4.7 Article

Optimized operation of recompression sCO2 Brayton cycle based on adjustable recompression fraction under variable conditions

Journal

ENERGY
Volume 227, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.energy.2021.120334

Keywords

Supercritical carbon dioxide; Recompression Brayton cycle; Recompression fraction; Thermal efficiency optimization; Heat exchangers

Funding

  1. CONICYT [22170880]
  2. Scientific Initiation and Innovation Program of the Universidad Tecnica Federico Santa Maria
  3. Solar Energy Research Center-SERC-Chile [ANID/Fondap/15110019]

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The study developed a power cycle model to assess the impact of fluctuations on a recompression sCO(2) Brayton cycle during off-design operation, finding that adjusting the recompression fraction according to heat addition and ambient temperature variations leads to superior performance, with up to 70% greater cycle efficiency when the heat addition ratio is reduced to 30%.
The use of supercritical carbon dioxide (sCO(2)) cycle has been proposed as a promising alternative to replace conventional steam Rankine cycle. This study entails the development of a power cycle model to assess the impact of fluctuations on the heat source and environmental conditions on a recompression sCO(2) Brayton cycle during off-design operation. Two operational strategies are tested during off-design operation, including fixed recompression fraction and adjusted recompression fraction. It is found that a superior performance is obtained when the recompression fraction is adjusted according to heat addition and ambient temperature variations. The variations of the heat addition have a greater impact than ambient temperature on the cycle's performance, showing up to 70% greater cycle efficiency when the heat addition ratio is reduced to 30%. In some conditions, the recompression cycle operates similarly to a regenerative cycle, hence no recompression fraction is required when the heat addition ratio is lower than 55%. The influence of the ambient temperature is more relevant when a dry cooler is used, and in this case, it is important to include a detailed cooler's model in order to account for the variability of the thermophysical properties of the carbon dioxide close to its critical point. (C) 2021 Elsevier Ltd. All rights reserved.

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