Use Of Exergy Analysis Research Articles

Definition of Exergetic Efficiency in the Main and Emerging Thermal Desalination Technologies: A Proposal

Increasing attention is being given to reduce the specific energy consumption in desalination processes, which translates into greater use of exergy analysis. An exergetic analysis provides relevant information related to the influence of the efficiency of a single component in the global plant performance and in the exergy cost of the product. Therefore, an exergy analysis identifies the main improvement potentials in a productive thermodynamic process. Related to desalination technologies, many previous papers deal with the calculation of the parameters involved in the exergy analysis, the exergetic efficiency of different processes, plants, and technologies among them. However, different approaches for formulating the exergetic efficiency have been suggested in the literature, often without sufficient understanding and consistency. In this work, these formulations, applied to the main desalination components and processes, are compared and critically reviewed. Two definitions of exergy efficiency are applied to the desalination components of the three main thermal desalination processes (multieffect distillation–thermal vapour compression, multistage flash distillation, and direct-contact membrane distillation). The results obtained for the exergy efficiency of the MED-TVC, MSF, and DCMD processes for the input–output approach are 21.35%, 17.08%, and 1.28%, respectively, compared to the consumed–produced approach that presented 3.1%, 1.58%, and 0.37%, respectively. The consumed–produced approach seems to better fit the thermodynamic behaviour of thermal desalination systems.

Performance evaluation of external compound parabolic concentrator integrated with thermal storage tank for domestic solar refrigeration system.

The aim of this research was to develop a model for a solar refrigeration system (SRS) that utilizes an External Compound Parabolic Collector and a thermal energy storage system (TESS) for solar water heating in Chennai, India. The system parameters were optimized using TRNSYS software by varying factors such as collector area, mass flow rate of heat transfer fluid, and storage system volume and height. The resulting optimized system was found to meet 80% of hot water requirements for the application on an annual basis, with an annual collector energy efficiency of 58% and an annual TESS exergy efficiency of 64% for a discharge period of 6h per day. In addition, the thermal performance of 3.5kW SRS was studied by connecting it to an optimized solar water heating system (SWHS). The system was found to generate an average cooling energy of 12.26MJ/h annually, with a coefficient of performance of 0.59. By demonstrating the ability to efficiently generate both hot water and cooling energy, the results of this study indicate the potential for utilizing a SWHS in combination with STST and SRS. The optimization of system parameters and the use of exergy analysis provide valuable insights into the thermal behavior and performance of the system, which can inform future designs and improve the overall efficiency of similar systems.

A comparative study of the entropy generation by an integrated fuel cell-intercooled gas turbine

Lower efficiency and a lower maximum output are causing problems for conventional gas turbine power plants. Additionally, the emission is the major issue that causes the global warming. Either modifying its settings or integrating it with another system will allow for an increase in productivity. With the goal of increasing efficiency and decreasing emissions, this paper describes how fuel cells can be combined with traditional ICGTs. Fuel cell is an electrochemical device which converts chemical energy to electrical energy and generates additional power. The high temperature fuel cell, a SOFC (Solid Oxide Fuel Cell) is integrated with the conventional ICGT cycle. The maximum level of irreversibility in a system can be identified with the use of exergy analysis and energy analysis. The maximum irreversibility is observed in the combustion chamber 55.1% in hybrid configuration and 47.3% in non-hybrid configuration. There is a 65.789% and 167.801% increase in energy and exergy efficiency, respectively. The environmental effect of the cycle is determined by evaluating the sustainability index, which is 100.78% greater for the hybrid cycle compared to non-hybrid cycle.

