Simulation of Methane Steam Reforming Enhanced by in Situ CO2 Sorption Utilizing K2CO3 Promoted Hydrotalcites for H2 Production
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The motivation to switch the fossil fuels to an alternative fuel is an emerging area of research and development during the past decade. Hydrogen is a clean energy carrier for sustainable consumption that can be used in various goals such as raw materials in ammonia and methanol manufactures as well as energy source for electrical power generation and transportation fuel. Sorption enhanced steam methane reforming process (SESMRP) is an interesting multifunctional reactor that is used to produce high-purity hydrogen in a single step. This process is occurred from the addition of an adsorbent into the reaction system for selective separation of a product, and thereby shifting the equilibrium of reversible reaction according to Le Chatelier’s principle. Hydrotalcites is a promising CO2 adsorbent used in a high temperature adsorption and sorption-enhanced reaction process with some main advantages such as high stability and resistance to steam in cyclic operation. For this work, the possibility of utilizing commercial K2CO3 promoted hydrotalcites in this process was tested in a fixed-bed experiment to find the adsorption capability at 350-450 °C. The effects of major operating parameters including temperature, pressure, steam to carbon ratio, GHSV and catalyst-adsorbent ratio on the CO2 adsorption capability and reaction activity which directly influences the process performance have been studied through a mathematical modelling of three kinetic reactions coupled with the equilibrium isotherm of this adsorbent. A 1-D heterogeneous dynamic fixed bed reactor model was constructed and employed in this study. The model considering multi-component and overall mass balance, Ergun relation for pressure drop and energy balance for the bed-volume element was derived to describe this process. The LDF model is used for the mass transfer rate of CO2 in the adsorbent. The bi-Langmuir model is appropriate to describe equilibrium isotherm of this adsorbent. From the simulation, it was observed that the sorption enhanced steam methane reforming in the fixed bed reactor produces more than 90% H2 in a single step operation.