DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OT1S SMITH, DIRECTOR

4O3

COMPARATIVE TESTS

OF

RUN-OF-MINE AND BRIQUETTED COAL

ON THE

TORPEDO BOAT BIDDLE

Made with the collaboration of Lieut. Commander Kenneth McAlpine, U. S. N., 

and Ensign J. W. Hayward, U. S. N.

BY

WALTER T. RAY AND HENRY KREISINGER

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1909

CONTENTS.

 Page.

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

General statement...................................................... 5

Tests at Norfolk....................................................... 5

Personnel................................................................. 6

Coals and briquets.......................................................... 7

Objects of the tests......................................................... 7

Appliances................................................................ 7

Boat and boiler plant................................................... 7

Flue-gas sampler....................................................... 10

Spark catchers........................................................ 11

The blower............................................................ 13

Methods of conducting testa................................................ 13

General statement. ................\.................................... 13

Starting and closing.................................................... 13

Weight of ash and refuse............................................... 13

Weight of coal fired....................."................................ 14

Weight of water fed to boiler............................................ 14

Feed-water temperature............................................... 15

Flue-gas sampling...................................................... 15

Flue-gas temperature................................................... 15

Furnace temperature.................................................. 15

Gas pressures("drafts")...............:............................... 15

Steam pressures........................................................ 15.

Moisture in steam...................................................... 15

Smoke................................................................. 15

Weight of sparks...................................................... 16

Chemical analyses...................................................... 16

Observed data and calculated items........................................ 16

Effect of rate of combustion............................................ 16

The tabular showing............................................... 16

Notes on individual tests........................................... 21

Data and calculations shown graphically........................... 23

Explanation of figures.......................................... 23

On capacity developed...........................:............. 23

On evaporation................................................ 23

On dry flue gases............................................... 25

On smoke...................................................... 26

On distribution of heat........................................ 28

On heat losses................................................. 28

On heat absorption............................................. 28

On unaccounted-for losses...................................... 31

3
4 CONTENTS.

Observed data and calculated items Continued. 

Effect of rate of combustion Continued.

Data and calculations shown graphically Continued. 

On run-of-mine coal and briquets.................

On flue-gas and furnace temperatures..............

On true boiler efficiency..........................

On pressure drop................................

On sparks........................................

On weight of air.................................

On speed of fan..................................

Deductions........................'......................

Economy............................................

Combustion space...................................

Relative capacity of storage space.........................

Transferring fuel from bunkers to fireroom...........'.....

Conclusions.............................................

A fundamental principle in the combustion of smoky fuels. 

Survey publications on fuel testing and briquetting............

ILLUSTRATIONS.

FIGURE

32

32

35

36

38

38

40

40

40

42

43

43

43

44

49

Page. 

9

11

12

Construction and setting of Normand water-tube boiler............

Flue-gas sampler................................................

Spark catchers.................................................

Effect of, rate of combustion on horsepower, equivalent evaporation, and flue gases.........................................

Effect of rate of combustion on flame and smoke.................

Effect of rate of combustion on heat losses........................

Effect of rate of combustion o'n three stated factors................

Effect of rate of combustion on temperature, and true boiler

efficiency................................................... 33

9. Effect of rate of combustion on pressure drop and sparks.......... 37

10. Effect of rate of combustion on air supply and speed of fan....... 39

TABLES.

TABLE 1. Dimensions of Normand water-tube boiler and plain-grate furnace...

2. Summary of observed data and calculated items....................

3. Data used in calculating true boiler efficiency.....................

4. Chemical analyses of coal and briquets.............................

5. Usual relation of combustion space to grate area, the rate of combustion, and the average time each cubic foot of gas stays in furnace.

Page. 

10 

17 

35

41

42
COMPARATIVE TESTS OF RM-OF-MINE AND BRIQUETTED COAL ON THE TORPEDO BOAT BIDDLE.

By WALTER T. RAY and HENRY KREISINGER.

INTRODUCTION.

General statement. The briquetting tests conducted by the United 

States Geological Survey had their beginning in the testing of coals

and lignites at the Louisiana Purchase Exposition, St. Louis, Mo., in 

1904, and were continued at the fuel-testing plants at St. Louis, Mo., 

and at Norfolk, Va. Such tests are now in progress at the Geological 

Survey testing station at Pittsburg, Pa., and form an essential part of 

the Survey's investigations looking to the determination of the fuel 

value .of the coals and lignites belonging to or for the use of the 

United States. *

The tests have comprised (1) the manufacture of briquets to determine the adaptability of different coals and lignites to the process and 

the merits of different binding materials; (2) physical tests to establish the fitness of the briquets to withstand weathering, transportation, and handling; and (3) steaming tests to prove thq calorific value 

of the briquets in boilers of different types used by the Government, 

and, by comparison with the raw coals, the benefits to be derived 

from briquetting.

Details of the tests are issued by the Survey in other publications. 

A list of Survey publications on fuel testing and briquetting is given 

at the close of this volume.

Tests at Norfolk. The fuel tests conducted at Norfolk included a 

detailed investigation of a number of Virginia and West Virginia 

coals that are bought by the United States Government for the navy 

and for use in constructing the Panama Canal, and that are extensively 

used by the merchant marine, manufacturing plants, and railroads. 

Through a cooperative arrangement with the Navy Department 

steaming tests of the coals were undertaken to determine the relative 

merits of the same coal when burned raw or as briquets in marine 

boilers.

Preliminary arrangements were made between Joseph A. Holmes, 

expert in charge of the technologic branch of the United States

5
6 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

Geological Survey, and Rear-Admiral Charles W. Rae, Chief Engineer of the United States Navy. The tests were made on board the 

U. S. torpedo boat Biddle, designated for the purpose, beginning 

December 6, 1907, and ending January 27, 1908.

The coal used in these tests came from the Sewell and Beckley 

beds in the New River district of West Virginia. With the particular 

equipment used in the tests both coal and briquets were far from 

smokeless; consequently the data of this bulletin are applicable only 

by analogy to parallel operation with a coal more nearly smokeless, 

but nevertheless applicable with much reliability. The possibilities 

of coals of different composition are indicated by the data to be 

published in a bulletin of the Geological Survey now in preparation, 

wherein the present authors describe a number of tests in which 

only a very slight amount of smoke was emitted while burning raw 

coal from the Pocahontas No. 3 bed, West Virginia, and briquets 

made therefrom at rates of combustion very much higher than any 

rates used in the torpedo-boat boiler. At a combustion rate of 120 

pounds of the Pocahontas briquets per square foot of grate surface 

there was scarcely any smoke.

It was the original intention to make a set of preliminary steaming 

tests alongside a dock (which tests furnish material for this bulletin) 

and to finish with a set of running tests at sea; but the running tests 

were never made, for lack of time and men.

PERSONNEL.

The conduct of the tests, on behalf of the navy, was under the 

immediate supervision of Lieut. Commander Kenneth McAlpine 

assisted by Ensign J. W. Hayward, in command of the Biddle. The 

Geological Survey was represented by Walter T. Ray and Henry

Kreisinger of the steam-engineering section.

Messrs. McAlpine and Hayward directed the preparation of the 

boat and other apparatus for the tests and had all the special appliances made in the navy-yard shops. All tests were supervised by 

Messrs. Hayward and Kreisinger. The navy supplied water tenders, 

firemen, and a number of machinists. The latter acted as observers 

and recorders of pressures, temperatures, and weight of water. 

Weight of coal fired was recorded currently by Mr. Kreisinger, who 

supervised the management of fires. Flue-gas analyses were made 

usually by a representative of the Geological Survey; many of them 

were made by J. K. Clement, physicist of the technologic branch, 

who very kindly volunteered to help with the work during the first 

eight tests. The flue-gas analyses on the rest of the tests were made 

by Mr. Ray. Firing on all the tests was done by the navy firemen, 

who were found to be exceptionally skillful in this work.
APPLIANCES. . 7

COALS AND BRIQUETS.

The coal used in these tests was all run-of-mine and came from 

four different mines, all of which are located on the Chesapeake and 

Ohio Railway and in the New River coal field. The designations 

given these four coals at the United States fuel-testing plant are 

followed in this bulletin.

Jamestown No. 6 coal came from the Sewell bed.at Red Star, 

Fayette County, W. Va. Jamestown No. 9 coal came from the 

Sewell bed, mined near Winona, Fayette County, W. Va. Jamestown 

No. 10 coal came from the Beckley bed, at Stanaford, Raleigh County, 

W. Va. Jamestown No. 11 coal came from the Beckley bed, at West 

Raleigh, Raleigh County, W. Va.

Part of the Jamestown 6 coal was made into briquets 6f by 4 J by 3

inches in size, at the United States fuel-testing plant on a briquettillg 

press built in England. The compression on thesis large briquets was 

about 2,500 pounds per square inch. The binder used was 6 per cent 

of water-gas pitch, described in Bulletin 385 a under laboratory number 5563.

Portions of the Jamestown 9 and 11 coals were made into briquets 

circular in horizontal section, 3£ inches in diameter, 2f inches thick 

in the center and \\ inches at the circumference. The compression 

on these small briquets was about 1,000 pounds per square inch. In 

both coals the binder used was 6 per cent of water-gas pitch, described 

in Bulletin 385 a under laboratory number 5941.

OBJECTS OF THE TESTS.

The main object of these tests was to determine whether the use of 

briquetted coal on torpedo boats has any advantages over the use of 

raw coal. Besides comparing the economy obtained with briquetted 

and raw coal, the following properties of the two fuels were given 

particular attention: (a) The tendency to smoke; (5) the amount of 

sparks emitted from the stack; (c) the rate at which steam can be 

made and the ease with which the fires are handled; (d) the ease of 

transferring fuel from the coal bunkers into the fireroom.

APPLIANCES.

BOAT AND BOILER PLANT.

The torpedo boat Riddle is 157 feet in length on load water line, 

17 feet 7£ inches extreme beam, and 175 tons displacement. Its 

equipment includes two triple-expansion engines and two water-tube

o Wright, Charles L., Briquetting tests at the United States fuel-testing plant, Norfolk, Va., 1907-8: 

Bull. TJ. S. Geol. Survey No. 385, 1909, p. 8.
8 TESTS OF COALS AND BRIQUETS ON TOEPEDO BOAT.

boilers. The engines are in separate compartments amidships. The 

boilers are in separate boiler rooms, one at each end of the engine 

compartments, the fronts of the boilers facing the latter. In front 

of each boiler is a space about 10 feet square used as the fireroom, 

in which is placed an auxiliary feed pump and the wheel of a blower 

fan. The blower is run by the engine in the main compartment. 

Alongside each boiler room are two coal bunkers, each capable of holding about 22.5 tons of soft coal. In cross section each coal bunker is 

approximately a segment of a circle with the chord of the segment 

placed vertically and with its tips cut off by the deck and the floor 

of the bunker. This floor of the bunker is, however, only about 8 to 

12 inches wide, which fact, in connection with the ribs of. the sides of 

the boat projecting inward, makes shoveling coal from the bunker 

rather difficult. Two feed-water reserve tanks alongside the engine 

compartments, of shapes similar to those of the coal bunkers, have 

each a water capacity of about 700 gallons.

The two boilers are exactly alike in size, construction, and setting 

(fig. 1). Only the forward boiler was used for tests. It is of the 

curved water-tube type known as the Normand boiler. The boiler 

proper consists of the steam drum S, connected to two mud drums M 

by 1,552 curved water tubes lf\ inches in external diameter and two 

1 Of-inch downcomers in the rear of the boiler. The steam drum is 

provided with a steam dome in which the intake of the steam pipe is 

placed. Feed water is fed into the steam drum.

The furnace is placed under the steam drum between the two nests 

of water tubes and the mud drums. It is equipped with a plain 

grate for hand firing. The coal is charged through two firing doors 12 

by 14 inches, the lower edges of which are 14 inches above the grate,

which feature of construction makes the process of removing clinker

from the fuel bed while running rather difficult. In the front portion of the boiler on both sides the first and second rows of tubes next 

the furnace are so curved and placed with respect to each other that 

they form a nearly gas-tight baffle. On the outside of each nest of 

tubes the last two rows are similarly placed along the full length of 

the boiler. This constructional feature is shown in figure I in the 

front view and in the section across the nest of tubes.

The products of combustion flow to the rear of the furnace, where 

they enter the tube nests through the spaces between the tubes, 

which are left open for this purpose. Through the nests of tubes the 

gases flow to the front of the boiler and there turn up into the hood 

and out through the stack. The gases pass through the tube spaces 

only once. The path of the gases is indicated in the longitudinal 

section through the boiler.
SECTION ON C-D

FRONT VIEW

TXIBES FORMING BAFFLES INSIDE O>ENING LEFT 

SECTION ON A-B

c

LONGITUDINAL SECTION THROUGH BOIL

FIGURE 1. Construction and setting of Normand wat
10 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

The principal dimensions of the boiler and furnace are shown in 

Table 1.

TABLE 1. Dimensions of Normand water-tube boiler and plain-grate furnace.

Diameter of steam drum.........................................inches.. 35. 43

Length of steam drum............................................ do.... 150. 00

Diameter of mud drums...........................................do.... 10. 75

Length of mud drums.............................................do.... 141. 75

Diameter of downcomers .........................................do.... 10. 75

Number of tubes....................................................... 1, 552

Outside diameter of tubes. .....................................inches.. 1 T^

Approximate length of tubes.......................................do.... 75. 5

Total heating surface.......................................square feet.. 2,776.19

Length of furnace.................................................. feet.. 9.16

Width of furnace.................................................. do.... 6. 40

Height of furnace from grate to steam drum......................... do.... 4. 65

Height of furnace from grate to bend of tubes......................do.... 3. 76

Approximate combustion space above grate....................cubic feet.. 136

Distance from front of furnace to opening among tubes.............. feet.. 5. 5

Length of bars..................................................inches.. 37. 5

Average width of grate bars on top................................ do.... . 375

Average width of air spaces........................................do.... .56

Air spaces in grate (approximate)............................... per cent.. .55

Area of grate..............................................square feet.. 58. 6

Ratio of grate area to combustion space.................................. ' 2. 33

Inner dimensions of stack ...................................... inches.. 36 x 40

Height of stack above grate ....................................... feet.. 15

The whole boiler and furnace were inclosed in a cast-iron casing, 

which was lined with fire brick at the front and rear of the combustion space and with sheet asbestos along the nests of tubes. In 

front the casing had tight-fitting doors opening into the tube nests 

to facilitate the cleaning of soot from the tubes.

