CFD Study Of Modified Fly Ash Ejection System In Coal-fired Power Stations

Mercury is released during coal combustion in coal-fired power station,and it is present in the combustion products in different valence states,and the elemental mercury in flue is very harmful and difficult to remove.In order to remove the elemental mercury in the flue gas,the research group developed the modified fly ash ejection system,and carried out the engineering demonstration and application in 300MW and 1000MW coal-fired power stations.As a new and economical method to remove mercury,the experiment results of modified fly ash ejection with mercury removal have good removal effect.The ejection mode and spray uniformity of fly ash affect the final removal efficiency.This paper studies the process of modified fly ash injection.Based on the study in modified fly ash of a 1000MW coal-fired unit injection system,the main research is to research the front of the air preheater after SCR flue in diffusion effect of modified fly ash after injection.Using CATIA modeling software to build the physical model of flue and spray gun,ANSYS Fluent software is used to do the simulate research finding modified fly ash particles and gas mixing and diffusion situation,using the standard deviation of average exit particle concentration coefficient as the main way of evaluation of diffusion.A DPM model was used to compare the distribution of the flow field between the added and unmodified fly ash adsorbent.The research is discussing the influence of different modified fly ash adsorbent particles on the spray velocity,nozzle Angle,particle size,number of nozzle and spray pipe arrangement.The study shows that when the gas inlet velocity is 5m/s,it shows good jet effect when the velocity speed bigger.In this working condition,particles with particle size less than 75 μ m are more likely to diffuse in the flue.When the injecting pipe’s angle is 20 °,the particles can be distributed more evenly.Increasing the number of sprays,setting up symmetrical jets,and inserting the nozzle into a deep alternate arrangement can make the particles spays better in the flue.Based on the comparison of various working conditions,this paper gives the optimization under certain conditions,compared with the original operating mode,the standard deviation coefficient of particle concentration distribution decreased by over 50%,it makes a more uniform distribution of particles,and more advantageous of modified fly ash to absorb mercury in flue gas.