Numerical Simulation Of High-Temperature Electrostatic Precipitation

Particle removal at high temperatures is a technology extensively applied in many processes, such as pressurized fluidized bed combustion combined cycle (PFBC) and integrated gasification combined cycle (IGCC). High-temperature electrostatic precipitator (ESP) is one of the major industrial devices for gas cleaning to meet the environmental requirements. Deep investigation of high-temperature electrostatic precipitation process is extremely helpful for exploring the dust removal mechanism. Most importantly, it can be used for the design and improvement of the electrostatic precipitator in the practical operation. A computational fluid dynamics (CFD) model is carried out to describe the wire-plate electrostatic precipitator in high temperature conditions, aiming to study the effects of high temperature on the electro-hydrodynamic (EHD) characteristics. In the model, the complex interactions between the electric field, temperature field, fluid dynamics and the particulate flow are taken into account.The finite volume method is used to solve the electric field and Euler-Lagrange model is used to describe particle-laden flows. The contents of this thesis can be divided into the following three parts.The contents of first part is related to the interactions between the electric field, fluid dynamics and the particulate flow. The results show that eddy is the main form of ionic wind and there is one pair of reverse vortex structures in the vicinity of each corona electrode. Coulomb force driving particles to the collection plate plays an important role for particle removal. There is a slight drcease in the electric potencial and the ion charge density due to the effect of particle charge density on EHD. Both the mean electric field intensity and ion charge density decrease as temperature goes up.The large transverse migration of particles via an ESP enhances turbulence. The turbulence fluctuations have an influence on particle deposit, either shorten or lengthen the deposit time.The second part focuses attention on investigating the influences of temperature on fluid dynamics, electric field and ionic wind. The results show that high temperature causes low gas density and high viscosity. High temperature thickens the boundary layer along the plate and strengthens the mean turbulent intensity. The ESP working voltage zone becomes narrow with an increase of temperature. High temperature presents less intensity of the effect of ionic wind but larger effect range.The third part explores the behavior of charged particles via electrostatic precipitators and the influences of temperature on it are studied. Initially, the process of particle charge along with its trajectory is studied. Meanwhile, the variation of drag force and Coulomb force along with particles trajectories is researched. Finally, the influences of high temperature on the collection efficiency in an ESP are explored and some feasible suggestions for increasing efficiency are proposed. The numerical results show that high temperature weakens the particle charging for10μm particle. With the increase of temperature, the Coulomb force decrease while the Saffman lift force, Brownian force and drag force increase. The Coulomb force and the drag force are the key forces acting on particles in the ESP. High temperature enhances the interaction between particles and fluid. The possible reasons for less coefficiencies at high temperatures are related to the decrease of operation voltage, the increase of gas flow rate, lower Coulomb force and higher drag force, and the strengthen of the interaction between particles and fluid.