Supercritical Carbon Dioxide Bottoming Cycles for Off-Shore Applications - An Optimization Study

Abstract

Closed Joule-Brayton thermodynamic cycles working with supercritical CO2 (sCO2) are presently receiving great attention, for multiple attractive aspects: high efficiency, compact size, flexibility of operation, integration with energy storage systems. A promising area of application of sCO2 systems is bottoming gas turbines in combined cycles in off-shore platforms, where the lack of space complicates the application of steam cycles. In such a context, the combination of gas turbines with sCO2 cycles could open the way for novel efficient, compact, and flexible combined cycles, attractive for all the sectors which might take advantage from footprint savings, enhanced flexibility, and fast dynamics of sCO2 systems.

In this work we investigate the thermodynamic potential of combining sCO2 cycles with a gas turbine for off-shore applications. We consider a mid-size (25 MW) gas turbine available on the market, and perform a series of thermodynamic optimizations of the sCO2 bottoming cycle to maximize the exploitation of the heat discharged by the gas turbine. We consider four alternative configurations, including realistic technical constraints evaluated by leveraging on the most recent technical outcomes from ongoing sCO2 research projects. A comparison is also proposed with a state-of-the-art steam Rankine cycle, in terms of system efficiency and footprint of the main components. The study clarifies the advantages and challenges of applying sCO2 in combination with gas turbines, and the comparison with steam technology confirms the relevance of sCO2 systems for off-shore applications and calls for further technical studies in the field.