Cumulative Exergy Consumption Research Articles

Exergetic life cycle assessment for green hydrogen production

Life cycle assessment (LCA) is a method for assessing the environmental impacts of products and processes. The life cycle inventory provides a measure of the quantitative throughput of a process, but it cannot measure the intrinsic quality of that throughput. Exergy is a measure of the quantity and quality of energy. When combining LCA and exergy analysis in an exergy-based life cycle assessment (ExLCA) a powerful tool for the quantification of resource efficiency can be established. This study performs a detailed bottom-up cradle-to-grave ExLCA based on cumulative exergy consumption and exergy analysis of the use phase for a state-of-the-art (SoA) and a future plant 5 MW proton exchange membrane (PEM) electrolyzer plant. Three scenarios are implemented, i.e. SoA plant operated in the German grid mix of 2018, SoA plant operated in a defossilized grid, and a future plant operated in a defossilized grid. In every scenario, more than 98 % of the resource demand originates from electricity generation alone and decreases significantly with renewable electricity operation. In plant construction, the anode catalyst material iridium causes approximately half of the resource demand and bears the largest lever for the resource reduction potential of the plant construction of 65 %.

Comparative exergy and economic analysis of deep in-situ gasification based coal-to-hydrogen with carbon capture and alternative routes

The deep in-situ gasification based coal-to-hydrogen (deep IGCtH) is attracting attention for its unique advantage in utilizing unrecoverable coal seam. In this paper, its improvement scope in energy conversion and utilization is analyzed using advanced exergy analysis, and the efficiency from cumulative exergy consumption (CExC) perspective and economic competitiveness with Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), coke-oven gas-to-hydrogen (COGtH) and natural gas-to-hydrogen (NGtH) are compared. Results indicate 39.9 % and 25.1 % of the exergy destruction of deep IGCtH and Lurgi SGCtH are unavoidable, while steam methane reforming and coal gasification possess the largest improvable potential, with avoidable endogenous/exogenous destruction of 96.63 MW/81.58 MW and 162.52 MW/151.19 MW, suggesting thermodynamic improvement can also be achieved by improving other components or optimizing process structure in addition to increasing its own efficiency. The CExC of deep IGCtH outputting 1 kg hydrogen is only 83.6 % that of Lurgi SGCtH, indicating it is more efficient route with significantly energy consumption reduction and can better demonstrate its efficiency advantage under large production capacity condition. The deep IGCtH shows only 68.7 % that of Lurgi SGCtH in investment and also presents significant advantage in cost. However, its profitability advantage over NGtH loses with hydrogen price increasing and there exists lower limit on capacity of 0.46 billion Nm3 to maintain cost and profitability competitiveness over COGtH. Furthermore, deep IGCtH shows emission reduction cost advantage over Lurgi SGCtH when capture rate exceeds 80 %, and profitability will not be limited by carbon tax and coal seam thickness within the considered range.

Evaluating ecological sustainability of mechanized and traditional systems of damaskrose production using extended exergy analysis

Environmental resource efficiency is a major challenge in the management of agroecosystems and their sustainability. The Extended Exergy Analysis (EEA) is a novel approach that assesses the total amount of resources extracted from the environment to produce agroecosystem products. This study applied the EEA to compare the sustainable development of Damask rose flower production in two mechanized and traditional systems in Nehbandan County, South Khorasan province, using the data of 2021–2022. The EEA calculated the flows of labor, capital, and environmental costs in the systems based on the first and second thermodynamic laws. The results showed that the traditional system had lower cumulative exergy consumption (CExC) and environmental modification cost than the mechanized system, indicating higher ecological sustainability. The extended exergy indices, such as the special capital conversion of energy and material input (kcap), the special capital conversion of product sale (KCAPEEA), extended exergy cost (eec) and the cumulative degree of perfection (CDP), also revealed that the traditional system was more cost-effective, economical, technologically efficient, and closer to the optimal conditions than the mechanized system. To achieve a sustainable agricultural crop production system, new patterns and models for selecting inputs and reducing environmental costs are recommended.

Ecological accounting of the Chinese society 2012–2020 based on extended exergy

China's social system has undergone unprecedented economic transformation in the past decade. It is essential that the relationship between the country's socio-economic development and natural ecosystem be revealed, thereby revealing the evolutionary trajectory of its biophysical sustainability. The extended exergy accounting (EEA) method offers a thermodynamics-based tool to evaluate the structure and function of a social system and objectively estimate the impacts of human activities on sustainable development and broader ecosystems. This study aims to perform extended exergy analysis to trace the flows of resources, labor, capital, and environmental remediation exegetics in China's society from 2012 to 2020. During the accounting period, the average annual growth rate of total extended exergy (TEE) was just 1.2%. The TEE in the conversion and tertiary sectors ew noticeably faster than those in other sub-sectors, while the TEE in the extraction and agriculture sectors showed a declining trend. The TEE in 2020 reached 764.50 EJ, of which 179.13 EJ were attributed to Cumulative Exergy Consumption, 74.89 EJ were attributed to labor, 68.85 EJ to capital, and 441.63 EJ to environmental remediation costs. The indicator assessment reflects an enhancement in the sustainability of the Chinese social system, particularly the rapid improvement in labor and capital-related indicators. Comparing the results with other countries demonstrates that the gap between China and developed nations has narrowed, with China's indicators for balancing resource production and capital flows rivaling those of the U.S. and the U.K. The objective revelation of the developmental and transitional trajectory of Chinese society, based on the EEA approach, provides valuable insights for other developing countries in achieving sustainable development.

