In the face of an escalating global water crisis,countries worldwide grapple with the crippling effects of scarcity,jeopardizing economic progress and hindering societal advancement.Solar energy emerges as a beacon of...In the face of an escalating global water crisis,countries worldwide grapple with the crippling effects of scarcity,jeopardizing economic progress and hindering societal advancement.Solar energy emerges as a beacon of hope,offering a sustainable and environmentally friendly solution to desalination.Solar distillation technology,harnessing the power of the sun,transforms seawater into freshwater,expanding the availability of this precious resource.Optimizing solar still performance under specific climatic conditions and evaluating different configurations is crucial for practical implementation and widespread adoption of solar energy.In this study,we conducted theoretical investigations on three distinct solar still configurations to evaluate their performance under Baghdad’s climatic conditions.The solar stills analyzed include the passive solar still,themodified solar still coupled with a magnetic field,and themodified solar still coupled with bothmagnetic and electrical fields.The results proved that the evaporation heat transfer coefficient peaked at 14:00,reaching 25.05 W/m^(2).℃for the convention pyramid solar still(CPSS),32.33 W/m^(2).℃for the magnetic pyramid solar still(MPSS),and 40.98 W/m^(2).℃for elecro-magnetic pyramid solar still(EMPSS),highlighting their efficiency in converting solar energy to vapor.However,exergy efficiency remained notably lower,at 1.6%,5.31%,and 7.93%for the three still types,even as energy efficiency reached its maximum of 18.6%at 14:00 with a corresponding peak evaporative heat of 162.4 W/m^(2).展开更多
In this study the performance of an ASHPWH （air source heat pump water heater） is assessed from exergy point of view in component wise. In order to investigate the work potential of energy, the destruction on the ex...In this study the performance of an ASHPWH （air source heat pump water heater） is assessed from exergy point of view in component wise. In order to investigate the work potential of energy, the destruction on the exergy is analyzed and results are summarized for the components individually. The exergy destruction of the system is studied by considering real paths of the pressure and temperature data which are collected during the experiments of the ASHPWH under varying environmental conditions. In the following step, the evolution of the exergy destruction of the system is calculated by a code which is compiled on MATLAB along these temperature and pressure paths. The obtained results reveal the importance of the transient exergy analysis by providing detailed information about exergy destruction of the system such as where it drives up and reaches up to its max and where it drops down and evolves on a smooth path.展开更多
In this paper, an efficient methodology for synthesizing the indirect work exchange networks(WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In co...In this paper, an efficient methodology for synthesizing the indirect work exchange networks(WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In contrast with superstructure method, the transshipment model is easier to obtain the minimum utility consumption taken as the objective function and more convenient for us to attain the optimal network configuration for further minimizing the number of units. Different from division of temperature intervals in heat exchange networks,different pressure intervals are gained according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and the characteristics of no pressure constraints for stream matches. The presented approach for WEN synthesis is a linear programming model applied to the isothermal process, but for indirect work exchange networks with adiabatic process, a nonlinear programming model needs establishing. Additionally, temperatures should be regarded as decision variables limited to the range between inlet and outlet temperatures in each sub-network. The constructed transshipment model can be solved first to get the minimum utility consumption and further to determine the minimum number of units by merging the adjacent pressure intervals on the basis of the proposed merging methods, which is proved to be effective through exergy analysis at the level of units structures. Finally, two cases are calculated to confirm it is dramatically feasible and effective that the optimal WEN configuration can be gained by the proposed method.展开更多
Based on the“three box”exergy analysis model,a black box-gray box hierarchical exergy analysis and evaluation method is put forward in this paper,which is applied to evaluate the power generation technology of diffe...Based on the“three box”exergy analysis model,a black box-gray box hierarchical exergy analysis and evaluation method is put forward in this paper,which is applied to evaluate the power generation technology of differential pressure produced by natural gas expansion.By using the exergy analysis theory,the black box-gray box hierarchical exergy analysis models of three differential pressure power generation technologies are established respectively.Firstly,the“black box”analysis models of main energy consuming equipment are established,and then the“gray box”analysis model of the total system is established.Based on the calculation results of exergy analysis indexes,the weak energy consumption equipment in the whole power generation process is accurately located.Taking a gas field in southwest China as an example,the comprehensive energy consumption evaluation of the three power generation technologies is carried out,and the technology with the best energy consumption condition among the three technologies is determined.Finally,the rationalization improvement measures are put forward from improving the air tightness,replacing the deflector and reducing the flow loss.展开更多
