| Nowadays,under the background of global energy consumption being always dominated by the consumption of primary energy resource,the energy utilization efficiency in China is low and a large amount of low-to medium-grade waste heat resources are directly discharged into the environment.Therefore,the utilization of low-grade waste heat resources is of great significance to reduce environmental pollution and achieve energy sustainable development.Organic Rankine cycle(ORC)with advantages of easy operation,simple structure,and low investment cost is considered as the most commercial potential technology for waste heat utilization.Based on the investigation of ORC technology research status,the steady-state experiments under variable heat source conditions were carried out on the micro ORC experimental platform.The ecological sustainability performance of the ORC system was studied,and the ecological life cycle assessment model framework was established.Comprehensive performance of ORC system in terms of energy,economy,environment,and ecology was compared and analyzed,and multi-objective optimization work of systems with different working fluids was carried out.The exergoeconomic analysis method was adopted to discuss the measures for further improving the exergoeconomic performance of the polygeneration system including ORC.An Off-design model of a cogeneration system containing ORC and other subsystems was established,and a novel combined control strategy for the gas turbine cycle was proposed,as well as a case study is carried out.The main research contents and conclusions are as follows:(1)The variations of net power output,thermal efficiency,and exergy efficiency with an evaporation pressure change of ORC systems with different working fluids were studied based on the thermodynamic model of the ORC system.The irreversible loss distribution of system components was analyzed.Under the open heat source conditions,there existed a matching relationship between the critical temperature of working fluid and inlet temperature of heat source,and the variation trend of system net power output and exergy efficiency was consistent.As system evaporation pressure increased,the thermal efficiency of the ORC system adopting most of the working fluids increased monotonically.The irreversible loss distribution of system components was arranged in descending order as the heat exchanger,expander,and pump.(2)The steady-state experimental study under variable heat source conditions was carried out based on the improved experimental bench of the micro-ORC system.The change of heat source temperature had a great influence on evaporator outlet temperature and pressure,as well as the ideal expansion power output.The variation of heat source parameters also affected expander pressure ratio with no obvious variation and caused system actual output power fluctuation in a small range.Finally,the improvement scheme was conducted forward to problems that existed in the experimental platform.(3)The sustainability assessment framework of the ORC system with R134 a as working fluid was constructed to evaluate the environmental sustainability performance from resource,economy,and environmental aspects.The difference between ORC technology and thermal power generation in ecological cumulative exergy consumption was compared and analyzed.Finally,the application of the ORC system ecological model was illustrated through a case study.In the ORC system with R134 a as working fluid,the proportion of ecological cumulative exergy consumption from social and economic inputs was the highest,followed by environmental pollution emissions and natural resources consumption.With the goal of sustainable development,the social and economic input needed to be reduced for the ORC system,and the key of thermal power generation was pollutant emission control.The case study showed that the sustainable performance of a system with R1336 mzz was the best among ORC systems with HFO working fluids,and the sustainable performance of the ORC system would be improved when the heat source temperature increased.(4)Multi-objective optimization framework of the ORC system was established,and the system comprehensive performance in terms of energy,economy,environment,and ecology was studied by taking net power output,electricity production cost,carbon dioxide emission reduction,and ecological accumulated exergy consumption as the objective functions.The investment cost of the evaporator was the highest among the system,and the emission of expander was the largest among equipment emissions.The emissions of working fluids were mainly from the system leak process.There also observed that ORC system with low GWP working fluid had better emission reduction potential.The multi-objective comparative study between ORC systems with different working fluids found that the system with R245 fa had outstanding thermal performance,a system with R601 had the best thermo-economic performance,and a system with R600 a possessed the best environmental performance.According to the different emphases,the system performances were different,and no universal optimal fluid was found to meet the above target conditions at the same time.(5)A novel trigeneration system model was proposed,and exergoeconomic analysis was used to study the system performance.The performance differences of trigeneration systems with different ORC working fluids and optimization objectives were compared and discussed.The gas turbine cycle had the highest proportion of investment cost,followed by the supercritical carbon dioxide cycle,ORC,and absorption refrigeration cycle,and the exergy loss rates of the latter two subsystems were relatively low.Trigeneration system using R600 as ORC fluid not only had the best exergoeconomic performance but also the highest thermal efficiency.The exergy efficiency of the trigeneration system using R601 as ORC fluid was the highest.Results of different optimization objectives showed that the combustion chamber was the most critical component in the trigeneration system,and the absorber was also very important to the refrigeration cycle.(6)Based on the thermodynamic off-design models of the cogeneration system,a novel combined gas turbine control strategy was proposed.Different integration schemes between the cogeneration system and refrigeration unit were analyzed through a case study.The new proposed control strategy had higher thermal efficiency than the traditional turbine inlet temperature control method and could avoid the low exhaust temperature of waste flue gas.From the case study,the novel control strategy had better energy,economic and environmental performance,and the electric chiller had better energy-saving effects,but its economic and environmental performance was worse than that of the absorption chiller.The highest energy saving rate was obtained from the integrated scheme adopting combined control strategy and electric chiller,while the best economic and environmental performance was from the integrated scheme using the same control strategy and absorption chiller. |
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