Method combining exergy and pinch analysis for the optimisation of a methanol production process based on natural gas and recovered CO2

Following the third part of the IPCC report (GIEC, 2022), carbon capture and utilisation of CO2 emitted by fossil fuel represents one of many ways to curb an increasingly alarming global warming. Reaching this goal implies the transition from a fossil fuel dependant and energy-intensive society to a sober and carbon-free one. According to the (ADEME et al., 2020), steam methane reforming, main production path for syngas, still generates 11 kg CO2/kg H2. Countless scientists have already studied different solutions aiming to lower these emissions, including through the design of innovative CO2 recovering processes. Among these solutions, the integration of CO2 within natural gas based methanol (MeOH) production processes appears to be promising (Nami et al., 2019 ; Wang et al., 2021). Contributing to the development of these more sober and sustainable production sectors involves the implementation of innovative conceptual approaches, along with the design of processes with excellent energetic performances. To this end, there has been a growing interest in exergy analysis in the last few years. This technique is able to identify and characterise a process’ thermodynamic inefficiencies, thus assisting the engineer in the development of innovative processes (Dincer and Rosen, 2015; Gourmelon et al., 2017). The COOPERE method (COmbiner Optimisation des ProcédEs, Récupération et analyse Exergétique), developed in the Laboratoire de Génie Chimique de Toulouse (Gourmelon, 2015), lies on the combined use of exergy analysis, a case based reasoning approach (Roldan Reyes, 2012) and pinch analysis. This method enables to design processes as energetically sober as economically viable. In this paper, the latter is applied to a MeOH production process based on natural gas and recovered CO2, described by (Yang et al., 2018).

Exergy analysis of organic Rankine cycle for waste heat recovery using low GWP refrigerants

The use of exergy analysis in thermodynamic systems, as well as energy analysis, is quickly increasing. Exergy analysis is useful for identifying processes that cause exergy destruction and losses, and it may be used in conjunction with energy analysis. Due to environmental concerns, the use of waste heat has received a lot of attention in recent years. The Organic Rankine Cycle (ORC) is a promising method for converting waste heat into usable work at low temperatures. In this research, both the Basic Organic Rankine Cycle and the Regenerative Organic Rankine Cycle are considered for the analysis. Python is used for the simulation process. This investigation shows that the regenerative ORC has higher thermal and second law efficiency and a lower exergy destruction rate compared to the basic ORC. The Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) of R1233zd(E), R1234ze(Z), R1234ze(E), and R1234yf are considered low. R1233zd(E) had a 1-5.66% and a maximum of 4.17% lower second law efficiency than R113 in regenerative ORC and basic ORC, respectively. On the other hand, R113 is not an eco-friendly fluid. As a result, R1233zd(E) can be used in place of R113 to assure better environmental quality by sacrificing a small portion of efficiency. The fluids which have a higher critical temperature showed better results compared to the fluids which have a lower critical temperature. Throughout the study, R1233zd(E) performed better than the rest of the three fluids. In both basic and regenerative ORC, R1233zd(E) has higher thermal and second law efficiency.

Exergy analysis and optimization of charging–discharging processes for cascaded latent heat storage system

The use of exergy analysis provides theoretical guidance for the cascaded latent heat storage system (CLHSS). However, the exergy analysis of the CLHSS charging–discharging processes is imperfect with two problems to be solved. One is the lack of exergy flow analysis, the other is the inaccurate expressions of the overall charging–discharging processes exergy efficiency. This paper aims to solve the above two problems. First, the exergy flow of the CLHSS charging–discharging processes was revealed, composed of one or more of the three exergy flow paths. Second, the overall exergy efficiency was derived by determining exergy produced and consumed. Only by satisfying the constraint that the exergy change of each PCM is equal to zero, the product of exergy efficiencies of charging and discharging processes can represent the overall exergy efficiency. On this basis, previous models that used the product of exergy efficiencies were modified by adding constraints. Compared to models without constraints, the model with constraints has more accurate and complete optimization results, which is conducive to the CLHSS stable operation. Finally, the model with constraints was adopted to guide the application of the CLHSS in the solar power tower.