After long-term operation,the performance of components in the GTCC system deteriorates and requires timely maintenance.Due to the inability to directly measure the degree of component malfunction,it is necessary to u...After long-term operation,the performance of components in the GTCC system deteriorates and requires timely maintenance.Due to the inability to directly measure the degree of component malfunction,it is necessary to use advanced exergy analysis diagnosis methods to characterize the components’health condition(degree of malfunction)through operation data of the GTCC system.The dissipative temperature is used to describe the degree of malfunction of different components in the GTCC system,and an advanced exergy analysis diagnostic method is used to establish a database of overall operating condition component malfunctions in theGTCC system.Ebsilon software is used to simulate the critical parameters of the malfunctions of the GTCC system components and to obtain the changes in the dissipative temperature of different components.Meanwhile,the fuel consumption and economic changes of the GTCC system on a characteristic power supply day under health and malfunction conditions are analyzed.Finally,the effects of maintenance costs,electricity,and gas prices on maintenance expenses and profits are analyzed.The results show that the GTCC system maintenance profit is 6.07$/MWh,while the GTCC system maintenance expense is 5.83$/MWh.Compared with the planned maintenancemode,the malfunction maintenance mode saves 0.24$/MWh.Simultaneously,the maintenance coefficient of GTCC should be adjusted under different malfunctions to obtain a more accurate maintenance period.展开更多
The parameter study of sinter waste heat recovery in vertical tank was conducted numerically by using energy and exergy analysis,and the experimental data obtained from a homemade experimental apparatus was applied to...The parameter study of sinter waste heat recovery in vertical tank was conducted numerically by using energy and exergy analysis,and the experimental data obtained from a homemade experimental apparatus was applied to verify the reliability of numerical model.Based on the first and second laws of thermodynamics,the effects of flow rate of cooling air(FRCA)and inlet temperature of cooling air(ITCA),as well as the inner diameter of cooling section(IDCS)and height of cooling section(HCS),on the sinter cooling process were analyzed in detail.The results show that the average deviation between the experimental data and calculation values is 4.93%,and the model reliability is verified.The enthalpy exergy of outlet air tends to increase first and then decrease with increasing the FRCA and ITCA,while increasing the IDCS only leads to the increase in enthalpy exergy of outlet air.For a given operational condition,the enthalpy exergy of outlet air can reach a maximum value with increasing the HCS.The vertical tank could obtain the maximum enthalpy exergy of outlet air through the adjustments of FRCA and ITCA,as well as the HCS.展开更多
In this study an energy and exergy analysis is made of moist air, it is used the psychometrics charts. A Visual Basic program is used to generate psychometrics charts. These charts are used to analyze the air thermody...In this study an energy and exergy analysis is made of moist air, it is used the psychometrics charts. A Visual Basic program is used to generate psychometrics charts. These charts are used to analyze the air thermodynamic behavior, considering the environmental variations, pressure, temperature and relative humidity. Also, the available energy in the cooling processes at constant enthalpy, humidification at constant temperature and heating with constant relative humidity is analyzed. For example, we obtained that the enthalpy and exergy in a thermodynamic state, with conditions, Patm = 1.013 bar, Tatm = 25oC and Φatm=50%, are h = 50.56 kJ/kga and ε =11.5 kJ/kga;and for Patm= 0.77 bar to the same conditions of Tatm and Φatm, the enthalpy and exergy increases in a 14% and 20%, respectively.展开更多
A new small concentrating solar power plant which is suitable for urban area is presented, and a theoretical framework for the energy and exergy analysis in the overall power plant is also constructed. The framework c...A new small concentrating solar power plant which is suitable for urban area is presented, and a theoretical framework for the energy and exergy analysis in the overall power plant is also constructed. The framework can be used to evaluate the energy and exergy losses in each component. Furthermore, the energy and exergy efficiencies have also been computed and compared for the individual components as well as for the overall plant.展开更多
Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps： Removing most of the water content at -40 ℃, removing siloxanes and SVOCs ...Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps： Removing most of the water content at -40 ℃, removing siloxanes and SVOCs at -85 ℃ and frosting CO2 at temperatures varying from -90 ℃ to -120 ℃. This process transforms biogas containing typically 60% methane, 35% CO2, 5% water vapor in methane containing 2.5% of CO2. This paper studies how a single low-temperature refrigeration system is able to cool biogas with an indirect system using low-temperature heat-transfer fluids. The exergy study defines the exergy losses and served as guidance for the energy/pinch analysis that is used for the design of the heat-exchanger series and the appropriate heat recovery. An optimal system could save up to 40% of the electric consumption of the refrigeration system.展开更多
