Search

Water scarcity threatens human life and it is likely to be a main concern in the next century. In this work, a novel multigeneration system (MGS) is introduced and assessed with energy, exergy, and economic analyses. This MGS includes a gas cycle, multieffect distillation, an absorption refrigeration cycle, a heat recovery steam generator, and electrodialysis. Electrodialysis is integrated into this configuration to produce sodium hydroxide and hydrogen chloride from brine to prevent its release to the environment with harmful impacts. The other products are electricity, cooling, and demineralized water. For the evaluation of the proposed system, one computer code is provided in engineering equation solver software. For physical properties calculation, the library of this software is used. The MGS produces 614.7 GWh of electrical energy, 87.44 GWh of cooling, 12.47 million m3 of demineralized water, and 0.092 and 0.084 billion kg of sodium hydroxide and hydrogen chloride over a year. Energy and exergy evaluations demonstrate that the MGS energy and exergy efficiencies are 31.3% and 18.7%, respectively. The highest and lowest value of exergy destruction rate is associated with the combustion chamber and pump, respectively. The economic evaluation indicates that the net present value of this proposed system is 3.8 billion US$, while the internal rate of return and payback period, respectively, are 0.49 and 2.1 years.

Biomass gasification technology is a promising process to produce a stable gas with a wide range of applications, from direct use to the synthesis of value-added biochemicals and biofuels. Due to the high capital/operating costs of the technology and the necessity for prudent management of thermal energy exchanges in the biomass gasification process, it is important to use advanced sustainability metrics to ensure that environmental and other sustainability factors are addressed beneficially. Consequently, various engineering techniques are being used to make decisions on endogenous and exogenous parameters of biomass gasification processes to find the most efficient, viable, and sustainable operations and conditions. Among available approaches, exergy methods have attracted much attention due to their scientific rigor in accounting for the performance, cost, and environmental impact of biomass gasification systems. Therefore, this review is devoted to critically reviewing and numerically scrutinizing the use of exergy methods in analyzing biomass gasification systems. First, a bibliometric analysis is conducted to systematically identify research themes and trends in exergy-based sustainability assessments of biomass gasification systems. Then, the effects of biomass composition, reactor type, gasifying agent, and operating parameters on the exergy efficiency of the process are thoroughly investigated and mechanistically discussed. Unlike oxygen, nitrogen, and ash contents of biomass, the exergy efficiency of the gasification process is positively correlated with the carbon and hydrogen contents of biomass. A mixed gasifying medium (CO2 and steam) provides higher exergy efficiency values. The downdraft fixed-bed gasifier exhibits the highest exergy efficiency among biomass gasification systems. Finally, opportunities and limitations of exergy methods for analyzing sustainability aspects of biomass gasification systems are outlined to guide future research in this domain.

The optimal equipment arrangement for a system for cogeneration of thermal and electrical energy for a total site is determined with exergoeconomic analysis. A steam power plant can operate concurrently in a dual-use mode producing steam and electricity. It is important to know the potential for cogeneration before designing and optimizing a central utility system in order to establish on site fuel demand targets. In the current study, two case studies with different backpressure steam turbines arrangement are considered and, if extra power generation is needed, designs with a system of condensing and gas turbines are examined. The minimum exergy destruction rate, maximum exergy efficiency, minimum total capital cost rate and minimum exergy destruction cost rate for these arrangements are investigated with exergoeconomic analysis. Finally, selected backpressure steam turbines arrangement in conjunction with the gas turbine system are introduced for finding the optimum arrangement of the cogeneration system in the total site with an exergoeconomic approach.

Due to continuous growth in population and sharp increase in energy and food demand, research on alternative energy sources independent of fossil fuels has increased over the last decade. Moreover, limitations on greenhouse gas emissions by developed and developing countries are imposing much pressure on the energy sector worldwide to use renewable energy sources such as solar, wind, biomass, hydro, and geothermal. Food production is one of the biggest industries in the world, and it consumes a large amount of energy in the form of heat and electricity. In this work, agro-product drying technologies powered by solar energy are presented and discussed. Different types of solar dryers based on direct, indirect and mixed modes are described. Moreover, energy, exergy, economic, and environmental analyses for these technologies are presented to determine the main parameters affecting the dryer performance. The results indicate that the air mass flow rate, temperature, moisture content, and drying time are the most important parameters in solar dryer performance. Finally, a comparative assessment of the performance of different existing solar dryer has been highlighted with a detail scope of future works.

