(150e) Simulation of Commercial Scale Autothermal Chemical Looping Unit for Syngas Production

Global demand for hydrogen and syngas is increasing to meet the growing market for clean energy and chemicals, in particular fertilizers. Today steam methane reforming (SMR) produces about 75% of world’s hydrogen. Heat for the strongly endothermic reactions is supplied from a fired furnace. The latter emits CO₂ directly to the atmosphere and lowers the energy efficiency. To improve the energy efficiency and facilitate CO₂ capture, autothermal Chemical Looping Reforming (a-CLR) has been proposed. The process typically makes use of a dual-fluidized bed reactor with a bubbling fuel reactor (FR) and a riser air reactor (AR). In the AR the oxygen carrier (OC) is oxidized with air and sensible heat stored in the OC particles. After exiting the AR, the OC particles are transported into the FR where they are reduced with syngas and methane and then catalyze the SMR reactions. The OC particles supply some of the heat required for the SMR reactions, some of the OC reduction reactions the remaining part as to ensure autothermal operation.

Commercialization of the technology requires fundamental understanding of the reactions and reaction kinetics and of the fluid dynamics and eventual transport limitations. Reactor simulations with a sufficiently fundamental model can then be used to predict the methane conversion, syngas composition and required solids circulation rate under typical commercial conditions and to study catalyst and reactor design optimization. A 1D a-CLR reactor model accounting for the presence of bubbles and axial dispersion in the emulsion phase in the FR and for detailed reaction kinetics and catalyst deactivation by Ni oxidation is presented. An a-CLR unit equivalent to 50 commercial SMR pipes was then considered and the conditions allowing autothermal operation and sufficiently high methane conversion studied. It is shown that only a few % Ni oxidation in the AR is optimal as fully reduced Ni is required in the FR to be catalytically active. Autothermal operation and up to 97% methane conversion can be achieved at reasonable operating temperatures and OC circulation rate. Transport limitations were found important, the catalyst activity having only a small impact on the methane conversion. In a last part of the presentation, the influence of the main operating conditions is discussed and recommendations for further development of the technology given.