Forest Service 

Mort heastern Forest 

Experiment Station 

Research 

Paper N E-508 

Converting Small Industrial Boilers 

to Burn Wood Fuels 

Raymond L. Sarles 

J. Penn Rutherfoord 
The Authors 

Raymond L. Sarles is a research forest products technologist 

at the Northeastern Forest Experiment Station's Forestry Sciences 

Laboratory, Princeton, West Virginia. J. Penn Rutherfoord, P.E., is 

president of Rutherfoord Associates, an engineering consultant 

firm, Marion, Virginia. 

Manuscript received for publication 

7 January 1982 

Abstract 

Investigates the engineering 

and economic feasibility of retrofitting two small industrial boilers (32 

hp and 52 hp, respectively) for firing 

green wood fuels. Subjects covered 

include fuel requirements and 

costs; availability, storage, and handling of wood fuels; and designs, 

specifications, stack emissions, 

cost estimates, and economic feasibility. The economics of boiler conversion projects are heavily dependent on annual savings in fuel costs. 

Analyses of variables affecting annual fuel savings determined that 

the boiler utilization rate (BUR) and 

the price of fuel oil had the greatest 

impact on the economic feasibility 

of this project. 
Introduction 

Interest in the use of wood 

fuels to replace ever more costly oil 

and gas continues to increase. More 

companies are installing new woodburning boilers or converting old 

ones to burn wood. Conventional 

technology is available to serve 

these needs. Usually, the decision 

to convert to wood is an economic 

one, and the economics of switching to wood become more favorable 

as the price of fossil fuels continues to increase. 

Today, nearly all wood-fired 

boiler installations serve forestindustry plants that generate their 

own wood wastes. However, we are 

beginning to see wood-fired boiler 

installations in other industries, 

e.g., textiles, power stations, brick 

plants, greenhouses, tanneries, and 

institutions such as the Waterbury 

(Vt.) State Hospital and the Northwest Regional Hospital, Rome, 

Georgia. < 

We attempted to convert two 

small industrial boilers at the 

Forestry Sciences Laboratory, 

Princeton, West Virginia. Both were 

designed and built to burn coal. Our 

objectives were to determine the engineering and economic feasibility 

of firing both boilers with green 

sawdust and wood chips. 

Bollsr DescrDptlon and 

Evaluation 

The smaller of the two boilers 

is a Spencer1#* low-pressure, hot wag 

tsr steel boiler that provides space 

heatlng for laboratory offices. It was 

fired with 8toker coal for seven1 

1 The use of trade, flrr,,sr czsrpsratlon 

names in thl8 publication 18 for the information and convenlen~e of the reader, Such ue)e doe8 not constitute an offlclal 

endorsement or approval by the U.8. Bepartrnent of Agriculture or the Foreat 

Senrice of any roduct or service to the 

exclusion of ot\srs that may be suitable. 

2 Spencer type A (Series 3M-40, #8102-365), Spencer Heater Dfvision, Avco Manufacturing Co,, Williamsport, PA. 

Gross rating 1,440 pounds of steam per hour. 

years in the 1960'~~ but then was 

retrofitted with a propane burner. 

The firebox was not large 

enough to install an underfeed, 

single-retort stoker and grate. Further, the insufficient clearance 

would not allow a good flow of the 

combustion gases and proper heat 

transfer to the boiler. The latter condition would result in a stress buildup in the boiler jacket, weakening it 

and shortening its life. For these 

reasons, we did not retrofit the 

Spencer boiler. However, should 

manufacturers build smaller stokers 

for firing wood fuels, conversion of 

the Spencer boiler could be reconsidered. 

The second boiler is a sectional 

cast iron unit manufactured by 

American Standard.3 It provides 

both hot water and low-pressure 

steam for heating our pilot testing 

plant. This unit was designed to 

burn coal but was converted to oil 

when installed. 

There was sufficient clearance 

(28 inches) between the built-up 

hearth and the top of the cast iron 

furnace arch. This height allows the 

installation of a standard stoker and 

grate and provides a good flow of 

hot gases to the boiler surfaces. 

Since the firebox construction 

and size was adequate for installing 

a stoker and firing green wood, we 

decided to retrofit the American 

Standard boiler. However, the bsiler's net rating had to be reduced. 

