Off-design modeling of gas turbines integrated with reverse Brayton refrigeration cycle for inlet air cooling

Abstract

This study develops and validates an off-design simulation framework for a gas turbine integrated with a reverse Brayton refrigeration cycle (RBC) for inlet air cooling. Compressed air is extracted from intermediate compressor stages and cooled before expansion to pre-cool the gas turbine inlet air stream, with the model accounting for off-design compressor performance, ambient conditions, humidity, and latent heat effects. Validation against published data shows close agreement in compressor relative power output and relative heat output across varying extraction ratios. Results demonstrate that integrating the RBC with the gas turbine power cycle significantly enhances performance characteristics under warm and humid conditions. Cooling capacity consistently increases with ambient temperature, rising by over 50% at high humidity levels compared with low-temperature conditions. Efficiency improvements also grow with temperature, with the divergence between cooled and uncooled cycles reaching up to 30% under hot and humid conditions. Optimal extraction pressure ratios (π_ext ≈ 3) and tuned extraction ratios (ER ≈ 0.25 to 0.5) provide sufficient cooling while balancing compressor work, resulting in reduced specific fuel consumption. Net power output similarly benefits from RBC integration, with relative gains increasing with ambient temperature and humidity, reaching improvements exceeding 40% under extreme climate conditions. These trends highlight that the combined effects of high temperature and humidity amplify cooling demands, making inlet air cooling increasingly advantageous. Overall, the study confirms that careful adjustment of extraction parameters enables substantial gains in cooling capacity, cycle efficiency, and net power output, providing a validated framework for optimizing RBC-gas turbine integration in challenging ambient environments.