smallest being 50. horsepower and the largest 1,000 horsepower. At 

45 per cent of these plants run-of-mine, egg, or lump coal was burned. 

The cost of coal at 31 plants averaged $2.49 per ton, ranging from 

$1.60 to $4.10. Uniform loads were carried by 34 plants and varied 

loads by 10. On the average 90 per cent of the rated boiler horsepower (boiler rated on 10 square feet of heating surface per horsepower) was developed on mean heavy load. The furnaces in use at 

the different plants included 10 types, as follows:

Furnaces used at plants with hand-fired furnaces under return tubular boilers.

Number of

plants. 

Dorrance (with Dutch oven).................................... 1

Down-draft .................................................... 10

McMillan...................................................... 5

Twin arch..................................................... 1

. Wooley......................................................... 1

Burke (western, with Dutch oven)................................ 2

Burke (eastern)................................................. 1

Plain.......................................................... 21

Cornell economizer. ............................................ 1

Puddington.................................................... 1

Of these furnaces, 20 had steam-jet attachments. Eleven were 

equipped with either rocking or dumping grates. At 33 plants either 

the spreading or the alternate method of firing was used; 5 plants 

used the coking method.

The average length of travel of the gases to the tube heating surface and the height of the combustion chamber are indicated by the 

following figures:

Average distance from grates to tube heating surface, 44 plants, 16.6'feet; shortest, 

13 feet; longest, 24 feet. Average least distance from grates to tube heating surface, 

44 plants. 14.2 feet; shortest, 11 feet; longest, 22 feet. Average vertical distance 

from grates to shell, 31 plants, 2.3 feet; shortest, 1.5 feet; longest, 5 feet. Average 

ratio of heating surface to grate surface, 44 plants, 45 to 1; lowest, 26 to 1; highest, 

67 to 1.

The draft readings taken at these plants may be summarized as 

follows:

Average furnace draft, 39 plants, 0.23 inch of water; range, 0.03 to 0.55 inch. 

Average draft at front tube sheet, 15 plants, 0.41 inch; range, 0.27 to 0.68 inch. 

Average draft in breeching, 25 plants, 0.51 inch; range, 0.22 to 1.42 inches. Average 

draft at base of stack, 16 plants, 0.66 inch; range, 0.35 to 1.10 inches.

The following approximate draft averages were deduced from the above: Furnace, 

0.25 inch of water; front tube sheet, 0.40 inch; breeching 0.50 inch; base of stack, 

0.70 inch. Approximate average drop through the boiler, 0.15 inch.

For convenience the furnaces and devices in use at these plants are 

discussed in* three groups down-draft furnaces, steam jets, and miscellaneous furnaces and devices.
118 SMOKELESS COMBUSTION OF COAL.

The essential features of the down-draft furnace are described in 

the account of hand-fired furnaces under water-tube boilers. Its setting and operation at the 10 return tubular boiler plants where it 

was found in use are taken up here. All the down-draft furnaces at 

these plants were set under units of 150 horsepower or less, and none 

were set in a Dutch oven. Nine of the plants carried a uniform load. 

At 4 of the plants the coal fired was run-of-mine, nut, or egg. The 

average cost of coal at 6 of them was $2.68 per ton. At all 10 plants 

firing was by the spreading method. The kinds of coal burned and 

the average depth of fire carried were as follows:

TABLE 21. Kind of coal and depth of fire at plants with down-draft furnaces under return

tubular boilers.

Kind of coal burned.

Ohio.........................

Number 

of 

plants.

1

4

1

Average 

depth 

of lire.

Inches.

7

8.5

9

Kind of coal burned.

Number 

of 

plants.

2

2

.Average 

depth 

of fire.

Inches. 

10

11

The draft, coal consumption, percentage of rated boiler horsepower 

developed, distance from grates to tube heating surface, and smoke 

observations show the following averages:

Draft through fire, 0.30 inch of water; range, 0.03 to 0.36 inch.

Coal as received burned per square foot of grate surface per hour, average heavy 

load, 20 pounds; least, 13.3 pounds; most, 24.4 pounds.

Percentage of rated boiler horsepower developed, average heavy load (boiler rated 

on 10 square feet of heating surface per horsepower), 96; range, 58 to 157.

Average distance from grates to tube heating surface, 17.1 feet. Least distance 

from grates to tube heating surface, 14.7 feet.

Smoke emitted, 5.6 per cent black.

The plants visited that had steam jets in the furnaces numbered 

20, one of which is included also in the group with down-draft furnaces. At all of them the furnaces were run under boiler units of 

150 horsepower or less. The coal burned came from eight States. At 

10 plants the size of coal was lump or run-of-mine; the cost ranged 

from SI.50 to $4.10 per ton, the average being $2.32. Eighteen 

plants carried fairly uniform loads. Nineteen had furnaces with flat 

grates. The kinds of coal and the thicknesses of fire carried are 

shown below.

TABLE 22. Kind of coal and depth of fire at plants with steam jets in furnaces under

return tubular boilers.

Kind of coal.

Ohio.........................

Number 

of 

plants.

2

1

3

3

Average 

depth 

of fire.

Inches. 

4.5

15

6

7.3

Kind of coal.

Number 

of 

plants.

1

5

c

Average 

depth 

of fire.

Inches.

g

8

C

7
HAND-FIRED FURNACES. 119
120 SMOKELESS COMBUSTION OF COAL.

The draft through the fire, the coal consumption, the furnace set-- 

ting, and the smoke given off were noted at only 20 plants. ,The 

average of the measurements were as follows:

Draft through fire, 0.23 inch of water; range, 0.15 to 0.37 inch.

Coal as received burned per square foot of grate surface per hour, average heavy 

load, 17.6 pounds; least, 11.2 pounds; most, 25.3 pounds.

Percentage of rated boiler horsepower developed, average heavy load (boiler rated 

on 10 square feet of heating surface per horsepower), 78: range, 46 to 174.

Average distance from grate to tube heating surface, 15.9 feet. Least distance 

from grate to tube heating surface, 13.7 feet. Vertical distance, grate to shell ,2.2 feet.

Smoke emitted, 4.2 per cent black.

The miscellaneous group includes all the hand-fired furnaces under 

return tubular boilers not already described. Three of these furnaces 

with their distinctive features are briefly described below. Three

FIGURE 33. A hand-fired furnace, cross section.

others, including the down-draft, are described in the account of 

hand-fired furnaces under water-tube boilers (pp. 104-106).

In the first furnace the coal is' fired from side hoppers in the furnace wall to a combustion chamber,' virtually a Dutch oven, having 

short sloping grates at the sides with a wide rocking grate between 

them. The furnace is thus practically a hand-fired side-feed stoker. 

The Dutch oven construction gives a hot combustion chamber and 

lengthens the travel of the burning gases. An elevation and a cross 

section of such a furnace placed in front of a Scotch boiler are 

presented in figures*32 and 33.

Another furnace having distinctive features intended to insure 

complete combustion and prevent smoke is shown on page 121. 

In this pattern (see fig. 34) the furnace gases pass through circular 

openings in the bridge wall. Immediately beneath these openings
HAND-FIRED FUKNACES. 121

are small rectangular holes by which air that comes through a passage 

in the bridge enters the furnace. The object of this construction is to 

admit air in such a way that any unconsumed carbon in the gases

will be brought into contact with the necessary air for burning it 

without cooling the combustion space.

Another furnace intended to effect smokeless combustion by special 

fire-brick piers and arches in the combustion space is shown in figures 35-37. Its characteristic features are two furnaces, each with
FIGURE 35. A hand-flred furnace and return tubular boi
HAND-FIRED FURNACES. 123

an arch extending the entire length of the grate, virtually making 

small Dutch ovens; a wide-arched passage, in which are openings for

air admission, in the wall back of thegrates; and another archedpassage 

of greater height back of this. This construction gives a long, irregu-
124 SMOKELESS COMBUSTION OF COAL.

lar combustion space, evidently intended to permit thorough mixing 

of gas and air. Figure 35 is an elevation of the furnace as usually 

installed under a return tubular boiler; figure 36 is a horizontal 

plan, and figure 37 a cross section.

oooooooo 

oooooooooo 

oooooooooo 

oooooooooo

O

FIGUKE 37. A hand-fired furnace and return tubular boiler, cross section.

The observations on seven different styles of furnaces were averaged 

to obtain the figures given in the tables below. All of these furnaces

were installed under boiler units of 150 horsepower or less. Nine 

were equipped with either rocking or dumping grates.

The coals burned and the thicknesses of fire carried at the 15 plants 

classed as miscellaneous were as follows:

TABLE 23. Kind of coal and depth of fire at plants with miscellaneous hand-fired furnaces under return tubular boilers.

Number 

of plants.

8

2

1

4

Kind of coal.

Average 

depth of 

fire.

Inches. 

6

4

7.7
HAND-FIRED FURNACES. 125

The average draft through the fire and the average coal consumption' were as follows:

TABLE 24. Average draft and coal consumption at plants with miscellaneous handfired furnaces under return tubular boilers. :

Kind of furnace.

Puddington. . ........................................................

Number 

of 

furnaces.

1

1

1

2

1

4

Furnace 

draft.

Inch of

water.

0.14

.23

.27

 .21

.11

.12

.28

Coal as

received

burned per

square foot 

of grate 

surface

per hour,

average

heavy load.

Pounds.

22

47

1C

18

13.2

14. G

The averages of various items are as follows:

Coal as received burrfed per square feet of grate per hour, average heavy load, 

21.8 pounds.

Percentage rated boiler horsepower developed, averaged heavy load (boiler rated 

on 10 square feet of heating surface per horsepower), 91.7; lowest, 53; highest, 184.

Average distance from grate to tube heating surface, 16.3 feet. Least distance 

from grate to tube heating surface, 14.1 feet. Vertical distance, grate to shell or 

arch, 2.1 feet.

Smoke, 6 per cent black.

Details of the observations at all the plants with hand-fired furnaces under return tubular boilers are given in Table 25.
TABLE 25. Details of observations at plants with hand-fired furnac

No. of 

plant.

241

242

940

245

246

247

248

94Q

251

2 

CO

9^**

9^4

occ

9cc

9^7

o CQ

259

260

262

263

264

9cc

266

267

9AQ

270

271

272

970

274

97c

277

State.

Illinois................

.....do................

.....do................

Ohio..................

Ohio ..................

.....do................

.....do................

Ohio......."...........

..... do......... ...... .

.....do........ ........

.....do................

Ohio........-.-.-.-...

.....do........-.--.-..

.....do................

..... do... .............

.....do................

.....do................

.....do................

.....do................

.....do................

.....do...........:....

Illinois................

.....do................

.....do. ...............

.....do................

.....do................

Device used to facilitate 

combustion.

.....do. .....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do. .....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

.. ...do. .................... .

.....do......................

.....do. .....................

.....do......................

.....do......................

Total

rated 

horsepower.

300

onn

160

300

500

160

400

300

150

100

1 1ft

230

88

250

170

cfln

450

350

100

on

86

411

onn

100

87

o en

166

116

Commercial name.

PittsburgNo. 8.........

Reynoldsville.

.....do..................

.....do..................

.....do..................

Block ...................

Whe

Carterville, 

.....do...

.....do...

Ohio....

-Pittsburg, 

Powellton, 

.....do...

Ohio ......

.....do...

.....do....

.....do... .

West Virgi

.....do...

.....do. ...

.....do...

.....do...

..... do....

.....do...

.... .do....

Carterville, 

.... .do. ...

... ..do... .
278

280

282

283

284

.....do................

.....do................

.....do................

.....do................

.....do................

Ohio ..................

.....do......................

.....do.......................

.....do.... ..................

.....do......................

580

240

180

160

50

500

160

.....do..................

.....do..................

Pittsburg...............

Carter-ville, 

.....do....

.....do....

.....do....

.....do....

.....do....
TABLE 25. Details of observations at plants with hand-fired furnaces unde

No. of 

plant.

241 

242 

243 

244 

245 

240 

247 

248 

249 

250 

251 

252 

253 

254 

255 

250 

257 

258 

259 

260 

261 

262 

263 

264 

265 

266 

267 

268 

269 

270

Load.

Requirement.

.....do. .....................

.....do......................

.....do. .....................

.....do......................

.....do......................

.....do......................

.....do......................

.....do......................

Heat........................

Power, light, and heat. .....

Heat........................

.....do. .....................

.....do......................

.....do......................

.....do......................

.....do......................

Power and heat .............

Nature.

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do..:..............

.....do.................

Variable ...............

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

Character.

.....do. .....................

.....do......................

Mill............... ..... .

Store building ..............

Average 

Heavy.

Hours 

per day 

load 

is on 

plant.

24 

24 

24 

16 

19 

10 

17 

10 

17 

13 

18 

10 

12 

9.5 

10 

10 

18 

24 

10 

7 

12 

19 

14 

10 

10.5 

10 

. 10.5 

12 

10 

11

Coal 

burned 

per day 

(short 

tons).

14 

10 

15 

3.25 

3.2 

3.6 

12.5 

5.25 

4.3 

10 

2.5 

3 

2 

8 

2.4 

2.4 

33 

8 

2 

6 

6 

5 

3 

3.25 

1.5 

1.5 

1.25 

6 

8.5 

1.8

H

pe

p
?71

979

O70

?74

975

97fi

 >77

?'S

279

 580

?S1

9«9

?S3

9Q<1

.....do......................

.....do......................

.....do......................

.....do......................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do.................

.....do......................

Distilling...................

10

10

9

10

S

10

10

12

15

18

24

2.5

1.5

3

3

3.5

26

6

is. 3

1.4

1

1

1

1

1

1

1

I

2

Boiler rated on 10 square feet of heating surface per hor
TABLE 25. Details of observations at plants with hand-fired furnaces under 

No. of 

plant.

241 

242 

243 

244 

245 

246 

247 

248 

249 

250 

251 

252 

253 

254 

255 

256 

257 

258 

259 

260 

261 

262 

263 

264 

265 

266 

267 

268 

269 

270 

271 

272

Stoking.

Method of 

firing.

Spreading. . .

.....do.......

.....do.......

.....do.......

.....do.......

Spreading. . .

.....do.......

.....do.......

.....do.......

.....do.......

Spreading. . .

Alternate.... 

Spreading. . .

Spreading. . . 

.....do.......

.....do.......

Spreading...

Alternate....

Frequency 

of firing 

(minutes).

20 

Var. 

Var. 

Var. 

Var. 

8-10 

Var. 

Var. 

20 

Var. 

15-17 

5-10 

20-40 

10 

12-18 

12-18 

10-20 

Var. 

12-20 

7-10 

10 

Var. 

Var. 

12-15 

7-12 

12-15 

15-20 

15-20 

15-20 

10-15 

3-8 

8-10

Coal 

fired at 

each 

firing per 

boiler 

(pounds).

200 

Var. 

Var. 

Var. 

Var.. 

90-110 

Var. 

Var. 

270-370 

120-150 

50-75 

30-50 

80 

60 

90-150 

90-150 

150-180 

60-80 

75-90 

40-50 

75-90 

Var. 

60 

60-80 

40-60 

60 

40-60 

100-140 

40-60 

50-60 

50-70 

40-50

Thickness of 

fire 

(inches).

6-8 

7-9 

8 

8-10 

8-10 

a 8-10 

alO-12 

8-10

10-12 

6 

3 

14-16 

4-5 

6 

6 

6-8 

6-8 

8-10 

4-10 

8 

12-14 

Var. 

6 

6-8 

6 

10 

6 

7-8 

6 

5-6 

7-S

Frequency of cleaning 

fire.

2 times in 16 hours. ....

2 times in 10 hours ..... 

2 times in 24 hours .....

3 times in 24 hours ..... 

2 times in 24 hours .....

2 times in 10 hours ..... 

.....do..................

.....do..................

Once in 8 hours ........ 

Once in 12 hours .......

.....do..................

.....do..................

.....do..................

.....do..................

1 to 2 times in 11 hours. 

2 times in 10 hours ..... 

Once in 10 hours .......

Size.

72" x IS', 62 4" tubes. ............

72" x 22', 26 6" tubes. .............

54" x 17', 44 3£" tubes. ...........

60" x 16', 48 4" tubes. ............

50" x 16', 34 3J" tubes.. . .........

66" x 18', 58 4" tubes. ............

72" x 16', 66 4" tubes. . ...........

60" x 18', 54 3J" tubes. ...........

48" x 18', 48 3i" tubes.. . .........

60" x 18', 54 4" tubes.. . ..........

66" x 16', 54 4" tubes. ............

50" x 14', 56 2J"; 50" x 16', 56 2J". . 

60" x 16', 47 4" tubes. ............

62" x 16', 53 4" tubes. ............

