Combined cycle power plant with chemically recuperated high-temperature gas turbine: Thermal efficiency, energy and material balance via comparative analysis

Abstract

The global transition to low-carbon energy systems drives the need for continuous efficiency improvements in fossil-fuel-based power generation. Combined cycle power plants (CCPPs) represent the state-of-the-art in commercial thermal power generation, yet further efficiency gains through conventional methods face diminishing returns. This paper presents a comprehensive thermodynamic analysis of a combined cycle power plant integrated with a chemically recuperated gas turbine (CCPP-CRGT) based on a modern high-temperature gas turbine with turbine inlet temperature of 1600 °C. Unlike conventional recuperation that transfers sensible heat, thermochemical recuperation utilizes exhaust heat to drive endothermic steam methane reforming, converting exhaust heat into chemical energy stored in hydrogen-rich syngas. The performance of the CCPP-CRGT is benchmarked against a conventional CCPP across a range of steam-to-methane molar ratios (S/C = 1.0–3.0). The results demonstrate that thermochemical recuperation shifts the power generation from the steam turbine cycle towards the more efficient gas turbine cycle, increasing the gas turbine net work from 465 MW in the conventional case to 598 MW at S/C = 3.0, while reducing condenser heat rejection from 327 MW to only 117 MW. The overall combined cycle efficiency improves from 62.49% to 65.42%, representing a gain of 2.93 percentage points. The temperature-heat transfer profiles reveal that the reformer consumes up to 28% of the available exhaust heat, displacing the superheater section of the heat recovery steam generator. The material balance shows a progressive reduction in air mass flow rate from 2680 t/h to 2463 t/h as S/C increases, while the syngas flow grows correspondingly to 323.3 t/h. These findings confirm that the CCPP-CRGT configuration offers a viable pathway to surpass the efficiency ceiling of conventional CCPPs by leveraging the high-temperature end of the exhaust heat cascade for thermochemical recuperation rather than for steam generation, thereby reducing the heat rejected in the bottoming cycle by redirecting a portion of the exhaust heat.