Exogenous Exergy Destruction Research Articles

Advanced exergy analysis of solar absorption-subcooled compression hybrid cooling system

ABSTRACT The solar absorption-subcooled compression hybrid cooling system (SASCHCS), in which the cooling capacity of absorption subsystem serves as the subcooling power of compression subsystem, is energy-efficient for high-rise buildings. Because the existing design guideline of system is based on the conventional exergy theory and the advanced exergy analysis of absorption and vapor compression chillers is from the endogenous avoidable portion instead of the sum of the avoidable exergy destruction, it is incapable to design the SASCHCS exactly by such findings. As a result, the systematical advanced exergy analysis of SASCHCS is performed. The advanced exergy model of facilities is built at first. Subsequently, various exergy destructions for different conditions are analyzed. Finally, the improvement potential of components is assessed based on the sum of the avoidable exergy destruction, defined as the sum of endogenous avoidable portion of k-th component and exogenous one of remaining components led by irreversibilities of k-th component. Though the compressor concentrates the most exergy destruction of SASCHCS, 62% of its exogenous exergy destruction is caused by the irreversibilities of the condenser of the compression subsystem, making the condenser the most important component of SASCHCS. The paper is helpful to promote the design of SASCHCS.

Novel combined extended-advanced exergy analysis methodology as a new tool to assess thermodynamic systems

In this study, a novel combined extended-advanced exergy analysis method is developed for assessing thermodynamic systems. The method is established by combining extended exergy analysis with advanced exergy analysis and the so-called extended-advanced exergy analysis. The methodology used in the novel analysis method is different from only extended exergy analysis and only advanced exergy analysis, but the criteria are the same to reach the goal. This proposed method is applied to a gas turbine system as a case study to show its variability. The gas turbine system considered consists of a combustion chamber, a compressor and turbine units. The conventional (Fuel-Product approach), advanced and extended exergy analyses are separately applied to the case study system for the comparison with the novel combined extended-advanced exergy analysis. It is seen that the combined extended-advanced exergy analysis results of the case study are not exactly the same with the advanced and extended exergy analyses’ results. The reason for this is its comprehensive joint of various thermodynamic analysis methodologies integrating all materials, capital, labor, energy and environmental effect instead of the relation between components and their improvement potentials in one analysis. But it is assessed that the novel analysis tool is able to apply all of those analyses into one simple methodology. The exergy efficiencies of the case study are 28% and 31% by considering the conventional and extended exergy analyses, respectively. This means that all input parameters including labor, capital and environment are used with better efficiency. Also, the exogenous exergy destruction rate (159 kW) is higher for the combined extended-advanced exergy analysis (384 kW). This shows that the relations between other components are increased for the turbine. Another important change is shown in avoidable exogenous exergy destruction rate for the turbine, increasing from 374 kW to 833 kW. This new combined method is useful to those, who wish to apply advanced and extended exergy analyses through a new practical assessment way.

Application of advanced exergy analysis for optimizing the design of carbon dioxide pressurization system

