Advanced Exergy-based Analyses Research Articles

Conventional and advanced exergy-based analyses and comparisons of two novel tri-generation systems based on solid oxide fuel cells and gas turbines

This study conducts conventional and advanced exergy, exergo-economic, and exergo-environmental analyses and comparisons of two tri-generation systems driven by solid oxide fuel cells (SOFCs) and gas turbines (GTs). The proposed systems mainly consist of SOFC, GT, heat recovery steam generator (HRSG), (organic) Rankine cycle, and heat exchanger. The analysis results indicate that the biggest cost rates of exergy destruction and component in both systems appear in SOFCs being 4.4333 $/h and 4.2760 $/h, while the highest environmental impact rates combined with exergy destruction and component in systems 1 and 2 are found in afterburner and HRSG, which are 645.9569 mPts/h and 849.2659 mPts/h. Compared to the conventional analyses, the advanced analyses demonstrate that air compressors own the largest avoidable-endogenous parts of cost rates, while HRSG of system 1 and steam turbine (ST) of system 2 own the highest avoidable-endogenous parts of environmental impact rates being 165.8482 mPts/h and 115.2299 mPts/h.

New procedure for an optimal design of an integrated solar tower power plant with supercritical carbon dioxide and organic Rankine cycle and MED-RO desalination based on 6E analysis

In this paper, an innovative structure for the production of electricity and freshwater in Kangan Port, located in southern Iran and close to the Persian Gulf, is developed and analyzed. Heliostat collectors are employed in this process to provide the necessary thermal energy in the supercritical carbon dioxide (S-CO2) cycle, the organic Rankine cycle (ORC) and desalination unit. Additionally, implementing the current multi-effect desalination (MED) processes unit with the reverse osmosis (RO) system as well as employing the sun's thermal collector field to enhance the system's achievement and propose the best plan for the unit that operates has been looked into. ASPEN HYSYS software, Meteonorm package, and MATLAB programming are used to simulate the proposed system. Concurrently, this integrated power plant exhibits the capacity to simultaneously generate 117 kg/s of freshwater and yield 25.14 MW of power. The integrated structure has a thermal efficiency of 36% and a overall exergy efficiency of 31.99. Exergy study reveals that heat exchanger 8 and turbine 3 experience the most exergy destruction. To recover lost heat and produce additional electricity, organic Rankine cycle are used. Investigations are done on seven organic fluids in the ORC unit. The system is better understood from several views with the assistance of energy, exergy, exergoeconomic, exergoenvironmental, emergoeconomic, and emergoenvironmental (6E) analyses. In this regard, m-file codes in MATLAB programming for 6E analyses are developed. The generated code's thermodynamic simulation is accurately compared to ASPEN HYSYS software. Additionally, sensitivity analysis depending on the primary parameters is carried out. For a thorough study of each component, advanced exergy-based analysis linked to avoidable/endogenous and unavoidable/exogenous segments is carried out. The objective functions and chosen variables are optimized using a genetic algorithm. The best organic fluid in terms of thermodynamics is n-hexane and the ideal organic fluid from an economic and environmental standpoint stands R-113. The overall system's cost rate and environmental impact are obtained at 0.1679 $/s and 0.000545 pts/s, respectively.

Advanced Exergy-Based Analysis of an Organic Rankine Cycle (ORC) for Waste Heat Recovery.

In this study, advanced exergy and exergoeconomic analysis are applied to an Organic Rankine Cycle (ORC) for waste heat recovery to identify the potential for thermodynamic and economic improvement of the system (splitting the decision variables into avoidable/unavoidable parts) and the interdependencies between the components (endogenous and exogenous parts). For the first time, the advanced analysis has been applied under different conditions: constant heat rate supplied to the ORC or constant power generated by the ORC. The system simulation was performed in Matlab. The results show that the interactions among components of the ORC system are not strong; therefore, the approach of component-by-component optimization can be applied. The evaporator and condenser are important components to be improved from both thermodynamic and cost perspectives. The advanced exergoeconomic (graphical) optimization of these components indicates that the minimum temperature difference in the evaporator should be increased while the minimum temperature difference in the condenser should be decreased. The optimization results show that the exergetic efficiency of the ORC system can be improved from 27.1% to 27.7%, while the cost of generated electricity decreased from 18.14 USD/GJ to 18.09 USD/GJ.

