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
Theoretical minimum and actual specific energy consumptions （SEC） of typical manufacturing process （SMP） were studied. Firstly, a process division of a typical SMP in question was conducted with the theory of SEC ...Theoretical minimum and actual specific energy consumptions （SEC） of typical manufacturing process （SMP） were studied. Firstly, a process division of a typical SMP in question was conducted with the theory of SEC analysis. Secondly, an exergy analysis model of a subsystem consisting of several parallel processes and a SEC analysis model of SMP were developed. And finally, based on the analysis models, the SEC of SMP was analyzed by means of the statistical significance. The results show that the SEC of typical SMP comprises the theoretical minimum SEC and the additional SEC derived from the irreversibility~ and the SMP has a theoretical minimum SEC of 6.74 GJ/t and an additional SEC of 19.32 GJ/t, which account for 25.88% and 74.12% of the actual SEC, respectively.展开更多
Current research and ways of capturing mechanical energy are discussed in this paper. By the aid of the comprehensive thermodynamic analysis and Aspen simulation tool, the amount of a vailable work that can be produc...Current research and ways of capturing mechanical energy are discussed in this paper. By the aid of the comprehensive thermodynamic analysis and Aspen simulation tool, the amount of a vailable work that can be produced from capturing the pressure energy has been calculated. Based on the comprehensive thermodynamic analysis, two systems have been proposed to capture pressure energy of natural gas to generate electricity. In this study, the expression of exergy is given which can be used in evaluating purposes. A problem with this multidisciplinary study is the complicated boundary condition. In conclusion, a technical prospect on recoverable natural gas pressure energy has been presented based on total energy system theory.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
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
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
There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level t...There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network （peak shaving） and the advantage of separating the production phase from the exertion phase （time shift）. CAES （compressed air energy storage systems） are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device.展开更多
In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy ...In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy analysis model is applied. The effects of heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures on the exergy loss, exergy efficiency and the coefficient of performance (COP) of the expansion turbine cycle are analyzed. It is found that the great percentages of exergy losses take place in the gas cooler and compressor. Moreover, heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures have strong influence on the exergy efficiency, COP and the exergy loss of each component. The analysis shows that there exists an optimal heat rejection pressure corresponding to the maximum exergy efficiency and COP, respectively. The results are of significance in providing theoretical basis for optimal design and the control of the transcritical carbon dioxide system with an expansion turbine.展开更多
Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines.Instead of wasting the exhaust stream of an energy conversion system into the environment,its residual ener...Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines.Instead of wasting the exhaust stream of an energy conversion system into the environment,its residual energy content can be usefully recovered,for example in Organic Rankine Cycles(ORC).This technology has been largely consolidated in stationary power plants but not yet for mobile applications,such as road transport,due to the limitations in the layout and to the constraints on the size and weight of the ORC system.An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated.The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation.The waste thermal power has been considered as heat input for the ORC plant simulation.A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance.The exergy analysis of the ORC was performed comparing different working fluids:R601,R1233zd(E)and two zeotropic blends of the two organic pure fluids.The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.展开更多
A novel heat-integrated distillation scheme on pilot scale for producing C5 foaming agent, a mixture of isopentane and pentane in a certain proportion, was proposed with the aid of process simulation. Compared with th...A novel heat-integrated distillation scheme on pilot scale for producing C5 foaming agent, a mixture of isopentane and pentane in a certain proportion, was proposed with the aid of process simulation. Compared with the conventional distillation scheme, C5 foaming agent was directly separated at the top of the original isopentane or pentane column in the novel scheme, instead of first refining the two isomerides to high purities and then mixing them into final products. This improvement reduced the difficulty of the separation and avoided meaningless exergy loss caused by re-mixing, which finally contributed to an energy-efficient design by a big margin. Moreover, the column grand composite curves(CGCCs)were used to modify all distillation columns, indicating that there is potential to improve the energy efficiency further. Therefore, double-effect, or heat-integrated distillation was also adopted. Energy and exergy analyses were then conducted to evaluate the effectiveness of the proposed scheme for the purpose of energy saving. The simulation results of the conventional distillation scheme were in agreement with its on-site counterpart. Analyses showed that the novel heat-integrated scheme reduced hot utility by 27.12%,, cold utility by 24.49%,, and total exergy loss by 23.95%,.展开更多