The pressurization of carbon dioxide is an integral step of the carbon capture and storage process; a key technology frontier for the decarbonization of power and heat industry. Effective measures to improve the pressurization scheme directly translate into the reduction of process costs. This study aimed to reduce the energy expenditure of the carbon dioxide pressurization process by assisting the conventional carbon dioxide multi-stage compressors with an Ammonia (R717) or Propane (R290) based heat-pump system. In these systems, carbon dioxide is liquefied in the heat-pump after being compressed to an intermediate liquefaction pressure. The liquefied carbon dioxide is subsequently pumped to the target pressure. In this study, the advanced exergy analysis, in addition to the conventional energy analysis is applied to design and optimize the carbon dioxide liquefaction system using a heat pump. The initial conventional exergy analysis reveals that 43.76% of total fuel exergy is destroyed and lost. Subsequently, the advanced exergy analysis is performed to pinpoint the source of total irreversibility (exergy destruction), calculate the avoidable exergy destruction in the system and figure out potential measures to improve the system’s performance. The advanced exergy analysis reveals the avoidable exergy destruction is 48.85% and 51.20% of the total exergy destruction for R290 and R717, respectively. Furthermore, the avoidable exogenous exergy destruction is 16% and 19%, respectively. The results also show that for R717, the extent of improvement is in the following order, Condenser > Compressor > Evaporator > Expansion valve. With this information, a systematic approach is devised and followed to optimize the operating parameters and design of the heat-pump system. Furthermore, in the proposed system, 2328.6 kW of exergy is lost to the environment. To recover this exergy loss, the heat pump-assisted pressurization scheme is integrated with a supercritical carbon dioxide power cycle which generated 1191.00 kW of electric power. The results reveal that the electrical power consumed by the proposed system optimized through advanced exergy analysis is 15.5% lower than that consumed by a benchmark system. The study demonstrates the effectiveness of advanced exergy analysis and the approach presented here can be extended to other energy conversion systems to maximize the energy and exergy savings for sustainable development.

Exergy destruction analysis of a low-temperature Compressed Carbon dioxide Energy Storage system based on conventional and advanced exergy methods

Compressed Carbon dioxide Energy Storage (CCES) system is a novel energy storage technology, which provides a new method to solve the unstable problem of renewable energy. Since the CCES system using low-temperature thermal energy storage can avoid the technical difficulties from high-temperature thermal energy storage, the low-temperature Compressed Carbon dioxide Energy Storage (LT-CCES) system has more obvious application feasibility compared with the high-temperature energy storage system. As the research on energy conversion, transfer, and loss in CCES system under low-temperature heat storage is still missing, while it is important to understand the energy losses for the further optimization of this kind of system, in this paper, the conventional exergy analysis and advanced exergy analysis were utilized to analyze the thermodynamic characteristics of a LT-CCES system consisting of CO2 Brayton cycle, low-temperature thermal energy storage and cold energy storage, whose thermal energy storage temperature is below 200 °C. As the advanced exergy analysis takes into account the correlation between system components as well as the technical limitations of each component, exergy destruction can be split into more detailed parts (i.e., avoidable exergy destruction, unavoidable exergy destruction, endogenous exergy destruction, and exogenous exergy destruction), which makes the results of the advanced exergy analysis different from those of conventional exergy analysis. The results showed that, advanced exergy analysis pointed out that HEX3 should be given priority as endogenous avoidable exergy destruction in HEX3 was the largest, while the results from the conventional exergy analysis showed that HEX1 should be given priority. For all the components, the two methods indicated that the compressor should be given the highest priority for improvement, followed by the turbine. Besides, as the total exergy efficiency of the system was 55.3% under the real condition and the total exergy efficiency was 76.7% under the unavoidable condition, there was still room for improvement of the system. In brief, based on the advanced exergy analysis method, the real component that should be paid attention can be determined, which gives the designers a more profound understanding of exergy destruction in the LT-CCES system.

Conventional and Advanced Exergy-Based Analysis of Hybrid Geothermal–Solar Power Plant Based on ORC Cycle

