Heat transfer and thermodynamic analysis of autothermal reactors by catalytic oxidation and steam-methanol reforming

Numerical simulations are carried out to understand the heat energy transport characteristics of an autothermal reactor by steam-methanol reforming on copper-based catalysts. Mathematical expressions are derived for the reactor system based upon the principles of chemical kinetics and fluid mechanics. Enthalpy analysis is performed and the evolution of energy in the reforming and oxidation processes is discussed in terms of reaction heat flux. The effects of different factors on the thermal behavior of the autothermal reactor is evaluated in order to fully describe the thermal energy change in the reactor. The objective of the present study is to understand the heat energy transport characteristics of microchannel reactors for hydrogen production by steam-methanol reforming on copper-based catalysts. Emphasis is placed on the effects of different factors on the thermal behavior of autothermal reactors. The results indicate that the heat required for the endothermic reforming reaction must pass through the wall of the tube. Minimal oxygen requirements serve to inhibit carbon formation in the catalyst bed. Small size and weight allow for rapid catalyst bed heat-up to operating temperatures which is a critical requirement for quick start capability necessary in most vehicle applications. The temperature within the hot spot can be increased or decreased respectively by increasing or decreasing respectively the amount of oxygen supplied to the mixture. Direct heating is of considerable advantage as it largely overcomes the problems encountered with reaction rates being limited by the rate of heat transfer through the tube wall. The intervening walls may be flat plates or cylindrical walls with heat transfer capabilities. The separation is often affected by an adsorption process after condensing out the steam from the shifted gas. Silicon is considered a good material for fabrication of microreactors due to the high strength of the silicon-silicon bonds which results in the chemical inertness and thermal stability of silicon.