Computational optimization and sensitivity analysis of fuel reformer

Abstract

In this study, the catalytic partial oxidation of methane is numerically investigated using an unstructured, implicit, fully coupled finite volume approach. The nonlinear system of equations is solved by Newton's method. The catalytic partial oxidation of methane over rhodium catalyst in a coated honeycomb reactor is studied three-dimensionally, and eight gas-phase species (CH4, CO2, H2O, N2, O2, CO, OH and H2) are considered for the simulation. Surface chemistry is modeled by detailed reaction mechanism including 38 heterogeneous reactions with 20 surfaceadsorbed species for the Rh catalyst. The numerical results are compared with experimental data and good agreement is observed. Effects of the design variables, which include the inlet velocity, methane/oxygen ratio, catalytic wall temperature, and catalyst loading on the cost functions representing methane conversion and hydrogen production, are numerically investigated. The sensitivity analysis for the reactor is performed using three different approaches: finite difference, direct differentiation and an adjoint method. Two gradient-based design optimization algorithms are utilized to improve the reactor performance. 1

Catalytic Reforming System Suitable for Transportation Applications

“…Increasing the air partial pressure improved CH 4 conversion and H 2 yield. According to modeling , for a ratio of CH 4 :O 2 below 1 the primary products of the chemistry are products other than hydrogen, mostly CO, CO 2 and H 2 O. The molar ratio of CH 4 :air 1:2.4 is close to the stoichiometric for the partial oxidation reaction Eq.…”

“…, there was not enough oxygen to convert all methane. For lower CH 4 :O 2 ratios, the active methane conversion region in the catalyst bed increases in size . However, the increased amount of air mixed with methane dilutes the fuel and increased GHSV.…”

“…With this rate of degradation in catalyst activity, the reactor should operate with high efficiency for a minimum of 5,000 h. No oxygen was observed at the reactor exhaust for all tested cases. In partial oxidation, oxygen is consumed in the first few millimeters of the catalyst bed by surface reactions .…”