Analysis of Recompression-Regeneration sCO ₂ Combined Cycle Utilizing Marine Gas Turbine Exhaust Heat: Effect of Operating Parameters

Gas turbines are fast being explored to replace the existing steam or diesel-based power packs to propel marine transportation. Marine gas turbines have already come to power high-speed marine vessels transporting perishable goods as well as high-speed naval fleets. This article investigates the potential of gas turbine to be made hybrid with supercritical recompression-regeneration carbon dioxide (CO₂) cycle drawing thermal energy from the exhaust of marine gas turbines. The recompression unit acts as the topping cycle and the regeneration unit acts as the bottoming cycle of the proposed combined supercritical CO₂ (sCO₂) cycle. The cycle has a maximum temperature of 530°C and supercritical pressure of 20 MPa. The proposed sCO₂ powerplant is compact because of the smaller size of the turbomachinery, owing to the low specific volume of working fluid in the supercritical range. The proposed combined cycle is analyzed for different operating conditions including maximum temperature, minimum temperature, and cycle pressure ratio. The thermal efficiency of the proposed sCO₂ cycle is 30.77% and efficiency of the hybrid cycle (including marine GT) is 58.17%, i.e., enhancement in thermal efficiency of the marine vessel power pack by 18.6%. Further the power output of the gas turbine-sCO₂ hybrid cycle is enhanced by nearly 23.5% to 45.7 megawatts (MW). The second law of thermodynamic efficiency of the proposed combined cycle is close to 52.5%. The proposed hybrid gas turbine-sCO₂ cycle has immense potential to replace the aging propulsion systems of existing marine vessels as the proposed power cycle is greener and more compact.