Exploring the improvement potentials in an existing industrial olefin plant through advanced exergy-based analyses

The production of light olefins via the thermal cracking of hydrocarbons is the most energy-demanding process in the petrochemical industry, and an important producer of greenhouse gasses worldwide. But, which sections or components of this process are major contributors to its energy-intensiveness, and high environmental impacts? And, how these problems can be avoided and to what extent?Presently, conventional and advanced exergetic, exergoeconomic, and exergoenvironmental analyses are introduced as the most promising methods which could answer these questions, therefore, in this work, are used to identify the real priorities of improvement in an olefin plant in the south of Iran (Assaluyeh), by first simulating the plant in ASPEN HYSYS simulator. The environmental impacts of components and input streams of plant were calculated using Eco-Indicator 99 method of Life Cycle Assessment (LCA). Results of the study indicated that although the cracking furnace causes 55.3% of total exergy destruction of the plant, only 15.36% of it is avoidable endogenous. Furthermore, the considerable share of steam system in the total exergy destruction of plant (as the second exergy destructive section with a share of 14%) showed that ignoring this zone of an olefin plant in the exergy-based analyses leads to major mistakes to diagnose the priorities of improvements. The results showed that considering prespecified costs and environmental impacts for internal material or energy streams produced within the process introduces a significant error to identify the improvement priorities regarding the economic and environmental aspects.

Exergy, Exergoeconomic, Exergoenvironmental, Emergy-based Assessment and Advanced Exergy-based Analysis of an Integrated Solar Combined Cycle Power Plant

The high amount of solar energy as clean and sustainable energy has increased awareness in solar energy concentration, especially in integrated concepts. One of the best and promising hybrid configurations for converting solar energy into power is an integrated solar combined cycle system (ISCCS). In this study, conventional and advanced analysis tools for the ISCCS located in Yazd (Iran) have been investigated. In this paper, thermodynamic simulation, exergy, exergoeconomic, and exergoenvironmental analysis based on Life Cycle Assessment (LCA) have been performed. In addition, an emergy-based concept, including emergoeconomic and emergoenvironmental assessment, has been performed. In-depth analysis of exergy, exergoeconomic, and exergoenvironmental modelling, advanced exergy analysis based on endogenous/exogenous and avoidable/unavoidable parts have been done. In this regard, MATLAB code has been developed for thermodynamic simulation, exergy, exergoeconomic, exergoenvironment, emergoeconomic and emergoenvironment analysis. Furthermore, THERMOFLEX (commercial software) applied for thermodynamic simulation and verification. The Sankey diagram based on each analysis tool has been constructed. Furthermore, the priority of improvement based on each analysis has been identified. The thermal efficiency and net power generation of ISCCS are 48.25% and 419600 kW, respectively. It was obsereved that in most equipment, less than 10% of exergy destruction and cost and environmental impact rates were avoidable/endogenous.

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.

Classical and advanced exergy-based analysis of a 750 MW steam power plant

ABSTRACT Both the conventional (classic) and advanced exergetic analytical methods were used to investigate the improvement potentials of a pulverised coal-fired 750 supercritical steam power plant. The results show that the subsystem that contributed the most to exergy destruction is the condenser (CND) at about 1.25% and closely followed by the boiler at 1.23%. Furthermore, the data obtained from the present study show that the dominant contributor to the overall exergy destruction in each of the subsystems was the endogenous part of exergy destruction, . In addition, the results show that steam turbines, especially TB1, TB4, TB5, TB6, TB7 to TB17, the condenser and the boiler would benefit immensely by improving their avoidable endogenous exergy destructions. This investigation also shows that the overall unavoidable exergy destruction within the entire power plant was about 42.8%, while the potential for improving the entire power plant was approximately 2.5%. Other important results from this study are comprehensibly documented in the conclusion section.