The purpose of this research is to reveal the exergy variation of each component in a direct-expansion solar-assisted heat pump(DX-SAHP)system.Exergy analysis of the DX-SAHP system with R134a is conducted.and the perf...The purpose of this research is to reveal the exergy variation of each component in a direct-expansion solar-assisted heat pump(DX-SAHP)system.Exergy analysis of the DX-SAHP system with R134a is conducted.and the performance evaluation is done.The proposed system is mainly composed of a bare plate solar collec-tor/evaporator,a hermetic variable-frequency rotary-type compressor,a micro-channel condenser and an electronic expansion valve.The experimental data include the exergy loss rates.irreversibility rates and exergy loss ratios of all components and the infuences of ambient temperature on these parameters.The analysis results show that the average irreversibility rate of the compressor is 204.8 W at an ambient temperature of 16℃,and 149.9 W atan ambient temperature of 27℃.The highest irreversibility rate occurs in the compression process,followed by the throttling process.the evaporation process and the condensation process.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 present work deals with the energy end exergy analysis of a system which includes photovoltaic panels providing electricity to a bakery oven. The photovoltaic system （PV） on the bakery unit serves as a model for...The present work deals with the energy end exergy analysis of a system which includes photovoltaic panels providing electricity to a bakery oven. The photovoltaic system （PV） on the bakery unit serves as a model for the installation of PV systems in urbanized areas, which could play a major role in the energy self sufficiency, while at the same time playing a role in the reduction of greenhouse gas emissions. The technology of these systems will be analyzed, as well as the installation of such a system in the building of a bakery unit at the Prefecture of Argolida in Greece with coordinates： latitude 37°34′27″North and longitude 22°50′17″ East. The annual average energy production in horizontal level for 1 kW installed power is 1400 kwh. The Kilowatt peak （kWp） needed for the oven system in the specified area is 29.63 kW. This need of energy can be provided by a PV system that is comprised of 129 PV panels ES-200M60（＋） manufactured by EMMVEE Company at 230 Watts of peak power （Wp） each. The installation of a solar cell is studied with energy storage since the bakery shall be operational at 03.00 am. The exergy of the operating system using electricity from the grid was calculated for the oven temperature of 150 ℃ and up to 220 ℃. The exergy and energy efficiencies were also obtained. The heat lost during the time the oven is not operational was taken into consideration. It was found that 50% of the exergy is being lost, despite the fact that a big amount of heat is being recovered.展开更多
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
Refrigeration plays a significant role across various aspects of human life and consumes substantial amounts of electrical energy.The rapid advancement of green cooling technology presents numerous solar-powered refri...Refrigeration plays a significant role across various aspects of human life and consumes substantial amounts of electrical energy.The rapid advancement of green cooling technology presents numerous solar-powered refrigeration systems as viable alternatives to traditional refrigeration equipment.Exergy analysis is a key in identifying actual thermodynamic losses and improving the environmental and economic efficiency of refrigeration systems.In this study exergy analyze has been conducted for a solar-powered vapor compression refrigeration(SP-VCR)system in the region of Gharda颽(Southern Algeria)utilizing R1234ze(E)fluid as an eco-friendly substitute for R134a refrigerant.A MATLAB-based numerical model was developed to evaluate losses in different system components and the exergy efficiency of the SP-VCR system.Furthermore,a parametric study was carriedout to analyze the impact of various operating conditions on the system’s exergy destruction and efficiency.The obtained results revealed that,for both refrigerants,the compressor exhibited the highest exergy destruction,followed by the condenser,expansion valve,and evaporator.However,the system using R1234ze(E)demonstrated lower irreversibility compared to that using R134a refrigerant.The improvements made with R1234ze are 71.95%for the compressor,39.13%for the condenser,15.38%for the expansion valve,5%for the evaporator,and 54.76%for the overall system,which confirm the potential of R1234ze(E)as a promising alternative to R134a for cooling applications.展开更多
