A micro-CHP system, rated at 5 kWel, based on a membrane reformer and a PEMFC is studied. The identification of the operative conditions of the PEMFC is crucial for a good integration with the membrane reformer: the hydrogen separated in the membrane reactor, after cooling, directly feeds the FC [1]. In principle, Pd-based membranes can produce high-purity hydrogen (target= 99.99%, i.e. selectivity=104). However, the selectivity may decrease, in particular when thin Pd-membranes on ceramic support are adopted, and determine low-purity hydrogen (e.g. 99.9% with 100ppm CO, i.e. selectivity=102). A methanator is therefore added along the hydrogen cooling line to prevent CO-poisoning of the FC anodes. The quality of hydrogen affects the cell voltage and the overall system performances, therefore FC control strategies must be investigated. Build-up of inert and poisoning species in the hydrogen recirculation loop can be limited by venting a fraction of the anodic off-gas, whose amount can be optimized. Efficiency losses are estimated around one percentage point for each decrement of the order of magnitude of the selectivity. Deviations from the nominal operation occur during transients, at part-load or in case of faults of the Pd-membranes. These circumstances are investigated by simulating the FCs subsystem that includes the stack, the air and hydrogen blowers and the air humidifier. A dynamic, 1D (along the channels) model of PEMFC has been developed to simulate mixed co/counter flow between anode and cathode streams, which characterize the flow field of large-surface cells. The poisoning effect of CO on Pt-Ru catalyst is also modeled [2]. An experimental campaign on an 8-cells stack (cell area 220 cm2) was performed to characterize the FC operation with reformate gas. The impact of fuel composition, containing up to 20% of inert gases (N2, CO2, CH4) and CO up to 40 ppm, and operative conditions (pressure and humidity) 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.
Off-design operation of a PEM fuel cell stack integrated into a m-CHP system with membrane reformer
FORESTI, STEFANO;MANZOLINI, GIAMPAOLO;
2017-01-01
Abstract
A micro-CHP system, rated at 5 kWel, based on a membrane reformer and a PEMFC is studied. The identification of the operative conditions of the PEMFC is crucial for a good integration with the membrane reformer: the hydrogen separated in the membrane reactor, after cooling, directly feeds the FC [1]. In principle, Pd-based membranes can produce high-purity hydrogen (target= 99.99%, i.e. selectivity=104). However, the selectivity may decrease, in particular when thin Pd-membranes on ceramic support are adopted, and determine low-purity hydrogen (e.g. 99.9% with 100ppm CO, i.e. selectivity=102). A methanator is therefore added along the hydrogen cooling line to prevent CO-poisoning of the FC anodes. The quality of hydrogen affects the cell voltage and the overall system performances, therefore FC control strategies must be investigated. Build-up of inert and poisoning species in the hydrogen recirculation loop can be limited by venting a fraction of the anodic off-gas, whose amount can be optimized. Efficiency losses are estimated around one percentage point for each decrement of the order of magnitude of the selectivity. Deviations from the nominal operation occur during transients, at part-load or in case of faults of the Pd-membranes. These circumstances are investigated by simulating the FCs subsystem that includes the stack, the air and hydrogen blowers and the air humidifier. A dynamic, 1D (along the channels) model of PEMFC has been developed to simulate mixed co/counter flow between anode and cathode streams, which characterize the flow field of large-surface cells. The poisoning effect of CO on Pt-Ru catalyst is also modeled [2]. An experimental campaign on an 8-cells stack (cell area 220 cm2) was performed to characterize the FC operation with reformate gas. The impact of fuel composition, containing up to 20% of inert gases (N2, CO2, CH4) and CO up to 40 ppm, and operative conditions (pressure and humidity) 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
