Techno-economic analysis of bio heavy-oil production from sewage sludge using supercritical and subcritical water

The economic feasibility of a bio heavy-oil (BHO) production process from 100 t/d sewage sludge (SS) using super- and sub-critical water was evaluated. The process included a super- or sub-critical reaction, BHO recovery via a condenser and centrifuge, BHO purification via extraction, phase separation and filtration, hydrotreating desulfurization, and wastewater treatment. For techno-economic analysis (TEA), two cases were considered: BHO production with supercritical (Case 1) and subcritical (Case 2) water. The four-level economic potential approach was used for the TEA. The minimum fuel selling price (MFSP) of the BHO plants was approximately 0.91 $/L, which was higher than the actual selling price of 0.55 $/L. Case 2 showed higher economic values than Case 1 owing to the lower capital and production costs. When the SS treatment credit is > 120 $/t or the BHO price is higher than the MFSP, the BHO plant with subcritical water (Case 2) is profitable. This study shows economic potentials for the SS hydrothermal liquefaction process with an upgrading unit.