Global Exergy Efficiency Research Articles

Exploring Exergy Performance in Tetrahydrofuran/Water and Acetone/Chloroform Separations

Distillation is significantly influenced by energy costs, prompting a need to explore effective strategies for reducing energy consumption. Among these, heat integration is a key approach, but evaluating its efficiency is paramount. Therefore, this study presents exergy as an energy quality indicator, analyzing irreversibility and efficiencies in tetrahydrofuran/water and acetone/chloroform distillations. Both systems have equimolar feed streams, yielding products with 99.99 mol% purity. The simulations are performed using Aspen Plus™, enabling evaluation at the column level, as a standalone process, or from a lean perspective that considers integration opportunities with other plants. The results show that, despite anticipated energy savings from heat integration, economic viability depends on pressure sensitivity. The results demonstrate that heat-integrated extractive distillation for acetone/chloroform raises utility energy consumption. Exergy calculations comparing standalone and total site integration reveal the variation in distillation efficiency with operation mode. Global exergy efficiency in both extractive and pressure-swing distillation depends on the fate of condenser duty. In heat-integrated extractive distillation, global exergy efficiency drops from 8.7% to 5.7% for tetrahydrofuran/water and 11.5% to 8.3% for acetone/chloroform. Similarly, heat-integrated pressure-swing distillation sees global exergy efficiency decrease from 34.2% to 23.7% for tetrahydrofuran/water and 9.5% to 3.6% for acetone/chloroform, underscoring the nuanced impact of heat integration, urging careful process design consideration.

Assessing Exergy Efficiency in Computer-Aided Modeled Large-Scale Production of Chitosan Microbeads Modified with Thiourea and Magnetite Nanoparticles

Chitosan, the deacetylated derivative of chitin, is a biopolymer with many applications in different sectors, such as pharmaceutical, food, and wastewater treatment, amongst others. It can be used as a source for synthesizing bioadsorbents modified with chelators and nanoparticles for the removal of pollutants. In this report, we conducted an exergy analysis to evaluate the large-scale production of chitosan-based bioadsorbents modified with iron nanoparticles and chelators. The objective was to identify energy inefficiencies and propose technological enhancements to improve energy utilization. The process was simulated using Aspen Plus V.10® software, enabling the quantification of chemical and physical exergies for the species and streams involved. We calculated process irreversibilities, exergy losses, waste exergy, and utility exergy flows for each stage and the overall process. These findings provide valuable insights into optimizing energy utilization in the production of chitosan-based bioadsorbents. The overall exergy efficiency was 4.98%, with the washing and drying stages of nanoparticles and adsorbent synthesis accounting for the largest contribution to process irreversibilities and exergy destruction. To increase the global exergy efficiency of the process, it is proposed to implement process improvement strategies, such as mass or energy integration, to obtain better energy performance.

Proposal of a new design of central solar receiver for pressurised gases and supercritical fluids

This work presents a novel design of microchannel central receiver for pressurised gases and supercritical fluids in solar tower plants. It consists of a radial arrangement of vertical absorber panels that converge on the central axis of the tower. The absorber panels comprise compact structures, whose compactness is increased in one flow pass compared to the previous one, as the fluid is heated. This concept reduces radiation heat losses due to its light-trapping geometry and increases heat transfer to the thermal fluid without over penalising its pressure drop.For the receiver assessment, it has been developed a thermal resistance model characterising the fluid heating along the panel height and the temperature gradient between parallel channel rows of the compact structure across the panel thickness. Once the thermal and optical boundary conditions are defined, an optimisation analysis of the main geometrical parameters of the receiver has been accomplished. The receiver performance is evaluated by means of a global exergy efficiency referred to the solar subsystem, which computes the receiver heat losses, the fluid pressure drop and the optical efficiency of the heliostat field in which the receiver is integrated. For each parametric optimisation, the configuration that maximises this efficiency is identified.

