A Demonstration of Fat and Grease as an Industrial Boiler Fuel 

Principal Investigator: 

Dr. Thomas T. Adams, P.E., Public Service Associate 

UGA Engineering Outreach Service (EOS) 

Coinvestigators: 

Jim Walsh, GA Tech EDI 

Mike Brown, GA Tech EDI 

Dr. John Goodrum, UGA Bio. & Ag. Eng. 

Dr. Jackie Sellers, UGA Bio. & Ag. Eng. 

Dr. Keshav Das, UGA Bio. & Ag. Eng. 

Project Administrator: 

Dr. E. Dale Threadgill, Director 

Faculty of Engineering 

The University of Georgia 

Project/Report Manager: 

Robert J. Synk, P.E., Project Management Resources, Inc. 

Project/Report Contributors: 

Erin Callaghan, Public Service Representative, UGA, EOS 

Bryan Graffagnini, Research Engineer, UGA EOS 

Javier Sayago, Chemist, UGA EOS 

The University of Georgia 

Engineering Outreach Service 

Driftmier Engineering Center 

Athens, GA 30606-4435 

June 30, 2002 

Jointly Funded by: 

Poultry Protein & Fat Council of the U.S. Poultry & Egg Association 

Fats and Proteins Research Foundation, Inc. 

The University of Georgia 
A Demonstration of Fat and Grease as Industrial Boiler 

Fuel 

EXECUTIVE SUMMARY 

The University of Georgia (UGA) Engineering Outreach Service (EOS) used fats and 

grease (chicken fat, yellow grease, choice white grease, and beef tallow) as industrial 

boiler fuels in the 100,000 lb./hr. No. 2 boiler at the UGA steam plant during January 

and February 2002. The project was funded by the Fats and Proteins Research 

Foundation, Inc. and the Poultry Protein & Fat Council of the U.S. Poultry & Egg 

Association. The objectives of the project were to publicly demonstrate the use of 

biofuel for industrial steam production and to examine the procedures necessary for 

its use. 

Fuel No. of Tests

Natural Gas 9

Choice White Grease 10

Choice White Grease - Fuel Oil Blend 12

Tallow 13

Tallow Fuel - Oil Blend 15

Yellow Grease - Fuel Oil Blend 19

Yellow Grease 21

No. 2 Fuel Oil 22

Chicken Fat - Fuel Oil Blend 23

Chicken Fat 29

Total 173

Tests were conducted Jan. 28 thru Mar. 15, 2002.

 Combustion Test Program Summary

Biofuels, either singly or blended with No. 2 fuel oil, are technically and 

economically viable alternatives to No. 2 fuel oil. Biofuels are user friendly and less 

hazardous than petroleum fuels. The addition of biofuel combustion capability is 

simple and inexpensive. It is not necessary to replace or compromise the operation of 

existing fossil fuel systems. 

Industrial boiler operators can use these results to economically justify the use of 

biofuels and to support air emissions permit submittals. Even lower emissions levels 

may be obtained from boilers employing advanced combustion systems. 

Summary of Results: 

1. Laboratory analyses showed that the fats and greases tested have high heating 

value, low ash, negligible sulfur, low moisture, and other physical and chemical 

properties conducive to their use as boiler fuel. Heating values for the biofuel 

blends tested are within 95% of the heating value of No. 2 fuel oil. 

i 
2. The 100,000 lb./hr. No. 2 boiler at the UGA steam plant was retrofitted to burn 

biofuels for approximately $31,000, including the cost to add flue gas 

recirculation (FGR). This amount does not include any expense for the 

construction of fuel storage facilities, which were not required for the 

demonstration program. The biofuel heat exchanger was obtained without cost to 

the project. It was not necessary to replace or modify the boiler fuel train or 

nozzle for these tests. 

3. The tests demonstrated that the biofuels burn cleanly, readily, without odor and 

without damage to boiler equipment. 

4. During this test program, biofuels produced steam within 3.8% to 5.3% of the 

efficiency of No. 2 fuel oil. Biofuels blended with No. 2 fuel oil were more 

efficient than unblended biofuels, and can actually produce steam with more 

efficiency than No. 2 fuel oil. Throughout the tests part load efficiency was 

greater than maximum load efficiency, and steam production with FGR was more 

efficient than without FGR. 

5. Biofuels are clean burning. They generally produce fewer combustion emissions 

than No. 2 fuel oil. 

6. Flue gas recirculation is an effective way to reduce NOx emissions for both fossil 

and biofuels. 

Impact of the Research Results relative to the requirements for Boiler No. 2 in 

the UGA Part 70 Operating (air emissions) Permit (“the Permit”): 

1. The Permit prohibits the burning of any fuel whose sulfur content exceeds 1.3% 

(para. 3.2.1). The maximum sulfur content of any biofuel tested was 0.007%, and 

0.13% for any biofuel blended with No. 2 fuel. 

2. The Permit limits particulate matter emissions to 0.417 lb/mmBtu (para. 3.4.1). 

The maximum total particulate (non-condensible and condensible) emission rate 

of any biofuel was 0.083 lb/mmBtu. 

3. The Permit limits visible emissions to 40% opacity (para. 3.4.9). Smokestack 

opacity ranged between 0% and 11% during the biofuel tests. 

Impact of the Research Results relative to the GA Rules for Air Quality Control 

(the “Rules”): 

1. The Rules (Sections (2)(d)2 & 3) limit particulate emissions from all fuel-burning 

equipment, of any size, to 0.10 lb/mmBtu and opacity to 20%. The maximum

total particulate (non-condensible and condensible) emission rate of any biofuel 

was 0.083 lb/mmBtu. Smokestack opacity ranged between 0% and 11% during 

the biofuel tests. 

ii 
2. The Rules (Section (2)(d)4) limit NOx emissions to 0.3 lb/mmBtu from fuel oil 

burning equipment, of any size, in an attainment area. The maximum NOx

emission rate of any biofuel tested was 0.23 lb/mmBtu. 

Contents 

Introduction Section 1 

Analysis of Fats and Greases Section 2 

Test Facility Description Section 3 

Combustion Demonstration Section 4 

Emissions Testing Section 5 

Conclusions Section 6 

References Section 7

Appendices Section 8 

Acknowledgements 

This research project was jointly funded by Poultry Protein & Fat Council of the U.S. 

Poultry & Egg Association, the Fats and Protein Research Foundation, Inc., and The 

University of Georgia 

The University of Georgia (UGA) Engineering Outreach Service (EOS) gratefully 

acknowledges the support of: 

• The test team: Erin Callaghan, Bryan Graffagnini, and Javier Sayago, 

• UGA steam plant personnel, in particular: John Benca, Jim Olbrych, Danny 

Langston, Jerry Bray, Dwight Epps and Doug Pittard, 

• UGA Environmental, Health & Safety personnel, in particular, Mike Stover, 

• UGA faculty, in particular: Dr. John Goodrum, Dr. Jackie Sellers, and Dr. 

Keshav Das, 

• UGA Physical Plant Plumbing, Sheet Metal, Electrical and Welding Shops, 

• American Proteins, Inc., especially: Roger Smith, Kevin Custer, and Gary 

Bottomley, 

• Griffin Industries: Shannon Behimer and Dana Hand, 

• The GA Dept. of Natural Resources: Don Holder and Susan Jenkins, and 

• The Georgia Environmental Partnership. 

iii 
2. ANALYSIS OF FATS AND GREASE 

2.1. Introduction 

Laboratory analyses of the fats and grease (biofuel oils) established their 

commercial specifications relative to standard market product designations. The 

physical properties of the biofuel oils were used to design the test facility at the 

UGA central steam plant. 

2.2. Sampling Procedures 

During the combustion test program, the test team randomly collected three 500-

ml samples of each fuel, one each at the beginning, middle and end of each test 

series. A total of (33) fuel samples were obtained: six (6) samples each of 

chicken fat and yellow grease; and three (3) samples each of choice white grease, 

tallow, No. 2 fuel oil and the blends of chicken fat, yellow grease, choice white 

grease and tallow. (All blends consisted of 33% fat or grease and 67% No. 2 fuel 

oil.) The team also collected four (4) samples of various solid combustion byproduct residues from inside the boiler. 

