Three-dimensional Coupled Simulation Study On The Heat Transfer In A 1000 MW Ultra-supercritical Boiler

Supercritical coal-fired units have become the mainstream coal-fired generating units,because of the characteristics of high efficiency,low coal consumption and less emission.In view of coal quality and thermal power operation situation,coal-fired generation in China is confronted with the challenge of the difficult operating conditions,such as the changeable quality of coal and complicated environment.Supercritical coal-fired units need to bear the economic and social responsibilities such as peak load regulation and ultra-low pollutant emission of power system,which is self-evident and needs to be further researched.The transfer process of heat from furnace to boiler in large high parameter unit is the key link of the whole unit.In this paper,the coupling simulation model of a 1000 MW supercritical tower boiler is implemented to realize the matching of furnace and boiler,and the model is used to research the influence of variable coal and variable working conditions on the operation of ultra-supercritical boilers.In the establishment of the model,FLUENT was used to simulate the three-dimensional furnace combustion and heat transfer simulation,and MATLAB was used to simulate the three-dimensional heating evaporation system of boiler side based on the grid nodes of the heating surface in the furnace side.The basic principle of the coupling is that the heat flux obtained from the furnace side is used as the heat source input of boiler side to compute the temperature of water wall,and then the wall temperature is obtained as the boundary condition of the furnace side,during this process,the heat flux density and the wall temperature data are transmitted through the grid nodes of the heating surface.This model is used to study the rated conditions of supercritical boilers,based on the analysis of the distribution of the velocity,temperature and burnout rate in the section of furnace near the burners,the main reaction areas and combustion conditions in the furnace are obtained,and the distribution of heat flux and the influence on wall temperature are obtained.The analysis of the boiler side shows that the heat absorption of the evaporation system is mainly concentrated in the water wall.In the spiral tubes,the wall temperature near the burner area fluctuates the most.In the vertical tubes,wall temperature rises first and then decreases after about 75 m.The maximum temperature difference between adjacent tube walls along the furnace width is within 10 ?.The slag working condition and no-slagging condition are compared and found that the slagging mainly influences the temperature distribution of the furnace wall,which affects the distribution of flue gas temperature and heat flux density on the heating surface.When the pulverized coal changes,the fineness mainly affects the burning distance and the burnout rate,in small fineness condition,heat flux density and the temperature distribution is more even,in big fineness condition,the carbon content of fly ash particle in export is higher,the total release heat is less,the water wall also absorbs less heat.When the coal is bituminous coal,the influence of the change of coal quality is not very big for the heat transfer of the supercritical boiler,and the ratio of heat absorption of water wall and heat exchanger is basically close.Under the operating conditions of different loads,the flue gas temperature distribution in the furnace under BMCR and 75%BMCR conditions are similar,and the flue gas temperature is obviously lower than the other two working conditions under the 50%BMCR working condition with small pulverized coal density and low wind speed.The proportion of heat exchanger in three working conditions is basically the same,in the high heat flux zone,the temperature of water shows an upward trend along the tube length in the BMCR and 75%BMCR conditions,and in the 50%BMCR conditions,temperature in the two-phase region is decreasing.