Off-design performance of supercritical carbon dioxide cycle combined with organic Rankine cycle for maritime nuclear propulsion system under different control strategies

A combined power conversion system, which consists of a supercritical carbon dioxide recompression cycle with an organic Rankine cycle as the bottoming cycle, has broad potential for maritime propulsion applications. However, the performance of the combined system under the off-design condition and operating states of compressors with a wide range of load variations and different control strategies have not been comprehensively investigated. Therefore, a simulation model for the combined system under off-design conditions is established in the present study to investigate the compressors operating states and the performance of the system under different control strategies. The result shows that a peak efficiency of 42.82% and total production unit cost of 11.6 $/GJ are achieved at the design point for the combined system, where the pressure ratio, flow split ratio, and evaporating pressure are 2.7, 0.27, and 770 kPa, respectively. When the relative load varies from 100% to 10%, the efficiency of the inventory-controlled system decreases by 19.07%, and the efficiency of the bypass-controlled system decreases by 34.3%. For the 10% load scenario, the compressors tend to surge under the inventory-controlled strategy and approach the choke area under the bypass-controlled strategy. The adoption of the inventory-bypass hybrid control strategy keeps the compressors of the low-load system away from the surge and choke areas, and the efficiency is between those of the systems controlled by the two separate strategies.