Introduction  In order to analyze the influence of excess air coefficient on the combustion stability of the furnace under the ultra-low load operation conditions of the thermal power unit, the unit is better guided to participate in peak shaving.

  Method  In this paper, through in-depth analysis of boiler operation and heat transfer mechanism in the furnace, the combustion temperature of the furnace was characterized by the outlet temperature of the furnace, and as the index of combustion stability, the furnace exit smoke temperature model was built in MATLAB/SIMULINK. Taking a 300 MW thermal power generating unit as an example, the paper first selected several typical operating conditions. Then the similarity solving method was used to calculate the furnace exit smoke temperature and compare with the design data given by the boiler manufacturer. Finally the test calculation method was basically correct and then substituted into ultra-low load operation parameters which calculated the furnace exit smoke temperature corresponding to different excess air coefficients under deep peaking conditions.

  Result  The simulation results show that the model calculates the furnace temperature and the design data given by the boiler manufacturer. The calculation error is less than ±15°C, and the calculation method is basically correct. It can be applied to the calculation of ultra-low load conditions.

  Conclusion  As the load is reduced, the optimum excess air ratio that maximizes the flue gas temperature at the exit of the furnace is gradually increased. Therefore, under the condition of ultra-low load operation, the excess air coefficient can be appropriately increased within a certain range to increase the flue temperature of the furnace outlet, thereby improving the stability of the combustion of the boiler, and when the excess air ratio is less than 2.0, the value is higher, the temperature is higher.