Numerical Simulation Of Gas-Solid Flow In Circulating Fluidized Beds With Multi-Cyclones Based On CPFD Approach

Multi-cyclone arrangement is a typical method to reduce the dimension of cyclone and improve the separation efficiency in large scale circulating fluidized beds (CFB) design. Experiment results revealed that the recirculation flux of particles tends to vary among different cyclones. In this thesis, a new approach based on computational particle fluid dynamics (CPFD) method is used to investigate the hydrodynamic behavior of gas-solid flow in a CFB with multi-cyclones in order to improve the design and performance of a large scale CFB boiler. By comparison with experimental results, the layout of multi-cyclones is improved and the original drag model is replaced by a more accurate model which can enhance the accuracy of numerical simulation.Based on the CPFD approach and the improved drag model, a cold CFB model with "H" style of cyclone arrangement was simulated for two types of cyclone arrangements, namely axis and point based symmetric. Key parameters including pressure, velocity, recirculation flux are given and compared with experimental results. The comparison results indicates that axis based symmetric arrangement is better than point based arrangement in terms of solids flux distribution among the cyclones.In this thesis, a600MW supercritical CFB with "M" style arrangement of cyclones was also investigated based on CPFD approach with different drag models and grid sizes. Based on the comparison of simulation results with experimental results, a combined drag model, i.e.0.8×Wen-Yu/Ergun drag model, gives the more accurate results and agree well with experimental data.