This dtaratlng resulted from firing 

green wood in 8 f lrtbbox r~izsd and 

designed to burn coal, Elliott (13380) 

explained why firebox chancterlstics anel the burning of green wood 

fuels rbaeult In defatlng of boiler capacity: 

""Three unique shera@teris= 

tics sf wood combustlon 

must be accounted for On 

furnace design: First, the 

high moisture content of 

3 Model A-713-50(f3) (Series 28-J2 

#97AH1 LO 7658). Gross rating 2,304 

pounds of steam per hour. 

green wood fuels causes 

large volumes of superheated steam to be evolved in 

the firebox and this depresses the combustion 

temperature; second, depending on fuel quality, 

large amounts of excess air 

are required for combustion; 

third, residence time in the 

firebox must be sufficient 

to allow combustion of volatiles and entrained particles. 

Therefore, the firebox must 

be large enough to maintain 

reasonable gas velocities 

and must contain significant refractory material to 

sustain the temperature of 

the fire when wet fuel is 

used." 

Boiler derating can be a crucial 

factor when converting to green 

wood fuel. Where boiler capacity is 

critical to meeting current steam 

needs, newly retrofitted boilers 

should be equipped with an oil or 

gas burner to provide full steam capacity when needed. Wood then becomes the base-load fuel with occasional peak demands supplied by 

firing the auxiliary burner. In our 

case, the American Standard boiler 

is oversized for our needs and is 

equipped with an oil burner, so berating can be tolerated. 

Fuel Requirements and Costs 

In 1979 the American Standard 

boiler consumed 12,496 gallons of 

No, 2 fuel all. Our oil bill, at an average price of $0.82 per gallon, was 

$7,747. 

Using our oil csnsumption figure, we calculated our total energy 

needs and determined the equivalent quantity of woad fuel required. 

At an avsraas heat value sf 142.000 

Btu per galhn, 12,488 gallons d 

fuel oil yleld ri total sf 1.774 x 1@ 

Btu, At ra csmbustlon efficiency of 

80 percent, net energy input with oil 

wars 1.419 x 1OF) Btu, 

Bone-dry hardwood fuels yield 

an average of 17 million Btu per ton, 

but the moisture content in green 

fuels plus losses during combustlon 

reduce heat ytelds substantially. 
Green sawdust, which typically is 

half water, has a net energy yield of 

5.525 million Btu per ton. Thus, the 

amount of sawdust required to meet 

our annual energy needs was 257 

tons (1.419 x lo9 Btu + 5.525 x 

1@ Btu). 

Considerable quantities of sawdust could be purchased from local 

sawmills in 1979 for $7.50 per ton 

delivered. At this price, our estimated annual wood fuel cost totaled 

$1,927, a reduction of $5,820 from 

the $7,747 paid for fuel oil; $5,820 

was our projected annual fuel savings. 

Retrofit Design and 

Specifications 

The underfeed stoker. Originally, the boiler was designed with 

open grates for the hand firing of 

lump coal. When installed it was 

modified by adding a second base 

to provide the proper setting and 

combustion space to burn fuel oil. 

For burning green sawdust and 

wood chips, the engineer recommended installing an underfeed, 

single-retort stoker system. Small 

stokers of this type are available 

from two U.S. manufacturers and 

several overseas firms (Fig. 1). 

To achieve maximum boiler output, green wood requires a larger 

firebox than is needed for coal or 

oil. However, enlarging the firebox 

was deemed impractical. Accordingly, the boiler's net output was reduced to approximately 30 hp, a 42 

percent reduction from 52 hp obtainable when firing coal or oil. 

With underfeed stokers, fuel is 

delivered to the grate from the fuel 

hopper by an auger powered by a 

motor-driven, variable-speed drive 

(Figs. 2-3). At its maximum speed ' 

(16 rpm), the auger will deliver 15.6 

cubic feet of sawdust per hour to 

the grate. The Btu yield of this 

quantity of fuel (at 50 percent moisture content) produces 1,035 

pounds of steam per hour (30 hp), 

the capacity of the derated boiler. 

The grate, which is an assembly of perforated cast iron sections 

called tuyeres, is positioned on top 

of the wind box. Fuel on the grate is 

ignited by the oil burner maintained 

as a backup firing system. Automatic controls shut off the burner after 

the wood fire is hot enough to maintain combustion. Most of the combustion air is supplied to the grate 

as underfire air forced through the 

wind box and the tuyeres. 