72" x 16', 92 3J" tubes. ...........

54" x 20', 4 SJ" and 2 10" tubes. . . 

72" x 18', 64 4" tubes. ............

80 4" x 18' tubes. .................

66" x 18', 54 4" tubes. ............

60" x 14', 46 4" tubes. . ...........

60" x 16', 72 3" tubes. ............

66" x 18', 54 4" tubes. ............

60" x 16'. 54 3A" tubes. . ..........

Nu

be

sta
273 

274

275

276

277

278

279

280

281

282

283

284

Spreading. . .

.....do.......

.....do.......

.....do.......

.....do.......

Var. 

2-5

10-12

10-15

4-5

12-15

Var.

Var.

Var.

Var.

7-8

100-120 

80-100

60-90

120-180

30-60

70-75

60-70

30-60

Var.

Var.

100-120

45-90

4 

4-106

3-54

5-6

6-8

5-6

Var.

Var.8

Once in 9 hours ........ 72" x 18', 70 4" tubes. ............ 

.....do............................

60" x 16', 46 4" tubes. ............

54" x 16', 52 3J" tubes. . ..........

60" x 16', 37 4" tubes. ............

60"xl8', 48 3J"; 13 4" water tubes.

60" x 16', 44 4" tubes. ............

.....do............................

52" x 16', 32 4" tubes. . ...........

72 4" x 16' tubes; 144 4" x IS' tubes

06" x 14', 94 3" tubes. . ...........

a On top grate.
TABLE 25. Details of observations at plants with hand-fired furnaces under re

No. of 

plant.

241 

242 

243 

244 

245 

246 

247 

248 

249 

250 

251 

252 

253 

254 

2-55 

256 

257 

258 

259 

260 

261 

262 

263 

264 

265 

266 

267 

268 

269

Furnaces.

Number.

2 

' 4 

4 

2 

2 

2 

4 

2 

4 

4- 

2 

1 

2 

4 

2 

1 

8 

2 

2 

5 

3 

3 

2

2 

1 

1 

1 

3 

4

Kind of furnace.

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do.....--....:......-...........

Plain ...............................

.....do..............................

.....do................... ..........

.....do..............................

.....do....... .......................

do

Kind of grate.

.....do......................... .... ...

.....do......................... ........

.....do..................................

.....do..................................

.....do... ...................... ..... .

.....do..................................

.....do... ...............................

.....do..................................

.....do......................... .... .

Flat............!.......................

Flat....................................

Flat.....................................

.....do.... ..............................

..;.. do... ...............................

.....do..................................

.....do.... ..................... .......

.do... . . . .....

. . . . . do ............................... I . . - . do ... . _ . . . . ... ..... ...

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do...... ........................

.....do..............................

.....do..............................

... .do.... ............... ..... .......

.....do.... ..................... ..... .

.....do.... ..'............................

.....do.... ..............................

.....do.... ..............................

.....do.......................... ........

.....do.... ..............................

.....do.... ..............................

Grate area 

per boiler 

(square 

feet). »

30 

25 

20.2 

23 

16.7 

29.5 

25 

22.4

20 

25 

20.7 

21, 23 

22.5 

30 

30 

36 

30 

18 

27 

30 

25,33

24.75 

20 

20.25 

20 

20 

36 

22.5

Distanc

tube h

Avera

(A)

2

6 13.5, 

1

1

1

1

1

1

1

1
270 

271 

272 

273 

274 

275 

276 

277. 

278 

279 

280 

281 

282 

283 

284

2 

1 

1 

2 

2 

2 

3 

2 

4 

3 

3 

2 

1 

3 

1

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do..............................

.....do...................... ........

.....do..............................

Woolley............................

.....do..............................

.....do..................................

.....do..................................

.....do..................................

Flat....................................

Flat....................................

.....do..................................

16 

27.5 

IS 

30 

309r

21 

22.5 

23 

28 

25 

19 

20. 25 

42 

25

c

In down-draft furnaces, area of upper grate only. 6 First dimension applies to small boile
TABLE 25. Details of observations at plants with hand-fired furnaces und

No. of 

plant.

241

242 

243

244 

245

246 

247 

248

249 

250 

251 

252 

253 

254 

255 

256 

257 

258 

259 

260 

261 

262 

263 

264

265 

266

2S7

Draft.

 Kind.

....do...... 

....do......

....do......

....do......

....do...... 

....do......

....do......

....do...... 

....do......

....do......

....do......

....do......

.-.-..do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do.....

Readings (inches of water).

Furnace.

0.25

0. 20-. 39

99

.55

.32

.03 

. 24-. 34

.21-. 51

.30-. 35 

.22-. 44

.19

.20

.25

. 18-. 27

.30

.23

. 14-. 18

. 28-. 30

.15

.37

.30

.18

Rear of 

boiler.

Front 

tube 

sheet.

0.60 

. 42-. 55

. 45-. 50

.27

.35

.30

.25-. 30

.40

Breeching.

0.53 

.40

.57

.47

.55

.85 

.60 

.28

.31 

.48

.40

.35 

0.35-.60

.60

>;n

.43

Base of 

stack.

" "6.46"

.60 

.67

.65

4=\

.70 

I .65 

0. 75-1

.85

Conditions under which readings were taken.

Damper open, ash-pit doors 

cracked. 

, Dampers and ash-pit doors open. 

Dampers open, ash-pit doors 

closed. 

Ash-pit doors closed, damper 

open. 

Damper open, ash-pit doors 

closed. 

Lower furnace doors cracked ....

Damper open, ash-pit doors 

cracked.

.....do...........................

Damper open ................... 

.....do...........................

.....do...........................

Damper open, ash-pit doors twothirds closed .

.....do...........................

Nu

of o

vat

(

(

(

(

(

(

(

(

(

(
269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

....do......

.20

.27-. 32

. 17-. 20

. 12-. 17

.20-. 22

.11

.06

.17 .28

.27

.08

. .10-. 13

. 24-. 33

cO.33-.48

.32-. 34

.45

.35

.68

.35

.42-. 45

.40

.44

. 47-. 56

.22

1.34-1.50

.64

.45

.35

.52

.62

i.io

.82

.47

ly closed.

:.. ..do..... ......................

.....do...........................

Several. b Various lengths. Combustion chambe
TABLE 25. Details of observations at plants with hand-fired furnaces und

No. of 

plant.

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

Length 

from 

stack to 

nearest 

boiler 

(feet).

27

55

30

20

0

10

22

10

Go

17

9

8

4

21

Size 

(feet).

3x4

2. 2 x 4

0

Breeching.

Place at which 

measur e m e n t 

was taken.

Number 

of elbows 

between 

boilers and 

stack.

0

0

3

2

0

0

1

3

1

9

0

0

Height 

(feet).

100

100

105

95

130

105

112

115

152

90

50

100

So

Stack.

Size 

(feet).

4.5x6

3x4

ol.8

0.4

3x4

04

a4

«3

9 ~X9 7

Area 

(square 

feet).

27

19.6

12

2.64

12.56

12

12.56

15.9

12.56

7.06

single row of tubes

ing surface do not 

' as good as recorded 

bustion chambers.

in water-tube grate

about one-half min

turned on before f

20, and 40 per cent 

heating surface in 

to 10-inch fire on se

two and one-half m

or less for one to tw

doors. Average fi

three-fourths of a m

at base of bridge w

three to four minut

air into furnace. A

over the top for gas 

jets across front of 

Smoke preventer i
?57

?SS

259

 >fiO

?B1

?,6?

?63

?64

?fi,5

266

?67

?fi,S

?(W

?70

?71

?7?

153

'243

5367

20909

12

14

42

23

6

091111110111

 309

*«

125

125

140

160

165

75

SO

110

125

75

OS

a 3. 75

<z4

"2. 5

06

o5

"5. 5

3x3

2.3x2.3

a4

o3

2.5x2.5

3.5x3.5

11.1

12.56

7.06

28. 3

19.6

23.8 9

5.4

12.56

7.06

6.25

12.25

Arch sprung under re

tributing gases. Sm

3%-inch steam jets ac

each furnace door.

Two steam jets, each w

Patent air-admission 

Success due to caref

Automatic steam and 

nace. At average fi

to two minutes. D

Four nVinch steam je

smokes 20 per cent b

Four J-inch steam jets

wall. Smokes abou

minutes. 1- ire carri

ings in each coking p

Steam jets turned on 

ing furnace pass thro

Automatic steam and a

During average firing 

Air openings 1 b.y 6 

Large combustion ch

matic; jets used duri

Retorts in bridge wall 

about one minute w

hot. Lumps of coal 

Automatic steam and 

At each firing stack 

12 inch air opening in 

Smoke observations in

Coal cokes badly, and 

stack smokes 60 per 

Lumps of coal up to 6 

and 40 per cent blac

Automatic steam jets 

also an 8 by 20 inch a

Automatic steam jets 

Four similar stacks. 

three-fourths to one 

Six Tvinch steam jets 

automatic; also a pa

careful firing and op

Steam jets and air adm

furnace.

Automatic steam jets 

40 to 60 per cent blac

jVinch steam jets an

.from three to five m

Diameter.
TABLE 25. Details of observations at plants with hand-fired furnaces und

No. of 

plant.

273

274

275

276

277

 27S

279

280

281

282

283

284

Length 

from 

stack to 

nearest 

boiler 

(feet).

0

04Orl

20

3

25

12

12

23

22

0

30

Size 

(feet).

3.5 x 3.5

3.5 x 4.5

3x3

2.5 x 2.8

0

Breeching.

Place at which 

measur e m e 11 1 

was taken.

Near stack ........

.....do............

.....do............

Near stack. .......

Number 

of elbows 

between 

boilers and 

stack.

1

1

1

1

1

!, 2

1

. 1

1

2

-o

1

Height 

(feet).

97

105

100

120

60

OOK/ 2M235

110

190

65

85, 125

80

Stack. -

Size 

(feet).

3.5x3.5

3x3

«5

ao.3

5.5x4.5 

65x3

6x6

03.5

2.2x2.2

a 3, a 3.5

«3. 75

Area 

(square 

feet).

12.25

9

19.6

22.3

24.7 

7.8

36

9.6

4.8

7.07,9.6

11.1

One mixing pier on 

usually run with o

Success due to care

Mixing pier on bridg

Large combustion ch

furnace doors for ai

Large combustion ch

Perforated furnace 

Fire thick, practically 

furnace doors.

1 Coal as fired runs abo

1 open when running

Two 4 by 6 inch open

water.

Side grates not inclu

in combustion cham

Large combustion ch

kept filled; probab

not full considerab

Large combustion ch

One large and one sm

in furnace; mixing 

Automatic steam je

Forty -Jj.-inch openin

cent black for one-h

a. Diameter. 
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 139 

SUMMARY.

The remarks in Tables 20 and 25 show that in many of the handfired furnaces an attempt was -made to lengthen the travel of the gases 

from the grates to the heating surface. -The design of some furnaces 

showed recognition of the value of mixing the air and the gases, and 

arches, retorts, piers, or steam jets were used to accomplish this end. 

Where steam jets were used they were usually installed so as to be 

automatically thrown in and out of service.

The regulation of air admission was accomplished at some plants 

by cracking the furnace door after firing, at others by taking air 

through the dead plates or through openings in patent furnace doors. 

These openings in the dead plates and furnace doors were usually 

automatic with the opening of the doors and were slowly closed by a 

weight and clash pot. This arrangement allowed the most air to 

enter the furnace at the required time.

All hand-fired furnaces which will burn coal without objectionable 

smoke approach the theory of the mechanical stoker, but owing to 

the variability introduced by the personal element, they can not under 

average conditions give as good results.

' SMOKE OBSERVATIONS AT GEOLOGICAL SURVEY 

FUEL-TESTING PLANTS.

TESTS AT NORFOLK, VA.

The boiler plant at Norfolk was equipped with two furnaces one 

fired by-hand, the other by a mechanical stoker. The hand-fired 

furnace had plain grates and mixing structures in the combustion 

chamber. The mechanical stoker was of the underfeed type. Figure 

38 shows the elevation,and plan of the boiler setting; figure 39 gives 

a cross section of the setting and the plan of the bridge wall. All of 

the coal used in the tests was of the same general grade; it coked and 

was low in volatile matter. An expert fireman was employed. Each 

test lasted about eight hours.

HAND-FIRED TESTS.

The hand-fired furnace was set under a Heine boiler which had 

C tile on the lowest row of tubes. The tile-roof furnace thus formed, 

in combination with the mixing structures, proved to be a good 

design for burning coal low in volatile matter. With this boiler six 

tests were made, a number too small to permit, the chawing of any 

very definite conclusions. The plant developed from 78 to 155 per 

cent of the builder's rated capacity and made very little smoke; on 

no test did the smoke average 10 per cent black. The boiler efficiency 

on the six tests averaged 66.90 per cent, varying from 65 to 69. The 

dry coal burned per square foot of grate per hour ranged from 13.7 to 

27.6 pounds.
140 SMOKELESS COMBUSTION OF COAL.

The tests showed that the percentage of volatile matter in the 

combustible is an element always to be considered. Even with

small variations the percentage of efficiency follows it closely, 

volatile matter gives low efficiency, and vice versa.

High
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 141

The highest efficiency was obtained when the plant was run at 

capacity. The most carbon monoxide was found in the flue gas 

the greatest unaccounted for loss in 

the heat balance when the plant was 

run at high capacity, showing that 

forcing the furnace decreased the efficiency. The smoke determinations do 

not seem to harmonize with some of 

the expected relations; but these readings va,ry a great deal and are not as 

reliable as some of the other items. In 

determining efficiency it must not be 

overlooked that incomplete combustion is not the only varying element. 

In all six tests the percentage of black 

smoke was so small that a variation in

low 

and

L

Plan of bridge waf/

-Sheet iron casing

FIGURE 39. Cross section of settlngof hand-fired Heine boiler at Norfolk, Va., and plan of bridge wall.

temperature could make the smoke determination and the efficiency 

noncomparable.
142 SMOKELESS COMBUSTION OF COAL.

Five tables compiled from the data collected during these tests are 

given below:

TABLE 26. Results of hand-fired smoke tests at Norfolk, Va., on basis of boiler efficiency

72*.

Efficiency

72* (per

cent). a

64.91

64.93

66.29

67.69

68. 61

68. 94

Black

smoke (per

cent).

5.5

6.2

5.6

8.2

8.6

8.4

Combustion-chamber temperature

(°F.).

2,192

2,523

2,442

2,678

2,264

2,016

Volatile 

matter in

combustible (per

(cent).

20.36

19.31

19.97

17. 05

16.78

16.48

Percentage

of builder's

rated capacity

developed.

81.0

129.5

154. 8

102.2

78.3

 80.6

COsin.flue

gas (per

cent).

6.26

6.73

10.93

6.96

7.04

a. Efficiency 72* figured from pounds of combustible ascending from the grate, the ash being determined 

by analysis of the dry coal.

TABLE 27. Results of hand-fired smoke tests, at Norfolk, Va., on basis of unaccounted

for loss in heat balance.

Unaccounted 

for (per 

cent).

5.02

9.42

9.86

11.02

13.05

CO 2 in flue 

gas (per 

cent).

6.73

7.04

6.26

6.96

10.93

CO in flue 

gas (per 

cent).

0

0

0

.06

.09

Percentage 

of builder's rated 

capacity 

developed.

154.8

80.6

81.0

78.3

102.2

Loss up 

stack (per 

cent).

23.67

18.14

21.51

16. 43

14.97

Black 

smoke (per 

cent).

5.6

8.4

5.5

8.6

8.2

TABLE 28. Results of hand-fired smoke tests at Norfolk, Va., on basis of black smoke.

Black 

smoke (per 

cent).

5.5 

5.6 

6.2

8.2 

8.4 

8.6

Combustion-chamber temperature (°F.).

2,192 

2,442 

2,523

2,678 

2,016 

2,264

Efficiency 

72* (per 

cent).

64. 91 

66. 29 

64. 93

67.69 

- 68. 94 

C8.61

Volatile 

matter in 

combustible (per 

cent).

20.36 

19.97 

19.31

17.05 

16.48 

16.78

Percentage 

of builder's 

rated capacity developed.

81.0 

154.8 

129. 5

102. 2 

80.6 

78.3

CO2 in flue 

gas (per

cent).

6.26 

6.73

- 10.93 

7.04 

0.96

TABLE 29.- -Results of hand-fired smoke tests at Norfolk,Va., on basis of combustionchamber temperature.

Combustionchamber temperature (° F.).

2,016

2,192

2,264

2,442

2,523

2,678

Efficiency 72* 

(per cent).

68. 94

64.91

68.61

66.29

64.93

67.69

Percentage of 

builder's rated 

capacity developed.