The stack, which was slightly elliptical in cross section, was made 

of two concentric tubes with 1^-inch annular air space between, open 

to the air at the top and also at the base of the stack. The object of 

this construction was to circulate air between the inner and outer 

tubes, thus keeping the outer shell cool.

FLUE-GAS SAMPLEE.

The flue-gas sampler was inserted in the stack immediately above 

the hood, as shown in the longitudinal cross section (fig. 1). The 

sampler was especially made for these tests and consisted of a f-inch 

pipe closed at both ends and having a number of sVinch. holes 

drilled in a staggered way on two opposite sides of the pipe. Through 

a cap closing one of the ends of this pipe was inserted a J-inch pipe, 

which extended to the middle of the f-inch pipe. The gas was 

drawn through the inner pipe.* The object of this construction was 

to draw gas at nearly the same rate from many places in the stack,
APPLIANCES. 11

so that the gas thus collected 

may be taken as a rough average of the gases flowing up 

through the stack. The construction of this sampler is 

shown in figure 2. Connection 

was made to a steam injector, 

which drew a continuous stream 

of gas through the sampler. 

The sample collected for analysis 

was drawn through a pet cock 

placed between the sampler and 

the injector.

SPARK CATCHERS,

Figure 3 shows four spark 

catchers in position, as used 

during the tests. Each spark 

catcher consists of a U-shaped 

sheet-iron vessel open at both 

ends and placed with the open 

ends down over the top of the 

stack. The end inside the stack 

is in shape nearly a sector of a 

circle covering an angular area 

of 9 degrees, so that the total 

area covered by the four spark 

catchers is 0.1 of the total crosssectional area of the stack. The 

outside end of the U-shaped vessel is nearly rectangular in cross 

section and terminates in a detachable sheet-iron receptacle. 

This U-shaped vessel catches 

gases and sparks from a' sector 

of the stack area and changes 

their direction downward. The 

gases are allowed to escape 

through an opening in the outside end of the U-shaped vessel, 

which opening is provided with 

wire netting of 24 meshes to an 

inch. The sparks are kept in by 

the wire netting and fall into the

r c 11

I \ "

I/^i/«1

/ / /J<

 rm*

a r

s^

:"-
12 TESTS OF COALS AND BRIQUETS ON TOEPEDO BOAT.

Stack

SECTION THROUGH STACK ON AFIGURE 3. Spark catchers.
METHODS OF CONDUCTING TESTS. 13

receptacle, where they accumulate. As these spark catchers cover 

about 0.1 of the area of the stack, the amount of sparks collected in 

the receptacle is about 0.1 of the total sparks ejected from the stack. 

These spark catchers were specially designed and constructed 

for these tests in order to determine the comparative losses in sparks 

when burning raw coal and the two kinds of briquets.

THE BLOWER.

The necessary air required for the combustion of the fuel in the 

furnace was supplied by a blower which forced air into the fireroom, 

which was kept as nearly air-tight as practicable. Thus, by changing the speed of the blower, any desired excess of pressure over the 

outside atmosphere could be kept in the fireroom and under the 

grate, and within certain limits any rate of combustion could be 

obtained.

The wheel of the blower was 5 feet in diameter and was placed 

directly in the fireroom; it had no .casing and was protected only 

by a wire screen. The blades were curved in the direction opposite 

to that of the rotation of the wheel. The maximum speed of the 

blower was about 1,000 revolutions per minute.

METHODS OF CONDUCTING TESTS.

General statement. All tests were made using the forward boiler 

while the boat was tied to the docks at the Norfolk Navy-Yard. 

Steam was generated at 200 pounds pressure and discharged into 

the atmosphere. The water tender on duty also regulated the 

steam pressure in the boiler. During a test all regular observations 

were made every twenty minutes.

Starting and dosing. In starting and closing the tests a modification of the "alternate method" was used. The boiler was kept 

under steam pressure all night with a low fire covering the front 

third of the grate. About one hour before starting a test the fire 

was spread over the whole grate and gradually built up to 3 or 4 

inches height. During this building of the fire about 500 pounds of 

coal were put into the furnace. On starting the test the height of 

the fuel bed was measured as accurately as possible with the prongs 

of a rake, and readings were taken of the steam pressure and height 

of water in the boiler. The reserve water tank from which the 

boiler was fed was always completely filled when a test was started. 

Closing conditions of the tests were made as nearly as possible the 

same as those of starting.

Weight of asTi and refuse. Before closing a test the fuel bed was 

burned down so that its height above the layer of clinker was the 

same as at trie start, as nearly as could be estimated by means of the
14 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

prongs of a rake. The test was started with the ash pan clean. 

After closing the test the free ash was removed from the ash pan, 

weighed, and charged to the test.- The fire was then burned down 

entirely, the clinkers pulled out through the fire doors, weighed, and 

also charged to the test. The small amount of free ash failing into 

the ash pan during the process of pulling out clinkers was not charged 

to the test. It was impracticable to clean the fire before the close of 

the test on account of the lower edge of the fire door being 14 inches 

above the grate.

Weight of coal fired. The fireroom was so small that it was impossible to place a scale in it and weigh the coal as it was fired; therefore on most of the tests the coal was weighed before the test and 

put in sacks of 100 pounds each and delivered to the coal bunkers. 

During the test 3 or 4 sackfuls of coal were emptied on the floor of 

the fireroom and fired in two to four firings. The number of sackfuls and the time of emptying them were recorded. This method of 

recording coal enabled the man having charge of the fire to keep the 

rate of combustion uniform. In a few tests a definite amount of the 

coal was weighed before the test and put into an empty coal bunker 

without sacking it. The small amounts of coal used before tests 

were delivered directly to the fireroom and were not taken from the 

weighed coal in the bunker. During a test an approximately known 

quantity of coal, measured with a large sheet-iron bucket, was put on 

the firing floor at a time, the approximate weight and time of delivery 

being recorded. In this manner the rate of combustion was maintained at the desired rate, and all the weighed coal in the bunker 

was burned before closing the test. On all tests when a new supply 

of coal was delivered from the bunker to the firing floor a sample for 

chemical analysis was taken and put into a covered can. This 

sample coal was weighed and subtracted from the total coal weighed 

for the test.

Weight of water fed to loiter. Water was measured in a tank with 

a capacity of 2,239 pounds placed on deck above the reserve water 

tank. The bottom of the measuring tank was funnel-shaped, to 

permit ^uick emptying. The top of the tank was .contracted by 

means of a cone into a narrow 8-inch neck in order that when filling 

the tank any difference of level due to tossing of the boat would 

introduce only an inappreciable error. From the measuring tank the 

water was run into the reserve tank and thence was pumped by the 

auxiliary feed pump into the boiler. Tests were started with the 

reserve tank full, and during the test the number of measuring tanks 

emptied and the times of emptying were recorded. At the end of a 

test any quantity of water left in the measuring tank and not required 

to fill the reserve tank completely was weighed in a smaller tank
METHODS OF CONDUCTING TESTS. 15

placed on a platform scale and proper correction made of the total 

water weight.

Feed-water temperature. A thermometer was immersed in the 

reserve tank and read at regular intervals.

Flue-gas sampling. Flue gas was sampled with the specially constructed gas sampler described on page 10-11. The sample was collected on the deck at the stack and then taken to the cabin, where 

it was analyzed for C02 , 02 , and CO. The location of the sampler is 

shown in figure 1.

Flue-gas temperature. The flue-gas temperature was measured 

with .a platinum and platinum-rhodium thermocouple. The thermocouple was placed in the center of the stack near the flue-gas sampler 

and was connected with a cord to a galvanometer placed on the dock 

and reading in degrees Centigrade.

Furnace temperature. Furnace temperature was measured with a 

Wanner optical pyrometer. For this purpose a hole \\ inches in 

diameter was drilled in the furnace casing in the back of the boiler 

and about 3 feet above the grate. This temperature was taken with 

other readings at regular intervals.

Gas pressures ("drafts"). Gas pressures were measured on all 

tests at the base of the stack, over the fuel bed, and in the fireroom. 

For pressures up to 1.5 inches of water above atmosphere the Ellison 

differential draft gages were used; high pressures were determined 

with an ordinary U-tube manometer. The gas-pressure gages were 

placed on the deck and properly piped.

Steam pressures. Steam pressures were read off a standard gage, 

which was located on the deck and which was reliable within a 

pound. The pressures were also automatically recorded by a 

Crosby recording gage, which was located in the fireroom and which 

was accurate within 3 pounds.

Moisture in steam. The moisture in the steam was determined 

with a throttling calorimeter on the upper end of a £-inch pipe 30 

inches long, which ascended vertically from a short piece of horizontal steam mam between the boiler and the throttle valve. It 

was impossible to get a horizontal piece of piping into the steam 

main for lack of space; therefore the vertical piece of piping was 

run up and the calorimeter placed above the deck. The connecting 

pipe and the calorimeter were well covered with hair felt. The 

nipple or the part of the pipe fitted into the steam main extended 

nearly across the mam and was perforated with £-inch holes in the 

usual manner. Readings of the calorimeter were taken at the 

regular twenty-minute intervals along with other readings.

Smoke. Observations of smoke were taken fifteen minutes out of 

every thirty minutes. Individual readings were taken fifteen
16 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

seconds apart. The density of smoke was estimated by comparison 

with Ringelmann's smoke charts. In the tests run at a high rate 

of combustion there was occasional flaming in the stack, the flame 

sometimes reaching 10 feet above its top,. The flaming was recorded 

by the smoke observer. )

Weight of sparks. The weight of sparks ejected from the stack 

was determined with the spark catchers shown in figure 3 and described on pages 11,13. These spark catchers collected sparks from 

0.1 of the total area of the stack, so that by multiplying by 10 the 

weight of sparks collected the approximate weight of all the sparks 

ejected from the stack was obtained. The spark receptacles were 

large enough to hold the sparks collected during the entire test. 

At the end of the test the receptacles were removed, the sparks 

weighed and carefully sampled. A sample of about 2 pounds was 

sent in an air-tight can for chemical analysis.

Chemical analyses. All chemical analyses of coal, ash, and sparks 

were made at the chemical laboratory of the technologic branch of 

the Survey at Pittsburg, Pa., in charge of F. M. Stanton.

OBSERVED DATA AND CALCULATED ITEMS.

EFFECT OF RATE OF COMBUSTION. 

THE TABULAR SHOWING.

In all, 21 tests were made, 10 with run-of-mine coal, 3 with large 

briquets, and 8 with small briquets. It was planned to make four 

tests with each run-of-mine coal, varying the rate of combustion 

from 15 to 60 pounds of coal per square foot of grate per hour, and 

then duplicate each test with briquets, but the fuel supply was

insufficient and only three tests could be made. For this reason 

no test was run with the rate of combustion below 20 pounds per 

square foot of grate per hour. For the sake of comparison the tests 

on briquets were made at approximately the same rates of combustion as the tests on the run-of-mine coal of which the respective 

briquets were made. The averages of the data taken during the 

test and the calculated results are given in Table 2. The calculated 

results given in the table were computed according to the method 

given in Bulletin 325, pages 151-153, being substantially the method 

recommended by the American Society of Mechanical Engineers.
OBSEBVED DATA AND CALCULATED ITEMS. 17

TABLE 2. Summary of observed data and calculated items of 21 tests made with the 

forward boiler, U. S. S. Biddle, December 6, 1907, to January 27, WOSfl

Test 

No.

1

1

2

3 

4

5 

6

7

8

9

10

11 

12

13

14

15

1C 

.17

18

19

20

21

Test 

No.

1

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

Designation of 

coal.

2

Jamestown 6 . .

Jamestown 11 .

Jamestown 9 . .

Jamestown 11 .

Jamestown 10 .

Revolutions per 

minute of 

fan.

11 (14.5)

312

276

347

544

426

324

635

389

626

320

744

357

436

701

309

375

382

750-800

Form of fuel.

*3

t

(Run of mine. .

[Large briquets

Run of mine..

Small briquets

("Run of mine..

(.Small briquets

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

Run of mine. .

Date of 

trial.

4(1)

1907.

fDec. 6

^Dec. 7

Pec. 10 

{Dec. 12

Dec. 13

Dec. '16

(Dec. 18

 mec. 19

[Dec. 20

1908.

(Jan. 3

(Jan. G 

[Jan. 8

[Jan. 10

(Jan. 13

pan. 14

(Jan. 17 

(Jan. 20

{Jan. 21

[Jan. 23

Jan. 25

Jan. 27

Duration 

(hours).

5(2)

5.25

3.33

7.15 

6.23

5.10 

4.03

4.70

5.98

4.05

3.97

4.08 

6.08

2.37

6.78

4.62

4.30 

5.30

4.20

3.85

1.58

4.10

Average temperatures (°F.) of 

Atmosphere.

12 (15)

54

53

66

44

40

57

60

45

49

45

43

49

40

47

42

42

55

60

50

31

44

Steam.

13(17)

380

380

381

378

379

380

379

380

379

379

380

379

383

383

383

384

382

380

383

Feed 

water 

in 

tank.

