Dynamic analysis and control strategies of Organic Rankine Cycle system for waste heat recovery using zeotropic mixture as working fluid

Highlights: • Dynamic characteristics of ORC using mixture fluid are analyzed. • The improved dynamic model is better adapted to the phase change process. • The areas required for different evaporation stages are investigated. • Different control strategies are proposed from external controllable conditions. -- Abstract: The Organic Rankine Cycle (ORC) system is a rather promising technology for waste heat recovery. However, waste heat source generally presents a fluctuating behavior, which is a big challenge to the security and efficiency of the ORC. An improved dynamic model of ORC system with zeotropic mixture is firstly developed, which can be better adapted to the phase change process of working fluid. Accordingly, dynamic behavior of the ORC and dynamic distribution of evaporation stages are investigated. Besides, three control strategies are proposed to improve the performance of steadiness with external controllable conditions. Results show that a sudden abnormal change occurs in specific enthalpy of working fluid at the evaporator outlet when different disturbances are imposed to the system. It is found that the proposed control strategies are adapted to different heat source fluctuation. The control strategies with feedforward control system work well with low frequency variation of heat source temperature.