80.6

81.0

78.3

154. 8

129.5

102.2

Black smoke 

(per cent).

8.4

5.5

8.6

5.6

0.2

8.2
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 143 

TABLE 30. Results of hand-fired smoke tests at Norfolk, Va., on basis of C02 in flue gas.

C02 in fine 

 gas (per 

cent).

6.26

6.73

6.96

7.04

10.93

Combustion-chamber temperature (° P.).

2,192

2,442

2,264

2, 016

2,678

Efficiency 

72* (per 

cent).

64.91

66.29

68.61

68.94

67.69

Volatile 

matter in 

combustible (per 

cent).

20.36

19. 97

16.78

16. 48

17.05

Black 

smoke (per 

cent).

5.5

5.6

8.6

8.4

8.2

Pounds of 

air per 

pound of 

combustible.

34. 96

32.74

31.81

31.74

20. 64

TESTS WITH MECHANICAL STOKER.

At the same plant 23 tests were made with an underfeed stoker 

under a Heine boiler. The boiler was baffled so as to form a tileroofed furnace. It contained 2,031 square feet of heating surface 

and was rated by its builders at 210 horsepower. The boiler efficiency 

72* averaged 67.4 per cent and varied from 61.83 to 73.71 per cent. 

On arranging the test data and calculated results on the basis of efficiency, it was shown that there was no general relation between efficiency and any other item. The combustion on all the tests was 

nearly perfect, the highest average percentage of black smoke being 

5.3. The percentage of rated capacity'developed ranged from 53.8 

to 175. The average percentage of C02 in the flue gases ranged from 

5.97 to 11.61. The average combustion-chamber temperatures varied 

between 1,792° and 2,575° F.

The results of these tests are shown in Table 31 on the basis of black 

smoke observed, and in Table 32 on the basis of dry coal burned per 

hour.

TABLE 31. Results of smoke tests withunderfeed stoker at Norfolk, Va., on basis of "black

smoke.

Black 

Smoke (per 

cent).

0

0

0

.5

.8

.8

.9

1.0

1.1

1.1

1.2

1.3

1.8

1.9

2.0

2.2

2.2

2.3

3.4

3.9

3.9

5.3

CO2 in flue 

gas (peicent.)

6.81

9.01

7.38

7.88

7.99

S.58

10.00

5.97

7.60

9.58

9.58

7.55

8.76

7.62

9.61

8.58

10.74

6.85

9.49

10.74

11.61

11.25

CO in flue 

gas (per 

cent).

0

0

0

0

0

0

0

0

0

0

0

0

0

0

.03

.00

.04

.10

.04

.03

.11

.16

Percentage 

of builder's 

rated capacity developed.

54.8

74.8

70.7

75.8

57.7

93.0

94.9

83.1

58.9

73.5

71.4

131.5

124.7

56.4

106.3

105.0

120. 0

124.0

91.9

115.3

175.0

127.9

Combustion-chamber temperature 

(° F.).

1,792

1,978

2,0.14

2,192

1,920

2,070

2,190

2, 136

2,053

2,133

2,003

2,381

2,311

2,016

2,205

2,192

2,352

2,290

2,336

2,298

2, 575

2,347
144 SMOKELESS COMBUSTION OF COAL.

TABLE 32. Results of smoke tests with underjeed stoker at Norfolk, Va., on basis of dry

coal burned per hour.

Dry coal

burned

per hour 

(pounds).

376 

396

414

421

469

482

489

497 ,

531

570

636

682

711

735

813

872

879

887

894

901

921

938

1, 209

Black

smoke

(per 

cent).

0 

.08

1.1

1.9

1.1

1.2

0

0

.5

1.0

.9

.8

2.2

3.4

2.0

2.2

3.9

2.9

1.3

2.3

5.3

1.8

3.9

Efficiency 72*

(per 

cent).

69.58 

67.00

66.52

65. 04

73.71

68. 62

68.44

70.01

66.62

68.47

69. 41

63.44

69. 62

68.98

63.91

68.00

63.90

65.97

69. 13

64.51

CS. 59

61. 83

68. 11

C02 in

flue gas

(Per

cent).

6.81 

7.99

7.66

7.62

9.58

9.58

7.38

9.01

7.88

5.97

10.00

8.58

8.58

9.49

9.61

10.74

10.74

10. 76

7.55

6.85

11. 25

8.76

11.61

CO in

flue gas

(per 

cent).

0 

0

0

0

0

0

0

0

0

0

0

0

.06

.04

.06

.04

.03

0

0

.10

.16

0

.11

Combustionchain her

temperature

1,792 

1,920

2,053

2,016

2,133

2,003

2,014

1,978

2,192

2, 136

2, 196

2,070

2,192

2, 336

2,205

2,352

2,298

2,381

2, 296

2,347

2,311

2,575

It will be noted that, as has been pointed out by Breckenridge, a 

a high percentage of C02 is not necessarily an indication of high economy. When the air supply is reduced, the furnace temperature, 

C02 , CO, and smoke are all increased after a certain capacity is 

reached.

Theoretically, better results should be obtained with only enough 

air to supply the necessary oxygen, but in practice with most equipments there is a limit to., the capacity of the furnace for burning the 

volatile matter in the coal, and the limited supply of air results in 

incomplete combustion, which more than offsets the effects of high 

furnace temperature and high CO2 .

The following general relations have been deduced from a study of 

the data collected: When the percentage of black smoke was the 

highest, the C02 and the CO in the flue gases, the capacity, and the 

combustion-chamber temperature were highest, and vice versa; there 

was no definite relation with boiler efficiency. This may be taken to 

mean that a stoker properly installed can be operated under wide 

variations in capacity with different conditions of operation, and yet 

run smokeless!}7" and with high efficiency.

TESTS AT ST. LOUIS, MO.

The plant at St. Louis had two hand-fired Heine boilers; one furnace had a flat grate, the other a rocking grate. Either natural draft 

or forced draft supplied by a fan could be used. The bottom row of

a Breckenridge, L. P., A study of four hundred steaming tests: Bull. U. S. Geol. Survey No. 325, 1907.
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 145

water tubes in each boiler was incased in tile, forming tile-roof furnaces. In most of the tests these furnaces contained some sort of 

structure to mix the air and the gases from the fire, and thus hasten 

combustion. An expert fireman working under the direction of a 

competent engineer was employed in all tests.

The following tables and deductions are compiled from tests 

made at this plant and supplement the observations in the field and 

at Norfolk, as they throw light on several points which have heretofore been little considered or at least not fully determined. All 

the tables have a bearing on the problem of smoke prevention and 

they are presented because they may be of assistance in its solution.

Table 33 shows the results of six tests made to determine the best 

method of hand firing a high-volatile Illinois coal, nut size, using 

natural draft. The proximate analysis of the "coal as fired showed 

the following: Volatile matter, about 36 per cent; ash, about 10 per 

cent; moisture, about 13 per cent; British thermal units average, 

10,948.

Four different methods of firing were used ribbon (firing alternately in'narrow strips across the full length of the grate), coking, 

. alternate, and spreading. In every test a reasonably thin fire was 

carried, from 2 to 3 inches of incandescent fuel above the clinker. 

Wheno firing by the spreading method'three shovelfuls of coal were 

thrown on the back of the grate and two on the front. When firing 

by the ribbon method the fire doors were kept cracked.

The average of tests 500 and 504 was taken as representative of 

the alternate method of firing. On test 500 the furnace doors were 

closed tightly after each firing; on test 504 they were kept cracked. 

This cracking of the furnace doors, while it caused a slight reduction 

in smoke compared with test 500, proved to be wasteful because the 

combustion space was not constructed so as to make the excess air 

of value in hastening combustion. A compromise method, cracking 

the doors for a short time after firing and then closing them, ought 

to give as good if not better results for alternate firing than those 

shown in the table.

The ribbon method of firing, where the coal was fired most frequently with the smallest amount per firing, gave the highest efficiency and practically no smoke. The usual spreading method of 

.firing gave the lowest efficiency and caused the most smoke. The 

results with the. alternate and the coking methods showed that one 

was about as good as the other. 

74897 Bull. 373 09 10
146 SMOKELESS COMBUSTION OF COAL.

TABLE 33. Results of comparative tests on Illinois coal to determine best method of firing.

No. 

of 

test.

503

502

0500

"504

501

505

Kind of 

draft.

Natural . . .

.....do.....

....do.....

.....do.....

Forced....

Method of 

firing.

Ribbon.....

Coking......

Alternate. ..

Spreading . .

Alternate . . .

Efficiency 72*.

Per ct.

62.22

 .60.49

59.87

57.56

60.20

Black 

smoke.

Perct.

5.0

15.0

c

15.8

32.0

14.9

Average 

interval 

between 

firings.

Minutes.

2.3

7.4

3.5

9.3

3.4

Coal 

per 

firing.

Pounds.

50

140

70

170

85

Percentage of 

rated 

capacity

developed.

100. 7

95.0

106.5

92.7

131.6

Observation of stack for 

one hour.

Twenty per cent black

smoke 15 minutes; clean

45 minutes.

Twenty per cent black

smoke 48 minutes, very

seldom as high as 40 per

cent; clean 12 minutes.

One hundred per cent

black smoke 4| minutes,

80 per cent 4J minutes,

60 per cent 3 minutes, 40

'per cent 1J minutes, 20

percent G minutes; clean

41 minutes.

Forty per cent black smoke 

6 minutes, 20 per cent 24

minutes; clean 30 minutes.

One hundred per cent

black smoke 15 minutes,

80 per cent 1£ minutes, 60

per cent 1$ minutes, 40

per cent 4> minutes, 20

per cent 6 minutes; clean

32 minutes.

Sixty per cent black smoke

4j minutes, 40 per cent 3

minutes, 20 per cent 24 

minutes; clean 29 minutes.

« Average.

Table 34 is instructive because it shows the possibility of utilizing 

high-ash coals. Although the grate area was too small to obtain the 

rated capacity of the boiler, steam was produced at a reasonable 

efficiency. Owing to the distribution of the combustible in the coal 

as fired and to the low rate of the combustion, no smoke was produced.

TABLE 34. Results of tests on high-ash coals.

No. 

of 

test.

451

458

47M

Field designation 

of fuel.

Argentina No. 1.....

Argentina . No. 1

(washed).

Kind of 

draft.

Forced. .

....do....

....do....

Clinker in 

refuse.

Perct.

60

48

69

59

Volatile 

matter 

in 

combustiPer ct.

39.32

34.41

36.35

36.69

Ash in 

coal.

Perct.

50.16

31.33

41.82

41.10

Percentage of 

rated 

capacity 

developed.

34.20

52.90

72.60

53.23

Efficiency 72*.

Perct.

51.01

57.82

57.08

55.30

Black, 

smoke.

Perct.

0

0

0

0

CO in

dry 

flue

Perct.

0.15

.26

.40

.27

Moisture in 

coal.

Perct.

6.94

16.48

10.83

11 42
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 147

Tables 35 and 36 were compiled to show the effect of size of coal 

on efficiency developed and smoke produced. All coal used in the 

tests summarized in Table 35 had an average diameter of over 1 inch; 

that used in the tests summarized in Table 36 had an average diameter of less than one-half inch.

TABLE 35. Results oj tests ivith coals having an average diameter of over 1 inch.

Field designation of coal.

Alabama': 

No.2B. ................................

Do..................................

Illinois: 

No 19 B

Do..................................

No. 22 A ................................

Do..................................

No. 24B. ...............................

No. 25...................................

Do..................................

No. 26......... .........................

Do..................................

No. 27. .................................

No.28C.................................

No. 29B. ...............................

N0.34B................................

Indiana: 

No. 13.. ....................:............

No. 14...... .............................

Do..................................

No. 15...................................

No. 17...................................

Kentucky: 

No. 5.... ................................

No. 6........... .........................

Do..................................

Ohio: 

No. 4. ...................................

No. 5.....................................

No.'7..... ...............................

No. 8.. .....................:............

No. 9 A................'. ................

No. 10...... .............................

No. 11..... ..............................

Do..................................

Pennsylvania: 

No. 5....................................

Do..................................

No. 19...................................

Tennessee: 

No. 1... .................................

Do..................................

Do..................................

No. 2..... ...............................

No. 3....................................

Do..................................

No. 4....................................

No. 7 A....................:............

Virginia: 

No. 2....................................

West Virginia: 

No. 16 A .................................

No. 21 (washed).........................

No.22B. ...............................

No. 23 A................................

Wyoming: 

No.2B. ................................

Do..................................

No. 3................. ...................

Do..................................

No. of 

test.

3S3

.382

175

205

324

325

337

338

339

341

342

353

452

461

509

432

431

430

428

441

276

271

270

254

186

269

287

249

469

474

475

286

194

195

498

344

345

369

350

349

356

372

247

260

274

438

439

196

213

212

211

Average 

diameter 

of coal

Inches. 

\ 1.12

I 1.97

1.27

| 

I 1.29

1

1. 58

j- 1.03

1 1.20

1

1 1.22

J

Efficiency. 72*.

Per cent.

65. 83

65.13

66. 82

67.27

60. 20

66. 26

66. 90

68.59

61.72

Black 

smoke. .

Per cent.

30.0

19.7

12.0

19.4

23.8

12.8

15. 0

Percentage of 

rated capacity developed.

97.8

90.3

96.2

99.6

106. 6

95.9

83 6

Pounds 

of air per 

pound of 

combustible.

23.73

20.33

20.55

19.74

19.26

19. 67

21.38

17. 63

19.89

20.61
148 SMOKELESS COMBUSTION OF COAL.

TABLE 36. Results of tests loith coals having an average diameter of less than one-half inch.

Field designation of coal.

Alabama: 

No. 4....................................

No. 5-........-.....-.......-.-.-....-.-.

Do..................................

Arkansas: 

No. 7 A.................................

Do..................................

Illinois: a 

No. 19 A................................

Do..................................

Do..................................

Do..................................

Do...................................

New Mexico* No 4 B

Pennsylvania: 

No. 8....................................

Do..................................

Do..................................

Do..................................

Do..................................

No. 15................................... DO..........................:.......

No. 10...................................

No. 17.. ..................."..............

West Virginia: 

No. 13. ..................................

No. 17...................................

No 19

Do..................................

No. 22 A ................................

. Do..................................

No. of 

test.

377

478

480

093

294

160

161

163

170

171

166

449

222

OQC

242

239

238

237

236

XT)

473

471

506

365

507

180

225

289

285

447

446

Average 

diameter.

Inches.

1 0.39

\ 37

/ ' 37

.36

.45

.35

.34"}Q

> .36

.44

.46

.46

Efficiency 72*.

Per cent.

07.25

67.20

C6.40

 «

66.38

65.20

65. 28

f><; 19

66.87

64. 24

63.39

- 68. 93

Black 

smoke.

Per cent.

8.5

0

13.5

2.0 < n

8.2

18.0

3.6

3.0

9.8

Percentage of 

rated 

capacity developed.

91.4

79.3

90.3

 74.7

97.0

80.1

100.6

87.5

98.8

101.8

86.9

Pounds 

of air per 

pound cf combustible.

26.53

26. 50

19.27

23.64

23.77

21.45

25.13

23.14

24.93

25.84

22.18

i Test 129 omitted, no smoke having been recorded.

b Tests.164 and 176 omitted, clinker having caused trouble.

These two tables show that both large and small sizes of coal from 

the same State were burned. All tests in which owing to some factor, 

such as trouble with clinker, the air distribution was not due to the 

size of the coal were omitted in compiling results. Table 37 gives a 

comparison of the average results of Tables 35 and 36. It shows that 

with either large or small coal about the same efficiency resulted. 

Unfortunately for direct comparison the large coals burned more 

readily and.produced higher capacities than the small in nearly every 

test; also with the large coal less air was used per pound of combustible. Nearly all the small coals burned with little smoke, while all 

the larger sizes caused considerable black smoke.

TABLE 37. Comparison of average results of tests with small and large sizes of coal.

Number 

of tests.

31

53

Average 

diameter.

Inches.

0.39

1.46

Efficiency 72*.

Per cent.

66.88

65.97

Black 

smoke.

Per cent.

7.4

21.3

Percentage 

of rated capacity developed.

88.6

98.3

Pounds of 

air per 

pound of combustible.

23.07

20.28
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 149

Table 38 is of especial interest, for it shows that lignites, peat, and 

subbituminous coals with 47 to 67 per cent of volatile matter in the 

combustible can be hand-fired with the production of only a small 

amount of smoke. The average indicates that the boiler was run up 

to the rating at an efficiency of about 60 per cent. The smoke 

averaged less than 10 per cent black.

TABLE 38. Results of tests on lignites, peat, and subbituminous coals.