14(18)

50

50

51

51

50

51

50

50

50

50

49

49

49

49

49

49

48

48

50

45

47

Gases 

leaving 

boiler 

tubes.

15 (21)

739

739

646

681

802

919

655

597

728

696

797

583

807

583

668

716

637

709

752

817

601

Furnace.

16(22.1)

2,673

2, 615

2,307

2,460

2,586

2,273

2,347

2,624

2,662

2,921

2,633

3,097

2,502

2,881

2,442

2,765

2,950

3,070

2,498

Average pressures.

Barometer 

(inches of 

' mercury), c

6 (3)

30

30

30 

30

30 

30

30

30

30

30

30 

30

30

30

30

30 

30

30

30

30 '30

Moisture 

" in fuel 

(per 

cent).

17 (26)

1.64

1.50

1.64

1.76

1.48

1.78

1.92

2.91

2.50

1.26

1.87

1.57

1.79

2.55

2.29

2.81

1.39

1.71

2.36

1.79

2.61

Steam

above 

atmosphere 

(pounds

per

square

inch).

7(11.1)

204.5

204.0

199.0 

206.0

199.0 

200.3

203.1

202.3

202.8

202.0

202.0 

207.0

203.0

204.1

203.0

202.8 

203.9

205.0

200.0

201.0

204.0

"Draft" b (inchesof 

water).

At base 

of 

stack.

8(12)

-0.11

- .44

- .10 

- .13

- .16 

- .21

- .23

- .19

- .51

- .29

- .50 

- .17

- .68

- .14

- .33

- .74 

- .11

- .29

- .55

- .60

- .16

Over 

fuel 

bed.

9(13)

+0.39

+ .98

+ .24 

+ .23

+ .39 

+ .83

+ -47

+ .34

+ 1.30

+ .48

+ 1.45 

+ .27

+2.22

+ .36

+ .57

+ 1.50 

+ .27

+ .88

+ 1.97

+2.32

+ .77

Fuel (total weight in 

pounds).

As 

fired.

18 (25)

9,171

8,076

8,283

7,771

8,678

10, 778

8,368

7,249

10, 941

7,390

10, 912

7,313

9,074

8,530

8,224

13, 375

7,464

9,239

11,836

6,670

7,098

Dry.

19 (27)

9,021

7,955

8,147

7,634

8,550

10, 586

8,207

7,038

10, 667

7,297

10, 708

7,198

8,912

8,312

8,036

12, 999

7,360

9,081

11,557

6,551

6,913

Ash 

and 

refuse.

20 (28)

1,423

642

739

707

519

615

666

828

605

487

643

617

351

597

481

839

485

423

447

343

432

In ash 

pit.

10 (14)

+1.23

+2.48

+ .57 

+ .54

+ .83 

+2.37

+ 1.13

+ .65

+ 2.35

+ .97

+2.55 

+ .84

+3.39

+ .79

+ 1.33

+3.95 

+ .83

+1.76

+3.73

+4.92

+1.67

Clinker in 

ash and 

refuse 

(per 

cent).

21 (29)

16.65

41.90

24.90

32.11

32.18

39.51

21. 62

26. 40

35.70

34. 70

23.48

28.04

15.10

28.81

36.59

38.74

30.93

45.15

32.89

44.02

69.44

a Code numbers (in parentheses at the top of certain columns) refer to corresponding items described in 

Bull. U. S. Oeol. Survey No. 325, pp. 151-153.

t> The word "draft" is placed in quotation marks because it is misused when applied to the moving of 

gases or to the pressure difference wnich causes them to move.

c Taken as constant.

4781 Bull. 403 09 2
18 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

TABLE 2. Summary of observed data and calculated items of 21 tests made with the 

forward, boiler, U. S. S. Biddle, December 6,1907, to January 27, 1908 Continued.

Test

No.

1

1

2

. 3

4

5

6

7

8

9

10

11

12

13

14

15

1C

17

18

19

20

21

Toe*- -L Cob

No.

1

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

"Combustible"*a

consumed

(pounds).

22 (30)

7,738

7,167

7,427

6,967

7,864

9, 804

7,364

6,243

9,694

6,684

9,740

6,529

8,195

7,422

7,291

12, 108

6,843

8,474

10, 739

6,054

6,114

Ash and 

refuse in

dry fuel

(per cent).

23 (31)

15. 77

8.07

9.07

9.26

6.07

5.81

8.12

11.76

5.67-

6.67

6.00

8.57

3.94

7.18

5.99

6.45

6.59

4.66

3.87

5.24

6.25

Proximate analysis (per cent).

Fixed carbon.

In

moist 

coal.

24 (32)

74.29

73.57

74.57

70.75

70.54

72. 34

77.54

74.69

74.32

75.71

74.21

75.11

74.48

67.46

68.98

69.24

69.74

69.37

69.44

69.75

72.62

In "combustible."

25

79.97

79.97

79.20

75.74

75.32

77.56

83.96

81.98

81.89

81.48

80.52

81.16

80.64

74.98

75.81

74.76

74.63

74.62

75.06

74.98

'82.53

Ultimate analysis, dry basis (per 

cent).

Carbon.

33 (37)

82.58

83.39

84.39

84.98

84.23

82.64

84.38

83.61

83.77

83.21

84.53

83.06

83.69

80.95

82.00

16 I 83. 95

17

18

' 2019

21

84.12

83.75

84.05

84.13

79.18

Hydrogen.

34 (38)

4.55

4.49

4.65

4.57

4.61

4.39

4.44

4.29

4.23

4.54

4.37

4.49

4.42

4.73

4.73

4.82

4.72

4.76

4.72

4.65

4.36

Oxygen.

35 (39)

5.10

3.42

4.63

3. LI

3.93

5.87

3.19

3.55

2.86

4.16

2.80

4.32

3.60

4.52

3.86

4.57

3.85

4.03

3.92

3.77

4.69

Nitrogen.

36(40)

1.45

1.38

1.39

1.50

1.39

1.18

1.44

1.39

1.48

1.41

 1.40

1.37

1.45

1.49

1.50

1.53

1.42

1.37

1.38

1.49

1.31

Ash.

37(42)

5.55

6.60

4.28

4.92

4.94

5.04

5.84

6.16

6.91

5.89.

6.08

5.98

5.96

7.68

6.88

4.70

5.23

5.41

5.25

5.27

9.65

Volatile matter.

In

moist 

coal.

26 (33)

18.61

18.43

19.58

22.66

23.11

20.93

14.81

16.42

16.44

17.21

17.95

17.43

17.88

22.51

22.01

23.38

23.71

23.60

23.07

23.28

15.37

Carbon 

in refuse(per 

cent).

38 (44)

54.95

40.99

50.22

41.29

50.73

40.44

54.63

43.70

39.00

37.56

49.14

38.61

53.02

42.16

39.88

33.40

 27.26

27.26

47.03

44.12

30.43

In "combustihlo "

U1G*

27

20.03

20.03

20.80

24.26

24.68

22.44

16.04

18.02

18.11

18.52

19.48

18.84

19.36

25.02

24.19

25. 24

25.37

25:38

24.94

25.02

17.- 47

Earthy 

matter in 

refuse, including 

moisture 

(per cent).

89 (45)

45. 05

59.01

49.78

58.71

49.27

59.56

45.37

56.30

61. 00

62.44

50.86

61. 39

46.98

57.84

60.12

66.60

72.74

72.74

52.97

. 55.88

69.57

Moisture.

In

fuel as 

fired.

28(34)

1.64

1.50

1.04

1.76

1.48

1.78

1.92

2.91

2.50

1.26

1.87

1.57

1.79

2.55

2.29

2.81

1.39

1.71

2.36

1.79

2.61

Accompanying

.100 per 

cent ''combustible."

29

1.77

1.63

1.74

1.88

1.58

1.91

2.08

3.19

2.75

1.30

2.03

1.70

1.94

2.83

2.52

3.03

1.49

1.84

2.55

1.92

2.97

Ash.

30(35)

5.46

6.50

4.21

4.83

4.87

4.95

5.73

5.98

6.74

5.82

5.97

5.89

5.85

7.48

6.72

4.57

5.16

5.32

5.13

5.18

9.40

Fired per hour 

(pounds).

Dry fuel.

For

grate.

40(46)

1,718

2,389

1,139

1,225

1,676

2,627

1, 746

1,177

2,634

1,838

2,625

1,184

3,760

1,226

1,739

3,023

1,389

2,162

3,002

4,146

1,686

Per 

square

foot of

' grate.

41 (48)

29.62

41.20

19.64

21.12

28.90

45.29

30.10

20.29

45.41

31.68

45.26

20.41

64.83

21.14

29.98

52.12.

23.95

37.28

51.76

71.48

29.07

"Combustible"

(*).

42 (47)

1,474

2,152

1,039

1,118

1,542

2,433

1,567

1,044

2,394

1,684

2,388

1,074

3,458

1,095

1,578

2,816

1,291

2,018

2,789

3,832

1,491

Sulphur (separately determined).

Moist 

basis.

31 (36)

0.76

.71

.65

.90

.89

.86

.70

.97

.73

.78

.80

.77

.86

.61

1.01

.42

.65

.67

.66

.68

.79

Dry

basis.

32 (41)

0.77

.72

.66

.92

.90

.88

.71

1.00

.75

.79

.82

.78

.88

.63

1.03

.43

.66

.68

.68

.69

.81

Heat value per 

pound (B.t.u.).

Dry 

fuel. 

43(50)

14,845

14, 591

15,098

14,927

14, 879

14,933

14, 769

14, 720

14,702

14,980

14, 816

14, 794

14,805

14,368

14,564

14, 884

14,949

14,803

14,906

14, 796

14, 180

"Combustible."

44(51)

15, 715

15,622

15, 773

15, 699

15, 652

15, 726

15, 685

15, 686

15, 793

15,918

15, 775

15, 735

15, 743

15,563

15,640

15, 618

15,774

15,650

15,732

15,619

15,695

a The "combustible" factor in all columns of this table marked thus (*) is obtained by subtracting from 

the total weight of dry fuel fired the weight of ash therein, as figured from the chemical analysis, and further 

subtracting weight of the combustible in the refuse, the latter combustible being calculated from the total 

weight of refuse andMts analysis; the composition of the refuse combustible is loosely considered to be 

the same as that of the "combustible" of the dry fuel.
OBSERVED DATA AND CALCULATED ITEMS. 19

2. Summary of observed data and calculated items of .21 tests made with the 

forward boiler, U. S. S. Biddk, December 6,1907,-to January 27,1908 Continued.

Test 

No.

1

1

2

3

4

5

G

7

8

9

10

11

12

13

14

15

10

17

IS

19

20

21

Test 

No.

1

1

2

3

4

5

fl

7

8

9

10

11

12

13

14

15

10

17

18

19

20

21

Steam.

Moisture in 

(per

cent).

45 (54)

1.10

1.13

1.07

1.73

1.55

1.01

1.57

1.61

1.73

1.90

2.35

1.85

2.42

2. 1.0

1.98

2.25

1.68

1.71

2.32

2.51

2.50

Quality 

of.

46 (50)

99.22

99.20

98. 81.

98. 77'

98. 90

08.80

98.89

98.80

98.77

98. U5

98.33

98.69

98. 29

98.47

98.00

98.41

98.81

98.83

98. 40

98.23

98.19

Water fed to boiler (pounds).

Total.

47 (57)

68.579

58,940

'64.985

59,102

57,483

68,569

59, 121

57,811

75,855

55,607

78, 415

00,065

57,697

64,975

58,024

88,247

54,875

05,493

82,503

41,270

51,075

Equivalent evaporated 

from and at 212°.

Total.

48 (58)

83,989

72, 184

79, 470

72,335

70,359

83,874

72, 400

70,784

92,884

68,085

90,090

73,640

70,708

79, 040

71,850

108, 147

67,315

80,347

100,992

50,741

62, 710

Equivalent evaporation per

pound of 

Fuel as 

fired.

55 (09)

9.09

8.87

9.48

9.19

8.02

7.69

8.50

9.05

8.39

9.09

8.00

9.94

7.00

9.19

8'. 61

7.90

8.91

8.59

8.40

7:47

8.67

Dry fuel 

fired.

66 (70)

9.24

9.00

9.04

9.36

8.14

7.83

8.72

9.94

8.01

9.20

8.82

10.10

7.80

9.43

8.82

8.19

9.04

8.74

8.60

7'. 61

8.91

"Combustible" (*) 

67 (71)

10.77

9.99

10.57.

10.25

8.85

8.46

9.72

11.21

9.46

10.05

9.70

11.13

8.48

10.57

9.72

8.79

9.72

9.37

9.25

8.23

10.07

Per 

hour.

49 (63)

15,873

21,503

10,983

11,468

13,644

20,575

15,233

11.702

22,652

16,918

23,158

11,954

29,324

11,567

15,334

24, 750

12,550

18,900

25,812

31,547

15,018

Into dry 

steam.

60 (61)

83,333

71,606

78,525

71,445

69,586

82,917

71,596

69,977

91,742

67, 166

94,484

72,081

69,498

78,422

70,843

106,427

66,514

79, 407'

99,376

49,844

61,575

Horsepower developed.

In boiler.

68 (65)

460.1

623.3

318.3

332.4

395.5

596.4

441.5

339.2

656.6

490.4

671.3

346.5

850.0

335.3

444.5

717.4

363.8

548.1

748.2

914.4

435.3

. Percent 

of builders' 

rated. 6

69 (67)

166

225

115

120

143

215

159

122

236

177

242

125

306

121

160

254

131

197

270

330

157

Actually evaporated.o

Total.

51 (59)

68,044

58,468

64,212

58,375

56,851

67,787

58,465

57,152

74,922

54,856

77, 105

59,278

56,710

63,981

'57,803

86,844

54,222

64,727

81,183

40,540

50, 151

Per 

hour.

