Effect of temperature and heat flux boundary conditions on hydrogen production in membrane-integrated steam-methane reformer

Abstract

In order to operate reforming plants at maximum efficiency it is important to investigate their operation under various conditions. This study aims to perform a comprehensive computational analysis to examine the effect of thermal boundary conditions on SMR and hydrogen recovery and, consequently, enriching the literature on hydrogen generation through steam-methane reforming. The studied thermal boundary conditions include constant and variable inlet temperature, outer wall temperature, and heat flux on outer wall of the reactor. A constant inlet flow rate of 0.001 kg/s (methane mass flow rate = 0.00018 kg/s), steam-to-methane ratio (or steam-to-carbon ratio, i.e., S/C) of 4 is considered in the reformer side for all the cases. Furthermore, the difference of pressure between both faces of the membrane is kept constant. Sweeping flow is incorporated to further raise the hydrogen partial pressure difference. Steam with flow rate of 0.001 kg/s is used to induce the sweeping effect throughout the study. Constant and variable temperatures/heat fluxes along with the effect of radiation in the reformer and transient inlet temperatures are examined in this study in terms of CH4 conversion ( %), H2 recovery ( %), H2 mass flow rates (kg/s), hydrogen mass flux through the membrane (kg.m−2. s−1), and other important parameters. About 1.7 times increase in methane conversion is noted as the reformer temperature is increased from 500 to 700 °C. The hydrogen recovery is found to decrease with the increase in temperature. Around 57 % and 56 % decrease in methane conversion and 42 % and 11.5 % rise in hydrogen recovery is observed with segmented case as compared to the constant heat flux and constant temperature cases, respectively. As compared to the reference 600 °C constant wall temperature, the increasing temperature profile results in 10.6 % rise in methane reforming and 11.2 % drop in the recovery of hydrogen. On the other hand, the decreasing temperature profile demonstrates 9.4 % decrease in conversion and 10.2 % elevation in recovery rate in contrast with the constant temperature case.