Techno-Economic Analysis of the Production of Liquid Biofuels from Sewage Sludge via Hydrothermal Liquefaction

This work addresses the process and economic performance of the production of gasoline and diesel range fuels from urban sewage sludge. The overall production route involves direct conversion of the sewage sludge to an intermediate oil phase, socalled biocrude, via hydrothermal liquefaction at near-critical water conditions and further upgrading of the biocrude based on conventional refinery processes. The overall mass and energy yields of combined naphtha and middle distillate from sewage sludge on dry basis are approximately 19 and 60%, where the naphtha fraction represents about 45% of the total, with a minimum fuel selling price ranging between 2.4 and 0.8 euro/liter assuming full investment in both the biocrude production and upgrading plant with sewage sludge feed capacities in the range of 3 to 30 dry-ton/day. If existing equipment at refinery can be used for upgrading of the biocrude, the minimum fuel selling price can be reduced by approximately 7%.