Dynamic performance of a dual-pressure waste heat recovery system under partial load operation

The dual-pressure power generation systems are particularly suitable for recovering medium-grade waste heat from industrial processes. However, the heat recovery system usually operates under partial load conditions due to the frequent variations of exhaust gas conditions. The traditional static model is unable to predict the system dynamic behaviors. Hence, a dynamic model of the dual-pressure power generation system is developed in this paper. The model covers the whole process including the high pressure cycle, the low pressure cycle, as well as the pressure control system. The temperature and flow rate fluctuations of exhaust gas were simulated and the dynamic behavior of the dual-pressure system was investigated. Control systems for both high pressure and low pressure cycles were designed. The system performances operating at different sets of combinations of high pressure and low pressure were studied. The simulation results show that the exhaust gas temperature has greater effect on the system performance than the flow rate does. The dynamic behaviors of the high pressure steam are different from that of the low pressure steam. When the system is operated under partial load conditions, keeping both the high pressure and low pressure steam pressures in sliding mode is the most efficient way.