62 (62)

12,961

17,558

8,981

9,370

11, 147

16,821

12, 439

9,557

18,499

13,818

18,898'

9,750

23,928

9,437

12,511

20, 196

10,231

15,411

21,086

25,658

12,232

Efficiency of the

boiler, etc.

(*)

60 (72)

66.17

61.75

64.71

63.05

54.60

51.95

59.84

69.01

57.85

60.97

59.38

68.31

52.02

65.58

60.02

54.35

59.51

57.82

56.78

50.89

61.96

Including 

grate.

.61 (73)

60.11

59.57

61.66

60.55

52.83

50.64

57.02

65.21

56.56

59.31

57.49

65.93

50.88

63.38.

58.48

53.14

58.39

57.02

55.72

49.67

60.68

Evaporation.

Apparent per 

pound of coal 

as fired.

58(08)

 7.48

7.30

7.85

7.61

6.62

6.30

7.06

7.98

6.93

7.52

7.19

8.21

6.36

7.62

7.13

6.60

7.35

7.09

6.97

6.19

7.20

Per cent 

smoke.

62 (77)

64.50

60.89

58.75

69.54

70.54

67.20

29.88

35.87

30.57

48.75

37.86

31.02

37.81

47.41

48.84

43.03

46.14

49.28

21.71

51.33

31.86

Factor 

of.

54 (60)

1.2247

1.2247

1.2229

1.2239

1.2240

1.2232

1.2246

1.2244

1.2245

1.2244

1.2254

1.2201

1.2255

1.2257

1.2256

1.2255

1.2267

1.2208

1.2241

].2295

1.2278

Average

thickness of 

fuel bed 

(inches). «

68 (81)

12

14

8

16

16

6

10

8

16

8

10

8

10-12

8

10

12 8-9

8-9

10-12

12

10

o Corrected for quality of steam.

6 Arbitrarily rated, counting 10 square feet of heating surface to a boiler horsepower.

c Method of firing, side alternate.
20 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

TABLE 2. Summary of observed data and' calculated items of 21 tests made with the 

forward boiler, U. S. S. Biddle, December 6, '1907, to January 27, 1908 Continued.

Test 

No.

Analysis of dry flue gases (per 

cent).

C02. Os. CO.

Pounds of 

dry flue 

gases per 

pound of "combustible."

Sparks ejected 

(pounds).

During 

test.

Per 

hour.

Heat 

Value of 

1 pound of "combustible" 

(B.t. u.).

Heat balance, o

Heat absorbed 

by boiler (1).

B. t. u. Pr.ct.

Heat lost in 

dry flue 

gases (4).

B.t. u. Pr.ct

64 (84) 65 (85) 66 (80) 67 (88) 68 69 70 71 72 73 75

7.90

9. 00

9.27

10.52

11.70

12.41

9.80

9.16

10.27

10.37

10.40

9.50

11.86

10.00

10.97

9.85

9.58

9.60

9.36

10.30

10.40

10.53 

9.60 

9.44 

7.30 5.03' 

4.64 

8.22 

9.30 

7.95 

7.65 

7.40 

9.13 

5.53 

8.40 

7.00 

8.07 

8.20 

8.10 

8.12 

0.85 

7.47

0.12 

.08 

.03 

.14 

.00 

.00 

.00 

.00 

.00 

.02 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

.00

81.45

81.26

81.26

82.04

83.27

82.95

81. 92

81.54

81.78

81.96

82.20

81.37

82.61

81.00

82.03

82.08

82.22

82.30

82.52

82.85

82.13

26.97 

24.28 

23.59 20. 94' 

18.98 

17.03 

22..6S 

24.18 

21.88 

21.25 

21.60 

23.15 

18.83 

21.87 

20.09 

22.28 

23.06 

22.95

200

412

125

35

205

230

38.2

123.7

17.0

5.6

52.0

57.0

21.50

21.04

400

80

380

.180

210

410

60

240

440

380

180

97.0

13.2

160.0

26.5

45.5

95.0

11.3

57.0

114.0

240.0

44.0

15,717

15,022

15,773

15,699

15,052

15,726

15.685

15.686

15,793

15,918

15,775

15,735

15,743

15,563

15,640

15,618

15,774

15.050

15,732

15,019

15,695

10,401

9,647

10,207

9,898

8,546

8,170

9,387

10,825

9,136

9,705

9,367

10,748

8,189

10.207

9,387

8,489

9,387

9,049

8,933

7,948

9,725

66.17

61.75

64.71

63.05

54.60

51.95

59.84

69.01

57.85

60.97

59.38

68.31

52.02

65.58

60.02

54.35

59.51

57.82

56.78

50.89

61.96

4,342 

3,933 

3,199 

3,087 

3,371 

3,000 

3,289 

3,111 

3,497 

3,233 

3.841 

2', 879 

3,420 

2,714 

2,951 

3,529 

3,121 

3,503 

3,900 

3,988 

27.67

27.63

25.18

20.28

19.66

21.54

22.89

20.97

19.83

22.14

20.31

24.35

18.30

21.76

17.44

18.87

22.60

19.79

22.38

24.83

25.53

17.62

Heat balance, o

Smoke and flame

showing above

stack.

Loss due to moistureTest 

No.

In fuel (2).

B.t.u. Pr. ct.

Formed by

burning 

hydrogen (3).

B.t.u. Pr. ct.

Loss due to incomplete combustion of carbon in CO (5).

B.t.u. Pr. ct.

Loss in sparks.

B.t.u. Pr. ct.

Loss in escaping 

hydrocarbons, 

radiation, and

unaccounted for 

(6). F.

B. t. u. Pr. ct.

Per

76 77 78 79 80 81 84 85 86 87

0.15 

.14 

.15 

.16 

.14 

.18 

.18 

.27 

.23 

.11 

.18 

.14 

.17 

.24 

.22 

.26 

.12 

.16

'.22 

.17 

.25

591

592 

571 

578 

611 

602 

569 

536 

557 585' 

587 

555 

598 

594 

613 

621 

587 

608 

617 

629 

569

3.76

3.80

3.62

3.68

3.90

3.83

3.63

3.42

3.53

3.68

3.72

3.52

3.80

3.82

3.92

3.98

3.72

3.89

3.92

4.03

3.63

133

79

29

119

0

0

0

0

0

17'0

0

0

.0 

0 

0 

0 

0 

0 

0 

0

0.85 

.50 

.18 

.76

307

648

186

51

348

248

1.96

4.15

1.18

.32

2.22

1.58

.11

389

113

470

266

295

309

87

314

443

744

323

2.40

.72

2.99

1.71

1.89

2.36

.55

2.01

2.82

4.76

2.06

-81 

703 

1,558 

1,941 

2,751 

3,078 

2,412 1,172' 

2,560 

2,360 

1,563 

1,418 

3,033 

1,745 

2,360 

2,569 

2,573 

2,151 

1,798 

2,283 

2,474

-0.52 

4.50 

9.88 

12.37 

17.60 

' 19. 57 

15.38 

7.47 

16.25 

14.82 

9.91 

9.01 

19.26 

11.21 

15.08 

10.45 

10.31 

13.74 

11.43 

14.62 

14.48

0

7

1

6

65

214

13

0

6

19

24

0

59

1

7

9

16

8

13

14

1

608

360

720

660

480

508

480

664

452

480

420

686

292

764

500

456

600

420

420

240

420

0.0

2.0

.1

.9

13.5

42.8

2.7

.0

1.3

4.0

5.7

.0

20.2

.1

1.4

2.0

2.7

1.9

3.1

5.8

.2

a- Heat balance items (designated by numbers in parentheses under this heading) are explained in Bull. 

U. S. Geol. Survey No. 325, p. 153. 

,. J Flame readings 6 Per cent - Smoke readings
TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT. 2.1.

NOTES ON INDIVIDUAL TESTS.

Test 1, J-6'coal, run-of-mine. Coal caked badly. Fuel bed required much attention; the cakes had to be broken about every other firing. During the test the fuel 

bed was 12 to 14 inches thick.

It was impracticable to clean fire before closing test. After test was closed- and 

the fuel bed had entirely burned down the clinkers were removed from the grate, 

weighed, and charged to the test;. All ashes were then taken out of the ash pan, 

weighed, and charged to the test. It is possible that the weight of ash on this test 

is too high, because, when removing the clinkers from the grate, some free ash which 

really did not belong to the test fell into the ash pan and was weighed with the rest.

Test 2, J-6 coal, run-of-mine. Coal caked badly; fires had to be raked after each 

firing. The fact that the fire doors had to be partly open while raking the fire possibly accounts for the high oxygen content in the flue-gas analysis. It was difficult 

to keep.the fuel bed in good condition.

The fire was not cleaned before closing the test. After the test was closed, all the 

ashes were pulled out of the ash pan, weighed, and charged to the test. Then, after 

the fuel bed had entirely burned down, the clinkers were removed from the grate, 

weighed, and charged to the test. The firing was better on this test than on test 1; 

less coal was allowed to fall through the grate.

Test 5, J-6 coal, run-of-mine. Coal caked badly; it was necessary to break the cakes 

after every other firing. After closing the test the free ash was pulled out of the ash 

pan and weighed. Then, after the fire had entirely burned down, the clinkers were 

pulled out of the furnace, weighed, and charged to the test. The free ash which fell 

through the grate during the process of pulling clinkers was not charged to the test, as 

there was about an equal quantity of ash on the grate when the test was started. This 

method of determining ash and clinkers was used for all the following tests.

Test 4, J-6 coal in large briquets. Briquets burned freely and quickly and stayed 

together in the fire. Fire handled easily. Thickness of fire during test, 12 to 14 

inches.

Test 5, J-6 coal in large briquets. Briquets burned freely and quickly and stayed 

together in the fire. The fire was easily handled. Thickness of fire, 14 to 1C inches.

Test 6, J-6 coal in large briquets. Briquets burned freely and quickly and did not 

crumble in the fire. The fire was apparently in good condition during the entire test. 

Thickness of fire, 14 to 16 inches. Excessive flaming in the stack was observed.

Test 7, 3-11 coal, run-of-mine. Coal caked badly; fire required raking after every 

other firing. About 100 pounds of coal fired at a time, alternately on each side half 

of the grate every three or four minutes. Thickness of fire, 10 to 12 inches. Water 

was used in the ash pan during the test.

Test 8, J-ll coal, run-of-mine. Coal caked badly; fire required breaking up every 

other firing. About 75 to 100 pounds of coal fired at a time, alternately on each side 

half of the grate every four or five minutes. Thickness of the fuel bed, about 8 inches. 

Water was used in the ash pan.

Test 9, J-ll coal, run-of-mine. Coal caked badly. It was necessary to break up 

the cakes after every other firing. About 100 pounds of coal was charged alternately 

on each side half of the grate every two or three minutes. Thickness of fuel bed, 

about 14 to 16 inches. Water was used in the ash pan during the test.

Throughout this test much fuel was blown out through the stack in the form of 

cinders or sparks. At the close of the test'the deck was covered with a layer of sparks 

varying from one-eighth to three-eighths of an inch thick.

Test 10, J-ll coal in small briquets. Briquets burned freely; stayed together in the 

fire. About 100 pounds were charged alternately on each side half of the grate every 

three or four minutes. Fire handled easily and did not require much attention. 

Thickness of the fuel bed, about 8 inches. Water was used in the ash pan.
22 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

Test 11, J-ll coal in small briquets. Briquets burned freely; stayed together in the 

fire. About 100 pounds were'fired alternately on each side half of the grate every 

two or three minutes. Fire handled easily. Effort was made to keep the fuel bed 

8 to 10 inches thick. Better results seemed to have been obtained with a light fire 

than with a heavy one. Water was used in the ash pan.

Test 12 j J-ll coal in small briquets. Briquets burned freely; did not crumble in 

the fire. About 100 pounds charged alternately on one-half of the grate every five 

or six minutes. Fire handled easily. Thickness of fuel bed, about 6 inches. Water 

was used in the ash pan.

Test 13, J-ll coal in small briquets. Briquets burned freely and made a very hot 

fire. About 130 pounds charged alternately on each side half about every one or 

two minutes. The fuel bed was easily handled. Thickness, about 10 to 12 inches. 

Water was used in the ash pan.

Test 14, J-9 coal, run-of-mine. ^Coal caked badly. Fire had to be raked after every 

other.firing. About 300 pounds was charged alternately on each side half of the 

grate every four or five minutes. Thickness of fuel bed, about 8 inches. Water was 

used in the ash pan.

Test 15, J-9 coal, run-of-mine. This coal was exceptionally bad in regard to caking. 

The fuel bed had to be raked every other firing and sliced about every fourth or fifth 

firing in order to keep it loose. About 300 pounds was charged alternately on each 

side half of the grate every two or three minutes. Thickness of fuel bed, about 10 

inches. Water was used in the ash pan.

Test 16, J-9 coal, run-of-mine. Coal caked considerably. Fuel bed had to be raked 

after every other firing. About 150 pounds fired alternately on each side half of the 

grate every three or four minutes. Thickness of fire, about 12 inches. Water was 

used in the ash pan. During the latter part of this test the screens in the spark catchers 

. were burned out so as to catch only about three-fourths of the full tenth of the sparks.

Test 17, J-9 coal in small briquets. The briquets swelled in the fire, and their surfaces opened cracks in many places, but did not crumble unless broken with a rake. 

About 75 pounds charged alternately on each side half of the grate every three or 

four minutes. These briquets burned best in this furnace at this rate of combustion, 

with about an 8-inch fuel bed. When the fuel bed was thickened the gases flamed in 

the stack.

Test 18, J-9 coal in .small briquets. About 120 pounds fired alternately on each 

side half about every three minutes. These briquets burned best at this rate of combustion, with about an 8 to 10 inch fuel bed. When the bed was thicker, gases flamed 

in the stack. Water was used in the ash pan.