Energy, exergy, exergoenvironmental, and exergoeconomic analyses of a natural gas boosting station are presented using a real‐gas model and actual operational data. The effect of varies performance parameters on the thermodynamic efficiencies, specific fuel consumption (SFC), gas‐phase emissions, and cost rates are assessed. The results show that, for the actual operational conditions of the gas boosting station, the exergy efficiencies are 76.1% and 73.9% in the hot and cold seasons, respectively. Moreover, the energy analysis at partial load reveals that the SFC varies from 0.285 kg/kWh to 0.302 kg/kWh, respectively, in maximum and minimum ambient temperatures. The exergoeconomic analysis along with the exergoenvironmental analysis shows that the total cost rate of gas boosting stations in hot and cold ambient conditions is 7390 US$/h and 8070 US$/h, respectively, with more than 60% related to the environmental impact. In this system, the highest exergoeconomic factor is attributed to the centrifugal gas compressor at 40.9%‐44.2% and the lowest to the air cooler at 0.030%‐0.036%, depending on the ambient temperature, which specifies the balance between capital cost and the cost of exergy destruction. The cost rate of the exergy destruction is more pronounced in the combustion chamber, and the overall cost rate of the exergy destruction can be improved significantly by increasing turbine inlet temperature which needs additional investment cost for the system.

Although energy is conventionally examined when studying thermodynamic flows and balances for the Earth and its systems, the planet does not consume energy as its energy inflows and outflows are in balance. Similarly, energy is conserved for systems on the Earth. The Earth does, however, consume exergy and generate entropy, and it is insightful to examine the thermodynamics of the Earth in terms of exergy, or the related quantity entropy. These perspectives are considered here for the Earth and its main systems: the biosphere, people and civilization. The work provides an enhanced understanding of the type, location and causes of thermodynamic losses for the Earth as well as its main systems and subsystems, and of the connections and relations between the Earth and its biosphere, as well as civilization and people. It is observed for the year 2019 that civilization uses exergy to create many products and services and that the exergy consumption rate of the Earth’s biosphere is approximately five times larger than that of civilization and 100 times larger than that of people as individuals. Also, the solar exergy rate provides the Earth with a very large exergy input rate, about 10,000 times greater than the needs.

Switching from fossil fuels to biofuels is an effective option for small-scale power production and cogeneration systems. The target of the current study is to propose and investigate a novel seasonal combined cycle driven by a biogas-fueled gas turbine from thermodynamic and economic viewpoints. Regarding the high-temperature of the turbine's exhaust gases, an integration of Rankine and ejector refrigeration cycles is configured. The bottoming cycle is designated for winter and summer conditions, independently. Hence, a combined cycle capable of operating as a cogeneration system producing electricity/heating or electricity/cooling, individually, is designed. Moreover, a parametric study based on assessing the impact of key parameters on the essential variables and a multi-criteria optimization trough a genetic algorithm are performed to attain the facilities of the proposal. According to the results, the capability of the whole system in winter conditions is significantly higher than that for summer conditions due to the higher heating capacity. Also, the evaluated variables are more affected by change in the environment temperature in both seasons. Additionally, the optimal overall energy, exergy and levilized cost of products are calculated as 79.2%%, 45.6%, and 21.7 $/GJ for summer and 70.7%, 37.0%, and 17.6 $/GJ for winter, respectively.

Transportation sector is one of the core parts of modern civilization. Proper utilization of energy and exergy in this sector is necessary to ensure energy loss and environmental sustainability. Increasing exergy efficiency will reduce carbon emissions from this sector. Since 1970, Reistad estimates have been widely used to determine the energy and exergy efficiencies of this sector. However, the modern transport sector has undergone significant changes in recent decades. Hence, it is necessary to apply new Reistad estimates in determining the energy and exergy efficiencies. This is the first study to apply updated Reistad estimates to explore the energy and exergy efficiencies in the transportation sector of Bangladesh based on the data from 2000 to 2017. The overall exergy efficiency is significantly lower than the energy efficiencies as it ranges from 27.7% to 30.0%. Efficiencies are lower as the maximum portion of input exergy is lost to the environment. The road subsector needs major improvements as it is responsible for major amount of exergy loss. A comparison is made between conventional and updated estimates which highlights that the updated estimates provide more accurate results. Thus, it is recommended to apply updated Reistad estimates in determining the energy and exergy efficiencies of the transport sector.

