Main Sources Of Exergy Destruction Research Articles

Exergy and thermoeconomic analysis of a novel polygeneration system based on gasification and power-to-x strategy

This study introduces a novel polygeneration system that integrates biomass gasification, anaerobic digestion, photovoltaic (PV) energy, and electrolysis to enhance system flexibility and efficiency. The system includes an allothermal gasification unit that processes lignocellulosic biomass sourced from a botanical garden. The gasifying agent, either steam or oxygen, is supplied by an alkaline electrolyzer, which operates under a Power-to-X strategy, utilizing surplus energy from a PV field. The resulting syngas and hydrogen are blended with biogas from an anaerobic digester, which treats municipal waste, to power a cogenerator. This cogenerator meets the electricity, heating, and cooling demands of a hospital, while the PV field powers the botanical garden. The systems components are modeled using various tools and integrated into the TRNSYS environment for dynamic simulation. An exergy analysis identifies the main sources of exergy destruction, while a thermo-economic analysis evaluates the energy, environmental, and economic impacts of a demonstration plant located in Bogotá’s Botanical Garden. Simulation results show that the system achieves an overall exergy efficiency of around 35 %, with a 96 % reduction in primary energy consumption compared to a reference system, avoiding nearly 6000 tons of CO2 emissions annually. From an economic perspective, the system is profitable, with a payback period of 3.02 years and a Net Present Value of $15.23 million, almost double the capital cost. The gasification unit's exergy efficiency is significantly higher when using oxygen (0.50) compared to steam (0.25), underscoring the importance of integrating electrolysis for improved biomass conversion. The alkaline electrolyzer operates efficiently within its optimal range, with an energy efficiency close to 0.70 and an exergy efficiency around 0.60, effectively utilizing 25 % of the total PV production.

Multi-aspect analysis and optimization of biomass-fueled multi-generation plant

Biomass fuels are an interesting renewable energy, which represents a higher performance, especially their integrated mode with the solid oxide fuel cell. This integration provides a higher thermodynamic performance along with a lower environmental impact. Hence, the current paper proposes an innovative multi-generation consisting of biomass-fueled solid oxide fuel cell combined with a gas turbine cycle. This integration's wasted heat is harnessed via a steam Rankine cycle, a double-effect refrigeration cycle, and a proton exchange membrane electrolyzer. Furthermore, the heat loss of the steam Rankine cycle is utilized to drive an organic Rankine cycle. The energy, exergy, economic, and environmental approaches are implemented to attain the designed scheme's performance. Five multi-objective optimization scenarios are applied to assess a proper optimal operating mode. The results showed that the gasifier is the main source of exergy destruction, with a value of 597.4 kW. Also, the increment of cell number in the fuel cell and gasification temperature reduces both thermodynamic and economic performances. At the optimal state, the deigned configuration’s exergy efficiency and payback period are attained about 60.03% and 1.45 years.

Analysis of a solar driven ORC-absorption based CCHP system from a novel exergy approach

The present study comprehensively analyses the thermodynamic performance of a zero-emissions solar driven trigeneration system using a numerical approach. The analysis is conducted from both the First and Second law of Thermodynamics viewpoints, employing a novel and coherent exergy approach. Solar parabolic trough collectors (SPTCs) provide the heat input to an organic Rankine cycle (ORC) system, while a single-effect H2O/LiBr absorption heat pump is coupled in cascade to the ORC. The proposed ORC layout is based on a single-pressure regenerated, recuperated and superheated cycle. There is divergence of opinion among researchers regarding key aspects of the exergy analysis of trigeneration systems. Therefore, this study proposes the definition of the dead state conditions for each subsystem individually, taking into account their specific constraints. Unlike temperature, specific dead state conditions for pressure and composition are defined separately. An energy-exergy parametric approach is conducted to evaluate the effects of different system parameters on the system performance. The system is also optimized following single and multi-objective approaches with different criteria. The optimum system achieve an energy efficiency of 152.4%, an exergy efficiency of 21.1%, and an electrical-exergy efficiency of 17.5%. The electricity, cooling and heating productions are 82.1 kW, 200.4 kW and 471.7 kW, respectively. The SPTCs are identified as the main source of exergy destruction, responsible for 73% of inlet exergy is destructed. In addition, the systeḿs performance is shown to be sensitive to the variations in the solar field outlet temperature and in the ORC condensation temperature. Consequently, controlling these parameters could be effectively utilized for regulating power generation as well as cooling and heating production.

