Numerical study on the hydrodynamics in high-density gas-solid circulating fluidized bed downer reactors

The hydrodynamics in a gas-solid circulating fluidized bed (CFB) downer reactor under high-density operating conditions is studied numerically using the Eulerian-Eulerian two-fluid model and compared with the low-density downers. Numerical results of both the axial and radial gas-solid flow structures have good agreements with the experimental data. The first and second acceleration regions, and a fully developed region along the CFB downer have been clearly shown. A correlation on the overall bed density is developed based on the numerical results as well as the experimental data, leading to 2D and 3D maps of the overall bed density profiles under different operating conditions. With the help of the two maps, the transition from a low-density operating condition to a high-density operating condition in the CFB downer is discussed. The scale-up effects are also numerically studied.