Proceedings available at: http://www.extension.org/67668 The purpose of this research is to review engine performance and technology issues relating to generating electricity from digester gas in reciprocating internal combustion engines. Research performed at the Colorado State University (CSU) Engines & Energy Conversion Laboratory (EECL) and published material from other organizations is utilized. Digester gas (digas) can be used effectively in internal combustion engines for electricity production to offset operating costs and/or sell to the electric utility. Stationary industrial engines are generally employed for this purpose. Four application areas where systems have been successfully demonstrated are sewage processing plants, animal waste facilities, landfills, and agricultural waste processing systems. Digas is generated through anaerobic digestion, or biomethanization, for all these cases. There are many common engine technical issues within these areas, although the digas generation systems employed in each case are different. In this presentation issues pertinent to running engines on digas are explored. The focus is on animal waste facilities, but the presentation draws upon the other application areas for technical insight related to engine technology. Specific stationary engine types are discussed. High engine efficiency and power density are important to the economic viability of anaerobic digestion systems. Engine operational and design changes to maintain high efficiency and power density for digas fueling are analyzed. Management of engine maintenance problems is also key to economic viability. Corrosive gases contained in digas, such as hydrogen sulfide (H2S), are evaluated.

1. ©2010 Engines and Energy Conversion Laboratory
Operation of Internal
Combustion Engines on Digas
for Electricity Production
Livestock & Poultry Environmental Learning Center
National Conference: From Waste to Worth:
“Spreading” Science & Solutions
Grand Hyatt Hotel, Denver, Colorado
April 1-5, 2013
Daniel B. Olsen
Associate Professor
Mechanical Engineering Dept.

2. 22 May 2013
• Stationary Gas Engines
• Digas Characteristics
• Engine Design Modifications for Digas
• Gas Scrubbers
• Digas Installation
Outline

3. Digas Engine Design Options
1. Compression Ignition (Diesel) Engine
– Blend biogas with intake air
– Requires two fuels on site
2. Spark Ignition Stoichiometric Gas Engine
– 3-way catalyst for emissions control
– Lower efficiency
3. Spark Ignition Lean-burn Gas Engine
– Low emissions
– High efficiency
– High power density (bmep)
3

4. Stationary
Gas Engines
Power generation, Combined
heat and power, Gas
compression Pumping
Wärtsilä 34SG
Waukesha VGF
KUBOTA DG972-E2
Jenbacher Type 2
Cummins Genset
Caterpillar 3516C
4
Guascor V16
MAN CHP

5. Efficiency Trends
5 Heywood, J. B., “Internal Combustion Engine Fundamentals”, McGraw-Hill, Inc., 1988.
34%
35%
36%
37%
38%
39%
40%
41%
42%
100 150 200 250 300 350 400
bmep (psi)
Increasing boost & power at constant A/F
• Higher power density
(bmep) results in higher
efficiency
• Higher compression ratio
yields higher efficiency
Waukesha VGF (F18GLD)
• Knock (detonation)
limits compression
ratio of engine
• Fuel quality
determines
knock limit
Fuel A Knock Limit
Fuel B Knock Limit
Efficiency

6. 62 May 2013
• Stationary Gas Engines
• Digas Characteristics
• Engine Design Modifications for Digas
• Gas Scrubbers
• Digas Installation
Outline

7. Biogas Composition
• Two general types of biogas
– Wood gas from a gasifier
– Digas from sewage
processing, landfill, etc.
• Very different properties
from each other and from
natural gas
• Our focus is on digas from
agricultural systems
7
Wood Gas % Composition
Nitrogen, 55.4%
CO, 20.6%
Hydrogen, 18.4%
Methane, 2.2%
Oxygen, 1.8%
CO2, 1.3%

8. Test Results
62.4
30.0
61.5
70.2 66.3
23.9
139.1 139.6
0
20
40
60
80
100
120
140
160
1, Reformed
Natural Gas
2, Coal Gas 3, Wood Gas 4, Wood Gas 5, Digester
Gas
6, Landfill Gas 7, Reformed
Natural Gas
8, Coal Gas
MethaneNumber
Typical Natural Gas
# Test Gas %CH4 %H2 %N2 %CO %CO2
1
Reformed
Natural Gas
39.7 46.7 0.8 0.9 11.9
2 Coal Gas * 24.8 16.3 58 1
3 Wood Gas 10 40 3 24 23
4 Wood Gas 1 31 35 18 15
5 Digester Gas 60 * 2 * 38
6 Landfill Gas 60 * * * 40
7
Reformed
Natural Gas
1.2 30.8 49.0 15.6 3.4
8 Coal Gas 7 44 * 43 6
8
CriticalCompressionRatio
Malenshek M., Olsen D.B., “Methane number testing of alternative gaseous fuels”, Fuel, Volume 88, pp. 650-656, 2009.

