Towards Novel Hybrid Biomass, Coal, and Natural Gas to Liquid Systems: Process Synthesis, Global Optimization, and Supply Chain Approaches

A novel framework has been developed using hybrid feedstocks and a thermochemical based process superstructure that considers various process alternatives to convert coal, biomass, and natural gas to liquid (CBGTL) transportation fuels. Using binary variables to model process decisions and constraints to model proper unit operations, a mixed-integer non-linear optimization model was developed to determine the topology of the CBGTL refinery that produced the lowest cost fuels. The model includes a simultaneous heat, power, and water integration to directly incorporate the tradeoffs between electricity recovery and wastewater treatment in the objective function. A branch-and-bound global optimization framework was developed using piecewise linear underestimators for the nonconvex terms to provide tight relaxations when calculating the lower bound. Based on the local solutions of the process synthesis model for the stand-alone plant design, an energy supply chain optimization problem was formulated to fulfill the transportation fuel demands for the United States with 50% emissions reduction. Results suggest that alternative fuels from domestically available resources can be produced in an economically competitive manner with improved environmental performance compared to petroleum-based fuels.