Advanced exergy and exergoeconomic analysis of a novel liquid carbon dioxide energy storage system

In the present study a liquid carbon dioxide energy storage system with 10 MW output power production is analyzed thermo-economically by utilizing conventional and advanced exergy-based analysis. New exergy-based concepts such as unavoidable/avoidable and endogenous/exogenous exergy destruction, exergy destruction costs and investment costs as well as the combination of the two concepts are introduced to provide valuable knowledge about the interchanges among system components and the true latent capacity for improvement of each significant system component. It is demonstrated from the overall system analysis that the avoidable endogenous value is only 42.1% for total exergy destruction, 43.42% for total exergy destruction costs and 55.43% for total investment costs in the proposed system. Results from conventional exergy analysis suggest that the compressor contributes the utmost influence to the overall exergy destruction, while results from both the advanced exergy and exergoeconomic evaluation introduce the expander as the most significant component that has the highest improvement priority. In brief, the advanced exergy-based analyses can enhance engineers perception on the processes of energy conversion in the proposed system and also can improve the quality of the conclusions.

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.

A Review of Evaluation, Optimization and Synthesis of Energy Systems: Methodology and Application to Thermal Power Plants

To reach optimal/better conceptual designs of energy systems, key design variables should be optimized/adapted with system layouts, which may contribute significantly to system improvement. Layout improvement can be proposed by combining system analysis with engineers’ judgments; however, optimal flowsheet synthesis is not trivial and can be best addressed by mathematical programming. In addition, multiple objectives are always involved for decision makers. Therefore, this paper reviews progressively the methodologies of system evaluation, optimization, and synthesis for the conceptual design of energy systems, and highlights the applications to thermal power plants, which are still supposed to play a significant role in the near future. For system evaluation, both conventional and advanced exergy-based analysis methods, including (advanced) exergoeconomics are deeply discussed and compared methodologically with recent developments. The advanced analysis is highlighted for further revealing the source, avoidability, and interactions among exergy destruction or cost of different components. For optimization and layout synthesis, after a general description of typical optimization problems and the solving methods, the superstructure-based and -free concepts are introduced and intensively compared by emphasizing the automatic generation and identification of structural alternatives. The theoretical basis of the most commonly-used multi-objective techniques and recent developments are given to offer high-quality Pareto front for decision makers, with an emphasis on evolutionary algorithms. Finally, the selected analysis and synthesis methods for layout improvement are compared and future perspectives are concluded with the emphasis on considering additional constraints for real-world designs and retrofits, possible methodology development for evaluation and synthesis, and the importance of good modeling practice.

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.

Evaluation the sustainable energy applications for fruit and vegetable productions processes; case study: Greenhouse cucumber production

Reducing fossil fuel application and also CO2 emissions are two main purposes of global energy politics. In this context, the provision of sustainable energy practices in vegetable productions is a very important subject in terms of food safety. Fruits and vegetables are called crops in agricultural activities. In this study, greenhouse cucumber production was assessment to determine the energy saving direction and also to find the interactions of the cucumber chemical structure with energy using and the impact of solar energy potential absorbed in photosynthesis on the performance of the cucumber production process with thermodynamic concept by using advanced exergy-based methods. It is also the first attempt to investigate the crop production processes with renewable and non-renewable energy sources. Data were collected from 30 cucumber greenhouses in Golshan city, Isfahan province of Iran (located within 51° 39′ north latitude and 31° 56′ east longitude) using face to face questionnaire method. According to the results of this study, cumulative degree of perfection (CDP) increased from 0.23 to 0.47, exergy efficiency from 0.18 to 0.30 and renewability indicator (RI) from −3.32 to −1.09 when the greenhouse cucumber production process was included renewable energies. The loss of exergy, however, decreased from 4809.18 MJ to 2415.41 MJ. The advantages of the presented applied method were compared with the conventional methods. The results showed that the advanced exergy-based analysis is more meaningful and effective tool for performance evaluation of vegetables than conventional approaches. Based on the guideline of this study, performance can be improved with respect to energy use in vegetable production processes.