At present,the dual-loop organic Rankine cycle(DORC)is regarded as an important solution to engine waste heat recovery(WHR).Compared with the conventional exergy analysis,the advanced exergy analysis can better descri...At present,the dual-loop organic Rankine cycle(DORC)is regarded as an important solution to engine waste heat recovery(WHR).Compared with the conventional exergy analysis,the advanced exergy analysis can better describe the interactions between system components and the irreversibility caused by economic or technical limitations.In order to systematically study the thermodynamic performance of DORC,the conventional and advanced exergy analyses are compared using an inline 6-cylinder 4-stroke turbocharged diesel engine.Meanwhile,the sensitivity analysis is implemented to further investigate the influence of operating parameters on avoidable-endogenous exergy destruction.The analysis result of conventional exergy analysis demonstrates that the priorities for the components that should be improved are in order of the high-temperature evaporator,the low-temperature turbine,the first low-temperature evaporator and the high-temperature condenser.The advanced exergy analysis result suggests that the avoidable exergy destruction values are the highest in the low-temperature turbine,the high-temperature evaporator and the high-temperature turbine because they have considerable endogenous-avoidable exergy destruction.The sensitivity analysis indicates that reducing the evaporation pinch point and raising the turbine efficiency can decrease the avoidable exergy destruction.展开更多
In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,thr...In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.展开更多
Air-conditioning system consumes a large amount of electricity in residential sections,and its efficiency has drawn extensive concerns in energy-conscious era.Liquid-vapor separation is a heat transfer enhancement tec...Air-conditioning system consumes a large amount of electricity in residential sections,and its efficiency has drawn extensive concerns in energy-conscious era.Liquid-vapor separation is a heat transfer enhancement technology that can effectively improve the performance of the heat exchanger as well as the system.In this paper,a regular air-conditioning system as the baseline(system-A)and other two air-conditioning systems with liquid-vapor separation heat exchanger(system-B and system-C)are comparatively studied.The component behaviors and system performances are deeply explored by using advanced exergy analysis with a focus on quantifying how much consequences come from the variants,i.e.liquid-vapor separation.The results indicate that the system-B has large reduced exergy destruction from the compressor and condenser at cooling mode relative to the system-A.The system-C has mainly diminished exergy destruction in the compressor caused by other components relative to the system-B.At heating mode,the system-C has an enhanced system exergy efficiency of 9.6%over the system-A,and it also has the decreased avoidable exergy destruction which is dominantly contributed by the compressor and evaporator.Furthermore,it is found that liquid-vapor separation mainly benefits the compressor and outdoor heat exchanger where it locates,leading to the system performance improvements.展开更多
In order to resolve the problems of the current air separation process such as the complex process, cumbersome operation and high operating costs, a novel air separation process cooled by LNG cold energy is proposed i...In order to resolve the problems of the current air separation process such as the complex process, cumbersome operation and high operating costs, a novel air separation process cooled by LNG cold energy is proposed in this paper, which is based on high-efficiency heat exchanger network and chemical packing separation technology. The operating temperature range of LNG cold energy is widened from 133K-203K to l13K-283K by high- efficiency heat exchanger network and air separation pressure is declined from 0.5MPa to about 0.35MPa due to packing separation technology, thereby greatly improve the energy efficiency. Both the traditional and novel air separation processes are simulated with air handling capacity of 20t＇h-1. Comparing with the traditional process, the LNG consumption is reduced by 44.2%, power consumption decrease is 211.5 kWh per hour, which means the annual benefit will be up to 1.218 million CNY. And the exergy efficiency is also improved by 42.5%.展开更多
This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program A...This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program Aspen Plus. The results indicate that the most important destruction of exergy is found to occur in the reactor and water quenching scrubber, amounting to 8.23% and 10.39%, respectively, of the entire system. Based on the results of thermodynamic and exergy analysis, the acetylene reactor has been retrofitted. The improvement ratios of molar 02 to CH4 and molar CO to CN4 are 0.65 and 0.20, respectively. An improvement of the acetylene production system is proposed. Adopting the improvement operation conditions and using oil to realize the reaction heat recovery, the feedstock of natural gas is reduced by 9.88% and the exergy loss in the retrofitting process is decreased by 19.71% compared to the original process.展开更多
To decrease energy consumption of ladle furnace, exergy analysis and optimization were conducted based on the ladle furnace refining process of modern clean steelmaking. Exergy analysis results showed that exergy loss...To decrease energy consumption of ladle furnace, exergy analysis and optimization were conducted based on the ladle furnace refining process of modern clean steelmaking. Exergy analysis results showed that exergy loss induced by unavailable electric energy is the largest, and the electric energy efficiency is 46.20%. To cut down the unavailable electric energy, industrial experiments of submerged arc heating were carried out combined with slag composition modification. Results showed that submerged arc heating can be achieved within most heating period, average heating rate increased by 0. 5 ℃/min, unavailable electric energy decreased by 21. 730 MJ per ton steel, and electric energy efficiency was enhanced by 14.84 %. As the refining cycle was shortened, the exergy loss induced by heat elimination decreased from 19. 455 MJ per ton steel to 11. 066 MJ per ton steel.展开更多