Test 19, J-9 coal in small fcn'gueis. Briquets swelled in the fire, but did not crumble. 

About 120 pounds fired alternately one each side half of the grate about every two 

minutes. To avoid flaming the stack, the fuel bed could not be made thicker than 

12 inches.

Test 20, J-ll coal in small briquets. About 10 per cent of the briquets were crumbled 

when fired. This test was short on account of shortage of fuel. After it was well 

under way the rate of combustion was much higher than the average given in the 

table. The method of firing used was side alternate, as in the previous tests. Thickness of fuel bed, about 12 inches; when thicker, flaming began in the stack. A 

higher rate of combustion and capacity of boiler could have been obtained with these 

briquets if more fuel had been available, and even higher rates would be obtainable 

by running the fan faster, as it well could be.

Test 21, J-10 coal, run-of-mine. Coal caked badly, making it necessary to rake the 

fuel bed after every other firing. Method of firing, side alternate, as in all the prior 

testa. Thickness of fire, about 10 inches.
TESTS OF COALS AHD BRIQUETS OK TORPEDO BOAT. 23

DATA AND CALCULATIONS SHOWN GRAPHICALLY.

EXPLANATION OF FIGURES.

Figures 4 to 10, inclusive, show graphically the relations of the 

results of the tests to the rate at which coal was burned. . The abscissas are pounds of dry coal fired per square foot of grate per hour; 

the ordinates are various quantities and are given directly at the 

left of each group of curves or group of points. All points are for 

individual tests; trials on large briquets are denoted by solid rectangles, those on small briquets by dots, and those on run-of-mine 

coal by light circles. Where it was possible to discriminate between 

the kinds of fuel solid heavy lines were drawn through points representing the results on coal, long dash lines through points representing results on large briquets, and short dash lines through points 

representing tests on small briquets.

ON CAPACITY DEVELOPED.

The points shown in succession at the top of figure 4 represent the 

relation between the rate of combustion and the capacity developed 

by the boiler. In order to have a basis of comparison between these 

tests and tests made on other boilers the rated capacity of the Normand boiler of the Biddle was assumed as 277.6 boiler horsepower; 

that is, 10 square feet of heating surface is taken to be equivalent to 

1 boiler horsepower. All the points of this group fall so nearly along 

one straight line that it is hard to tell whether the run-of-mine coal 

or the briquets did better. The shape and the inclination of the curve 

passing through these points indicate that the capacity increases 

almost directly with the rate of combustion; this fact is perhaps 

self-evident the greater the amount of coal burned the greater the 

amount of heat generated in the furnace and the greater the amount 

of heat absorbed by the boiler. . It is worthy of note that on all the 

tests this particular boiler with its heating surface developed two 

or three times as much boiler horsepower as stationary boilers ordinarily do. This indicates that the rule of thumb which states that 

10 square feet of heating surface are required to give 1. boiler horsepower has no substantial foundation.

ON EVAPORATION.

The points in the middle group of figure 4 show the relation between rate of combustion and evaporation per pound of dry fuel 

fired, and indicate that the run-of-mine coal and the small briquets 

do about equally well, the briquets probably giving a very slightly 

better evaporation than the coal. The large briquets fall considerably lower in evaporation than the other two fuels. This lower 

evaporation, however, was not caused by the inferiority of the
TESTS OP COALS AND BRIQUETS ON TORPEDO BOAT.

51 300

1. s

>>

200

ss

25

.2 20

|& 

II

10 ZO- 30 40 50 60 - 70 80 90

Pounds of dry coal fired per hour per square foot of grate surface

100,

FIGURE 4. Effect of increasing rate of combustion on (1) percentage of boiler's arbitrarily rated horsepower developed; (2) equivalent evaporation per pound of dry coal fired; and (3) pounds of dry 

chimney gases per pound of "combustible."
DATA AND CALCULATIONS SHOWN GRAPHICALLY. 25

briquets as a fuel, but was due to the fact that the fuel beds carried 

on these tests were too thick, and the resulting insufficient air supply 

caused incomplete combustion. Although the flue-gas analyses on 

these tests show a very low CO percentage, the presence of flames in 

and above the stack indicated that combustible gases other than CO 

were escaping. It was thought, because the voids in the fuel bed 

of large briquets were higher in percentage than with the other 

fuels, that better results could be obtained with the thicker fuel beds. 

This reasoning, however, proved false, at least with the particular 

briquets tested.

A general curve drawn through these points indicates that the 

evaporation per pound of dry coal drops considerably as the rate of 

combustion increases. Thus at the rate of 20 pounds the equivalent 

evaporation per pound of dry coal is a little above 10 pounds, while 

at the rate of 71 pounds the equivalent evaporation is less than 8 

pounds of water. This drop in evaporation when the rate of combustion increases is chiefly due to less complete combustion of the 

fuel; it will be shown later that only a little of it is due to the inability 

of the boiler proper to absorb the heat.

ON DRY FLUE GASES.

The points in the lowest group of figure 4 show the relation between 

the rate of combustion and the weight of dry flue gases per pound 

of "combustible" a ascending from the grate.

In general, the points indicate that with all three kinds of fuel 

the weight of air used to burn 1 pound of "combustible" decreases 

as the rate of combustion increases. This feature is well worthy 

of note in the respect 'that the higher the gas-pressure drop through 

the fuel bed (the resistance of the latter remaining about the same) 

the higher is the velocity of air passing through the burning fuel 

and the higher is the rate of combustion; now, the dropping of the 

points at the right hand tells us that the combustion ^more than 

keeps up with the velocity of the current of air through the fuel bed. 

This statement is true throughout the full range of rate of combustion 

ordinarily used in practice.

The points also show that on the average about the same weight 

of air is used to burn 1 pound of "combustible" whether the fuel 

be run-of-mine coal or small briquets. With the large briquets the 

weight of air used was much less. This fact undoubtedly accounts for 

the less perfect combustion and lower evaporation on tests with 

large briquets.

o The combustible here referred to is the "combustible" in the fuel as fired, figured from chemical analysis 

minus the combustible lost in ash and refuse, but including the combustible ejected in sparks. In this ' 

bulletin the word combustible is placed in quotation marks whenever it is loosely used in the sense of 

"coal free from moisture and ash."
TESTS OP COALS AND. BBIQUETS ON TOKPEDO .BOAT.

ON SMOKE.

The points in the lower group of figure 5, that is, the points which 

are connected by broken lines, are intended to show the relation 

between the per cent of black smoke and the rate of combustion. Each 

point in the figure represents the average of the whole test. The percentage of black smoke refers to Kingelmann smoke charts; chart 

1 is called 20 per cent black .smoke, and each successive chart is 20 

per cent higher, so that chart 5 is 100 per cent black. Fractional 

gradations are similarly interpreted within the respective 20 per 

cent steps.

The lines connecting the points of each kind of fuel fall in such 

a zigzag fashion that there does not seem to be any relation between 

the blackness of smoke and the rate of combustion. The most 

reasonable conclusion probably is that the combustion space of the 

furnace is so small and the "cold" heating surface of the boiler is 

so near the fuel that even the rate of combustion of 20 pounds of 

fuel per square foot of grate is too high to burn the gases and tarry 

vapors so that the smoke-producing property of the furnace apparently 

can not be made any worse by increasing further the rate of combustion. The smoke-producing property of this furnace lies in the 

fact that the path of the gases from the fuel bed into the nests of the 

water tubes is so short that the tar vapors which are important 

constituents of visible smoke have not sufficient time to burn before 

they are driven among the tubes where the combustion stops. As 

all these visible tars are in liquid or solid form their complete combustion requires considerably more time than is afforded to them 

on their way from the fuel bed to the nests of tubes. It seems then 

that no amount of care taken in firing smoky fuels in this type of 

furnace will produce smokeless combustion.

The points of the same group show that the tendency of a coal 

to smoke is not reduced by briquetting the fuel; in fact it is shown 

that rather more smoke was made with briquetted than with runof-mine coal. The high percentage of black smoke made with the 

large briquets is partly due to a smaller supply of air, as is shown 

by the lowest group of points in figure 4.

The points of the upper group of figure 5 show the amount of 

flaming observed above the stack. Every time the smoke observer 

read smoke he also made a note of flaming above the stack when 

the same was observable. The upper ordinate of figure 5 represents 

the number of times flame was observed above the stack expressed 

as a percentage of total smoke readings. It is shown that there was 

more flaming with either style of briquet than with run-of-mine coal.
DATA AND CALCULATIONS SHOWN GRAPHICALLY.

40

35

1

30

Is 25 

3

«+H

o 

<u 20

8, l5

1" 43

80

70

60

 g;

50

I 30 

*

20

20 30 50 60 70 80 90. 100'

: Pounds of dry coal fired per hour per square foot of grate surface

FIGURE 5. Effect of increasing rate of combustion on flame observations as a percentage of total 

number of smoke observations (above) and percentage of black smoke (below).
28 TESTS OF COALS AND BKIQUETS ON TORPEDO BOAT.

ON DISTRIBUTION OP HEAT.

Figure 6 and the two lower groups of points of figure 7 show how 

the distribution of the heat of the "combustible" ascending from 

the grate varied with the rate of combustion. 'All heat quantities 

in these two figures are expressed in percentage of the total heat in 

"combustible" ascending from grate.

ON HEAT LOSSES.

The points grouped at the top of figure 6 represent the heat carried 

up the stack in the moisture formed, by burning of hydrogen and 

also in the free moisture in the coal (item 2 + item 3 in the heat 

balance). The points show that the heat loss due to moisture in 

the flue gases is very nearly the same for all rates of combustion. 

There is also little or no difference between the three kinds of fuel.

The points of the middle group of figure 6'show the relation of the 

heat lost in dry flue gases (item 4 in the heat balance) and the rate 

of combustion. In general, the points show that this heat loss 

increases but little with the rate of combustion. On the average 

this increase is 4 to 5 per cent as the rate of burning the fuel increases 

from 20 to 70 pounds. This item does not show any essential difference between the three kinds of fuel.

The points in the lowest group of figure 6 show the relation of the 

heat loss in sparks to the rate of combustion. The indication is that 

this loss increases almost directly with the rate of combustion. The 

points also show somewhat higher losses in sparks in the tests of 

run-of-mine coal than of the small briquets. There are not enough 

tests on large briquets to warrant definite conclusions regarding the 

spark losses. The higher spark loss shown in tests with run-of-mine 

coal was undoubtedly due to the high percentage of slack in the coal 

and also to the fact that the fuel bed had to be frequently stirred. 

The stirring of the fuel bed loosened small particles of burning 

fuel which were apt to be carried out through the boiler and stack 

by the current of gas. The higher spark loss with increasing rate 

of combustion resulted from higher pressure drops ("drafts") and 

higher velocities of the furnace gases which had to be maintained in 

order to effect the higher rates of combustion.

ON HEAT ABSORPTION.

The points in the middle group of figure 7 show the relation of the 

rate of combustion to the heat absorbed by boiler (item 1 in heat 

balance). As stated before, this heat is expressed as a percentage 

of the total heat of the "combustible" ascending from the grate; in 

.other words, this item is the ratio of the two heats multiplied by 100. 

Generally this ratio is called the " efficiency of the loiler," and is so
DATA AND CALCULATIONS SHOWN GRAPHICALLY. 29

s 4

o 

« ~2

30

.£ 20

§ o

I

10 30 30 40 50 ' 60 70 80 90.

.Pounds of dry coal fired per hour per square foot of grate surface

100

FIGURE 6. Effect of increasing rate of combustion on (1) percentage of heat lost in moisture in stack 

gases; (2) percentage of heat lost in dry chimney gases; and (3) percentage of heat lost in sparks.
30 TESTS OP COALS AND BRIQUETS ON TORPEDO BOAT.

^ 90 :::::-::::E::

j^CO : ------- ^^Q 

,o> <u ------~X^C

^ § ~' 2:

«% 85 "L-

£ <U. ^ __

 f... p>? : :::::: ::

*> C x«

sg ::::::::::::: ^n*n

P« '

75 - -- 

S

 * ^

"Q) "^.^ S1jj£ es - fc£T -4-3 0) <M wv ^

l^t- -L-v

 §£& -

£ o c

0«J3 <" rn

^j ojtc

"ga <u " ts-2 &

,g£| 55 -- 

«H-e°

O <u O)

§S-| 50

«SJ<8 '° = = =

1^

45 _______ 

20 -- ------ --- -

* W _

og ________:::::

 + * C3 i cr- g-S 15

5+j sS :::::::::: [:: 8* - Z -

~ S 10 J 

t^j O V) fc g^ *" :

ts c $ -

8 & _

43 5

 HlR

o J 

 £ c

|| o :::::::::::::

§sl °:: ::::: :::: ft S - -

J^Lj. ____ 

 ^ l " i~\*~~ ~~"

cy "~~rK = ~-=

i *

,

-~Q-- -- -- -----

^^ ^

^- v O~ J3: Ix ^

S ^ v «

s ,~

m **\^J~

^^ ^ ^

"1 ' '§^^

" 

_.

' '

1 L-__

i r

f ijj-.

3? r- -

1

J l

E'

- = - = -- -----

^

L_

"1

10 . ZO 30 40 50 60 70 80 90

Pounds of dry coal fired per hour per square foot of grate surface

100

FIGURE 7. Eflect of increasing rate of combustion on (1) percentage of true boiler efficiency; (2) percentage of heat of "combustible" absorbed by boiler, from heat balance (boiler efficiency 72*); and 

(3) percentage of heat of " combustible" unaccounted for in the heat balance.
DATA AND CALCULATIONS SHOWN GRAPHICALLY. 31

denoted by the code of the American Sbciety of Mechanical Engineers, where it is defined as "the heat absorbed by the boiler per 

pound of combustible divided by. the heat of 1 pound of combustible."

