Numerical Simulation Study On Flow Field And Performance Of Induced Draft Fan For Large Power Plant Boiler

In large power plant boilers,because of its good system matching,adjust the characteristics of high performance and good running characteristics,two-stage moving blade adjustable axial flow fan has been widely used,but in actual operation,under certain circumstances there are problems such as abnormal rotor blade,unstable operation,stall and surge,and and so on,which will seriously affect the safe and stable operation of power plant boiler.Due to the variable working conditions and more equipment involved in induced draft fan,all kinds of complex problems are more prominent.Therefore,it is of great significance to study the fan operation characteristics and internal flow characteristics,deeply analyze the relationship between the rotor blade installation angle of the fan and performance,and understand the flow field interference between the fan and the import and export flue,so as to improve the performance of the fan and improve the operation reliability of the fan.It takes 600 MW unit two-stage moving blade adjustable axial flow fan and the import and export flue as the research object.Firstly,the multi-reference model is used for the coupling calculation of the rotating region and the stationary region,the Simple algorithm is used to solve the pressure-velocity coupling equation and the RNG k-ε turbulence model is used to simulate the flow process of flue gas in the fan.So as to analyze the operating characteristics and internal flow characteristics of the fan,and the reliability of the simulation results is verified.Through the analysis of the simulation results,they show that from the leading edge to the trailing edge of the blade,the total pressure on the suction surface increases gradually,while the total pressure on the pressure surface decreases first and then increases.In the middle and upper part of the blade,the power generating capacity is the strongest.The total pressure at the impeller outlet section is asymmetrically distributed along the circumferential direction between high and low pressure zones.Secondly,in order to understand the relationship between rotor blade installation angle and fan operation characteristics and internal flow characteristics,numerical simulation is carried out for two-stage adjustable axial flow fans with different rotor blade installation angles.The conclusions are as following: The influence of negative installation angle of rotor blade deflection on the total pressure and efficiency of the fan is higher than that of positive deflection,compared with only the first level installation angle of deflection,two-stage synchronous deflection has a greater impact on the fan performance and is more likely to cause the deterioration of the fan performance;With the increase of deflection angle △β,the change gradient of total pressure on the blade surface increases,and the high speed area,high turbulent kinetic energy area,vorticity intensity and influence area in the impeller passage all increase.Finally,by induced draft fan with the import and export flue system to carry on the numerical simulation,and compared with pure fan and induced draft fan import and export flue section of the results of numerical simulation,it compares and analyzes the import and export flue flow field characteristics of induced draft fan and fan operation characteristics and the relationship between the internal flow characteristics,and then discusses the influence of different flue geometric characteristics for the fan performance.The results show that the flow field in the fan is interrelated with the flow field distribution in the inlet and outlet flue.Under design conditions,the flow field characteristics in the fan are beneficial to improve the airflow stability and flow field uniformity in the inlet flue,but it will aggravate the energy loss in the outlet flue and disturb the flow field distribution in the outlet flue.Increasing the vertical height of the import flue is helpful to improve the performance of the fan.With the increase of the vertical height of the import flue,the total pressure and efficiency of the fan increase,and the average turbulent kinetic energy of the export section of the first stage impeller decreases gradually.Under the low flow condition,the fan performance of the export flue "confluence first and then climb up" is better,while under the high flow condition,it is just the opposite.The geometric characteristics of export flue have little influence on the flow characteristics inside the fan.