This paper considers the combination of hydrothermal degradation （HTD） and superheated steam （SHS） drying in disposal and processing of degradable organic wastes in municipal solid wastes （MSW）. In SHS drying, a...This paper considers the combination of hydrothermal degradation （HTD） and superheated steam （SHS） drying in disposal and processing of degradable organic wastes in municipal solid wastes （MSW）. In SHS drying, a fraction of dryer thermal energy input can be recovered and used to satisfy the heat requirement in maintaining the HTD operating temperature. Both energy and exergy analysis are applied to the combined process. The analysis covers ranges of dryer inlet temperatures of 202.38-234.19~C and feed water content of 32.5-65%. Thermal energy analysis shows that the combination of HTD and SHS drying can achieve thermal energy self-sufficiency （TES） by manipulating process variables. The exergy analysis indicates the location, type, and magnitude of the exergy losses during the whole process by applying the second law of thermodynamics.展开更多
In this study, exergy dynamic and advanced exergy analyses are applied to theturbojet engine to assess its mexogenous, endogenous, exogenous, avoidable and unavoidableexergies under the environment conditions of 15 C...In this study, exergy dynamic and advanced exergy analyses are applied to theturbojet engine to assess its mexogenous, endogenous, exogenous, avoidable and unavoidableexergies under the environment conditions of 15 C temperature and 1 bar pressure. Themaximum exergy point in the turbojet engine is found for the combustor in which C11H23(Jet-A1) fuel is combusted with air, while the minimum one is determined for the aircompressor head where the free air enters. The combustion chamber has the maximum fuel,product and irreversibility rates and the air compressor has the minimum fuel and product ex-ergy values, while the minimum irreversibility is found for the turbine. Maximum improvementpotential rate is found for the combustion chamber (5141.27 kW), while minimum rate is deter-mined for the turbine of system (6.95 kW). Also, the turbine component has the highest exergyefficiency (97.20%) due to its expansion process, while combustion chamber component hasthe lowest exergy efficiency (55.39%) due to low efficient combustion process of the fuel.Furthermore, the mexogenous exergy destructions from maximum to minimum are found for the combustion chamber, air compressor and gas turbine units, respectively. Considering exergydynamic analysis, the mexogenous exergy destruction rates of the combustion chamber, aircompressor and gas turbine are found as 184.4 kW, 103.97 kW and 9.99 kW, respectively.Considering all results, the combustion chamber is the primer component to be handled for bet-ter efficiency and improvement.展开更多
Gas turbine (GT) power plants operating in arid climates suffer a decrease in output power during the hot summer months because of the high specific volume of air drawn by the compressor. Cooling the air intake to the...Gas turbine (GT) power plants operating in arid climates suffer a decrease in output power during the hot summer months because of the high specific volume of air drawn by the compressor. Cooling the air intake to the compressor has been widely used to mitigate this shortcoming. Energy and exergy analysis of a GT Brayton cycle coupled to a refrigeration air cooling unit shows a promise for increasing the output power with a little decrease in thermal efficiency. A thermo-economics algorithm is developed to estimate the economic feasibility of the cooling system. The analysis is applied to an open cycle, HITACHI-FS7001B GT plant at the industrial city of Yanbu (Latitude 24o 05” N and longitude 38o E) by the Red Sea in the Kingdom of Saudi Arabia. Result show that the enhancement in output power depends on the degree of chilling the air intake to the compressor (a 12 - 22 K decrease is achieved). For this case study, maximum power gain ratio (PGR) is 15.46% (average of 12.25%), at an insignificant decrease in thermal efficiency. The second law analysis show that the exergetic power gain ratio drops to an average 8.5%. The cost of adding the air cooling system is also investigated and a cost function is derived that incorporates time-dependent meteorological data, operation characteristics of the GT and the air intake cooling system and other relevant parameters such as interest rate, lifetime, and operation and maintenance costs. The profit of adding the air cooling system is calculated for different electricity tariff.展开更多
Large grid-connected photovoltaic(PV)plants are increasingly being installed around the world,including in harsh desert climates.Evaluating their performance can help improve the design and operation of PV systems.Thi...Large grid-connected photovoltaic(PV)plants are increasingly being installed around the world,including in harsh desert climates.Evaluating their performance can help improve the design and operation of PV systems.This study performed an energy and exergy analysis of a 20-MW grid-connected PV plant under desert climatic conditions in southern Algeria over a period of 1 year.The PV plant was divided into two 10-MW subsystems.Energy analysis was performed using actual irradiation,power output,wind speed and ambient temperature data.The annual average energy efficiency of the plant and subsystems was 10.82%,10.95%and 10.69%,respectively.Solar radiation had the most significant impact(80%determination coefficient)on thermal exergy loss.The exergy efficiency of the plant was lower than the literature values,likely due to the harsh desert conditions.The comprehensive energy and exergy analysis provides insights into the performance of large-scale PV plants in desert climates.The results can help guide the system design and operation improvements for such conditions.Regular cleaning and cooling could improve performance.展开更多