The indication of the points is that as the rate of combustion increases the boiler absorbs a considerably smaller percentage of the 

total heat of the "combustible" ascending from the grate. This 

apparently large decrease in the boiler efficiency is, however, rather 

the fault of the furnace as a heat generator than of the boiler as a 

heat absorber; in other words, it is mainly due to the drop in furnace efficiency. As the rate of firing coal increases, the volume of 

gases generated in the fuel bed per unit of time increases in the same 

ratio. The result is that this increasing volume of gases must pass 

through the combustion space of the furnace at a higher velocity, 

and therefore a proportionately shorter time is afforded for burning 

any combustible gases or tar vapors contained in the furnace gases. 

As a result of this shortened time the combustible gases and tars are 

only partly burned. Thus, as the rate of firing coal increases, the 

combustion becomes more.and more incomplete.

The potential heat of the combustible gases and tars leaving the 

furnace and passing out through the boiler and stack is not liberated 

and therefore is not available for absorption by the boiler. Liberation of heat from fuel is the function of a furnace, and therefore 

any olrbp in "boiler efficiency," as the term is commonly used, caused 

by failure of the furnace to liberate all the heat of the fuel, is directly 

chargeable to the furnace.

ON UNACCOUNTED-FOR LOSSES.

The determination of the tars and the combustible gases, other 

than CO, escaping from the furnace is extremely difficult, so that 

the incompleteness of combustion ordinarily can be estimated only 

by an indirect method.. The usual method is that employed in making a heat balance such as is presented for these tests in columns 

72-85, of Table 2. In this heat balance all the losses are accounted 

for except the radiation loss, the loss due to incomplete combustion 

of hydrocarbon gases and tars, and a few other minor losses. The 

remainder of the heat not accounted for (commonly called the "unaccounted for") is principally the loss due to radiation and to incompleteness of combustion. . Unfortunately all the errors of observations, of sampling, and of chemical determinations .are accumulated 

in the "unaccounted for," so that the losses by radiation and by 

incomplete combustion can be only roughly estimated by taking all 

the possibilities of error into consideration.

The points in the lowest group of figure 7 have been plotted to 

show the relation between the "unaccounted for" in the heat balance and the rate of combustion. For reasons previously given, the 

points do not fall along a single line. The two lowest points in the
32 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

figure represent the first two tests made, in which the flue-gas analysis is unreliable because of leaky joints in the gas-sampling device. 

On account of this leak the weight of air used to burn 1 pound of 

" combustible/; calculated from the gas analysis, is too high, and 

consequently the loss up the stack unduly high, leaving the unaccounted-for loss either too low or negative. This illustrates how 

errors in data affect this item.

The general indication of this group of points is that the unaccounted-for loss increases with the rate of combustion. The radiation loss depends on the temperature of the radiating surfaces of the 

boiler and therefore should rather decrease in percentage with the 

increasing capacity accompanying the increased rate of combustion. 

The increasing unaccounted-for loss when the rate of combustion 

increases may then be rightly ascribed to the increasing incompleteness of combustion. This fact supports the conclusion arrived at 

in discussing the middle group of points of the same figure, namely, 

that the drop in the percentage of heat absorbed by the boiler is 

mostly due to incomplete combustion of tar vapors and combustible 

gas other than CO.

ON RUN-OF-MINE COAL AND BRIQUETS. .

Referring again to the middle group of points of figure 7, and considering the three kinds of fuel, it is plain that as far as efficiency of 

the steam-generating apparatus is concerned, there is no advantage 

in briquetting the fuel. The run-of-mine coal does as well as the 

small briquets and perhaps better than the large ones. However, 

any deductions in regard to the efficiency of large briquets must 

necessarily be reserved until more tests have been made with them. 

The three tests herein reported were run under rather unfavorable 

conditions for the good combustion of these briquets. It has been 

already said that in an attempt to reduce the amount of excess air 

used in combustion, for the purpose of obtaining high furnace temperature, the latter being one of the requisites for high economy, 

the fuel bed was carried somewhat too thick (14 to 16 inches). This 

thickening of the fuel bed and the resulting reduction of air supply 

very likely caused so much incomplete combustion that the over-all 

efficiency dropped considerably. Subsequent tests disclosed the fact 

that in this particular furnace it is not well to increase the C02 in 

the flue gases over 10 or 11 per cent, inasmuch as the combustion 

space above the fuel bed is too small. This deduction applies to 

Now River coals; for Pocahontas coal it would probably have to be 

somewhat modified.

ON FLUE-GAS AND FURNACE TEMPERATURES.

In figure 8 the points of the highest group are the averages of furnace temperatures for each test; the points in the middle group are 

the averages of flue-gas temperatures for each test; both are platted
DATA AND CALCULATIONS SHOWN GEAPHICALLY. 33

'3000

2900

 fa

*>.

2700

2600

J.-2500

2400

,2300

,2200

(fa 

fi

1

il

I

IE

$00

800

700

600

500

90

80

70

O

O O

/£: 0 10 .20 30 40 50 ,60 TO .80 90 100

Pounds of dry coal fired per hour per square foot .of grate surface

FIGURE 8. Relation between rate of combustion and (1) furnace temperature in degrees Fahrenheit; (2) 

flue-gas temperature In degrees Fahrenheit; and (3) true boiler efficiency In percentage.

4781 Bull. 403 09 3
34 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

with the rate of combustion as abscissas. In general, both temperatures seem to rise with the rate of combustion; however, this rising * l O

may be an incidental feature whose portrayal was not the object of 

platting the temperatures. The object of platting was to show a 

peculiar relation between the two temperatures, which relation 

seems to be but little affected by the rate of combustion. The furnace temperature here platted is the temperature of the furnace 

gases as they enter the boiler. The flue-gas temperature is the temperature of the gases as they leave the heating surface of the boiler. 

The difference between the two is the drop in temperature of these 

gases due to the absorption of heat from them by the boiler. As the 

weight of gases entering the boiler and the weight of gases leaving the 

boiler is the same (neglecting leakage), the temperature drop of the 

gas is proportional to the heat absorbed by the boiler. In this 

reasoning it is assumed that the specific heat of furnace gases at 

constant pressure remains constant, which is not strictly true. 

Recent'experiments show that the specific heat of C02 and other 

gases increases appreciably with temperature. However, as the 

consideration of the small variations in the specific heats of furnace 

gases would change the final results only by a fraction of a per cent, 

it was thought best not to complicate the course of reasoning by considering the variations in specific heat of the furnace gases. Since 

heat flows only from a hotter body to a colder one, it is possible for 

the boiler to reduce the temperature of the gases down to its own, 

or to the temperature of the water in the boiler, which is presumably 

the same as the temperature of the steam at the pressure under 

which the boiler is working. Therefore, the difference between the 

furnace and the steam temperature is called the available temperature drop for the furnace gases, and the heat in the furnace gases

which is above the temperature of the steam in the boiler is called 

the heat available for absorption. The ratio of the heat which the 

boiler actually absorbs to the heat which is available .for absorption 

is called the true boiler efficiency. This ratio is the only true measure 

of the boiler's ability to absorb heat. The boiler efficiencies ordinarily 

used do not take into consideration the fact that part of the heat in 

the furnace gases is below the temperature of the boiler and, therefore, can not be absorbed by the boiler.

It has been stated that the heat absorbed by the boiler is proportional to the temperature drop of the furnace gases as the latter pass 

through the boiler. Applying the same reasoning, it can be said that 

the heat available for absorption is proportional to the available 

temperature drop. Therefore the ratio of the two temperatures is the 

same as the ratio of the two heats. This being so, it is possible to 

obtain the true boiler efficiency by calculating the ratio of the actual 

drop to the available drop in temperature of the furnace gases.
DATA AND CALCULATIONS SHOWNA GRAPHICALLY. 35

This ratio has been calculated for most of the tests reported in this 

bulletin and is given, with the method of calculating it, in Table 3.

TABLE 3. Data used in calculating that portion of true boiler efficiency which is a consequence of heat absorption by convection only.

Test 

No.

1

1 

2. 

3 

4 

5

G

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21

Fuel used.

2

Hun-of-minecoal. . .. 

.....do.'..............

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

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

Run-of-mine coal. . . . 

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

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

Small briquets.......

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

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

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

Run-of-mine coal.. . . . 

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

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

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

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

Run-of-mine coal.. . . .

Dry fuel 

fired per 

square foot 

of grate 

per lioiir 

(pounds).

3

' 29. 62 41.20' 

19. 64 

21.12 

 28. 90 

" 45. 29 

30.10 

20.29 

45.41 

31.68 

45. 26 

20. 41 

64.83 

21.14 

29.98 

52.12 

23. 95 

37.28 

51.76 

71.48 

29.07

Temperature (° F.).

In stack.

4

739 

739 

646 

681 

802 

919 

655 

597 

728 

696 

797 

583 

807 

583 

668 

716 

637 

709 

752 

817 

601

In furnace.

5

2,673 

2,615 

2,367 

2,460

2,580 

2,273 

2,347 

2,624 

2,662 

2,921 

2, 633 

3, 097 

2,502 

2,881

2,442 

2,765 

2,950 

3,070 

2,498

Of steam.

6

380 

380 

380 

381 

379 

380 

379 

380 

379 

379 

380 

379 

380 

383

383 

384 

382 

380 

383

Column 5 minus 

Column 

4.«.

7

1,934 

1,876 

1,721 

1,779

1,007 

1,018 

1,750 

1,896 

1,966 

2,124 

2,050 

2,290 

1,919 

2,213

1,805 

2,056 

2,198 

2,253 

1,897

Column 

6.&

8

2,293 

2, 235 

1,987 

2,079

2,207 

1,893 

1,968 

2,244 2,283' 

2,542 

2,253 

2,718 

2,122 

2,498

2,000 

' 2, 381 

2,568 

2,690 

2,115

Column 7 

divided by 

column 8.c

9

84.7 

84.0 

80.6 

85.6

75.6 

85.4 

89.0

.84. 6 

86.1 

83.6 

90.9 

84.3 

90.5 

88.5

87.6 

86.3 

85.5 

83.8 

89.6

a Column 5 column 4 = approximately the actual temperature reduction effected by the boiler. 

f> Column 5 column 6 = maximum theoretical reduction of temperature by a perfect boiler, 

c Column 7 -f- column 8 = the true boiler efficiency so far only as heat absorption by convection is concerned.

ON TRUE BOILER EFFICIENCY.

The results shown in the last column of Table 3 are platted at the 

bottom of figure 8 as true'boiler efficiency. These points and the 

curve passed through them show the relation between the true boiler 

efficiency and the rate of combustion. Thus as the rate of combustion 

increases from 20 to 71 the true boiler efficiency drops only 4 per cent. 

The indication is that as the rate of combustion increases the true 

boiler efficiency remains .nearly constant. This is the relation of the 

temperature of the furnace to that of the flue gas already discussed; 

that is, the temperature difference between the gas in the furnace and 

in the flue bears a constant ratio to the temperature elevation of the 

furnace gases above the temperature of the steam in the boiler, or, in 

other words, the flue-gas and furnace temperatures rise and fall 

together, no matter what the rate of combustion may be. It should 

be borne in mind, however, that in these statements the phrase "heat 

absorbed by the boiler" refers only to the heat which the boiler 

absorbs from the furnace gases as the latter pass through the boiler, 

or the heat which the boiler receives by convection. The boiler 

receives heat also by radiation from the fuel bed and from the incan-
36 TESTS OF COALS AND BRIQUETS ON TOEPEDO BOAT.

descent gases while the latter flow'through the furnace. The furnace 

temperature recorded on these tests is the temperature of the gases 

about as they enter the nests of tubes.

This agrees very well with laboratory experiments made by the 

United States Geological Survey on small multitubular boilers fed 

with air heated in an electric furnace. The results of these experiments are to be given in a bulletin of the United States Geological 

Survey now in preparation.

One point in figure 8, representing a test on large briquets, shows 

low efficiency because of the unduly high temperature of the flue 

gases. By referring to figure 5 it is seen that the same test shows 

unusual flaming in the stack. The explanation is that the flue gas 

contained a large percentage of combustible gases which burned in the 

stack and caused the flaming and also produced a much higher fluegas temperature. This high flue-gas temperature is not chargeable 

against the boiler for the reason that the heat was generated in the 

stack after the gases had passed the heating surface of the boiler. 

Such heat could not be available for absorption.

The true boiler efficiency has been also platted in figure 7 on the 

same scale as the commonly used boiler efficiency (item 72*) for 

the purpose of comparing the two. It is quite apparent that the 

"boiler efficiency" drops much faster than the true boiler efficiency 

with the increasing rate of combustion. In previous discussion of 

the middle curve.of figure 7 it has been said that the boiler efficiency 

drops at the high rates of combustion because the furnace fails to 

develop all the heat in the fuel and not because the boiler does not 

absorb heat fast enough. This statement is confirmed by the true 

boiler-efficiency curve; the latter drops only about 4 per cent while 

the boiler efficiency, or rather the efficiency of the whole steamgenerating apparatus which it really is, drops 14 per cent. At least 

10 per cent of this total drop of 14 per cent is very likely due to 

the drop of furnace efficiency.

ON PRESSURE DROP.