9. Hydrogen Sulfide (H2S)
• Digas levels ~2000-5000 ppm H2S from hog and
cattle digesters
• Impact on engines
– Corrodes copper-based bearing materials
– Contaminates oil via blow-by
– Combustion of H2S produces SO2
9
/

10. 102 May 2013
• Stationary Gas Engines
• Digas Characteristics
• Engine Design Modifications for Digas
• Gas Scrubbers
• Digas Installation
Outline

11. Case Study: Waukesha 16V150LTD
(152 mm Bore x 165 mm Stroke)
• 1.1 MW at 1800 rpm, 15.8 bar
bmep
• Regulator spring replaced with
stiffer spring to increase fuel
pressure
• Fuel piping from regulator to
mixer increased from 3” to 4”
• Mixer insert flow area for digas
increased by 2.3X relative to
natural gas
11
Reinbold, E. and von der Ehe, James, “Development of the Dresser Waukesha 16V150LTD Engine for Bio-Gas Fuels”, ASME
Internal Combustion Engine Division 2009 Spring Technical Conference, ICES2009-76079, May 3-6, 2009.

12. Case Study: Waukesha 16V150LTD
(152 mm Bore x 165 mm Stroke)
• For 1 g/bhp-hr NOx for
NG (900 Btu/SCF) to
digas (400 Btu/SCF),
respectively,
– Timing 21to 30bTDC
– Lambda 1.70 to 1.42
• Slightly lower digas boost
requirement due to richer
lambda
12
Reinbold, E. and von der Ehe, James, “Development of the Dresser Waukesha 16V150LTD Engine for Bio-Gas Fuels”, ASME
Internal Combustion Engine Division 2009 Spring Technical Conference, ICES2009-76079, May 3-6, 2009.
Biogas operating
envelope shift
LeanRich

13. 132 May 2013
• Stationary Gas Engines
• Digas Characteristics
• Engine Design Modifications for Digas
• Gas Scrubbers
• Digas Installation
Outline

14. 142 May 2013
Digas Specifications
Guascor Power, “Anaerobic Digestion Gas Fuel Specifications – Landfill and Digester Gas”, Product Information IC-G-D-30-003e, Sept 2011.
Manufacturer
Relative
Humidity (%)
Temperature
(C)
H2S (mg/MJfuel, ppm) NH3 (mg/MJfuel, ppm) PM (mg)
D-R Guascor < 80 > 15 above DP < 70, 990 < 1.5, 42 < 5
Jenbacher < 80 < 40 < 21, 290 < 1.4, 39 < 5
Caterpillar < 80 -10 to 60 < 57, 810 < 2.8, 79 < 1
Notes:
1 - Relative humidity specification is at the engine fuel gas inlet connection.
2 - Calulation of ppm values based on Guascor SFGLD240 Biogas engine flowrates,
operating on biogas 60% CO2, 38% CO2, and 2% N2.
3 - Caterpillar values given as an example; actual specification is dependent on
engine and application.
4 - Sulfur specifications are without a catalyst; limits are lower if a catalyst is required.

15. 152 May 2013
• Iron Oxides
– Remove sulfur by forming insoluble
iron sulfides
– Iron-oxide-impregnated material (wood-chips,
ceramic, ..)
– Removal reaction
Fe2O3 + 3H2S  Fe2S3 + 3H2O, ΔH= -22 kJ/g-mol H2S
– Regeneration reaction
2Fe2S3 + O2  2Fe2O3 + 3S2, ΔH= -198 kJ/g-mol H2S
H2S Removal: Iron Oxide
Steven McKinsey Zicari, “Removal of Hydrogen Sulfide from Biogas Using Cow-Manure Compost”, MS Thesis, Cornell University, 2003.

16. 162 May 2013
• Filter media provides
environment for establishment of
a bacteria biofilm.
• As the biogas comes in contact
with the biofilm, hydrogen sulfide
is solubilized and subsequently
oxidized by the microbes.
• Sulfur and sulfate compounds
are formed as by-products and
are collected at the bottom or
purged with re-circulated water.
H2S Removal: Biotrickling

17. 172 May 2013
• Stationary Gas Engines
• Digas Characteristics
• Engine Design Modifications for Digas
• Gas Scrubbers
• Digas Installation
Outline

18. 182 May 2013
• Raw digas contains 4000-5000 ppm H2S
• Biotrickler is used to reduce H2S to 200-300 ppm
• Typical gas composition supplied to engines: 57% CH4,
40% CO2, 2% O2, 250 ppm H2S, and 1% other trace
species.
• Two Guascor SFGLD560 V16 engines, rated at 788 kW at
1200 rpm
• Nominal Operating Parameters:
− 525 CFM total digas supply (both engines)
− Engines typically produce 730 kW each, supplying just over 100% of
dairy electricity in winter and 2/3 of electricity in summer
• Oil is changed every 500 hours; currently 8500 hours since
install without rebuild
Windy Ridge Dairy Farm, Fair Oaks,
Indiana (Martin Machinery Installation)

19. 192 May 2013
Windy Ridge Dairy Farm, Fair Oaks,
Indiana (Martin Machinery Installation)
Digester maximum manure temperature 105F.
Digester residence time typically 25-30 days.

20. 202 May 2013
Windy Ridge Dairy Farm, Fair Oaks,
Indiana
Manure Supply to Digester
Digester : 100 X
80 yards X 20 feet
deep
Clockwise from left: biotrickler, rough
water dropout, and iron sponge
Biotrickler control skid
Sulfur and sulfate
compound collection
Guascor
SFGLD560 V16
engine

21. 212 May 2013
Contact:
Daniel B. Olsen
Associate Professor
Mechanical Engineering Department
(970) 491-3580
daniel.olsen@colostate.edu