Environment Impact And Sustainability Assessment Of Low Temperature Waste Heat Organic Rankine Cycle(ORC)

In recent years, energy shortages and global environment problem are getting worse. Our country is rich in low grade energy, such as industrial waste heat, geothermal energy, solar energy, etc. Converting low grade heat energy into electricity is the effective measures to improve energy efficiency and reduce environmental pollution. Organic Rankine Cycle becomes the focus in the study of low grade thermal energy development and utilization, which has the advantages of simple equipment and wide range of applications.The organic fluid applied to the ORC system has the certain environmental characteristic of GWP and ODP, which is different from conventional thermal power plants that using water as working medium. The organic fluid in the ORC system will spread to the atmosphere inevitably and destroy of the ozone layer. At present, the evaluation of the ORC system is focused on the hot economic indicators. Related literatures qualitatively consider the influence of the environment, but not qualitative analysis of the environmental impact when selecting working medium. The thermal efficiency and environmental performance of ORC system were not evaluated together. The exergy cost is used to quantify the environmental impact of organic working medium under the basic characteristic of the ORC system. And then the ORC system exergy balance model is developed with the considering of environmental impact.The main research content of this paper is as follows:①Exergy cost of environmental impact was made a quantitative analysis in the ORC system. Part of effective energy that was took from the net output power was managed to deal with the effect to environment. Exergy balance model with environmental impact was established. The new model contains environmental impact of working fluids and deals with consumption caused by working fluids to reach a new exergy balance.②The leakage model of ORC was established. Environmental impact of exergy in the subcritical and supercritical ORC system was analyzed and environmental impact of working fluids was made a quantitative analysis.③There is no documents to study a quantitative analysis of Exergy cost of environmental impact in the ORC system. The paper researches this problem and propose a comprehensive evaluation index which bonds environmental impact of working fluids with cycle thermal economic performance, namely exergy efficiency of comprehensive environmental impact. Relational expression of the evaluation index was raised. The index was verified by theoretical analysis and case study. Environmental impact of exergy in the subcritical and supercritical ORC system was compared. Results show that R123 and R32 are suitable for subcritical ORC system and transcritical ORC system respectively when considering the cycle thermal economic performance and refrigerant environmental impact;④The basic characteristics of subcritical ORC circulation system and the critical circulation system are studied firstly. In the case of known cold heat source temperature and flow rate, the performance of subcritical and critical organic rankine circulation system are calculated and analyzed. The effects of expander inlet temperature, condensation temperature on the performance of ORC system thermodynamic are discussed. And then the best of expander inlet temperature, condensation temperature and cyclic working substance are obtained.