Today, as fossil fuels are depleted, renewable energy must be used to meet the needs of human beings. One of the renewable energy sources is undoubtedly the solar–geothermal power plant. In this paper, the conventional and advanced, exergo-environmental and exergo-economic analysis of a geothermal–solar hybrid power plant (SGHPP) based on an organic Rankin cycle (ORC) cycle is investigated. In this regard, at first, a conventional analysis was conducted on a standalone geothermal cycle (first mode), as well as a hybrid solar–geothermal cycle (second mode). The results of exergy destruction for simulating the standalone geothermal cycle showed that the ORC turbine with 1050 kW had the highest exergy destruction that was 38% of the total share of destruction. Then, the ORC condenser with 26% of the total share of exergy destruction was in second place. In the hybrid geothermal–solar cycle, the solar panel had the highest environmental impact and about 56% of the total share of exergy destruction. The ORC turbine had about 9% of all exergy destruction. The results of the advanced analysis of exergy in the standalone geothermal cycle showed that the avoidable exergy destruction of the condenser was the highest. In the hybrid geothermal–solar cycle, the solar panel, steam economizer and steam evaporator were ranked first to third from an avoidable exergy destruction perspective. The avoidable exergo-economic destruction of the evaporator and pump were higher than the other components. The hybrid geothermal–solar cycle, steam economizer, solar pane and steam evaporator were ranked first to third, respectively, and they could be modified. The avoidable exergo-environmental destruction of the ORC turbine and the ORC pump were the highest, respectively. In the hybrid geothermal–solar cycle, steam economizers, solar panel and steam evaporators had the highest avoidable exergy destruction, respectively. For the standalone geothermal cycle, the total endogenous exergy destruction and exogenous exergy destruction was 83.61% and 16.39%. Moreover, from an exergo-economic perspective, 89% of the total destruction rate was endogenous and 11% was exogenous. From an exergo-environmental perspective, 88.73% of the destruction rate was endogenous and 11.27% was exogenous. For the hybrid geothermal–solar cycle, the total endogenous and exogenous exergy destruction was 75.08% and 24.92%, respectively. Moreover, 81.82% of the exergo-economic destruction rate was endogenous and 18.82% was exogenous. From an exergo-environmental perspective, 81.19% of the exergy destruction was endogenous and 18.81% was exogenous.

Advanced Exergy Analysis in the Dynamic Framework for Assessing Building Thermal Systems.

This work applies the Dynamic Advanced Exergy Analysis (DAEA) to a heating and domestic hot water (DHW) facility supplied by a Stirling engine and a condensing boiler. For the first time, an advanced exergy analysis using dynamic conditions is applied to a building energy system. DAEA provides insights on the components’ exergy destruction (ED) by distinguishing the inefficiencies that can be prevented by improving the quality (avoidable ED) and the ones constrained because of technical limitations (unavoidable ED). ED is related to the inherent inefficiencies of the considered element (endogenous ED) and those coming from the interconnections (exogenous ED). That information cannot be obtained by any other approach. A dynamic calculation within the experimental facility has been performed after a component characterization driven by a new grey-box modelling technique, through TRNSYS and MATLAB. Novel solutions and terms of ED are assessed for the rational implementation of the DAEA in building energy installations. The influence of each component and their interconnections are valuated in terms of exergy destruction for further diagnosis and optimization purposes.

Advanced exergy analysis of recompression supercritical CO2 cycle

Conventional and advanced exergy analysis of a recompression supercritical CO2 cycle was investigated in this study. The first and second splitting levels of exergy destruction are calculated to determine the real potential of enhancement for the S-CO2 cycle performance. The thermodynamic cycle method of advanced exergy analysis is applied in the present work to reveal the endogenous, exogenous, avoidable, unavoidable, avoidable endogenous, unavoidable endogenous, avoidable exogenous, and unavoidable exogenous exergy destruction for each system component. The overall exergy efficiency for the system are determined as 16.63% and 17.13% under real and unavoidable conditions, respectively. Based on the total avoidable exergy destruction rate, the maximum improvement potential for the system is 106.855 MW (about 50% of the total exergy destruction), and of this avoidable value, 34.59% is endogenous, and 65.41% is exogenous. It is also revealed that, for improving the overall system performance, the priority order of components obtained by the conventional exergy analysis is different from that achieved by the advanced exergy analysis. The former suggests this order as: the reactor, the pre-cooler, the LTR, the HTR and the turbine, while the latter recommends the priority as the HTR, the turbine, and the main compressor. The results also indicate that the reactor has the least potential for improvement despite its highest exergy destruction.