The forced air system. Because 

of the highly variable conditions associated with stoker-fed fuels, underfeed systems are less efficient 

than suspension or vortex combustion systems in achieving a good 

mixture of air and fuel in the firebox. To overcome this problem, our 

design features two forced-air systems: an underfire forced draft and 

an overfire swirling draft. The overfire draft is intended to create a turbulence over the grate for mixing air 

with the volatile gases and entrained fuel particles. In practice, 

not all of the oxygen combines with 

Figure 1.-Industrial stoker of U.S. manufacture. (Photo by Will-Burt Co., Orrille, Ohio). 
Figure 2.-Plan and sectional views of Will-Burt industrial stoker installed in American Standard A-7 boiler. 

Figure 3.-Underfeed stoker fuel delivery parts: hopper, variable-speed 

drive, auger, auger housing, retort, and grate. 
the carbon and hydrogen in the fuel 

during combustion, To obtain complete combustion, the air system 

was designed to supply excess 

air-in amounts of 150 percent or 

more of theoretical air-to allow for 

variability in fuel conditions, e.g., 

moisture content, particle sizes, and 

species of wood. Firing the boiler at 

full capacity with wet sawdust requires about 400 cubic feet of air 

per minute. Dampers in the air 

ducts allow adjustment of the quantity of air supplied to achieve optimum combustion. Proper adjustment of air reduces visible stack 

emissions to a minimum. 

The underfire forced-draft system is part of the stoker and consists of wind box, air duct, fan, and 

drive motor. The overfire system 

conslsts of custom-fabricated ductwork fitted with four loinch air nozzles, and a direct-connected motor 

driving an industrial blower which 

supplies the air (Fig. 4). 

Emissions control. Because the 

chemical makeup of wood is almost 

pure hydrocarbon, the stack pollutants of concern are mainly solid 

particulates. Sulfur is present only 

in very small amounts. The following shows the chemical makeup of 

coal and wood (on a dry-weight basis): 

Item Coal Wood 

- - Percent - - 

Carbon 7 5.5 52.0 

Hydrogen 5.0 6.3 

Oxygen 4.8 40.5 

Nitrogen 1.2 0.1 

Sulfur 3.1 0.01 

Ash 10.3 1 .0 

Carbon monoxide may be emitted if there is insufficient air for 

complete combustion. However, 

this is unlikely unless the damper 

settings are tampered with as the 

air system is designed to supply extra excess air for complete combustion. Proper draft settings also will 

control oxides of nitrogen well below toxic levels, Some of the excess 

nitrogen from draft air will be emitted from the stack as oxides of nitrogen, but most of it will leave the 

system uncombined. 

Though it is commonly thought 

that the particulate in smoke is 

composed of fly ash, analysis 

shows that very little of the smoke 

from wood fires contains uncombustible ash. At least 50 percent of 

the ash residue remains in the combustion chamber or settles in the 

furnace flues. What we see in 

smoke is mostly unburned carbon 

which settles out as soot. 

Environmental Protection Agency regulations allow a maximum of 

0.6 pound of particulate matter per 1 

million Btu of heat input when firing 

wood fuel. In our case, the maxlmum rate of heat input on the coldest of days could be 2.8 million Btu 

per hour for short intervals. At this 

Figure 4.-Overfire forced-air system designed to produce a swirling draft for more complete combustion. 
level of fuel consumption, the EPA 

allows 1.68 pounds of particulate 

matter per hour, Expressed as parts 

per million of emitted hot gases, 

EPA regulations allow particulate 

matter emissions of 560 parts by 

weight or 4.20 parts by volume. At 

this emission rate, a stationary 

wood-burning facility would not produce visible smoke. 

These allowable limits are 

based on the boiler operating at 100 

percent of rated capacity. But, as 

we determined, firing the boiler with 

wet sawdust reduces heat input 

from 2.8 to 1.6 million Btu per hour. 

At this level, we estimate that 0.96 

pound of particulate matter will be 

emitted per hour, well below the allowable EPA maximum. However, it 

remains to be seen if emissions will 

be at this level under actual operating conditions. If fire conditions are 

less than optimum for complete 

cambustion, and the boiler is in 

noncompllance, a cyclone separator 

wlll be used to control emfssions of 

solid matter. 

Firing system controls. The 

electrically operated system controlling the boiler is fully automatic. It 

provides for two options: firing with 

stoker-fed wood fuels or fuel oil. 

The options are selected manually 

by operating a dipole switch. Firing 

with either fuel will produce enough 

Btu for sufficient steam and hot water to meet space heating needs of 

the plant during the coldest winter 

months. 

Automatic controls for burning 

wood are more complex than the 

controls needed to burn fuel oil. 

