Comprehensive evaluation of part-load exergy performance of a supercritical carbon dioxide recompression cycle controlled by various strategies

Abstract

This study seeks to provide guidance for the efficient operation of a supercritical carbon dioxide recompression cycle (sCO2-RC) by conducting a comprehensive assessment of the exergy performance under various load-following strategies. As the load decreases, we analyze the operational characteristics of the compressor and identify the components with higher irreversible proportions for the single strategy-controlled system. When the load diminishes to 10%, specific components exhibit significant irreversibility, excluding the compressor, as follows: 14.48% for the turbine under inventory control, 12.64% for the bypass mixer under turbine bypass control, and 22.10% for the bypass mixer under intermediate heat exchanger (IHX) bypass control. Owing to the compressor's near-surge operation, the turbine throttle control only minimally reduces the system load to 30%, with the throttle valve incurring the highest loss proportion of 26.33% at that point. To both ensure safe compressor operation and enhance system efficiency, auxiliary strategies such as inventory and turbine bypass are recommended to implement hybrid control. The assisted inventory improves the exergy efficiency of the system under turbine bypass control and IHX bypass control by 4.14% and 7.16% at 10% load, respectively. However, the adoption of auxiliary strategies may introduce additional losses while improving the performance of existing components. Although the assisted turbine bypass widens the adjustable load range of the turbine throttle-controlled system, it decreases the system's exergy efficiency by 3.65% at 30% load due to the introduction of a bypass mixer with higher exergy loss.