Thermal economy analysis of flue gas waste heat utilization system of 1000MW secondary reheat unit

Deep utilization of flue gas waste heat is an important means to ameliorate the power generation productivity of coal-fired units. Aiming at the waste heat cascade utilization system which is composed of “air preheater bypass + two-stage low-temperature coal economizer + thermal primary air temperature regulating device” proposed in a certain project, using the energy balance method and the equivalent enthalpy drop method, the mathematical model of the impact of waste heat utilization devices at all levels on the unit economy is established from the boiler efficiency and steam engine heat rate. Combined with the rated operation data of the unit, the thermal economy of the system is analyzed. The results show that the bypass of the air preheater and the temperature regulating device of the hot primary air can effectively improve the utilization efficiency of the waste heat of the flue gas at the tail of the boiler, the coal consumption of power supply can be reduced by 3.47 g/kWh under rated working conditions.