Numerical Simulation Of Ash Deposition On Heat Exchanger Surface Under Various Conditions Based On Dynamic Mesh

In practical utility boilers,fly ash formed by combustion of power coal will deposit on the surface of heat exchangers,resulting in pollution,slagging,corrosion and wear,which will reduce the heat transfer efficiency and affect the overall operation efficiency.Scholars at home and abroad have carried out a lot of experiments and simulation studies on the problem of ash deposition and slagging.Based on the one-dimensional slagging experiment,CFD simulation of fly ash deposition on heat exchanger under different conditions was carried out based on dynamic mesh technique: slagging process simulation under different furnace temperature and slagging process simulation under different proportion of corn straw burning.Firstly,the dynamic mesh method used in ash deposition simulation is introduced in detail,and the corresponding one-dimensional furnace test bench is briefly introduced.The grid partition,grid independence verification and boundary condition setting of the computational domain are explained.In terms of the models,several kinds of judging models of fly ash deposition are theoretically explained and compared.Due to the problem of "negative volume" in the execution of moving grids,a set of profile optimization schemes for moving grids is proposed and applied in the following simulation.Secondly,the effects of different furnace temperatures(1473 K,1523 K and 1573 K)on slagging on heat exchanger surface are studied.The melting ratio of SM coal ash at different temperatures is obtained by chemical equilibrium calculation,and the calculated results are used to determine the probability of sticking in the simulation.The effects of surface temperature and effective thermal conductivity of slag are considered in the simulation.The results show that higher furnace temperature will lead to higher slag surface temperature.The effective thermal conductivity of slag increases linearly with slagging.The deposition efficiency of the three furnace temperature conditions is 59%,68% and 80%,respectively,and the large particles tend to deposit on the windward side.The simulated slag shape and heat transfer characteristics of the slag are close to the experimental values.Finally,the effects of different proportion of corn straw(0%,5% and 10%)on slagging process of heat exchange surface are studied.Three melting ratio curves of Shenhua coal and corn straw mixed with ash at different temperatures were obtained by chemical equilibrium calculation,and the calculated results were used to determine the probability of adhesion in simulation.Based on the dynamic mesh technique,the changes of shape,surface temperature and effective thermal conductivity of slag during slagging are considered.The results showed that the deposition efficiencies were 75%,80% and 87% at 100 min respectively,which indicated that the ash content of corn straw was more prone to slagging.The parameters of slag growth rate,slag surface temperature and heat flux were in good agreement with the experimental values.