Transient analysis and control of a heat to power conversion unit based on a simple regenerative supercritical CO<inf>2</inf> Joule-Brayton cycle

Abstract

Supercritical carbon dioxide (sCO2) heat to power systems are a promising technology thanks to their potential for high efficiency and operational flexibility. However, their dynamic behaviour during part-load and transient operation is still not well understood and further research is needed. Additionally, there is not enough literature addressing suitable control approaches when the objective is to follow the dynamics of heat load supplied by the topping process to maximise the power recovery. The current research aims to fill these gaps by proposing a one- dimensional transient modelling formulation calibrated against the major components of a 50 kWe sCO2 test facility available at Brunel University London. The dynamic analysis showed that the system quickly adapts to a 2800s transient heat load profile, proving the flexible nature of the sCO2 system investigated. The turbine by- pass, during startup and shutdown modes of operation, enabled gradual and safe build-up/decline of the pres- sures and temperatures throughout the loop. The regulation of the inventory in the range 20–60 kg allowed a 30% variation of the turbine inlet temperature with lower penalties on system performance than the turboma- chinery speed control. The designed proportional-integral inventory controller showed a rapid response in the control of the turbine inlet temperature around the set point of 773 K during large variations of the heat load.