文摘In the face of an escalating global water crisis,countries worldwide grapple with the crippling effects of scarcity,jeopardizing economic progress and hindering societal advancement.Solar energy emerges as a beacon of hope,offering a sustainable and environmentally friendly solution to desalination.Solar distillation technology,harnessing the power of the sun,transforms seawater into freshwater,expanding the availability of this precious resource.Optimizing solar still performance under specific climatic conditions and evaluating different configurations is crucial for practical implementation and widespread adoption of solar energy.In this study,we conducted theoretical investigations on three distinct solar still configurations to evaluate their performance under Baghdad’s climatic conditions.The solar stills analyzed include the passive solar still,themodified solar still coupled with a magnetic field,and themodified solar still coupled with bothmagnetic and electrical fields.The results proved that the evaporation heat transfer coefficient peaked at 14:00,reaching 25.05 W/m^(2).℃for the convention pyramid solar still(CPSS),32.33 W/m^(2).℃for the magnetic pyramid solar still(MPSS),and 40.98 W/m^(2).℃for elecro-magnetic pyramid solar still(EMPSS),highlighting their efficiency in converting solar energy to vapor.However,exergy efficiency remained notably lower,at 1.6%,5.31%,and 7.93%for the three still types,even as energy efficiency reached its maximum of 18.6%at 14:00 with a corresponding peak evaporative heat of 162.4 W/m^(2).
文摘In this study the performance of an ASHPWH （air source heat pump water heater） is assessed from exergy point of view in component wise. In order to investigate the work potential of energy, the destruction on the exergy is analyzed and results are summarized for the components individually. The exergy destruction of the system is studied by considering real paths of the pressure and temperature data which are collected during the experiments of the ASHPWH under varying environmental conditions. In the following step, the evolution of the exergy destruction of the system is calculated by a code which is compiled on MATLAB along these temperature and pressure paths. The obtained results reveal the importance of the transient exergy analysis by providing detailed information about exergy destruction of the system such as where it drives up and reaches up to its max and where it drops down and evolves on a smooth path.
基金Supported by the National Natural Science Foundation of China(21576036 and 21776035)
文摘In this paper, an efficient methodology for synthesizing the indirect work exchange networks(WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In contrast with superstructure method, the transshipment model is easier to obtain the minimum utility consumption taken as the objective function and more convenient for us to attain the optimal network configuration for further minimizing the number of units. Different from division of temperature intervals in heat exchange networks,different pressure intervals are gained according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and the characteristics of no pressure constraints for stream matches. The presented approach for WEN synthesis is a linear programming model applied to the isothermal process, but for indirect work exchange networks with adiabatic process, a nonlinear programming model needs establishing. Additionally, temperatures should be regarded as decision variables limited to the range between inlet and outlet temperatures in each sub-network. The constructed transshipment model can be solved first to get the minimum utility consumption and further to determine the minimum number of units by merging the adjacent pressure intervals on the basis of the proposed merging methods, which is proved to be effective through exergy analysis at the level of units structures. Finally, two cases are calculated to confirm it is dramatically feasible and effective that the optimal WEN configuration can be gained by the proposed method.
基金financially supported by the National Natural Science Foundation of China(52074089 and 51534004)Natural Science Foundation of Heilongjiang Province of China(LH2019E019)。
文摘Based on the“three box”exergy analysis model,a black box-gray box hierarchical exergy analysis and evaluation method is put forward in this paper,which is applied to evaluate the power generation technology of differential pressure produced by natural gas expansion.By using the exergy analysis theory,the black box-gray box hierarchical exergy analysis models of three differential pressure power generation technologies are established respectively.Firstly,the“black box”analysis models of main energy consuming equipment are established,and then the“gray box”analysis model of the total system is established.Based on the calculation results of exergy analysis indexes,the weak energy consumption equipment in the whole power generation process is accurately located.Taking a gas field in southwest China as an example,the comprehensive energy consumption evaluation of the three power generation technologies is carried out,and the technology with the best energy consumption condition among the three technologies is determined.Finally,the rationalization improvement measures are put forward from improving the air tightness,replacing the deflector and reducing the flow loss.
