Research On The Turbulent Particle Dispersion In Baffle Demisters

At present,China’s haze problem has become increasingly prominent,and its causes have big concern with the mist eliminator of Wet FGD system in Coal-fired power plant which has a lower removal efficiency of fine particulate matter.In the past,the study of the defogger exist problems that the particle size was big(>20μm)and the influence of turbulence diffusion on the movement of fine particles was neglected.In order to research the turbulence diffusion law of fine particles in demister,and provide ideas to improve the removal efficiency of fine particles in defogger.Based on the combination of numerical simulation and experiment,the proliferation and deposition law of particle in the turbulent flow with different eliminator structures were analyzed,which mainly includes the following contents:(1)A mathematical model was established for the Zig-zag demister with hook plate.Different particle turbulence diffusion model and large eddy simulation method were used to calculate the movement of the droplet with particle size below 15μm.The results indicated that consideration of the effects of turbulence diffusion has necessity.At the same time,the CRW and DRW models can effectively improve the accuracy of the removal efficiency calculation of small droplets(<10μm)and predict the turbulence diffusion of droplets in the demister.The two random orbital models are more accurate in predicting the velocity and pulsation of droplets in a locally uniform small-scale turbulent pulsating flow field which have unsatisfactory results in large-scale anisotropic turbulent vortices.The large eddy simulation(LES model)can effectively predict the pulsating and vortex distribution of the flow field which calculated results have great agreement with the experimental value.(2)The vortex defogger was selected as the physical model,and the experimental platform of the fine particle distribution in vortex defogger was established.The particle size distribution and the distribution density of the fine particles were observed under different inlet gas velocity conditions and different baffle by optical microscope.With numerical simulation method,the proliferation and deposition rules of particle were analyzed and summarized.For the different baffle position,the larger particles(>12μm)deposited on the wall of the baffle in the front position in the vortex defogger,and the smaller particles(<12pm)are more distributed in baffle of the rear position.For flow field characteristics,the local wall deposition efficiency in the vortex defogger has a great relationship with the local velocity and the angle of the direction of the flow field with the baffle wall.The intensity of turbulence pulsation has a great influence on the motion diffusion of particles and wall deposition rate and that the baffle with strong local velocity fluctuation has a high wall particle deposition rate.(3)Two simplified physical models were used to research the influence factors of the particle wall deposition in the defogger,including the flow rate,the angle between the main flow direction and the wall surface,and the turbulence structure size.The results show that the overall wall deposition rate of fine particles is positively correlated with the angle between velocity and flow velocity-wall angle.Wherein the effect of increasing the flow velocity on wall deposition rate of the particle(>12μm)is larger than that of fine particles having a particle size of less than 12μm.Large-scale flow field vortex pulsation can significantly increase the dispersion range of the particle flow,so that the deposition rate of the particles in the wall decreased.By contrast,in the narrower defogger channel,the higher vortex intensity increases the deposition rate of the fine particles on both sides of the wall,and the 10mm wall spacing model is affected by the turbulence intensity increase of more than 30mm.In this case,with high flow pulsating intensity,the deposition rate of different particle size particles has a great relationship with the period of the particle flow field response time and the characteristic time of the vortex structure,higher anastomosis leads to higher wall particle deposition rate.The local uniform small-scale pulsation near the wall has a great influence on the wall penetration probability of the smaller particles(<10μm),and the strength of the small-scale pulsation in the vicinity of the wall can improve the wall deposition rate of the fine particles with smaller particle size.