Field designation of fuel.

Florida No. 1 (briquets).

North Dakota No. 3.....

Washington No. IB.....

No. of 

test.

, 340

386 

470

477

200 

I 291

{ 298

I 303 

290 

400

Kind of 

draft.

Forced .

Natural 

...do....

...do....

Forced . 

...do....

...do....

...do.... 

Natural 

...do....

Clinker 

i n refuse.

Per ct. 

0

29 

0

58

57 

0

0

28 

0 

14

18.0

Volatile 

rhatter 

in combustible.

Per ct. 

53.77

C7.24 

42.07

41.70

50.71

55.14

53.07 

47.99 

47.19

51. 98

Percentage 

of rated 

capacity developed.

104. 0

113. 2 

113.2

90.7 

89.1

104.1

90.4 

81.8 

93.1

100.1

Efficiency 

72*.

Per ct. 

CO. 25

58.19 

1 68.11

G5. 78

57. 40 

61.37

52. 01

53.05 

65.04 

57.84

59.91

Black 

smoke.

Per ct. 

0

13 

18

10 C

0 

0

12

14 

10 

3.5

8.3

COin 

dry flue 

gases.

Per ct. 

0.34

.10 

.02

.07

0 

0

0

.24 

.07 

.04

.08

Unaccounted 

for in 

heat 

balance.

Per ct.

9.34 

0.00

8.65

13.32

6.88

17.59

14. 84 

8.89 

16.22

11. 30

Tables 39 to 41 supplement one another. Table 39 gives the 

average results of tests which showed a high percentage of black 

smoke; Table 40 gives the coals used in these tests and contains some 

remarks explanatory of the high percentage of smoke in particular 

tests; and Table 41 gives the results of tests with coal which made 

little smoke.

A comparison of Tables 40 and 41 shows that the coals which 

smoked the worst clinkered the most. The smoky coals also had 

higher percentages of volatile matter in the combustible, were burned 

at higher capacities, and gave a lower efficiency than the less' smoky 

coals.

Among the comparatively smokeless tests were two on Utah coal 

and two on Missouri coal in which, for some unaccountable reason, 

the coals burned with a low efficiency; with these four tests omitted 

from the average, the low-smoke tests gave an average efficiency of 

66.93 per cent, with a percentage of builder's rated capacity developed 

of 96.6. The high-smoke tests gave an average efficiency of 64.32 

per cent, with a percentage of rated capacity developed of 99.2, 

showing a good percentage in efficiency in favor of the low-smoke 

tests. There are many briquet tests included in Table 41, and Table 

42 shows that as a general rule the briquets made very little smoke. 

The other tests which gave low percentage of smoke were made with 

coals low in volatile matter, or slow burning, or else some means 

besides the automatic operation of the air-admission doors was 

employed to supply more air.
150 SMOKELESS COMBUSTION OP COAL.

TABLE 39. Results of tests showing 35 per cent or over of black smoke. 

[Tests using natural draft, 34; forced draft, 5.]- ^

.....................do....

.....................do....

Average.

49.9

42.88

99.2

04. 32

41.8

.28

. 12.55

Range.

0 to '67

36.38 to 51.58

84.4 to 129.9

56.04 to 09.36

35.0 to 54.8

. 07 to . 73

5.71 to 19.03

TABLE 40. Coal giving over 35 per cent black smoke.

Field designation of fuel.

Illinois: 

No.7E. ...........................

NO. 16........:.. ...................

Indiana: 

No. 5.. .............................

No. 7 A............................

No.9 A............................

No. 10..............................

Ohio: 

No. 3.......... ........-.--..-. -----

No. 4.... ...........................

Do.............................

No. 5...... .........................

Do.............................

No. 7..... ...........................

No. 9 A. ...........................

Pennsylvania:

No. 6... ............................

Virginia: 

No. 2..............................

Do.............................

No. 4.......... .....................

West Virginia: 

No. 15..... .........................

Do.............................

Wyoming: No. 2 B. ....................

No. of 

test.

516 

144 

152

150 

153

159 

158 

184 

168 

334 

107 

177 

323 

332

203

. 202

220 

219

190 

186 

269

241 

243

195 

217 

367

251 

247 

200 

240

216 

215 

267 

213

Remarks.

Forced draft; automatic air admission not operated. 

Automatic air admission operated. 

Clinker removed with difficulty; automatic air admission 

operated. 

Automatic air admission operated.

Heavy clinker formed on grate; automatic air admission 

operated. 

Automatic air admission operated. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Forced draft; clinker solid; automatic air admission not 

operated; maximum-capacity test.

Automatic air admission operated. 

Clinker adhered to grate; automatic air admission operated. 

Automatic air admission operated; coal caked badly. 

Clinker fused into grate; automatic air admission operated. 

Automatic air admission operated. 

Do. 

Clinker adhered to grate; automatic air admission operated.

Automatic air admission operated.

Do. 

Do.

Do. 

Maximum-capacity test; doors cracked after each firing; 

combustion wall down during test.

Automatic air admission operated. 

Do. 

Do. 

Clinker fused into grate; automatic air admission operated.

Forced draft; automatic air admission operated. 

Automatic air admission operated. 

Do. 

Forced draft; maximum-capacity test; automatic air admission not operated.
TABLE 41. Results of tests showing less than 6 per cen

Field designation of fuel.

Alabama: 

No. 2 B (briquets)...'.........

No. 3.. .......................

No. 4..........................

Arkansas: 

« No. 7 A......................

No. 8.........................

Illinois: 

No. 6 B (briquets) ...........

No. 9C(briquets). ...........

No. 19 C......................

No. 19 D. .....................

No. 20........................

No. 21... .....................

No. 23 A (washed)............

No. 25........................

No. 26........................

No. 28 A (washed; briquets).. 

No. 28 B (briquets)...-..-..-.

No. 29 B (washed; briquets).. 

No. 30 (washed; briquets). ...

No. 33 (briquets) .............

Indiana: 

No. 4..........................

No. 15........................

No. 16........................

No. 19 (briquets). ............

No. of

test.

410

390

378

413

293,294

297

308,309

481

313

492, 497

312

463

424,425

292

316

318

317

338,339

342

459 

457

465 

511 

489, 491

513

=;03

166

288

429

427

464

Clinker 

in 

refuse.

Per cent.

39

1 «

1

65

49

1 

Volatile 

matter 

in combustible.

Per cent.

35.13

21.21

42.01

43.28

Ash in 

dry coal.

Per cent.

16.18

i fl no

14.04

Moisture 

in coal 

as received.

Per cent.

4.22

5.21

3.11

11.94

11.49

Percentage of 

rated capacity 

developed.

93.0

85. 2

111.8

92. G

83.4

Efficiency 

72*.

Per cent.

66.88

66.17

64.58

65.34

Blac

smok

Per ce
TABLE 41. Results of tests showing less than 6 per cent black 

Field designation of fuel.

Indian Territory:

No. 9................ .

Kansas: 

No. 2 B (briquets).. . .........

No. 2 B (washed; briquets)... 

Maryland:

No. 2. .........................

Missouri: 

No. 5.. ...... .................

No. 10 (briquets) .............

New Mexico; No. 3 B'.. ...........

Pennsylvania: 

No. 8........ .................

No. 15........................

No. 20 (washed; briquets) ....

Tennessee: 

No. 1 (washed; briquets)..... 

No. 5............. ............

No. 9 B (washed; briquets)... 

No. 10 (washed; briquets) ....

No- of. 

test.

449

Ar.n

487, 488

495

490

493

320

486

389

236, 237

467

468

498

. 508

514

512

409 

352

388

393 

407, 408

Clinker 

in 

refuse.

Per cent.

}.........

> 46

1 

}.........

0

I 40

47

0

Volatile 

matter 

in combustible.

Per cent.

37 14

19.42

45.11

25.30

37.34

Ash in 

dry coal.

Per cent.

7 64

9 16

io. y^

17.87

8.86

13.40

6.99

Moisture 

in coal 

as received.

Per cent.

3.50

7.24

4 29

. oo

3.01

3.75

3.32

Percentage of 

rated capacity 

developed.

101.4

110.3

98.5

74.8

Efficiency 

72*.

Per cent.

65.88

60.50

68.45

66. 79

OG 21

Bla

smo

Per c
OBSERVATIONS AT SUKVEY FUEL-TESTING PLANTS. 153

S 88 8

IN "?CN U5

ofc

ss

OO5

S3

..«
TABLE 42. Results of tests on briquetted co

Field designation of coal.

Alabama: 

No. 2 B...... I.........*...................

No. 4. ....................:...............

Illinois: 

No. 6 B ...................................

No. 9C...................................

No. 11C..................................

No. 12 B ..................................

No. 21 ....................................

No. 23 B ..................................

No. 28 B ..................................

No. 29 A (washed). .......................

No. 29 B ..................................

No. 30 (washed) ..........................

No. 31 ....................................

No. 33....................................

Indiana: 

No. 7 A ...................................

No. 19....................................

Indian Territory: 

No. 2 B (lump) ...........................

No. 2 B (slack)...........................

No. 9.....................................

Kansas: 

No. 2 B ...................................

Do....................................

No. 2 B (washed) .........................

Maryland : No. 2 ..............................

Pennsylvania: 

No. 6.....................................

No. 15....................................

No. 16....................................

No. 18....................................

Do....................................

No. 19....................................

No. 20 (washed) ..........................

No. 20....................................

No. 22....................................

Size of briquets.

Large and small. ......

.....do................

.....do............:...

.....do................

Small.................

Small.................

.....do................

....do .................

.....do................

Large. ................

No. of 

test.

410

^llo

313

492, 497

312

463

318

321,322

. 459

457

465

466

511

489, 491

288

464

456

407

450

407

488

495

493

333

467

468

4QQ

515

508

512

514

510

Kind of draft.

j-Natural ...............

1

I. ...do.. ..............

1.... do.. ..............

.....do. ...............

.....do..:.............

Clinke

in refus

Per cen

23

45

oo

29

45

56

39 
Tennessee:

No. 4.....................................

No. 7B (washed).........................

No. 9 B (washed) ......................... 

No. 10 (washed) ..........................

Do. ...................................

.....do................

Large. ................

.....do................

Small.................

409

405

406

393 

407

408

494

412

.....do................

.....do................

46

26

38

39
156 SMOKELESS COMBUSTION OF COAL.

Table 42 is a compilation of results from all tests made on briquets 

at the St. Louis fuel-testing plant. The briquets all had a pitch 

binder and gave off little or no smoke, showing that the tile-roofed 

furnace used is satisfactory for burning such briquets. The volatile matter in the combustible varied from 23 to 46 per cent and 

averaged about 38 per cent. The smokeless combustion of coals so 

high in volatile shows that briquetting has an appreciable effect 

on burning, especially in the furnaces of steam boilers at the rates 

of combustion common in stationary practice. The average percentage of the rated capacity developed on these tests was 100.6.

Table 43 is compiled from results of tests made on raw coals and 

the same coals washed. All the coals were washed at the fuel-testing 

plant, and the reductions or additions in moisture, ash, and sulphur 

are of interest. Most of the washed coal either burned freely (was noncoking) or seemed to burn more rapidly than the raw coal. In fact, 

the average percentage of rated capacity developed was considerably greater with the washed than with the unwashed coal. This 

result does not indicate that the combustion chamber was more 

effective in one case than in the other, for .the table shows that the 

washed coals burned with lower efficiency and made more smoke. .

The average results show that the washed coals developed 96.6 

per cent of the rated capacity, with an efficiency of 64.82 per cent, 

and the unwashed coals 89.9 per cent of the rated capacity, with an 

efficiency of 66.95 per cent. This difference in efficiency in favor 

of raw coal is more consistent and greater with the poorer coals than 

with the best.

The table emphasizes the difficulty of burning wet coal in any but 

a properly designed furnace. However, with a good furnace washing should be of advantage, as the washed coal burns more rapidly 

than the unwashed..

Table 44 is compiled from the results of tests made on the same 

coals raw and briquetted, natural draft being used in every test but 

one. It shows that the briquets usually burned with 1 to 3 per cent 

greater efficiency, developed higher capacity, and were consumed 

much more completely than the raw coal. Briquetting thus offers 

to hand-fired plants a means of developing high capacity. The plant 

can be run practically without smoke and obtain good efficiency by 

the use of briquets.

Table 45 is a comparison of results of tests made on the same coals 

burned with natural and with forced draft. Whenever forced draft 

was used the attempt was made to attain high capacity. Usually 

this was accomplished at the expense of efficiency. In the tests with 

forced draft the average percentage of black smoke was about double 

that, in those with natural draft. The combustion space not being
OBSERVATIONS AT SURVEY FUEL-TESTING PLANTS. 157

designed for high rates of combustion, an average variation in capacity of 92.6 to 108.4 caused an average drop in efficiency from 64.31 

to 60.94; This table demonstrates that forced draft supplied through 

the average grate and fuel bed will neither intimately mix the air and 

gases nor allow coal to be burned at high and low rates of combustion 

with equal efficiency.

Table 46 is a comparison of results of tests of the same coals burned 

on flat and on rocking grates. In all the tests but one higher efficiency (from 1 to 5 per cent, with an average of 2) was obtained with 

the rocking grate. The average difference in proportion of rated 

capacity developed was about 2 per cent and was in favor of the flat 

grate. However, as the rocking grate had an area of 36.4 square feet 

and the flat grate of 4.0.55 square feet, it is evident that the rate of 

combustion per square foot of grate area was at least equal on the 

rocking grate to that on the flat grate, or perhaps slightly greater, but

as the total weight of coal burned on the flat grates was greater it 

involved an increased tax on the efficiency of the combustion space. 

The average figures for over-all efficiency of the plant show that more 

coal was lost in the ash pit with the rocking grate than with the flat 

grate, but this loss did not counterbalance the efficiency, which still 

shows a gain of a little more than 1.50 per cent in favor of the rocking 

grate.

The ash in the dry coal varied from 5.39 to 23.16 per cent and the 

sulphur from 0.58 to 4.78 per cent. In the sole test in which the 

rocking grate failed to show better results the dry coal contained 

about 4.50 per cent of sulphur. With both flat and rocking grates the 

sulphur caused trouble. The clinker fused to the grate bars so that 

the rocking grate as constructed was practically inoperative and was 

actually used as a flat grate. However, as more difficulty was experienced in getting the clinker off the rocking grate, the time of 

cleaning and inefficient operation was longer with that grate and the 

tests showed less efficiency, but as most plants would not have a rocking grate to burn coal so high in sulphur, this point is unimportant. 

In practice about 2 per cent of sulphur is ass.umed to be the maximum 

content desirable for a coal to be burned on rocking grates, but this 

limit may be exceeded if experience shows that the sulphur is in 

organic form or that the sulphur and ash combined have no ill effects. 

The high sulphur and ash in the Wyoming coal did not cause trouble; 

in fact, the test was exceptional, for the coal did not clinker at all.

The black smoke was about 5 per cent less in the rocking-grate tests 

than in those with the flat grate. While this reduction is small the 

gain in efficiency with the rocking grate shows the advantage of having some means of keeping the fire clean. Such a grate would be of 

value in hand-fired plants for decreasing smoke and increasing the 

efficiency of operation.
TABLE 43. Comparison of results of tests on washed a

Field designation of 

coal.

Illinois: 

No. 20..............

No. 22 A............

No. 23 A............

Indiana: 

No. 4...............

No. 6...............

No.8.... ...........

No. 10..............

No. 12. .............

Kansas: No. 6 .........

No. 

of 

test.

f 301 

1 292 

f 328 

1 325 

f 317 

I 306 

f 154

1 165

r 159

1 157

J 184 

1 185

I'"

I 167

f 310 

(300 

J 323 

1 311

Description 

of coal.

Washed.....

Washed..... 

Raw........

Washed.....

Washed..... 

Raw........

Washed..... 

Raw........

Washed.....

Washed..... 

Raw........

Washed .....

Washed..... 

Raw........

Moisture in 

coal as 

fired.

Perct. 

16.51

14! 52 

14.35 

10.53 

14.64 

14.49 

14.80

13.82 

11.27

10.51

11.87 

10.12 

10.98 

10.60

12.87 

12.41 

11.71 

8.28

Ash in 

coal as 

fired.

Perct. 

10.45

15.49 

8.22 

13.80 

8.88 

13.45 

7.19

17.26 

9.63

12.76

9.29 

12.89 

6.24 

10.16

7.94 

13.86 

10.45 

15.53

Sulphur in 

coal as 

fired.

Per ct. 

3.25

4.32 

3.75. 

6.07 

3.23 

4.62 

2.12

2.43 

3.57

4.55

2.87 

3.54 

3.50 

4.21

3.02 

4.21 

2.64 

3.42

Sulphur in 

dry 

coal.

