An economic comparison of high moisture feedstock biofuel production

This study compares final fuel production costs of multiple biomass-to-liquid production facilities. Process economics are estimated for four different high moisture feedstocks, four different biomass supply chain pathways and three different conversion and upgrading technologies. Two biorefinery capacities are examined, small (200 tonne per day) and large (2000 tonne per day). Corn stover, corn silage giant miscanthus and sweet sorghum are the feedstocks considered for conversion via hydrothermal liquefaction (HTL) and anaerobic digestion (AD). Final product finishing is done by hydroprocessing of the HTL biocrude and either Fischer-Tropsch (FT) synthesis or methanol-to-gasoline (MTG) conversion of the AD biogas. Water footprints are estimated for blue, green and grey water consumption during the entire biofuel production process for each scenario. In efforts to decrease the production costs, moisture and size reduction steps are omitted during the biomass supply chain stage. Multi-pass and single pass harvesting scenarios are considered along with wet and dry storage techniques. These steps lead to an estimated delivered feedstock cost ranging from $63.84-$86.19 per tonne; comparable with recent literature. Conversion and upgrading pathways were chosen based on ability to handle high moisture feedstock. Capital investments were estimated for each technology scenario and ranged from $424-$538 MM for the 2000 tpd biorefinery, within a degree of uncertainty; HTL resulted in the lowest estimated capital costs. Final fuel production costs ranged from $2.04-$6.39 per gallon for all feedstocks and all conversion pathways, with stover and sorghum resulting in the lowest. The total water footprints were estimated to range from 5.92-23.21 Lw/Lb and 5.58-14.89 Lw/Lb for the conservative and optimal blue water scenarios, respectively. The green and grey water footprints ranged from 232.30-2,568.27 Lw/Lb and 296-526 L, respectively