Calculating Endogenous and Exogenous Exergy Destruction for an Experimental Turbojet Engine

Abstract Thermodynamic analysis that provides the status and amount of irreversibility is a powerful tool to determine performance parameters of energy conversion systems. However, specifying the location and amount of irreversibility of a system or component does not reveal the full extent of the relationship of the irreversibility between component-component/component-system. Therefore, splitting the exergy destruction into endogenous and exogenous parts provides detailed information on the relationship of the irreversibility between component-component/component-system. The purpose of this paper is to identify the endogenous and exogenous parts of exergy destruction of an experimental turbojet engine (Unmanned Aerial Vehicle Turbojet – UAVT). Test data used for exergy analysis were evaluated at the maximum load of the experimental turbojet engine which consisted of a compressor, a combustion chamber and a turbine. As a result of the endogenous and exogenous parts of the exergy destruction, the majority of the total exergy destruction (15.1416 kW) was calculated as the endogenous part of exergy destruction (13.5473 kW), and the exogenous exergy destruction rate was calculated to be 1.5943 kW in the compressor component of the turbojet engine. In this study, the endogenous and exogenous exergy destruction amounts of other components are also presented in details.

Improvements perspectives of cryogenics-based energy storage

Advanced exergy-based analyses provide the information for potential of improvement of energy- conversion systems from exergetic, economic and environmental point of view. These analyses are applied to Cryogenic-based Energy Storage (CES) also known as Liquid Air Energy Storage (LAES). Advantages such as (a) lack of geographical restrictions, (b) low environmental impact and the fact that it is (c) based on mature technology, drive further the research on this energy storage system. An adiabatic LAES system charged with Heylandt liquefaction of air process is analysed. Parameters such as exergy destruction, investment cost, cost associated with the exergy destruction, as well as the environmental impact associated with the thermodynamic irreversibilities are split into avoidable/unavoidable and endogenous/exogenous parts. Aspen Plus® software was used to simulate the LAES system and Engineering Equation Solver was used to conduct the conventional and advanced exergy-based analyses. The dependence of the improvement of each component with the rest of the system was found and all components present higher exogenous exergy destruction than endogenous. The component with the highest potential for improvement is the main heat exchanger in the discharge unit. Focusing on improvement of the components that were found to be the most inefficient ones with the highest exergy destruction, CES is expected to become thermodynamically and economically feasible.

Advanced exergy-based methods used to understand and improve energy-conversion systems

Exergy-based methods are powerful tools for developing, evaluating, understanding, and improving energy conversion systems. This paper deals with integrated advanced exergy-based evaluations. In addition to conventional methods, advanced exergy-based analyses consider (a) the interactions among components of the overall system, and (b) the real potential for improving each important system component. The main role of an advanced analysis is to provide energy conversion system designers and operators with information useful for improving the design and operation of such systems. Splitting the exergy destruction, the capital investment cost, and the component-related environmental impact associated with each single component of an energy conversion system into endogenous/exogenous and avoidable/unavoidable parts and using a further splitting of the exogenous exergy destruction improves (a) our understanding of the processes that take place, and (b) the quality of the conclusions for improvement obtained from the analysis. This paper discusses the main features and some recent developments in the area of advanced exergy-based methods. Application of the method to a simple air refrigeration machine confirms the correctness of the approach.

Thermodynamic analysis of a novel supercritical compressed carbon dioxide energy storage system through advanced exergy analysis

