Reaction engineering simulations of oxidative coupling of methane in a circulating fluidized-bed reactor

Oxidative coupling of methane in a circulating fluidized bed (ID = 1 m, H = 20 m) was investigated by means of reaction engineering modeling and simulations. The hydrodynamics of the catalytic bed was described applying a two-phase (core and annulus) and two-zone (acceleration and fully developed flow) model. Chemical reactions were described by two separate networks for the heterogeneous and homogeneous reactions. The one for the heterogeneous steps was developed for a La(2)O(3)/CaO catalyst. Concentration profiles revealed that due to the high activity of the catalyst, almost complete conversion of oxygen was already obtained in the acceleration zone. Reactor performance was found to be strongly influenced by mass transport limitation between the core and annulus and by gas-phase reactions. The maximum C(2+) yield of 13 % (T = 800 degrees C, X(CH4) = 34.5 %, S(C2+) = 37.5 %) was obtained at a high solids circulation rate (G(s) = 800 kg/m(2) s) and a low methane-to-oxygen ratio (CH(4)/O(2) = 3). The C(2+) yields in the CFB are comparable to the ones predicted for an industrial-scale bubbling-bed reactor.