Experimental Study On Thermal Deviation At Furnace Exit Of Large Square Tangentially Fired Boiler

With the continuous increase in the capacity and parameters of coal-fired boilers in China,the problem of the thermal deviation at the furnace outlet of tangentially fired boiler is becoming increasingly severe.The existence of the thermal deviation may cause the tube over-temperature explosion and steam temperature fluctuations easily,which would further affect the safety of the boiler and thus impact revenue.To reduce the thermal deviation of the furnace outlet,this paper analyzes the existing methods and points out their shortcomings.Based on that,this paper proposes a combustion adjustment method that can dynamically reduce the thermal deviation of the furnace outlet during variable load and variable parameter operation of the boiler,which can be easily achieved through daily operation of the power plant.For a 660 MW boiler,the following studies were performed:Using gas temperature deviation of furnace outlet or the superheater outlet steam temperature deviation to indicate the furnace outlet thermal deviation is not comprehensive and accurate,so this paper proposes a more reasonable evaluation index: heat absorption deviation on two sides of superheater.After analyze the typical historical operating data of this boiler,we find that there is a strong correlation between two sides of the SOFA damper opening deviation and heat absorption deviation of the superheater unit.Adjusting the deviation of the SOFA damper opening on two sides can dynamically reduce the thermal deviation of the furnace outlet.Herein,cold state numerical simulation and calculation of the aerodynamic field on three different working conditions of the boiler furnace are done,and the calculation results further verify the historical data analysis conclusions.At the end of this paper,field test is performed to study the quantitative influence between two sides of the SOFA damper opening deviation and the thermal deviation of the furnace outlet under different boiler loads,meanwhile,the field test also investigates how the SOFA damper opening deviation would inference the boiler efficiency and pollutant emissions.The test results showe that heat absorption deviation on two sides of superheater can be used as an evaluation index for the furnace outlet thermal deviation.Under different loads,adjusting SOFA damper opening deviation can effectively reduce the furnace outlet thermal deviation.Adjusting the opening deviation of the upper four-layer SOFA damper has the best effect of reducing the thermal deviation of the furnace outlet.Under the load of 600 MW,450MW,and 300 MW,the degree by percent of adjustment of the original thermal deviation can reach 100%,100%,and 82.7%,respectively.This adjustment method has basically no effect on boiler efficiency and pollutant emissions.