According to studies of solid-state cooling devices, the elastocaloric cooling device is now considered as a promising future cooling device that will soon reach the market and be competitive, as well as meet the increasing cooling demands of the hot regions in the world. Thus, in this work, the viability of using an elastocaloric cooling device with a solar energy-driven system is assessed and compared thermodynamically to a typical combined cooling and power system for the first time. These two systems are then compared first under the conditions of electricity and cooling demands of a community in Jeddah City. The present results show the overall energy and exergy efficiencies are higher for the novel system than the conventional system by differences of 4.63% and 1.10%, respectively. Also, the elastocaloric cooling device has a lower exergy destruction rate than the absorption chiller by a factor of 1.7. Then, parametric studies are conducted, and the findings show two main things. Firstly, the elastocaloric cooling device is more flexible in meeting higher cooling demands, above 262% cooling percentage, than the absorption chiller is. Secondly, the threshold point for the energetic COP of the elastocaloric cooling device has been identified to be 4.25 so that it becomes competitive in the market of cooling devices.

ispartof: APPLIED ENERGY vol:329 status: published

Based on the benefits of integrated gasification combined cycles (IGCCs), a cogeneration plant for providing electricity and freshwater is proposed. The main novelties of the devised system are the integration of biomass gasification and a regenerative gas turbine with intercooling and a syngas combustor, where the syngas produced in the gasifier is burned in the combustion chamber and fed to a gas turbine directly. The energy discharged from the gas turbine is utilized for further electricity and freshwater generation via Kalina and MED hybridization. The proposed system is analyzed from energy, exergy, exergoeconomic, and reliability–availability viewpoints. The optimal operating condition and optimum performance criteria are obtained by hybridizing an artificial neural network (ANN), the multi-objective particle swarm optimization (MOPSO) algorithm. According to results obtained, for the fourth scenario of the optimization process, optimal values of 45.10%, 14.27 kg·s−1, 12.95 USD·GJ−1, and 8141 kW are obtained for the exergy efficiency, freshwater production rate, sum unit cost of products, and net output power, respectively. According to reliability and availability assessment, the probability of the healthy working state of all components and subsystems is 88.4403%; the system is shown to be 87.74% available of the time over the 20-year lifetime.

This work introduces and develops the concepts of solar exergoeconomic and exergoenvironmental maps for photovoltaic systems. These maps are developed to complement the information provided by solar exergy maps for recognizing the most appropriate sites for hosting photovoltaic power plants. A detailed case study is carried out to demonstrate how the proposed approaches can be practically applied to promote solar photovoltaic systems. More specifically, the exergoeconomic and exergoenvironmental performances of a 100 kW grid-connected photovoltaic plant are assessed for several Iranian cities over the year based on actual climatic, economic, and environmental impact data. The spatio-temporal solar maps for unit exergoeconomic cost and unit exergoenvironmental impact of electricity generation are then developed for the investigated climatic conditions for the first time. In order to demonstrate the suitability and reliability of the developed maps, their interoperations are assessed and compared to those for exergy efficiency. The results show that solar exergoeconomic and exergoenvironmental maps provide more valuable information on the performance of solar photovoltaic systems than exergy efficiency maps, demonstrating their robustness for optimum site selection and plant sizing. In addition, the exergy efficiency maps may result in inappropriate site selection of photovoltaic solar farms. The central, south, southeast, and some west parts of Iran are the most suitable locations for implementing photovoltaic power fields from exergoeconomic and exergoenvironmental viewpoints. The developed approaches can also be used for locating and sizing other renewable energy systems under different climatic conditions.