Assessment of Whole Milk Powder Production by a Cumulative Exergy Consumption Approach

The production of food is a sector that consumes a significant amount of energy and encompasses both agricultural and industrial processes. In this study, the energy consumption of whole milk powder production, which is known to be particularly energy-intensive, was examined. The study used a cumulative exergy consumption approach to evaluate the overall production process of whole milk powder, including the dairy farm (raw milk production) and dairy factory (powder production) stages. The results showed that raw milk production dominated energy and exergy consumption and carbon dioxide emissions. An amount of 68.3% of the total net cumulative exergy consumption in the system was calculated for raw milk production. In the dairy factory process, the highest energy/exergy consumption occurred during spray drying, followed by evaporation and pasteurization. In these three processes, 98.3% of the total energy consumption, 94.6% of the total exergy consumption, and 95.7% of the total carbon dioxide emissions in powder production were realized. To investigate the improvement potentials in the system, replacing fossil fuels with renewable energy sources and using pasture feeding in animal husbandry were evaluated. While using alternative energy sources highly influenced powder production, pasture feeding had a high impact on consumption in raw milk production. By using renewable energy and pasture feeding, the exergy efficiency, cumulative degree of perfection, renewability index, and exergetic sustainability index values for the overall process increased from 40.5%, 0.282, −0.22, and 0.68 to 68.9%, 0.433, 0.65, and 2.21, respectively.

Exergoenvironmental damages assessment in a desert‐based agricultural system: A case study of date production

AbstractDeveloping countries, especially those in hot and dry areas, need more attention to achieve sustainable development as they apply excessive inputs in production processes. The present study aims to quantify the amount of environmental emissions and determine the most appropriate pattern of energy use in the date (Phoenix dactylifera L.) production process using thermodynamic analysis. The information was gathered through questionnaires and face‐to‐face interviews. From the results, cumulative exergy and energy demand for one Mg of date fruit production were calculated as 697 and 1640 MJ, respectively. Carbon dioxide emission was also measured at 197 kg Mg–1. Moreover, cumulative exergy consumption illustrated that manure and diesel fuel consumption is high, though diesel fuel and N consumption are given the most cumulative energy demand. Renewability indicator, cumulative degree of perfection, and the recoverable exergy ratio value of the date fruit production process were calculated as 0.62, 2.68, and 4.32, respectively. The date's chemical exergy value was calculated to be 14.96 MJ kg–1. Dates have a high chemical exergy value because of their high carbohydrate content and low water content. As a result, crop chemical combinations have a direct impact on the production process. The total direct greenhouse gas emissions induced by the inputs consumption were 310.02 kg Mg–1. Emissions to air, soil, and water were 308.76, 5.60 × 10−1 and 6.96 × 10−1 kg Mg–1. In general, date production in Khuzestan province is partially renewable.

Thermo-ecological cost optimization of a solar thermal and photovoltaic integrated energy system considering energy level

Integrating renewable resources into traditional tri-generation systems helps to reduce fossil fuel use and emissions. A solar thermal and photovoltaic assisted integrated energy system is proposed here using high- performance cooling approaches to provide cooling, heating, and electricity. To find the best system configurations with a focus on the ecological performance, the specific thermo-ecological cost of the energy products considering energy level is optimized employing the cumulative exergy consumption over the whole life-cycle. The results show that the ideal specific costs for cooling, heating and electricity demands are 8.699, 7.129, and 1.970 J/J, respectively. Compared to the method without the energy level consideration, the specific cost of the hybrid system is 0.47 J/J higher due to the lower energy level of water products. Moreover, the specific thermo-ecological cost of natural gas has higher impacts on the performance of hybrid system than the other parameters.

The Thermoeconomic Environment Cost Indicator (iex-TEE) as a One-Dimensional Measure of Resource Sustainability

This paper presents a conceptual development of sustainability evaluation, through an exergy-based indicator, by using the new concept of the Thermoeconomic Environment (TEE). The exergy-based accounting methods here considered as a background are Extended Exergy Accounting (EEA), which can be used to quantify the exergy cost of externalities like labor, monetary inputs, and pollutants, and Cumulative Exergy Consumption (CExC), which can be used to quantify the consumption of primary resources embodied in a final product or service. The new concept of bioresource stock replacement cost is presented, highlighting how the framework of the TEE offers an option for evaluating the exergy cost of products of biological systems. This sustainability indicator is defined based on the exergy cost of all resources directly and indirectly consumed by the system, the equivalent exergy cost of all externalities implied in the production process and the exergy cost of the final product.

