Multi-scale CFD simulations of bubbling fluidized bed methanation process

The two-fluid model coupled with the improved local-structure-dependent drag model and the modified chemical kinetics is employed to account for the multi-scale phenomenon in a bubbling fluidized bed methanation process for the production of synthetic natural gas. The accuracy of this multi-scale CFD model is verified by a series of experimental data under different operating temperatures, inlet compositions, inlet velocities and initial bed heights. The cold flow CFD simulations are further carried out to evaluate the effects of the chemical reactions on the meso-scale structure. The results demonstrate that the bubble volume fraction and bubble velocity decreases due to the gas volume contraction caused by the methanation reactions. Three-region distribution of the gas temperature is obtained by simultaneously solving the multi-scale CFD model and the energy equations and the simulation results are compared with those based on the isothermal flow assumption. The results indicate that the distributions of solid volume fraction and mole fractions obtained based on the isothermal flow assumption are almost coincident with those obtained by solving the energy equations, which confirms the rationality of the isothermal flow assumption in a fluidized bed reactor.