Numerical simulation of exhaust reforming characteristics in catalytic fixed-bed reactors for a natural gas engine

Abstract

Coupled with detailed catalytic reaction mechanism, the exhaust reforming process in a fixed bed reactor was simulated using a porous media model to investigate the reforming characteristics under different initial conditions. The effects of gas hourly space velocity (GHSV), feed component, steam addition and wall temperature on the methane conversion rate, hydrogen yield and other characteristic parameters were analyzed. The simulation results show that the oxygen is consumed rapidly when the reforming gas enters the reaction zone and the steam reforming plays a dominant role in the latter part. The exhaust reforming process mainly involves oxidation reaction, steam reforming reaction and water gas shift reaction. The methane conversion and hydrogen production decrease with the rise of GHSV, while the molar ratio of H2 to CO first increases and then decreases and reaches its peak value when GHSV ranges from 30,000 h−1 to 35,000 h−1. As the ratio of methane to exhaust increases, a higher molar fraction of hydrogen at the outlet can be achieved owing to a bigger proportion of partial reforming reaction of methane, and methane conversion rate decreases. It also suggests that a modest steam addition is preferable for both the reforming performance and the life span of the fixed bed.