(55f) The Effect of Psd and Particle Load On the Grade Particle Separation Efficiency of Large Cyclone

Fluidized bed incinerators are used to burn various fuels, such as low- quality coal, biomass and trash. Cyclones are used to separate particles from exhaust gas. Due to the difference of fuel burned, the Particle-size Distribution (PSD) in the bed is different from the PSD of original bed material. The particle load at the inlet of the cyclone is different for different fuel, because the calorific value is different for different fuel. The gross separation efficiency of cyclone was conventionally predicted by integration of grade separation efficiency, on the assumption that the grade separation efficiency was independent of PSD and particle load at the inlet of cyclone. This paper is to investigate the precision of the above assumption when the PSD and the load of particle have a large diversification.

The numerical study is made by using Barracuda, a commercial code, in which Eulerian–Lagrangian procedure is used. In order to evaluate the code, the calculated results have been compared with measurement data taken from the literature. The comparisons showed that the numerical simulation is reasonable. A large centrifugal cyclone with the diameter of 5 m has been numerically studied. Two kinds of particles, one is sand, the other is ash, are employed in this study. The weight percentage of ash changes from 0% to 10%, and particle load changes from 16kg/(m²s) to 64 kg/(m²s), with a constant velocity at the inlet of the cyclone. The numerical results showed that the grade particle separation efficiency is not constant when PSD and particle load are changed. The method of predicting the gross particle separation efficiency and grade particle separation efficiency of large cyclones have  been proposed based on the numerical results.