A Comprehensive Thermodynamic Analysis of Gas Turbine Combined Cycles With Pressure Gain Combustion Based on Humphrey Cycle

Abstract

The paper describes a comprehensive thermodynamic analysis of the gas turbine combined cycle (CC) equipped with pressure gain combustion (PGC) based on the Humphrey cycle. PGC is represented by a steady-state zero-dimensional constant volume combustion (CVC) model with practical loss models for a realistic interpretation. Simulations were performed in WTEMP (web-based thermo-economic modular program) software, a modular cycle analysis tool developed at the University of Genova. PGC gas turbine combined cycle is studied using methane as fuel with three different configurations of heat recovery steam generator, namely, one pressure level without reheat, two pressure levels with reheat and three pressure levels with reheat, in order to study a wide range of CC applications. An on-design performance map of the PGC gas turbine is presented, and a sensitivity analysis is performed to understand the impact of cycle loss parameters and turbine cooling technology. Results were analyzed at the optimistic and realistic PGC loss scenarios. For the PGC open cycle, with optimistic combustor losses, efficiency was higher than Joule at all operating conditions. However, with realistic combustor losses, a higher turbine inlet temperature (TIT) was found to alleviate some of the losses in the combustor, and at a pressure ratio of 25, a 1700 °C TIT cycle showed a benefit of 1.7 p.p., while 1300 °C TIT showed no advantage. Moreover, with the reduction in first turbine stage efficiency from pulsating outflow, only the high TIT cycle showed benefit at pressure ratios less than 15. Looking into combined cycles with realistic combustor losses, PGC was found to be advantageous in terms of specific work but not efficiency at actual operating conditions. However, with a further reduction of combustor-related losses, the PGC CC could outperform the Joule equivalent in terms of efficiency. The sensitivity analysis with losses showed that the mitigation of constant pressure combustion loss is more important than the inlet pressure loss for PGC in CC application. Finally, it was shown that the improvements in turbine cooling technology could increase the efficiency of a high TIT PGC combined cycle by 0.25 p.p. and specific work output by 4.1 p.p.