Analysis on the performance of low-load feed water heating system with jet heat pump under variable working conditions

To improve the denitration effect and the thermodynamic performance of generator unit under low loads, a new feed water heating system coupled with steam ejector is required. A 660 MW coal-burning supercritical unit is taken as the research object. A boiler/steam turbine coupled model is established based on the simulation platform of GSE. On the basis of this model, the steam ejector and the new No.0 high-pressure heater are embedded in by a self-programming model. The platen super-heater outlet steam is the primary steam and the steam from No.1 steam extraction is the induced steam, then the mixture steam flows into the No.0 high-pressure heater to heat the water. The effects of entrainment ratio on the denitration efficiency, the thermal efficiency and the performance under variable working conditions are investigated. Results show that when the design load of the steam ejector is 50% load condition, the optimal design entrainment ratio is 0.56 and the temperature of feed water rises by 30℃; the standard coal consumption rate is decreased by 0.52 g·(kW·h)^-1 and the denitration efficiency is increased by 13.29%. Considering the running stability of the ejector and the thermal efficiency of the unit, the optimized system is suggested to operate in the range of 45%-90% load to obtain the best energy-saving and emission reduction effect and thermodynamic performance.