Dynamic exergy analysis of a recuperative dual-pressure ORC driven by waste heat

To absorb the waste heat from low-temperature heat source more effectively, an ORC system is proposed. Compared with the traditional ORC system, an evaporator and a recuperator is added to the cycle. It is driven by the waste heat of solid bulk, R1234ze(E) is chosen as the working fluid. To study the dynamic characteristics of the system, disturbance is applied to the hot air inlet temperature. The results indicate that under 10℃ step decrease of hot air inlet temperature, the exergy efficiency of three heat exchangers all rises to the peak first, and then gradually declines. Compared with the initial state, the exergy efficiency of the high-pressure evaporator (HPE) increases the most in the end, which is 1.07%. Both high-pressure evaporator and low-pressure evaporator (LPE) take 700 seconds to return to steady state, while the recuperator only takes about 200 seconds. The exergy efficiencies of turbine, HPE and LPE drop directly when the disturbance occurs. The turbine exergy efficiency has a decline of 0.52%, from 81.1% to 80.58%. The system exergy efficiency firstly jumps from 35.67% to 43.28% and then slowly decreases to 34.65%.