Numerical investigation of tubular exhaust reformer with thermochemical recuperation for LNG engine

A three-dimensional tubular exhaust reformer was investigated to study the effects of EGR ratio and the amount of the steam addition on the methane-exhaust gas reforming process under different excess air coefficients. The objective was to maximize hydrogen production economically, by regulating the amount of exhaust gas and the steam addition at the inlet of the reaction tube with the amount of methane addition fixed. Coupled with the detailed catalytic reaction mechanism based on Rh-Al₂O₃ catalyzer, the exhaust gas reforming process in a fixed bed reactor was simulated by using a porous media model. The results showed that, in the entry region of the reaction zone, oxidation reaction dominates with significant heat release; whilst after the entry region steam reforming reaction dominates with heat absorbing. The exhaust gas outside the reaction tube played the role of preheating the mixture before the reaction zone and heat preservation in the reaction zone. Results showed that with the methane addition fixed, there is an optimum M/O value (about 2) and W/M value (about 1.25) for maximum hydrogen production. In addition, the surface coverage ratio of coke deposit in the reaction bed decreases with the increase of EGR ratio and steam addition.