A comparative study of solar heliostat assisted supercritical CO2 recompression Brayton cycles: Dynamic modelling and control strategies

• Published in: The Journal of supercritical fluids Vol. 120; pp. 113 - 124
• Main Authors: Milani, Dia, Luu, Minh Tri, McNaughton, Robbie, Abbas, Ali
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-02-2017
• Subjects: Brayton cycle; Central receiver; Intercooling; Recompression; Reheat; Solar heliostat; Supercritical CO2; Intercooling; Solar heliostat; Central receiver; Brayton cycle; Recompression; Supercritical CO2; Reheat
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2016.09.009

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•Flexible operation for solar-assisted sCO2 recompression Brayton cycle was analyzed.•Two operational modes for dealing with solar transient periods were identified.•The role of solar multiple factor on the design operation was examined.•Constant power production from various operation regimes was targeted.•A significant fuel saving ratio for indirect configuration was found.
Electrical power generation by closed loop Brayton cycle using supercritical CO2 (sCO2) as a working fluid has gained significant interest in recent years. Integrating sCO2 cycle with renewable energy technology (i.e. solar heliostat field) at high temperature ranges has shown promising results. This study highlights the thermodynamic benefits of recompression sCO2 Brayton cycle and presents a modelling and control strategy to optimize operating conditions for a constant power output utilising solar- and fossil-based heat sources. This optimization maximizes solar field contribution and minimizes the role of auxiliary fossil-fuelled back-up (AFB) heating system. The performances of two common solar heat input (direct and indirect) configurations are compared. It is found that for a specific day, an indirect cycle consumes 19.5% less fossil fuel compared to an equivalent direct cycle. This is mainly attributed to the usage of thermal energy storage (TES) in the indirect cycle. However, the high capital cost of TES and operability/controllability issues may decrease the merits of the indirect cycle. Although the reliance on fossil fuel contribution in direct cycle is higher by a magnitude of 4.2% or less, this may be economically admissible compared to the substantial reduction in capital cost as in the case of indirect cycle.