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

USA average

NE average

Iowa average

coal 1.40 1.33 1.46

natural gas 1.49 1.41 1.57

natural gas, wet DG 1.85 1.73 1.97

closed-loop facility 2.45 2.17 2.71

Corn Production SystemEth

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www.bess.unl.edu

GHG Emissions Reduction (%)

USA average

NE average

Iowa average

coal 26 24 29

natural gas 52 50 55

natural gas, wet DG 65 63 67

closed-loop facility 78 75 81

Corn Production SystemEth

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Component GHG emission category (#2, IA)

% of LC (#3, NE) % of LC

(#4, NE) % of LC

CROP Production Nitrogen fertilizer, N* 7.5 7.5 8.6 Phosphorus fertilizer, P* 1.7 1.1 1.2 Potassium fertilizer, K* 1.0 0.1 0.1 Lime* 5.0 1.3 1.5 Herbicides* 2.7 3.2 3.7 Insecticides* 0.0 0.3 0.3 Seed* 0.3 0.3 0.3 Gasoline** 0.6 1.1 1.3 Diesel** 3.1 8.1 9.4 LPG** 2.2 1.2 1.4 Natural gas** 0.0 2.7 3.1 Electricity** 0.5 4.6 5.3 Depreciable capital 0.5 0.5 0.5

N Fertilizer emissions (N2O) 13.6 13.5 15.6 TOTAL 38.7 45.4 52.4

BIOREFINERY Biorefinery model component Natural Gas Input*** 30.7 27.4 31.6 NG Input: drying DG*** 15.0 13.4 0.0 Electricity input*** 10.5 9.4 10.8 Depreciable capital 0.8 0.7 0.9 Grain transportation 4.2 3.7 4.3 TOTAL 61.3 54.6 47.6 CO-PRODUCT CREDIT Cattle model component**** Diesel -0.0 -0.0 -0.0 Urea production -9.5 -8.4 -10.1 Corn production -16.3 -19.1 -24.7 Enteric fermentation (CH4) -5.0 -4.4 -10.0 TOTAL -30.8 -32.0 -42.2 Default co-product credit (-45.1) (-40.2) (-46.4) GHG reduction relative to gasoline, %

Life-cycle GHG emissions 54.9 50.4 63.1

GHG-intensity, g CO2eq MJ-1 of Ethanol

Life-cycle GHG emissions 40 44 32

BESS Results: Default Scenarios #2-4

www.bess.unl.edu

GHG-intensity of Corn production: BESS results

267276

239

357

172

202

177

189230

181

278

217 226 247

291

300

273

208

172

kg GHG per Mg Grain

150 - 173

174 - 197

198 - 220

221 - 243

244 - 267

268 - 290

291 - 313

314 - 337

338 - 360

48%

56%54%

53%

52%50%

44%46% 45%

53% 48%

51%

48%

53%

58%

43%

48%

45%

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