Advanced life cycle integrated exergoeconomic analysis of building heating systems: An application and proposing new indices

Advanced exergy-based analysis and assessment tools have been considered very useful tools for detecting the interactions among components of energy-conversion systems and the real potential for improving each component in any system. In this study, a building heating system is analyzed using advanced life cycle integrated (LCI)exergoeconomic analysis method, which combines cost and environmental impacts. Some new indices (metrics) such as advanced exergy destruction ratio, advanced LCIexergoeconomic ratio, advanced LCIexergoeconomic sustainability index and advanced indices are presented. These metrics are also applied to the main components of the system. The boiler has the maximum LCI endogenous exergy destruction cost ratio while the maximum LCI exogenous destruction ratio is due to the water heater. The advanced LCIexergoeconomic depletion ratios are 0.187, 0.599, 0.414 and 0.371 for the endogenous, exogenous, unavoidable and avoidable parts, respectively.

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 the Stirling engine driven with cryogenic exergy of LNG (liquefied natural gas) for the production of electricity

LNG (liquefied natural gas) delivered by means of sea-ships is pressurized and then regasified before its introduction to the system of pipelines. The utilization of cryogenic exergy of LNG for electricity production without combustion of any its portion is analyzed. For the conversion of LNG cryogenic exergy into electricity, the Stirling engine is proposed to be applied. The theoretical thermodynamic model of Stirling engine has been applied. This model is used to investigate the influence of pinch temperature in heat exchangers, engine compression ratio and dead volumes ratios on the thermodynamic parameters of the Stirling engine. The results of simulation represent the input data for investigations of thermodynamic performance of the proposed system.In order to evaluate the thermodynamic performance of the proposed process, an exergy analysis has been applied. The exergy efficiency and influence of design and operational parameters on exergy losses are determined for each of the proposed system configurations. The obtained results represent the background for advanced exergy-based analyses, including thermo-ecological cost.

Advanced Exergoeconomic Analysis of a Power Plant with CO2 Capture

Conventional exergy-based analyses reveal options for improving energy conversion systems, but they suffer from some limitations that are addressed by advanced exergy-based analyses. Advanced exergy-based methods are capable of (1) identifying interdependencies among plant components (endogenous/exogenous values), and (2) revealing the potential for improvement (avoidable/unavoidable values). Thus, data obtained from these methods pinpoint strengths and weaknesses of energy conversion systems and are of great importance when complex plants with a large number of interconnected components are considered. This paper presents one of the first applications of an advanced exergoeconomic analysis to a complex power plant. The plant includes a mixed conducting membrane for oxy-fuel combustion and CO2 capture. The results show that for the most influential components of the plant, the largest part of investment cost and of the costs of exergy destruction is unavoidable. Additionally, in most cases the interactions among the components are of lower importance and, for the majority of the components, the endogenous parts of the costs (related to the internal operation of each component) are significantly larger than the corresponding exogenous parts (related to component interactions). Nevertheless, relatively strong interactions have been found among the components that constitute the mixed conducting membrane reactor of the plant.

Advanced exergoeconomic analysis of a gas engine heat pump (GEHP) for food drying processes

Exergetic and exergoeconomic analyses are often used to evaluate the performance of energy systems from the thermodynamic and economic points of view. While a conventional exergetic analysis can be used to recognize the sources of inefficiencies, the so-called advanced exergy-based analysis is convenient for identifying the real potential for thermodynamic improvements and the system component interactions by splitting the exergy destruction and the total operating cost within each component into endogenous/exogenous and unavoidable/avoidable parts. In this study for the first time an advanced exergoeconomic analysis is applied to a gas-engine-driven heat pump (GEHP) drying system used in food drying for evaluating its performance along with each component. The advanced exergoeconomic analysis shows that the unavoidable part of the exergy destruction cost rate within the components of the system is lower than the avoidable part. The most important components based on the total avoidable costs are drying ducts, the condenser and the expansion valve. The inefficiencies within the condenser could particularly be improved by structural improvements of the whole system and the remaining system components. Finally, it can be concluded that the internal design changes play a more essential role in determining the cost of each component.

