Investigation of Bypass Valve Positions on Performance of Closed Brayton Cycle

HTR-10GT is a closed Brayton cycle with two-stage compression and heat recuperation. Bypass control was adopted for rapid power regulation and safety protection. A bypass valve could be set between any two positions at different pressure levels, there would be in total 21 setting possibilities, whose regulating behaviors remained to be fully clarified. The dynamic characteristics of these settings were thus analyzed by implementing numerical simulation on the integrated system model. The reactor was modeled with point-kinetics and 1D thermal-hydraulics model; compressor performance calculation was based on digitization of the performance map and Reynolds number correlation; Flügel formula was chosen to calculate turbine performance. The system was modeled with Modelica, and the DASSL code was used to solve the Differential and Algebraic Equations. The results showed that only 6 choices among the 21 remained acceptable for engineering practice. The degree and rate on power output reduction, anti-surge effect and long-term thermal effects at reactor inlet and along recuperator’s metal wall were evaluated and compared among these choices to give out proposals. This research clarified the characteristics of bypass valves at different positions to give a reference on the final design of the control methods, and proposed a combination of valves for multi-valve cooperative regulation.