Abstract
This article deals with the thermodynamic assessment of supercritical carbon dioxide (S-CO2) Brayton power cycles. The main advantage of S-CO2 cycles is the capability of achieving higher efficiencies at significantly lower temperatures in comparison to conventional steam Rankine cycles. In the past decade, variety of configurations and layouts of S-CO2 cycles have been investigated targeting efficiency improvement. In this paper, four different layouts have been studied (with and without reheat): Simple Brayton cycle, Recompression Brayton cycle, Recompression Brayton cycle with partial cooling and the proposed layout called Recompression Brayton cycle with partial cooling and improved heat recovery (RBC-PC-IHR). Energetic and exergetic performances of all configurations were analyzed. Simple configuration is the least efficient due to poor heat recovery mechanism. RBC-PC-IHR layout achieved the best thermal performance in both reheat and no reheat configurations ( = 59.7% with reheat and = 58.2 without reheat at 850 °C), which was due to better heat recovery in comparison to other layouts. The detailed component-wise exergy analysis shows that the turbines and compressors have minimal contribution towards exergy destruction in comparison to what is lost by heat exchangers and heat source.
Highlights
Efficient conversion of heat to electrical power is an issue of global interest
Compressor inlet temperature and pressure are maintained at 32 ◦ C and 7.5 MPa corresponding to state ‘6’ for Simple Brayton cycle (SBC), state ‘7’ for recompression Brayton cycle (RBC), state ‘9’ for Recompression Brayton Cycle with Partial Cooling (RBC-PC), and state ‘10’ for RBC-PC-IHR
There are a number of parameters that may significantly affect the performance of S-CO2 Brayton cycle, like the turbine inlet pressure and temperature, heat exchanger effectiveness, minimum allowable pinch temperature in the heat exchanger, flow split ratio for the configurations involving recompression, compressor inlet temperature and pressure [1,2,3,34,35]
Summary
Efficient conversion of heat to electrical power is an issue of global interest. This has led researchers to continuously strive for a better power generation cycle with improved thermodynamic performance. Al-Sulaiman and Atif [16] investigated the thermodynamic performance of various S-CO2 Brayton cycles integrated with solar power tower Their findings demonstrated that the recompression cycle has the highest thermal efficiency and the highest net power output, whereas, regenerative cycle stands second. Later, they performed detailed energy and exergy analysis of recompression cycles driven by solar thermal systems. Siddiqui et al [24] performed energy and exergy analysis of S-CO2 recompression Brayton cycle in cascade arrangement with bottoming Rankine cycle exploiting cold energy of LNG to sink the heat from the bottom cycle They considered four different working fluids for the bottoming cycle and proposed CO2 due to better thermodynamic performance and compactness of the system. The effect of high temperature of the cycle, cycle pressure ratio, cycle minimum pressure and cycle configuration on energy and exergy efficiency is discussed
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