Thermodynamic analysis of SOFC–CCHP system based on municipal sludge plasma gasification with carbon capture

To solve the environmental problems associated with municipal sludge incineration and landfilling, a combined cooling, heating, and power (CCHP) system integrating plasma gasification, solid oxide fuel cell (SOFC), gas turbine, supercritical carbon dioxide (S-CO2) cycle, and double-effect absorption refrigeration cycle (ARC) is proposed. Additionally, the CO2 generated in the system is captured to reduce the environmental impact. Energy, exergy, and sensitivity analyses of the developed system are conducted. Key parameters such as the SOFC temperature, SOFC pressure, and fuel utilization rate affecting the system performance are studied. The results show that net electrical efficiencies of the SOFC and the system are 41.96 % and 50.00 %, respectively. The exergy efficiency and comprehensive energy utilization rate of the system are 47.04 % and 87.59 %, respectively. The system can generate a power of 175.03 kW, cooling of 45.70 kW, and heating of 85.82 kW under the design conditions, accounting for 67.46 %, 21.23 %, and 11.31 % total energy output of system, respectively. The three main sources of exergy destruction of the system are the plasma gasification, SOFC, and supercritical CO2 cycle subsystems, accounting for 36.8 %, 12.2 %, and 10.7 % exergy destruction, respectively. The system performs the best when the SOFC temperature is 910 °C and the fuel utilization rate is between 0.85 and 0.90. The SOFC pressure has little effect on the system performance. In addition, the carbon capture rate of the system can reach 97.50 %. The CCHP system has high thermodynamic efficiency and hence can convert municipal sludge efficiently into clean energy; therefore, this study provides a new concept for resource treatment of urban sludge.

Conventional and advanced exergy analysis of large-scale adiabatic compressed air energy storage system

Identifying the main sources of exergy destruction is a significant method for promoting high-efficiency operation of compressed air energy storage (CAES) systems. Advanced exergy analysis is free from the limitations of traditional exergy analysis and identifies the optimization order of the components and clarifies their relationships. This method is significant for developing system improvement strategies for optimization. In this study, based on the actual engineering of an adiabatic compressed air energy storage (A-CAES) power plant, real, unavoidable, and hybrid thermodynamic cycles were established, and conventional and advanced exergy analyses were conducted for it. The results showed that the endogenous exergy destruction of the main components was greater than the exogenous exergy destruction, implying the importance of optimizing the components. In addition, endogenous and exogenous exergy destructions indicate a highly complex relationship between the components. The avoidable exergy destruction indicated the highest potential for improvement of the third-stage heat exchanger (HEX3) contributing to 13.15 % of the total avoidable exergy destruction of the system; therefore, HEX3 has the highest optimization value. In addition, the second-stage heat exchanger (HEX2) and first-stage heat exchanger (HEX1) also exhibited higher potential for improvement.

Performance enhancement in hybrid static power generation by AMTEC–TEG systems: Energy, exergy, and interactions analyses and optimizations

Alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) are two static energy conversion devices with attractive attributes including high scalability and the ability to utilize renewable energy sources. The present study analytically simulates and optimizes the performance of a novel hybrid AMTEC–TEG system from energy and exergy perspectives. The study scrutinizes interactions between the two devices, exergy destruction sources, solutions toward enhancing exergy efficiency, and the impacts of the heat sink, not accomplished in the open literature. The results reveal that exergy loss within the AMTEC condenser is the main source of exergy destruction; nonetheless, there exists a number of optimal designs by which the TEG can effectively recover this lost exergy. Also, the results show that a simple fin-fan or a passive heat exchanger can be sufficient for cooling the hybrid system while protecting the hybrid system’s valuable features like static and maintenance-free operation. The maximum values of energy and exergy efficiencies and generated power, attained within an improved load-following range for the hybrid system, are respectively 35.6%, 47.8%, and 8136 W. Furthermore, comparisons with similar systems acknowledge the superiority of the proposed hybrid system. Overall, the hybrid system is seen to be of high potential as a flexible, modular, static power generation system whose advantages are thoroughly discussed alongside its weaknesses, providing beneficial information for future studies.

