Exergy analysis of the Allam cycle: Assessing the impact of regenerator performance on the cycle efficiency

Carbon capture technologies represent a crucial step towards the decarbonization of power production. The most common alternatives focus on separating the CO2 from the power plant's exhaust, which markedly increases the power plant's footprint and complexity and reduces the net power output. Innovative power cycle development is a promising alternative, allowing for a much easier CO2 separation. The Allam cycle represents one of the most advanced and close to deployment of these cycles. It is a semi-closed loop, direct-fired with an oxyfuel combustion cycle, which allows for the CO2 direct separation from the cycle fluid in the supercritical state – a considerable advantage compared to post-combustion CO2 removal technologies. The Allam cycle is considered a highly recuperated and trans-critical Brayton cycle. For this reason, the purpose of this paper is to simulate the Allam cycle by highlighting its performance's dependence on the regenerator at different maximum cycle temperatures. The proposed Allam cycle layout includes a three pumping/compression stages phase and a bypass flow reheating and it is designed to produce up to 300 MW. Results demonstrate that a maximum recuperator UA from 30,000 to 43000 kW/K is required, and reducing the maximum cycle temperature from the highest to the lowest analyzed values leads to a decrease in the net electric efficiency of around 5 percentage points. An exergy analysis is conducted to examine the performance of each component and its impact on the overall system in terms of losses, helping to pinpoint the cycle's sources of thermodynamic inefficiencies at the component level.