The Off-design Performance Optimization And Economic Analysis Of The Gas Turbine Combined Cycle System Based On A New Type Of Variable Back Pressure Modification System

As China's environmental protection requirements continue to increase,the proportion of gas power generation installed capacity in China increased year by year.One gas-steam combined cycle generating set due to its high efficiency,start and stop fast become the best choice for peak power plant.Increasing the efficiency of combined cycle in variable conditions is of great significance to the better participation of gas-fired power plants in peak-shaving.At the same time,improving the economy of gas power generation is also the top priority for accelerating gas power generation.In order to optimize the performance of gas turbine combined cycle,this paper retrofitted the conventional gas turbine combined cycle system,and proposed a variable back pressure reforming system.The retrofit system arranges the draft fan in the flue of the tail race of the conventional combined cycle unit and reduces the gas turbine back pressure under some conditions by the induced draft fan.Taking S109FA gas turbine combined cycle unit as the research object.The conventional combined cycle unit adopting IGVT3-F and other IGVT3-T4-F operation strategies as the reference unit is selected.Through comparing the three units' transformation performance by modeling the reference unit and the retrofit unit,the calculation results show that the overall downward trend of the combined cycle efficiency of the reformed unit is more gentle than that of the reference unit,and the efficiency is increased by 0.6%at the maximum between 84%and 50%of the load of the T4 operating unit.Compared with other T3 units,the efficiency of combined cycle was reduced by 84%to 35%,and the efficiency increased by 0-2.5%.The performance of combined cycle was significantly improved.Based on the analysis of the variable working conditions of variable back pressure retrofit unit and conventional combined cycle unit,the economy of each unit is compared with the flattened power generation cost model LCOE.The results show that LCOE of full back pressure retrofits unit of full life cycle is about 0.007-0.012 yuan/kWh lower than that of conventional combined cycle unit.Among them,natural gas prices,annual operating hours and load rates have a significant impact on generating costs.