Perct. 

3.89

5.05 

4.38 

6.78 

3.78 

5.40 

2.49

2.82 

4.02

5.08

3.26 

3.94 

3.93 

4.71

3.47 

4.81 

2.99 

3.73

A shin 

dry 

coal.

Perct. 

12.51

18.12 

'9.60 

15.43 

10.40 

15.73 

8.44

20.03 

10.85

14.26

10.54 

14.34 

7.01 

11.36

9.11 

15.82 

11.83 

16.93

Clinker 

in refuse.

Per ct. 

45

55 

53 

60 

50 

66 

44

53 

51

53

50 

54 

51 

49

26 

30 

57 

56

Volatile 

matter 

in combustible.

Perct. 

44.04

45.69 

47.60 

47.09 

46.71 

44.92 

42.43

42.25 

47.92

45.35

47.15 

46.17 

49! 69 

47.83

45.27 

46.28 

38.84 

39.81

Percentage 

of rated 

capacity developed.

99.3 

66.3 

121.8 

101.0 

90.4 

84.3 

95.3

88.9 

96.7

84.9

97.0 

89.0 

105.3 

99.4

97.8 

103.9 

106.6 

82.2
New Mexico: 

No.3B.... .........

No. 4 A.............

Ohio: 

No. 2...............

No. 4...............

No. 6...............

No.9B.. ...........

Pennsylvania: 

No.5...............

No. 7..... ...

Tennessee: Nos. 8 A and 

8B.

Virginia: No. 2.........

1 232

1 222

f 392

[ 391

J 398

1 397

f 197

[ 193

f 220

1 201

f 253

1 284

| 241

f 195

( l9?

1 307

f 388 

1 384

J 200 

1 256

Washed.....

Washed.....

Raw........

Washed.. ...

Raw........

Washed.....

Raw ........

Washed.....

Raw........

Washed.....

Washed.....

Washed.....

Washed.....

Washed.....

Washed..... 

Raw........

3.43

1.84

4.77

2.47

3.86

2.30

8.99

8.86

4.30

3.73

3.26

3.71

7.92

7.84

2.97

4.11 

4.80

5.80

2.83 

2.40

3.34 

4.22

10.13

12.52

12.23

16.91

11.40

14.58

7.74

13.81

6.69

9.73

6.88

12.07

7.08

14.89

4.73

10.94

13.63

10.23 

14.87

4.48 

6.19

I.'IO

1.52

.71

.67

.63

.60

3.15

4.37

2.97

2.65

3.01

3.77

2.86

.'94

1.01 

1.62

2.92 

5.28

.85 

.82

1.14

1.55

.75

.69

.66

.61

3.46

4.79

3.10

2.75

3.11

3.91

3.11

.97

1.05 

1.70

2.36

3.00 

5.41

.88 

.86

10.48

12.76

12.85

17.34

11.86

14.92

8.50

15.15

6.99

10.11

7.11

12.54

7.69

16.16

4.88

o. /y 

11.50

14.47

10.53 

15.24

4.63 

6.46

22

38

0

0

0

0

50

42

34

, 51

60

52

56

48

40

*J

33

0

51 

57

40 

47

16.29

16.38

39.88

40.92

40.19

41.61

45.29

45. 27

43.60

42.44

43.11

43.43

45.39

45.61

38.04

26.87

27.04

39.91 

39.42

39.21 

37.37

93.2

80.1

119.2

114.8

108.1

103.9

84.4

80.3

93.2

93.2

79.4

81.3

92.7

87.8

96.9

88.6

85.0

106.1 

72.8

87.7 

87.6
TABLE 43. Comparison of results of tests on washed and r

Field designation of 

coal.

West Virginia: 

No. 17..............

No. 20..............

No. 21..............

No. 22 A............

No. 23B. ............

Average ..........

No. 

of

test.

( 230

[ 226 

J 266 

1 273

267 

296 

454

447 

f 444

1 445 

223 

212

Description 

of coal.

Washed.....

Washed..... 

Raw ........

Washed.....

Washed.....

Washed.....

Washed..... 

Raw........

/Washed.....

Moisture incoal as 

fired.

Perct. 

4.35

4.10 

3.14 

2.89

4.24 

3.42 

5.24

5.55 

4.06

2.44 

19.08 

13.60

8.06 

7.48

Ash in 

coal as 

fired.

Perct. 

6.17

7.40 

5.53 

8.43

3.67. 

6.12 

6.10

13.47 

4.80

10.59 

6.78 

16.21

7.84 

12.48

Sulphur in 

coal as 

fired.

Perct. 

1.36

1.21 

1.10 

'1.50

1.'07 

1.22 

.90

1.04 

.95

1.40 

4.26 

7.90

2.24 

2.99

Sulphur in 

dry 

coal.

Perct. 

1.42

1.26 

1.14 

1.54

1.12

1.26 

.95

1.10 

.99

1.43 

5.26 

9.14

2.50 

3.29

Ash in 

dry 

coal.

Per ct. 

6.45

7.72 

5.71 

8.68

3.83 

6.34 

6.44

14.26 

5.00

10.85 

8.38 

18.76

8.58 

13.54

Clinker 

in refuse.

Perct.

48

34 

45 

34

52 

47 

25

33 

30

41 

53

58

41 

42

Volatile 

matter 

in combustible.

Perct. 

31.68

31.55 

36.57 

35.80

39.59 

37.87 

37.98

36.61 

39.17

38.29 

49.34 

51.46

40.82 

40.50

Percentag

of rated 

capacity de

veloped.

89.0

87.6 

86.7 

83.6

95.4 

101.8 

110.3

99.1 

88.0

95.9 

81.0 

88.2

96.6 

89.9
TABLE 44. Comparison of results of tests on raw and b

Field designation of coal.

Alabama: 

No. 2 B ..... ,. .....

No. 4...............

Illinois: 

No. 21..............

No.29B.. .........

Indiana: No. 7 A .......

Indian Territory: 

No.2B...... .......

No. 9...............

Maryland : No. 2. ......

Pennsylvania:

No. 15..............

No. 16..............

No 19

T nnesseeNo. 1. ..............

Condition of fuel as fired.

/Large and small briquets. .

/Large and small briquets..

/Large briquets ............

/Small briquets ............

(Large briquets. ...........

(Small briquets from slack

/Small briquets ............

\Raw. ..................... 

/Large briquets. ..........

Large briquets ............

Small briquets ............

Large briquets ............

....do....................

No. of 

test.

410

OO^

413

G/O

318

O1U

466

288

453

418

450

449 

493

333

217

467

468

471

508

498 

409

345

346

Kind of 

draft.

Natural . . .

...do...... 

...do.......

...do...... 

Forced....

...do......

...do...... 

...do.......

...do...... 

...do.......

...do......

...do......

...do...... 

...do......

...do...... 

...do......

...do......

...do....... 

...do......

...do......

...do.......

...do......

...do....... 

...do......

...do......

...do......

...do......

Clinker 

in refuse.

Per cent. 

0

oo

47

\r±

47

38

37

34

48

26 

56

OA

43

54

39

41

40

34

46 

26

0

44

53

Volatile 

matter 

in combustible.

Per cent. 

38.94

OO. Ol

36.33

41.83

42.35 

45.79

42.84

39.88

40.81

19.23

22.99

39.45

38.59

26.53

27.43

24 24

37.77

40.56

40.31

39.87

38.83

Percentage of 

rated 

capacity 

developed.

91.4

108.6 

109.5

1UU. o

115.3

Oy. O

109.2

84! 5

105.1

95.0

102.2

121.2

105.9

97.1

99.0

105.7

98 9

113.7

106.8 

110.3

134.7

111.7

109.5

Efficien

72*.

Per cen

69.5

64.9

64.0

66.9

o*±. o

66.0

69.6

68.3

07.7

65.2

69.1

65.6

66.3

70.0

68.2

fiQ O

67.2

65.8

68.0

70.2

66.0

67.9

w
TABLE 44.- Comparison of results of tests on raw and brique

Field designation of coal.

Tennessee Continued.

No. 4..............

Washington: No. 2. ....

Condition of fuel as fired.

Raw. .....................

No. of 

test.

355

412

359

Kind of 

. draft.

...do......

...do......

...do......

...do......

Clinkor 

in refuse.

Per cent. 

25

38

26

61

32.8

48.3

Volatile 

matter 

in combustible.

Per cent. 

39.92

38.44

43.34

43.14

36.44

35.19

Percentage of 

rated 

capacity 

developed.

105.3

110.8

99.3

97.4

107.0

102.2

Efficien

72*.

Per ce

69.0

67.0

66.0

66.

67.

66.
TABLE 45 Comparison of results of tests of the same fuels when us

Field designation of fuel.

Arkansas: 

No. 7 A ..........................:...................

Illinois:

West Virginia : 

No. 5 A..............................................

No. 15. ..............................................

No. of 

test.

/ 294

\ 293 

/ 309

\ 308 

/ 505

500 

492

497 

322

321 

/ 332

1 330 

/ 506

\ 496 

/ 385

\ 384 

I 482

) 476 

/ 216

1 215 

f 213

I 210

Kind of draft.

Forced .................

Forced .................

Forced .................

Forced .................

Forced .................

Natural ................ 

Forced .................

Natural ................ 

Forced .................

Forced .................

Natural ................ 

Forced .................

Natural ................ 

Forced .................

Natural ................ 

Forced .................

Natural ................

/Forced. .................

^Natural................

Clinker in 

refuse.

Per cent.

57

52

28

36 

57

55 

. 51

36 

62

62 

61

55 

Stt

51 

55

57 

62

51 

49

0

0

48.9

Volati

matter 

combus

ble.

Per ce

19

19

12

45

10

45

rtZ

46

44

45

32

OO

39

14

J.f>

42

42

51

50

35
TABLE 46. Comparison of results of tests on the same coals wit

Field designation of coal.

Illinois: 

No. 13 (washed). .............................

No. 19 A .....................................

Indiana:

No. 7 B ......................................

West Virginia: 

No. 15 .......................................

No. 19 .......................................

No. 20 (washed).. ...........................

No. of 

test.

I 145

\ 144 

1 171"

/ 205

/ 166

\ 151 

/ o!64

/ 263

\ 265 

/ 201

\ 188 

/ 256

\ 251 

f 214

/ 285

t 289 

1 264

\ 266 

/ 210

\ 196

Kind of grate.

Rocking.......

Flat.:........ 

Rocking.......

Flat.......... 

Rocking.... ...

Flat.......... 

Rocking. ......

Flat.......... 

Rocking. .....

Flat.......... 

Rocking.......

Flat.......... 

Rocking. ......

Flat.......... 

Rocking. ......

Flat.......... 

Rocking. ......

Flat.......... 

Rocking.......

Flat.......... 

Rocking.......

Flat.......... 

Rocking. ......

Flat..........

/Rocking. ......

\Flat..........

Clinker 

in refuse.

Per cent. 

45

47 

45

Oo

41

10 

44

Oo

43

42 

49

51 

51

Oo 

47

46

56

48 

33

0

0

41.7

Volatile 

matter in 

combustible.

Per cent. 

38.17

oy. Oo 

35.38

oO. Oo

36.74

42.85

44.15 

47.79

48.25 

38.68

o/. yo

42.44

14. Ot

37.37

37.43 

42.38

22.' 62

££. OJ.

36.07

50.01

OU. UJ

37.54

37. 95

Percentage of 

rated 

capacity 

developed.

94.7

J,Uo- o

90.6

Of. O

94.9

104.7

74.7

ou. o

75.5

/o. o 

78.9

i i. £i

9a2

95.0 

87.6

75.2

81.8

79. 6 

90.5

oO. /

88.3

79.3

85.5

87.8

Effic

cy 7

Per c

69

69

71

66

60

O^

68

65

66

65

65

68

\j£

70

70

61

UO

67

a Clinker fused into grate and was removed with diff
TABLE 47. Comparison of results of tests on the same coals showing the variation in boiler eff

Field designation of fuel .

Alabama:

No. 3................

Indiana: 

No. 4................

No. 15. ..............

Indian Territory: No. 2 B 

(briquets).

Maryland: No.l (washed)

Missouri : No. 5. ..........

No. of 

test.

J 390

1 394

1

378

376

375

f 166

\ 165 

f 429

J 49Q

/ 427

X 426 

1453

455

f 231

I 232

J 320 

1 319

Kind of 

draft.

.....do......

.....do......

.....do......

.....do......

.....do......

.....do...... 

.....do......

.....do......

.....do......

.....do...... 

.....do......

.....do......

.....do......

.....do......

.....do...... 

.....do......

Clinker 

in ash 

and 

refuse.

Per cent. 

43

52

54

44

44

53 

41

53

50

53 

34

26

17

22

63 

61

Volatile 

matter 

in combustible.

Per cent. 

36.75

37.59

35.24

34.83

35.41

42.85

41.16

40.12

43.59

44.89 

39.88

40.16

16.31

16.29

44.03 

44.16

Ash in 

dry coal.

Per cent. 

21.42

18.97

13.97

15.02

10.92

18.49

20.03 

9.44

14.21

13.75 

8.59

8.28

10.48

18.36 

17.76

Moisture 

in coal as 

fired.

Per cent. 

2.93

2.88

5.27

4.84

14.79

13.82 

12.83

13.05

10.09

9.09 

3.29

2.70-

3.70

3.43

12.24 

13.37

Percentage of 

rated 

capacity 

developed.

92.7

94.8

77.4

83.2

74.7

88.9 

87.9

9

C C\

78.6

89.1 

105.1

93.2

94.7 

78.1

Efficiency 72*.

Per cent. 

67.43

65.62

65.61

65.82

66.38

66.38

64 43

65.32

66.30 

69.66

60.41

68.56

67.64

64.87 

63.28

P
TABLE 47. Comparison of results of tests en the same coals showing the variation in boiler ef

Continued.

Field designation of fuel.

Tennessee: No. 5. ........

Virginia: No. 5 A.....

"Wyoming: 

No.2B. .............

1

No. 3.-......'.....

No. of 

test.

352

357

476

1 482

f 210

1 213

j 211

1 212

Kind of 

draft.

Natural .... 

.....do......

.....do......

Natural and

Natural .....

Natural and 

forced.

Clinker 

in ash. 

and 

refuse.

Per cent. 

47

49

46

51

62

0

0

60

58

Volatile' 

matter 

in combustible.

Per cent. 

39.72

39 11

39.37

15.18

14.75

50.01

51.58

50.40

51.46

Ash in 

dry coal.

Per cent. 

10.34

9 98

9.41

19.50

16.22

20.98

23.57

19.67

18.76

Moisture 

in coal as 

fired.

Per cent. 

5.59

5.82

4.73

4.60

9.55

8.94

15.12

13.60

Percentage of 

rated 

capacity 

developed.

95.4 

115.5

111.2

99.7

147.7

88.3

99.9'

67.0

88.2

Efficiency 72*.

Per cent. 

65.62

67.13

61.06

56.98

64.08
METHODS OF SUPPLYING AIK FOE COMBUSTION. 167

Table 47, compiled from the results of tests made on the same coals, 

shows the variation in boiler efficiency as the smoke increases. The 

tests of each coal compared were made with the same boiler and same 

grate. All the tests but two were made with natural draft; but 

inasmuch as the use of forced draft only increased the rate of combustion, as was shown by Table 45, the tests are comparable both as 

to efficiency and smoke.

In general the results show that as the percentage of rated capacity 

developed increased the percentage of black smoke increased and the 

efficiency decreased. . This proves that the combustion space was 

not efficient over a wide range of working conditions, but there was 

a limit for rate of combustion for each kind of coal, above which efficient operation was impossible. The table also demonstrates that 

with hand-fired furnaces the combustion space to be most efficient 

must have some means of mixing the air and gases. The results 

with Maryland and Indian Territory coals show that the most smoke 

was made on the tests showing low capacity. Methods of operation 

may account for this efficiency variation, as with the Maryland coal 

the automatic air admission was used on the high-capacity test and 

not on the low. The discordant results in the tests of Indiana coals 

are probably due to the variation in air admission. The beneficial 

effect of the automatic air admission in reducing the smoke and 

increasing efficiency is noticeable in several tests.

The three tests on Alabama coal were run at about equal efficiency 

over a wide range of capacity, but as-the methods of operating were 

dissimilar -these apparent discrepancies could easily result.

High smoke values gave high unaccounted for values in the heat 

balance. "Usually the percentage of CO in the'flue gas was much 

greater when the smoke was high, showing a cause for the decreasing 

efficiency and increasing visible evidence of loss noted with high 

rates of combustion.

COMPARISON OF METHODS OF SUPPLYING AIR FOR

COMBUSTION.

