压力对旋风分离器内颗粒浓度分布影响的模拟

SIMULATION OF INFLUENCE OF PRESSURE ON SOLIDS CONCENTRATION DISTRIBUTION IN CYCLONE SEPARATOR

为了分析压力变化对旋风分离器内颗粒浓度分布的影响,利用Fluent 6.1软件,气相流场采用修正的雷诺应力模型,颗粒相运动采用颗粒随机轨道模型,对0.1～6.5 MPa压力下旋风分离器内气、固两相流流场进行了模拟。结果表明,在入口浓度一定的条件下,随着压力的升高(<3.0 MPa),器壁颗粒浓度逐渐呈螺旋状灰带分布,旋风分离器内旋流区域的颗粒浓度减小,旋风分离器分离能力增强。压力增加一方面使气体切向速度增加,颗粒所受离心力增加;另一方面,气体的湍流强度增大,颗粒的扩散作用增强。当压力超过3.0 MPa后,压力增加对气体切向速度影响不大,而颗粒扩散增加,旋风分离器内旋流区域颗粒浓度增加,对颗粒分离不利。旋风分离器的径向颗粒浓度分布可以用指数函数描述,其中颗粒的径向速度、颗粒的扩散系数和边壁的颗粒浓度是影响颗粒浓度分布的主要因素。旋风分离器粒级效率随压力的增加而增大,当压力超过3.0 MPa后,压力增加对粒级效率影响不大。

In order to investigate the effects of pressure on the solids concentration distribution in a cyclone separator, the gas-solid two-phase flow field within a pressure range of 0.1-6.5 MPa has been simulated by using the stochastic trajectory model on the platform of Fluent 6.1. The results showed that under a certain inlet solid concentration, when the pressure increased（（3.0 MPa）, the solid concentration on the cyclone walls developed to the helix dust band gradually. The solid concentration in the inner swirl decreased and the cyclone separation ability increased. The pressure increase, on one hand, made the gas tangential velocity increase, so the centrifugal force acting on the particle increased. On the other hand, it made the gas flow turbulence intensity increase, so the particles diffusion increased. When the pressure exceeded 3.0 MPa, the pressure increase affected the gas tangential velocity a little, while the particles diffusion increased and the particles reflected and re-entrainment from wall become worse. Therefore, the solid concentration in inner swirl region increased, the cyclone collection efficiency decreased. The radial distribution of solid concentration fit for an exponential function. The factors which influence the solid concentration distribution were solid radial velocity, diffusion coefficient and solid concentration on walls. With pressure increasing, the grade efficiency of cyclone increased. When the pressure exceeded 3.0 MPa, the pressure increase affected the grade effieieney a little.