(136b) Enabling Process Innovation through Computational Optimization of the Chemical Engineering Process Plant Design of Stationary, High Temperature Fuel Cell Systems that Co-Produce Hydrogen

U.S. automobiles consume about 16.17 Exajoules (EJ) of primary energy, which translates into about 2.59 EJ of useful motive energy and about 13.58 EJ of energy dissipated to the environment. On a well-to-wheels basis, the U.S. automotive transportation supply chain is, on average, only about 16% efficient (2.59 EJ/13.58 EJ). Studies indicate that an automotive supply chain based on hydrogen-fueled fuel cell vehicles (FCVs) may be ~two times more efficient on a well-to-wheels basis. Substitution of gasoline fuel with hydrogen fuel derived from local sources of natural gas and renewables can help address this energy efficiency bottleneck, while also increasing security of fuel supply and reducing air pollution and greenhouse gas emissions.

One of the most efficient ways to produce hydrogen fuel for FCVs is with stationary, high temperature fuel cell systems (FCSs) that co-produce hydrogen. These hydrogen co-production systems (H₂-FCSs) can be fueled by renewable methane (such as biogas) or natural gas, and can be designed to produce electricity, heat, and hydrogen simultaneously. This research investigates the chemical engineering process plant design of H₂-FCSs. Process models are developed and deployed to optimize H₂-FCS design for maximum hydrogen yield per unit of methane input, and other parameters. Special attention is paid to scenarios in which H₂-FCSs are designed to be more energy efficient by recovering electrochemical heat from the high temperature fuel cell stack to heat the endothermic steam reforming process to generate additional hydrogen for vehicles. Process plant models are used to explore the impact of key input parameters (including (A) stack/reformer operating temperature, (B) steam-to-carbon ratio for the fuel processing sub-system, (C) heat transfer effectiveness between inlet and outlet gases, etc.) on important design parameters, including, but not limited to, (1) hydrogen output, (2) overall energy conversion efficiency, and (3) net water balance. Model results indicate that, compared with stand-alone natural gas steam methane reforming (SMR) hydrogen generators, H₂-FCSs can reduce fuel consumption by about 20%.