基金supported by the China Postdoctoral Science Foundation(Grant number:370140).
文摘After long-term operation,the performance of components in the GTCC system deteriorates and requires timely maintenance.Due to the inability to directly measure the degree of component malfunction,it is necessary to use advanced exergy analysis diagnosis methods to characterize the components’health condition(degree of malfunction)through operation data of the GTCC system.The dissipative temperature is used to describe the degree of malfunction of different components in the GTCC system,and an advanced exergy analysis diagnostic method is used to establish a database of overall operating condition component malfunctions in theGTCC system.Ebsilon software is used to simulate the critical parameters of the malfunctions of the GTCC system components and to obtain the changes in the dissipative temperature of different components.Meanwhile,the fuel consumption and economic changes of the GTCC system on a characteristic power supply day under health and malfunction conditions are analyzed.Finally,the effects of maintenance costs,electricity,and gas prices on maintenance expenses and profits are analyzed.The results show that the GTCC system maintenance profit is 6.07$/MWh,while the GTCC system maintenance expense is 5.83$/MWh.Compared with the planned maintenancemode,the malfunction maintenance mode saves 0.24$/MWh.Simultaneously,the maintenance coefficient of GTCC should be adjusted under different malfunctions to obtain a more accurate maintenance period.
基金The authors wish to thank the financial support for this work provided by the National Natural Science Foundation of China(51974087)China Postdoctoral Science Foundation(2018M642538)+1 种基金Fundamental Research Funds for the Central Universities(WK2090130025)Anhui Provincial Natural Science Foundation(19O8O85QE2O3).
文摘The parameter study of sinter waste heat recovery in vertical tank was conducted numerically by using energy and exergy analysis,and the experimental data obtained from a homemade experimental apparatus was applied to verify the reliability of numerical model.Based on the first and second laws of thermodynamics,the effects of flow rate of cooling air(FRCA)and inlet temperature of cooling air(ITCA),as well as the inner diameter of cooling section(IDCS)and height of cooling section(HCS),on the sinter cooling process were analyzed in detail.The results show that the average deviation between the experimental data and calculation values is 4.93%,and the model reliability is verified.The enthalpy exergy of outlet air tends to increase first and then decrease with increasing the FRCA and ITCA,while increasing the IDCS only leads to the increase in enthalpy exergy of outlet air.For a given operational condition,the enthalpy exergy of outlet air can reach a maximum value with increasing the HCS.The vertical tank could obtain the maximum enthalpy exergy of outlet air through the adjustments of FRCA and ITCA,as well as the HCS.
文摘In this study an energy and exergy analysis is made of moist air, it is used the psychometrics charts. A Visual Basic program is used to generate psychometrics charts. These charts are used to analyze the air thermodynamic behavior, considering the environmental variations, pressure, temperature and relative humidity. Also, the available energy in the cooling processes at constant enthalpy, humidification at constant temperature and heating with constant relative humidity is analyzed. For example, we obtained that the enthalpy and exergy in a thermodynamic state, with conditions, Patm = 1.013 bar, Tatm = 25oC and Φatm=50%, are h = 50.56 kJ/kga and ε =11.5 kJ/kga;and for Patm= 0.77 bar to the same conditions of Tatm and Φatm, the enthalpy and exergy increases in a 14% and 20%, respectively.
文摘A new small concentrating solar power plant which is suitable for urban area is presented, and a theoretical framework for the energy and exergy analysis in the overall power plant is also constructed. The framework can be used to evaluate the energy and exergy losses in each component. Furthermore, the energy and exergy efficiencies have also been computed and compared for the individual components as well as for the overall plant.
文摘Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps： Removing most of the water content at -40 ℃, removing siloxanes and SVOCs at -85 ℃ and frosting CO2 at temperatures varying from -90 ℃ to -120 ℃. This process transforms biogas containing typically 60% methane, 35% CO2, 5% water vapor in methane containing 2.5% of CO2. This paper studies how a single low-temperature refrigeration system is able to cool biogas with an indirect system using low-temperature heat-transfer fluids. The exergy study defines the exergy losses and served as guidance for the energy/pinch analysis that is used for the design of the heat-exchanger series and the appropriate heat recovery. An optimal system could save up to 40% of the electric consumption of the refrigeration system.