Abstract To reveal the sources of energy-saving potential of each component and compare the thermodynamic properties of the compressed air energy storage (CAES) system and the supercritical compressed CO2 energy storage (SC-CCES) system, most related works have been done using conventional exergy analysis. However, conventional exergy analysis cannot reveal the thermodynamic interactions among components. Therefore, conventional and advanced exergy analyses are applied to evaluating the CAES and SC-CCES performances in this paper. In addition, sensitivity investigations are conducted to evaluate the influence of decision variables on the performances of CAES and SC-CCES. The results show that the SC-CCES exergy efficiency is 57.02%, which is preferable and performs better than that of CAES (50.86%) and the interactions among different components are not strong since the endogenous exergy destruction rates of the components are larger than the exogenous exergy destruction rates in CAES and SC-CCES. Sensitivity analyses show that a larger efficiency of compressor, turbine, and combustor improves the SC-CCES and CAES performances. The effects of pressure drops in high pressure reservoir in SC-CCES are similar to those in storage cavern in CAES. Improving the performance of reservoir throttle valve itself is an effective way to improve the SC-CCES and CAES performances.

Advanced exergetic analysis of a heat pump providing space heating in built environment

In addition to conventional exergy-based methods, advanced exergetic analyses consider the interactions among components of the energy-conversion system and the real potential for improving each system component. The paper demonstrates the results of application of a detailed advanced exergetic analysis to a wastewater source heat pump providing space heating in the built environment. In order to determine thermodynamic parameters of the refrigeration vapour compression cycle in different operating modes, the simulation model has been used. The analysis includes splitting the exergy destruction within each component of a heat pump into unavoidable, avoidable, endogenous and exogenous parts as well as detailed splitting of the avoidable exogenous exergy destruction. Besides, variabilities of heating demands of a building within both the chosen heating season and also from year to year are taken into account. Distribution of the split exergy destructions during different periods of time is also presented for the analysed cases of the heat pump and built environment. It is shown that in the investigated system only about 50% of the total annual destruction in components of the heat pump can be avoided. About 30…40% of this avoidable thermodynamic inefficiency is caused by interactions among components. Based on the applied advanced exergetic analysis it is possible to receive more precise and useful information for better understanding and improving the design and operation of the analysed energy-conversion system.

Advanced exergy analysis for an anode gas recirculation solid oxide fuel cell

Abstract Advanced exergy analysis is performed for a solid oxide fuel cell with anode gas recirculation. For this purpose, the unavoidable conditions are determined by specifying the most important electrochemical parameters resulting in the best possible performance. It is observed that, under the unavoidable conditions, the fuel cell exergy efficiency can be 32% higher and the exergy destruction can be 38% lower, compared to the corresponding values under real conditions. The analysis revealed the values of first level splitting of exergy destruction including the avoidable/unavoidable and endogenous/exogenous exergy destructions for all the system components. In addition, the second level splitting of exergy destruction including the unavoidable endogenous, unavoidable exogenous, avoidable endogenous and avoidable exogenous exergy destructions are determined for all the system components. The results show that of the total exergy destruction in the system, 62% is endogenous and 38% is exogenous. Also, 54% of the total exergy destruction is avoidable and the rest, 46%, is unavoidable. In addition, it is observed that the order of component contribution in the total avoidable endogenous exergy destruction of the system is: the inverter, 6.52 kW, the stack, 3.6 kW and the afterburner, 0.62 kW. This result is different from that obtained from conventional exergy analysis suggesting that attention should be paid first on the stack, then on the afterburner and afterward on the inverter. Furthermore, it is observed that almost half of the avoidable exergy destruction in the stack,7.56 kW (51%), occurs exogenously. Therefore, for reducing exergy destruction in the stack an enhancement in the stack and the other system component is required.

Parametric study of a hybrid one column air separation unit (ASU) and CO2 power cycle based on advanced exergy cost analysis results