The project procedures maintained sample chain of custody from initial sampling 

through analysis. 

After initial cooling, the test samples were secured in refrigerated storage (4 deg. 

C.) while at UGA. The test samples were divided into smaller samples for 

analyses by the UGA laboratories and by commercial laboratories. The samples 

analyzed by commercial laboratories were overnight shipped in “cold packs”. 

 Fig. 3. Fuel sampling during test 

2 - 1 
2.3. Fat and Grease Properties 

Test Chicken Fat Yellow

Grease

Choice White

Grease

Tallow

C08:0 <0.10% <0.10% <0.10% <0.10%

C10:0 <0.10% <0.10% <0.10% <0.10%

C11:0 <0.10% <0.10% <0.10% <0.10%

C12:0 <0.10% <0.10% <0.10% <0.10%

C14:0 0.57% 0.70% 1.57% 2.73%

C14:1 0.26% 0.14% 0.36% 0.50%

C15:0 <0.10% 0.11% 0.26% 0.43%

C15:1 <0.10% <0.10% <0.10% 0.16%

C16:0 22.76% 14.26% 22.04% 22.99%

C16.1 8.37% 1.43% 5.03% 2.86%

C16.2 <0.10% <0.10% <0.10% <0.10%

C16.3 <0.10% <0.10% <0.10% <0.10%

C16.4 <0.10% <0.10% <0.10% <0.10%

C17:0 0.11% 0.33% 0.63% 1.35%

C17:1 0.12% 0.23% 0.43% 0.75%

C18.0 5.36% 8.23% 9.95% 19.44%

C18.1 42.07% 43.34% 42.45% 41.60%

C18.2 17.14% 26.25% 13.17% 3.91%

C18.3 1.07% 2.51% 0.97% 0.49%

C18.4 0.22% 0.47% 0.29% 0.36%

C20.0 <0.10% 0.33% 0.14% 0.14%

C20.1 0.45% 0.48% 0.56% 0.33%

C20.2 0.20% <0.10% 0.19% <0.10%

C20.3 0.19% <0.10% 0.12% <0.10%

C20.4 0.45% <0.10% 0.34% <0.10%

C20.5 <0.10% <0.10% 0.11% <0.10%

C21:5 <0.10% <0.10% <0.10% <0.10%

C22:0 <0.10% 3.50% <0.10% <0.10%

C22:1 <0.10% <0.10% <0.10% <0.10%

C22:2 <0.10% <0.10% <0.10% <0.10%

C22:3 <0.10% <0.10% <0.10% <0.10%

C22:4 0.10% <0.10% <0.10% <0.10%

C22:5 <0.10% <0.10% 0.14% <0.10%

C22:6 <0.10% <0.10% 0.22% <0.10%

C24:0 <0.10% 0.12% <0.10% <0.10%

C24:1 <0.10% <0.10% <0.10% <0.10%

unknown

components 0.56% 0.72% 1.03% 1.96%

Moisture & 

Volatiles

0.12% 0.38% 0.24% 0.17%

Insoluble

Impurities

0.08% 0.06% 0.29% 0.12%

Unsaponifiable

Matter

0.51% 0.42% 0.73% 0.30%

Table 1 , Fat and Grease Properties1

1) Woodson-Tenent Laboratories, Memphis, TN

Fatty Acid Profile, % Relative:

MIU Analysis:

2 - 2 
To establish the commercial specifications of the fats and greases relative to 

standard market product designations, Woodson-Tenent Laboratories Division 

of Eurofins Scientific, Inc., Memphis, TN performed a fatty acid analysis of one 

sample each of chicken fat, yellow grease, choice white grease and tallow, 

Table 1. The fatty acid profiles were determined using gas chromatography 

(AOCS method CE2-66/CE1-620, 0.01% accuracy). 

In addition, Woodson-Tenent performed MIU (moisture, impurities, 

unsaponifiables) analyses of eight (8) biofuel samples, two (2) samples each of 

chicken fat, yellow grease, choice white grease and tallow, Table 1. 

2.4. Viscosity and Specific Gravity 

In the summer of 2001, the UGA Biological and Agricultural Engineering (BAE) 

Department analyzed representative samples of chicken fat and yellow grease, 

obtained from a local company, to establish a range of viscosity and specific 

gravity for the design of the test facility. 

In the spring of 2002, BAE analyzed fuel samples collected during the test 

program. The UGA laboratory used a Brookfield LVT viscometer to determine 

dynamic viscosity (1% accuracy and 0.2% full-scale reproducibility). Specific 

gravity was measured directly. The dynamic viscosity of each fat and grease, of 

four (4) biofuel blends and of No. 2 fuel oil was measured over a range of five (5) 

temperatures and five (5) shear rates. The specific gravity of each fat and grease 

and of No. 2 fuel oil was measured over a range of five (5) temperatures. One 

sample of each fuel was tested. All biofuel blends consist of 33% biofuel and 

67% No. 2 fuel oil. No. 6 fuel oil viscosity and specific gravity are given below 

for reference. 

Fuel Dynamic

Viscosity, cP Specific Gravity

No. 2 Fuel Oil 1 2.3 4, 5 0.83 4

Choice White Grease Blend 1 4.7 4, 5 not analyzed

Yellow Grease Blend 1 4.9 4, 5 not analyzed

Tallow Blend 1 5.2 4, 5 not analyzed

Chicken Fat Blend 1 12.6 4, 5 not analyzed

Chicken Fat 1 23.3 4, 5 0.89 4

Yellow Grease 1 23.3 4, 5 0.89 4

Tallow 1 24.2 4, 5 0.89 4

Choice White Grease 1 25.0 4, 5 0.88 4

No. 6 Fuel Oil 2 490 3 0.97 3

Table 2 , Biofuel & Fuel Oil Physical Properties

1) Goodrum et al., 2002; 2) Babcock & Wilcox, 1976; 3) data at 38 deg. C.; 4) data at

54.4 deg. C.; 5) data at 12.94 s-1 shear rate

2 - 3 
2.5. Ultimate Analysis and Heating Value 

PSC Analytical Services, Reading, PA analyzed a total of (33) biofuel, 

biofuel/fuel oil blends and fuel oil samples to establish their comparative 

combustion chemistry and heating values. (All biofuel blends consist of 33% 

biofuel and 67% No. 2 fuel oil.) PSC used standard ASTM test methods for all 

analyses. PSC is certified/ accredited by the USEPA, NIOSH, the US Corp of 

Engineers, and (12) states. 

Fuel

Energy

Content,

Btu/Lb.

Ash Carbon Hydrogen Nitrogen Oxygen Sulfur Moisture

Chicken Fat 16,873 0.14% 75.3% 11.4% 0.04% 13.1% 0.006% (trace)

Chicken Fat - Fuel Oil Blend 18,223 0.02% 82.7% 12.2% 0.06% 3.83% 0.12% (trace)

Yellow Grease 16,899 0.02% 76.4% 11.6% 0.03% 12.1% 0.005% (trace)

Yellow Grease - F.O. Blend 18,543 0.01% 80.2% 11.6% 0.07% 8.01% 0.13% (trace)

Choice White Grease 16,893 0.08% 76.5% 11.5% 0.05% 11.6% 0.007% (trace)

Ch. Wht. Grease - F.O. Blend 18,493 0.01% 82.2% 12.1% 0.09% 5.48% 0.13% (trace)

Tallow 16,920 0.03% 76.6% 11.9% 0.02% 11.4% 0.003% (trace)

Tallow Fuel - Oil Blend 18,523 0.06% 80.7% 11.9% 0.01% 7.22% 0.13% (trace)

No. 2 Fuel Oil 19,237 0.02% 84.0% 11.9% 0.01% 3.78% 0.35% (trace)

Table 3 , Fuel Energy Content and Ultimate Analysis 1 

1) PSC Analytical Services, Reading, PA

2.6. General Characterization 

The Material Safety Data Sheets (MSDS) included in the Appendix indicate that 

the fats and greases tested are neither hazardous nor explosive. From the test 

team’s experience, these fats and greases have a distinct and unpleasant odor. 