In conventional absorption refrigeration systems(ARS),the heat from the condenser is usually rejected by the environment in place to be used in the system,so recuperating this is a good alternative to enhance the sys...In conventional absorption refrigeration systems(ARS),the heat from the condenser is usually rejected by the environment in place to be used in the system,so recuperating this is a good alternative to enhance the system’s performance.For instance,in this paper,an alternative ARS in which LiBr/Water is used as a refrigerant mixture,where part of condensing heat is recovered via the solution heat recovery generator absorption cycle(HR-ARS)was energy and exergy evaluated.The influence of generator,condenser and evaporator temperatures,as well as the efficiency of the solution heat exchanger on the coefficient of performance,exergy performance and exergy destroyed of the HR-ARS system,were analyzed and compared with the traditional ARS system at the same working conditions.The results showed an increase between 5.8%–6.3%on the COP and 3.7%–9.5%in the exergy efficiency when condenser/absorber temperature was reduced from 40℃ to 30℃.However,when the evaporation temperature rose from 5℃ to 15℃,the COP(coefficient of performance)increased by around 8%,although this could be increased by 2.3%–6.3%if the generator temperature decreases from 100℃ to 80℃.Moreover,the COP and exergetic performance for the HR-ARS is more significant at the lowest generator,condenser and evaporator temperatures,as well as at high efficiency in the solution heat exchanger,in comparison to ARS system.Furthermore,the COP and exergy performance for the HR-ARS system was improved by 2.57%to 3.11%and 0.22%to 0.7%,respectively,while the recovering condensation heat for generation is around 1.51%–3.76%lower than with the ARS.It also was found that for all ranges of evaporator and condenser temperatures,the COP for the HR-ARS system is around 3%higher than that obtained with the ARS at the three different generator temperatures here analyzed,while when the solution heat exchanger effectiveness was increased from 0.7–1.0,the total exergy destruction for the HR-ARS resulted be 3.24%–5.01%smaller than the ARS system.Finally,it can be concluded that the components with the most exergy destroyed in the systems(80%to 94%)are the generator and absorber.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
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
Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem ...Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem from the fact that there are no extra moving parts introduced into the system.The rotary valve is a key component in GM-PTCs that transfers the output exergy from the compressor to the cold head.Because a low Carnot efficiency of 1.58%is achieved at liquid helium temperatures,optimizing the rotary valve is crucial for improving the efficiency of GM-PTCs.In this regard,an exergy-loss analysis method is proposed in this paper to quantitatively obtain the leakage loss and viscosity loss of a rotary valve by experimental measurements.The results show that viscosity loss accounts for more than 97.5%of the total exergy loss in the rotary valve,and that it is possible to improve the structure of the rotary valve by expanding the flow area by 1.5 times.To verify the method,the cooling temperature and power of a remote two-stage GM-PTC were monitored,with original or optimized rotary valves installed.The experimental results show that compared to the original rotary valve,the optimized rotary valve can improve the cooling efficiency of a GM-PTC by 16.4%,with a cooling power of 0.78 W at 4.2 K.展开更多
A grey-box modelling framework was developed for the estimation of cut point temperature of a crude distillation unit(CDU)under uncertainty in crude composition and process conditions.First principle(FP)model of CDU w...A grey-box modelling framework was developed for the estimation of cut point temperature of a crude distillation unit(CDU)under uncertainty in crude composition and process conditions.First principle(FP)model of CDU was developed for Pakistani crudes from Zamzama and Kunnar fields.A hybrid methodology based on the integration of Taguchi method and genetic algorithm(GA)was employed to estimate the optimal cut point temperature for various sets of process variables.Optimised datasets were utilised to develop an artificial neural networks(ANN)model for the prediction of optimum values of cut points.The ANN model was then used to replace the hybrid framework of the Taguchi method and the GA.The integration of the ANN and FP model makes it a grey-box(GB)model.For the case of Zamama crude,the GB model helped in the decrease of up to 38.93%in energy required per kilo barrel of diesel and an 8.2%increase in diesel production compared to the stand-alone FP model under uncertainty.Similarly,for Kunnar crude,up to 18.87%decrease in energy required per kilo barrel of diesel and a 33.96%increase in diesel production was observed in comparison to the stand-alone FP model.展开更多
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.
