Study on performance of high temperature proton exchange membrane fuel cell operated on hydrogen from glycerol reforming process

Abstract

This research concentrates on the performance analysis of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) integrated with a glycerol reforming process. Firstly, the thermodynamic analysis of steam and autothermal reforming of pure glycerol and crude glycerol derived from a biodiesel production process is investigated as a basis of the development of a hydrogen production process from a renewable resource. The simulation results of both the glycerol steam and autothermal reforming show that under isothermal condition, increases in operating temperature and steam to crude glycerol increase hydrogen yield, whereas increasing oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermo-neutral condition that no external heat to sustain the reformer operation is required, is investigated. When considering the steam reforming of glycerol, it is found that to maintain the CO content of the reformate gas at a desired range for HT-PEMFC, the steam reformer can be operated at lower temperatures; however, a high steam to glycerol ratio is required. This requirement results in an increase in the energy consumption for steam generation. To determine the optimal conditions of glycerol steam reforming for HT-PEMFC, both the product composition and energy requirement are taken into consideration. The operational boundary of the glycerol steam reformer is also explored. Secondly, the efficiency and output power density of an integrated HT-PEMFC system and glycerol reformer is studied by using thermodynamic analysis and pseudo 2D model of HT-PEMFC. The theoretical analysis shows that increase in the anode stoichiometric ratio and steam to carbon (S/C) operation of reformer reduce CO poisoning effect at cell’s anode and therefore leads to enhanced cell performance. In addition, the optimum gas composition and flow rate is very dependent on cell operating current density and temperature. High S/C is essential when operating the HT-PEMFC at high current densities where CO has considerable impact on its performance. Optimal conditions that provide the maximum power density at a given efficiency are reported. Considering design of HT-PEMFC system for stationary application, the HT-PEMFC system with a water gas shift reactor in the glycerol processor shows the highest overall system efficiency compared to that without the water gas shift reactor and low-temperature proton exchange membrane fuel cell (LT-PEMFC) system.