Dynamic simulation of an integrated energy system for buildings in cold climates with thermal energy storage

In the current study, a building of a Hotel in cold weather conditions is simulated to be powered by a Combined Cooling, Heating and Power (CCHP) system in a transient manner. The system is comprised of photovoltaic thermal panels as renewable technology, coupled with a power block of MGT and cooling devices to produce the needs of the building. To handle the energy flows effectively, the system is able to sense the temperate of ambient with different controllers occupied in the system. Using TRNSYS as a promising and powerful tool to carry out the research dynamically, the thermodynamic, economic, and environmental behavior of the system is investigated. Research results dawned on the fact that the integrated system can generate all the needs of the proposed Hotel. Simulation outcomes indicate that an auxiliary heater plays a critical role since the temperature of 120 °C is constantly required for heating and cooling generation, and the power input to the heater is a challenging value. Although the heater is on and working 85% of the year, the results of the system show that in 65% of the year, the generated power is more than the power demand of the house. Moreover, the annual GHG emission is 0.16 Ton/MWh, in which the minimum of CO2 to the environment happens in July, and the maximum happens in January with 0.085 Ton/MWh and 0.17 Ton/MWh, respectively. Exergy analysis results show that the combustion chamber and PVT are the main sources of exergy destruction in the whole system. The building dynamic simulation results show that the system requires 34 kW cooling demand and 47 kW heating demand.

Modeling and performance analysis of a hybrid conventional solar still–adsorption desalination system

This study presents a thermodynamic modeling and performance analysis of a hybrid desalination system consisting of a conventional solar still (CSS) and an adsorption desalination system (ADS). To evaluate the performance of the system, a small scale model of a hybrid CSS-ADS system is designed, fabricated and tested under the meteorological condition of Kollam, Kerala, India. Water productivity of the hybrid CSS-ADS, followed by, assessing the coefficient of performance of the system is also carried out. The maximum water productivity of the system is estimated as 750 ml. The proposed hybrid system is able to produce the cooling effect along with desalination during its operation. The coefficient of performance (COP) is obtained as 0.58. The performance of the system is also assessed based on the second law of thermodynamics to study exergy loss and exergy efficiency of each and every component of the system. It is observed that the main sources of exergy destruction in the hybrid system occurs in the solar still basin and adsorbent bed of ADS. The total exergy loss and exergy efficiency of the hybrid system is found to be 0.224 W and 29.6%, respectively. Variation of brine water temperature, heat transfer coefficients, water productivity of CSS and ADS are also presented in this study. The study aims at a formidable solution to the low performance of conventional solar still.

Comparative analysis of compressed carbon dioxide energy storage system and compressed air energy storage system under low-temperature conditions based on conventional and advanced exergy methods

It is of great significance to determine the main source of exergy destruction for the optimal design of the high-efficiency energy storage system. In this paper, conventional exergy analysis and advanced exergy analysis methods were adopted to analyze the exergy destruction in the low-temperature Compressed Carbon dioxide Energy Storage (LT-CCES) system and low-temperature Compressed Air Energy Storage (LTA-CAES) system under the same system configuration as well as key parameters. Conventional exergy analysis is a commonly used method to show the exergy destruction in system components, while advanced exergy analysis takes into account the interactions between system components as well as the technical limitations of each component, and can get more detailed exergy destructions in system components. The results showed that, according to conventional exergy analysis, the exergy efficiency of the LT-CCES system was 56.28% and the exergy efficiency of the LTA-CAES system was 63.93%, indicating that the exergy destruction in the LT-CCES system was larger than that in the LTA-CAES system. In terms of components, the cold energy storage tank (CEST) had the largest exergy destruction, accounting for 30.97% and 32.23% of the total exergy destruction in the LT-CCES system and LTA-CAES system respectively. According to advanced exergy analysis, in both systems, the major exergy destruction in each component was the endogenous exergy destruction, implying the importance to optimize components themselves. In terms of the avoidable exergy destruction, the proportion of the CEST in the two systems were the largest (45.17% in LT-CCES and 44.51% in LTA-CAES). According to the results of conventional and advanced exergy analyses, in the LT-CCES system, CEST should be given the first priority for optimization, followed by turbine2 and compressor1, while in the LTA-CAES system, CEST should be given the first priority for optimization, followed by turbine1 and turbine2.