An integrated system for the simultaneous production of electricity and fresh water is proposed based on a solid oxide fuel cell (SOFC). In this system, a Kalina cycle is utilized to recover waste heat from the SOFC stack. Furthermore, a thermoelectric generator is employed to recover the heat dissipated in the Kalina condenser. In the proposed configuration, the energy required for reverse osmosis desalination can be supplied by a Kalina cycle and a thermoelectric generator. The system uses methane as its primary fuel. Electrochemical equations for the fuel cell are considered, as are thermodynamic and exergy-economic relations for the components of the system. The effects on the performance of the proposed hybrid system of variations in design parameters such as current density, SOFC inlet temperature, fuel utilization factor, inlet pressure of the Kalina cycle turbine and concentration of water-ammonia solution in the Kalina cycle are examined. The SOFC stack is seen to make the highest contribution to the total exergy destruction of the system. To strive simultaneously for maximum efficiency and minimum total cost, optimization is carried out using a genetic algorithm. The total optimum point of the system is the trade-off between the optimization objectives. At this point, the net electrical power production is about 1.3 MW and the production rate of fresh water reaches 226 m3/day, while the exergy efficiency and total cost rate are 54% and 36.8 $/hr, respectively.

Roasting is one the most widely used unit operations for the processing of pistachio nuts. The operation is aimed at improving their appeal to consumers. The process is energy-intensive, re...

A transient thermodynamic analysis is reported of a novel chemical hydrogen storage system using energy and exergy approaches. The hydrogen is stored chemically in ammonia using the proposed hydrogen storage system and recovered via the electrochemical decomposition of ammonia through an ammonia electrolyzer. The proposed hydrogen storage system is based on a novel subzero ammonia production reactor. A single stage refrigeration system maintains the ammonia production reactor at a temperature of −10 °C. The energy and exergy efficiencies of the proposed system are 85.6% and 85.3% respectively. The proposed system consumes 34.0 kJ of work through the process of storing 1 mol of hydrogen and recovering it using the ammonia electrolyzer. The system is simulated for filling 30,000 L of ammonia at a pressure of 5 bar, and the system was able to store 7500 kg of ammonia in a liquid state (1% vapor) in 1500 s. The system consumes nearly 45.3 GJ of energy to store the 7500 kg of ammonia and to decompose it to reproduce the stored hydrogen during the discharge phase.

In this paper, a parallel flow double-effect water-lithium bromide absorption refrigeration cycle is investigated using comprehensive exergy-based analyses. The exergy destruction of each device is calculated and used for further analysis. The performance of the system is optimized for maximum coefficient of performance and exergy efficiency, considering the distribution ratio as a variable using the Golden Section method. The maximum coefficient of performance, i.e. 1.295, is obtained at a high pressure generator temperature of 169.6 °C, and the maximum exergy efficiency, i.e. 0.225, is obtained at a high pressure generator temperature of 142.7 °C. Advanced exergy analysis, a state of the art thermodynamic method, is employed for diagnosing equipment and cycle malfunctions. Not only can the aforementioned analysis pinpoint the source of irreversibility, it also provides the avoidable irreversibility as well. The results show that the endogenous part of the exergy destruction is much larger than the exogenous part, implying it is better to focus on component efficiencies to improve system performance. Moreover, the unavoidable part of the total exergy destruction is much larger than the avoidable portion, indicating that exergy destruction cannot be decreased owing to technical limitations of equipment.

Energy, exergy, economic, advanced exergy, and extended exergy analyses are reported of a Bergey Excel-S wind turbine with nominal power of 10 kW in two cities: Tehran (medium wind potential) and Manjil (high wind potential). The results show that the energy efficiency of the wind turbine is higher in Manjil (3.33%) than Tehran (1.08%). The exergy efficiency in these areas is lower. This means that the exergy efficiency in Manjil is 10.8% but in Tehran is 6.43%. The cost of electricity generated by the wind turbine in Tehran is 0.23 U S $ kWh . This cost is reduced to 0.73 U S $ kWh in Manjil. The advanced exergy analysis demonstrates that the avoidable exergy destruction percentage of the wind turbine increases with wind speed. The extended exergy analysis shows that, in windy areas, the highest exergy percentage is exhibited by the system’s input and output exergy flows and power production (88.7%), while, in areas with medium wind speed potential, the exergy is equal to is the equivalent extended exergy content of the influx of capital cost (58.9%).

