Optimization Analysis Of Low-Temperature Waste Heat Power Generation System In Chemical Industry

There is much low-temperature waste heat which is not recycled in chemical industry,resulting in energy loss and environmental thermal pollutin.A new method of recovering low-temperature waste heat was studied,converting low-temperature waste heat into electricity by using organic Rankine cycle(ORC)power generation technology,which had great practical value.At present,ORC low-temperature waste heat power generation system had problems of low power generation and low efficiency,and the optimization analysis of ORC low-temperature waste heat power generation system had the problems that evaluation standard was not comprehensive,the correlation analysis of organic working fluid selection and operation parameters determination were not enough,studies on the interaction between operation parameters were few,and there was no optimization analysis of its heat exchanger.In response to these problems,the main work of this paper as follows:(1)ORC system was designed by Aspen Plus software.In response to the problem that evaluation standard was not comprehensive,comprehensive evaluation model was developed in this paper.Net output power,heat exchanger area and mass flow of organic working fluid were used as evaluation indexes of ORC system generation performance,and the new economic performance evaluation models were established in order to evaluate waste heat recovery performance of ORC system comprehensively.(2)For the problem that the correlation analysis of organic working fluid selection and operation parameters determination and study on the interaction between operation parameters were few,six working fluids including R245fa?R245ca?R236ea?R600?R601 and R601 a,and three operation parameters including evaporation pinch point temperature difference ? evaporation temperature and condensing temperature,were selected.Based on fluid catalytic cracking(FCC)unit and aromatic unit,the ORC system was used to recover the low-temperature waste heat,and then the correlation analysis of organic working fluid and operationg parameters on ORC system performance were studied in order to determine the best parameters.(3)For the problem that there was no optimization analysis of heat exchanger,the effect of high flux heat exchanger as evaporator of ORC system on generation power was studied in this paper,and then based on the the ORC system of aromatic unit,the comparative analysis with common heat exchanger was carried out.(4)The analysis results of FCC unit and aromatic unit show that the low-temperature waste heat sources of two chemical units are different,so the differences include the influence of operation parameters on ORC system performance,proper working fluid and optimal parameters.For the ORC system of FCC unit,the optimum evaporation temperature is affected by evaporation pinch temperature difference and condensing temperature.The most suitable organic working fluid is R245 fa.When condensing temperature is 45°C,evaporation pinch temperature difference is 8°C and the optimal evaporation temperature is 68°C,the net generation power is 277 kW.For the ORC system of aromatic unit,the most suitable organic working fluid is n-pentane(R601).When the condensing temperature and evaporation pinch temperature difference are 45°C and 12°C respectively,the evaporation pressure is 1.26 MPa,and the net generation power is 3040 kW.However,there are similarities between the two cases.One same place is that the lower the condensing temperature is,the more the output power is,so the temperature of cold utility using for ORC system is as low as possible if conditions permit.The other same place is that the smaller the evaporation pinch temperature difference is,the more the output power is and the larger the evaporator area is,so it can be said that the evaporator area limits the generation performance improvement.The optimization ananlysis of evaporator shows that the high flux heat exchanger can reduce the evaporation pinch temperature difference,thereby improving the generation performance of ORC system,so there is certain feasibility.