However, their volatility is low and the odors do not diffuse readily. 

Reports from industry indicate that chicken fat is very miscible in fuel oil and 

does not readily separate in solution. The test team subjectively confirmed 

miscibility during the demonstration project; however, definitive data was not 

collected. 

2.7. Discussion 

Preliminary laboratory analyses indicated that fats and greases could be used with 

the No. 2 boiler burner nozzle and that the fuel handing system designed for the 

test program could easily handle these biofuels. Actual combustion testing 

demonstrated these findings. Later testing confirmed that biofuels, both singly 

and blended, have high heating value, low ash, and low sulfur content. Heating 

values for the biofuel blends tested are within 95% of the heating value of No. 2 

fuel oil. 

2 - 4 
The test team concluded that the chicken fat delivered on January 29, 2002 was 

substandard; the results from the analyses and combustion of this biofuel were 

omitted from the report. Initially, the particulate content in the chicken fat caused 

repeated plugging of the fuel handing system filters. Flue gas testing indicated 

high levels of NOx. Subsequent laboratory analyses showed high levels of 

insoluble impurities. 

Two additional deliveries of chicken fat were ordered and tested. Their 

particulate content was negligible, and the fuel handling system filters did not 

plug. Insoluble impurity content and emissions of NOx were consistent with the 

other biofuels tested. Insoluble impurities were 20% and NOx emissions were 

66% of that from the initial chicken fat delivery. This report includes the 

findings from the latter chicken fat deliveries. 

These results confirm the need for a high degree of filtration for fats and greases 

delivered as boiler fuel. Inadequately pre-filtered biofuel causes fuel handing 

problems and may increase gaseous emissions. 

PSC Analytical Services reported problems maintaining data consistency due to 

the lack of homogeneity of the fuel samples they analyzed. The unblended 

biofuel samples separated into fractions at room temperature. Heating and stirring 

of the samples is necessary before they can be analyzed. 

Research by Dr. John Goodrum at UGA (see References, Section 8) showed that 

at 40° C chicken fat, yellow grease, choice white grease and tallow were almost 

entirely solid. Their liquid-solid transition occurs over 40 – 48° C, and they are 

all completely liquid by approximately 50° C. 

All of the samples (biofuels, both singly and blended, and No. 2 fuel oil) 

examined by Dr. Goodrum exhibited viscosity that transitioned from nonNewtonian to Newtonian. The viscosity of Newtonian fluids does not vary with 

shear rate. The viscosity of these fuels initially decreased with increasing shear 

rate (non-Newtonian fluid behavior), followed by viscosity that became 

independent of shear rate when the shear rate was increased beyond 12.94s-1. In 

other words, the viscosity curves leveled off (viscosity became fairly constant at a 

given temperature) once the fluid was in motion. 

The blends of chicken fat, yellow grease, choice white grease and tallow with No. 

2 fuel oil showed rheological properties very similar to those of pure No. 2 fuel 

oil. 

2 - 5 
3. TEST FACILITY DESCRIPTION 

3.1. The University of Georgia Steam Plant No. 2 Boiler 

All combustion testing was conducted using the No. 2 boiler located at the central 

steam plant at The University of Georgia campus in Athens, Georgia. 

Combustion Engineering, Inc. manufactured this boiler in 1970. It was designed 

to combust natural gas, No. 2 oil and No. 6 oil for the production of 100,000 

lbs./hr. of saturated steam at 250 psig. This boiler currently operates at 100 psig. 

using natural gas, with No. 2 fuel oil as an alternative. 

The No. 2 boiler is a pressurized, water-tube design, package unit. It includes a 

forced-draft fan and a single steam/air atomized fuel nozzle (Todd Combustion, 

Inc. TCD Atomizer). The TCD Atomizer nozzle was developed in 1958, and 

does not include air or fuel staging to reduce NOx formation. This boiler does not 

have combustion air preheating or an economizer. Flue gas emissions control is 

not required. 

 Fig. 4, Burner nozzle for the No. 2 boiler 

3 - 1 
3.2. Steam Plant Modifications 

Neither the boiler burner nozzle nor the fuel train were changed or modified for 

the combustion tests. The biofuel handling system was piped into the fuel oil 

delivery piping upstream of the fuel train. For further details, please refer to the 

Appendix, Dwg. No. SK-001, Central Steam Plant Site Plan, and Dwg. No. SK002, Boiler No. 2 Process Flow Diagram. 

A 7 hp gear pump supplied biofuel to the boiler fuel train at a maximum of 22 

gpm. A pressure control valve and a safety relief valve maintained the pump 

discharge pressure to a maximum of 275 psig. Two (2) cast iron basket strainers 

in parallel protected the pump. A shell and tube heat exchanger, which 

maintained biofuel temperature, was rated for 150 psig and was installed on the 

gear pump suction side. 1-1/2” dia. carbon steel sch. 40 piping and 300-lb. 

malleable iron screwed fittings were used throughout. Some sections of the 

piping were steam traced. 

The biofuel delivery system was manually controlled. Instrumentation consisted 

of two (2) fuel flow meters, a rotary flow indicator, and necessary pressure and 

temperature gauges. 

The only modification to the boiler was the temporary addition of a flue gas 

recirculation (FGR) duct and damper. No modifications were made to either the 

boiler internals or instrumentation. 

3.3. Fuel Handling System

The biofuel handling system consisted of both mobile equipment and equipment 

temporarily installed for the tests. Biofuels were transported to the University and 

stored on site in a 7,000 gallon tanker-trailer. A second tanker trailer was utilized 

for biofuel/ fuel oil batch mixing. The test protocols were planned so that the 

quantity of biofuel available at the beginning of each testing period was sufficient 

for the completion of that test, thus avoiding the complexity of changing fuel 

supply during a test. 

3 - 2 
 Fig. 5, Delivery and mixing tankers at UGA steam plant. 

Previous industrial experience had indicated that after a 24 hour exposure to 

extreme winter ambient temperatures, a 7,000 gallon tanker load of biofuel could 

become too viscous for handling. Therefore, all biofuel was delivered warm (over 

100° F) and within 4 hours after loading. All biofuel suppliers were located near 

Atlanta, GA, less than 80 miles from the steam plant. Delivery tankers were 

piped to the fuel system immediately after they arrived at the UGA steam plant. 

The fuel system continuously recirculated the biofuel to the tanker and kept it 

warm and mixed. 

A heat exchanger was included in the fuel handling system prior to fuel transfer to 

the boiler. The heat exchanger maintained the biofuel temperature to 

approximately 165° F to reduce its viscosity to that of No. 2 fuel oil. The source 

of heat for this unit was 5 psig steam. 

3 - 3 
 Fig. 6, Fuel heating, pumping and mixing system. 

3.4. Flue Gas Recirculation System

The FGR system consisted of a 20 inch diameter duct connecting the boiler flue 

gas breaching (at 0.0 in. wg. static pressure) and the forced draft fan inlet (at 

negative 0.25 in. wg. static pressure). An adjustable butterfly damper was 

installed in the duct to control flow. Pitot tube flow measurements indicated that 

7 to 10% of the flue gas exiting the boiler was recirculated back into the burner. 

3.5. Environmental Protection 

Provisions were made to maintain personnel safety and to avoid and control spills 

in accordance with the UGA Spill Prevention Control and Countermeasure Plan 

(SPCCP) and the UGA Storm Water Pollution Prevention Plan (SWPPP). The 

biofuel transfer pump, two fuel strainers, and the heat exchanger were located in a 

diked containment area to isolate them from the sanitary sewer system. 

