A numerical study of pellets having both catalytic- and capture properties for SE-SMR process: Kinetic- and product layer diffusion controlled regimes

Abstract Sorption enhanced steam methane reforming (SE-SMR) is a promising process for the production of H 2 . The in situ removal of CO 2 in the steam methane reforming (SMR) process shifts the reaction equilibrium according to the Le Chatelier's principle towards higher H 2 production. Most of the earlier studies worked on the SE-SMR process using two different pellets (2-P): one for the reforming catalyst and the other one for the CO 2 adsorbent. In this study, we propose a novel pellet design where both the catalyst and sorbent are put together in a support (1-P). In the 1-P system, the produced CO 2 molecules due to the reforming reactions will be captured by the sorbent inside the pellet. Whereas in the 2-P system, the CO 2 molecules have to transported in between the pellets to be captured by the sorbent. Hence, 1-P design has less resistance for mass transfer between the catalyst and sorbent active sites. In this study, the internal mass transport limitations of the 1-P design for the SE-SMR process have been investigated. The dusty gas multicomponent mass diffusion pellet model formulated for the SE-SMR process describes the evolution of species mole fractions, pressure, total concentration, temperature, fluxes, and convection within the voids of the porous pellet. The internal effectiveness factors of the SE-SMR process have been calculated for the SE-SMR process. The effective diffusivities are described according to the parallel pore- and random pore models. The carbonation reaction in the SE-SMR process is a gas–solid reaction system, which generally follows one out of two controlled regimes, namely the kinetic- and product layer diffusion (PLD) controlled regimes. A mathematical model based on the grain model was applied modelling the carbonation reaction. The change in pellet void-fraction due to the formation of the solid CaCO 3 , the diffusion of gaseous phase through the product layer, the structural changes of the spherical grains by the inclusion of variable diffusion coefficient and multiple carbonation/calcination cycles were considered in the pellet model. The effect of pellet diameter on the carbonation reaction rate is investigated to observe the complex mechanism of gas–solid reaction system. The 1-P performance is promising compared to the conventional 2-P design. Further, the reduction in void-fraction with the CaO conversion, product layer diffusion, pellet diameter and multiple cycles are all important effects in the SE-SMR process because these mechanisms influence on the reaction rate, capture capacity, and the effectiveness factors.