Evaluating the Potential for Improvement of an Oxy-Fuel Power Plant with CO2 Capture Using an Advanced Exergetic Analysis

Conventional exergy-based analyses provide useful information that can be used to improve the thermodynamic, economic, and environmental performance of energy conversion systems. However, when the complexity of a system is high, component interactions increase, and improvement strategies become more difficult to detect. Advanced exergy-based analyses have been developed to address such issues, to aid further assessment and to reveal options for improving the overall thermodynamic, economic, and environmental-impact-related effectiveness of energy conversion systems. Specifically, with an advanced exergetic analysis, exergy destruction is separated into (a) avoidable/unavoidable parts that deal with the potential for improving a component and/or a system and (b) endogenous/exogenous parts that show the way and magnitude of component interactions. The purpose of this paper is two-fold: first, to demonstrate the applicability of the method to a complex system by applying it to a new power plant concept and, second, to evaluate the design and operation of the plant and the improvement potential of the implemented CO2 capture technology. The results from this analysis can be used in improving the design of the power plant. The considered power plant is an advanced zero-emission plant that incorporates oxy-fuel technology and has been selected because of its relatively high efficiency in comparison with other alternatives. Overall, the improvement potential of the plant is rather limited due to the relatively low values of the avoidable exergy destruction. Additionally, the analysis shows that component interactions are of relatively low importance because of low exogenous values. However, when the exogenous exergy destructions within the components are further split, additional improvement possibilities are revealed.

Evaluation of a power plant with chemical looping combustion using an advanced exergoeconomic analysis

Advanced exergy-based analyses extend engineering knowledge beyond the respective conventional methods by quantifying the potential for improvement and the component interactions and facilitating the optimization of a system. In this paper, the first application of an advanced exergoeconomic analysis to a complex combined-cycle power plant with CO2 capture is presented and the obtained results are assessed. The power plant incorporates a chemical looping combustion unit that facilitates the CO2 capture process and has been chosen as one of the most promising oxy-combustion technologies with respect to efficiency, economic feasibility and environmental footprint. The largest avoidable costs, which represent the potential for improvement, are associated with the components constituting the main gas turbine system. The most important components based on the total avoidable cost are the reactor, expander and compressor. Furthermore, the relatively low component interactions show that most of the costs are associated with the operation of these components; i.e., no intense process interdependencies exist.

Advanced Exergoenvironmental Analysis of a Near-Zero Emission Power Plant with Chemical Looping Combustion

Carbon capture and storage (CCS) from power plants can be used to mitigate CO(2) emissions from the combustion of fossil fuels. However, CCS technologies are energy intensive, decreasing the operating efficiency of a plant and increasing its costs. Recently developed advanced exergy-based analyses can uncover the potential for improvement of complex energy conversion systems, as well as qualify and quantify plant component interactions. In this paper, an advanced exergoenvironmental analysis is used for the first time as means to evaluate an oxy-fuel power plant with CO(2) capture. The environmental impacts of each component are split into avoidable/unavoidable and endogenous/exogenous parts. In an effort to minimize the environmental impact of the plant operation, we focus on the avoidable part of the impact (which is also split into endogenous and exogenous parts) and we seek ways to decrease it. The results of the advanced exergoenvironmental analysis show that the majority of the environmental impact related to the exergy destruction of individual components is unavoidable and endogenous. Thus, the improvement potential is rather limited, and the interactions of the components are of lower importance. The environmental impact of construction of the components is found to be significantly lower than that associated with their operation; therefore, our suggestions for improvement focus on measures concerning the reduction of exergy destruction and pollutant formation.