Process modeling and economic analysis for bio-heavy-oil production from sewage sludge using supercritical ethanol and methanol

The solvothermal liquefaction of sewage sludge (SS) has received much attention as an ecofriendly method of liquid fuel production. In this study, we evaluated the economic feasibility of bio-heavy-oil (BHO) production from 100 t/d SS using supercritical ethanol (scEtOH) and methanol (scMeOH). The process included a dryer, supercritical reactor, BHO separator, steam boiler, wastewater treatment unit and storages. Two cases for the techno-economic analysis (TEA) were considered: BHO production with scEtOH (Case 1) and with scMeOH (Case 2). The four-level economic potential approach (4-level EP) was used for the TEA. The total capital investments of Cases 1 and 2 were 19.6 and 19.5 million dollars, respectively. Case 2 showed higher economic potential than Case 1 because of the low price of methanol. The BHO plant using scMeOH was economically feasible with a return on investment of 21%/a.