Numerical Simulation Of Gas Deviation At Furnace Outlet In A Tangentially Pulverized Coal-fired Boiler

In recent years,gas deviation at furnace outlet in a tangential pulverized coal-fired boiler has gradually become an important factor affecting the safe and stable operation of boiler units.Due to gas temperature and gas velocity deviation,the phenomenon of boiler unit's superheater high temperature tube burst occurs frequently,which seriously affects boilers'safety and economic performance.Therefore,the paper takes 600MW boiler unit as the research object,using Fluent simulation software to simulate the phenomenon that the residual rotation of tangentially coal-fired boiler leads to gas deviation at furnace outlet,in order to find the appropriate measures to reduce gas deviation at the furnace outlet.The influence that the left and right sides of horizontal flue gas deviation cause the superheater tube's steam temperature deviation is analyzed,and it is find that the boiler superheater prone to high temperature tube explosion location.The main research contents are as follows:(1)According to simulation study of gas deviation in a tangentially coal-fired boiler,based on ECR condition,different angle of over fire air(OFA)reversed tangential affect on gas deviation at furnace outlet is studied,under the conditions of 5°?10°?15°and 20°.The results show that there is little effect on the velocity field and temperature field in the main burner area,and the gas flow field in the upper area of the over fire air can be changed.When the over fire air is reversed tangential to 15~0,the furnace's combustion condition is better and the peak-like high temperature region is more uniform.The furnace outlet temperature deviation is the smallest.(2)In order to further study the influence of different over fire air rates on gas deviation at furnace outlet under over fire air reversed tangential conditions,a simulation study was carried out on the basis of over fire air reverse-tangent 15°,over fire air rate by the reduction of 10%,the increase of 10%and 20%,respectively,and the simulation study on the effect of over fire air rate on gas deviation at furnace outlet.The results show that under the condition of keeping the reverse-tangent 15°,the reversed tangential effect can be enhanced by increasing over fire air rate,which has a significant effect on the reduction of furnace outlet's residual rotation,but it makes the upper of the furnace arch nose's temperature is too high,which easily causes the high temperature deviation in the platen superheater region.Increasing the over fire air rate affect the distribution of the component field in the furnace,and the mass concentration of NO_x at the furnace outlet can be decreased.(3)The vertical upwind of over fire air is mainly set to adjust the steam temperature.It has been found through analysis that the adjustment of the burner also has influence on the residual rotation and gas deviation at the furnace outlet.The combustion process under the vertical angle of 10°and 20°was studied by numerical simulation,and the influence of different working conditions on the aerodynamic field in furnace was compared with the ECR condition.The results show that increasing the vertical angle of over fire air reduces the horizontal velocity on the XZ section and decreases the rotation intensity of the flow field in the over fire air area,which can weaken the gas deviation at the furnace outlet caused by the residual rotation.By increasing the vertical angle of over fire air,the mass concentration of NO_x at furnace outlet can also be decreased.(4)Based on the coupled heat transfer simulation of gas and steam at superheater,the influence of the gas deviation in the boiler horizontal flue on the superheater tube burst is studied.The results show that the outlet steam temperature of the same superheater outer tube is higher than the inner tube's.The outlet steam temperature of right superheater's outer tube is higher than the outlet steam temperature of left superheater's outer tube,and the heat flux at the elbow of right superheater tube is higher,so the horizontal flue right superheater outer tube's outlet and elbow are more likely to occur tube burst phenomenon.