A three-dimensional hot flow model for simulating the alumina encapsulated NI-NIO methane-air CLC system based on the computational fluid dynamics-discrete element method

摘要

A three-dimensional hot flow model for simulating the alumina encapsulated Ni/NiO methane-air CLC system is developed. The temperature of particles (i.e., metal/metal oxides) is calculated based on exothermal/endothermal reactions and the convective heat transfer between particles and the gas mixture. The temperature of the gas mixture is solved by incorporating the energy exchange with the oxygen carrier particles into the governing equations. The motion of particles is tracked using the discrete element method, whilst the fluid flow is governed by the modified Navier-Stokes equations derived by replacing the point and fluid mechanical variables with locally averaged variables and the inclusion of local gas volume fraction. Two different CLC systems with different initial particle conversion rates have been simulated and the characteristics of the CLC hot flow system in terms of distributions of particle and gas mixture temperatures, solid circulation rate and particle conversion rate have been analysed and discussed. The results showed that the transient solid circulation rate varied but fluctuated around a certain value. Heterogeneous distributions of particle temperature and conversion rate have been observed in both fuel and air reactors. The model has been validated by comparing the solid circulation rate and pressure distribution against the experimental data. The hot flow model proves capable of reproducing the CLC mechanism, i.e., transferring oxygen atom from the air reactor to the fuel reactor.