EXERGY ANALYSIS OF DIRECT SUN RADIATION CONCENTRATION

In the article substantiates that the exergy method of thermodynamic analysis, along with the entropy method, makes it possible to determine the locations of the most significant thermodynamic losses in energy conversion processes. It is shown that the use of exergy analysis makes it possible to estimate the thermodynamic losses at each stage of the energy conversion scheme and to reduce them. It is proved that exergetic analysis of the concentration of solar radiation in solar installations with paraboloid mirrors, as well as in optical systems of tower solar thermal plants with horizontal fields of flat heliostats and thermal power plants with horizontal parabolic cylindrical mirrors will allow to increase the energy of these transformations. Exergy analysis of the concentration of solar radiation was performed. For the first time, solar radiation is treated as radiant heat flux, which is characterized by its own temperature, and its exergy is determined within the canonical Carnot cycle. On the basis of the new interpretation of the temperature of the radiant flux, an analytical expression was obtained for the radiation temperature of the thermal radiation of the Sun, both for direct radiation and for diffuse. The dependence of the direct solar radiation density on the mass of the atmosphere is found. The above formulas allow to calculate the radiation temperature of solar radiation and the density of exergy flux on the Earth's surface and in the focus of the concentrator mirror.

Performance maps for an air-cooled air conditioning system as a preliminary instrument for the diagnosis of evaporator fouling

During the past few decades, there has been increased interest in the development of automated approaches for detecting and diagnosing faults in air conditioning systems. Among them, thermoeconomic diagnosis is a technique which involves the use of exergy analysis. As a first step towards improving its performance, this work is focused on the thermodynamic and exergy analysis of a direct expansion air conditioning system used in small commercial building applications. The analysis was carried out by means of experimental activities on a 17.5 kW rooftop unit installed at the Herrick Laboratories, Purdue University, Indiana (USA). The system under investigation was equipped with a variable-speed compressor and variable-speed fans, thus allowing the unit to meet different loads. A detailed mapping of the performance of this system was carried out by considering the effect of the outdoor temperature and the cooling load. In addition, the effect of evaporator fouling was investigated. Results showed that poor exergy performance were achieved due to the exergy destruction occurring in the evaporator. Also, when testing evaporator fouling, results showed that this fault contributed to increase the consumption of the mechanical exergy of the air, thus allowing for an easy detection of this fault.

Use of Exergy Analysis to Quantify the Effect of Lithium Bromide Concentration in an Absorption Chiller

Absorption chillers present opportunities to utilize sustainable fuels in the production of chilled water. An assessment of the steam driven absorption chiller at the University of Idaho, was performed to quantify the current exergy destruction rates. Measurements of external processes and flows were used to create a mathematical model. Using engineering equation solver to analyze and identify the major sources of exergy destruction within the chiller. It was determined that the absorber, generator and condenser are the largest contribution to the exergy destruction at 30%, 31% and 28% of the respectively. The exergetic efficiency is found to be 16% with a Coefficient of performance (COP) of 0.65. Impacts of weak solution concentration of lithium bromide on the exergy destruction rates were evaluated using parametric studies. The studies reveled an optimum concentration that could be obtained by increasing the weak solution concentration from 56% to 58.8% a net decrease in 0.4% of the exergy destruction caused by the absorption chiller can be obtained. The 2.8% increase in lithium-bromide concentration decreases the exergy destruction primarily within the absorber with a decrease of 5.1%. This increase in concentration is shown to also decrease the maximum cooling capacity by 3% and increase the exergy destruction of the generator by 4.9%. The study also shows that the increase in concentration will change the internal temperatures by 3 to 7 °C. Conversely, reducing the weak solution concentration results is also shown to increase the exergetic destruction rates while also potentially increasing the cooling capacity.

