Estimating Greenhouse Gas Emissions in Corn-Ethanol Production using the BESS Model
Adam J. Liska, Haishun S. Yang, Kenneth G. Cassman Department of Agronomy and Horticulture, University of Nebraska-Lincoln
BESS Model : Life-Cycle Energy & Emissions
BESS Model includes 4 components: • Crop production • Ethanol biorefinery
• Cattle feedlot for feeding co-product distiller’s grains
• Anaerobic digestion unit (optional, closed-loop facility) Three types of life-cycle analysis: • Energy analysis—life-cycle net energy yield & efficiency • Emissions analysis—net carbon dioxide (CO2) and trace greenhouse gases (CH4, N2O), and global warming potentional (GWP) • Resource Requirements—crop production area, grain, water, fossil fuels (petroleum, nat. gas, and coal)
BESS results: Net Energy Ratio
Corn Production System
Ethanol Biorefineries
USA average
coal natural gas natural gas, wet DG closed-loop facility 1.40 1.49 1.85 2.45
NE average
1.33 1.41 1.73 2.17
Iowa average
1.46 1.57 1.97 2.71
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GHG Emissions Reduction (%)
Corn Production System
Ethanol Biorefineries
USA average
coal natural gas natural gas, wet DG closed-loop facility 26 52 65 78
NE average
24 50 63 75
Iowa average
29 55 67 81
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Component CROP Production
GHG emission category Nitrogen fertilizer, N* Phosphorus fertilizer, P* Potassium fertilizer, K* Lime* Herbicides* Insecticides* Seed* Gasoline** Diesel** LPG** Natural gas** Electricity** Depreciable capital N Fertilizer emissions (N2O) TOTAL Biorefinery model component Natural Gas Input*** NG Input: drying DG*** Electricity input*** Depreciable capital Grain transportation TOTAL Cattle model component**** Diesel Urea production Corn production Enteric fermentation (CH4) TOTAL Default co-product credit Life-cycle GHG emissions Life-cycle GHG emissions
(#2, IA) % of LC 7.5 1.7 1.0 5.0 2.7 0.0 0.3 0.6 3.1 2.2 0.0 0.5 0.5 13.6 38.7 30.7 15.0 10.5 0.8 4.2 61.3 -0.0 -9.5 -16.3 -5.0 -30.8 (-45.1) 54.9 40
(#3, NE) % of LC 7.5 1.1 0.1 1.3 3.2 0.3 0.3 1.1 8.1 1.2 2.7 4.6 0.5 13.5 45.4 27.4 13.4 9.4 0.7 3.7 54.6 -0.0 -8.4 -19.1 -4.4 -32.0 (-40.2) 50.4 44
(#4, NE) % of LC 8.6 1.2 0.1 1.5 3.7 0.3 0.3 1.3 9.4 1.4 3.1 5.3 0.5 15.6 52.4 31.6 0.0 10.8 0.9 4.3 47.6 -0.0 -10.1 -24.7 -10.0 -42.2 (-46.4) 63.1 32
BESS Results: Default Scenarios #2-4
BIOREFINERY
CO-PRODUCT CREDIT
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GHG reduction relative to gasoline, % GHG-intensity, g CO2eq MJ-1 of Ethanol
GHG-intensity of Corn production: BESS results
202
48%
177 172
56% 54%
189
53%
172 230
51% 58%
239
50%
181
52%
208 247
48% 53%
217
53%
226
48%
276
44%
267
46%
278
45%
291
43%
273
48%
300
45%
kg GHG per Mg Grain
150 - 173 174 - 197 198 - 220 221 - 243 244 - 267 268 - 290 291 - 313 314 - 337 338 - 360
357
41%
Life-cycle GHG reduction compared to gasoline; w/ natural gas ethanol plant with dry distillers grains
Support for BESS Development
• Western Governor’s Association • Nebraska Energy Office • Environmental Defense • Nebraska Center for Energy Sciences Research • University of Nebraska-Lincoln, Institute of Agriculture and Natural Resources
FREE Model Download: www.bess.unl.edu