The points grouped at the top of figure 9 show the relation between the pressure drop through the fuel bed and the rate of combustion. The pressure drop through the fuel bed was obtained by 

subtracting the absolute pressure over the fuel bed from the absolute pressure in the ash pit. Although the points do not fall along 

a single curve, the indication is that the pressure drop through the 

fuel bed increases with the rate of combustion. With any fuel of 

uniform size this relation is a necessity; to burn more fuel more air 

must be passed through the fuel bed, and to pass more air through 

the fuel bed there must be a higher pressure drop. Different sizes 

of fuel offer different resistances to the passage of air through them
DATA AND CALCULATIONS SHOWN GRAPHICALLY. 37

It

-2t»H >-> o

O OJ

*O o 

gS |

I

I 300

§ 200

100

10. ZQ 30 40 50 60 70 80 90

Pounds of dry coal fired per hour per square foot of grate surface

100

FIGURE 9. Relation of increasing rate of combustion to (1) pressure drop ("draft") through fuel bed 

in inches of water; (2) pressure drop through boiler in inches of water; and (3) pounds of moist sparks 

ejected from the stack per hour.
38 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

and therefore different pressure drops must be used with different 

fuels to obtain the same rate of combustion. As three different 

kinds of fuels are represented on the figure, the points are somewhat scattered. The run-of-mine coal was a mixture of various, 

sizes and therefore offered higher resistance to the passage of air, 

and a higher pressure drop than with the briquets had to be maintained to obtain the same rate of combustion.

In the same figure the points of the middle group show the relation 

between the pressure drop through boiler and the rate of combustion. 

The pressure drop through the boiler was obtained by subtracting 

the absolute pressure at the base of the stack from the absolute 

pressure in the furnace. Since the pressure at the base of the 

stack was recorded in inches of water below atmospheric pressure 

and the pressure'in the furnace in inches of water above atmospheric pressure, the required difference is obtained by adding the 

two quantities.

These points fall much better along a single curve than the upper 

group. This close agreement among the points is due to the fact 

that the resistance of the gas passage of the boiler remains constant. To put the same volume of gas through the boiler the same 

pressure drop is needed, no matter what the fuel burned may be, 

so long as the temperature remains about the same. The curve 

shows that the pressure drop through the boiler increases a little 

faster than the rate of combustion. The shape of the curve suggests 

the law which is commonly used in connection with the flow of 

gases; that is, the pressure drop through the boiler varies as the 

square of the rate of combustion.

ON SPARKS.

The points of the lowest group of figure 9 show that the weight 

of sparks ejected from the stack rises rapidly as the rate of combustion increases. . This, of course, can be expected, because in 

order to obtain a higher rate of combustion a higher pressure drop 

had to be maintained through the fuel bed, and the resulting increased Velocity of gases carried more sparks away. There does 

riot seem to be much difference in the weight of sparks when using 

the three kinds of fuel; briquets are nearly as bad as run-of-mine 

coal, at least within the range of the rates of combustion investigated.

ON WEIGHT OF AIIl.

The upper curve of figure 10 shows the relation between the weight 

of air supplied to the furnace and the rate of combustion. The weight 

of air for platting these points was obtained by multiplying the total 

weight of "combustible" burned per hour by the weight of air used 

per pound of "combustible," as figured from the analysis of the flue 

gases. The curve shows that the total weight of air supplied to the
DATA AND CALCULATIONS SHOWN GRAPHICALLY. 39

80

2 70

60

.2 50

1in 

 3 '40

30

20

800

700

600

400

200

100

BL

0

10 20 30 40 50 60 70 80 90 '100

Potmds of dry coal fired per hour per square foot of grate surface

FIGURE 10. Relation between rate of combustion and thousands of pounds of air supplied by the fan 

per hour (above), and speed of fan in revolutions per minute (below.)
40 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

furnace increases directly with the rate of combustion. In other 

words, to double the rate of combustion twice as much air must be 

supplied; to triple the rate three times as much air must be supplied, 

and so on. This relation is quite natural and could be expected. 

The kind of fuel seems to make no difference.

ON SPEED OF FAN.

The lower curve of figure 10 shows, the relation of the rate of combustion to the speed of the fan, which was obtained by direct measurement with a speed indicator. The curve indicates that the speed of 

the fan varies directly with the rate of combustion; this means that 

to obtain twice the rate of combustion the speed of the fan must be 

doubled, approximately, and to triple the rate the speed of the fan 

must be tripled, approximately, and so on. It must not, however, be 

assumed that since the air supplied to the furnace and the speed of 

the fan vary directly with the rate of combustion the work required 

from the fan varies in the same way. This is far from being the case. 

It has been shown in figure 9 that both the pressure drops, through the 

fuel bed and through the boiler, increase faster than the rate of combustion. This means that when the rate of combustion is to be increased the fan has to supply not only proportionately more air, but 

that it has to force it against much higher pressure. As the work of 

the fan is equal to the product of the volume of air which the fan displaces multiplied by the pressure against which this volume of air is 

forced, it is quite apparent that the work required from the fan increases much faster than the rate of combustion. In Bulletin 367 a 

it is shown that the work of a fan varies approximately as the cube of 

the rate of combustion or the capacity of the boiler.

All points representing raw coal are above the curve (lower curve,

fig. 10), and nearly all points representing briquets are below the 

curve. This means that less work was required from the fan to burn 

briquets than to burn run-of-mine coal. This fact is undoubtedly 

due to the smaller resistance of the fuel bed to the passage of air when 

burning briquets. The run-of-mine coal contained a high percentage 

of slack, which stopped the air passages in the fuel bed. Then, to 

obtain the same rate of combustion with coal as with the briquets, 

greater pressure drop through a fuel bed is required and more work 

must be done by the fan.

DEDUCTIONS. 

ECONOMY.

It was found on many locomotive tests and on some tests made 

under stationary boilers that briquets gave better economy than runof-mine coal. The question may be asked why similar results were

a Ray, W. T., and Kreisinger, Henry, The significance of drafts in steam-boiler practice: Bull.U. S. 

Geol. Survey No. 367, 1909, p. 55.
DEDUCTIONS. 41

not obtained on the fuel tests made under a torpedo-boat boiler. At 

present no definite answer can be given.

It may be that the combustion space of the furnace, which is less 

than one-half of the combustion space in an ordinary locomotive, is 

far too small to show any of the advantages due to the better burning 

qualities of the briquets. It may also be that what little betterment 

is gained by the size and uniformity of the briquetted fuel is more than 

offset by the increase in percentage of volatile combustible due to the 

addition of pitch as a binder. Table 4 gives for comparison the proximate analyses of the run-of-mine coal and briquets used in these tests/ 

moisture-free basis. The large briquets, which have shown the lowest 

efficiency, indicate the largest increase in percentage of volatile matter. The same percentage of pitch was used in making both sizes of 

briquets. However, as the small briquets exposed to the atmosphere 

a larger surface than the large ones, compared with their volume, and 

also as they were exposed longer to the atmosphere before testing, it is 

possible that more of the pitch was evaporated from the small briquets.

TABLE 4. Comparison of proximate analyses of coal and briquets.

Test 

No.

1 

2 

3

4

0

0

7 

8 

9

10 

11 

12 

13

14

15 

1C

17 

18 

19 

20

Designation of coal.

Jamestown 11 .................

Jamestown 9. .................

Form of use.

Average. ........;....

Average. .............

Proximate analysis of dry fuel.

Volatile 

matter.

| 18. 92 

\ 18. 71 

I 19. 91

19.18

I 23. 07 

{ 23. 40 

I 21. 31

22. 01

| 15. 10 

{ 10. 91

1 10. 80

10.29

( 17. 43 

I 18. 29 

V. 71 

[ 18. 21

17.91

I 23. 10 

{ 22. 53 

[ 24. 00

23. 23

f 24. 04 

1 24. 01 

1 23. 03 

I 23. 70

23.84

Fixed carbon.

75.53 

74.09 

75.81

75.34

72. 01 

71.00 

73.05

72.42

79.00 

70.93 

70.23

77.41

70.08 

75.03 

70.31 

75.83

70.11

09.22 

70.59 

71.24

70.35

70.73 

70.58 

71, 12 

71.03

70.87

Ash.

5.55 

0.00 

4.28

5.48

4.92 

4.94 

5.04

4.97

5.84 

0.10 

0.91

0.30

5.89 

0.08 

5.98 

5.90

5.98

7.08 

0.88 

4.70

0.42

5.23 

5.41 

5.25 

5.27

5.29
42 TESTS OF COALS AND BRIQUETS ON TORPEDO BOAT.

COMBUSTION SPACE.

The size of combustion space of a furnace and its relation to the 

grate area and the rate of combustion is very important with volatile 

fuels such as soft coal, because a considerable percentage of the combustible has to be burned as gas and tar vapors. In a furnace which 

affords insufficient space these forms of combustible remain in the 

combustion space only a fraction of a second, which is far too short a 

time for their complete oxidation. Table 5 gives, for three furnaces, 

the usual relation of combustion space to grate area, the rate of combustion, and the average time each cubic foot of gas is allowed to stay 

in the furnace.

TABLE 5. Usual relation of combustion space to grate area, ihe.rate of combustion, and 

the average time each cubic foot of gas. stays in the furnace.

Type of furnace.

1

Torpedo boat Biddle. . . Modern locomotive. ....

Stationary boiler,

Heine, 200 horseGrate 

area 

(square 

feet).

a

58.6

30

35

Combustion space 

(cubic feet).

Total.

3

136

160

250

Effective 

when fuel 

bed is 12

inches

thick.

 t

78

130

215

Ratio of 

columns 

' 2 

and

3.

a

2.34

5.34

7.14

2 

and

4.

6

1.33

4.33

6.14

Customary 

rate of combustion 

(pounds. of 

fuel per 

square foot

of grate per

hour).

7

40

60

25

Gases generated per 

second 

(cubic 

feet) .a

8

1,010

780

380

Time each 

cubic foot of 

gas stays in 

furnace 

(seconds).

9

0.077

.17

.58

a Assuming that 20 pounds of gas and water vapor are formed per pound of coal and that the furnace 

temperature is 2,500° F.

Columns 5 and 6 show that the ratio of combustion space to grate 

area in the torpedo-boat furnace decreases much more rapidly with

the thickness of fire than it does in either of the other two furnaces. 

A thick fuel bed reduces not only the supply of air to the furnace, but 

also the available space for the burning of combustible gases and tars. 

These facts applied to the fuel tests made under a torpedo-boat 

boiler help to explain why better results were obtained with comparatively thin fuel* beds. Column 9 gives approximately the average length of time each cubic foot of gas is allowed to sitay within the 

combustion space of the furnace. In the case of the torpedo-boat 

boiler the time usually is very short; in fact, too short for any chemical reaction which is not almost instantaneous. For this reason fuels 

which burn on the grate and not in the space above would be burned 

most economically in this particular type of furnace. Such fuels, 

however, are slow burning, and therefore not quite suitable for a torpedo boat where the rate of making steam is very important. Again, 

the limitations of a torpedo boat do not permit the combustion space 

to be enlarged. Therefore, the selection of fuel is usually a compromise between efficiency and rate of making steam.
CONCLUSIONS. 43 

RELATIVE CAPACITY OF STORAGE SPACE.

To determine the approximate relative storage capacity of coal 

bunkers when filled with run-of-mine coal, small briquets, and large 

briquets, a large rectangular wooden box was filled even full with 

each of the three fuels and the contents were weighed in each case. 

All three fuels were shoveled into the box in the same way as they 

would be into the coal bunkers of a boat. The box was 8 by 6 feet 

inside, and 3 feet deep.

When level full the box held 8,593 pounds of coal, 6,645 pounds of 

small briquets, and 6,272 pounds of large briquets. Considering the 

capacity of the coal bunkers when filled with coal as 100 per cent, this 

space when filled with each of the two kinds of briquets is reduced to 

6,645-r 8,593 = 77.4^per cent for small briquets and 6,272-=-8,593 =73 

per cent for large briquets, showing a considerable loss in the storage

capacity of coal bunkers when filled with briquets. This is a serious 

obstacle to the use of briquets for naval purposes.

TRANSFERRING FUEL FROM BUNKERS TO FIREROOM.

The coal bunkers on a torpedo boat are long, narrow spaces, the 

floors of which are elevated only about 2 feet above the floor of the 

fireroom. On account of their shape and location a large part of the 

contents of the coal bunkers must be .shoveled out when wanted in 

the fireroom. The spaces are so narrow that a man can not turn 

around inside of them with a shovelful. The openings into the bunkers are near their ends, and fuel at the far ends has first to be shoveled 

to the opening and then out upon the floor of the fireroom. In doing 

this work the coal shoveler has to dig with his shovel into the coal pile 

from the top as he recedes toward the farther end of the coal bunker, 

always facing the end where the opening is. It is comparatively 

easy to force the shovel into run-of-mine coal, but almost impossible 

to force it into a pile of briquets. Starting at the opening and forcing 

the shovel under the briquets on the floor would be a slow process, 

because as the coal shoveler got farther away from the opening he 

would have to walk backward to the opening with every shovelful. 

Besides, the numerous ribs of the boat would be frequently in the way 

of his shovel. During the test the quickest way of getting the briquets 

out of the farther portions of the bunker was by throwing them by hand 

toward the opening and then shoveling them into the fireroom.

CONCLUSIONS.

The following conclusions apply only to the tests of New River runof-mine coals when burned under a boiler of the Normand type and 

on vessels of the torpedo-boat class.

There is little or no gain in efficiency in burning briquets of either 

size.
44 TESTS OF COALS AND BKIQUETS ON TORPEDO BOAT.

Both large and small briquets make as much (or more) smoke as 

run-of-mine coal.

There seems to be more flaming in stack with briquets than with 

run-of-mine coal.

About the same amount of sparks are emitted from the stack 

whether briquetted or run-of-mine coal is burned.

When burning briquets the fire does not need to be disturbed; 

with coal the fuel bed has to be broken up, generally after each 

firing.

A somewhat higher boiler capacity can be obtained with briquets 

than with run-of-mine coal.

Steam can be raised more quickly with briquets than with run-ofmine coal.

Run-of-mine coal is transferred much more readily than briquets 

from the coal bunker to the fireroom.