3 - 4 
3. TEST FACILITY DESCRIPTION 

3.1. The University of Georgia Steam Plant No. 2 Boiler 

All combustion testing was conducted using the No. 2 boiler located at the central 

steam plant at The University of Georgia campus in Athens, Georgia. 

Combustion Engineering, Inc. manufactured this boiler in 1970. It was designed 

to combust natural gas, No. 2 oil and No. 6 oil for the production of 100,000 

lbs./hr. of saturated steam at 250 psig. This boiler currently operates at 100 psig. 

using natural gas, with No. 2 fuel oil as an alternative. 

The No. 2 boiler is a pressurized, water-tube design, package unit. It includes a 

forced-draft fan and a single steam/air atomized fuel nozzle (Todd Combustion, 

Inc. TCD Atomizer). The TCD Atomizer nozzle was developed in 1958, and 

does not include air or fuel staging to reduce NOx formation. This boiler does not 

have combustion air preheating or an economizer. Flue gas emissions control is 

not required. 

 Fig. 4, Burner nozzle for the No. 2 boiler 

3 - 1 
3.2. Steam Plant Modifications 

Neither the boiler burner nozzle nor the fuel train were changed or modified for 

the combustion tests. The biofuel handling system was piped into the fuel oil 

delivery piping upstream of the fuel train. For further details, please refer to the 

Appendix, Dwg. No. SK-001, Central Steam Plant Site Plan, and Dwg. No. SK002, Boiler No. 2 Process Flow Diagram. 

A 7 hp gear pump supplied biofuel to the boiler fuel train at a maximum of 22 

gpm. A pressure control valve and a safety relief valve maintained the pump 

discharge pressure to a maximum of 275 psig. Two (2) cast iron basket strainers 

in parallel protected the pump. A shell and tube heat exchanger, which 

maintained biofuel temperature, was rated for 150 psig and was installed on the 

gear pump suction side. 1-1/2” dia. carbon steel sch. 40 piping and 300-lb. 

malleable iron screwed fittings were used throughout. Some sections of the 

piping were steam traced. 

The biofuel delivery system was manually controlled. Instrumentation consisted 

of two (2) fuel flow meters, a rotary flow indicator, and necessary pressure and 

temperature gauges. 

The only modification to the boiler was the temporary addition of a flue gas 

recirculation (FGR) duct and damper. No modifications were made to either the 

boiler internals or instrumentation. 

3.3. Fuel Handling System

The biofuel handling system consisted of both mobile equipment and equipment 

temporarily installed for the tests. Biofuels were transported to the University and 

stored on site in a 7,000 gallon tanker-trailer. A second tanker trailer was utilized 

for biofuel/ fuel oil batch mixing. The test protocols were planned so that the 

quantity of biofuel available at the beginning of each testing period was sufficient 

for the completion of that test, thus avoiding the complexity of changing fuel 

supply during a test. 

3 - 2 
 Fig. 5, Delivery and mixing tankers at UGA steam plant. 

Previous industrial experience had indicated that after a 24 hour exposure to 

extreme winter ambient temperatures, a 7,000 gallon tanker load of biofuel could 

become too viscous for handling. Therefore, all biofuel was delivered warm (over 

100° F) and within 4 hours after loading. All biofuel suppliers were located near 

Atlanta, GA, less than 80 miles from the steam plant. Delivery tankers were 

piped to the fuel system immediately after they arrived at the UGA steam plant. 

The fuel system continuously recirculated the biofuel to the tanker and kept it 

warm and mixed. 

A heat exchanger was included in the fuel handling system prior to fuel transfer to 

the boiler. The heat exchanger maintained the biofuel temperature to 

approximately 165° F to reduce its viscosity to that of No. 2 fuel oil. The source 

of heat for this unit was 5 psig steam. 

3 - 3 
 Fig. 6, Fuel heating, pumping and mixing system. 

3.4. Flue Gas Recirculation System

The FGR system consisted of a 20 inch diameter duct connecting the boiler flue 

gas breaching (at 0.0 in. wg. static pressure) and the forced draft fan inlet (at 

negative 0.25 in. wg. static pressure). An adjustable butterfly damper was 

installed in the duct to control flow. Pitot tube flow measurements indicated that 

7 to 10% of the flue gas exiting the boiler was recirculated back into the burner. 

3.5. Environmental Protection 

Provisions were made to maintain personnel safety and to avoid and control spills 

in accordance with the UGA Spill Prevention Control and Countermeasure Plan 

(SPCCP) and the UGA Storm Water Pollution Prevention Plan (SWPPP). The 

biofuel transfer pump, two fuel strainers, and the heat exchanger were located in a 

diked containment area to isolate them from the sanitary sewer system. 

3 - 4 
4. COMBUSTION DEMONSTRATION 

4.1. Introduction 

Industrial boiler operating experience and data were obtained while firing natural 

gas, No. 2 fuel oil, biofuels, and biofuels blended with No. 2 fuel oil. Baseline 

combustion testing was conducted by firing natural gas and fuel oil. Testing was 

conducted both with and without flue gas recirculation and with a range of boiler 

loads to evaluate emissions and combustion efficiencies under a wide range of 

operating conditions. The tests demonstrated that the biofuels burn efficiently, 

cleanly, readily, without odor and without damage to boiler equipment. 

4.2. Test Schedule 

The University of Georgia in Athens, GA is subject to mild winter conditions and 

considers the winter heating season to extend from late November to midFebruary. Steam demand on the central steam plant is in the 100,000 to 200,000 

lb/hr range during the winter heating season. This demand reduces to less than 

50,000 lb/hr during the summer. Throughout the year, daily load peaks in the 

early morning. 

The project team scheduled the tests during the winter heating season to allow for 

testing of the No. 2 boiler at maximum load. The tests began January 28, 2002 

and continued daily for three weeks until February 15, 2002. Maximum load tests 

were conducted in the morning, part load tests in the afternoon. A follow-up test 

on chicken fat was conducted on March 15, 2002. 

In general, the sequence of the testing was chicken fat and blend, yellow grease, 

choice white grease and blend, tallow, yellow grease blend and tallow blend. All 

blends consisted of 33% fat or grease and 67% No. 2 fuel oil. Natural gas and 

No. 2 fuel oil testing was conducted periodically throughout the test period. 

4.3. Boiler Efficiency 

Boiler efficiency is calculated as boiler steam energy output (btu/hr), less 

feedwater energy input, as a percentage of boiler fuel energy input (btu/hr). 

Steam plant instrumentation measured the flow (lb/hr) and pressure (psig) of the 

saturated steam produced by the boiler. Feedwater energy input was based on the 

temperature at the deaerator. 

Fuel energy input is the product of the flowrate and the energy content of the fuel. 

The flowrate was determined from the flow at the boiler burner nozzle flowmeter 

divided by the time interval between meter readings. PSC Analytical Services 

analyzed samples of each fuel to determine specific energy content. 

4 - 1 
Fig. 7, Boiler Efficiency,

Biofuels and Fuel Oil

70%

72%

74%

76%

78%

80%

82%

84%

T Y C W WB YB CB F TB

Fuels

1) Max. and part load conditions are averaged.

2) Error bars show std. error, n=4 or greater.

T 74.9% TALLOW

Y 75.6% YELLOW GREASE 

C 75.9% CHICKEN FAT 

W 76.4% CHOICE WHITE GREASE

WB 77.6% CHOICE WHITE GREASE - FUEL OIL BLEND

YB 78.0% YELLOW GREASE - FUEL OIL BLEND

CB 79.0% CHICKEN FAT - FUEL OIL BLEND

F 80.2% No. 2 FUEL OIL

TB 81.9% TALLOW - FUEL OIL BLEND

Fuel

Abrev.

Average 

Efficiency

Fuels

 Fig. 7, Legend 

 

4 - 2 
Fig. 8, Boiler Efficiency,

Max. and Part Load Conditions

72%

74%

76%

78%

80%

82%

84%

ABC D E F

Fuel/ Boiler Load

Error bars show std. error, n=4 or greater. 

