In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). One component of solving this problem is reducing the cost of the power block while simultaneously increasing the efficiency of the thermodynamic cycle. One disruptive technology that has the promise to accomplish this is supercritical CO2 (sCO2) based power cycles. These cycles are conceptually similar to steam cycles; however, they have substantially smaller turbomachinery at equivalent power while also delivering more efficiency at turbine inlet temperatures of 500-700°C.
Previous work has thoroughly investigated the sCO2 turbomachinery design and its impact on power cycle performance and LCOE. However, the precooler (upstream of the first stage compressor) has received significantly less attention. The pr-cooler design is not trivial because minimizing the compressor inlet temperature and temperature variation are critical to cycle performance. Compressor performance and cycle efficiency vary significantly with low-side temperature. Also, operating with a compressor inlet temperature away from the design point (above or below) significantly degrades cycle efficiency. Because CSP plants are generally planned for installation in remote, arid areas where water is scarce, dry cooling is required. The current state-of-the-art dry cooling technology consist of large bays of finned tubes, cooled by fan-driven air in cross flow. The fan-driven air allows for low power consumption and low operating cost. However, the cross-flow configuration results in low thermal effectiveness and maldistribution of air throughout the tube banks. This requires the interface area between streams to be very large, meaning very large installations incurring large capital cost. It has been found that improvements to the dry cooler technology can further reduce the power block contribution to LCOE.
This study investigated the impact of the precooler on the LCOE for a CSP facility utilizing a sCO2 recompression Brayton cycle. This paper presents the high-level sensitivity studies used to determine the best path forward for reducing the precooler’s contribution to LCOE. The sensitivity study included investigation of the cooler performance (approach temperature), CO2-side pressure drop, air-side pressure drop, air-supply power consumption, and cooler system capital cost. Results of the study show that utilizing a dry cooler with a high effectiveness (achieved at higher heat exchanger capital cost) and low air-side power consumption levels produced the lowest LCOE contribution. Applying more advanced heat exchanger technologies will be required to reach the higher heat transfer effectiveness values, while maintaining reasonable capital cost values.
