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Table 1 Five sorghum-based ethanol production pathways and scenarios

From: Life-cycle energy use and greenhouse gas emissions of production of bioethanol from sorghum in the United States

Pathway Ethanol feedstock Process fuel supply Vinasse fertigation CHPafeedstock Co-product Co-product handling methods
I Grain, GS FNG, electricity   None WDGSb Displacement
II Grain, GS RNGc from ADd of animal waste   RNG WDGS Displacement
III(a) Sugar, SS Steam and electricity from CHP facilities No Sorghum bagasse Grain and electricity Displacement for grain (animal feed), energy-based allocation for electricitye
III(b) Sugar, SS Steam and electricity from CHP facilities Yes Sorghum bagasse Grain, vinasse and electricity Displacement for grain (animal feed) and vinasse (fertilizer), energy-based allocation for electricity
IV Cellulosic biomass, FS Steam and electricity from CHP facilities   Lignin residue and a portion of cellulosic biomass Electricity Energy-based allocation
V(a) Sugar and bagasse, SS Steam and electricity from CHP facilities No Lignin residue and a portion of the bagasse Grain and electricity Displacement for grain (animal feed) and energy-based allocation for electricity
V(b) Sugar and bagasse, SS Steam and electricity from CHP facilities Yes Lignin residue and a portion of the bagasse and Grain, vinasse and electricity Displacement for grain (animal feed) and vinasse (fertilizer) and energy-based allocation for electricity
  1. a Combined heat and power;
  2. b Wet distillers grains with solubles. The current grain sorghum ethanol industry produces an average of 92% WDGS [18];
  3. c Renewable natural gas. We assume that the animal waste is transported by trucks from the farms to the AD plants, and the RNG produced at the AD plants is assumed to be transported to the ethanol plants via pipeline;
  4. d Anaerobic digestion;
  5. e The displacement method is used to handle SS grain, because it, instead of being an energy product like ethanol or electricity, can be used as animal feed like corn grain. The energy-based allocation is used for electricity because it is an energy product like ethanol.