Activated Carbon from Winemaking Waste: Thermoeconomic Analysis for Large-Scale Production

An activated carbon manufacturing process from winemaking waste is analyzed. In that way, vine shoots conversion is studied as a basis for plant designing, and mass and energy balances of hydrothermal carbonization and physical activation are fulfilled. To develop an energy-integrated plant, a network of heat exchangers is allocated to recover heat waste, and a cogeneration cycle is designed to provide electricity and remaining heat process demands. Furthermore, thermoeconomic analysis is applied to determine the thermodynamic efficiency and the economic viability of the plant. Energy balance indicates that heat exchangers energy integration covers 48.9% of the overall demands by crossing hot and cold streams and recovering heat from residual flue gas. On the other hand, the exergy costs analysis identifies combustion of pruning wood as the main source of exergy destruction, confirming the suitability of the integration to improve the thermodynamic performance. Attending to economic costs analysis, production scale and vineyard pruning wood price are identified as a critical parameter on process profitability. With a scale of 2.5 ton/h of pruning wood carbonization, a break-event point to compete with activated carbons from biomass origin is reached. Nevertheless, cost of pruning wood is identified as another important economic parameter, pointing out the suitability of wet methods such as hydrothermal carbonization (HTC) to treat them as received form the harvest and to contribute to cutting down its prices.

Numerical and experimental work to assess dynamic advanced exergy performance of an on-grid solar photovoltaic-air source heat pump-battery system

In the near future, renewable energy powered air conditioning systems will play an important role in the building sector. In this study, a solar photovoltaic powered air source heat pump with a battery system was modeled and numerically simulated using Transient System Simulation Tool. The experimental studies were also carried out to validate the developed model. The novelty concerns to integrate conventional and advanced exergy analyses into the numerical model to annually determine the exergy destructions with main sources (exogenous, endogenous, unavoidable, avoidable and their combination) at a component level.The results obtained from the experiments showed that on-site weather conditions, air temperature difference occurring between inlet and outlet of the evaporator unit, and the power flow between the main system components were considerably modeled well. Based on the simulated studies, conventional exergy analysis revealed that the highest annual exergy destruction amount was due to the photovoltaic panels with 23.3 MWh while the lowest one occurred in the batteries with 156.1 kWh. This also indicated that the highest potential for improvement lays within the photovoltaic panels. According to the simulated results considering the advanced exergy analysis, the yearly exergy destruction amount in the photovoltaic panels and in the heat pump (920.6 kWh) were fully endogenous corresponding to unavoidable values of 21.3 MWh and 455.3 kWh, respectively. On the other hand, all the main sources of exergy destruction were seen for both inverter and batteries where the contribution of the unavoidable endogenous (429.9 kWh) and unavoidable exogenous (66.2 kWh) parts were annually found to be significant for the inverter and the batteries, respectively.

Energy, exergy and exergoeconomic analysis of a combined cooling, desalination and power system

Ocean thermal energy has attracted much attention for its unique advantages. Multi-generation systems are emerging as an effective solution to further improve energy efficiency and economy of ocean thermal energy conversion (OTEC) system. In this paper, a novel hybrid OTEC system combing cooling, desalination and power (CCDP) is proposed facing the actual demands of remote islands at low latitudes. The cogeneration of cooling capacity, fresh water and power are achieved by the subsystems of ejector refrigeration cycle (ERC), multi-effect distillation (MED) desalination and organic Rankine cycle (ORC). A detailed mathematical model for the proposed system is developed based on the thermodynamics and exergoeconomics. The effects of key operating parameters on the system performances are investigated from the perspectives of energy, exergy and exergoeconomic. The results indicate that the highest primary energy saving ratio (PESR) and exergy efficiency of the proposed system are up to 33.72% and 29.33%, respectively. The main sources of exergy destruction are the MED unit, generator and ejector, accounting for about 80% of the total exergy destruction. The improvement of both thermodynamic and exergoeconomic performances can be achieved at a higher generation pressure and a larger distillate production. The rise of condensing pressure is conducive to cutting down the unit costs of products, but will result in lower exergy efficiency and PESR.

