(731c) Life Cycle Cost of Greenhouse Gas Reduction through Lignin-Land Application

Continuous exhaustion of fossil fuels and increasing greenhouse gas (GHG) emissions have led to a growing attraction toward using low carbon renewable and sustainable energy sources. Lignocellulosic biomass is attaining interest as a ?second generation? feedstocks because it is renewable and if grown on marginal land or sourced from waste, can be used without disrupting global food market prices or contributing to land clearing and the consequent CO2 release. Corn Stover, the biomass residue of corn grain can be used as a feedstock for lignocellulosic ethanol production. Lignin, one of the main fractions of the corn stover, and a by-product of bioconversion, can be combusted for energy recovery (steam and electricity), or it may be separated, dried, and returned to the land as a soil amendment, where its slow decomposition can provide needed soil organic carbon (SOC) while allowing up to 80% of corn stover to be removed for ethanol production. This strategy could increase the ethanol yield per hectare of land, avoid more GHG emissions per hectare from displaced gasoline, and potentially provide carbon storage benefits due to lignin's slow decomposition. We test the cost-effectiveness of this hypothesis by comparing the life cycle GHG emissions and costs of two options for using the lignin fraction of the corn stover feedstock. In particular, we examine separating the lignin for use as a land amendment and implementing a conventional natural gas boiler to produce process steam and electricity for the biorefinery. We contrast this option with the most widely option discussed in literature, where the lignin is separated and delivered to a combustor, boiler, and turbogenerator system that produces steam and electricity for the conversion facility, and excess electricity is sold on the market. Both options require that sufficient SOC is returned to the land; however the lignin-land application option allows for greater corn stover removal from the field, and therefore greater gasoline fuel displacement and the associated avoided GHGs, and possible benefits from carbon storage from the lignin and how this is temporally allocated within the life cycle assessment (LCA) model. Simulation of the two biorefinery models was done using Aspen plus in conjunction with a stochastic LCA model to estimate the differences in GHG emissions and costs in two scenarios. Results show that differences are largely due to the uncertainty of today's conversion technology, and expected variability in ethanol yield.