Abstract
This work presents a simple novel feeding method for a methanol steam reformer (MSR). Using a single heat source, a fixed ratio of water and methanol vapor can be fed into the reformer in a passive way. By adjusting the thermal resistances of the two separate heat paths, different amounts of heat, related to the stoichiometric ratio and heats of evaporation, are conducted to two separate evaporators to vaporize the liquid fuels. Compared with the conventional practice that the feeding ratios are actively controlled with two pumps, no pump is needed in this novel feeding system. Thus, the controlling system can be simplified and the auxiliary power consumption can be minimized. Experiments are conducted to verify the feasibility of this novel fuel-feeding method. In the first stage, an electric heater is used as the heat source. In the second stage, a methanol-burning catalytic combustor in a u-turn-channel is integrally machined under a two-turn serpentine channel reformer to replace the electric heater. Water/methanol feed ratios of 0.8~1.47 are managed under different reaction temperatures. Highly uniform temperature distributions throughout the reformer are demonstrated. The third stage is to make the catalytic combustor workable with both hydrogen and methanol fuels. The aim is to reutilize the exhaust hydrogen from a fuel cell under stable operation but burn methanol during the start-up. To resolve the highly different fuel reactivities, a suitably diluted catalyst formula demonstrates uniform temperature distributions burning with either liquid methanol or an H2/CO2 mixture simulating the exhaust gas from a fuel cell. In a two-stage process, it first takes 25 min to reach 270 ℃ by burning methanol. After the fuel is switched to the H2/CO2 mixture, another 20 min is needed to attain an optimal steady state which yields a high methanol conversion of 95% and acceptably low CO fraction of 1.04% at a reaction temperature of 278 ℃. The H2 and CO2 concentrations are 75.1% and 23.6%. Finally, the CO product in the reformate is successfully removed using the preferential oxidation (PROX) method. Thus, the reformate of the present novel MSR is readily applicable to anti-CO fuel cells.