When wood is burned, more operations must occur elther simultaneously or, more critically, sequentially. For example, with a cold startup, 

ignition of wood fuel depends on 

the oil burner igniting, burning for a 

period of time, and then shutting off 

when combustion of the wood is 

well advanced, Simultaneously, the 

draft system (underfire and overfire 

air) and the induced-draft stack fan 

must start up. AS wood fuel is consumed, the stoker auger is activated 

to feed more fuel to the grate. It 

shuts off automatically when 

enough fuel is loaded on the grate. 

Should the stoker auger jam, or for 

any reason fail to deliver fuel to the 

grate, the oil burner ignites automatically and takes over as the 

back-up source of heat to operate 

the boiler. 

Fuel storage and handling. A 

complete fuel-handling system was 

designed to handle sawdust and 

whole-tree chips. Fuels wlll arrive by 

truck and be dumped into a concrete pit fitted with a vibratory 

screen (Fig. 5). Screening separates 

oversized pieces and trash from particles passing through the 1-inch 

holes. The latter are sucked up and 

blown into the top of a 3,000-cubicFigure 5.-Sawdust receiving dump pit, vibratory screen, and silo loading 

system. 
foot silo calculated to hold sufficient fuel for 10 days during the 

coldest weather (Fig. 6). Collected 

trash will be disposed of; oversized 

pieces will be collected and fed 

manually into the boiler firebox as 

needed. 

Movement of fuel from the silo 

to the stoker hopper is controlled by 

the bin-level switch mounted on the 

hopper. The hopper is equipped 

with an electric vibrator to break up 

compacted fuel in the hopper. As 

the fuel level in the hopper drops, 

the switch activates electric motors 

that drive augers in the silo and the 

screw conveyor. These, in turn, deliver fuel to the hoppe'r. When the 

hopper is full, the control switch 

shuts off the auger motors. Barring 

equipment breakdowns, jamming of 

the augers, or power failure, fuel is 

conveyed automatically to the boiler 

house as needed. 

Boiler Otilliration Rate 

An important variable in the operation and evaluation of a boiler is 

how much it is used and how hard it 

is used. Usage, expressed in percent, is termed the boiler utilization 

rate (BUR). It is a product of several 

factors: fuel consumption, fuel energy value, boiler efficiency, boiler rating, and hours of operation per year. 

Our American Standard boiler is 

started up in the fall and shut down 

about June 10; annual hours of 

scheduled operation total 6,072. In 

practice, office and working spaces 

are heated only 40 hours a week, 

and thermostats are set back at 

night and on weekends. As a result, 

our average annual BUR is only 10 

percent. Our estimate of the average 

annual BUR for the wood-fired boiler, operating on the same schedule, 

is 15 percent. Compared with industrial plants, these are low rates; 

however, they may be similar to 

rates for boilers in public institutions, for example, schools. The 

BUR has an important bearing on 

the economics of converting a boiler to wood fuels (Figs. 7-8). 

Conversion Costs and Economic 

Feasibility 

In 1979, our cost estimate for 

converting the boiler to wood fuels, 

in accordance with the engineer's 

design and specifications, was 

$65,500.4 This estimate was developed from contractors' bids for 

equipment and services, plus estimates of equipment purchased by 

the USDA Forest Service and services provided by our own crew: 

4 Rutherfoord Associates, Marion, VA. 

Figure 6.-Fuel storage silo with concrete foundation, unloading mech- anism, and concrete stave construction. 
1 tem Cost 

ft)ollars) 

1. Rebuild boiler firebox; install underfeed stoker complete with 33,500 

hopper, auger feed, retort, grates, variable-speed drive, etc.; 

install new oil burner; fabricate new forced-air system; provide 

all controls and electric service for full automatic operation. 

Turnkey job by mechanical contractor. 

2. Concrete stave silo (3,000 cubic feet) complete with unloading 23,500 

auger, delivered and erected in place on foundation built by 

owner. 

3. Fuel receiving facility, boiler room addition, and 24-foot screw 8,500 

conveyor; construction by owner. 

To determine the economic 

feasibility of this investment, we 

used The New England Regional 

Commission's "Wood Conversion 

Economic Model, WOOD Ill1 (Ewing 

and Cody 1980). The model provides: (1) annual fuel costs for oil 

and wood-fueled boiler systems, (2) 

annual net cash flows over the life 

of a proposed wood replacement 

system, and (3) economic indexes 

including net present value (NPV), 

internal rate of return (IRR), and 

years to pay back (YPB). 

Total 

Figure 7.-Effect of the boiler utilization 

rate and year of investment on net pres- ent value of boiler conversions in 1979, 

1981, and 1983. 

