Simulation of Optimizing the Partial Load Performance of a Gas Turbine Combined Cycle Using Exhaust Heat Recuperation and Inlet Bleed Heating

Abstract

Abstract Extending the operating range and improving the partial load efficiency of the gas turbine combined cycle (GTCC) is becoming increasingly important. This paper proposes a novel method to achieve the two goals simultaneously. To fulfill the research objective, the combination of exhaust heat recuperation and inlet bleed heating (IBH) was adopted and evaluated. A cycle simulation was conducted to confirm whether the research goal could be achieved. A recuperator was installed between the compressor and combustor of the gas turbine, and the degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency compared to the conventional GTCC plant. In contrast to the conventional GTCC plant, the recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. The simulation showed that both IBH and recuperation are effective in extending the operating range. The predicted reduction in the turndown ratio was approximately 10%p. The partial load efficiency improvement by the recuperation was sensible. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.