Comprehensive parametric investigation of methane reforming and hydrogen separation using a CFD model

Abstract

Steam-methane reforming is the primary method for industrial hydrogen production. High energy consumption and elevated greenhouse gas (GHG) emissions call for a significant improvement in the reforming process for optimum methane conversion and hydrogen production. Enhanced fuel conversion also produces more CO2 than CO, making the carbon capture process easier, consequently reducing harmful emissions. In this work, a membrane-integrated reformer reactor (MRR) has been investigated through an experimentally validated computational fluid dynamics (CFD) model using ANSYS-Fluent. The MRR model constitutes of Ni-based catalyst filled reforming zone, Pd-based hydrogen-selective membrane, and permeate zone for hydrogen recovery. The developed model has been examined for several parameters including steam-to-methane ratio, flow rate, sweeping conditions, flow direction, reformer pressure and membrane length. The results indicated a substantial increase in methane conversion with a higher steam-to-carbon (S/C) ratio for a given feed flow rate. The methane conversion increased from 34% to 63% when the S/C ratio is increased from 2 to 6 at a methane mass flow rate of 0.0018 kg/s. The results also indicate an increase in hydrogen recovery with the decrease in feed flow rate for a fixed steam-to-methane ratio. Hydrogen recovery decreased from 28% to 2% when the mass flow rate of methane is increased from 5 × 10-5 kg/s to 1.8 × 10-3 kg/s, at a fixed S/C of 4. The incorporation of sweeping steam demonstrated a significant improvement in hydrogen recovery increasing from 15% to 33% with a sweep flow rate equal to the feed flow rate and methane mass flow rate of 1.8 × 10-4 kg/s. Further increase in sweep flow rate showed very small increase in hydrogen recovery, therefore in order to minimize the use of sweeping steam, a sweeping steam flow rate equal to the feed flow rate is suggested. Furthermore, flow direction, reformer pressure and membrane length were also found to play vital role in MRR performance.