(749h) Dynamic Modeling for Improved Operation and Control of a Supercritical CO2 Brayton Power Cycle
Considering Carnot's rule, the sCO2 cycle efficiency is maximized by keeping the ratio between the hot turbine inlet temperature (TIT) and the cold main compressor inlet temperature (MCIT) as high as possible. To maintain the TIT at its maximum design point during cycle turndown and ramp-up operations, this study uses inventory control wherein sCO2 is removed and added, respectively, from the closed cycle. The impacts of inventory tank capacity and initial pressure on maximum sCO2 cycle turndown are investigated. An advanced controller logic is developed that regulates the inventory inlet and outlet valves in a fast and effective manner to achieve the TIT control objectives while satisfying process constraints. Similarly, cooling water flow is used to maintain the MCIT at its minimum design point slightly above the critical temperature of CO2, thereby avoiding transition to the two-phase region. In addition, a controller is designed that aims to maintain an optimal flow split between the main compressor and bypass compressor streams during transient operations. The presentation will include results for various cycle turndown and ramp-up scenarios, as well as analysis of trade-offs between systems efficiency and control system performance.