Modeling of chemical-looping combustion process of methane with nickel-based oxygen carrier

The chemical-looping combustion of methane in a three-dimensional cylindrical fuel reactor is numerically studied using the developed multiphase particle-in-cell reactive model, featuring the multi-phase flow, heat transfer, reduction of oxygen carriers, and particle shrinkage. After model validation, the general flow patterns, and the thermophysical properties of oxygen carriers (e.g., temperature, heat transfer coefficient) and gas phase (e.g., temperature, density, thermal conductivity, specific heat capacity, and viscosity) are comprehensively studied with the discussion on several crucial operating parameters. The results show that bubble dynamics (e.g., generation, rising, coalescence, and eruption) induce the segregation of small- and large-mass particles. CH4 is thoroughly converted in a very short distance above the bottom distributor while CO and H2 increase above the bottom distributor and then decrease axially. The temperature of particles ranges from 1275 to 1295 K, leading to a 20 K temperature difference in the bed. The heat transfer coefficient (HTC) of particles is in the range of 50-150 W/(m2 center dot K). Increasing the investigated operating parameters (i.e., superficial gas velocity, methane ratio, and wall temperature) enlarges the particle properties (i.e., temperature, HTC) and most of the gas properties (i.e., temperature, thermal conductivity, specific capacity, and viscosity), but decreases the gas density. The findings shed light on the reactor design and process control of the chemical-looping combustion systems.