Toward Novel Hybrid Biomass, Coal, and Natural Gas Processes for Satisfying Current Transportation Fuel Demands, 1: Process Alternatives, Gasification Modeling, Process Simulation, and Economic Analysis

Abstract

This paper, which is the first part of a series of papers, introduces a hybrid coal, biomass, and natural gas to liquids (CBGTL) process that can produce transportation fuels in ratios consistent with current U.S. transportation fuel demands. Using the principles of the H2Car process, an almost-100% feedstock carbon conversion is attained using hydrogen produced from a carbon or noncarbon source and the reverse water-gas-shift reaction. Seven novel process alternatives that illustrate the effect of feedstock, hydrogen source, and light gas treatment on the process are considered. A complete process description is presented for each section of the CBGTL process including syngas generation, syngas treatment, hydrocarbon generation, hydrocarbon upgrading, and hydrogen generation. Novel mathematical models for biomass and coal gasification are developed to model the nonequilibrium effluent conditions using a stoichiometry-based method. Input−output relationships are derived for all vapor-phase components, char, and tar through a nonlinear parameter estimation optimization model based on the experimental results of multiple case studies. Two distinct Fischer−Tropsch temperatures and a detailed upgrading section based on a Bechtel design are used to produce the proper effluent composition to correctly match the desired ratio of gasoline, diesel, and kerosene. Steady-state process simulation results based on Aspen Plus are presented for the seven process alternatives with a detailed economic analysis performed using the Aspen Process Economic Analyzer and unit cost functions obtained from literature. Based on the appropriate refinery margins for gasoline, diesel, and kerosene, the price at which the CBGTL process becomes competitive with current petroleum-based processes is calculated. This break-even oil price is derived for all seven process flowsheets, and the sensitivity analysis with respect to hydrogen price, electricity price, and electrolyzer capital cost, is presented.