基金Item Sponsored by Fundamental Research Funds for the Central Universities of China(N090602007)National Key Technology Research and Development Program in 11th Five-Year Plan Project of China(2006BAE03A09)
文摘Theoretical minimum and actual specific energy consumptions （SEC） of typical manufacturing process （SMP） were studied. Firstly, a process division of a typical SMP in question was conducted with the theory of SEC analysis. Secondly, an exergy analysis model of a subsystem consisting of several parallel processes and a SEC analysis model of SMP were developed. And finally, based on the analysis models, the SEC of SMP was analyzed by means of the statistical significance. The results show that the SEC of typical SMP comprises the theoretical minimum SEC and the additional SEC derived from the irreversibility~ and the SMP has a theoretical minimum SEC of 6.74 GJ/t and an additional SEC of 19.32 GJ/t, which account for 25.88% and 74.12% of the actual SEC, respectively.
基金Supported by Tianjin Institute of Urban Construction(03046)
文摘Current research and ways of capturing mechanical energy are discussed in this paper. By the aid of the comprehensive thermodynamic analysis and Aspen simulation tool, the amount of a vailable work that can be produced from capturing the pressure energy has been calculated. Based on the comprehensive thermodynamic analysis, two systems have been proposed to capture pressure energy of natural gas to generate electricity. In this study, the expression of exergy is given which can be used in evaluating purposes. A problem with this multidisciplinary study is the complicated boundary condition. In conclusion, a technical prospect on recoverable natural gas pressure energy has been presented based on total energy system theory.
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.
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.
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.
文摘There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers＇ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network （peak shaving） and the advantage of separating the production phase from the exertion phase （time shift）. CAES （compressed air energy storage systems） are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device.
基金SupportedbytheSpecializedResearchFundfortheDoctoralProgramofHigherEducation (No .D0 2 0 0 10 5)
文摘In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy analysis model is applied. The effects of heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures on the exergy loss, exergy efficiency and the coefficient of performance (COP) of the expansion turbine cycle are analyzed. It is found that the great percentages of exergy losses take place in the gas cooler and compressor. Moreover, heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures have strong influence on the exergy efficiency, COP and the exergy loss of each component. The analysis shows that there exists an optimal heat rejection pressure corresponding to the maximum exergy efficiency and COP, respectively. The results are of significance in providing theoretical basis for optimal design and the control of the transcritical carbon dioxide system with an expansion turbine.
基金The authors gratefully acknowledge Universitàdegli studi della Campania“L.Vanvitelli”for funding the research project CHIMERA with V:ALERE 2019 grant。
文摘Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines.Instead of wasting the exhaust stream of an energy conversion system into the environment,its residual energy content can be usefully recovered,for example in Organic Rankine Cycles(ORC).This technology has been largely consolidated in stationary power plants but not yet for mobile applications,such as road transport,due to the limitations in the layout and to the constraints on the size and weight of the ORC system.An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated.The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation.The waste thermal power has been considered as heat input for the ORC plant simulation.A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance.The exergy analysis of the ORC was performed comparing different working fluids:R601,R1233zd(E)and two zeotropic blends of the two organic pure fluids.The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.
基金Supported by the Program of Introduction of Talents of Discipline to Universities(B06006)
文摘A novel heat-integrated distillation scheme on pilot scale for producing C5 foaming agent, a mixture of isopentane and pentane in a certain proportion, was proposed with the aid of process simulation. Compared with the conventional distillation scheme, C5 foaming agent was directly separated at the top of the original isopentane or pentane column in the novel scheme, instead of first refining the two isomerides to high purities and then mixing them into final products. This improvement reduced the difficulty of the separation and avoided meaningless exergy loss caused by re-mixing, which finally contributed to an energy-efficient design by a big margin. Moreover, the column grand composite curves(CGCCs)were used to modify all distillation columns, indicating that there is potential to improve the energy efficiency further. Therefore, double-effect, or heat-integrated distillation was also adopted. Energy and exergy analyses were then conducted to evaluate the effectiveness of the proposed scheme for the purpose of energy saving. The simulation results of the conventional distillation scheme were in agreement with its on-site counterpart. Analyses showed that the novel heat-integrated scheme reduced hot utility by 27.12%,, cold utility by 24.49%,, and total exergy loss by 23.95%,.