A Technoeconomic Resilience and Exergy Analysis Approach for the Evaluation of a Vaccine Production Plant in North-East Colombia

Influenza is an acute infection that can cause diabetes and heart and lung disease disorders. This illness affects more than 9 million people around the world. The best way to control the transmission of the virus is vaccination. Studies, performed in Santander, Colombia, have found the existence of this disease. Despite the above, there are no companies dedicated to producing influenza vaccines in Colombia. For the first time, exergetic analysis and technical-economic resilience are being performed as combined decision-making tools for the evaluation of an influenza vaccine production plant. The results of exergetic analysis showed that the global exergy efficiency of the process was estimated at 93%. The exergy of waste that resulted was 61.70 MJ/h. The most critical stage of the process is milling, representing 83% of the total destroyed exergy. On the other hand, the results of technoeconomic resilience showed that the break-even point capacity of the process is 2503.15 t/y, representing only 24% of the installed capacity of the plant. The analysis of the effect of raw materials cost on profits showed that the process only resists a rise of 4% in the cost of raw materials, and higher values show economic losses. A value of 215,500 USD/t establishes a critical point for the normalized variable operating costs because higher values do not provide a return on investment.

Dynamic and thermodynamic characterization of a resonance tube-coupled free-piston Stirling engine-based combined cooling and power system

This paper proposes a novel resonance tube-coupled free-piston Stirling engine-based combined cooling and power (FPS-CCP) system for future application in scavenging unconventional natural gas from coal mines and oil fields. Unlike the traditional duplex Stirling system, the proposed system employs a resonance tube to couple an engine and a cryocooler. In addition, a linear alternator is introduced to facilitate startup and meet multiple demands, resulting in flexible adjustments and even higher exergy efficiency. A novel time-domain unsteady model based on thermoacoustic theory was developed to investigate the onset behavior of the (FPS-CCP) system. The proposed model successfully predicted the onset temperature and onset frequency. Results indicated that within the calculation range, the resonance tube with either a larger diameter or a shorter length leads to a lower onset temperature. Furthermore, the system performance under the steady-oscillating state was studied in terms of the typical operation characteristics and energy flow distribution. When the heating temperature is 833 Kand the mean pressure of helium gas is 5 MPa, the proposed system can provide a cooling capacity of 1000 W at 110 K and an electric power of 800 W with a global exergy efficiency of 29.4%, demonstrating an efficient power matching among the subsystems.

Optimization and comparison of two improved very high temperature gas-cooled reactor-based hydrogen and electricity cogeneration systems using iodine-sulfur cycle

To enrich the existing research methods and content, two improved very high temperature gas-cooled reactor and iodine-sulfur (I–S) cycle-based nuclear hydrogen and steam and helium gas turbines electricity cogeneration systems, including the series connection system (SCS) and the parallel connection system (PCS), are proposed and studied. The energy and exergy analysis methods are used to model these two systems, and Aspen Plus is adopted to build the I–S hydrogen production system. The energy consumption and thermal efficiency of the I–S system are analyzed in detail, and the parametric optimization of two improved systems is performed using particle-swarm optimization (PSO) algorithm. Lastly, the performance comparison of the two systems under different operating conditions is conducted. The simulation results show that more than 99% of the energy consumption of the I–S system is occupied by H2SO4 section and HIx section, and the system's thermal efficiency is estimated to be in the range of 17.7%–43.3%. After using an internal heat exchange network, a conservative thermal efficiency of 23.7% is achieved. The optimization results show that under zero hydrogen production load, the proposed PCS and SCS can respectively achieve the net electrical power outputs of 172.8 MW and 125.7 MW, the global thermal efficiencies of 49.36% and 35.91%, and the global exergy efficiencies of 51.94% and 37.79%. With the increase of hydrogen production load, the global efficiencies of both systems decrease significantly, but the decreasing rate of PCS is faster than that of SCS. In addition, the performance comparison results indicate that when the hydrogen production load is small or the intermediate heat exchanger's primary side helium outlet temperature is close to the reactor inlet temperature, the PCS would be a better option than the SCS.