A 75.6% BIOFUELS @ MAX. LOAD

B 77.2% BIOFUELS @ PART LOAD

C 77.4% BLENDED BIOFUELS @ MAX. LOAD

D 80.0% No. 2 FUEL OIL @ MAX. LOAD

E 80.5% No. 2 FUEL OIL @ PART LOAD

F 80.9% BLENDED BIOFUELS @ PART LOAD

Fuel/ 

Load

Average 

Efficiency

Fuel & Boiler Loading

 Fig. 8, Legend 

There was no significant difference in boiler efficiency when using 100% #2 fuel oil and 

blends with 33% biofuel oil according to a Student’s t-test at the α = 0.05 significance 

level. Boiler efficiency of #2 fuel oil was significantly higher compared to biofuel oil 

alone. Boiler efficiency was significantly higher using tallow blend compared to #2 fuel 

oil under half load conditions. 

4 - 3 
Fig. 9, Boiler Efficiency,

 with and w/o FGR

70%

72%

74%

76%

78%

80%

82%

A B C D E F

Fuel/ FGR Operation

1) Maximum boiler load conditions shown. 

2) Error bars show std. error, n=4 or greater. 

3) 1% error assumed for case E. 

A 74.7% BIOFUELS, w/o FGR

B 77.0% BIOFUELS with FGR

C 77.2% BLENDED BIOFUELS w/o FGR

D 77.4% BLENDED BIOFUELS with FGR

E 79.6% No. 2 FUEL OIL w/o FGR

F 80.4% No. 2 FUEL OIL with FGR

Fuel/ FGR.

Operation

Average 

Efficiency

Flue Gas Recirculation (FGR)

Status

 Fig. 9, Legend 

4.4. Combustion Characteristics 

The steam plant did not experience any unusual operating problems while burning 

biofuel or biofuel blends. The boiler lit off quickly and ran quietly. There were 

no fat and grease odors in the plant. 

Observations through the furnace sight glasses indicated that biofuels generally 

burn with a flame that is more yellow-colored and widely dispersed than with 

either natural gas or No. 2 fuel oil. However, the flame pattern was well 

contained within the furnace, as was verified by later internal inspection of the 

furnace. 

4 - 4 
At maximum load, fuel pressure to the boiler nozzle averaged 160 psig for 

unblended biofuels, 157 psig for blended biofuels, and 119 psig for No. 2 fuel oil. 

Atomizing steam pressure averaged 97 psig under all conditions. 

A thermocouple was installed in the furnace to measure its internal temperature. 

The thermocouple projected approximately 3 ft. into the back of the furnace, at 

the flue gas backpass. Temperature readings were read from a handheld digital 

thermometer.

 Fig. 10, Furnace temperature measurement system

4.5. Inspection of Boiler Internals 

The test team inspected the interior of the boiler after several months of firing 

natural gas exclusively; then, after firing No. 2 fuel oil exclusively; and, finally, 

after three weeks of biofuel combustion testing. The test team observed that the 

water tube exterior surfaces were clean and soot-free after natural gas firing. The 

tube surfaces were soot-covered, black-colored, and somewhat greasy after firing 

with No. 2 fuel oil. 

Following biofuel burning, the interior of the furnace appeared to be almost as 

clean as it was after firing natural gas, and much cleaner than it was after burning 

No. 2 fuel oil. A slight blackening of the tube surfaces, following the flame 

pattern, was observed in the front half of the 25-ft. long furnace. 

4 - 5 
A scattering of baked-on solid deposits (each approximately 2-3 mm in diameter) 

was found on the tube surfaces in the back half of the furnace. The UGA 

Chemical Analysis Laboratory analyzed three (3) samples of this material with an 

ICP mass spectrometer and found that they consist predominately of the elements 

Fe, Na, P, K, and Ca. 

 Fig. 11, Inspection of boiler heat transfer surfaces after testing biofuels 

4.6. Discussion 

The standard error calculated for the efficiency data ranged from 0.3% to 1.4%, 

plus or minus, with one data point showing a 2.6% +/- standard error, n = 4. The 

instrumentation used is standard industrial class equipment, and was not specially 

calibrated for this test. The greatest potential for error is the time recording taken 

between fuel meter readings. A time interval of 13 minutes was the minimum

used. All time readings were taken with a wristwatch to the nearest minute. 

There was no significant difference in efficiency under part load conditions versus 

full load according to an unpaired Student’s t-test at the α = 0.05 significance 

level. Also, there was no significant difference in efficiency with or without FGR. 

However, combustion with FGR resulted in significantly less excess air in the flue 

gas and indicates more complete combustion and less loss of energy to the stack. 

4 - 6 
5. EMISSIONS TESTING 

5.1. Particulate Testing 

Advanced Air Consultants Inc. (AAC), Murrayville, GA performed emissions 

tests for condensible (both organic and inorganic) and non-condensible 

particulate. Two test runs, each one hour long and conducted under normal boiler 

operation, were performed on each of five different fuels (chicken fat, yellow 

grease, choice white grease, tallow, and No. 2 fuel oil). Simultaneously with the 

particulate tests, the UGA Engineering Outreach test team measured gaseous 

emissions. 

AAC conducted all particulate testing according to the reference methods 

developed by the US EPA and promulgated in the Code of Federal Regulations, 

Title 40, Parts 51 and 60. AAC is certified per NELAC procedures to perform

EPA Method 5 particulate measurement. All of the test equipment was 

manufactured and calibrated as specified in the EPA methods. 

The particulate testing location was in a straight section of the No. 2 boiler 

breaching, between the boiler and a combined boiler stack. The number of 

velocity traverse points was chosen based on the distance of the test ports from up 

and downstream flow disturbances. Flow disturbances were located 2.5 diameters 

upstream and 1.0 diameters downstream from the test ports. Twenty traverse 

points were sampled. 

 Fig. 12. Inserting particulate testing probe into breaching. 

5 - 1 
AAC used a sampling train consisting of a stainless steel nozzle, stainless steel 

union, stainless steel lined probe, glass filter holder with Teflon filter support, 

four glass impingers, umbilical cord, vacuum pump, dry gas meter and orifice. 

Both the probe and filter compartment were heated to 250 deg. F. The impingers 

were placed in an ice bath to remove moisture from the sample gas stream. A "S" 

type pitot tube and an inclined manometer measured the gas velocity pressures. A 

type K thermocouple and a digital thermometer measured the gas temperature. 

The Denver Instruments Model A-250 analytical balance in the AAC laboratory 

weighed the particulate samples. 

In accordance with US EPA Method 19 (40CFR60), AAC calculated fuel FFactors using the fuel analysis data presented in Section 3 of this report. FFactors are used to calculate emission rates in pounds per million Btu, per US 

EPA methodology. 

The US EPA “F Factor” technique is a more convenient method to determine 

emissions on a mass per unit heat input basis. This technique allows the 

calculation of emissions without the need for precise measurement of fuel flow 

and combustion efficiency. 

Fuel F-Factor, Fd

Chicken Fat 8,865

Yellow Grease 9,108

Choice White Grease 9,145

Tallow 9,179

No. 2 Fuel Oil 8,850

Source: Advanced Air Consultants, Inc., Murrayville, GA

Ref.: Federal Register , 40:194, Part V, Oct. 6, 1975,

Table 4 , F-Factors

Fd is the ratio of the quantity of dry effluent gas generated by

combustion to the gross calorific value of the fuel, dscf/106

Btu.

AAC also monitored smokestack opacity. Maximum opacity with chicken fat 

was 4% and yellow grease was 6%. There was no opacity observed while 

burning tallow. Opacity was not monitored while burning choice white grease. 

Opacity testing was not performed in strict accordance with GA EPD compliance 

regulations, which require an average value for a series of opacity observations 

over a one-hour period. Instead, opacity testing during the program consisted of a 

series of spot observations. However, all opacity readings were taken by GA 

EPD-certified opacity readers. 