The current study is directed at the optimization and energy, exergy, and economic analyse of a solid oxide fuel cell, integrated with gas and steam trigeneration systems. The variables considered are the fuel cell’s temperature and pressure, air-to-fuel molar ratio, the compressor and gas turbine pressure ratio, combustion chamber temperature, steam cycle pinch point. The objective functions are the exergy efficiency and the electricity cost. The results show that by selection of the optimal values of the fuel cell’s temperature and pressure, air-to-fuel molar ratio, compressor and gas turbine pressure ratio, and the cycle pinch point as 809.8 K, 360 kPa, 2, 2.05, 11.6, and 34.9, the exergy efficiency is increased by 8%, and the produced electricity cost is reduced by 9.7%. The sensitivity analysis shows that an increase in compressor pressure ratio leads to a decrease in the energy and exergy efficiencies and entropy production rates. A change in air-to-fuel molar ratio from 2 to 3 causes the triple cycle electricity cost first to increase and then to decrease.

A solar based biomass co-fired combined cycle with hydrogen production is proposed and assessed with conventional and modified thermodynamic and exergoeconomic analyses. The cycle uses biomass and solar energy as renewable energies along with the fossil fuel natural gas. Hydrogen is produced by the photovoltaic/thermal system and in one option is injected to the combustion chamber of combined cycle to reduce fossil fuel usage and CO2 emissions. Modified analyses are based on avoidable and unavoidable exergy destruction and component investment costs. Although hydrogen injection does not increase efficiencies, it reduces the exergy destruction by 0.24%, the total exergy destruction cost rate by 3.36%, the CO2 discharge rate by 2% and the total unit product cost by 3%. Based on conventional analysis, the gasifier, the post combustion chamber and the combustion chamber are the components with high exergy destructions, while based on modified analysis the combustion chamber, the gas turbine and the air compressor have highest exergy destructions. The components with the highest investment cost rates are shown to be the steam turbine, gas turbine and air compressor by conventional method while with the modified method they are found to be the gas turbine, the air compressor and the steam turbine.

The use of solar energy to preheat natural gas before a city gate station (CGS) for reducing fuel consumption and environmental emissions is investigated in a real CGS. All analyses are conducted with a 1-h time-step throughout the entire year so that seasonal climate changes are accounted for precisely. A thermodynamic analysis of the hybrid system is performed with TRNSYS and verified with THERMOFLEX so as to ensure reliability. In addition, dynamic exergetic, exergoeconomic, and exergoenvironmental analyses for the proposed system are carried out. A life cycle assessment (LCA) based on Eco-indicator 99 is performed using SIMA PRO to compute the environmental impacts for each component of the system. The exergetic, exergoeconomic, and environmental analyses are performed in Engineering Equation Solver (EES) software. To perform the transient exergetic, exergoeconomic, and environmental analyses, the results of the thermodynamic analysis from TRNSYS are automatically imported into the EES code. The advanced exergetic, exergoeconomic, and exergoenvironmental analyses are performed to better determine components that have high potentials for improving the system; potentials are considered based on the exergy destruction, exergetic cost of destruction, and environmental impacts associated with exergy destruction.

This chapter covers the basic thermodynamic principles of various types of geothermal power plants. Energy and exergy analyses are provided for each type of geothermal power plant. Numerical examples of power plants are also presented.

In this paper, a multigeneration system is proposed, which utilizes geothermal energy and a lithium-bromide absorption cooling cycle. The proposed system is capable of providing electricity, heating, cooling, and domestic hot water to a small residential community in Vancouver, British Columbia, Canada. The performance of the system's heating and cooling capabilities were evaluated energetically and exergetically. A case study is presented by considering human occupancy loads and the impact of building material conditions on heating and cooling. System performance was investigated using parametric studies, where the operating conditions and ambient conditions were varied. Similar systems in the open literature were found to have an energetic and exergetic coefficient of performance (COP) of 0.8 and 0.3 for heating, while the proposed multigeneration system resulted in an energetic and exergetic coefficient of performance of 1.14 and 0.63 for heating, an increase of 30–52%. Additionally, the literature revealed that some systems resulted in an energy and exergy efficiency of 26.2% and 36.6%. The proposed multigeneration system achieved an energy and exergy efficiency of 31.86% and 63.33%, an improvement of 5.66–26.73%. The study was able to utilize the existing recommendations made by British Columbia to determine the necessary heating and cooling loads while also being able to successfully generate four useful outputs with a smaller footprint than those in the literature.