Evaluation of dual crude palm and kernel oil production in North Colombia via computer-aided exergy analysis

Palm production chains in Colombia have some unsatisfied demands that affect their competitiveness. Specific demands include efficiency in energy use. Therefore, in the present report, an exergy analysis for the dual crude palm and kernel oil production process was carried out to determine the main energy sinks and suggest technological improvements that allow better use of energy. For this study, the process was initially simulated in the Aspen Plus ® software, where the chemical and physical exergies of the species and streams involved were quantified. The process irreversibilities, the exergy loss, the exergy of waste, and the exergy of utilities were calculated for each stage and the whole process. An overall exergy efficiency of 18% was achieved, while the highest process irreversibilities contribution was due to the destroyed exergy with the waste in the threshing stage. To increasing the global exergy efficiency of dual crude palm and kernel oil production, it is proposed the evaluation of palm rachis use to obtain biofuels and/or high-value products.

Environmental and Exergetic Analysis of Large-Scale Production of Citric Acid-Coated Magnetite Nanoparticles via Computer-Aided Process Engineering Tools.

Considering that functional magnetite (Fe3O4) nanoparticles with exceptional physicochemical properties can be highly applicable in different fields, scaling-up strategies are becoming important for their large-scale production. This study reports simulations of scaled-up production of citric acid-coated magnetite nanoparticles (Fe3O4-cit), aiming to evaluate the potential environmental impacts (PEIs) and the exergetic efficiency. The simulations were performed using the waste reduction algorithm and the Aspen Plus software. PEI and energy/exergy performance are calculated and quantified. The inlet and outlet streams are estimated by expanding the mass and energy flow, setting operating parameters of processing units, and defining a thermodynamic model for properties estimation. The high environmental performance of the production process is attributed to the low outlet rate of PEI compared to the inlet rate. The product streams generate low PEI contribution (−3.2 × 103 PEI/y) because of the generation of environmentally friendlier substances. The highest results in human toxicity potential (3.2 × 103 PEI/y), terrestrial toxicity potential (3.2 × 103 PEI/y), and photochemical oxidation potential (2.6 × 104 PEI/y) are attributed to the ethanol within the waste streams. The energy source contribution is considerably low with 27 PEI/y in the acidification potential ascribed to the elevated levels of hydrogen ions into the atmosphere. The global exergy of 1.38% is attributed to the high irreversibilities (1.7 × 105 MJ/h) in the separation stage, especially, to the centrifuge CF-2 (5.07%). The sensitivity analysis establishes that the global exergy efficiency increases when the performance of the centrifuge CF-2 is improved, suggesting to address enhancements toward low disposal of ethanol in the wastewater.

Energetic and exergetic study of dual slope solar distiller coupled with evacuated tube collector under force mode

In this article, energetic and exergetic analysis of symmetric dual-slope solar still, oriented East-West at a latitude of 28°35′ N and integrated with ETC under forced operation is carried out. The performance is evaluated at an optimal flow rate within the vacuum tubes with a viewpoint of maximum heat extraction. The energetic and exergetic efficiencies are increased by ~ 8.0% and ~ 6.0%, respectively, with an increase in flow rate from 0.01 to 0.24 kg/s. With increased water temperature, evaporative fraction exergy increases, ranging 0.2–0.9. The liner, water mass, glass cover, and collector have daily exergy efficiencies of ~ 8.12, ~30.1, ~41, ~18.0%, while overall exergy efficiency and global exergy efficiency are estimated as 4.9 and ~ 7.1%, respectively.

Assessment of a Sour Water Treatment Unit Using Process Simulation, Parametric Sensitivity, and Exergy Analysis.

In this work, a sour water treatment unit was evaluated combining exergetic analysis and parametric sensitivity analysis. Process simulation was performed using Aspen HYSYS 10.1 following real refinery configurations, and the results were validated with existing data. The parametric sensitivity was evaluated by varying the effect of process variables to identify an alternative case with the best technical performance. The exergy analysis was applied to both base and alternative cases. The outcomes were exergy efficiency by stages, global exergy efficiency, total irreversibilities, and exergy by industrial services. A comparison of both cases was performed to identify opportunities for improvement in real sour water treatment. Results revealed that the overall exergy efficiency for the base case was 44.28%. After improving the technical performance, the overall exergy efficiency decreased to 36.12%; the latter indicated higher irreversibilities due to the increase in the use of industrial services. This finding suggested that those process improvements may affect the performance of this refinery unit from an exergetic point of view.