Thermodynamics, economic and environmental analyses of a hybrid waste–solar thermal power plant

A novel hybrid configuration of solar parabolic trough collectors–waste incineration power plant was recently analyzed energetically in Denmark. Taking into account the true meaning of sustainability which is environmental friendliness and cost-effectiveness, and considering the existing gap of knowledge on the thermodynamic performance aspects of this hybrid system, this work conducts a thorough thermodynamic and sustainability analysis of this power plant. The main aim is to give a clear picture of the main advantages and any possible shortcomings of the hybrid power plant. For this purpose, the performance of the system is simulated for an entire year of operation under realistic solar irradiation fluctuations. The energy performance indices of the system are quantified and discussed. The exergy assessment of the hybrid cycle is accomplished, and the main sources of exergy destruction and economic losses are identified. The results show that the steam generator and the turbine cause the largest rates of irreversibilities of 36% and 20.8%. The environmental benefits and the overall cost of energy production of the system are calculated and compared to some other alternative power plants. In addition to the consistency of electricity production, the LCOE of the hybrid power plant decreases by 67% in comparison with the solar power plant. Comparing the system with a natural gas-fired power plant in terms of CO2 emission, it is shown that the hybrid system leads to less 74.5 thousand tonnes of CO2 emitted over an entire year.

Energy, Exergy and Economic Analyses of a Combined Heating and Power System with Turbine-Driving Fans and Pumps in Northeast China

The combined heating and power (CHP) system with turbine-driving fans and pumps is more efficient and economical in meeting heat demand in cold areas, however, there are no detailed studies that investigate its thermodynamic performance, improvement possibilities and economy. In this paper, the energy, exergy and economic analysis of a CHP system with turbine-driving fans and pumps operated in Northeast China were conducted to provide insights into improvement options. It is revealed that the boiler is the main source of exergy destruction, followed by the steam-water heat exchangers (SWHE), temperature and pressure reducer (TPR), turbines, and deaerator. The energy and exergy efficiencies of the system are 89.72% and 10.07%, while the boiler’s are 84.89% and 30.04%. The thermodynamic performance of the boiler and turbines are compared with other studies, and the inefficiencies of major components are analyzed and some advice for further improvement is given. As the reference state changes, the main conclusions stay the same. The turbine-driving mode saves an electricity cost of 16,654.08 yuan on 15 December 2018. The effect of electricity price and on-grid price on the saved daily electricity cost is investigated and it proves that the turbine-driving mode is more economical in China.

Second-law analysis of the reforming-controlled compression ignition

This paper presents the optimization of energy conversion in a novel reforming-controlled compression ignition system, combining the benefits of low-temperature combustion with high-pressure thermochemical recuperation (mostly from the perspective of the second law of thermodynamics). Further, new insights into ways of improving efficiency are provided. A promising renewable fuel dimethyl ether is analyzed for the first time as a primary fuel. A comprehensive analysis of various factors influencing exergy destruction in the reforming-controlled compression ignition system in their complex interdependence is also performed for the first time. Exergy mapping results show that approximately 33% of the exergy supplied to the system is destroyed owing to irreversible processes in the cylinder itself, and approximately 5% is destroyed in the reforming system (intercooler, vaporizer, and reformer). The reformer is the main source of exergy destruction in the reforming system. Approximately 45% and 38% of the engine exergy destruction is related to chemical reaction and in-cylinder-walls heat interaction, respectively. The results indicate that the efficiency improvement due to second-law optimization reaches up to 7.1%, and if the compression ratio is increased to 18:1 instead of 16:1, this reaches up to 9.2%. The higher improvement is achieved at the highest loads.

Energetic and exergetic performance analysis of a solar driven power, desalination and cooling poly-generation system

This paper presents a thermodynamic analysis of a poly-generation system powered by solar thermal energy using parabolic trough collectors. The proposed system consists of an organic Rankine cycle, a multiple effect distillation and an absorption cooling unit. The performance analysis of the solar system is conducted for different configurations: power generation only, cogeneration power and cooling, cogeneration power and desalination, and poly-generation. The effects of turbine inlet temperature and pump inlet temperature on the energetic and exergetic system performance as well as the net power output and total exergy loss of the system are examined. In addition, exergetic parameters, including system total exergy loss, fuel depletion ratio and improvement potential were analyzed. The study reveals that increasing the turbine inlet temperature increases the performance while it reduces the total exergy destruction rate of the system. The result of the study also shows that the two main sources of exergy destruction are the solar thermal collector and desalination unit; with 49.3% of the input exergy (76% of the total exergy loss) destructed in the collector while 9.6% of the inlet exergy (14.9% of the total exergy loss) is destroyed in the desalination system. The overall improvement potential of the system was found to be 64.8%.