Exergization

Exergization

Sustainability assessment of oilseed fractionation processes: A case study on lupin seeds

Traditional ingredient production focusses on high purity and yield, resulting in energy- and resource-intensive fractionation processes. We explored alternative fractionation routes for oilseeds by focussing on functionality and optimal resource use. Lupin seeds were taken as model material because they are rich in protein and oil and they can be grown in moderate climate conditions. Dry fractionation yields functional protein-enriched flours without using water, consumes the least energy and exergy losses are low. Purer protein fractions are obtained via conventional wet or aqueous fractionation, but these processes require large amounts of water and an energy-intensive drying step. With the use of exergy analysis, we demonstrate that water and energy consumption can be reduced by replacing drying steps with concentration steps and by combining dry and aqueous fractionation processes. Finally, by valorising side streams, the exergetic efficiency of all fractionation processes increases.

Exergy Analysis of Omotosho Phase 1 Gas Thermal Power Plant

This paper describes the use of exergy analysis in evaluating the performance of Omotosho Phase I Gas Thermal Power Plant. The data used were obtained from data record book. The exergy analysis, mass and energy conservation laws were applied to each component. Results obtained show that the gas turbine had the largest exergy efficiency of 96.17%, while that of the total plant was 41.83%, the combustion chamber had the largest exergy destruction of 54.15% while that of the total plant was 58.17%.In addition, the effect of the gas turbine load variation and ambient temperature from 210C – 330C are investigated. The exergy efficiency decreases and exergy destruction efficiency increases as ambient temperature increases in the plant and its components. Therefore, turbine air inlet cooling system is recommended for the plant to solve this problem.

A Review of Performance Appraisals of Nigerian Federal Government-Owned Refineries

The aim of this paper is to review previous works on the performance appraisal of Nigerian government-owned refineries. The review has been done in a general sense, covering appraisal works by engineers, scientists, management experts, economists, sociologists and even historians. The outcome indicates that while there seems to be several works directly and/or indirectly assessing the performance of the refineries in a general sense, there is a dearth of such in the specific area of energy consumption. There also appears to be no single one appraising energy utilisation of all the refineries at the same time in the open literature. This is in spite of the fact that refining processes are energy intensive. Despite popularisation of exergy analysis as a veritable tool, the only energy utilisation appraisal within our reach which was carried out on just one of the refineries has not been done exergetically. However, the work still reveals, within the limitations of 1st Law energy analysis that the energy consumption patterns are below international benchmarks in the oil and gas industry. Some suggestions have also been offered to take care of the energy efficiency challenges in these refineries. These include plant to plant analyses of energy utilisation patterns in the four refineries, periodical determination of GHG emission levels in the refineries using current international best practices as benchmarks, use of exergy analysis to check avoidable energy wastage in the refining processes, shifting refinery fuelling pattern in favour of low carbon content fuels like natural gas and ensuring regular turnaround maintenance of the system.

Work flow in process development for energy efficient processes

Increasing expenditures for energy require an optimization of chemical processes with regard to energy efficiency. Energy efficiency is of course only one aspect of a multi-objective optimization during process development. It will be shown how methods for increasing energy efficiency are integrated in the workflow of BASF’s process development for new and existing processes. Special focus will be on the use of exergy analysis and its high relevance to industrial chemical processes. It will be shown how exergy analysis might be used for comparison of different process concepts. Additionally examples will emphasize how an increase of energy efficiency by change of operational conditions can be reached. Also these measures can be interpreted in terms of reduced exergy losses. For all examples the additional investment, if needed, is justified by the savings, which were altogether approximately 7 million euro per year.

Exergy Analysis of Drying Process: An Experimental Study in Solar Greenhouse

This article examines the exergy variation during drying in solar greenhouses. Exergy efficiencies were derived as functions of drying time and temperature of the drying air. An illustrative example is considered to verify Dincer and Sahin's model and to show the applicability of the model to actual drying processes at different drying air temperatures. This work is intended not only to demonstrate the usefulness of exergy analysis in thermodynamic assessments of drying processes but to provide insights into their performances and efficiencies. In this study, the drying performance of the passively heated solar greenhouse has been investigated. Experimental results under the meteorological conditions of Izmir, Turkey (latitude 38.24 N, longitude 27.50 E), are presented.