A new three step high temperature Cu-Cl thermochemical cycle for hydrogen production is presented. The performance of the proposed cycle is investigated through energy and exergy approaches. Furthermore, the effects of various parameters, such as the temperatures of the steps of the cycle and power plant efficiency, on various energy and exergy efficiencies are assessed with parametric studies. The results show that the exergy and energy efficiencies of the proposed cycle are 68.3% and 32.0%, respectively. In addition, the exergy analysis results reveal that the hydrogen production step has the maximum specific exergy destruction with a value of 150.9 kJ/mol. The results suggest that proposed cycle may provide enhanced options for high temperature thermochemical cycles by improving thermal management without causing a sudden temperature jump/fall between the hydrogen production step and other steps.

A novel and practical hydrogen storage system is developed and analyzed thermodynamically through transient energy and exergy approaches. The proposed hydrogen storage system stores the hydrogen chemically in the form of ammonia, and it is a pressurized in the multistage ammonia production system. The pressurized multistage ammonia production system stores the produced ammonia in a novel conceptual design of an ammonia tanker truck equipped with an ammonia electrolyzer, which transports and delivers the stored hydrogen. The energy and exergy efficiencies of the proposed system are found to be 72.3% and 71.8%, respectively. The proposed system consumes an amount of 59.5 kJ of work per mole of hydrogen stored and recovered using the ammonia electrolyzer. The system is simulated on filling 21,000 L of ammonia at a pressure of 61 bar, and the system is able to store 13,225 kg of ammonia in a liquid state in 0.518 h. The system consumes nearly 61.4 GJ of energy to store the 13,225 kg of ammonia and to decompose it during the discharge phase.

Two configurations of double-flash geothermal power plants, one is combined with water desalination and one integrated with absorption heat transformation and water desalination, are proposed and investigated from the viewpoint of exergoeconomics. The main purpose of investigated systems is the simultaneous generation of electrical power and distilled water. A three-objective optimization procedure is performed to determine the optimal design points, considering for all configurations the decision parameters to be the pressures of low and high-pressure flash chambers and the temperatures of the evaporator and generator. The optimization aims to minimize the product unit cost, while maximizing the electric power generated and the production rate of distilled water. The Pareto frontiers for each configuration are drawn as part of the procedure. It is shown that, at constant and equal pressures of the high-pressure flash chamber, the product unit cost for the system combined with the absorption heat transformer is the lower of the two systems considered. In addition, under the optimized conditions, the product unit costs are approximately equal for the two studied configurations. However, the value of generated power for the system with an absorption heat transformer is about 17% greater than for the alternate system. Moreover, the system integrated with an absorption heat transformer has higher thermal and exergy efficiencies, at about 20% and 3%, respectively.

In this paper, an integrated coal gasification combined cycle system for the production of hydrogen and electricity is optimized in terms of energy and exergy efficiencies, and the amount and cost of the produced hydrogen and electricity. The integrated system is optimized by focusing on the conversion process of coal to syngas. A novel optimization process is developed which integrates an artificial neural network with a genetic algorithm. The gasification system is modeled and simulated with Aspen Plus for large ranges of operating conditions, where the artificial neural network method is used to represent the simulation results mathematically. The mathematical model is then optimized using a genetic algorithm method. The optimization demonstrates that the lower is the grade of coal of the three considered coals, the less expensive is the hydrogen and electricity that can be produced by the considered integrated gasification combined cycle (IGCC) system.

