# A Novel Parallel-Preheating Supercritical CO2 Brayton Cycle for Waste Heat Recovery from Offshore Gas Turbines: Energy, Exergy, and Economic Analysis Under Variable Loads

## TL;DR

A new supercritical CO2 power cycle is proposed for offshore gas turbines to recover waste heat, showing improved efficiency and cost savings.

## Contribution

The novel parallel-preheating Brayton cycle (PBC) is introduced, offering enhanced performance for waste heat recovery on offshore platforms.

## Key findings

- The PBC achieves a 27.9% higher power output and 41.4% better thermal efficiency than the simple cycle under full load.
- The PBC reduces electricity generation cost by 21.23% compared to the simple cycle.
- The PBC maintains high efficiency even at 30% load, with thermoelectric and exergy efficiencies of 30.54% and 35.43%.

## Abstract

Supercritical carbon dioxide (SC-CO2) power cycles offer a promising solution for offshore platforms’ gas turbine waste heat recovery due to their compact design and high thermal efficiency. This study proposes a novel parallel-preheating recuperated Brayton cycle (PBC) using SC-CO2 for waste heat recovery on offshore gas turbines. An integrated energy, exergy, and economic (3E) model was developed and showed good predictive accuracy (deviations < 3%). The comparative analysis indicates that the PBC significantly outperforms the simple recuperated Brayton cycle (SBC). Under 100% load conditions, the PBC achieves a net power output of 4.55 MW, while the SBC reaches 3.28 MW, representing a power output increase of approximately 27.9%. In terms of thermal efficiency, the PBC reaches 36.7%, compared to 21.5% for the SBC, marking an improvement of about 41.4%. Additionally, the electricity generation cost of the PBC is 0.391 CNY/kWh, whereas that of the SBC is 0.43 CNY/kWh, corresponding to a cost reduction of approximately 21.23%. Even at 30% gas turbine load, the PBC maintains high thermoelectric and exergy efficiencies of 30.54% and 35.43%, respectively, despite a 50.8% reduction in net power from full load. The results demonstrate that the integrated preheater effectively recovers residual flue gas heat, enhancing overall performance. To meet the spatial constraints of offshore platforms, we maintained a pinch-point temperature difference of approximately 20 K in both the preheater and heater by adjusting the flow split ratio. This approach ensures a compact system layout while balancing cycle thermal efficiency with economic viability. This study offers valuable insights into the PBC’s variable-load performance and provides theoretical guidance for its practical optimization in engineering applications.