A numerical study of multicomponent mass diffusion and convection in porous pellets for the sorption-enhanced steam methane reforming and desorption processes

• Published in: Chemical engineering science 2011-09, Vol.66 (18), p.4111-4126
• Main Authors: Rout, K.R., Solsvik, J., Nayak, A.K., Jakobsen, H.A.
• Format: Article
• Language: English
• Subjects: adsorbents; Applied sciences; Chemical engineering; CO 2 capture; Desorption; Diffusion; Diffusion models; Exact sciences and technology; Flux; Fluxes; Intra-particle mass diffusion; Mathematical models; Methane; Pellet; Pellets; Porous media; Reforming; Sorption-enhanced steam methane reforming; steam
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2011.05.040

Mass-based mathematical models have been formulated to describe the evolution of species mass fraction, pressure, velocity, density and mass diffusion flux in porous pellets for steam methane reforming (SMR) and sorption-enhanced steam methane reforming (SE-SMR) with CO 2 capture and desorption. The internal- and overall effectiveness factors have been calculated for the steam methane reforming, the sorption-enhanced steam methane reforming with a CaO-based adsorbent and the desorption processes. The accuracy of choosing the Wilke model to describe multicomponent diffusion instead of using the more costly Maxwell–Stefan- and Dusty gas models have been investigated. The different effects of choosing the random pore-, multi-grain- and the parallel-pore models have been investigated. Using an average size of the micro-particle the results obtained by in the multi-grain model, are slightly different than those for the parallel-pore model. The model evaluations revealed that: • The rate determining steps for the SMR process are basically the chemical kinetics, but the internal diffusion flux rate is also important as the main conversion takes place close to the external surface of the pellet. The SE-SMR process is basically chemical kinetics controlled. The approximate values of the efficiency factors for SE-SMR processes are around 1 and for the desorption it is around 0.02. • In general, the optimal diffusion flux model is the dusty gas model. • The multi-grain model is optimal pore model for the SMR and SE-SMR pellets. • There is a uniform temperature within the pellet. • The diffusion fluxes dominate over the convective fluxes. The pressure gradients and velocity vanish due to the imposed symmetry conditions. ► Mass based pellet models have been formulated for SE-SMR and desorption processes. ► The internal and overall effectiveness factors have been calculated for these processes. ► The accuracy of the Wilke model to the more costly Maxwell–Stefan and Dusty gas models has been investigated.