Post on 19-Apr-2020
THE NET ENERGY BALANCEOF CORN ETHANOL
Roger ConwayOffice of Energy Policy and New Uses/USDA
The Intersection of Energy and Agriculture:Implications of Biofuels and the Search for a Fuel
of the FutureThe Faculty Club
University of California, BerkeleyOctober 4-5, 2007
Comparison of the Pimental and Patzek results to the USDA resultsProcess Pimentel and Patzek [2] USDA [3] Difference
Btu per Gallon of Ethanol
Corn Production 37,860 18,713 -19,147
Corn Transportation 4,834 2,120 -2,714
Ethanol Conversion 56,399 51,220 -5,179
Energy Input ExcludingCoproducts
99,093 72,053 -27,040
Coproduct Value 6,680 26,250 19,570
Energy Input IncludingCoproducts
92,413 45,803 -46,610
Total Energy Output 77,011 76,330 -681
Net Energy Balance -15,402 30,527 45,929
[1] The study by Shapouri and McAloon, “The 2001 Net Energy Balance of Corn-Ethanol” is available at the USDA, Office of Energy Policy and New Uses web site:
http://www.usda.gov/oce/oepnu/. The Wang study can be found at the following web site: http://www.transportation.anl.gov/research/systems_analysis/fuel_ethanol.html.
[2] Pimentel and Patzek report their results (Table 2 of their paper) in kcal x 1000 per 1000 litres of ethanol. Converted to Btu per gallon using 1 litre = 0.26 gallons and 1
kcal = 3.96 Btu.
[3] Estimates are based on a weighted average of dry and wet milling. Ethanol conversion includes 1,588 Btu per gallon for ethanol distribution.
Net Energy Balance of Corn-Ethanol and 9-State Average Corn Yield per Acre
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Net Energy Balance Results
• Data quality
• Feedstocks, grains, sugar, biomass materials
• New technologies:– Crop production
– Processing
• Methodology used to allocate total energyto ethanol and by products
Sources of Data
• USDA/ Economic Research Service (ERS),2001 Agricultural Resources ManagementSurvey (ARMS)
• USDA/ National Agricultural StatisticsService (NASS), 2001 AgriculturalChemical Usage and 2001 Crop Production
• Stokes Engineering Company, energy usedin production of fertilizers
Sources of Data--Continued
• Greenhouse Gas Regulated Emissions and EnergyUse in Transportation (GREET) model, energyused in production of chemicals
• 2001 survey of ethanol plants, BBI International,thermal and electrical energy used in ethanol plant
• ASPEN Plus, a process simulation program, toallocate energy used in ethanol plant to ethanoland byproducts
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Sample Size, the 2001 ARMS Corn Survey
Energy inputs used per acre of corn, 2001
Pimentel, 2005 USDA/U.S. ave.
Labor, hours 4.62 1.88
Diesel, gallons 9.41 6.2
Gasoline, gal. 4.28 1.7
Nitrogen, lbs 136.28 122
Phosphate, lbs 57.89 34.8
Potash, lbs 68.58 36.21
Lime, lbs 997.57 393
Herbicides, lbs 5.52 2.18
Insecticides, lbs 2.49 0.04
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Labor Use per Acre of Corn, 2001
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Fuel Use per Acre of Corn, 2001
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Fertilizer and Lime use per acre of Corn
USDA, 2001 Pimentel
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Pesticides Use per Acre of Corn, 2001
Pimentel USDA
Comparison of Amount of Energy Used to Produce Corn
Input Pimentel and Patzek[1] USDA Difference
Btu per Gallon of Ethanol from Corn Production
Labor 2,155 0 -2,155
Machinery 4,749 0 -4,749
Diesel 4,679 2,816 -1,864
Gasoline 1,890 1,323 -567
Nitrogen 11,421 8,824 -2,597
Phosphorus 1,260 613 -647
Potassium 1,171 714 -457
Lime 1,470 24 -1,446
Seeds 2,426 227 -2,199
Irrigation 1,493 62 -1,431
Herbicides 2,893 1,105 -1,787
Insecticides 1,306 -- -1,306
Electricity 159 849 690
Transport 788 76 -713
LP Gas 792 792
Natural Gas 694 694
Custom Work 594 594
Total 37,860 18,713 -19,147
[1]
[1] The amount of Btu per gallon of ethanol for each corn input is calculated by taking the share of energy used to producecorn (Table 1 in Pimentel and Pazek) and applying that share to the total amount of energy from corn in ethanol production(Table 2 in Pimentel and Pazek).
New Technologies
• Crop Production:– Genetically modified crops, yield map, global
positioning system, slow release fertilizer, andmore efficient irrigation system
• Ethanol plants:– Heat exchanger, heat tolerance yeast, Molecular
sieves, cold cook, dry fractionation, newenzymes, process automation, Combined heatand power, and nano filtration
Corn: Harvested Area and Yield per Acre, 1965-04
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Bushels of Corn per Pound of Fertilizer, 1966-03
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Dry-Mill: Thermal Energy Use per Gallon of Ethanol and Ethanol Yield per Bushel
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Dry mill Gallon per bushel
How to Allocate Total Energy toEthanol and Byproducts
• Methodology:– Energy content– Market value– Output weight basis– Replacement value– Process energy for energy used in plant and %
weight of starch and non-starch for energy usedto grow corn and transport corn to ethanol plant
Allocation Rules
• Energy used in corn production:– 66% to ethanol and 34% to byproducts
• Energy used in transporting corn to ethanol plant:– 66% to ethanol and 34% to byproducts
• Energy used in conversion of corn to ethanol andbyproducts, ASPEN Plus:– Wet mill, 64% to ethanol and 36% to byproducts
– Dry mill, 59% to ethanol and 41% to byproducts
Conclusions
• Corn yield per acre will continue to increase• Fertilizer industry has become more energy
efficient• Energy used to produce a bushel of corn will
continue to decline• Ethanol yield per bushel of corn will increase to
its theoretical limit• Ethanol plants will become more energy efficient• Net energy value of corn-ethanol will continue to
improve