基金the National Natural Science Foundation of China(No.51776115)the Shandong Province Graduate Student Supervisor Guidance Ability Promotion Program(No.SDYY17037)the Shandong University of Science and Technology Graduate Student Supervisor Guidance Ability Promotion Program(No.KDYC17009)。
文摘The purpose of this research is to reveal the exergy variation of each component in a direct-expansion solar-assisted heat pump(DX-SAHP)system.Exergy analysis of the DX-SAHP system with R134a is conducted.and the performance evaluation is done.The proposed system is mainly composed of a bare plate solar collec-tor/evaporator,a hermetic variable-frequency rotary-type compressor,a micro-channel condenser and an electronic expansion valve.The experimental data include the exergy loss rates.irreversibility rates and exergy loss ratios of all components and the infuences of ambient temperature on these parameters.The analysis results show that the average irreversibility rate of the compressor is 204.8 W at an ambient temperature of 16℃,and 149.9 W atan ambient temperature of 27℃.The highest irreversibility rate occurs in the compression process,followed by the throttling process.the evaporation process and the condensation process.
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.
文摘The present work deals with the energy end exergy analysis of a system which includes photovoltaic panels providing electricity to a bakery oven. The photovoltaic system （PV） on the bakery unit serves as a model for the installation of PV systems in urbanized areas, which could play a major role in the energy self sufficiency, while at the same time playing a role in the reduction of greenhouse gas emissions. The technology of these systems will be analyzed, as well as the installation of such a system in the building of a bakery unit at the Prefecture of Argolida in Greece with coordinates： latitude 37°34′27″North and longitude 22°50′17″ East. The annual average energy production in horizontal level for 1 kW installed power is 1400 kwh. The Kilowatt peak （kWp） needed for the oven system in the specified area is 29.63 kW. This need of energy can be provided by a PV system that is comprised of 129 PV panels ES-200M60（＋） manufactured by EMMVEE Company at 230 Watts of peak power （Wp） each. The installation of a solar cell is studied with energy storage since the bakery shall be operational at 03.00 am. The exergy of the operating system using electricity from the grid was calculated for the oven temperature of 150 ℃ and up to 220 ℃. The exergy and energy efficiencies were also obtained. The heat lost during the time the oven is not operational was taken into consideration. It was found that 50% of the exergy is being lost, despite the fact that a big amount of heat is being recovered.
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Refrigeration plays a significant role across various aspects of human life and consumes substantial amounts of electrical energy.The rapid advancement of green cooling technology presents numerous solar-powered refrigeration systems as viable alternatives to traditional refrigeration equipment.Exergy analysis is a key in identifying actual thermodynamic losses and improving the environmental and economic efficiency of refrigeration systems.In this study exergy analyze has been conducted for a solar-powered vapor compression refrigeration(SP-VCR)system in the region of Gharda颽(Southern Algeria)utilizing R1234ze(E)fluid as an eco-friendly substitute for R134a refrigerant.A MATLAB-based numerical model was developed to evaluate losses in different system components and the exergy efficiency of the SP-VCR system.Furthermore,a parametric study was carriedout to analyze the impact of various operating conditions on the system’s exergy destruction and efficiency.The obtained results revealed that,for both refrigerants,the compressor exhibited the highest exergy destruction,followed by the condenser,expansion valve,and evaporator.However,the system using R1234ze(E)demonstrated lower irreversibility compared to that using R134a refrigerant.The improvements made with R1234ze are 71.95%for the compressor,39.13%for the condenser,15.38%for the expansion valve,5%for the evaporator,and 54.76%for the overall system,which confirm the potential of R1234ze(E)as a promising alternative to R134a for cooling applications.
