| Over the past few years,the share of renewable energies including wind and photovoltaic power has improved a lot in the power system.To cope with the severe challenge of renewables accommodation,gas turbine generator sets tend to act as peak load-regulation units which degrade the thermodynamic performance and operation economy for the long-time part load conditions.Besides,alternative part-load control strategies can be adopted to regulate the gas turbine combined cycle(GTCC)output,which may accordingly present different off-design characteristics.Hence,it is of both theoretical and practical significance to investigate the overall performance of GTCC and the feasibility of performance improvement under part-load operation.Much focus in this paper has been placed on the performance study on PG 9351 FA based GTCC.To comprehensively investigate the part-load characteristics under alternative load-control strategies including constant turbine inlet temperature(TIT),constant turbine exhaust temperature(TET)and fuel flow control,both mathematical and physical modelings are respectively established in detail.Besides,physical model under constant TIT control strategy is validated with operation data of the units.For mathematical simulation,the compressor,combustion chamber and gas turbine are respectively modeled by one-dimensional stage-stacking method based on average blade diameter,heat balance equation and Flügel equation with cooled turbine stage model.Heat recovery steam generator and steam turbine are modeled respectively by analytical method of pinch-point temperature difference and Flügel equation.For physical simulation,GT-PRO and THERMOFLEX are respectively employed to set up the design and off-design models of GTCC system,based on which the retrofitted system with inlet air heating(IAH)is proposed and further the part-load performance improvement is discussed.The analysis indicates that with inlet guide vane(IGV)opening degree gradually decreasing from fully-open 88° to the minimum 49°,the gas turbine load rate region under constant TIT and constant TET strategies is respectively 100%～64% and 100%～60%;IGV involved strategies help to raise TET,strengthen the waste heat utilization of flue gas and improve the steam turbine output.Gas turbine efficiency rank from high to low under the three strategies is fuel flow control,constant TET and constant TIT strategy.GTCC efficiency rank from high to low is constant TIT,constant TET and fuel flow control strategy;the operating charts of IAH-GTCC system under constant TIT and constant TET strategies almost overlap at different inlet air temperatures,whose performance is superior to that under fuel flow control strategy;at a certain gas turbine load rate under IGV regulation,there exists the optimum GTCC efficiency with the compressor inlet air temperature rising;as compressor inlet air temperature rises at a certain GTCC output,gas turbine output decreases with the increase of gas turbine load rate and GTCC efficiency improves;IAH helps to improve the GTCC part-load efficiency and the effect will be more obvious at a lower ambient temperature;there exists the optimum inlet air heating temperature to meet the highest GTCC efficiency at a certain output and it falls with the ambient temperature rising. |