In this paper, a new concept called “exergoeconoenvironmental” analysis is proposed for a better understanding of energy conversion systems with respect to thermodynamic, economic, and environmental perspectives simultaneously. The proposed methodology integrates exergy analysis, economic principles, and environmental assessment into a single framework to provide the decision-maker with information not accessible through available exergy-based methods like exergoeconomic and exergoenvironmental evaluations. In this methodology, the eco-costs/value ratio model is interfaced with exergetic cost theory in order to develop exergoeconoenvironmental balances for components of a given energy system. The systematic methodology used in exergoeconomic and exergoenvironmental analyses, i.e., Specific Exergy Costing, is employed to calculate the eco-costs/value for each stream of the system. The proposed methodology is applied to a well-known gas turbine-based cogeneration system consisting of an air compressor, an air preheater, a combustion chamber, a gas turbine, and a heat-recovery steam generator. The results obtained with the developed approach are compared with those of exergy, exergoeconomic, and exergoenvironmental analyses. The highest eco-costs/value ratio (3.806 USD eco-cost/USD value) is found for the heat-recovery steam generator, followed by the air preheater (2.919 USD eco-cost/USD value). Accordingly, these units are ranked first and second for improvement using exergoeconoenvironmental analysis. The exergoeconoenvironmental factor is small for all components of the plant, indicating the fact that the eco-costs/value ratio associated with exergy destruction is higher than the component-related eco-costs/value ratio. Accordingly, minimizing the exergy destruction can be recommended as a practical and sound strategy for improving the economoenvironmental performance of the plant. Overall, the proposed method appears to be a practical and powerful tool that assesses the efficiency, productivity, and sustainability of energy systems better than available exergy-based methods.

In this study, a high temperature electrolyser for the gas phase electrolysis of hydrogen chloride for hydrogen production is proposed and assessed. A detailed electrochemical model is developed to study the J-E characteristics for the proposed electrolyser (a solid oxide electrolyser based on a proton conducting electrolyte). The developed model accounts for all major losses, namely activation, concentration and ohmic. Energy and exergy analyses are carried out, and the energy and exergy efficiencies of the proposed electrolyser are determined to be 41.1% and 39.0%, respectively. The simulation results show that at T = 1073 K, P = 100.325 kPa and J = 1000 A/m2, 1.6 V is required to produce 1 mol of hydrogen. This is approximately 0.3 V less than the voltage required by a high temperature steam electrolyser (based on a proton conducting electrolyte) operating at same condition (T = 1073 K, P = 101.325 kPa and J = 1000 A/m2), suggesting that the proposed electrolyser offers a new option for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The proposed electrolyser may be incorporated into thermochemical cycles for hydrogen production, like Cu Cl or chlorine cycles.

In this study for the first time a new air separation unit with a carbon dioxide power cycle based on cold energy recovery of liquefied natural gas is investigated by conventional and advanced exergoeconomic analyses. With conventional exergy analysis, the source of irreversibility in the process can be determined, while with advanced exergy analysis, the real potential can be determined for improving the process operating performance as well as component interactions. The exergy destruction rate and total operating cost are divided into two catagories which are sub-parts of each other: endogenous/exogenous and unavoidable/avoidable. The exergy and exergoeconomic analyses indicate that the total process cost can be decreased by improving the performance and efficiencies of compressors and heat exchangers. This is because these types of process components have the largest and smallest exergoeconomic factor values, respectively. Results of the advanced exergy and exergoeconomic analyses demonstrate that, when considering the avoidable endogenous investment cost rate, compressors have priorities for modification. Also, based on the avoidable endogenous cost rate, one of the heat exchangers should be modified at first. The exergy destruction and investment cost rates in most of the process components are endogenous. A sensitivity analysis is performed to evaluate the effects of economic and thermodynamic parameters on the advanced exergoeconomic parameters. It is concluded that the configuration of the process components has a significant impact on their costs.