METHODS COMPARED.

As supplementing the data already presented to show the results 

obtained in tests at the fuel-testing plants, a number of tables have 

been compiled to show the relative value of different methods of 

supplying air for combustion. The following methods are compared: 

(1) Air supplied continuously by means of openings in grates; (2) air 

taken continuously through the grates and an extra amount supplied 

automatically at times of greatest distillation of volatile matter; 

(3) air taken continuously through the grates and more supplied at 

times of firing by cracking the furnace doors. All full-length St. 

Louis tests (except the briquet tests) and the hand-fired Norfolk tests 

have been used in this compilation.
168 SMOKELESS COMBUSTION OF COAL.

RELATION OF EFFICIENCY TO CAPACITY WITH AIR ADMITTED 

THROUGH GRATES AND BY AUTOMATIC DEVICES.

To permit fair comparison of the boiler efficiency and rated capacity 

developed, tests were selected on which the same kind of coal was 

used and the same method of supplying air for combustion. These 

tests include two series, one.in which the automatic air-admission 

device for the furnace was not operated and another in which it was. 

The results of the first series are given in the following table:

TABLE 48. Relation of efficiency to capacity, automatic air-admission device not operated.

Kind of coal.

Do....................

Do....................

Do....................

Do....................

Do....................

Do....................

Virginia...................

Percentage 

of rated 

capacity 

developed.

106.3

85.7

85.0

80.9

72.8

108.2

108.1

103.9

147.7

Efficiency 72*.

Per cent. 

62.92

65.07

65.90

67.64

69.32

67.19

65.83

63.86

60.23

Kind of coal.

Virginia...................

Do....................

Do....................

Do....................

Do....................

Do....................

Do....................

Do....................

Percentage 

of rated 

capacity 

developed.

101.8

99.7

92.3

81.6

QQ Q

95.2

93.1

88.2

81.0

Efficiency 72*.

Per cent. 

63.39

67.13

68.25

65.77

56.98

59.63

57.84

64.08

63.34

The above table shows that, in general, when the air was supplied 

by means of the air spaces in the grates the boiler efficiency was 

highest at the lowest capacities and decreased as the capacity 

increased.

. Data from the second series of selected tests are presented in 

Table 49. .

TABLE 49. Relation of efficiency to capacity, automatic air-admission device operated.

Kind of coal.

Do....................

Do....................

Percentage 

of rated 

capacity 

developed.

113.9

93.2

80.1

Efficiency 72*.

Per cent. 

68.54

67.64

65.28

Kind of coal.

Wyoming. ................

Do....................

Do....................

Percentage

of rated 

capacity 

developed.

88.3

79.3

67.0

Efficiency 72*.

Per cent. 

61.06

58.20

67.62

This table shows that the automatic air admission is not always 

of equal value. With the Maryland coal too much air was supplied 

at the capacity of 80.1 per cent, for even at the highest capacity 

given neither the greatest possible reduction of air supply nor the 

highest efficiency had been reached. With the Wyoming coal not 

enough air was supplied at 88.3 per cent capacity to maintain the 

same efficiency as at 67 per cent.
METHODS OF SUPPLYING AIR FOE COMBUSTION. 169

COMPARISON OF RESULTS FROM DIFFERENT COALS WITH 

VARIED AIR ADMISSION.

In Table 50 the volatile matter in the coal as received, the percentage of rated capacity developed, the efficiency 72*, and the smoke 

readings have been averaged for the coals from each State according 

to the method of supplying air for combustion. The data show that 

no unvarying rule can be formulated to cover all coals, but in general 

a higher capacity and a higher efficiency resulted when additional air 

was supplied at times of firing. Many of the smoke averages do not 

fall as might be expected.

TABLE 50. Relation of air admission to results when burning different coals.

Kind of coal.

Illinois.........'.....

Indian Territory ....

West Virginia 

(Jamestown) .....

Ohio................

Tcnn6ss6 6

Virginia............

West Virginia.......

Method of supplying air.

| Automatic air admission off .......

iFurnace doors cracked after firing.

f... .do...... ......................

(.Furnace doors cracked after firing.

IFurnace doors cracked after firing.

IFurnace doors cracked after firing.

(Furnace doors cracked after firing. 

/Automatic air admission on. ......

(Furnace doors cracked after firing. 

/Automatic air admission off. ......

\Automatic air admission on ....... 

| Automatic air admission off .......

\Automatic air admission on .......

....do............................

Furnace doors cracked after firing.

Furnace doors cracked after firing, 

f Automatic air admission off .......

Automatic air admission on .......

iFurnace doors cracked after firing.

i....do............................

\Automatic air admission on. ......

Furnace doors cracked after firing.

Furnace doors cracked after firing. 

/Automatic air admission off .......

^Automatic air admission on .......

Number of 

tests.

5 

2 

4 

6 

32 

40 

11 

1 

35 

1 

1 

1 

2 

2 

1 

13 

1 

3 

1 

1 

6 

2 

3 

4 

1 

24 

2 

12 

10 

4 

12 

7 

2 

5 

9 

1 

1 

1 

2 

27 

2 

5 

3

Volatile 

matter in 

coal as 

fired.

Per cent. 

27.3 

29.7 

28.1 

15.0 

32.5 

32.2 

31.6 

34.1 

34.8 

33.5 

13.6 

35.4 

 16.9 

17.1 

15.3 

33.1 

33.7 

15.0 

14.0 

32.0 

32.5 

31.7 

33.8 

32.6 

36.6 

36.6 

39.0 

22.7 

31.2 

32.8 

32.1 

33.0 

30.6 

22.5 

34.7 

35.6 

34.5 

36.5 

20.6 

32.7 

34.3 

37.0 

35.0

Percentage of 

rated capacity developed.

95.5 

78.3 

98.8 

89.1 

91.7 

91.9 

92.7 

103.9 

90.1 

93.1 

97.0 

90.5 

128.5 

80.8 

78.3 

92.2 

68.4 

95.7 

95.9 

129.4 

97.7 

114.3 

106.7 

107.9 

81.3 

92.1 

118.4 

91.4 

93.5 

89.8 

103.0 

110.2 

96.6 

104.6 

92.3 

108.4 

81.8 

97.4 

80.7 

93.8 

103.9 

91.5 

78.2

Efficiency 72*.

Per cent. 

66.56 

65.92 

66.88 

65.18 

58.56 

66.05 

65.04 

67.15 

65.13 

65.36 

65.20 

68.10 

66.99 

66.93 

68. 61 

66.47 

67.08 

67.15 

68.56 

56.64 

63.12 

66.95 

65.63 

67.08 

69.01 

65.69 

68.02 

67.43 

67.67 

65.71 

66.02 

65.16 

56.69 

64.95 

66.77 

63.98 

65.04 

66.65 

70.71 

67.59 

69.10 

60.37 

62.29

Black

smoke.

Perct. 

14.4 

0 

8.0 

0 

24.7 

18.8 

5.4 

31.4 

21.9 

28.2 

3.0 

19.5 

6.9 

7.0 

8.6 

20.1

6.8 

0 

42.5 

12.8 

15.3 

17.3 

17.8 

13.1 

33.1 

13.0 

6.2 

23.7 

20.1 

14.2 

21.9 

6.0 

10.4 

34.2 

17.0 

10.0 

33.5 

0 

21.5 

16.0 

21.6 

3.2
170 SMOKELESS COMBUSTION" OF COAL..

RELATION OF EFFICIENCY TO CAPACITY WITH VARIED AIR

ADMISSION.

Table 51 gives averages for all tests made with automatic air admission not operated, automatic air admission operated, and furnace 

doors cracked, not classified according to States.

TABLE 51. Relations of air supply to averages of results.

Method of supplying air. Number 

of tests.

88 

185 

35

Volatile 

matter 

in coal 

as fired.

Per cent. 

28.0 

33.2 

31.2.

Percentage of 

rated 

capacity developed.

93.8 

92.9 

99.7

Efficiency 72*.

Per cent. 

62.95 

66.06 

' 66.21

Black smoke.

Amount.

Per cent. 

11.8 

21.6 

15.4

Number 

of tests.

59 

162

28

The subjoined list shows the names of the coals which fell in the 

final grouping of Table 51:

AUTOMATIC AIR ADMISSION NOT OPERATED.

Indian Territory.

Arkansas.

Maryland.

West Virginia (Jamestown).

West Virginia..

Virginia.

Pennsylvania. 

Alabama.

Illinois.

Missouri.

Montana.

Tennessee. 

Indiana. 

New Mexico. 

Washington. 

Ohio. 

Wyoming.

AUTOMATIC AIR ADMISSION OPERATED.

Maryland.

West Virginia (Jamestown).

Alabama.

Pennsylvania.

Illinois.

West Virginia (Jamestown).

Alabama.

Illinois.

New Mexico.

Missouri. 

Tennessee'. 

West Virginia. 

Kansas. 

Indiana.

FURNACE DOORS CRACKED.

Indiana. 

Kansas. 

Tennessee. 

West Virginia.

Virginia. 

Washington. 

Wyoming. 

Ohio.

Indian Territory. 

Washington. 

Ohio.

.Tables 52 to 54 give averaged results showing the relation of efficiency to capacity under the three methods of air admission when 

high-volatile coals are burned, all the tests on low-volatile coals 

being excluded.

TABLE 52. Relation of efficiency to capacity, automatic air admission not operated.

Percentage 

of rated

capacity

developed.

108.4

106.3

105.3

98.0

Efficiency 72*.

Per cent.

63.98

61.97

66.39

66.19

Percentage 

of rated

capacity

developed.

96.6

95.5

86.4

80.7

Efficiency 72*.

Per cent.

56.69

66.56

64.69

70.71
METHODS OF SUPPLYING AIR FOE COMBUSTION, 171

Table 52 shows that the highest efficiency was obtained with the 

lowest capacity and that the efficiency decreased as the capacity 

increased.

TABLE 53. Relation of efficiency to capacity, automatic air admission operated.'

Percentage

of rated

capacity 

developed.

98.6

93.5

92.2

92.1

Efficiency

 72*.

Per cent.

05.70

67.67

66.47

65.69

Percentage

of rated

capacity 

developed.

88.1

78.3

78.2

Efficiency 72*.

Per cent.

65. 65

65.92

62.29

Table 53 shows that the lowest efficiency was obtained when running at the lowest capacity and that the efficiency increased as the 

capacity increased.

TABLE 54. Relation of efficiency to capacity, furnace doors cracked after each firing.

Percentage 

of rated

capacity

developed.

118.4

107.9

103.9

98.8

Efficiency 72*.

Per cent.

68.02

67.08

69.10

 66.88

Percentage 

of rated

capacity

developed.

97.4

92.7

90.6

90.5

Efficiency 72*.

Per cent.

66.65

65.04

65.87

68.10

Table 54 shows that the highest efficiencies were obtained when 

running at high capacity and that with one exception, the reverse was 

true. Supplying air by cracking the door, while it results in high 

efficiency, is more liable to furnish a variable supply than an automatic device, as it introduces the personal element.

With the furnace door cracked after firing, the lowest efficiency was 

65 per cent. With the automatic air admission operated, the lowest 

.efficiency was 62.3 per cent. With the automatic air admission not 

operated, the lowest efficiency was 56.7 per cent.

CONCLUSIONS.

Air supply should be regulated to' suit the combustion of different 

kinds of coal.

With the same coal burned in the same furnace, a proper amount of 

air supplied at times of greatest distillation of volatile matter will 

aid in obtaining higher capacity and higher efficiency than can be 

had without such regulation.

When air is supplied in the same manner to the same coal in the 

same furnace, the efficiency is practically determined by the rate of 

combustion.

On the average, cracking the furnace door resulted in highest 

capacities with the highest efficiencies, from which it would seem that
172 SMOKELESS COMBUSTION OF COAL.

in general not enough air was supplied by the automatic air-admission 

openings.

Air should be supplied automatically to the furnace, as this overcomes in a measure the personal element.

In the average furnace the gases and air are not mixed thoroughly 

and it is possible, especially-by cracking the furnace doors, to admit 

large amounts of air into the furnace and reduce the visible products 

of incomplete combustion at the expense of efficiency. (See tests of 

Illinois coal in Table 50.)

INFLUENCE OF VOLATILE MATTER IN FUEL ON THE 

SMOKE PROBLEM.

From a study of the tables giving the results of the tests made 

under Heine boilers, it appears that in all tests coal with low volatile 

matter was burned most efficiently and with the least smoke. Highvolatile coals are more difficult to burn without loss than low-volatile 

Coals, but the difficulty is not directly proportional to the percentage 

of volatile matter. Some coals with less than 30 per cent of volatile 

matter give off more smoke than others having 40 per cent. Observations of the behavior of coals when thrown into the furnace 

indicated that some coals gave off their volatile matter at lower 

temperatures than others, and that there was a difference in the 

nature of the volatile matter.

This phase of the composition of coals is now undergoing laboratory 

investigation under the direction of N. W. Lord. When these 

investigations are completed valuable data will be at the command of 

engineers who are called on to design furnaces for burning coal. 

Horace C. Porter, who is conducting the experiments, has furnished 

the following preliminary statement, which shows that among the 

coals tested there is a wide difference in the character of the volatile 

matter:

TABLE 55. Results of heating 10 grams of air-dried coal ten minutes.

Kind of coal.

At heating temperature 

0/600° C.

Connellsville, Pa .....

At heating temperature 

0/600° C.

Connellsville, Pa ..... 

Zeigler, 111............

Highest 

temperature in 

coal in 

retort.

0 C. 

335 

325

441

440

Tar.o

P.ct.

4.9 

6.8

Water.

P.ct.

3.2 

13.0

Gas'.

C.c.

8 

90

190 

173

Gas composition (calculated to undiluted gas).

C02 .

30.0 

14.8

6.3 

15.7

Illuminsvnts.o

0 

0

8.2 

7.0

CO.

6.5 

5.3

5.9 

14.4

CH4 .

6.5 

8.0

36.9 

19.0

C2H8 .« b

7.0

23.7 

22.2

 Hi.

0 

0

2.0 

2.8

N2 .

c50.0 

c?1.9

C17.0 

cl8.9

n Smoke-forming matter.

& Includes all higher paraffin calculated as Cj

c Includes small amount of air.
HORSEPOWER FROM DIFFERENT COALS. 173 

TABLE 55. Results of heating 10 grams of air-dried coal ten minutes Continued.

Kind of coal.

At heating temperature 

of700° C.

Zeiglor, 111............

Pocahontas, W. Va...

At heatinq temperature 

0/800° C.

Zeigler, 111............

Highest 

temperature in 

coal in 

retort.

0 C.

562 

545 

580 

599

687 

680

Tar.

P.ct. 

11.0 

7.8 

8.2 

4.2

12.6 

9.3 

7.9 

6.5

Water.

P.ct. 

3.5 

14.0 

18.5 

1.9

4.5 

13.9 

19.1 

2.4

Gas.

C.c.

583 

471 

1,020 

675

1,375 

1,251 

1,780 

1,590

Gas composition (calculated to undiluted gas.)

COj.

3.0 

8.5 

28.8 

1.9

1.5 

3.8 

19.8 

1.2

Illuminants.

7.2 

5.1 

3.7 

4.4

5.5 

3.8 

2.7 

3.4

CO.

5.4 

13.7 

20.0 

3.9

6.9 

16.0 

21.4 

4.8

CH<.

44.1 

59.6 

18.6 

44.4

24.9 

27.7 

14.1 

24.4

CaH6 .

17.7 

0 

6.8 

16.1

12.1 

6.1 

4.0 

11.6

H8 .

13.5 

1.1 

15.1 

28.5

33.1 

33.7 

30.0 

43.2

Ni.

9.1 

12.0 

7.JO 

.8

ol6.0 

o8.9 

8.0 

11.4

"Includes small amount of air.

The differences in the ease with which various coals give off their 

smoke-producing constituents are strikingly shown by the accompanying diagram (fig. 40), in which all these volatile substances are 

grouped, the total percentages given off being represented by the> 

vertical scale and the temperatures by the horizontal scale. The 

behavior of the Illinois coal at temperatures between 600 and 

700° C. contrasts strongly with the progressive distillation of Connellsville coal, and the decline in production of volatile compounds 

at temperatures over 700° shown -by Wyoming coal is notably different from the even increases shown by Illinois, Pocahontas, and Connellsville coals.

HORSEPOWER FROM DIFFERENT COALS.