With briquets the capacity of a coal bunker is reduced by 23 to 

27 per cent.

A FUNDAMENTAL PRINCIPLE IN THE COMBUSTION OF

SMOKY FUELS.

On page 26 of this bulletin it was reasoned that in the torpedoboat furnace the combustion of fuels was imperfect because the combustion space was too small and that the combustible gases and tar 

vapors a did not stay within the furnace a sufficient length of time to 

become completely oxidized. This means that time is an important 

element in the combustion of fuels.

The combustion of coal in a boiler furnace is a chemical process 

in which the oxygen reacts with the carbon and the latter's various 

combinations with hydrogen. This reaction, being between the

gaseous oxygen on one side and gaseous, "liquid/' and solid combustibles on. the other, is very complicated.

The word " liquid" as used in this discussion denotes all the forms 

of combustible between gaseous and solid; that is, such substances as 

in a strict physical sense are not gases or solids. For example, if 

we pour some coal tar in its viscous semiliquid form into a hot coal 

fire, a very dense brown "smoke" will issue from it. We know that 

this smoke is not gas; it is also hard for us to believe that all this 

smoke would consist of tiny, angular pieces of solid carbon. It is 

perhaps easier to think that at least a part of the smoke is composed of 

minute globules of the tar which have been boiled off, somewhat like 

the visible "steam" coming out of boiling water. For lack of better 

expression, we say that the combustible in the globules is in "liquid" 

form.

o In a strict physical sense these tars are not in the form of vapor at all, but rather in the form of visible 

mist consisting'of minute globules of liquid, or a pasty softening solid. Preston, in his " Theory of heat," 

defines vapor as transparent gas which is below its critical temperature.
THE COMBUSTION OF SMOKY FUELS. 45

When in the use of a hand-fired furnace a fresh charge of soft coal 

is spread over the hot fuel bed, the coal is heated up very rapidly and 

part of the combustible matter is boiled or distilled off immediately 

after the coal reaches the fuel bed. This combustible which is distilled off is perhaps mostly in the form of gases and such forms as 

are here called "liquids. 77 There are also numerous tiny pieces of 

solid fuel in the form of lampblack and even pieces of coal carried 

along with the gases. The combustible left on the grate is the " fixed 

carbon 7 ' in solid form, which burns there. The gaseous combustible 

which has been distilled off is free hydrogen, carbon monoxide, and 

some of the lighter hydrocarbons. The "liquids 77 are heavy hydrocarbons and carbon-hydrogen compounds of the benzine series, which, 

although surrounded by gases at a high furnace temperature, may 

exist as minute tar globules. It is these globules of tars which 

greatly add to the apparent brown smoky color of the gases. All of

these forms of combustible driven off from the fuel bed are in more 

or less perfect mechanical mixture with the air, with the alreadyformed carbon dioxide, and with the water vapor resulting from 

evaporating the moisture in the coal, and from the combustion of 

part of the free hydrogen. The velocity of chemical reaction (combination) between the combustible gas and the free oxygen (or the 

rapidity with which the combustible gas burns) depends upon the 

concentration of the two gases; that is, the rapidity of combustion 

will be the product of the amount of free oxygen times some power 

of the amount of combustible gas present in a unit of volume. The 

combination of simple gases, such as hydrogen and carbon monoxide, 

perhaps consist of a single reaction, while the combustion of the 

unsaturated hydrocarbons, as ethylene, and acetylene may be series 

of two or three, or even more, reactions, the first reactions of each 

series partly burning, the gases and partly reducing them to simple 

combustibles, either gaseous or solid. Ordinarily, the velocity of 

these reactions or the rapidity of burning gaseous combustible is 

high, so that with any reasonable amount of oxygen this combustion is 

nearly complete in a fraction of a second. The tar vapors, however, 

being partly in " liquid 77 form, require, even in the case of a uniform 

mixture with oxygen, a much longer time for their complete combustion, because oxygen can act only on the surface of each minute 

globule. As each globule burns, an insulating film of the products of 

combustion is formed around it, preventing contact with more oxygen. 

The globules are carried in the current of gas, and since they have 

very nearly the same velocity, there is little or no friction between the 

gas stream and the globules. The chief way in which the insulating 

film around each globule can be dispersed and more oxygen brought 

into contact with the surface of the globule is by natural diffusion 

between the gas comprising the film and the free oxygen outside the
46 TESTS OF COALS AND BEIQUETS ON TORPEDO BOAT.

film. This process of natural diffusion is rather slow, and as each 

globule contains many times more combustible matter than a like 

volume of gas, the process of oxidation of the globules of tar may 

extend over a considerable length of time, during which they may be 

carried out of the furnace and cooled below their ignition point. 

Such unoxidized tar globules appear at the top of the stack as dark 

smoke, and probably form the greater part of the loss in incomplete 

combustion.

These tar globules are similar in character to tobacco smoke, which 

is not a product of combustion, but a product of decomposition; it is 

not a slightly colored gas, but a large number of tobacco-oil globules 

held in suspension by the current of gas. Every smoker knows that if, 

he pass the smoke from his cigar through a clean, white linen cloth, the 

visible smoke which consists of the tobacco-oil globules will condense 

and leave a light-brown oil spot on the linen, having a very strong, 

characteristic smell. The tarry globules escaping from a coal fire, if 

collected and condensed in some such way, generally appear as a thick, 

black, pasty liquid, having the strong coal-tar odor, which we are accustomed to smell around a certain class of gas producers or around 

gas works. Tar vapors from a wood fire have a different odor than 

those coming from a coal fire. In fact, every fuel gives off tar vapors 

with odors peculiar to that fuel and somewhat different from those 

of any other.

In the case of a boiler furnace, any attempt to determine the tar loss 

by volumetric chemical analysis of the flue gases must necessarily fail, 

because these tars have comparatively little volume; furthermore, 

they generally condense in the gas-sampling apparatus.

The slow combustion of the tar globules can be made faster by increasing the rate of diffusion of the film of products of combustion 

enveloping the globule. This can be done by creating a relative 

velocity between the gas stream and the globules; that is, by 

making one move faster than the other or by changing slightly 

the direction of the main stream of gas. The resulting friction facilitates diffusion by a process of scrubbing, which removes from the 

globules the insulating film of products of combustion. Insertion of 

brick piers in the path of the gases or changing the cross section of the 

gas passages so that the gases have to contract and expand perhaps 

induces such relative difference of velocities.

That some such film as is herein described does prevent, the-free 

oxygen from coming into contact with the surface of the globules 

seems to be certain from the fact that gas samples taken by waterjacketed samplers from a stream of gas apparently rich in the tar 

vapors show usually several per cent of free oxygen.

As the tar vapors are perhaps a whole series of very complex hydrocarbons, their complete oxidation .undoubtedly consists of several
THE COMBUSTION OF' SMOKY FUELS. 47

simultaneous or consecutive reactions more or less dependent on each 

other. This is probably another cause of their slow combustion.

What has been said about the slow combustion of the tars is perhaps in an intensified degree true of the small particles of solid 

combustible held in suspension by the gases.

By far the larger part of the coal burns on the grate, where the 

combustion is mostly a reaction between the solid carbon and gaseous 

oxygen. The rate of formation of C02 seems to vary directly with 

the velocity of the free oxygen passing over the surfaces of the pieces 

of solid carbon. The higher the blast of air passing through the fuel 

bed of burning carbon the faster the latter burns, the chemical composition of the products of combustion remaining about the same. 

Undoubtedly the scrubbing action of the blast of air removes from the 

surfaces of the solid carbon the film of the products of combustion and

facilitates the access of free oxygen. If the fuel bed is not carried 

too thick, very good combustion of the fixed carbon is obtained 

without any difficulty.

In the preceding discussion of the combustion of the various forms 

of combustibles in a boiler furnace it has been shown that the gaseous 

combustible is easy to burn because it burns quickly, and that the 

fixed carbon is easy to burn because it stays' on the grate until completely burned; also, that the tar vapors, the lampblack, and the 

tiny pieces of coal held in suspension by the gases are difficult to burn 

because they burn slowly, and usually can not be kept long enough 

within the furnace to be completely burned. The proper way to burn 

coal would be to treat it in such a way as to distill as volatile matter 

only light, easily burning gases, and leave all the rest of the combustible on the grate and burn it as a fixed solid. Laboratory experiments a show that the amount and quality of the combustible driven 

off the coal by heating depends largely on the rate of heating; 

that is, when the rate of heating is slow, the total combustible matter driven off as volatile is small in quantity and gaseous in composition, while if the rate of heating the coal is very rapid the total volatile matter driven off is not only high in quantity but contains much 

tar vapor. It seems as though the hydrogen of the coal must be 

distilled off before burning and that when the coal is .heated slowly 

the hydrogen on distillation takes only a small amount of carbon 

with it, leaving most of the latter on the grate as "fixed carbon;" 

if, however, the coal is heated very rapidly, the hydrogen comes off 

with a large amount of carbon and escapes as volatile matter, leaving a smaller quantity of the carbon on the grate in a fixed form. 

These facts bring us to the realization that there is no definite line 

between "fixed carbon" and "volatile matter." We know, for

« See Porter, H. C.,and Ovitz, F. K., The nature of the volatile matter of coal as evolved under 

different conditions: Jour. Am. Chem. Soc. vol. 30 (Sept.), 1908, p. 1486.
48 TESTS OF COALS AND BEIQUETS ON TOEPEDO BOAT.

instance, that 'coal tars which escape from a gas producer entirely 

as volatile matter show from 40 to 50 per cent of "fixed carbon" 

when subjected to proximate analysis. Similarly, if the tars from 

a boiler furnace, particularly from a hand-fired one, were caught 

and analyzed by the proximate method, they would likely show a 

considerable percentage of "fixed" carbon. This "fixed carbon" of 

the tar should have been left on the grate and not carried away by 

the process of distillation.

According to the above, firing coal by hand is not the right way to 

burn it, because the pieces of coal fall on a very hot fuel bed and are 

heated in two or three minutes through a range of temperature of 

about 2,400° F. This is a very high rate of heating and much of 

the carbon which, with a slow rate of heating would be left on the 

grate as "fixed," is driven away in combination with hydrogen in 

the form of heavy tar vapors. These tar vapors generally do not 

stay long enough in the furnace to burn, and hence leave the stack 

as smoke. a

Most mechanical stokers are designed so that the coal is fed into 

the furnace gradually, and therefore the rate of heating is slow. 

The result is that a comparatively small amount of combustible is 

driven off as volatile matter, and it consists chiefly of easily burning 

gases, most of the carbon being left and burnt on the grate as fixed 

carbon; very small amounts of tarry vapors are distilled, whence 

the success of most mechanical stockers in burning smoky fuel. 

As an example, on a well-operated chain-grate stoker, it takes perhaps fifteen to twenty minutes to heat the coal through the same 

temperature range of 2,400° F., which takes only two or three minutes in the hand-fired furnace. In general, the success of these 

mechanical stokers lies not in the fact that they consume smoke but 

that they burn the coal without producing much smoke at all.

Tar vapors and other heavy carbon-hydrogen compounds which 

are the product of distillation of coal under certain treatment burn 

slowly, and in order to burn them nearly completely they must be 

kept a- comparatively long time within the furnace. To fulfill this 

condition the furnace must be provided with a large combustion 

space. Such furnaces, however, are objectionable for obvious reasons. The best remedy probably is to avoid the formation of all 

these slow-burning volatile compounds by using the principle of the 

low rate of heating of fresh fuel.

o It must not be understood that these tar vapors are the only constituents of visible smoke. Small 

particles of carbon or soot, resulting from the decomposition of illuminant gases such as CjlT^and CjHjadd: 

to the darkness of the smoke; however, the tar vapors probably represent the greatest loss of heat.
TESTS OP COALS AND BKIQUETS ON TOKPEDO BOAT. 49

SURVEY PUBLICATIONS ON FUEL TESTING AND 

BRIQUETTING.

The following publications, 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. 172 pp. 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.

240pp. 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., 1904-1906, by I.,. P. Breck.enridge. 1907. 196 pp. 10 cents. 

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. 27pp. Scents. 

BULLETIN 343. Binders for coal briquets, by J.'E. Mills. 1908. 56 pp. 

BULLETIN 362. Mine sampling and chemical analyses of coals tested atthe United States

fuel-testing plant, Norfolk, Va.,in 1907,by J.S.Burrows. 1908. 23pp. Scents. 

BULLETIN 363. Comparative tests of run-of-mine and briq'uetted coal on locomotives,

including torpedo-boat tests and some foreign .specifications for briquetted fuel,

by W. F. M. Goss. 1908. 57 pp., 4 pis. 

BULLETIN 366. Tests of coal and briquets as fuel for house-heating boilers, by D. T.

Randall. 1908. 44 pp., 3 pis. 

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. 

BULLETIN 373. The smokeless combustion of coal in boiler plants, by D. T. Randall

and H. W. Weeks. 1909. 

BULLETIN 378. Results of purchasing coal under government specifications, by J. S.

Burrows; burning the small sizes of anthracite for heat and power purposes, by

D. T. Randall. 1909. 44pp.

BULLETIN 385. Briquetting tests at Norfolk, Va., by C. L. Wright. 1909. 41pp., 9pls. 

BULLETIN 393. Incidental problems in gas-producer tests, by R. H. Fernald, C. D.

Smith, J. K. Clement, and H. A. Grme. 1909. 29 pp. 

BULLETIN 402. The utilization of fuel in locomotive practice, by W. F. M. Goss.

1909. 28pp.

MINERAL RESOURCES, 1907. Coal briquetting in 1907, by E. W. Parker, pp. 223-228. 

MINERAL RESOURCE'S, 1908. Coal briquetting in 1908, by E. W. Parker.

4781 Bull. 403 09 4

PROPEI