Design and operating condition analysis of pre-reformer and membrane reactor through CFD modeling and process simulation

Abstract

Membrane reactors include both a chemical conversion process for producing hydrogen from fossil fuels through steam reforming reactions and a separation process for selectively permeating hydrogen through membranes. The hydrogen permeation through membranes overcomes the equilibrium state of steam reforming reactions by Le Chatelier’s principle, and induces forward reactions to increase its conversion. The hydrogen separation process is advantageous for high pressure, but steam reforming reactions have an adverse effect on hydrogen production at high pressure. Therefore, a pre-reformer is required to convert fossil fuels into methane rich gas, and hydrogen is further produced and collected through a membrane reactor. As the products of a pre-reformer are directly connected to the reactants of a membrane reactor, it is necessary to understand the chemical reactions and thermodynamics that occur in each process in order to design the integrated process. This paper proposes the guideline of designs and operating conditions in a pre-reformer and a membrane reactor through 3D CFD process simulation. Both process models are validated by comparison with experiment results at various pressure, and understand the mechanism of steam reforming reactions by plotting the reaction rates depending on the position. A pre-reformer analyzes the maximum flow rate at which the gas composition can reach an equilibrium state, and requires attention to heat supply through observing the effect of temperature reduction by reactions in a horizontal section. A membrane reactor analyzes the reason why methane conversion increases rapidly with the pressure by confirming that the hydrogen permeability and steam reforming reaction rates are strong at the front of the membrane tube. Efficiency of the membrane reactor is analyzed by comparing conversion, yield, and the product of dimensionless numbers for three designs with different length and diameter ratios. Eventually, understanding of the overall processes and analysis of design and operating conditions provide insight into the integration of the two processes.