High-Purity Hydrogen Production by CO₂ Addition for Sorption-Enhanced Steam Methane Reforming at a Temperature Below 600 °C

Abstract

The sorption-enhanced steam methane reforming (SE-SMR) process is promising for in situ CO2 capture and high-purity hydrogen production with a low CO concentration. SE-SMR using a CaO-based sorbent was operated at a temperature of 600–750 °C. High-purity H2 production (defined as the H2 molar fraction at outlet ≥90%) by SE-SMR using a CaO sorbent is generally not achievable at a temperature of 550 °C with a commonly used steam/methane molar ratio (S/C) of 3. CO2 is the main greenhouse gas. The utilization of CO2 to improve high-purity H2 production through SE-SMR by adding CO2 at the inlet in a fixed-bed reactor at 550 °C and S/C = 3 is numerically studied. The results show that high-purity H2 production is achieved when the extra CO2 addition at the inlet is at least 12% of the original mass flow rate (denoted as ≥12% CO2,in), based on the parameters in this work. The remarkably higher reaction rate of the strongly exothermic CO2 sorption reaction is obtained for CO2,in ≥ 12% in the inlet region of the catalyst/sorbent bed for the earlier time stage. Consequently, the temperature and the rate of steam methane reforming are significantly enhanced by the CO2 sorption reaction. CH4 conversion, the rates of H2 production and CaO conversion, and total H2 production (based on per unit mass of supplied CH4) are enhanced by an increase in the level of CO2,in.