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

Abstract

This paper proposes a novel method to extend the operating range and improve the partial load efficiency of the gas turbine combined cycle (GTCC). The combination of exhaust heat recuperation and inlet bleed heating (IBH) was evaluated through a cycle simulation. The degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency. 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 (TIT) 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. Both IBH and recuperation were effective in extending the operating range. The turndown ratio was predicted to decrease by approximately 10%p. 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.