文摘In conventional absorption refrigeration systems(ARS),the heat from the condenser is usually rejected by the environment in place to be used in the system,so recuperating this is a good alternative to enhance the system’s performance.For instance,in this paper,an alternative ARS in which LiBr/Water is used as a refrigerant mixture,where part of condensing heat is recovered via the solution heat recovery generator absorption cycle(HR-ARS)was energy and exergy evaluated.The influence of generator,condenser and evaporator temperatures,as well as the efficiency of the solution heat exchanger on the coefficient of performance,exergy performance and exergy destroyed of the HR-ARS system,were analyzed and compared with the traditional ARS system at the same working conditions.The results showed an increase between 5.8%–6.3%on the COP and 3.7%–9.5%in the exergy efficiency when condenser/absorber temperature was reduced from 40℃ to 30℃.However,when the evaporation temperature rose from 5℃ to 15℃,the COP(coefficient of performance)increased by around 8%,although this could be increased by 2.3%–6.3%if the generator temperature decreases from 100℃ to 80℃.Moreover,the COP and exergetic performance for the HR-ARS is more significant at the lowest generator,condenser and evaporator temperatures,as well as at high efficiency in the solution heat exchanger,in comparison to ARS system.Furthermore,the COP and exergy performance for the HR-ARS system was improved by 2.57%to 3.11%and 0.22%to 0.7%,respectively,while the recovering condensation heat for generation is around 1.51%–3.76%lower than with the ARS.It also was found that for all ranges of evaporator and condenser temperatures,the COP for the HR-ARS system is around 3%higher than that obtained with the ARS at the three different generator temperatures here analyzed,while when the solution heat exchanger effectiveness was increased from 0.7–1.0,the total exergy destruction for the HR-ARS resulted be 3.24%–5.01%smaller than the ARS system.Finally,it can be concluded that the components with the most exergy destroyed in the systems(80%to 94%)are the generator and absorber.
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.
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 National Key Research&Development Program of China(No.2023YFF0721304)the Key Research&Development Program of Jiangsu Province(No.2021015-4),China。
文摘Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem from the fact that there are no extra moving parts introduced into the system.The rotary valve is a key component in GM-PTCs that transfers the output exergy from the compressor to the cold head.Because a low Carnot efficiency of 1.58%is achieved at liquid helium temperatures,optimizing the rotary valve is crucial for improving the efficiency of GM-PTCs.In this regard,an exergy-loss analysis method is proposed in this paper to quantitatively obtain the leakage loss and viscosity loss of a rotary valve by experimental measurements.The results show that viscosity loss accounts for more than 97.5%of the total exergy loss in the rotary valve,and that it is possible to improve the structure of the rotary valve by expanding the flow area by 1.5 times.To verify the method,the cooling temperature and power of a remote two-stage GM-PTC were monitored,with original or optimized rotary valves installed.The experimental results show that compared to the original rotary valve,the optimized rotary valve can improve the cooling efficiency of a GM-PTC by 16.4%,with a cooling power of 0.78 W at 4.2 K.
基金Higher Education Commission,Pakistan,under the National Research Program for Universities Project,Grant/Award Number:NBU-FPEJ-2024-1243-02。
文摘A grey-box modelling framework was developed for the estimation of cut point temperature of a crude distillation unit(CDU)under uncertainty in crude composition and process conditions.First principle(FP)model of CDU was developed for Pakistani crudes from Zamzama and Kunnar fields.A hybrid methodology based on the integration of Taguchi method and genetic algorithm(GA)was employed to estimate the optimal cut point temperature for various sets of process variables.Optimised datasets were utilised to develop an artificial neural networks(ANN)model for the prediction of optimum values of cut points.The ANN model was then used to replace the hybrid framework of the Taguchi method and the GA.The integration of the ANN and FP model makes it a grey-box(GB)model.For the case of Zamama crude,the GB model helped in the decrease of up to 38.93%in energy required per kilo barrel of diesel and an 8.2%increase in diesel production compared to the stand-alone FP model under uncertainty.Similarly,for Kunnar crude,up to 18.87%decrease in energy required per kilo barrel of diesel and a 33.96%increase in diesel production was observed in comparison to the stand-alone FP model.