Process Simulation and Exergy Analysis of a Mercaptan Oxidation Unit in a Latin American Refinery.

In this work, the mercaptan oxidation unit of an oil and gas refinery was simulated and assessed using exergy and parametric sensitivity analysis to identify opportunities for improvement from a technical and energy point of view. The process simulation was performed using Aspen HYSYS V10.1 to obtain extended mass and energy balances. The simulation results were validated with the data available in the literature. The effects of operating conditions on technical performance were analyzed via parametric analysis. The exergy analysis was applied to two case studies: the base case and the resulting case from technical improvements. The global exergy efficiency, irreversibilities, exergy of utilities, and efficiencies per stage were calculated to map process equipment with the highest losses of exergy. A comparison between both base and alternative cases was introduced in order to analyze increments in exergy efficiencies. An exergy efficiency of 84.21% was found for the base case, while for the alternative case after applying parametric sensitivity, it was calculated to be 81.95%. This decrease by 2.26% was attributed to the increase of irreversibilities and exergy of wastes to achieve a product with better quality standards.

Energy- and exergy-based optimal designs of a low-temperature industrial waste heat recovery system in district heating

This paper illustrates how the choice of indicators changes the design of a waste heat recovery system in district heating. A prospective system in Grenoble (France) aims to valorize waste heat from the French National Laboratory of Intense Magnetic Fields (LNCMI) by injecting it at 85 °C to the nearby district heating network. We optimize its design for three possible waste heat temperatures: 35 °C (current), 50 °C (viable) and 85 °C (innovative). As major components, the system includes a thermal storage (ranging from 10 MWh to 40 MWh) and may include a heat pump depending on the waste heat’s temperature. Different optimizations are guided by two energetic indicators (one source-oriented, the other demand-oriented) and by the overall exergy efficiency. The system’s annual performance is assessed through the Sankey and Grassman diagrams and compared between optimal designs. Yearly simulation included optimal management of the thermal storage, through mixed-integer linear programming. The demand-oriented optimal design suggests recovering waste heat at 35 °C with a heat pump and a 40-MWh storage, granting the highest coverage of residential needs (49%). On the other hand, the source-oriented optimal design suggests recovering waste heat at 85 °C without heat pump and with a 40-MWh storage, reaching the highest recovery of waste heat (55%). Exergy analysis supports the source-oriented design, as it reaches the highest global exergy efficiency (27%). Our prospective techno-economic and exergo-economic analyses should complement these results and may change some conclusions, especially regarding the storage capacity.

Influencing factors of Solid Waste Management global cost and efficiency: a multi-objective optimization focusing on the collection system

Development of an Integrated Solid Waste Management (ISWM) system is a continuous challenge for local communities. These systems should be properly designed, paying particular attention to the optimal connection of their subsystems. Among them, the Solid Waste (SW) collection system has a primary influence. The design variables (e.g. unit collection basin and weekly removal) can be optimized according to the variation of external parameters (e.g. penetration of selective collection, population density). The objective is the minimization of specific collection cost, maintaining the maximum collection efficiency. Once the collection system is optimized, its influence on the entire SW treatment chain is evaluated. To this end, a multi-objective optimization is implemented taking into account the global cost and exergy efficiency of waste treatment. The analysed system is composed by a paper recycling plant for cardboard production and a Mechanical Biological Treatment plant for the Residual Unsorted Waste treatment, with production of Refused Derived Fuel.

Evaluating the Exergetic Performance of the Amine Treatment Unit in a Latin-American Refinery.

