Numerical simulation of commercial scale autothermal chemical looping reforming and bi-reforming for syngas production

He, Zirui [UCL] De Wilde, Juray [UCL]

Autothermal Chemical Looping Reforming (a-CLR) is an emerging technology that facilitates CO2 capture and minimizes energy losses in syngas production. The dual-fluidized bed process uses a bubbling fuel reactor (FR) and a riser air reactor (AR). A 1-D multiscale model was developed that couples fluidized bed hydrodynamics with intrinsic reaction kinetics, including catalyst deactivation by oxidation and coke formation. An a-CLR unit with a capacity equivalent to 50 conventional reformer tubes was considered to demonstrate feasibility. The effects of the catalyst activity, main operation conditions and CO2 co-feeding on the performance were then analyzed. The results confirm a-CLR is feasible with realistic reactors dimensions and solids circulation rate. To avoid the risk of sintering and catalyst deactivation, the oxygen carrier should only be slightly oxidized in the AR. Autothermal operation then requires an oxygen-to-CH4 feed ratio of around 1.2. The high catalyst-to-gas feed ratio in the FR and bubble-emulsion phase mass transfer limitations result in a low sensitivity of the methane conversion to the catalyst activity. A low H2O-to-CH4 feed ratio introduces a risk for coke formation in the bottom of the FR, but part of the feed methane is fully oxidized, producing H2O and CO2 in the emulsion phase and mitigating this risk. Co-feeding CO2 with CH4 and H2O is seen to allow adjusting the H2/CO-ratio of the syngas, but increases the risk of coke formation. Finally, heat recovery from the flue gas and syngas from both reactors by preheating the feed gases further increases the energy efficiency.