Dynamic characteristic analysis of SCO2 Brayton cycle under different turbine back pressure modes

Abstract

Closed supercritical carbon dioxide Brayton cycle has the advantages of high efficiency and high compactness. The response speed of SCO2 cycle is much faster than that of steam Rankine cycle since the compact system structure and small amounts of heat storage, but the complex mutual effect of multi facilities and closed loop iteration of operation parameters makes the system control difficult. In order to examine the iteration of pressure and temperature in the SCO2 closed cycle, the dynamic characters of SCO2 cycle and the related facilities were investigated with different turbine back pressure modes, such as normal operation mode (unconfined back pressure), fixed pressure mode and open loop mode. It has been shown that for different disturbances in the dynamic characteristics of the heat exchanger, the response time of the return heaters is about 4–5 times longer than the response time of the precoolers and heaters. For the dynamic characterization of the SCO2 cycle in different turbine backpressure modes, the effect of pressure iteration on the SCO2 system characteristics is less important than that of temperature iteration. In addition, the fixed turbine backpressure operation mode has the advantages of fast response and easy control for the SCO2 cycle.