Experimental and simulation study on optimal operation of flue gas waste heat utilization system of coal-fired unit

China’s energy sector is characterized by rich in coal, poor in oil and little in gas, which determines that China’s coal-based energy pattern is difficult to change in the short term, and the heat loss in flue gas from coal-fired power plants accounts for more than half of the boiler heat loss. Making full use of the waste heat resources of flue gas can not only reduce environmental pollution, but also improve the energy utilization rate and reduce the coal consumption in power generation. According to the national standards, a 1 000 MW ultra-supercritical double reheat coal-fired unit was tested under multiple operating conditions to comprehensively analyze the impact of the operating parameters of the flue gas waste heat utilization system with air preheater bypass flue on the unit economic performance. Based on the test operation data, the Ebsilon system simulation model was established. The accuracy of the model was verified by comparing the simulation results with the test data. The influence of different inlet flow rates of high and low bypass economizers and the proportion of flue gas in air preheater and bypass flue on the thermal performance of the unit were explored through simulation models, and the optimal inlet flow rates of high and low bypass economizers under different loads were also obtained. The optimization results show that: ① Under different loads, the optimal criteria for economic performance of the unit include that the temperature difference between the main water supply pipeline and the bypass water supply pipeline is close to 0 ℃, and the outlet temperature difference between the low bypass economizer and the No.6 LP heater is within the range of 0−5 ℃. At this time, the inlet flow rate of the high bypass economizer and the low bypass economizer are the optimal flow rate; ② The optimal inflow flow of high and low bypass economizers under different conditions will also increase with the increase of unit load; ③ During operation, it is necessary to ensure the outlet temperature of the coal pulverizer is above 70 ℃. In addition, the bypass flue gas flow can be increased to improve the unit economic performance. Meanwhile, the influence law and parameter optimization setting obtained from the model simulation can provide a reference for the deep energy saving of ultra-supercritical double reheat coal-fired units. © 2023 China Coal Society. All rights reserved.