Plate Type Methanol Steam Reformer Using New Catalytic Combustion for a Fuel Cell

Methanol steam reforming, which is an endothermic reaction, needs some heating. Both methanol conversion ratio and carbon monoxide (CO) concentration increase when temperature is elevated. As CO poisons a typical polymer electrolyte of a fuel cell, the relationship between methanol conversion ratio and CO concentration is a trade-off one. It was found from preliminary researches that the reforming reaction speed is controlled by heat transfer rate at large methanol flow rate, where methanol conversion ratio becomes lower and CO concentration becomes higher. Therefore it is necessary to develop a new methanol reforming concept that provides stable combustion for heating and enhanced heat transfer for improving the trade-off relationship and making a compact reformer. Reforming catalyst using metal honeycomb support and a new catalytic combustion were applied to a new concept plate type methanol steam reformer, which is used in a fuel cell of 3 kW-class electric generation. The new catalytic combustor system consists of fuel injection plate, combustion chamber and combustion plate, which has protuberances coated with combustion catalyst. The protuberances take the role of flame holder and enhance the heat transfer. The backside of combustion plate is in contact with the reforming catalysts and transfers the combustion heat to the reforming gas. There is the optimal height of the protuberances and it was decided to be 0.6 - 0.75 mm from experiments, under a condition of very small pressure loss.

The conversion performances of the presented methanol steam reformer are, {methanol conversion ratio} >99% and {CO concentration} <1 % at {methanol liquid hourly space velocity} = 0.4 - 4.0 h^-1. Combustion-emission levels are also very low. Thermal efficiency for hydrogen generation is higher than 80%. It corresponds to hydrogen generation specific power ability of 6kW-H₂/L, assuming the present concept reformer for a scale of automotive use.