Exergy Analysis of Fluidized Desiccant Cooling System.

One of the main challenges in the design and implementation of fluidized desiccant cooling (FDC) systems is increasing their low COP (coefficient of performance). Exergy analysis is one of the tools especially suitable for improvement and optimization of FDC systems. The improvement of performance is impossible as long as the main sources of exergy destruction are not identified and evaluated. In this paper, the exergy analysis was applied in order to identify these components and processes of the FDC system that are mainly responsible for exergy destruction. Moreover, the exergy efficiency of a simple fluidized desiccant cooler was determined. The results showed that fluidized beds and regenerative heat exchanger were the main exergy destruction sources with a 32% and 18% share of total exergy destruction, respectively. On the other hand, the direct evaporative cooler and air cooler placed after the desorbing fluidized bed were characterized by the lowest exergy efficiencies. This work contributes to better understanding of FDC operation principles and improvement of the performance of FDC technology.

Exergy and network analysis of chemical sites

Chemicals production is responsible for 10% of global energy consumption and 7% of greenhouse gas emissions. Material and energy efficiency are the focus of industrial and policy decision-makers but are often pursued as separate strategies. In addition, the solutions investigated are often localised without exploring the dynamics and efficiency relationships between different areas of a chemical site. Past studies have applied network analysis to study large complex systems such as national economies. The applicability to complex systems at the scale of a chemical site are clear but unexplored so far. This paper uses an integrated energy and materials metric to study an ammonia site and a steam methane reforming (SMR) plant in detail. Exergy flow maps are constructed using Sankey diagrams to illustrate the resource (material and energy) flows around the site and the principal sources of exergy loss and destruction. Exergy efficiencies and exergy destruction values are calculated for every plant, equipment within the SMR plant and mechanism of exergy destruction. This information can guide improvement interventions. The site is then modelled using a network analysis approach to improve the understanding of the energy and material interactions within it. The SMR plant is the main source of exergy destruction with an exergy efficiency of 68% and exergy destruction of 600 GJ/h, followed by the ammonia synthesis and water gas shift (WGS) plants with 99 and 59 GJ/h respectively. Within the SMR plant, the two main burners contributed the most destruction with a total of 190 GJ/h. Combustion and heat exchange are the main exergy destruction mechanisms with 206 and 141 GJ/h respectively, a result that could guide higher-level improvement efforts. More realistic transit and fuel-product exergy efficiencies definitions are found to be consistently lower than conventional efficiency definitions, an effect most pronounced in heat exchangers. The network analysis detected communities of tightly connected plants in the ammonia site and can indicate groups where cascading effects of resource efficiency improvements could materialise. The different network metrics quantifying the importance of individual plants ranked some plants, such as the steam and ammonia synthesis plant, consistently highly. Other plants, like the tail gas stripping, ranked highly on some metrics and low on others. Further work can be undertaken to better tailor some of the network metrics for the purposes of a chemical site modelled as a network. This study’s focus is ammonia production and the SMR process, but the methodology can be applied to any industrial process, particularly chemical sites, with minimal adjustments.

Exergy analysis for the multi-effect distillation - reverse electrodialysis heat engine

Reverse electrodialysis (RED) heat engine is a novel technology to convert low grade heat into electricity. Through combining the multi-effect distillation (MED) with RED, the so-called MED-RED heat engine has received increasing attention over the recent years. In this paper, a comprehensive theoretical exergy analysis for the MED-RED heat engine has been carried out based on a validated mathematical model. And the influences of relevant operation and design parameters on the exergetic performance of the heat engine were investigated. The results showed that the preheater, condenser and RED unit were main sources of exergy destruction in the heat engine. The total relative exergy destruction of these three components was 59.8% and the exergetic efficiency of the heat engine reached 4.7% under the design condition. Moreover, elevating the temperature of hot water had a negative effect on enhancing the exergetic performance of the heat engine. On the contrary, increasing the concentration of initial brackish solution or the number of effect evaporators in the MED was helpful for improving the exergetic performance of the heat engine. Finally, discussion in terms of improving the exergetic performance of the heat engine was carried out and relevant approaches were presented.

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.