Flue-gas Temperature Deviation Of A 660MWe Tower Boiler And Its Optimization Methods Under Low Load

In recent years,more and more tower boilers have been applied in China due to their advantages in high parameters,large scale and so on.In the actual operation of some tower boilers,serious flue gas temperature deviation is gradually exposed,which affects the economic and safe operation of boiler units.At present,there is relatively little research on the temperature deviation of tower boilers.This paper takes a 660 MWe supercritical tower boiler as the research object,and makes a detailed study on fluegas temperature deviation,including the formation mechanism,the variation law with load and the optimization method.In this paper,FLUENT 16.0 software is used.Firstly,an appropriate numerical simulation method is selected,and the formation mechanism of flue gas temperature deviation of tower boiler is studied under 100% load.When the flue gas enters the panel heat exchangers zone,large velocity deviation and temperature deviation began to appear.The devation of velocity and temperature is casused by the rotating flow of flue gas,the dividing and rectifying function of panel heat exchangers,and the suction of induced draft fan.The size of the recirculation zone on the right side is larger than that on the left side,and the larger flow resistance force flue gas skew to the left.On the left side,the flue mass flow rate is larger,the velocity and the temperature are higher.In the lower part of panel heat exchangers zone,the velocity deviation and temperature deviation are larger than that in the upper part.Secondly,the variation law of the temperature deviation of the tower boiler with the operating load is studied.Impeded by SOFA(seperated over fire air),the flue gas reaches the cross section of the last layer of SOFA nozzles: under 100% load and 50% load,almost only the counterclockwise rotating vortex formed by the SOFA is left;under 75% load,there are two vortexs with similar size and opposite rotation direction.Under all the three operating loads,the flue gas in the panel heat exchangers zone is skwed to the left.On the left side,the flue mass flow rate is larger,the velocity and the temperature are higher.Under 75% load,the velocity and temperature deviation are relatively smaller,while 100% load and 50% load much larger.Finally,based on 50% load,the optimization effect of yaw angle and velocity bias set of SOFA on the gas temperature deviation of tower boiler under low load is studied.When the yaw angle is too small or too large,the flue gas is skwed to the left side or the right side,and the velocity and temperature deviation are large.When the yaw angle of the SOFA is 34° and 45°,the flue gas is almost centered in the panel heat exchangers zone,with significantly smaller velocity deviation and temperature deviation.Increasing the velocity of SOFA on the right side will aggravate the skewness of flue gas to the left,and the velocity deviation and temperature deviation will increase further.Appropriately increasing the velocityof SOFA on the left side can suppress the flue gas from skewing to the left side.When the velocity of SOFA in the left side to that in the right side is 1.2:1,the velocity deviation and temperature deviation are significantly smaller.