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Operation of Internal Combustion Engines on Digas for Electricity Production

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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.

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Operation of Internal Combustion Engines on Digas for Electricity Production

  1. 1. ©2010 Engines and Energy Conversion LaboratoryOperation of InternalCombustion Engines on Digasfor Electricity ProductionLivestock & Poultry Environmental Learning CenterNational Conference: From Waste to Worth:“Spreading” Science & SolutionsGrand Hyatt Hotel, Denver, ColoradoApril 1-5, 2013Daniel B. OlsenAssociate ProfessorMechanical Engineering Dept.
  2. 2. 22 May 2013• Stationary Gas Engines• Digas Characteristics• Engine Design Modifications for Digas• Gas Scrubbers• Digas InstallationOutline
  3. 3. Digas Engine Design Options1. Compression Ignition (Diesel) Engine– Blend biogas with intake air– Requires two fuels on site2. Spark Ignition Stoichiometric Gas Engine– 3-way catalyst for emissions control– Lower efficiency3. Spark Ignition Lean-burn Gas Engine– Low emissions– High efficiency– High power density (bmep)3
  4. 4. StationaryGas EnginesPower generation, Combinedheat and power, Gascompression PumpingWärtsilä 34SGWaukesha VGFKUBOTA DG972-E2Jenbacher Type 2Cummins GensetCaterpillar 3516C4Guascor V16MAN CHP
  5. 5. Efficiency Trends5 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 400bmep (psi)Increasing boost & power at constant A/F• Higher power density(bmep) results in higherefficiency• Higher compression ratioyields higher efficiencyWaukesha VGF (F18GLD)• Knock (detonation)limits compressionratio of engine• Fuel qualitydeterminesknock limitFuel A Knock LimitFuel B Knock LimitEfficiency
  6. 6. 62 May 2013• Stationary Gas Engines• Digas Characteristics• Engine Design Modifications for Digas• Gas Scrubbers• Digas InstallationOutline
  7. 7. Biogas Composition• Two general types of biogas– Wood gas from a gasifier– Digas from sewageprocessing, landfill, etc.• Very different propertiesfrom each other and fromnatural gas• Our focus is on digas fromagricultural systems7Wood Gas % CompositionNitrogen, 55.4%CO, 20.6%Hydrogen, 18.4%Methane, 2.2%Oxygen, 1.8%CO2, 1.3%
  8. 8. Test Results62.430.061.570.2 66.323.9139.1 139.60204060801001201401601, ReformedNatural Gas2, Coal Gas 3, Wood Gas 4, Wood Gas 5, DigesterGas6, Landfill Gas 7, ReformedNatural Gas8, Coal GasMethaneNumberTypical Natural Gas# Test Gas %CH4 %H2 %N2 %CO %CO21ReformedNatural Gas39.7 46.7 0.8 0.9 11.92 Coal Gas * 24.8 16.3 58 13 Wood Gas 10 40 3 24 234 Wood Gas 1 31 35 18 155 Digester Gas 60 * 2 * 386 Landfill Gas 60 * * * 407ReformedNatural Gas1.2 30.8 49.0 15.6 3.48 Coal Gas 7 44 * 43 68CriticalCompressionRatioMalenshek M., Olsen D.B., “Methane number testing of alternative gaseous fuels”, Fuel, Volume 88, pp. 650-656, 2009.
  9. 9. Hydrogen Sulfide (H2S)• Digas levels ~2000-5000 ppm H2S from hog andcattle digesters• Impact on engines– Corrodes copper-based bearing materials– Contaminates oil via blow-by– Combustion of H2S produces SO29/
  10. 10. 102 May 2013• Stationary Gas Engines• Digas Characteristics• Engine Design Modifications for Digas• Gas Scrubbers• Digas InstallationOutline
  11. 11. Case Study: Waukesha 16V150LTD(152 mm Bore x 165 mm Stroke)• 1.1 MW at 1800 rpm, 15.8 barbmep• Regulator spring replaced withstiffer spring to increase fuelpressure• Fuel piping from regulator tomixer increased from 3” to 4”• Mixer insert flow area for digasincreased by 2.3X relative tonatural gas11Reinbold, E. and von der Ehe, James, “Development of the Dresser Waukesha 16V150LTD Engine for Bio-Gas Fuels”, ASMEInternal Combustion Engine Division 2009 Spring Technical Conference, ICES2009-76079, May 3-6, 2009.