Figure 8.-Effect of boiler utilization rate 

and year of investment on internal rate 

of return of boiler conversions in 1979, 

1981, and 1983. 

0 30 60 90 120 

Boiler Utilization Rate (percent) 

Boiler Utilization Rate (percent) 
The model uses 32 variables 

which describe the existing and proposed boller systems, operation and 

maintenance costs, fuel characteristlca and prices, inflation rates, 

taxes, tax credits, and financing 

terms. Federal and state tax rates 

and tax credits do not apply to our 

sltuatlon, or to other tax exempt in. ' 

stitutions, hence zero values were 

assigned to these variables. Data for 

other variables were either known 

(e.g., boiler rating, fuel oil grade) or 

were calculated, estimated, or assumed: 

A key feature of WOOD II is its 

abiltty to assess the impact of 

changes in any of the variabies. 

Groups of variables can be changed, 

or individual variables can be varied 

systematically over a range of 

values. We found these characteristics of the model to be useful in exploring the range of economic feasibility for different years. 

Applying the model to our basIc data set (which includes a dise 

count rate of 20 percent), we determlned that the investment to conVaria bls 

Pounds of steamihour 

Annual operating hours 

Average utIlizatlon (%) 

Boiler efficiency (%) 

Btulpound of steam 

Costlgallon (dollars) 

Costlton (dollars) 

Dry wood energy (million Btu) 

Moisture content, wet basis (%) 

Annual operation and 

maintenance cost (dollars) 

Operation and maintenance 

inflation rate (%) 

Inflation rate (%) 

Tax rate (%) 

Federal 

State 

Tax credit (YO) 

Federal 

State 

Depreciation period (years) 

Depreciation method 

Loan period (years) 

Loan interest rate (%) 

Equity capital (dollars) 

Capital cost (dollars) 

Operating life (years) 

Discount rate (Oh) 

011 Wood 

a Calculated. 

Assumed. 

No. 2 oil. 

Estimated. 

vert the boiler to wood was not economically viable. Actual annual savings in fuel costs were not sufficient to generate a positive net 

present value (NPR) over the project's 220-year Ilfe. 

We then tested several of the 

variables to determine their effect 

on economic outcomes. The variables selected were those that either 

the boiler designer, user, or passing 

of time could change. For example, 

we ranged values for wood boller efficiency from 50 to 75 percent and 

wood fuel moisture content from 

zero to 60 percent. In a similar manner, we tested a range of values for 

annual hours of boiler operation, 

average annual boiler utilization 

rate, price of oil, price of wood, 

amount of equity capital, and capital 

cost. In only three cases did the 

change of variables result in positive outcomes: Increasing the prlce 

of oil to $1 .OO per gallon resulted in 

an N PV of $3,816 and an IRR of 19 

percent; doubling the average boiler 

utilization rate to 30 percent gave an 

NPV of $14,638 and an IRR of 21 

percent; decreasing capital cost to 

$18,000 resulted in an NPV of $941 

and an IRR of 21 percent. 

Two of these three positive outcomes, that is, those due to increases in oil price and boiler utilization rate, represented realistic options. Since higher oil prices are almost a certainty, one could justify 

an investment in boiler conversion 

on the basis of anticipated increases to $1.00 or more per gallon. 

Similarly, increasing the BUR 

through planning for use of more 

steam and hot water, for example, 

additional space heating, cooling, 

and drying, also could justify the investment. The third option, decreasing the capital cost to $18,000, was 

not viable because the conversion 

job could not be done for that price. 

Analyses for 1981 and 1983. 

Knowing the effect of oil price increases, we analyzed the economic 

feasibility of boiler conversion for 

the years 1981 and 1983. To correct 

the data set for increased prices 
Table 1 .--.Values for SIX cost lternr increased to reflect 

changing economlc condltfons In 1981 and 1983 

Variable 

1979 

base case 

1981 

scenario 

1 983 

scenario 

Cost of oillgallon 

Cost of woodlton 

Annual operation and 

maintenance cost 

Oil 

Wood 

Capital cost 

Equity capital 

and costs, we changed six variables: price of oil and wssd, operation and maintenance costs, capital 

cost, and amount of equity (Table 1). 

The 1981 oil price was obtained 

from our purchase records. Other oil 

and wood prices and operation and 

maintenance costs were increased 

in accordance with stated inflation 

rates. Capital cost was increased by 

approximately 25 percent for each 2- 

year period, and equity capital was 

maintained at approximately onethird of capital cost. 