5 - 2 
Fig. 13 , Particulate Emissions,

Biofuels and Fuel Oil

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

Fuels

lb./mm Btu

cond. particulate 0.003 0.005 0.012 0.003 0.006

non-cond. particulate 0.009 0.014 0.010 0.038 0.077

Y T F W C

1) Test conditions: maximum boiler load with FGR. 

2) Condensible particulate = organic + inorganic condensible particulate. 

3) Total particulate = non-cond. + cond. particulate. 

4) Error bars show std. error for total particulate. 

Y

T

F

W

C

Fuel

Abrev. Fuel

CHICKEN FAT

YELLOW GREASE

TALLOW

No. 2 FUEL OIL

CHOICE WHITE GREASE

 Fig. 13. Legend 

5.2. Gaseous Emissions Testing 

The UGA Engineering Outreach team used an ENERAC 3000E analyzer to 

measure the gaseous emissions from the No. 2 boiler. The team recorded both 

average and instantaneous measurements of flue gas concentrations for oxygen, 

carbon monoxide, carbon dioxide, combustible gases, excess air, nitric oxide, 

nitrogen dioxide, NOx (NO + NO2), and sulfur dioxide. The analyzer software 

5 - 3 
program enabled the recording of emissions data directly to a spreadsheet file on 

the hard drive of a laptop computer. Data was recorded during steady state 

operations for each fuel tested, at both maximum and part loads and at each FGR 

damper setting. 

The ENERAC 3000 portable emissions analyzer is a self-contained, extractive 

flue gas monitoring system utilizing electrochemical sensors with an internal 

sample pump designed for 600-900 cc/minute. A separate vacuum pump extracted 

flue gas from a breaching port and discharged it to the ENERAC. Teflon tubing 

interconnected a filter probe in the breaching through two moisture condensers to 

the vacuum pump and then to the analyzer. 

The ENERAC sensors use an electronically controlled circuit to minimize zero 

drift and reject cross interference from other compounds, in compliance with EPA 

Conditional Test Methods (CTM) –022, -030 and –034. The performance 

specifications of the CTM-022 method are equivalent to US EPA Method 7E 

requirements. The accuracy of the sensors is +/-2%, and they are capable of 

operating at 1.5 orders of magnitude of gas concentrations. 

Equipment was calibrated several times per week, and was checked daily for 

accuracy. The system was allowed to autozero daily. Span calibration of CO, 

NO, SO, NO2 was performed 2-3 times per week using calibrated gases (CO at 78 

ppm, NO at 124 ppm, SO2 at 25 ppm, and NO2 at 92 ppm.) 

 Fig. 14. Logging of emissions data from Enerac 3000E. 

5 - 4 
Fig. 15 , NOx Emissions

0

20

40

60

80

100

120

140

 N 

w.

FGR

 Y 

w.

FGR

 T 

w.

FGR

 YB 

w.

FGR

 N YB CB 

w.

FGR

 T F 

w.

FGR

 Y TB 

w.

FGR

 WB 

w.

FGR

 F TB CB WB W 

w.

FGR

 W C 

w.

FGR

 C 

Fuel/ FGR Operation

NOx, ppm

1) All tests were conducted at maximum boiler load. 

2) Error bars show std. error calculated for cases: CB with FGR (n=2) and T w/o FGR (n=3). 2% error assumed 

for all of the other cases. 

w/o FGR w. FGR % reduction w/o FGR w. FGR delta

N 80 54 32.5% 1,983 2,010 27

Y 93 71 23.7% 1,755 1,830 75

T 90 77 14.4% 1,824 1,928 104

YB 89 80 10.1% 1,773 1,811 38

CB 99 90 9.1% 1,756 1,843 87

F 98 91 7.1% 1,836 1,901 65

TB 98 95 3.1% 1,714 1,790 76

WB 101 97 4.0% 1,860 1,954 94

W 108 105 2.8% 1,855 1,886 31

C 118 112 5.1% 1,776 n.a. n.a.

NOx emissions, ppm Furnace Temperature, deg. F. Fuel Legend

CHOICE WHITE GREASE - FUEL OIL BLEND

CHOICE WHITE GREASE

CHICKEN FAT 

NATURAL GAS

YELLOW GREASE 

TALLOW

YELLOW GREASE - FUEL OIL BLEND

CHICKEN FAT - FUEL OIL BLEND

No. 2 FUEL OIL

TALLOW - FUEL OIL BLEND

 Fig. 15. Legend 

5 - 5 
Fig. 16 , SO2 Emissions

0

20

40

60

80

100

120

140

 C N 

w .

FGR

 N W 

w .

FGR

 W Y C 

w .

FGR

 Y 

w .

FGR

 T T 

w .

FGR

 YB YB 

w .

FGR

 TB TB 

w .

FGR

 WB CB CB 

w .

FGR

 F WB 

w .

FGR

 F 

w .

FGR

Fuel/ FGR Operation

SO2, ppm

1) All tests were conducted at maximum boiler load. 

2) Error bars show std. error (n=2 or greater) calculated for cases: Y, YB, F, W, and C with FGR; and cases 

T, CB and W w/o FGR. 2% error assumed for all of the other cases. 

w/o FGR w. FGR delta

N 0

Y 0

W 0

C 0

T 1

YB 20 48 28

TB 59 69 10

WB 69 109 40

CB 72 80 8

F 8 No. 2 FUEL OIL 7

NATURAL GAS

YELLOW GREASE 

CHOICE WHITE GREASE

CHICKEN FAT

TALLOW

YELLOW GREASE - FUEL OIL BLEND

TALLOW - FUEL OIL BLEND

CHOICE WHITE GREASE - FUEL OIL BLEND

CHICKEN FAT - FUEL OIL BLEND

Fuel Legend SO2 emissions, ppm

0 0

1 1

0 0

0 0

4 3

127 40 Fig. 16. Legend 

5 - 6 
Fig. 17, CO2 Emissions

5

6

7

8

9

10

11

12

13

14

15

 W CB T C WB W 

w .

FGR

 Y TB YB Y 

w .

FGR

 C 

w .

FGR

 CB 

w .

FGR

 TB 

w .

FGR

 T 

w .

FGR

 WB 

w .

FGR

 YB 

w .

FGR

 N N 

w .

FGR

 F F 

w .

FGR

Fuel/ FGR Operation

CO2, %

1) All tests were conducted at maximum boiler load.

2) Error bars show std. error (n=2 or greater) calculated for cases: CB, F, and W with FGR, and T and W w/o FGR. 

3) 2% error assumed for all of the other cases.

w/o FGR w. FGR delta

W 6.9 7.5 0.6

CB 7.0 8.0 1.0

T 7.1 8.2 1.1

C 7.3 7.9 0.6

WB 7.3 8.3 1.0

Y 7.6 7.8 0.2

TB 7.7 8.1 0.4

YB 7.7 8.5 0.8

N 9.0 10.0 1.0

F 12.6 13.5 0.9

Fuel Legend CO2 emissions, %

No. 2 FUEL OIL

CHOICE WHITE GREASE

CHICKEN FAT - FUEL OIL BLEND

TALLOW

CHICKEN FAT

CHOICE WHITE GREASE - FUEL OIL BLEND

YELLOW GREASE 

TALLOW - FUEL OIL BLEND

YELLOW GREASE - FUEL OIL BLEND

NATURAL GAS

Fig. 17. Legend 

5 - 7 
Fig. 18 , CO Emissions

0

5

10

15

20

25

30

35

40

45

 C C 

w .

FGR

 CB TB 

w .

FGR

 TB YB N CB 

w .

FGR

 T WB Y W 

w .

FGR

 W Y 

w .

FGR

 F T 

w .

FGR

 N 

w .

FGR

 F 

w .

FGR

 WB 

w .

FGR

Fuel/ FGR Operation

CO, ppm

1) All tests were conducted at maximum boiler load. 

