Comparison of control strategies and dynamic behaviour analysis of a Kalina cycle driven by a low-grade heat source

Kalina cycle is a promising heat-to-power technology in low-grade heat recovery applications. Most previous research concerning the Kalina cycle systems focused on the analysis and optimization based on static models with less consideration given to dynamic performance. It is important to explore the dynamic behaviour of the Kalina cycle system for operation safety due to the fluctuation of low-grade heat sources and the external load. In this paper, a dynamic model of a Kalina cycle system driven by a low-grade heat source is established to analyse the dynamic behaviour of the system. The valve-pump coordination control strategy and the pump control strategy are proposed and compared with the valve control strategy, with the turbine rotational speed as the controlled variable. Result reveals that the valve-pump coordination control strategy reduces the transient time and overshoot by 56.3% and 67.9%, respectively. The dynamic behaviours of the Kalina cycle system under valve-pump coordination control strategy subjecting to disturbance are then studied, including heat source temperature disturbance, heat source mass flow rate disturbance, and system load disturbance. The results show that for these disturbances, the transient times of the turbine rotational speed are 11.8 s, 12.1 s and 11.7 s while the overshoots of that are 1.30%, 1.67% and 1.33%, respectively.