Endothermic methane steam-reforming reactions in heat integrated microchannel reactors within the framework of pressurized fuel cell systems

The synthesis gas is produced in an exchanger-reactor, an assembly of stages consisting of millimetric channels and comprising two distinct zones on each stage. A first zone is devoted to the endothermic methane steam-reforming reaction; a second zone is devoted to the exothermic water-gas shift reaction. In the first zone, this reactor comprises at least one stage where a hot gas circulates in order to provide some of the heat needed for the reaction, at least one reactive stage that is covered with catalyst and where the steam-reforming reaction takes place and at least one stage where the synthesis gas produced circulates, providing heat to the reaction. The stage where a hot gas circulates comprises a second zone where a coolant circulates, which makes it possible to cool the zone where the water-gas shift reaction takes place. The reactive stage comprises in the first zone a catalyst for the steam reforming and the second zone is completely or partly covered with a catalyst for the water-gas shift reaction. It is also possible to envisage depositing, in a controlled manner, several water-gas shift reaction catalysts in order to best respond to the range of operating temperatures that may be encountered along a channel devoted to the water-gas shift reaction. The various water-gas shift reaction catalyst sections will be catalysts consisting of nanometric metal particles highly dispersed on inorganic oxides that act as supports or blocking agents. At smaller excess-air factors, the increase in temperature in the entry zone of the reactor is less pronounced. In this case, moreover, the temperature in the exit zone can decrease due to the endothermic reformation to such an extent that the high reaction rates required for complete conversion of the hydrocarbons are no longer reached. In this case, the hydrogen yield decreases and residual hydrocarbons remain in the product gas. The conversion of the residual hydrocarbons could be kinetically favored by injecting secondary air, that is, by increasing the excess-air factor in the end region of the reactor. To this end, however, the secondary air would have to be compressed, involving an additional expenditure of not immediately available electric energy for a corresponding compressor. This turns out to be problematic, especially also when using such reactors for autothermal reforming of hydrocarbons within the framework of pressurized fuel cell systems. Here, apart from the fuel cell air, the reformer educt air must also be compressed to system pressure through energy-consuming compression. The electric power consumption of the compressor required for this reduces the attainable efficiency of the fuel cell system.