Hardwood Biomass to Gasoline, Diesel, and Jet Fuel: 1. Process Synthesis and Global Optimization of a Thermochemical Refinery

A process synthesis framework is introduced for the conversion of hardwood biomass to liquid (BTL) transportation fuels. A process superstructure is postulated that considers multiple thermochemical pathways for the production of gasoline, diesel, and jet fuel from a synthesis gas intermediate. The hardwood is dried and gasified to generate the synthesis gas, which is converted to hydrocarbons via Fischer–Tropsch or methanol synthesis. Six different types of Fischer–Tropsch units and two methanol conversion pathways are analyzed to determine the topology for liquid fuel production that minimizes the overall system cost. Several upgrading technologies, namely, ZSM-5 catalytic conversion, oligomerization, hydrocracking, isomerization, alkylation, and hydrotreating, are capable of outputting fuels that meet all necessary physical property standards. The costs associated with utility production and wastewater treatment are directly included within the process synthesis framework using a simultaneous heat, power, and water integration. The solution quality of the optimal topology is mathematically guaranteed to be within a small fraction of the best possible value through the use of piecewise linear underestimation of nonlinear terms and a rigorous global optimization branch-and-bound strategy. A total of 12 case studies are investigated to determine the effect of refinery capacity and liquid fuel composition on the overall system cost, the BTL refinery topological design, the process material/energy balances, and the lifecycle greenhouse gas emissions.