Our analysis showed that an investment in boiler conversion in 

1981 and 1983 would be economically feasible, given the changes in 

fuel prices and other costs as stated. Net present values for both 

years were $2,510 and $2,428, respectively. The IRR was 18 percent 

in both instances, The effect of BUR 

and year of investment on NPV and 

IRR of boiler conversions are shown 

in Figures 7 and 8. 

A small tax paying business: To this point our analysis has 

examined conversion of a small 

boiler owned and operated by a public agency. We might ask what the 

results would be if the boiler were 

privately owned and operated by a 

small corporation. We examined this 

possibility for the same set of years: 

1979,1981, and 1983. However, to 

correct the data for a tax paying 

business, we changed seven variables in the basic data set: taxes, tax 

credits, depreciation period and 

method, and interest rate. 

Tax exempt Tax paylng Variable institution corpora tion 

Federal tax rate (%) 0 17.5 

Federal tax credit (%) 0 20.0 

West Virginia tax rate (%) 0 4.0 

West Virginia tax credit (%) 0 0 

Depreciation period (years) NA 10 

~epreciation met hod NA straight line 

Loan interest rate (%) 12 18 

Federal tax rate and loan interest were based on assumptions that 

the corporation's annual taxable income was $30,000, and that the interest rate was higher. 

Surprisingly, these changes did 

not change the outcome of the 1979 

analysis as much as might be expected. For that year, the NPV was 

negative and IRR was only 8 percent. Thus, as in the case of the tax 

exempt institution, the boiler conversion was not economically feasible for 1979. However, the scenarios 

for 1981 and 1983 were economically feasible. In both cases, NPV's 

were positive-$5,124 and $5,848, 

respectively; I RR's were 19 percent. 

The effects of BUR on NPV and IRR 

were simrlar to those for the tax exempt cases. 

Equipment and technology are 

available to retrofit small industrial 

coal-fired boilers for automatic firing of wood fuels. However, limltations of firebox size and construction can affect wood combustion efficiency and heat release to the extent that derating of the boiler may 

be required. 

Conversions of boilers to wood 

fuels are technically feasible, but 
may not be economically feasible. 

Economic feasibility depends to an 

extent on savings achieved in annual fuel cost. Given the owner's expected rats of return for capital, 

these savings dictate how much 

capital can be prudently invested in 

a boiler conversion project. 

Our analyses showed that the 

price of oil and the BUR had the 

greatest impact on the project's 

economic feasibility, and that the 

project's feasibility was approxlmately similar for tax exempt and 

tax paying organizations. 

Literature Cited 

Elliott, R. N. Wood combustion. In 

Decisionmaker's guide to wood 

fuel for small industrial energy users. Golden, GO: Solar Energy 

Res. Inst.; 1980; p. 31-34. 

Ewing, Thomas S.; Cody, Eric. Wood 

conversion economlc model, 

WOOD II. (computer program). 

Boston, MA: New England Regional Commission; 1980. 
Investigates the engineering and economic feasibility of retrofitting two smali industrial boilers (32 hp and 52 hp, respectively) for firing green wood fuels. Subjects covered include 

fuel requirements and costs; availability, storage, and handling of wood fuels; and designs, specifications, stack emissions, cost estimates, and economic feasibility. The economics of boiler conversion projects are heavily dependent on annual savings in fuel costs. Analyses of variables affecting annual fuel savings determined that the boiler utilization rate 

(BUR) and the price of fuel oil had the greatest impact on the 

economic feasibility of this project. 

s; boiler retrofitting; emissions con- 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

a Amherst, Massachusetts, in cooperation with the University of 

Massachusetts. 

Berea, Kentucky, in cooperation with Berea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont. 

Delaware, Ohio. 

Durham, New Hampshire, in cooperation with the University of 

New HmpsMm. 

Hamden, Connecticut, in cooperation with Yale University. 

Morgantown, West Virginia, in cooperation with West Virginia 

University, Morgantown. 

Orono, Maine, in cooperation with the University of Maine, 

Orono. 

Parsons, West Virginia. 

Princeton, West Virginia. 

Syracuse, New York, in cooperation with the State University of 

New York College of Envimnrnental Sciences and Forestry at 

Syracuse University, Syracw. 

University Park, Pennsylvania, In cooperation with the 

Peamyivmh Sterte University* 

0 Warren, Penmylvmia. 

L U.S. GOVERNMENT PRINTING OFFICE: 1982-505-012:28