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

Table 1 Five sorghum-based ethanol production pathways and scenarios

Pathway	Ethanol feedstock	Process fuel supply	Vinasse fertigation	CHP^afeedstock	Co-product	Co-product handling methods
I	Grain, GS	FNG, electricity		None	WDGS^b	Displacement
II	Grain, GS	RNG^c from AD^d 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 electricity^e
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

^a Combined heat and power;
^b Wet distillers grains with solubles. The current grain sorghum ethanol industry produces an average of 92% WDGS [18];
^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;
^d Anaerobic digestion;
^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.

ISSN: 2731-3654