The facts presented in Table 56 were obtained by averaging more 

than 200 tests on coals and lignites from 17 different States. All 

these fuels were hand fired under a Heine boiler. The furnace was 

set with flat grates, which were 26 inches from the U tile on the lower 

row of tubes, measured at about the center of the grate. Natural 

draft was used in nearly all the tests. The damper was usually set 

so as to get a draft of about 0.6 inch of water in the hood, this giving 

from 0.12 to 0.30 inch in the furnace, varying with the coal and the 

condition of the fire. On the assumption that the boilers at the 

average good plant are run at approximately the same efficiency as 

those at the government testing plant, the figures given in Table 56 

for coal per boiler horsepower per hour may be used as a basis for an 

approximate determination of the total boiler horsepower at any 

plant by dividing the amount of coal used per hour by the figures in 

the table opposite the State from which the coal is supplied. For
20.0

~ 15.0

10.0

11

Is5.0

500

330

550 600

440

650 

Temperature of fu

Temperature of 

FIGURE 40. Proportion of smoke-producing compounds given off at di
CENTRAL HEATING STATIONS. 175

instance, a consumption of 460 pounds of best Illinois coal per hour 

indicates that the total boiler horsepower developed would be about 100.

TABLE 56. Efficiency 72* and coal burned per boiler horsepower per hour.

, State.

Colorado (lignite)....

Number of 

tests 

averaged.

3

4

1

23

21

27

4

8

Efficiency, 72*.

Per cent. 

66

6761'

66

*

61

63

64

6163"

Coal 

burned 

per boiler 

horsepower 

per hour.

Pounds.

d 9

3.9

6.0

,- 4.6

5.0

5.5

4.4

State.

Missouri .............

New Mexico.........

Ohio.................

Virginia..............

Number of 

tests 

averaged.

13

3

7

2

26

21

12

8

Efficiency, 72*.

Per cent. 

65

66

63

60

64

67

65

67

59

Coal 

burned 

per boiler 

horsepower 

per hour.

Pounds. 

4.0

3.8

5.1

5.5

4.2

^ fi

3 7

3.G

6.1

CENTRAL HEATING STATIONS.

The possibility of reducing smoke in cities by the use of central 

heating plants was taken up as part of the general study of the smoke 

problem. There is no doubt that in winter the small heating plants, 

both in residences and in store buildings, contribute largely to the 

smoke nuisance. This is because the small plant is poorly designed 

for burning any but low-volatile fuels. When an attempt is made to 

burn the cheaper coals, such as large stations utilize, dense black 

smoke results, often lasting for several minutes after each coaling. 

Moreover, the plant is not large enough to warrant careful operation 

and the coal is fired in large quantities and at long intervals. To 

obviate the difficulties of combustion high-priced coal is burned, this 

being especially true in congested areas. It is evident that if for the 

heating plants of several buildings could be substituted a central 

station where a power-plant boiler of standard type could be installed, 

a correct furnace constructed, cheap fuel utilized, and the plant 

operated intelligently, much of the nuisance and discomfort from 

the small plants would be overcome.

The central heating plant is not a new thing; in fact some of the 

plants have been in operation for twenty to twenty-five years. 

Development in this direction has been very slow, however, until 

within the last five or six years, when the idea has received renewed 

attention.

The data presented in Table 57 were obtained by sending a circular 

letter to each of the central heating plants supposed to be in operation in the United States 150 in all. Of these, 77 responded, 57 

giving the information as tabulated; twenty stated that they were 

out of business or inactive. The location of the 130 is given in the
r

176 SMOKELESS COMBUSTION OF COAL.

statement below. The tabulated statistics may be taken as fairly 

representative of central heating plant conditions. It will be noted 

that the plants are most numerous in the States where coal is relatively cheap.

Location and number of central heating plants.

Idaho..............

Kansas. .............

Minnesota... .......

Number 

of plants.

............. 1

............ 2

............ 1

............ 1

............ 1

24

............ 17

............ 1

2

............ 3

............ 3

Montana ..............

Missouri. ..............

New Hampshire .......

New York....... ......

North Dakota .........

Ohio..................

Pennsylvania. .........

Rhode Island .........

Wisconsin.. ...........

Number 

of plants.

......... 1

4

......... 1

......... 10

......... 2

......... 24

......... 25

......... 1

......... 1

......... 1

......... 4
TABLE 57. Details of operation of central hea

No.

1

2 

3

4 

5 

6 

7 

8

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37

Location of 

plant.

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do.........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........ 

.....do.........

New York.... 

.....do........

.....do........

.....do........

.....do........

.....do........

North Dakota. 

.....do........

Purpose of plant.

Light, heat, and power

.....do................

.....do................

.....do...............

Light, heat, and power 

.....do................

.....do........... .

.....do...............

.....do................

Light, heat, and power 

.....do................

Light, heat, and power

Light, heat, and power

Light, heat, and power 

.....do................

.....do................

.....do................

Heat..................

Light, heat, and power 

.....do................

Heat..................

Light, heat, and power

Heat. .................

Light, heat, and power 

.... .do. ...............

Heating 

system.

Steam..... 

...do......

...do......

...do......

...do......

...do......

...do......

Steam and 

hot water. 

...do......

...do......

...do......

...do......

...do:..... 

...do......

...do......

...do...... 

...do......

...do......

...do......

Steam..... 

...do......

...do......

...do......

...do......

...do......

...do...... 

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

Boilers.

Character.

(Tire tube...........

\\Vater tube. ........

.....do..............

.....do..............

Fire and water tube.

.....do..............

.....do..............

.....do..............

.....do..............

.....do..............

.....do..............

.....do..............

Fire and water tube.

.....do.............

.....do..............

Fire and water tube.

.....do..............

.....do..............

.....do..............

.....do..............

.....do..............

Fire tube... ........

Horsepower.

1,500 

2,200 

4,200 

2,520 

1,800 

1,350 

600 

450 

2,970

2

QAA

1,100 

400 

1,800 

1,720 

1,000 

400 

800 

800 

800 

400 

300 

2,150 

600 

725 

900 

900 

750 

450 

400 

1,500 

16,000 

11,000

2,368

1,600 

700 

405 

1,000 

600

Style of furnace.

Chaingrates; Roneysto

Common and chain gra

.....do................

.....do................

.....do................

Detroit and Roney sto

.....do................

.....do................

1 common; 2 Honey sto

2 chain grates; 7 comm

.....do................

.....do................

.....do................
TABLE 57. Details of operation of central heating pla

No.

38

39

40

41

4?:

43

44

45

4fi

47

48

49

50

51

52

53

54

55

56

57

plant.

Ohio..........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

Rhode Island.

.....do........

Purpose of plant.

.....do................

.....do................

.....do................

Heat. .................

.....do................

.....do................

.....do................

Heat. .................

.....do.....:..........

Heat..................

Light, heat, and power

.....do. ...............

system.

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

...do......

Boilers.

Character.

.....do..............

.....do..............

tube.

Water tube. ........

Horsepower.

2,800

1,400

1,100

950

1,200

1,600

1,700

1,550

1,500

1,400

1,200

1,000

950

900

725

600

600

3,315

600

600

Style of furnace

.....do..............

.....do..............

.....do..............

.....do..............

.....do..............
TABLE 57. Details of operation of central heating pla

No.

1 

2 

3

4

5

6

7

S

9

10 

11 

12 

13 

14

15 

16 

17

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30

Location of 

plant.

.....do........

.....do.........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

.....do........

Indiana.......

.....do........

.....do........

.....do........

.....do........

.....do........

Iowa..........

.....do........

.....do........

.....do........

Michigan.

Minnesota.....

.....do........

.....do......... 

.....do.........

.....do.........

Montana......

New York.....

Live steam 

used (per 

cent).

100

33 

0

0 

50

65 

0 

0

16 

15

33J 

75 

O

66 

(/)

(0) 

100

50

ioo

Mains leading from 

plants.

Number.

< i \< j

f ol 

1 61 

/ ol 

{ "1 

6 

1 

1 

2 

2

{ i

cl 

f cl 

\ °1

cl

1 

1

2 

1 

1 

2 

1 

. .7 

1 

8 

3

Size 

(inches).

8 

12 

20 

10 

6 

5 

8 

8 

8 

16 

12 

12 

8 

7 

' 10 

20 

12 

10 

7 

6 

12 

6 

7 

8 

7 

5 

- 12 

10 

8 

16 

12 

10 

6 

10 

12 

15

Pressure (pounds).

On mains 

at plant.

50

} »

20

i W |3-6

6-15 

2

| og-650

6

60 

88 

30 

48 

70

| 40 

50 

| 60

45-60 

51 

30 

17 

3 

5 

3

*

5 

1J 

5J 

10 

95

Drop in 

main.

42 

12 

15 

6

2 

1-3

i

6

10 

9

20 

40

10 

25 

15

10-15 

8

15

o4

0 

1 

0 

1 

i 

10

Greatest 

distance 

heat is 

conveyed 

(feet;.

7,550, 

3,960 

7,200 

2; 000

3,960

2,640 

1,300

5,280

1 o3,000 

\ 66,600 

7,920 

2,640

3,960 

4,500

5,280 

1,500 

5,000

3,520 

3,000 

2,000 

4,500 

1,300 

1,600 

1,072 

400 

4,600 

130 

400 

2,000 

3,200

Total 

length of 

heating 

mains 

(feet).

38, 173 

10,560 

14,784" 

4,000

7,920

2,640 

4,000 

( o 15, 840 

\ 6 31, 680

58,080 

17,500

10, 560 

34,000

15/840 

12,000 

18,480

d8,800 

4,000 

12,000 

4,000 

3,960 

1,460 

700 

7,920 

600 

700 

4,000 

29,040

5-inch air sp

Wood .....

1-inch air sp

o Steam. 6 Hot water. d Double pipe. Very little. 
.TABLE 57. Details of operation of central heating pla

No.

31

32

33 

34 

35 

36

37

38 

39 

40 

41 

42 

43 

44

45

46 

47 

48 

49 

50 

51

52

53 

54 

55 

56 

57

Location of 

plant.

New York. . . . 

.....do.........

.....do.........

.....do.........

.....do.........

North Dakota. 

.....do.........

.....do.........

.....do.........

.....do......... 

.....do.........

Pennsylvania.

.....do.........

.....do.........

.....do......... 

.....do.........

.....do.........

.....do.........

.....do......... 

.....do......... 

.....do.........

.....do.........

Rhode Island. 

Wisconsin. .... 

.....do.........

Live steam 

used (per 

cent).

100

70 

100 

100± 

50

0

' 0 

20 

(°) 

100

( c )

100 

100

100 

100 

100 

50 

100

100

100 

100 

. 90 

0

Mains leading from 

plants.

Number.

i j

4 

1 

1 

1

{ !

2 

2 

2 

62

1 

12 

10

{ !i 

i 

i 

i {. |

i 

i 

i

2

Size 

(inches).

15 

24 

15 

12 

, 14 

10 

8 

10 

12 

8 

12 

8 

8

14 

3 

3 

10 

6 

14 

12 

8 

10 

12 

10 

8 

12 

8 

8 

8 

4 

8

Pressure (pounds).

On mains 

at plant.

} ' »

} 

4J 

20 

 5 

71

Y

70 

30 

40 

5-6 

50 

5-20

| 12-25

2-6 

15 

20 

30 

4 

50-70

| 10-20

6 

15-40 

14 

55 

60

Drop in 

main.

5-15

31 

5 

0

30

6 "15

i

47

7

11

25 

2J

35-40

5-15

(«) 

10-35 

5 

15 

40

Greatest 

distance 

heat is 

conveyed 

(feet).

7,500

922

3,960 

5,280 

1,200 

1,500'

1,000

11,880 

6,600 

5,500 

3,520 

3,178 

5,280 

5,280

3,917 

4,000

3,960 

6,000 

3,550 

5,000

4,620

3,960 

2,640 

2,042 

2,000 

7,920

Total 

length of 

heating 

mains 

(feet).

58,080

4,070

31,680 

7,000

3,000 

2,000

47, 520 

21, 120 

10. 560 

7,000 

5,492 

46,200 

11,880

28, 945

13, 200 

9,500 

3,960 

6,000

8,777 

7,200'

17,911

7,920 

10,560 

5,285 

4,000 

31,680

1-inch air s

4-inch kiln-

1-inch asbe

/3-inch conc

\ 3-inch air 

o Very little. 6 Pair. 
TABLE 57. Details of operation of central heating plants 

No.

1 

2 

3 

4 

5 

6 

7

8

9 

10

11 

12 

13 

14

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

,30 

31 

32

m

Location of 

plant.

Illinois........

do

Space in 

buildings 

(cubic feet).

700,000 

1,200,000

.....do......... ..............

.....do......... ..............

. do .. ... '-.

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do... .....

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do......... 

.....do.........

.....do.........

.....do......... 

.....do.........

/ 09,000,000 

\ 69,450,000

10,000,000

2,389,900

3,771,515 

3,634,365 

5,391,295 

1,650,000 

2,204,612 

7,777,000

100, 000, 000 

15, 500, 000 

10-0n° 000

Average price of heating.

Per square 

foot.

SO. 65 

.24

.25 

.28 

a. 25 

6.15

{ 1-3,1 .15

.20 

.20 

.18 

.15£ 

.12J 

.15 

.17 

.18 

.20 

.15

""""."25"

.60

Per 1,000 

pounds of 

water.

SO. 45

j.. .........

J

}

.50

.60

.56

.50 

.50

.42*

Average 

cost per 

year for 

repairs on 

mains, tunnels, and 

insulation.

SI, 500

None. 

Very small.

S100 

None.

............

10 per cent.

3400

5 per cent. 

S300 

 8100

S359 

S150 

S6

325 

0 

0 

0 

Very small.

Small. 

3175

Years in 

operation.

26 

12 

3

7 

5 

2 

1 o!7 

i 65

6i 

6

7 

5 

5 

5 

7 

5 

10 

7 

6 

5 

15 

3 

8 

5 

4 

7 

15 

10 

7 

25

10 

28

Condensation loss, 12 per cent

34 per 1,000 cubic feet of conte

Live steam one- tenth of seaso

Radiation direct and indirect

Direct system. 

Profitable when heat is furnis

| Do.

Would advise concentration o

Would advise use of larger ma

improved.

Profitable when heat is furnis

Charge too low for successful 

Do. 

Condensation loss, 5 per cent. 

Radiation mostly direct. He

Mains should not extend, too 

Profitable when exhaust stea

Radiation mostly direct.

Radiation direct and indirect

Radiation direct and indirect

Mains should not extend too 

88,000,000 pounds steam sold 

Over one-half of the steam is 

Profitable when exhaust stea

Condensation loss. 3 to 6 per c

o Steam. 
TABLE 57. Details of operation of central heating plant

No.

34

35 

36 

37 

38 

39 

40 

41 

42 

43

44

45

46

47 

48 

49

50 

51 

52 

53 

54 

55 

56 

57

Location of 

plant.

New York...... 

.....do.........

North Dakota. 

.....do.........

Ohio ..........

.....do.........

.....do.........

.....do.........

.....do. ........

Pennsylvania . 

.....do......... 

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

.....do.........

Rhode Island.

.....do.........

Space in 

buildings 

(cubic feet).

7, 000, 000

5,000,000

1. 200, 000 

10, 000, 000 

26,000,000

10,000,000

3, 360, 000

5,000,000

Average price of heating.

Per square 

foot.

............

SO. 15 

.15 

.20 

.17|

.25

.34 

 33J

.25 

.20

Per 1,000 

pounds of 

water.

$0.48 

.60 

.40

.50

.40

.66

Average 

cost per 

year for 

repairs on 

mains, tunnels, and 

insulation.

3 per cent.

Verv small. 

0

0 

Very small. 

$300 

0 

0 

$2, 000 

80.41 per 

1,000 cubic feet 

of space 

heated. 

$300

$250 

$702 

8500

0 

$700 

$500 

$100

Years in 

operation.

10

6 

7 

6 

3 

5 

7 

4 

7 

10

19

14

5 

9 

20 

20

5 

19 

14 

10 

24 

6 

6 

8

Condensation loss, 5 to 12 pe

residence rate $4.50 per 1,0

Condensation loss, 5 per cen

Profitable when exhaust ste

Natural gas 9 cents per 1,000 

$4.50 per 1,000 cubic feet of c

34.43 per 1,000 cubic feet of c

Radiation should be direct a

cubic contents.

Radiation both direct and in

$5.45 per 1,000 cubic feet of c

$4.50perl,000 cubic feet of co

steam pressure at plant. 

Condensation loss, 9 per cent

Radiation about 5 per cent. 