In this study advanced exergy and exergoeconomic analyses are performed on the integrated cryogenic air separation unit (ASU), oxy-fuel carbon dioxide power cycle and LNG vaporization process. Advanced exergy results show that endogenous part of exergy destruction is more than exogenous part which means interactions between the process components is not significant. CR-4 compressor with 190,095 kW exogenous exergy destruction rate has the highest share of this type of exergy destruction among the process components. Advanced exergoeconomic analysis results show that interactions between the process components are weak. That is because of large values of endogenous part towards the exogenous part. Among investigated process components unavoidable exergy destruction cost rate of heat exchanger (H-1) and combustion chamber is higher than the avoidable part. Avoidable/endogenous exergy destruction cost rate of P-1, CR-1 and H-8 components is the highest and consequently these elements will have the highest priority for the optimization. The capital investment and operating and maintenance cost rate of pump (P-1) is 10,018 $/h. This value reveals that saving the money from the operating and maintenance costs will make up the replacement cost of this component with the high-tech ones. Based on the parametric analysis, the optimum design parameters of pump (P-1), compressor (CR-1) and heat exchanger (H-8) are ηis=82%, rp=6.195 and ΔTmin=2K, respectively.

Malfunction diagnosis of thermal power plants based on advanced exergy analysis: The case with multiple malfunctions occurring simultaneously

During continuous operation of energy systems, the performance of components will mostly, gradually deviate away from the reference conditions due to performance degradation, which may eventually lead to malfunctions or operation failure. The complex interconnection among components and the propagation nature of additional irreversibility caused by malfunctions increase the difficulty of malfunction diagnosis. Particularly, in common real-world cases, multiple malfunctions usually happen simultaneously in several different components, imposing additional difficulty for effective malfunction identification and quantification. In this paper, we generalize an effective diagnosis method recently proposed by the authors to accurately locate the malfunction component and quantify the effect caused by anomalies of multiple malfunctions. The generalized method is based on advanced exergy analysis, where exergy destruction within each component is split into endogenous and exogenous parts. The endogenous exergy destruction is due to the irreversibility of the component itself, while the exogenous is caused by the inefficiencies of the remaining components. The exogenous exergy destruction is, in fact, the major obstacle to accurately pinpoint the origins of performance degradation. In the generalized approach, an internal exergy indicator is recommended to be applied first to identify the malfunction components in a fast and effective manner. Then the endogenous exergy destruction of the identified malfunction components under the reference and degradation conditions is calculated and compared for accurate quantification. The generalized diagnosis approach is applied to a complex real-world case studies, in which several malfunctions are introduced simultaneously into different components. The results show that the proposed indicator could fast identify the source of anomalies while the endogenous exergy destruction successfully and effectively quantifies all introduced malfunctions.

A decomposition method for the evaluation of component interactions in energy conversion systems for application to advanced exergy-based analyses

A new approach for the calculation of the interactions among the components of a thermal system for application to the concept of advanced exergy-based analysis is presented. The approach can be used to determine the thermodynamic interactions of system components, and to evaluate alternative designs. The new approach puts the calculation of endogenous and exogenous exergy destruction on a proper thermodynamic basis and introduces a straightforward and time-saving calculation procedure in contrast to various approaches used in the past. When employed to the analysis of the CGAM-problem, the new approach complies with qualitative reasoning, resolves the shortcomings and shows comparable results with previous approaches. The top-down hierarchical approach assists in achieving the best system design possible by identifying the effects of design decisions and by stimulating the engineer's creativity in terms of design alternatives and optimization options. Furthermore, the generalization of the approach allows for any level of aggregation, thus, making the determination of improvement potentials easier. By providing profound thermodynamic understanding for processes, the advanced exergy-based analysis is a promising tool for designing, analyzing and optimizing processes for higher efficiencies and lower costs.

Application of exergoeconomic, exergoenvironmental, and advanced exergy analyses to Carbon Black production

Carbon Black is an industrial produced material of fine carbon particles. These particles are aggregates of primary particles having a mean diameter usually below 1μm. Carbon Black is mainly used in printing and coating applications as a pigment, in plastic applications as a UV protector, and in rubber applications as filler material to improve mainly the mechanical properties of the rubber like stiffness and abrasion resistance. Volume wise the most important production technique is the furnace black production. For this work, a Carbon Black Plant is modeled using a free available tool called COFE. The behavior of the components was verified by measurements. The effects of components' exergy destruction on the system's exergoeconomic and exergoenvironmental behavior are analyzed. Furthermore, the interdependencies between components are studied. The burners have the highest exergy destruction among all components of the total plant. These burners however, neither have the highest impact on cost generation caused by exergy destruction, nor the highest impact on the exergoenvironmental values. Nonetheless, they contribute significantly to the exogenous exergy destruction within other components. The largest cost generation takes place within the boilers' heat exchangers. The most important components for the exergoenvironmental analysis are the reactors.

