Thermo-economic Analysis Of Organic Rankine Cycle Based On Zeotropic Mixtures And Hazardous Waste Incinerator Excess Steam Heat Utilization

There is a large amount of low-and medium-temperature waste heat in nature and industrialization such as geothermal energy,solar energy,and industrial waste heat.Using Organic Rankine Cycle(ORC)to recover such thermal energy can alleviate energy shortage and environmental pollution and increase energy utilization efficiency.Working fluids can be classified into pure working fluids and mixtures based on its composition.Employing zeotropic mixtures for variable temperature heat sources can optimize evaporator temperature match.For heat sources with latent heat,the use of pure working fluid can optimize the temperature match in the evaporator.To solve the mixtures screen problem of ORC system driven by variable temperature heat source,the thermodynamic and thermo-economic model is established and the exergy efficiency is selected as the thermodynamic optimization index to study the thermal coupling characteristic between ORC and closed heat source.Results show that the temperature drop of heat source make difference to the working fluid selection.The temperature drop can be classified into small temperature drop,transition temperature drop,big temperature drop according to the upper and lower bound formula of the temperature drop zone.Furtherly,the low critical temperature working fluids can match better with a big temperature drop heat source and the high critical temperature working fluids match better with a small temperature drop heat source.Finally,the selection criteria of zeotropic mixtures with closed heat source is proposed which determines the optimal working fluid critical temperature according to the difference between the heat source temperature in and pinch temperature,and determines the optimal condensation temperature glide according to the temperature match in condenser.To verify the consistency of different thermo-economic indexes,four thermo-economic indexes are chosen in this paper to evaluate the thermodynamic and thermo-economic performance of ORC with different types of heat source and verify the thermo-economic performance of ORC which using the working fluid selected by the selection criteria.Results show that the optimal working fluids under open heat source had higher exergy efficiency but the suboptimal thermo-economic performance.The optimal working fluids under closed heat source performed better both in thermodynamic and thermo-economic.Aiming at the diversity of heat sources and the utilization of latent heat source,the ORC system driven by 200℃ excess saturated steam generated by the hazardous waste boiler is studied.It is found that the inconsistent between the ratio of latent heat to sensible heat of heat source(4.49)and working fluid(0.42-0.98)is the main reason causing the heat transfer temperature mismatch and big exergy destruction.The saturated steam heat source has an exothermic process with constant temperature,which increases the heat transfer temperature difference in the preheat section of evaporator.In order to solve this problem,saturated water is added to the heat source to adjust the ratio of latent heat to sensible heat of the heat source.The temperature drop curve of heat source and the temperature rise curve of working fluid achieve the best fit when the ratio of latent heat to sensible heat of heat source equal to the ratio of latent heat to sensible heat of working fluid.The capacity of the system is improved with a constant thermal efficiency,and net output power is increase.For example,the net output power is increased by 170%form 1180.87kW to 3193.81kW with a constant thermal efficiency of 17.9%.But the exergy efficiency decreases from 46.7%to 45.6%due to the added saturated water causes more heat source exergy destruction.Furtherly,the method of optimizing the heat source outlet temperature is adopted to decrease the heat source exergy destruction and the system exergy efficiency is increased from 45.6%to 51%.When the front turbine is adopted,the working condition 2 has the highest thermal efficiency of 23.34%and exergy efficiency of 66.2%,the net output power is 1674.59kW.Use parabolic trough solar collector provide the supplementary thermal energy to heat saturated water.The influence of solar direct normal irradiance(DNI)on the ORC configuration and thermal performance is studied.Results show that the net power output of ORC have the same trend with the DNI.Toluene and the benzene have the highest net power output,the exergy efficiency fluctuate type is categorized into three types based on the ratio of latent heat to sensible heat of the working fluid.When the ratio of latent heat to sensible heat of the working fluid is less than 0.433,the exergy efficiency fluctuates gently,when the ratio is greater than 0.96,the exergy efficiency fluctuates greatly,and when the ratio is greater than 0.433 and less than 0.96,the fluctuation is between the two situations.Finally,the steady state simulation of ORC coupling with parabolic trough solar collector is carried out for R113.The net output power of the system was reduced when the pressure drop is taken into account,and the net output power gap increased by 2774%with the increase of the solar direct radiation intensity of 179%.