Recently, exergy analysis has attracted great attention of the scientific community as an attractive tool for evaluating energetic efficiency of any process. In this work, the simulation of the amine treatment unit in a Latin-American refinery was performed in order to apply the exergy analysis tool to identify alternatives of improvement. The industrial amine treatment unit was simulated using Aspen plus software, which provided extended energy and mass balances. To calculate irreversibilities of the process and global exergy efficiencies per stages, the general methodological procedure of exergy analysis was used. To this end, physical and chemical exergies were found for compounds involved within the process. The values estimated for total irreversibilities, exergy of utilities, and exergy of wastes in the treatment of the sulfur-rich amine allowed us to analyze the stages that require reductions in waste generation and utility consumption. For a processing capacity of 72.08 t/h of rich amine, results revealed that the overall exergy efficiency was 83.81% and the total irreversibility was 1.69 × 105 MJ/h, where 23.6% corresponds to the total exergy by residues (3.98 × 104 MJ/h). The novel strategy to use exergy analysis for process optimization proved to be useful to detect critical stages and prioritize actions to improve.

Exergetic sensibility analysis and environmental evaluation of chitosan production from shrimp exoskeleton in Colombia

Waste valorization is one of the key aspects of cleaner production, there are a large number of residues such as crustacean exoskeletons which can be potentially used for obtaining valuable products. A comprehensive analysis involving both exergy and environmental aspects of chitosan production from shrimp shell wastes is presented. Mass and energy balances, needed to assess the presented process, were obtained by using Aspen Plus ® software. It was obtained a chitosan production rate of 12,152 t/y from a fed flow of 57,000 t/y of shrimp exoskeleton. Process simulation allowed estimation of environmental performance by applying the Waste Reduction Algorithm (WAR). The results revealed that the process consumes potential environmental impacts (PEI), obtaining negative values for these variables (in terms of generation rates) in all cases. Besides, the exergy analysis reported a global exergy efficiency of 4.58%, obtaining that astaxanthin removal stage reached the highest irreversibilities and exergy of wastes (707,699.57 MJ/h and 707,738.09 MJ/h). The sensitivity analysis showed that the efficiency of depigmentation stage can be increased by 92%, applying process improvements. This means an increase of the global exergy efficiency by 58.93%.

Reverse electrodialysis heat engine with multi-effect distillation: Exergy analysis and perspectives

The increasing worldwide energy demand is rising the interest on alternative power production technologies based on renewable and emission-free energy sources. In this regard, the closed-loop reverse electrodialysis heat engine is a promising technology with the potential to convert low-grade heat into electric power. The reverse electrodialysis technology has been under investigation in the last years to explore the real potentials for energy generation from natural and artificial solutions, and recent works have been addressing also the potential of its coupling with regeneration strategies, looking at medium and large energy supply purposes. In this work, for the first time, a comprehensive exergy analysis at component level is applied to a reverse electrodialysis heat engine with multi-effect distillation in order to determine the real capability of the waste heat to power conversion, identifying and quantifying the sources of exergy destruction. In particular, sensitivity analyses have been performed to assess the influence of the main operating conditions (i.e. solutions concentration and velocity) and design features (aspect ratio of the pile), characterizing the most advantageous scenarios and including the effect of new generations of membranes. Results show that the multi-effect distillation unit is the main source of exergy destruction. Also, using high-performing membranes, inlet solutions concentration and velocity of 4.5–0.01 mol/L and 0.2–0.36 cm/s, respectively, a global exergy efficiency of 24% is reached for the system, proving the high potential of this technology to sustainably convert waste heat into power.

Computer-Aided Exergy Sensibility Analysis of Nitrobenzene Production through Benzene Nitration Using an Acid Mixture

Nitrobenzene is widely produced via benzene nitration to be applied in several industries such as pharmaceutical, textile, and agricultural. In this work, an exergy sensibility analysis was performed with the aim of identifying possible opportunities of process improvements. The irreversibilities, exergy of wastes, and efficiency were calculated per stage through exergy balance. The simulation software Aspen plus V10.1 provided the physical exergies of process streams while chemical exergies were found in literature. A sensibility analysis was also carried out in order to study the effect of efficiency of some stages (polyfunctional reaction and cooling 1) on global exergy efficiency. This analysis reveals that nitrobenzene production from benzene is an efficient process from an exergy viewpoint (88%). The total irreversibilities, total exergy of wastes, and exergy of utilities-inlet were calculated in 41,647,341.85 MJ/h, 5,537,487.3 MJ/h, and 18,137,363.71 MJ/h, respectively. The results obtained from sensibility analysis suggested that heat flow of heat exchangers HE-201, HE-303, and HE-301 could provide energy requirements for heating.