Performance degradation diagnosis of thermal power plants: A method based on advanced exergy analysis

The performance of energy systems usually degrades gradually away from the best operation conditions during continuous operation. Since the components in an energy system are interconnected with each other, the performance degradation or anomalies occurring in one component can propagate downstream, affecting the performance of other components and even that of the whole system: Any anomaly occurring in a component may cause obvious performance degradation. However, locating the components where anomalies occur in an effective and accurate way is often difficult due to the interactions among components. Therefore, in this paper, we propose a diagnosis method to effectively locate the components with performance degradation, to find the sources over the system which may cause the degradation, thus to prevent the energy systems from anomalies. The proposed diagnosis method is based on the advanced exergy analysis, in which the exergy destruction within each component is split into endogenous and exogenous parts. The endogenous exergy destruction is due to the irreversibility of the component itself, while the exogenous is caused by the inefficiencies of the remaining components. The exogenous exergy destruction is, in fact, the major obstacle to accurately pinpoint the original sources causing the performance degradation. Therefore, the proposed method compares only the endogenous exergy destruction between the reference and degradation conditions for degradation quantification, once the degraded components are identified by an effective internal indicator. The diagnosis method is then applied to a case study of coal-fired power plant, in which the anomalies is introduced to one specific component. It is shown that the proposed method successfully and readily locates, and more importantly, quantifies the degradation.

Advanced exergy analyses of an ejector expansion transcritical CO2 refrigeration system

This paper presents a thermodynamic investigation on an ejector expansion transcritical CO2 refrigeration system with advanced exergy analysis. By splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts, more valuable information of the interactions among the system components and the components improvement potential is provided. The results indicate that the compressor with largest avoidable endogenous exergy destruction possesses the highest priority of improvement, followed by the ejector, evaporator and gas cooler. The system exergy destruction is dominantly endogenous, and 43.44% of the total exergy destruction can be avoided by improving the system components. The evaporator has a serious impact on the exogenous exergy destruction within the compressor and ejector, and its own exergy destruction is entirely belongs to endogenous part. The effects of the discharge pressure, compressor efficiency and ejector efficiency on the system exergetic performance are discussed. There is an optimal discharge pressure with respect to the minimum endogenous exergy destruction in the compressor. Avoidable endogenous exergy destruction rates of the compressor and ejector are respectively reduced by 93.6% and 81.7% when the corresponding component efficiency varies from 0.5 to 0.9.

SPLITTING THE TOTAL EXERGY DESTRUCTION INTO THE ENDOGENOUS AND EXOGENOUS PARTS OF THE THERMAL PROCESSES IN A REAL INDUSTRIAL PLANT

The total exergy destruction occurring in a component is not only due to the component itself (endogenous exergy destruction) but is also caused by the inefficiencies of the remaining system components (exogenous exergy destruction). Hence care must be taken in using the total exergy destruction of a component for making decisions to optimize the overall energy system. In this paper, a complex industrial plant is analyzed by splitting the component’s exergy destruction into its endogenous part (the part resulting totally from the component’s irreversibilities) and its exogenous part (resulting from the irreversibilities of the other components within the system). It is observed that the steam generator has the dominant effect. From the total exergy destruction in the steam generator, 1,097.63 kW or 96.95% come from internal irreversibilities in the component, while the influence of other components on the loss of useful work in the steam generator is only 3.05%.