Kinetic-embedded CFD modeling of integrated steam methane reforming and limestone calcination in a fluidized bed reactor

Abstract

The combination of limestone calcination, catalytic methane reforming, and combustion in one reactor (MRCCAL) was previously proposed to achieve autothermal and hydrogen-producing sorbent regeneration for calcium-looping technology. However, this technology was only assessed using kinetic-only simulations. To further evaluate its viability, the present study developed an Eulerian-Eulerian CFD model with full reaction kinetics in a bubbling fluidized bed reactor. Three different operating parameters were studied: the inlet gas velocity, the sorbent to catalyst ratio, and the sorbent calcination extent. CFD simulations demonstrated that increasing the inlet gas velocity increased the H₂ production by altering the particle distribution through the bed. Decreasing the catalyst-to-sorbent ratio improved local mixing whereas the catalyst tended to locate at the bottom of the bed where an increased total solid holdup was also found. Sorbents with higher calcination extent led to a decreased CO₂ composition in the off-gas whilst increasing the H₂ composition. When compared with kinetic-only simulations of a continuous reactor, the CFD results showed a noticeable discrepancy in the gas compositions mainly due to the free gas expansion and the more rigorous calculation of the particle mixing patterns, which were not included in the kinetic simulations. The sharp differences emphasized the importance of hydrodynamics in developing novel processes.