$6 per 1,000 cubic feet of cont

Very little indirect radiation

Condensation loss, 4 to 15 pe

Profitable when exhaust ste

Insulation could be improv

when exhaust steam is use
CENTRAL HEATING STATIONS. 183

Of the 57 plants included in Table 57 only 12 were operating for 

the express purpose of central heating. The remaining 45 were 

supplying either light and heat, power and heat, or power, light, and 

heat. Steam heat is furnished by 38 plants, hot water by 17, and a 

combination of steam and hot water by 2. The plants which have 

been installed in the last five or six years show about an equal proportion of steam and hot-water heating. The plants range in size from 

300 to 16,000 horsepower; only 25 per cent are of 600 horsepower or 

less. Sixteen of the plants have mechanical stokers. The price of 

coal ranges from $4.60 per short ton in Montana to 90 cents in Illinois, 

the average cost from all the plants being $2.05 per short ton. Both 

direct and indirect radiation are used, but by far the greater proportion is direct. The greatest distance to which heat is sent from the 

station varies considerably, but a reasonable distance seems to be 

about 4,000 to 5,000 feet.

Payment for the use of steam is made in two ways (1) at a flat 

rate, based on square feet of radiating surface installed or on 1 ;000 

cubic feet of contents heated, or (2) at a meter rate, based on 1,000 

pounds of condensed steam. The price paid per square foot of radiating surface averaged 33£ cents, and varied from 22£ to 65 cents. 

The plants selling on a basis of 1,000 cubic feet of contents charged an 

average of $4.46, the price varying from $2 to $6. On the basis of 

1,000 pounds of condensed steam the payments averaged 50£ cents, 

ranging from 40 to 66 cents. One plant that sold heat on this basis 

for 40 cents intimated that such a rate was not profitable.

The hot-water plants sold heat only on the basis of square feet of 

radiating surface installed, the average rate being 17£ cents and the 

range from 12£ to 25 cents per square foot. Two plants, one selling 

at 12£ and the other at 15£ cents, claimed that their prices were too 

low for successful operation.

A comparison of the prices charged by central stations, as given in 

Table 57, with the cost of fuel only for a house-heating boiler, as 

published in Bulletin 366,a shows that in many cases the cost of producing heat on the premises equals the price charged by the central 

station. When heat is purchased the customer avoids the annoyance 

of having to supervise the operation of the heating plant, as well 

as the dust resulting from the delivery of fuel and the removal of 

ashes. Some allowance should also be made for the space that would 

be occupied by the heater and for the expense necessary to install 

and keep a boiler in repair.

The following suggestions have been made by the managers of the 

plants and are worthy of consideration:

Heat from a central plant should be, as largely as possible, a 

secondary product.

«llandall, D. T., Tests of coal and briquets as fuel for house-heating boilers: Bull. U. S. Geol. Survey 

No. 366, 1908, p. 39.
184 ' SMOKELESS-COMBUSTION OF COAL.

Heating mains should be concentrated and should not extend too 

far from the station.

Direct radiation should be installed.

Mains should be of sufficient size to avoid the necessity of high 

pressure at the station.

Heat should be under automatic control.

The flat rate is not a successful basis for payment; the service 

should be metered.

GENERAL CONCLUSIONS ON SMOKE ABATEMENT.

Some general conclusions from the facts set forth in this volume 

are as follows:

The flame and the distilled gases should not be allowed to come 

into contact with the boiler surfaces until combustion is complete.

Fire-brick furnaces of sufficient length and a continuous or nearly 

continuous supply of .coal and air to the fire make it possible to burn 

most coals efficiently and without smoke.

Coals containing a large percentage of tar and heavy hydrocarbons are difficult to burn- without smoke and require special 

furnaces and more than ordinary care in .firing.

Briquets are suitable for use under power-plant conditions when 

burned in a reasonably good furnace at the temperatures at which, 

such furnaces are usually operated. In such furnaces briquets, 

generally give better results than the same coal burned raw.

In ordinary boiler furnaces only coals high in fixed carbon can. 

be burned without smoke, except by expert firemen using more thani 

ordinary care in firing.

Combinations of boiler-room equipment suitable for nearly all 

power-plant conditions can be selected, and can be operated without 

objectionable smoke when reasonable care is exercised.

Of the existing plants some can be remodeled to advantage. 

Others can not, but must continue to burn coals high in fixed carbon 

or to burn other coals with inefficient results, accompanied by more 

or less annoyance from smoke. In these cases a new, well-designed 

plant is the only solution of the difficulty.

Large plants are for obvious reasons usually operated more economically than small ones, and the increasing growth of central 

plants offers a solution of the problem of procuring heat and power at 

a reasonable price and without annoyance from smoke.

The increasing use of coke from by-product coke plants in sections 

where soft coal was previously used, the use of gas for domestic purposes, and the purchase of heat from a central plant in business and. 

residence sections all have their influence in making possible a clean, 

and comfortable city.
SMOKELESS COMBUSTION OF COAL. 185

BIBLIO GRAPHY.

SURVEY PUBLICATIONS ON COAL AND FUEL TESTING.

A classified list of Survey papers dealing with coal is given in Bulletin 316, and in an abstract from that bulletin, pp. 439 to 532, published separately.

The following publications on fuel .testing, except those to which a 

price is affixed, can be obtained free by applying to the Director, 

Geological Survey, Washington, D. C. The priced publications can 

be purchased from the Superintendent of Documents, Government 

Printing Office, Washington, D. C.

BULLETIN 261. Preliminary report on the operations of the coal-testing plant of the 

United States Geological Survey at the Louisiana Purchase Exposition, in St. Louis, 

Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in charge. 1905. 

172pp. 10 cents.

. PROFESSIONAL PAPER 48. Report on the operations of the coal-testing plant of the 

United States Geological Survey at the Louisiana Purchase Exposition, St. Louis, 

Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in charge. 1906. 

In three parts. 1492 pp., 13 pis. $1.50.

BULLETIN 290. Preliminary report on the operations of the fuel-testing plant of the 

United States Geological Survey at St. Louis, Mo., 1905, by J. A. Holmes. 1906. 

240 pp. 20 cents.

BULLETIN 323. Experimental work conducted in the chemical laboratory of the 

United .States fuel-testing plant at St. Louis, Mo., January 1, 1905, to July 31, 1906, 

by N. W. Lord. 1907. 49 pp. 10 cents.

BULLETIN 325. A study of four hundred steaming tests, made at the fuel-testing 

plant, St. Louis, Mo., 1904, 1905, and 1906, by L. P. Breckenridge. 1907. 196 pp.

BULLETIN 332. Report of the United States fuel-testing plant at St. Louis, Mo., 

January 1, 1906, to June 30, 1907; J. A. Holmes, in charge. 1908. 299 pp.

BULLETIN 334. The burning of coal without smoke in boiler plants; a preliminary 

:report, by D. T. Randall. 1908. 26 pp. 5 cents.

BULLETIN 336. Washing and coking tests of coal and cupola tests of coke, by Richard Moldenke, A. W. Belden, and G. R. Delamater. 1908. 76 pp. 10 cents.

BULLETIN 339. The purchase of coal under government and commercial specifications on the basis of its heating value, with analyses of coal delivered under government contracts, by D. T. Randall. 1908. 27 pp. 5 cents.

BULLETIN 343. Binders for coal briquets, by J. E. Mills. 1908. 56 pp.

BULLETIN 362. Mine sampling and chemical analyses of coals tested at the United 

States fuel-testing plant, Norfolk,Va., in 1907, by J.S. Burrows. 1908. 23pp. 5 cents.

BULLETIN 363. Comparative tests of run-of-mine and briquetted coal on locomotives, by W. F. M. Goss. 1908. 57 pp.

BULLETIN 366. Tests of coal and briquets as fuel for house-heating boilers, by D. T. 

Handall. 1908. 44pp.

BULLETIN 367. Significance of drafts in steam-boiler practice, by W. T. Ray and 

Henry Kreisinger. 1909. 61 pp.

BULLETIN 368. Washing and coking tests of coal at Denver, Colo., by A. W. Belden, 

G. R. Delamater, and J. W. Groves. 1909. 54 pp., 2 pis.
186 SMOKELESS COMBUSTION OF COAL.

MISCELLANEOUS PUBLICATIONS ON SMOKE ABATEMENT.

The following references supplement the list of books and papers 

given in Bulletin 334.

BRECKENRIDGE, L. P., How -to burn Illinois coal without smoke: Univ. Illinois 

Eng. Exper. Sta. Bull. No. 15, Urbana, 111., 1907, pp. 43. Discusses principles of 

smokeless combustion and causes of smoke; describes various types of furnaces and 

boiler settings that have given satisfactory results.

KERSHAW, J. B. C., The smoke problem in large cities: Fortn. Rev., February, 

1908, pp. 286-299. Mentions measures taken in France, Germany, and Austria to 

abate smoke; refers to the work of the Hamburg Society for the Prevention of Smoke 

and of the London Coal Smoke Abatement Society.

KRAUSE, JOHN W., Smoke prevention: Proc. Eng. Soc. Western Pennsylvania, 

March, 1908, pp. 101-120. Reviews progress in smoke prevention in several cities, 

particularly Cleveland, Ohio; discusses causes of smoke and methods of abatement.

KUNZE, EDWARD J., Smoke suppression: Engineer, January 31,1908. Describes an 

instrument for smoke determination and a method of recording observations.

Smoke Prevention in Newark, N. J.: Eng. Record, January 18, 1908, pp. 72-73. 

Gives new city ordinance against dense smoke and describes an automatic steam-.jet 

device for preventing smoke.
INDEX.

A. Page.

Air, admission of, effect of........... 6,139,171-172

methods of.............................. 167

Air, supply of, to capacity developed...... 169-171

relation of, to efficiency......... 11,108-172

to size of coal.................. 147-148

to smoke................... 11,109-170

to volatile matter.............. 169-170

Arch, ignition, height of..................... 17,77

B.

Beers, L. F., work of........................ 7

Bibliography.............................. 185-186

Boiler horsepower, definition of............. 8

relation of, to efficiency.................. 99

chart showing....................... 100

Boiler plants. See Industrial plants.

Boilers, capacity of.......................... 8

See also Water-tube boilers; Return tubular boilers. 

Briquets, character of..................... 1. 156

tests Of.......... 10-11,154-155,150,101-162,184

C.

Capacity developed, relation of, to efficiency. 168 

relation of, to size of coal.............. 147-148

Carbon dioxide, relation of, to draft.......... 143

relation of, to efficiency ................. 143

to smoke........................... 11,143

to temperature...................... 143

to volatile matter.................... 143

Chain grates, draft measurements on ........ 18

observations on......................... 15-32

summary of......................... 33

relation of, to smoke.................. 17-18,33

types of................................. 12-15

figures showing................ 13,14,15,16

Clinker, relation of, to smoke.............. 149-153

Coal, briquets of, tests of.................. 154-156

consumption of, relation of, to capacity

developed................... 10

relation of, to Carbon dioxide........ 144

to carbon monoxide............. 144

to efficiency..................... 144

to temperature.................. 144

horsepower from...................... 173-175

kinds of, relation of, to chain grates...... 16-17

relation of, to front-feed stokers...... 38

to hand-fired furnaces..... 107,118,124

to side-feed furnaces............. 55,64

to under-feed furnaces........... 84,92

size of.................................. 7-8

Coal, size of, effect of, on air supply ....... 147-148

on capacity developed...... 10,147-148

on efficiency................... 147-148

on smoke................... 10,147-148

temperature of, relation of, to smoke... 172-173

relation of, to smoke, chart showing.. 174

Coals, high-ash, tests on..................... 146

Coking furnace, description of............... 101

Combustion, complete, necessity for......... 184

requirements of......................... 6

Combustion, smokeless. See Smoke.

D.

Data, collection of........................... 7

.Draft, measurement of, with chain grates.... 18

measurement of, with front-feed stokers.. 3G 

readings of, object of..................... . 7

relation of, to smoke................... 156,163

Draft, forced. See Forced draft.

E.

Efficiency, relation of, to air supply......... 11

relation of, to boiler horsepower......... 99

to boiler horsepower, chart showing. 100 

to capacity developed......... 141,142,168

to carbon dioxide.................. 141,142 '

to coal consumed.................... 175

to size of coal................... 10,147-148

to smoke................... 11,142,165-167

to volatile matter.............. 10,140,142

to washing.......................... 11

Fire, depth of, relation of, to chain grates.... 16-17

relation of, to front-teed stokers.......... 38

to hand-fired furnaces......... 107,118,124

to side-feed stokers.................. 55,64

Firing, methods of, relative efficiencies of.. 145-146 

Forced draft, relation of, to efficiency........ 11

relation of, to smoke............... 11,156,163

Front-feed stokers, observations on.......... 37-47

observations on, summary of............ 48

types of................................. 34-37

figures showing............ 34,35,36,37,38

Furnaces, coal supply to, variations in, effects

of........................... 10

placing of............................... 6

G. 

Geological Survey, tests by........... 9-10,139-167

tests by, conclusions from............... 10-11

Grates, style of, relation of, to smoke.... 11,157,164

187
188 INDEX.

H.

Haud-fired plants, defects of................ 101

furnaces at, figures showing.............. 105,

106,107; 119,120,121,122,123,124 

observations on........................ 103-138

smoke prevention in..................... 101

tests of................................ 139-143

types of............................. 12,99-103

descriptions of...................... 99-139

Hand firing, best methods of ................ 10

difficulties of............................. 6-7

Heating stations, details of................. 177-184

development and use of................ 175-176

heating cost of........................... 183

Heating surface, determination of............ 9

I. 

Industrial plants, investigation of........... 5-9

types of................................ 11-139

divisions of.......................... 12

L. 

Lignite,tests of............................. 10,149

M. 

Mixing devices, figure showing.............. 103

value of........................... 102-103,167

N. 

Norfolk, Va., plant at, description of........ 131

plant at, figures showing.............. 140,141

tests at................................ 139-144

0. 

Overfeed stokers, descriptions of............. 12-77

See also Chain grates; Front-feed stokers; 

Side-feed stokers.

P. 

Peat, tests on............................... 10,149

Personnel of work........................... 7

Plants. See Industrial plants.

Publications, list of........................ 1S5-18G

R.

Randall, D. T., work of..................... 7

Rate of work, unit of........................ 8

Representative plants. See Industrial plants. 

Return tubular boilers, plants with, observations of........ 64-76,92-98,117-138

Ribbon firing, test of...................... 145-146

S.

St. Louis, plant at, description of............ 144

smoke prevention tests at.............. 145-167

Scotch marine boilers, observation on...... 103-116

Side-feed stokers, observations on........... 55-76

observations on, summary of............ 77

types of................................. 48-54

figures showing.......... 49,50,51,52,53,54

Smoke, observations on, making of.......... 7

prevention of, publications on............ 186

conclusions on....................... 184

devices for.......................... 99-100

economy in.......................... 7

factors in............................ 5

f ormer report on..................... 5

in hand-fired plants................ 101,184

Smoke, prevention of, possibility of......... 6,184

problem of.......................... 5

solution of........................... 5

relation of, to air supply.................. 11

to ash........'............. 151-153,158-162

to capacity developed............... 142,

143,151-155,158-162 

to carbon dioxide................. 142,143

to carbon monoxide. 11,143,151-155,158-166 

to chain grates ...................... 33

to clinker.................. 149-155,158-166

to consumption.................... 149-153

to draft........................ 156-157,163

to efficiency......................... 10,

142,149-155,158-166,165-167 

to forced draft....................... 11

to front-feed stokers................. 48

to load.............................. 99

to moisture........ 151-153,158-162,165-166

to size of coal................... 10,147-148

to style of grate...................... 11

to sulphur......................... 158-162

to temperature of coal..... 142,143,172-173

chart showing................... 174

to underfeed stokers................. 99

to volatile matter.................... 142,

149-155,158-166,172-173 

chart showing.................... 174

to washing........................ 156-160

Stack, relation of, to underfeed stokers....... 99

Steam jets,- use of.......................... 101-102

use of, figures showing................... 105

Stokers, placing of............................ 6

relative values of........................ 6

tests of................................ 143-144

types of................................. 12

descriptions of....................... 12-99

See also Overfeed stokers; Underfeed

stokers. 

Subbituminous coal, tests of:............... 10,149

T.

Temperature, relation of, to capacity, developed ........................ 142

relation of, to efficiency.................. 142

to smoke...................... 142,172-173

chart showing................... 174

U. 

Underfeed stokers, observations on.......... 84-98

observations on, summary of............ 99

.tests with ..................I...........? 143

types of................................. 77-84

figures showing.......... 78,79,80,81,82,83

V.

Volatile matter, relation of, to efficiency.. 10-11,140 

relation of, to smoke........... 149-153,172-173

"* to smoke, chart showing............. 174

W.

Washing, relation of, to efficiency..........; 11

relation of, to smoke................... 156-160

Water-tube boilers, plants with, observations on....... 55-63,84-91,103-117

Weeks, H. W., work of...................... 7

Work, rate of, unit of........................ 8

o