Innovative membrane reformer for hydrogen production applied to PEM micro-cogeneration: simulation model and thermodynamic analysis

This paper illustrates an innovative concept of hydrogen production, applied to microcogeneration systems based on polymer electrolyte membrane (PEM) fuel cells fed with natural gas. Three options to generate the hydrogen rich mixture required by the fuel cell are compared: (i) a conventional steam reformer, (ii) an auto-thermal reformer and (iii) an innovative membrane reformer. In the first two cases, the syngas generated by the reformer requires a water gas shift reactor (WGSR), where the majority of carbon monoxide is converted into hydrogen, as well as a preferential oxidation (PROX) reactor to further reduce the CO content before entering the fuel cell. In the third case, hydrogen is simultaneously produced by the reformer and separated at high temperature by a Pd-based membrane, selective to pure hydrogen, and, directly fed to the fuel cell after cooling. The model simulates the PEM performance with a lumped-volume approach. It calculates energy balance and flow composition at the cell outlet based on available information about utilization factors and reactant compositions; cell voltage is predicted with theoretical correlations calibrated over available experimental data. After a description of the adopted calculation model, the paper carries out a thermodynamic analysis of the considered system configurations and discusses the issue of thermal integration among the various heat exchange processes, in order to achieve maximum heat recovery efficiency and avoid the use of an external water supply. The obtained results show that the innovative membrane reforming solution yields several advantages in terms of electric efficiency and plant layout simplicity, suggesting interesting potential applications and the possibility to achieve relevant energy savings when applied to typical residential loads