Iterative numerical calculations of hydrogen production in microchannel reactors for the purpose of validating and improving designs

Direct oxidation of fuels such as methanol in fuel cells at practical current densities with acceptable catalyst loadings is not as economically attractive as conversion of methanol fuel to a hydrogen-rich mixture of gases via steam reforming and subsequent electrochemical conversion of the hydrogen-rich fuel stream to direct current in the fuel cell. In the present study, iterative numerical calculations are performed using a number of different numerical arithmetic formats. Computer systems are used to solve complex numerical calculations and to solve fluid flow problems related to the production of hydrogen in a microchannel reactor by steam-methanol reforming. The computational method involves the solution of the three-dimensional, compressible, Navier-Stokes equations with all viscous and laminar effects included. The thermal transport characteristics are investigated by solving the model to compute a solution associated with the model. The solution can be used to validate and improve reactor designs. The results indicate that to prevent the carbon monoxide gas in the gas mixture from reacting back to elemental carbon at the end of the reactor, it is required for the gas mixture to be quickly cooled down to a low temperature level. The endothermic heating requirements for steam reforming reactions occurring within the reformer tubes are provided by burners firing into the furnace that are fueled by part of the natural gas. The densification of the catalyst bed may occur locally leading to maldistribution of the reactant gases flowing through the packed bed which can lead to hot spot formation on the tube walls. The catalyst material may contain metals but the ceramic material is typically inorganic and nonmetallic. 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. The gas-liquid mixture acting as heat exchanging medium moves internally in the reactor without the need of any mechanical means.