  12. 12. Case Study: Waukesha 16V150LTD(152 mm Bore x 165 mm Stroke)• For 1 g/bhp-hr NOx forNG (900 Btu/SCF) todigas (400 Btu/SCF),respectively,– Timing 21to 30bTDC– Lambda 1.70 to 1.42• Slightly lower digas boostrequirement due to richerlambda12Reinbold, E. and von der Ehe, James, “Development of the Dresser Waukesha 16V150LTD Engine for Bio-Gas Fuels”, ASMEInternal Combustion Engine Division 2009 Spring Technical Conference, ICES2009-76079, May 3-6, 2009.Biogas operatingenvelope shiftLeanRich
  13. 13. 132 May 2013• Stationary Gas Engines• Digas Characteristics• Engine Design Modifications for Digas• Gas Scrubbers• Digas InstallationOutline
  14. 14. 142 May 2013Digas SpecificationsGuascor Power, “Anaerobic Digestion Gas Fuel Specifications – Landfill and Digester Gas”, Product Information IC-G-D-30-003e, Sept 2011.ManufacturerRelativeHumidity (%)Temperature(C)H2S (mg/MJfuel, ppm) NH3 (mg/MJfuel, ppm) PM (mg)D-R Guascor < 80 > 15 above DP < 70, 990 < 1.5, 42 < 5Jenbacher < 80 < 40 < 21, 290 < 1.4, 39 < 5Caterpillar < 80 -10 to 60 < 57, 810 < 2.8, 79 < 1Notes: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 onengine and application.4 - Sulfur specifications are without a catalyst; limits are lower if a catalyst is required.
  15. 15. 152 May 2013• Iron Oxides– Remove sulfur by forming insolubleiron sulfides– Iron-oxide-impregnated material (wood-chips,ceramic, ..)– Removal reactionFe2O3 + 3H2S  Fe2S3 + 3H2O, ΔH= -22 kJ/g-mol H2S– Regeneration reaction2Fe2S3 + O2  2Fe2O3 + 3S2, ΔH= -198 kJ/g-mol H2SH2S Removal: Iron OxideSteven McKinsey Zicari, “Removal of Hydrogen Sulfide from Biogas Using Cow-Manure Compost”, MS Thesis, Cornell University, 2003.
  16. 16. 162 May 2013• Filter media providesenvironment for establishment ofa bacteria biofilm.• As the biogas comes in contactwith the biofilm, hydrogen sulfideis solubilized and subsequentlyoxidized by the microbes.• Sulfur and sulfate compoundsare formed as by-products andare collected at the bottom orpurged with re-circulated water.H2S Removal: Biotrickling
  17. 17. 172 May 2013• Stationary Gas Engines• Digas Characteristics• Engine Design Modifications for Digas• Gas Scrubbers• Digas InstallationOutline
  18. 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 tracespecies.• Two Guascor SFGLD560 V16 engines, rated at 788 kW at1200 rpm• Nominal Operating Parameters:− 525 CFM total digas supply (both engines)− Engines typically produce 730 kW each, supplying just over 100% ofdairy electricity in winter and 2/3 of electricity in summer• Oil is changed every 500 hours; currently 8500 hours sinceinstall without rebuildWindy Ridge Dairy Farm, Fair Oaks,Indiana (Martin Machinery Installation)
  19. 19. 192 May 2013Windy Ridge Dairy Farm, Fair Oaks,Indiana (Martin Machinery Installation)Digester maximum manure temperature 105F.Digester residence time typically 25-30 days.
  20. 20. 202 May 2013Windy Ridge Dairy Farm, Fair Oaks,IndianaManure Supply to DigesterDigester : 100 X80 yards X 20 feetdeepClockwise from left: biotrickler, roughwater dropout, and iron spongeBiotrickler control skidSulfur and sulfatecompound collectionGuascorSFGLD560 V16engine
  21. 21. 212 May 2013Contact:Daniel B. OlsenAssociate ProfessorMechanical Engineering Department(970) 491-3580daniel.olsen@colostate.edu

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