Inverted Brayton Cycle for Improving the Performance of Carbon-free Gas Turbine Combined Cycle

Hydrogen and ammonia are attracting increasing attention as carbon-free fuels to replace fossil fuels in power generation. However, when used in gas turbines under constrained operation of an existing core engine, fuel conversion can alter exhaust-gas characteristics and reduce gas-turbine combined-cycle (GTCC) performance. This paper proposes a 20 MW-class GTCC integrated with an Inverted Brayton Cycle (IBC) to partially compensate for the performance loss caused by carbon-free fuel conversion and enhance total power output. The IBC recovers additional power from the final low-temperature exhaust gas downstream of the heat-recovery steam generator through sub-atmospheric expansion, cooling, H 2 O separation, and recompression. This makes IBC integration particularly advantageous for H 2 - and NH 3 -fueled GTCCs because their H 2 O-rich exhaust gases increase the effective heat capacity and provide greater power-recovery potential than conventional NG exhaust. Compared with a conventional natural-gas GTCC, the H 2 - and NH 3 -fueled GTCCs without IBC showed power reductions of 456 kW (2.0%) and 1,241 kW (5.5%), respectively. After IBC integration, they recovered 151 kW and 239 kW, reducing the power deficits relative to the NG-GTCC case to 1.4% and 4.4%, respectively. Compared with the corresponding GTCC cases without IBC, the efficiencies improved by 0.34 and 0.55 percentage points, respectively.