基金supported by the Science and Technology Major Project of Tibet of China(Grant No.XZ201801-GA-03)the Natural Science Foundation of Hunan Province,China(Grant No.2018JJ2399)。
文摘At present,the dual-loop organic Rankine cycle(DORC)is regarded as an important solution to engine waste heat recovery(WHR).Compared with the conventional exergy analysis,the advanced exergy analysis can better describe the interactions between system components and the irreversibility caused by economic or technical limitations.In order to systematically study the thermodynamic performance of DORC,the conventional and advanced exergy analyses are compared using an inline 6-cylinder 4-stroke turbocharged diesel engine.Meanwhile,the sensitivity analysis is implemented to further investigate the influence of operating parameters on avoidable-endogenous exergy destruction.The analysis result of conventional exergy analysis demonstrates that the priorities for the components that should be improved are in order of the high-temperature evaporator,the low-temperature turbine,the first low-temperature evaporator and the high-temperature condenser.The advanced exergy analysis result suggests that the avoidable exergy destruction values are the highest in the low-temperature turbine,the high-temperature evaporator and the high-temperature turbine because they have considerable endogenous-avoidable exergy destruction.The sensitivity analysis indicates that reducing the evaporation pinch point and raising the turbine efficiency can decrease the avoidable exergy destruction.
基金The support of the National Natural Science Founda-tion of China (50976002) is gratefully acknowledged
文摘In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.
基金supported by State Key Program of National Natural Science Foundation of China(51736005)Science and Technology Program of Guangzhou(201704030108)+1 种基金Foshan Municipal Science and Technology Bureau Project(2015IT100162)Guangdong Special Support Program(2017TX04N371)。
文摘Air-conditioning system consumes a large amount of electricity in residential sections,and its efficiency has drawn extensive concerns in energy-conscious era.Liquid-vapor separation is a heat transfer enhancement technology that can effectively improve the performance of the heat exchanger as well as the system.In this paper,a regular air-conditioning system as the baseline(system-A)and other two air-conditioning systems with liquid-vapor separation heat exchanger(system-B and system-C)are comparatively studied.The component behaviors and system performances are deeply explored by using advanced exergy analysis with a focus on quantifying how much consequences come from the variants,i.e.liquid-vapor separation.The results indicate that the system-B has large reduced exergy destruction from the compressor and condenser at cooling mode relative to the system-A.The system-C has mainly diminished exergy destruction in the compressor caused by other components relative to the system-B.At heating mode,the system-C has an enhanced system exergy efficiency of 9.6%over the system-A,and it also has the decreased avoidable exergy destruction which is dominantly contributed by the compressor and evaporator.Furthermore,it is found that liquid-vapor separation mainly benefits the compressor and outdoor heat exchanger where it locates,leading to the system performance improvements.
文摘In order to resolve the problems of the current air separation process such as the complex process, cumbersome operation and high operating costs, a novel air separation process cooled by LNG cold energy is proposed in this paper, which is based on high-efficiency heat exchanger network and chemical packing separation technology. The operating temperature range of LNG cold energy is widened from 133K-203K to l13K-283K by high- efficiency heat exchanger network and air separation pressure is declined from 0.5MPa to about 0.35MPa due to packing separation technology, thereby greatly improve the energy efficiency. Both the traditional and novel air separation processes are simulated with air handling capacity of 20t＇h-1. Comparing with the traditional process, the LNG consumption is reduced by 44.2%, power consumption decrease is 211.5 kWh per hour, which means the annual benefit will be up to 1.218 million CNY. And the exergy efficiency is also improved by 42.5%.
基金Supported by the National Natural Science Foundation of China （90210032, 50576001）.
文摘This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program Aspen Plus. The results indicate that the most important destruction of exergy is found to occur in the reactor and water quenching scrubber, amounting to 8.23% and 10.39%, respectively, of the entire system. Based on the results of thermodynamic and exergy analysis, the acetylene reactor has been retrofitted. The improvement ratios of molar 02 to CH4 and molar CO to CN4 are 0.65 and 0.20, respectively. An improvement of the acetylene production system is proposed. Adopting the improvement operation conditions and using oil to realize the reaction heat recovery, the feedstock of natural gas is reduced by 9.88% and the exergy loss in the retrofitting process is decreased by 19.71% compared to the original process.
文摘To decrease energy consumption of ladle furnace, exergy analysis and optimization were conducted based on the ladle furnace refining process of modern clean steelmaking. Exergy analysis results showed that exergy loss induced by unavailable electric energy is the largest, and the electric energy efficiency is 46.20%. To cut down the unavailable electric energy, industrial experiments of submerged arc heating were carried out combined with slag composition modification. Results showed that submerged arc heating can be achieved within most heating period, average heating rate increased by 0. 5 ℃/min, unavailable electric energy decreased by 21. 730 MJ per ton steel, and electric energy efficiency was enhanced by 14.84 %. As the refining cycle was shortened, the exergy loss induced by heat elimination decreased from 19. 455 MJ per ton steel to 11. 066 MJ per ton steel.
