<p>Supercritical CO2 (sCO2) power cycles have gained increasing interest over the past several years due to their compact turbomachinery at equivalent power (as compared to steam cycles) while also delivering more efficiency at turbine inlet temperatures of 500-700℃. However, before this technology can be implemented for large-scale grid support, uncertainty around the design and control of this cycle must be reduced. One aspect of this is being able to model and predict the power cycle operation with a high degree of accuracy and confidence. Several cycle modelling efforts have been published demonstrating the achievable power output and efficiencies for various power cycle configurations, turbomachines, and heat exchangers. However, many cycle modelling efforts use assumptions around certain components to simplify the modelling effort and reduce the computational time. Furthermore, many cycle modelling efforts only consider the design-point operation of the cycle. To better understand the day-to-day performance of a sCO2 power cycle, off-design performance calculations must be included for all power block components.</p><p>In order to further understand the sCO2 power cycle, this study has expanded the modelled scope to include the air-side performance for the dry cooler and used discretized heat transfer calculations for both streams through the cooler to better predict off-design performance. This study considered a recompression Brayton cycle in a concentrating solar power (CSP) application. The cycle model utilized fixed sCO2 turbomachinery maps for the main compressor, recompressor, and expander operating to supply approximately 10 MW net at the design point. Fixed vendor-supplied fan curves were used to calculate the air-side performance of the dry cooler. The primary heater was modelled considering both the sCO2 and heat transfer fluid (HTF) streams. Off-design performance was predicted for an ambient temperature range of 0-55℃, a HTF temperature range of 705-735℃, and a HTF mass flow range of 50-105% of the design point value. To understand the importance of modelling the air-side performance, the cycle off-design performance was also calculated using a constant approach temperature assumption for the dry cooler. Results show that using a constant approach temperature assumption can significantly alter the predicted power output and cycle efficiency, adding inaccuracies to the cycle performance predictions.</p>

Impact of Dry Cooler Air-Side Performance on a Sco2 Power Cycle for a Csp Application

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

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