Dynamic response and emergency measures under failure conditions of sCO₂ Brayton cycle

Abstract

The sCO 2 Brayton cycle has gained interest because of its flexibility and ability to provide higher thermomechanical conversion efficiency. Studies on failure conditions and corresponding emergency measures are of great significance to ensure the safety of the system, while there are limited studies related to the sCO 2 Brayton cycle because the test circuit has not been applied in practice at present. In this study, we have developed a dynamic model of the CO 2 Brayton cycle, and carefully validated its components against experimental data. Preliminary safety assessment and dynamic response under loss of cooling water (LOCW), loss of heat source (LOHS), and pipeline leakage have been analyzed. Emergency strategies are proposed to maintain the safe operation under failure conditions. The primary objective of this study is to reveal the dynamic performance and emergency measures under failure conditions of the sCO 2 Brayton cycle. The results demonstrate that the system net power decreases at rates close to 10%/s and less than 0.1%/s under LOCW and LOHS, respectively. The system responds more dramatically under LOCW compared with LOHS. The system needs emergency measures under LOCW, while it has sufficient time to realize a normal slow shutdown under LOHS. The leakage rate is at least five times higher in the high-pressure pipeline compared with the low-pressure pipeline for the same area of the leakage hole. Under pipeline leakage, the heat source should be cut-off slowly, and the rotation speeds of the main compressor and recompressor should be reduced simultaneously to protect the system.

Action mechanism of axial flow on windage loss in open shaft‐type gap with CO2

“…Over the past decades, more attention toward supercritical CO 2 (sCO 2 ) Brayton cycle, which has the potential to attain higher efficiency than either the steam Rankine cycle or even the state-of-the-art ultrasupercritical steam Rankine cycle, has been paid. [1][2][3][4][5] Furthermore, the density of CO 2 is relatively higher compared to the conventional working fluid, such as air or steam, as sCO 2 Brayton cycle operates at high pressure, which automatically results in exceedingly smaller sizes and higher rotational speed of rotating machinery, [6][7][8] including radial turbine, compressor, and generator. For the Brayton cycle with sCO 2 as working fluid, where the output power is below 1 MW, all rotating machines are incorporated into a sCO 2 turbinealternator-compressor (TAC) unit, [9][10][11] which can reduce the cost and enable modular construction technology.…”

“…Over the past decades, more attention toward supercritical CO 2 (sCO 2 ) Brayton cycle, which has the potential to attain higher efficiency than either the steam Rankine cycle or even the state‐of‐the‐art ultra‐supercritical steam Rankine cycle, has been paid 1–5 . Furthermore, the density of CO 2 is relatively higher compared to the conventional working fluid, such as air or steam, as sCO 2 Brayton cycle operates at high pressure, which automatically results in exceedingly smaller sizes and higher rotational speed of rotating machinery, 6–8 including radial turbine, compressor, and generator.…”