Numerical Simulation Of Gas Temperature Deviation Of A 700MW Tangentially Boiler Under Medium–Low Loads

At present,deep peak shaving is common in large coal-fired power plants in China.Tangentially fired coal-fired boilers are widely used.There are flue gas flow and temperature deviation in the operation of tangentially fired boilers,which can easily lead to the temperature deviation of main steam and reheater steam,and also make the wall of superheater or reheater overtemperature,affecting the safety and economy of boiler operation.Boiler operating conditions,such as boiler load,vertical burner swing angle and operating oxygen,have a vital impact on boiler combustion characteristics.In this paper,the influence of boiler load,vertical burner swing angle and operating oxygen on flue gas flow and temperature deviation in a 700 MW tangentially fired boiler under medium and low loads is studied by combining numerical simulation with power plant test measurement.The optimal operating parameters for reducing flue gas flow and temperature deviation are obtained.According to the actual structure and size of the boiler,the geometric modeling and meshing were carried out,and the combustion numerical simulation was carried out.The results were compared with the actual measured data of the boiler to verify the rationality of the results.The influence of changing load on flue gas flow and temperature deviation characteristics of boilers was studied.The results show that the flue gas flow and temperature deviation in the horizontal flue superheater and reheater area are caused by the large rotational momentum before the flue gas enters the screen area in tangential combustion mode,and the flue gas flow and temperature deviation in the superheater and reheater area decrease with the decrease of load.The effects of vertical swing angle of burner and operating oxygen on flue gas temperature deviation characteristics of boiler under medium load were studied.The results show that with the increase of the vertical swing angle of the burner,the central zone of the high temperature flame in the furnace rises,the upper temperature of the furnace rises,the residual rotational momentum of flue gas entering the screen decreases,and the deviation of flue gas temperature decreases;with the increase of the operating oxygen,the residual rotational momentum moment of flue gas entering the screen decreases,and the deviation of flue gas temperature decreases.The effects of burner vertical swing angle and operating oxygen on flue gas temperature deviation characteristics of two boilers under low load were studied.The results show that under the load of 350 MW or 300 MW,there is a smoke temperature deviation in the superheater and reheater area;with the increase of vertical swing angle of burner,the residual rotational momentum of smoke entering the screen area decreases,and the smoke temperature deviation in the superheater and reheater area decreases;with the increase of operating oxygen,the smoke temperature deviation decreases.However,the effect of vertical swing angle of burner and operation oxygen adjustment on reducing flue gas temperature deviation under low load is not as good as that under medium load.