2) Error bars show std. error (n=2 or greater) calculated for cases: Y, T, CB, F, W, and C with FGR, and T w/o 

FGR. 2% error assumed for all of the other cases. 

w/o FGR w. FGR delta

C 0

CB 8 14 6

TB 9 9 0

YB

N 1

T 1

WB 14 39 25

Y 1

W 1

F 2

CHOICE WHITE GREASE - FUEL OIL BLEND

YELLOW GREASE

CHOICE WHITE GREASE

not available

Fuel Legend CO emissions, ppm

No. 2 FUEL OIL

CHICKEN FAT

CHICKEN FAT - FUEL OIL BLEND

TALLOW - FUEL OIL BLEND

YELLOW GREASE - FUEL OIL BLEND

NATURAL GAS

TALLOW

8 8

0 22 12

4 21 7

4 19 5

7 16 -1

0 23 3

Fig. 18. Legend 

5 - 8 
Fig. 19 , Combustibles in Flue Gas

0.00%

0.05%

0.10%

0.15%

0.20%

0.25%

0.30%

0.35%

 C Y 

w .

FGR

 CB 

w .

FGR

 C 

w .

FGR

 N TB WB W 

w .

FGR

 Y CB T F 

w .

FGR

 F N 

w .

FGR

 T 

w .

FGR

 TB 

w .

FGR

 WB 

w .

FGR

 W YB 

w .

FGR

 YB 

Fuel/ FGR Operation

Combustible 

Gases, %

1) All tests were conducted at maximum boiler load.

2) Error bars show std. error (n=2 or greater) calculated for cases: Y, T, YB, CB, F, W, and C with FGR; and cases T, CB and W w/o FGR.

3) 2% error assumed for all of the other cases.

w/o FGR w. FGR delta

CHICKEN FAT 0.14% 0.23% 0.09%

NATURAL GAS 0.23% 0.31% 0.08%

TALLOW - FUEL OIL BLEND 0.23% 0.31% 0.08%

CHOICE WHITE GREASE - FUEL OIL BLEND 0.23% 0.31% 0.08%

YELLOW GREASE 0.23% 0.16% -0.07%

CHICKEN FAT - FUEL OIL BLEND 0.26% 0.19% -0.07%

TALLOW 0.28% 0.31% 0.03%

No. 2 FUEL OIL 0.31% 0.31% 0.00%

CHOICE WHITE GREASE 0.31% 0.23% -0.08%

YELLOW GREASE - FUEL OIL BLEND 0.31% 0.31% 0.00%

Legend Combustibles in Flue Gas, %

Fig. 19. Legend 

5.3. Odor Sampling 

At no time during the demonstration program did the test team receive any 

complaints about odor originating from the steam plant. Test team members, 

BAE faculty and staff associated with the project, and the steam plant personnel 

(10 individuals, in total) monitored the campus for odor and recorded their 

findings at least twice for each test series. Odor was monitored (36) times 

throughout the demonstration program. Each odor test began at the steam plant; 

and, if the wind speed exceeded 1 to 2 mph, was repeated again 0.5 to 1.0 miles 

down wind of the steam plant. A check of the UGA campus weather website 

preceding each test confirmed the wind direction and velocity. All odor testers 

were asked to verify that they were not suffering from any nasal congestion. 

5 - 9 
Odor was not detected during any of the (17) tests taken down wind of the steam

plant. However, there were noticeable fat and grease odors detected in the 

vicinity (within 100 ft.) of the biofuel tankers. 

5.4. Flue Gas Recirculation (FGR) Flow Measurement 

Approximately 7 to 10 % of the boiler breaching flue gas was recirculated to the 

forced draft fan inlet with the recirculation damper 100% open. The test team

performed a series of flowrate measurements using standard pitot tube traverse 

methodology. Measurements were made for all fuels, at both full and part load 

conditions. 

The arrangement of the FGR ducting made pitot traversing difficult and impeded 

the accuracy of the tests. However, the tests are deemed accurate within 25%, 

which is sufficient to determine that the system was functioning. 

5.5. Discussion 

The most significant source of data inaccuracy during the particulate testing is the 

% of isokinetic sampling, which is the ratio of flue gas flow rate to the sampling 

flow rate. The GA EPD allows these rates to average within 10% of each other 

during a one-hour sample period, i.e., a test accuracy of 10%+/-. For compliance 

testing, two out of three samples must meet the 10% criteria. During this test 

program, at least one particulate test for each fuel met the EPD requirement. 

Odor and opacity test readings were subjective. Their degree of accuracy cannot 

be documented. Statistical analysis using the Student’s t-test statistic was used to 

test for significant difference (α = 0.05) for other data using Sigma-Plot version 

2.01 software (Jandel Corporation, San Raphael, CA). 

Total particulate emissions from biofuel oil as a group were not significantly 

different from particulate emissions from #2 fuel oil. However, total particulate 

emissions from chicken fat fuel was significantly higher than the other biofuel oils 

and both chicken fat and choice white fat particulate emissions were significantly 

higher than #2 fuel oil. Particulate emissions from chicken fat fuel were 

significantly higher than those from choice white grease. 

In general, the most significant source of data inaccuracy during gaseous emission 

testing is the specified 2%+/- accuracy of the ENERAC sensors. 

Most of the NOx formed during combustion is from high temperature oxidation of 

atmospheric nitrogen. This NOx is referred to as “thermal NOx and is popularly 

modeled as an exponential function of flame temperature and a square root 

function of oxygen concentration. Thus, the formation of thermal NOx can be 

controlled by manipulating the flame temperature or the oxygen concentration 

(Agrawal and Wood, 2002). Average emissions of NOx from the combustion of 

5 - 10 
all biofuel oils were not found to be significantly different than emissions from #2 

fuel oil (Student’s unpaired t-test, 0.05 significance level). However, the NOx

emissions from chicken fat alone were significantly higher than the other biofuel 

oils and #2 fuel oil and natural gas. This result is confounding, the chicken fat 

fuel contained higher ash (Table 3), however, total nitrogen was low and 

combustion conditions were identical to the other combustion tests. 

The procedures used in this testing of FGR both reduced oxygen (which decreases 

NOx) and increased furnace temperature (which increases NOx, see Fig. 15,

Legend). The net result was that for all cases when flue gas recirculation was 

used, NOx decreased in the range of 2.8% to 32.5%, significantly different from

emissions without FGR according to a Student’s paired t-test (α = 0.05). The 

discrepancy between the factors simultaneously driving the increase and the 

decrease of NOx should be further studied. 

The ENERAC may have recorded SO2 readings significantly lower than actual. 

Gas samples extracted from the breaching were cooled below the SO2

condensation temperature (to remove excess moisture) before the sample was 

analyzed by the ENERAC. However, the relative SO2 data values presented in 

Fig. 16 are considered valid because this data is proportional to % sulfur analyzed 

in the fuels. The biofuel oils had practically zero amounts of SO2 in emissions 

and they were significantly less than the biofuel oil blends and #2 fuel oil. 

Additionally, biofuel oil blends had significantly lower SO2 emissions that #2 fuel 

oil. 

There were significantly lower CO2 emissions from biofuel oil versus #2 fuel oil. 

Additionally, 33% blends of biofuel oil in #2 fuel oil had significantly lower CO2

emissions. 

There was no significant difference in CO emissions between the biofuel oils, 

blends, or #2 fuel oil. FGR had no significant effect on CO or combustibles 

emissions. Chicken fat and yellow grease emissions were significantly lower in 

combustibles than #2 fuel oil. 

5 - 11 
6. CONCLUSIONS 

Fats and greases were demonstrated as industrial boiler fuels. These biofuels easily and 

economically displace No. 2 fuel oil using the same boiler operating procedures as fuel 

oil without any modifications to internal boiler combustion equipment. The biofuels 

need to be kept warm during cold weather in order to flow through piping and equipment. 

