Simulation Research On Heat Transfer And Erosion Of Superheater At Inlet Flow Field Of AQC Boiler

The AQC boiler of waste heat recovery system of a cement plant in Xiangtan is taken as the research object in the paper,the method of numerical simulation is adopted for the flow field optimization of the flue of the AQC boiler to obtain the results with two optimization methods,which respectively are piecewise inlet and the installation of guide plate.Then under the optimum scheme,the heat transfer characteristics of convection tubes in superheater area are studied further,and the erosion characteristics of annular fins tubes are studied simultaneously,the research results provide technical support for the efficient design and operation of AQC boiler.The specific research contents and conclusions are as follows:(1)When the method of piecewise diffusion is adopted for inlet flue,the influence of the first diffusion angle(a)and diffusion length(L)are researched,the results show that when L=3.0m and a=15°,the flow field in the inlet flue is the best,and the mean cross-section variance and the total pressure drop of the inlet flue outlet decrease by 56.63%and 27.0%respectively.Through the optimization research of the structure parameters of the guide plate,the optimal value of the length of the guide plate(La)and the distance ratio between the guide plate(K)are obtained,which are Ld=4.5m.K=1.8.Under the optimized structure parameters,the mean cross-section variance and the total pressure drop at the outlet section of the inlet flue are reduced by 82.4%and 9.5%respectively.(2)Under the optimization scheme of optimal inlet flue flow field,the superheater is studied in hot state.It is found that the optimization of the flow field of the inlet flue can significantly improve the flow field in the flue pipes of the superheater section,and improve the heat transfer capacity of the pipes.Compared with the original superheater,the heat transfer coefficient of the pipes' surface is increased by 5%and 15%respectively with the scheme of piecewise diffusion and arranging the guide plate.At the same time,the heat transfer performance and pressure drop of the original superheater model at different flue gas temperature and different flow rate are analyzed,the results show that the heat transfer coefficient of the pipes' surface increases with the increase of the flue gas temperature or the flow rate,and the pressure drop decreases with the increase of the temperature,and increases with the increase of the flow rate.(3)The erosion characteristics of the staggered-arranged annular finned tubes under the parameters of gas-solid two-phase flow are studied,and the erosion rules of different tube rows with different particle size,flue gas velocity and dust content of flue gas are obtained;meanwhile,on the basis of the field optimization of inlet flue flow,and comparing the erosion of fin tubes under different schemes,it is found that taking the areas with the most severe erosion as example,under the scheme 2 model,the erosion rate of the second row base tubes is 1.98x10-10kg/m2s,which is reduced by 2 orders of magnitude than the original scheme,and the erosion rate at the top of the fourth row fin is 1.14×10-9kg/m2s,which is reduced by 50 times compared to the original scheme.(4)Through research,it is found that by arranging the guide plate at the inlet flue,the flow field inside the flue can be effectively improved,the heat transfer performance of the superheater tube bundle can be improved,and the erosion degree of the tube bundle can be reduced at the same time,thereby effectively improving the heat recovery efficiency of the AQC boiler.