文摘This paper considers the combination of hydrothermal degradation （HTD） and superheated steam （SHS） drying in disposal and processing of degradable organic wastes in municipal solid wastes （MSW）. In SHS drying, a fraction of dryer thermal energy input can be recovered and used to satisfy the heat requirement in maintaining the HTD operating temperature. Both energy and exergy analysis are applied to the combined process. The analysis covers ranges of dryer inlet temperatures of 202.38-234.19~C and feed water content of 32.5-65%. Thermal energy analysis shows that the combination of HTD and SHS drying can achieve thermal energy self-sufficiency （TES） by manipulating process variables. The exergy analysis indicates the location, type, and magnitude of the exergy losses during the whole process by applying the second law of thermodynamics.
文摘In this study, exergy dynamic and advanced exergy analyses are applied to theturbojet engine to assess its mexogenous, endogenous, exogenous, avoidable and unavoidableexergies under the environment conditions of 15 C temperature and 1 bar pressure. Themaximum exergy point in the turbojet engine is found for the combustor in which C11H23(Jet-A1) fuel is combusted with air, while the minimum one is determined for the aircompressor head where the free air enters. The combustion chamber has the maximum fuel,product and irreversibility rates and the air compressor has the minimum fuel and product ex-ergy values, while the minimum irreversibility is found for the turbine. Maximum improvementpotential rate is found for the combustion chamber (5141.27 kW), while minimum rate is deter-mined for the turbine of system (6.95 kW). Also, the turbine component has the highest exergyefficiency (97.20%) due to its expansion process, while combustion chamber component hasthe lowest exergy efficiency (55.39%) due to low efficient combustion process of the fuel.Furthermore, the mexogenous exergy destructions from maximum to minimum are found for the combustion chamber, air compressor and gas turbine units, respectively. Considering exergydynamic analysis, the mexogenous exergy destruction rates of the combustion chamber, aircompressor and gas turbine are found as 184.4 kW, 103.97 kW and 9.99 kW, respectively.Considering all results, the combustion chamber is the primer component to be handled for bet-ter efficiency and improvement.
文摘Gas turbine (GT) power plants operating in arid climates suffer a decrease in output power during the hot summer months because of the high specific volume of air drawn by the compressor. Cooling the air intake to the compressor has been widely used to mitigate this shortcoming. Energy and exergy analysis of a GT Brayton cycle coupled to a refrigeration air cooling unit shows a promise for increasing the output power with a little decrease in thermal efficiency. A thermo-economics algorithm is developed to estimate the economic feasibility of the cooling system. The analysis is applied to an open cycle, HITACHI-FS7001B GT plant at the industrial city of Yanbu (Latitude 24o 05” N and longitude 38o E) by the Red Sea in the Kingdom of Saudi Arabia. Result show that the enhancement in output power depends on the degree of chilling the air intake to the compressor (a 12 - 22 K decrease is achieved). For this case study, maximum power gain ratio (PGR) is 15.46% (average of 12.25%), at an insignificant decrease in thermal efficiency. The second law analysis show that the exergetic power gain ratio drops to an average 8.5%. The cost of adding the air cooling system is also investigated and a cost function is derived that incorporates time-dependent meteorological data, operation characteristics of the GT and the air intake cooling system and other relevant parameters such as interest rate, lifetime, and operation and maintenance costs. The profit of adding the air cooling system is calculated for different electricity tariff.
文摘Large grid-connected photovoltaic(PV)plants are increasingly being installed around the world,including in harsh desert climates.Evaluating their performance can help improve the design and operation of PV systems.This study performed an energy and exergy analysis of a 20-MW grid-connected PV plant under desert climatic conditions in southern Algeria over a period of 1 year.The PV plant was divided into two 10-MW subsystems.Energy analysis was performed using actual irradiation,power output,wind speed and ambient temperature data.The annual average energy efficiency of the plant and subsystems was 10.82%,10.95%and 10.69%,respectively.Solar radiation had the most significant impact(80%determination coefficient)on thermal exergy loss.The exergy efficiency of the plant was lower than the literature values,likely due to the harsh desert conditions.The comprehensive energy and exergy analysis provides insights into the performance of large-scale PV plants in desert climates.The results can help guide the system design and operation improvements for such conditions.Regular cleaning and cooling could improve performance.