When heated to about 160° F. biofuels are easily atomized and ignited. Construction 

costs for the pump, heat exchanger, instruments, piping, valves, fittings, and electrical 

system for a system to maintain the 160° F. temperature and to transfer fuel from storage 

to the boiler was less than $31,000. This total does not include the cost of engineering or 

the procurement cost for the heat exchanger. Extra costs would be incurred if separate 

storage tanks were needed for biofuel storage. Research should be accomplished 

focusing on the issues associated with using existing No. 2 fuel oil storage tanks for the 

storage of biofuel and biofuel blends. 

Air emissions from the combustion of the biofuel oils met or exceeded state and federal 

air quality permit requirements for The University of Georgia. Nitrogen oxides and 

particulate emissions were comparable to emissions from the combustion of No. 2 fuel 

oil, Table 4. Sulfur dioxide emissions and deposits on boiler tubes were similar to those 

encountered when burning natural gas. Biofuels also have low carbon monoxide 

emissions. The fuel nozzle used in the UGA boiler was a 1950’s design and no special 

procedures were used to minimize emissions through nozzle placement. Flue gas 

recirculation (FGR) was tested with 7% to 10% of flue gas being recirculated. FGR did 

not significantly increase boiler efficiency but did significantly reduce NOx emissions 

compared to tests without FGR according to a Students t-test at the α = 0.05 significance 

level. NOx emissions were not reduced enough to meet regulations for new sources and 

for non-attainment areas. Additional testing is required using low NOx nozzle designs 

and other methods for minimizing emissions. When the boiler was operated at half load, 

boiler efficiency was significantly greater for a blend of 33% tallow with 77% #2 fuel oil 

than when using 100% #2 fuel oil (α = 0.05). 

The biofuel oils have high heating value; low amounts of ash, nitrogen, and moisture; and 

negligible amounts of sulfur. Heating values of the biofuel oil blends tested are within 

95% of the heating value of No. 2 fuel oil. The specific gravity of the biofuels is close to 

that of No. 2 fuel oil. The biofuels are more viscous than No. 2 fuel oil, but much less 

viscous than No. 6 fuel oil. However, a blend of 30% biofuel with No. 2 fuel oil has a 

viscosity that is close to that of No. 2 fuel oil. Boiler efficiency while burning biofuel oil 

is comparable to that of No. 2 fuel oil. 

6 - 1 
NOx,

lb./MMBtu

Filterable PM,

lb./MMBtu

CO, 

lb./MMBtu

SO2, 

lb./MMBtu 5

UGA Boiler No. 2 Emissions, Tested at Max. Steam Load 1:

Chicken Fat, controlled with FGR 7 0.156 0.077 0.008 0.000

Yellow Grease, controlled with FGR 7 0.097 0.009 0.016 0.001

Choice White Grease, controlled with FGR 7 0.150 0.038 0.014 0.000

Tallow, controlled with FGR 7 0.101 0.014 0.018 0.007

No. 2 Fuel Oil, controlled with FGR 7 0.116 0.010 0.004 0.219

UGA Boiler No. 2 Emissions, Estimated at Max. Steam Load 2

:

Chicken Fat, uncontrolled (w/o LNB or FGR) 0.164 not available 0.000 0.000

Yellow Grease, uncontrolled (w/o LNB or FGR) 0.127 not available 0.012 0.000

Choice White Grease, uncontrolled (w/o LNB or FGR) 0.154 not available 0.014 0.000

Tallow, uncontrolled (w/o LNB or FGR) 0.118 not available 0.012 0.002

No. 2 Fuel Oil, uncontrolled (w/o LNB or FGR) 0.125 not available 0.003 0.150

Chicken Fat, blended 6

, uncontrolled 0.137 not available 0.008 0.124

Yellow Grease, blended 6

, uncontrolled 0.122 not available not available 0.034

Choice White Grease, blended 6

, uncontrolled 0.144 not available 0.012 0.119

Tallow, blended 6

, uncontrolled 0.129 not available 0.008 0.102

Chicken Fat, blended 6, controlled w. FGR 7 0.125 not available 0.014 0.138

Yellow Grease, blended 6

, controlled w. FGR 7 0.109 not available not available 0.083

Choice White Grease, blended 6

, controlled w. FGR 7 0.138 not available 0.033 0.188

Tallow, blended 6

, controlled w. FGR 7 0.125 not available 0.008 0.119

US EPA Emission Factors for Criteria Pollutants (boilers > 100 MMBtu/hr heat input) 3, 4:

0.071 0.014 0.036 0.393

0.098 0.002 0.082 0.000

0.171 0.014 0.036 0.393

0.186 0.002 0.082 0.000

1) Advanced Air Consultants, Murrayville, GA

2) Emissions data have been estimated using the test results from Advanced Air Consultants and ENERAC 3000E testing.

3) US EPA Fifth Edition 1995, with Supplements: A (1996), B ( 1996), D (1998), and E (1998)

4) The UGA No. 2 Boiler Operating Permit is based upon a 130 MMBtu/hr heat input.

5) SO2 emissions data have been reviewed in report Section 5.5, Discussion.

6) All blended fuels consist of 33% biofuel and 67% No. 2 fuel oil.

7) The FGR system was limited to 7% - 10% flue gas recirculation, see report Section 3.4.

Table 5 , Comparison of UGA Test Emissions to US EPA Criteria Pollutant Emission Factors 

Fuel & Firing Condition

No. 2 Fuel Oil fired, uncontrolled (w/o LNB or FGR)

Natural Gas fired, uncontrolled (w/o LNB or FGR)

No. 2 Fuel Oil fired, controlled with FGR

Natural Gas fired, controlled with FGR

Additional research is needed to understand: 

1. What is the effect of biofuel/fuel oil blend proportions on viscosity and miscibility? 

What blend proportions maintain fluidity (low viscosity) over the range of ambient 

storage temperatures (say, 32 to 100° F.) typical in industrial applications? What is 

the minimum amount of agitation required?

2. What are minimum required specifications for fats and greases used as biofuel? What 

are the requirements for solids removal (screening), MIU (moisture, insolubles, 

unsaponifiables), Ultimate analysis (C, H, N, S), energy content, specific gravity, 

viscosity, etc.? How shall biofuels be specified for environmental permitting? 

6 - 2 
7. REFERENCES 

1. Miller, G., Badger, M., Larsen, J., Clemens, T., Moyer, D., Wehr, T., 1999. A 

demonstration of pig lard as an industrial boiler fuel; presented at the 24th

International Conference on Coal Utilization & Fuel Systems, Clearwater, FL. 

2. Pearl, G., April 2001. Turn up the heat, Render (18-21).

3. Shigehara, R. T., Neulicht, R. M., Smith, W. S., Peeler, J. W., Summary of F Factor 

Methods for Determining Emissions from Combustion Sources. 

4. Goodrum, J. W., Geller, D. P., Adams, T. T., 2002. The rheological characterization 

of animal fats and their mixtures with #2 fuel oil. The University of Georgia, Athens, 

GA. Unpublished results.

5. The Babcock & Wilcox Company, 1976. Steam/ Its Generation and Use, 39th

edition., Babcock & Wilcox, New York, NY 

6. Energy Efficiency Systems, Inc., description of the ENERAC 3000. 

7. Advanced Air Consultants, Inc., 2002. Air emissions report for boiler number 2, 

animal fats engineering trials at UGA steam plant, Athens, GA, January 30 – March 

15, 2002. 

8. Georgia Department of Natural Resources,, Environmental Protection Division, Air 

Protection Branch, Part 70 Operating Permit, GA Environmental Protection Division 

Permit No. 8221-059-0059-V-01-0, for The University of Georgia, Oct. 30, 2000. 

9. Agrawal, R. K., Wood, S. C., 2002. Innovative solutions for cost-effective NOx 

control, Pollution Engineering; 34(6): 18-25. 

10. Georgia Department of Natural Resources, Environmental Protection Division, Air 

Protection Branch, Rules for Air Quality Control Chapter 391-3-1, effective 

December 26, 2001. 

11. U. S. Environmental Protection Agency, 1998. Emission Factors. 

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