Chemical Exergies of Some Coals in Turkey

Exergy analysis is a general method for efficiency analysis of systems and processes. The use of the exergy concept and the analysis of ultimate efficiencies of processes is more or less still limited to the academic world. There are several reasons why its industrial use is still limited. To overcome some of the difficulties in industrial applications of energy analysis, it has made use of exergy analysis. The chemical exergy of a substance is the maximum work that can be obtained from it by taking it to chemical equilibrium with the reference environment at a constant temperature and pressure. The first law analysis gives only the quantity of energy, while the second law defines the quality of energy also. The projected increase in coal utilization in power plants makes it desirable to evaluate the energy content of coal both quantitatively and qualitatively. In the present study, the chemical exergies of some coals of good quality in Turkey were calculated with the BASIC program by using second law analysis and the results were given as tabulated.

Exergy efficiency applied for the performance optimization of a direct injection compression ignition (CI) engine using biofuels

The need to decrease the consumption of materials and energy and to promote the use of renewable resources, such as biofuels, stress the importance of evaluating the performance of engines based on the second law of thermodynamics. This paper suggests the use of exergy analysis (as an environmental assessment tool to account wastes and determine the exergy efficiency) combined with gas emissions analysis to optimize the performance of a compression ignition (CI) engine using biofuels such as cottonseed and palm oils, pure or blended with diesel for different engine loads. The results show that the combination of exergy and gas emissions analyses is a very effective tool for evaluating the optimal loads that can be supplied by CI engines. Taking into account technical constraints of engines, a tradeoff zone of engine loads (60% and 70% of the maximum load) was established between the gas emissions (NO and CO 2) and the exergy efficiency for optimal performance of the CI engine.

06/02259 Thermodynamic-behaviour model for air-cooled screw chillers with a variable set-point condensing temperature: Chan, K. T. and Yu, F. W. et al. Applied Energy, 2006, 83, (3), 265–279.

In this paper we present a new model for thermodynamic analysis, in terms of exergy, of a drying process. Exergy efficiencies are derived as functions of heat and mass transfer parameters. An illustrative example is considered to verify the present model and to illustrate the applicability of the model to actual drying processes at different drying air temperatures, specific exergies of drying air, exergy differences of inlet and outlet products, product weights, moisture contents of drying air, and humidity ratios of drying air. As a result, this work is intended not only to demonstrate the usefulness of exergy analysis in thermodynamic assessments of drying processes, but also to provide insights into their performances and efficiencies. It is believed that the present model should be useful to people seeking (i) to optimize the design of drying systems and their components and (ii) to identify appropriate applications and optimal configurations for drying systems.

Exergy as a Driver for Achieving Sustainability

Exergy analysis is shown to be an important tool for achieving sustainable development. By noting that energy can never be “lost,” as it is conserved according to the first law of thermodynamics, while exergy can be lost due to internal irreversibilities, the study suggests that exergy losses, particularly due to the use of nonrenewable energy forms, should be minimized to attain sustainable development. Furthermore, several key thermodynamic concepts and the potential usefulness of exergy analysis are discussed, the linkages between exergy and environmental impact and sustainable development are introduced; and several key issues regarding sustainability and its consequences are addressed. Several case studies highlight the insights revealed using exergy and exergetic aspects of sustainability. It is concluded that the potential usefulness of exergy analysis in addressing sustainability issues and solving environmental problems is substantial.

Exergy Analysis of Chromatographic Separations in a Fixed-Bed Column

In this work, we evaluate the use of exergy analysis on a single chromatographic column. A sensitivity analysis was done to unravel the relation between several parameters that might influence the quality of separation and the associated exergy loss. From the resulting analysis we concluded that the division of the exergy content in its components is important in revealing the nature of process irreversibilities. In addition, results show that the dilution problem is adequately described by the exergy change of mixing. All in all, results have shown that a minimum exergy loss occurs for a high production rate while keeping purity requirements constant. Consequently, exergy loss can be used as a tool for chromatographic separation optimization.