Research on Multi-Parameter Collaborative Operation Optimization of Bypass Flue Gas Waste Heat Recovery System of 1000MW Coal-Fired Unit

Abstract Flue gas waste heat recovery is an important means to improve the efficiency of coal-fired units and reduce carbon emissions per unit of power generation, and the flue gas waste heat recovery system using the arrangement of front heater and air preheater bypass flue heat exchanger has the advantage of large energy-saving potential, but the system structure is complex, and the collaborative operation and optimisation of multi-parameters is difficult. Taking a 1000MW coal-fired generating unit as example, a variable operating condition calculation model of bypass flue gas waste heat recovery system is established to analyse the actual operation effect of the system and the influence law of regulating operation parameters on the energy-saving benefit of the unit and the operation safety of the system (mainly the risk of acid corrosion on low-temperature heating surfaces); increasing the proportion of flue gas flow in the bypass of the air preheater, the standard coal saving is firstly increased and then reduced, and the operation safety of the system is reduced; adjusting the water flow rate of bypass flue heat exchanger has an influence on the economy of the unit. Adjusting the bypass flue heat exchanger water flow rate has a more sensitive effect on the unit economy, and when it is larger than a certain threshold, the standard coal consumption rate of power generation increases, but the effect on the heat recovery system safety is smaller; adjusting the circulating water flow rate of the front preheating system and the circulating water splitting coefficient is an effective measure to improve the system operation safety, but it needs to be combined with other control measures to reduce the effect on the system economy. Further, the NSGA-II algorithm was used to perform a multi-parameter collaborative optimisation of the system, after which the coal consumption rate was reduced by 0.63 g (kWh)−1 compared to the pre-optimisation rate while ensuring safe operation under the turbine heat acceptance (THA) condition.