Particle-scale study of coal-direct chemical looping combustion (CLC)

The hydrodynamic and thermochemical characteristics in the coal-direct chemical looping combustion (CLC) process are studied by a self-developed computational fluid dynamics - discrete element method (CFD-DEM) approach featuring particle-scale simulations of collisions, heat and mass transfer, drying process, coal pyrolysis, gasification, and heterogeneous reactions between gas species and oxygen carriers. A polydisperse drag model is adopted to accurately calculate gas-solid interactions. After comprehensive model validations, the flow pattern, pressure drop, gas products composition, particle temperature, combustion efficiency, and solid residence time (SRT) are qualitatively and quantitatively analyzed. The results show that increasing the coal feeding rate slightly improves the temperature of coal particles and accelerates the release of moisture in coal particles. Finer oxygen carriers promote the conversion of intermediate gas products into CO 2 and H 2 O, therefore improving the combustion efficiency in the CLC process. The SRT distribution with an early peak and a long tail is profoundly revealed under different operating parameters. A dual-side coal feeding arrangement remarkably improves the uniformity in the CLC system. • A reactive CFD-DEM model is developed for the coal-direct CLC unit. • The proposed model is validated with the experimental data. • The underlying mechanism in the CLC system is explored at particle-scale.