Theoretical Research Of The Mid-Low-Temperature Waste Heat Generation Using Organic Rankine Cycle (ORC)

There is large amount of waste heat in China, especially in the industrial field. The technology to make use of high-temperature waste heat is mature now while that of mid-and-low-temperature waste heat is under developing and much less to be used. But the proportion of it is about 40%~50% in the total amount of the waste heat. If it can be used fully, we will save tremendous energy for the whole country, and reduce the carbonic dioxide emission and heat pollution. We can use the Organic Rankine Cycle to make use of mid-low-temperature waste heat to generate. It is better than the water-steam Rankine Cycle.The paper will build a theoretical model for the mid-low-temperature waste heat ORC system. The model includes evaporator, waste-heat fluid and the working-fluid cycle. Use a program of working-fluid characteristics and Matlab to calculate the parameters of the whole cycle. Select some suitable working fluids for the model and make analysis and comparison among three pure fluids and one mixture. Then the optimization of ORC system will be discussed in the next part of the paper. Internal heat exchanger(IHE), reheating system and steam-suction system will be used for the optimization. Analyze and compare them with each other to find their superior or inferior.Some important conclusions is summarized below: to the pure fluid, evaporating temperature get higher leads to higher efficiency, and the output work has a maximum which corresponds to the optimal evaporating temperature. The mixtures have some advantages over the pure fluids such as the range extension of working fluids'selection, the reduction of the exergy loss in evaporation, and the higher efficiency in IHE ORC system. By analyzing the steam-suction ORC system, we find the mixture is not suitable because of its low efficiency and low output work. In the reheating ORC system, we find only when both reheating system and IHE are used in the ORC, the efficiency can be improved.Finally, a software for ORC system simulation is written which simulate and control the running conditions of the mid-low-temperature waste heat ORC for generation.