Publication
In order to improve the performance of the combined cycle gas turbine (CCGT) under off-design conditions, an intermediate recuperated combined cycle gas turbine (IRCCGT) system was proposed, which was designed to suppress turbine inlet temperature (TIT) from decreasing as the load drops. In this system, a heat exchanger is installed between the third and fourth turbine stages, wherein a portion of the exhaust from the third turbine stage was used to heat the compressed air. In addition, the system-based operation strategy (maximizing the load range that employs constant TIT operation mode) was also analyzed. The results indicate that the TIT can be maintained at the design value until the gas turbine power load is reduced to 49% of the design value. When the inlet guide vane (IGV) angle reached the minimum value, the IRCCGT system increased gas turbine efficiency and combined cycle electrical efficiency by 4.7 and 3.1 percentage points. At the same gas turbine (GT) load, the maximum gains of GT efficiency and combined cycle efficiency were 2.15 and 1.04 percentage points, respectively. The pressure drops in the recuperator had a great impact on system performance, while the minimum recuperative mass flow rate had little effect. Overall, the proposed IRCCGT system can reduce the slope of the efficiency and load curve and improve the operating performance of the system under off-design conditions.