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In the late 1960s, a handful of inspired researchers predicted the great potential of supercritical CO2 (“sCO2”) cycles for the production of electricity and highlighted the prospects for dramatic reductions in component sizes and efficiency increases. Since then, considerable development programs have been deployed around the world to “tame” this new technology. Despite these efforts, in-depth engineering studies and extensive testing are still necessary today before viable designs can be released for large-scale industrial applications. This raises questions as to the reasons for this delay, this debate being rarely addressed in the current literature. This situation has motivated the present study. Trying to unravel such an intricate topic requires to understand the distinctive properties of supercritical CO2 and the particular requirements of closed, high-pressure power systems. This article aims then to provide a broad overview of sCO2 power cycles, highlighting their main advantages and limitations and reflecting the challenges associated with the industrialization of that technology which actually requires disruptive and innovative designs.

Improving the efficiency and flexibility of fossil-fired power plants remains a current and challenging issue. In that regard, supercritical CO2 Brayton cycles offer promising potential. This paper aims to apply a process synthesis approach to the design of a closed Brayton cycle using supercritical CO2 as a working fluid with a coal furnace as a heat source. The general methodology presented here for designing closed power cycles includes the construction of a superstructure containing all relevant possible cycle layouts, the formulation of the cycle-synthesis problem as a mathematical optimization problem, and its solution using an appropriate algorithm. This study was conducted with the help of a process simulation commercial software (PROSIM) and using the Mixed-Integer Distributed Ant Colony Optimization (MIDACO) as a commercial optimization algorithm. This work highlights the limits of a purely technical optimization approach that would ignore the economical layer. The optimal structure obtained regarding Levelized Cost Of Electricity (LCOE) minimization is a configuration with one reheat of the supercritical CO2 in the boiler, two recuperators, and one recompression loop around the low-temperature recuperator; it is associated with a cycle efficiency of 49.35 % and a 10% reduction in the LCOE in comparison to the optimal case found through energy optimization under typical design heuristics constraints.