Control strategy of a metal-fueled closed-loop steam Rankine power cycle with large time-delay characteristics

This paper investigates the control strategy of a novel metal-fueled closed-loop steam Rankine cycle with large time-delay characteristics. The lumped parameter model is first established to describe the dynamics of boiler reactor and the one-dimensional distributed parameter model is used to describe the dynamic characteristics of the spiral evaporator and shell condenser. The turbine is modeled using the quasi-steady approach. The accuracy of the model for the boiler reactor and spiral evaporator is validated against experimental results, with a maximum relative error of 8.7% and 1.7% and for the boiler reactor and evaporator, respectively. The open-loop characteristics are then investigated. The system dynamic process with and without boiler reactor is approximately 85s and 4.2s, respectively, indicating significant time-delay effect caused by boiler reactor. Two control strategies are further proposed to adjust the turbine rotational speed. The settling time using the combination of the open-loop and closed-loop control strategy is approximately 30s and the settling time with the dual closed-loop control strategy is 28s, however the overshoot of 15.8% and 16.9% is found during deceleration and acceleration process, respectively. It is suggested that the combination of the open-loop and closed-loop algorithms is used since it can mitigate the overshoot caused by controlling the mass flow rate of SF6 and water simultaneously. This paper provides insight into the control strategy for the metal-fueled closed-loop steam Rankine cycle.