PEMFC operation with reformate gas in a micro-CHP system based on membrane-assisted reformer

摘要

A micro-CHP system fueled with bio-ethanol, rated at 5 kWel, based on a membrane-assisted reformer and a LT-PEM fuel cell is studied. The water-ethanol-air feed undergoes auto-thermal reforming reactions inside the fluidized bed membrane reactor where hydrogen is removed by Pd-based membranes. In principle, Pd-based membranes can produce high-purity hydrogen (99.99%, i.e. selectivity=104). However, the selectivity may decrease, determining low-purity hydrogen (e.g. 99% with >100 ppm CO, i.e. selectivity=102). Hydrogen quality affects the cell voltage and the overall system performance, therefore fuel cell control strategies must be investigated. Build-up of inert and poisoning species in the hydrogen recirculation loop is limited by venting a fraction of the anodic off-gas, whose amount can be optimized. A dynamic model has been developed to simulate the cell, including the poisoning effect of CO on Pt-Ru catalyst. An experimental campaign was performed to characterize the fuel cell operation with reformate gas. The impact of operative conditions (pressure and relative humidity) and fuel composition, containing up to 20% of inert gases and up to 40 ppm of CO, was analyzed on the overall stack performance as well as on the current density distribution along the cell surface. Experimental data constituted a valuable source for the validation of the model. The model of the fuel cell is then integrated with the auxiliary components of the PEM-subsystem, which includes the air blower and humidifier, the anode off-gas blower and vent system. Results of the simulations of this section are presented in this work. Finally the PEM-subsystem is integrated into the complete m-CHP system, which includes the innovative membrane reformer and the heat exchangers network for feed pre-heating and heat recovery for cogeneration purposes. The part/over load operation of the system is still under investigation.