Identification of Optimal Parameters for a Small-Scale Compressed-Air Energy Storage System Using Real Coded Genetic Algorithm

Compressed-Air energy storage (CAES) is a well-established technology for storing the excess of electricity produced by and available on the power grid during off-peak hours. A drawback of the existing technique relates to the need to burn some fuel in the discharge phase. Sometimes, the design parameters used for the simulation of the new technique are randomly chosen, making their actual construction difficult or impossible. That is why, in this paper, a small-scale CAES without fossil fuel is proposed, analyzed, and optimized to identify the set of its optimal design parameters maximizing its performances. The performance of the system is investigated by global exergy efficiency obtained from energy and exergy analyses methods and used as an objective function for the optimization process. A modified Real Coded Genetic Algorithm (RCGA) is used to maximize the global exergy efficiency depending on thirteen design parameters. The results of the optimization indicate that corresponding to the optimum operating point, the consumed compressor electric energy is 103.83 kWh and the electric energy output is 25.82 kWh for the system charging and discharging times of about 8.7 and 2 h, respectively. To this same optimum operating point, a global exergy efficiency of 24.87% is achieved. Moreover, if the heat removed during the compression phase is accounted for in system efficiency evaluation based on the First Law of Thermodynamics, an optimal round-trip efficiency of 79.07% can be achieved. By systematically analyzing the variation of all design parameters during evolution in the optimization process, we conclude that the pneumatic motor mass flow rate can be set as constant and equal to its smallest possible value. Finally, a sensitivity analysis performed with the remaining parameters for the change in the global exergy efficiency shows the impact of each of these parameters.

Exergetic evaluation of a conceptual design for hydrogen production and seawater desalination using an advanced nuclear reactor as energy source

In this work, a computational model to develop the conceptual design for hydrogen production and seawater desalination based on a modular nuclear reactor as an energy source is presented. The four-step copper-chlorine (Cu-Cl) process is used to produce hydrogen coupled to the gas turbine modular helium reactor (GT-MHR) nuclear system through a Brayton cycle for the electrical energy generation. A fraction of the thermal energy from the GT-MHR system is used to reach and maintain the temperature requirements in the Cu-Cl process. The rejected heat from the oxy-decomposition reaction is used to desalinate seawater through a multi-stage flash (MSF) process. It is employed a chemical process simulator in order to develop a computational model of the proposed system. The global energy and exergy efficiencies of the proposal are 32.47% and 52.20% respectively, producing 0.2190 kg/s of hydrogen and desalinating 4.9492 kg/s of seawater. It is made an estimate of the cost of hydrogen produced using HEEP®, resulting in 2.77 $/kgH2.

Exergy, environ–economic and economic analyses of a tubular solar water heater assisted solar still

Active solar stills are well known for their higher amount of distillate production than conventional stills. In this paper, a tubular solar collector assisted solar still was suggested for desalting saline water. Its exergy performance, enviro–economic and economic analysis has been carried out. The obtained findings were compared to a simple solar still of similar dimensions. Results revealed that the annual yield of the traditional and modified solar stills was estimated to be ∼405.04 and ∼549.77 kg/m2. The hourly exergy efficiency and global exergy efficiency of the passive system attained ∼7 and ∼30% and similarly for the active system ∼11 and ∼41%, respectively. The economic analysis shows that distilled water cost is minimum when the interest rate and the lifespan are 5% and 30 yrs, respectively, for the simple solar still (i.e. ∼0.018 $/L), while under same conditions, it reaches ∼0.036 $/L in case of improved still. Further, the payback period of the passive and active solar distillers was estimated to be around 7.7 yrs and 21 yrs, respectively, based on the lowest interest rate (5%) and selling price of distilled water of 0.04 $/L. The environmental cost parameter (ZCO2) comes out to be ∼4.42 $/annum on the basis of exergy for the active solar unit. It can be concluded that high distilled water production and less space occupancy are making the enhanced solar unit competitive and feasible.