Effect of catalyst support material porosity on the steam reforming process in heterogeneously catalyzed reactor systems
Description
The steam mole fraction data are presented for illustrating the effect of catalyst support material porosity on the steam reforming process in heterogeneously catalyzed reactor systems. The steam reforming process has several drawbacks, the primary ones being that the porosity of the catalyst supports is not as high as would appear to be optimum. The reforming process proceeds in one set of the channels through which the endothermic reactants flow, and the exothermic oxidation process proceeds in the second set of the channels. Exothermic and endothermic reactions take place simultaneously whereby the heat required for the latter is supplied by the former. Heat transfer occurs via conduction through the walls of the reactor. For the endothermic reaction, the structure is especially effective because both the internal surfaces of the walls are coated with structured catalysts, which is capable of providing more efficient heat exchange and minimizing the problem of loss of catalytic activity. Only two half oxidation and reforming channels as well as the surrounding walls are modeled due to the symmetry of the structurally integral system. To facilitate computational modeling of transport phenomena and chemical kinetics in the flowing system of complex chemical reactions involving gas-phase and surface species, steady-state analyses are performed and computational fluid dynamics is used. ANSYS FLUENT is applied to the problem involving surface chemistry. ANSYS FLUENT handles thermodynamic properties, transport properties, gas-phase equation-of-state, and chemical kinetics. A surface species is defined to be the chemical species at the gas-solid interface. A surface does not necessarily have to be flat, and each surface species occupies one surface site. A site is considered to be a position or location on the surface at which a species can reside. A site does not necessarily have a composition itself or have to be a particular atom, and the total number of sites per unit area is conserved. Therefore, the sum of the site fractions of the species on the sites is unity. The Reynolds numbers are very small so that the gases flow through the channels in a laminar flow regime. The contribution of homogeneous chemical reactions involving gas-phase species is insignificant under the conditions of interest. The rate-of-progress variable for a surface reaction is given by the difference of the forward rates and the reverse rates. The forward rate constant of the surface reaction as a function of thermodynamic temperature is given by the modified Arrhenius expression. Contributor: Junjie Chen, E-mail address: koncjj@gmail.com, ORCID: 0000-0002-5022-6863, Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China
Files
Steps to reproduce
The exothermic process is modeled by a chemical kinetic model. Additionally, the endothermic process is modeled in such a way as to take into account methanol steam reforming and decomposition and the water-gas shift reaction using another chemical kinetic model. Boundary conditions are specified and physical properties are defined for the fluids, solids, and mixtures.