Modelling of multiphase reactive flows in a full-loop coal-direct chemical looping combustor

Abstract

The coal-direct chemical looping (CDCL) process is a promising clean coal combustion technology, yet the internal multiphase reactive flows in the full-loop system are not clear. In this paper, for the first time, a multi-fluid CFD model of gas–solid-powder reactive flow is developed to describe the gas-oxygen carrier-coal reactive flow in a full-loop CDCL unit, based on Eulerian-Eulerian-Lagrangian framework. The model is validated by comparing with experimental data in terms of flow and reaction behaviours. The model predicts the unique gas-oxygen carrier-coal flow in the full-loop moving-bed CDCL unit, including multiple fluidisations, mixing and separation between the oxygen carrier and coal. The mean residence time of coal particles is around 13 s ∼ 20 s through statistics of discrete particles at the reducer outlet. The high temperature in the CDCL system is observed in the AR riser, cyclone and the top section of the fuel reactor (FR); whereas the low temperature is observed at the bottom of the FR and the l-valve, as a collected result of endothermic and exothermic reactions. A less than 5 mol%, leaks of O2 from the combustor to the reducer can be captured, which is caused by the unbalanced pressure distribution. Overall, over 90 vol% CO2 concentration and 100 % coal carbon conversion are achieved at the FR outlet, which indicates a high CO2 separation efficiency and coal carbon conversion of this CDCL system. This work provides a useful tool for designing and optimising CLC processes.