Off-Design Performance of sCO2 Waste Heat Recovery Cycles- implications of System Design

Abstract Supercritical Carbon Dioxide (sCO2) Brayton cycles offer a promising solution for small-scale (≤ 10 MW) waste heat recovery (WHR), combining high efficiency and compact design suitable for retrofitting into existing industrial or gas turbine plants. While much research has focused on these systems’ design and off-design performance, their interdependence has not been adequately explored. This study investigates the impact of system design on off-design performance of a WHR plant using a recuperated Brayton cycle. Design space exploration identifies optimal trade-offs between thermodynamic and economic performance. The impact of varying design characteristics along this trade-off on off-design performance is studied, particularly under reduced waste heat parameters and ambient temperatures. Results indicate that thermodynamically optimal and economically optimal designs exhibit distinct offdesign behaviors. While the performance difference at the design point dictates the efficiency levels near nominal conditions, their impact is neutralized at low waste heat flow parameter values. The paper also quantifies the impact of inventory control as a strategy, showing that some designs perform optimally at constant inventory while others benefit significantly from inventory management. These findings enhance the understanding of sCO2 cycle responses and offer insights into improving WHR systems for diverse applications.