A biomass integrated co-fired combined cycle is proposed, in which hydrogen is produced using steam turbine output power. The product hydrogen, when there is temporarily no market for it, is injected into the combustion chamber to raise efficiency and lower fossil fuel consumption. Advanced exergy and advanced exergoeconomic analyses are applied for the first time to this plant. The following benefits are obtained: hydrogen injection results in 67% less fossil fuel consumption and 19% less CO2 emissions, while the energy efficiency decreases by almost 37% and the exergy efficiency by 39%. Also hydrogen injection decreases the plant’s total exergy destruction and, more importantly, total exergy loss. Similarly, the exergy destruction cost and exergy loss cost rates are lowered by hydrogen injection into the combustion chamber of the co-fired combined cycle. The total unit product cost for the combined cycle with hydrogen injection is lower than for the cycle without hydrogen injection. Finally, the relative cost difference and exergoeconomic factor both increase with hydrogen injection. This demonstrates that there are higher component purchase and maintenance costs relative to the exergy destruction costs for the corresponding components in a biomass integrated co-fired combined cycle with hydrogen production and injection into the combustion chamber. Advanced exergy and advanced exergoeconomic analyses yield some contradictory results relative to common analyses.

A natural gas firing and biomass post-firing combined cycle is proposed and analyzed with thermodynamics and exergoeconomics. To enhance performance, hydrogen is produced in a proton exchange membrane electrolyzer and when there is temporarily no market for hydrogen is injected into the combustion chamber of the natural gas firing and biomass post-firing combined cycle with hydrogen injection. Advantages and disadvantages are reported for the cycle with hydrogen injection (NFBPC-HI) relative to the cycle without hydrogen injection (NFBPC-H) with an equivalent biomass flow rate. In this case, the natural gas flow rate reduces by 46% through hydrogen injection. The plant energy efficiency with hydrogen injection decreases by 36% and the exergy efficiency by 37%. The exergy destruction rate decreases and the exergy loss rate becomes slightly lower with hydrogen injection. Regarding environmental impact, hydrogen injection decreases the plant CO2 emission rate by 27%. Also with hydrogen injection, the exergy destruction cost rate decreases and the exergy loss cost rate declines slightly. The product cost using hydrogen injection decreases by up to 9% point as does the exergoeconomic factor for the biomass integrated post-firing combined cycle with hydrogen injection, especially at higher gas turbine inlet temperatures and lower compressor pressure ratios. Overall, the plant with hydrogen injection exhibits some better facets of thermodynamic and economic performance and cleaner production, e.g. lower exergy destruction and loss rates and CO2 emissions and lower total unit product economic costs, although it has lower energy and exergy efficiencies.

Background:District Energy (DE) is a technology capable of using renewable energy (e.g., solar thermal systems) and waste heat as energy sources efficiently. DE technology nonetheless has potential for improvement. Thermal Energy Storage (TES) can enhance DE performance significantly.Objective:An exergy analysis of a DE system which includes a solar thermal energy system and TES is performed, so as to improve understanding of its performance.Method:A case study based on the Friedrichshafen DE system in Germany is used to assess thermodynamically the role of solar energy and TES in a DE system. The system performance is separated into three modes: (1) fossil fuel is the only source of energy, (2) a discharging TES and fossil fuel provide heat for the DE system, and (3) solar energy and fossil fuels are the energy supplies. Exergy analyses are conducted for each performance mode and the overall DE system.Results:The results quantify the benefits of incorporating solar energy and TES on the performance of the Friedrichshafen DE system, and demonstrate that the overall exergy efficiency of the DE system increases from 23% to 27% with assistance of solar thermal collectors and TES, while the total energy efficiency increases from 83% to 87%.Conclusion:An increase of exergy efficiency is observed when TES is added to a DE system, due to a reduction in solar thermal energy loss by the TES, which allows more solar energy to be converted to useful energy to satisfy the DE system thermal energy demand.

A novel hybrid Cu–Cl thermochemical cycle is developed and assessed for the co-production of hydrogen and copper using copper waste. An experiment is also conducted to establish the high-temperature electrolytic step as a proof of concept. A detailed parametric study is conducted to assess the effects of such parameters as process step temperature and energy efficiency of the electrical power plant that provides electricity to the cycle on the energy and exergy efficiencies of the overall cycle. The values of the energy and exergy efficiencies of the cycle are 31.8 and 69.7%, respectively. The maximum specific exergy destruction occurs in the electrolytic step. The results show that the proposed cycle performs better in terms of energy and exergy efficiencies compared to similar four-step Cu–Cl cycles. Using the proposed cycle, a new avenue may be open for copper waste to be more advantageously managed, potentially enhancing the sustainability of the relevant processes through improved environmental prote...