Numerical Simulation Of Hydrodynamics And Abrasion Characteristic In Circulating Fluidized Bed By Discrete Element Method

Energy saving and environmental protection are two major issues in China,combustion technology of circulating fluidized bed(CFB) has received the widespread attention as a clean coal combustion technology. However, the complexity of the gas-solid flow, and the multi recirculation of materials cause the abrasion in different degrees at various position of the boiler. Therefore, studying the rules of abrasion in the boiler becomes an urgent problem for the safety operation of CFB. The complexity of the gas-solid flow and the diffculties of measuring the data from CFB restrict the, application of traditional experimental methods for studying the performance of CFB. With the rapid development of computer technology, more and more studies were performed using numerical simulation.In this study the gas-solid two-phase flow in two dimensional CFB is stimulated by the soft-sphere model of DEM in Euler-Lagrange coordinate system. The flow of particle phase is simulated by DEM(discrete element method), and that of the gas phase is simulated by the algorithm of SIMPLER respectively. The interaction of gas phase and solid phase is considered by Newton third law. A calculating program calculates developed by FORTRAN.Firstly the characteristics of flow in single-hole jet fluid bed were stimulated in two dimensional coordinates assuming to ignore heat transmission, combustion and particles'motion. The states of the gas-solid flow in different time were obtained which including the variation of bed's height when the air's velocity of inlet change, the state of the particle's mixture, the contribution of void ratio, the velocity distribution in space of the gas phase and solid phase, the flow's character of the gas-solid phase and the like. Has analyzed the elasticity coefficient to the analogue result influence, and compared the simulation results in different drag model. The results show that: the bed of the CFB would rise when the velocity of the air in the inlet increased. In the middle part of CFB, particles moved up and spread to both sides; in the both sides, they moved down; in the bottom, they assembled to the center because of the engulfment of the jet steam. The top where the particles'concentration was low was called dilute phase region and the bottom where the concentration was high was known as dense phase region. Particles collide and mix with each other, it reflects that the gas-solid two-phase flow complicated and fierce movement in CFB.According to the result, the contribution law of the particles'concentration was got, the wall's location, the times and the velocity when the particles impacting were obtained. The different heights'wearing quantity of wall and the wearing character in CFB during cold state were calculated. In the end, the means of reducing wear was raised. The results show that, the results show that, the frequency of the collision in the dense phase region was higher than that in the dilute phase region. In the dilute phase region, the collision frequency in the both sides was higher than the middle part. In the dense phase region, the times of the particles collided with the wall was the most and the wear volume was also the largest.The research in the paper provides the foundation for the further study on numerical simulation of the heat transimission and combustion in the CFB.