Evaluation of the Water–Energy nexus in the treatment of urban drinking water in Chile through exergy and environmental indicators

This research assessed water–energy nexus (WEN) efficiency in Chile's drinking water treatment plants by integrating the life cycle concept and exergy analysis principles. The cumulative exergy consumption (CExC) attributed to freshwater and the energy required by drinking water facilities during the whole life cycle were determined. Water-related indicators, such as the water stress index (WSI) and blue water footprint (BWF), differentiated by region, were used to highlight the critical role of water resources within the nexus. The CExC depicted significant differences between regions (10–30 MJex/m3), depending on the quality of raw water sources, pumping, and drinking water treatment (DWT) configurations. The WSI and the BWF varied spatially across the country due to climatic variability. Regions with a higher WSI (0.4–1) also implied higher CExC. This pattern can be justified by low water availability and poor water quality, which, at the same time, implied more energy-intensive technologies. Improving water and energy efficiency were identified as critical strategies for reducing the water and energy demand in the urban DWT systems.

Ecological life cycle analysis-based installation capacity determination of building energy-supply systems

Based on the ecological life cycle analysis (Eco-LCA) theory, this study focused on constructing the ecological life cycle analysis framework and model of a combined cooling heating and power (CCHP) system equipped a gas internal combustion engine (GICE) in which the ecological cumulative exergy consumption (ECEC) is minimized to maximize ecological sustainability. This method solves the problem of low-efficiency operation resulting from the implementation of an unsuitable GICE installation capacity; additionally, the ecological view is first introduced into the stage of scheme decision to achieve the maximum ecological benefits. Moreover, a case study that involved implementing the GICE capacity design in a typical hospital building in Chongqing was performed to demonstrate the capability of the proposed model. The simulation results revealed that the operation-stage ECEC accounts for approximately 97% of the total ECEC for each design scheme. The 600-kW GICE installation capacity yielded the best ecological sustainability under the condition of satisfying the energy demand of the building; the ECEC of the CCHP system with a GICE was approximately 4.45E + 18 seJ, and the GICE equivalent full-load running time in one typical year is approximately 3289 h. In comparison to system of the case building, the installation capacity of GICE equipped according to the normal economic index is 400 kW. It shows that the optimal size of GICE is not always the same from economic and ecological perspectives, but the Eco-LCA can make more objective authentic decision due to without the arbitrary weighting of different ecological factors. Further, a simplified Eco-LCA of the CCHP system with GICE method is given out and it can provide reference for related engineering application.

Exergy flow of rice production system in Italy: Comparison among nine different varieties

Exergy analysis is receiving considerable attention as an approach to be applied for making decisions toward moving to a sustainable and energy-efficient food supply chain. This study focuses on how the selection of variety affects the exergy flow of a paddy rice production system. In this regard, nine varieties of rice in Italy, the largest rice producer in Europe, were evaluated using the cumulative exergy analysis approach. Sensitivity analysis of inputs consumption and the exergy management scenarios of the most sensitive inputs are also provided in this study. The results indicated that the cumulative exergy consumption value of the investigated rice varieties ranges from 16.09 GJha−1 to 25.80 GJ ha−1. Fossil fuels and chemical fertilizer consumption were the most significant contributors to the total energy consumption in all investigated varieties. Luna variety, with the cumulative degree of perfection value of 7.96 and renewability indicator of 0.88, was identified as the most exergy-efficient variety of rice in Italy.

Thermodynamic performance analysis and modified thermo-ecological cost optimization of a hybrid district heating system considering energy levels

Utilization of the renewable resources in district heating systems can reduce the use of fossil fuels, operating costs and protect the environment. In this study, an integrated hybrid system consisting of concentrating photovoltaic/thermal collectors (PV/T), geothermal (GSHP) and absorption (AHP) heat pumps is considered for district heating. The thermodynamic performance of the system at various conditions is explored through detailed simulations. A modified thermo-ecological cost (TEC) method is used to optimize the structure of the PV/T by considering contributions of different flows. The results show that a higher solar irradiance level and a higher PV coverage ratio have a positive impact on the thermal performance of the hybrid system. The TEC-based optimization shows that a 66% PV coverage ratio of PV/T yields a minimum thermo-ecological heating cost of 6.86 J/J, which is slightly lower than cost with a conventional method. Based on the sensitivity analysis, other key parameters except the operating time and the PV coverage ratio have a negative influence on the economic performance of the district heating system, because of the increasing cumulative exergy consumption of the GSHP or PV/T.

Renewable energy utilization in apple production process: A thermodynamic approach

Horticultural inputs have various potential environmental impacts which can be simultaneously evaluated by input–output energy methods. This technique is considered as an appropriate evaluation method to analyze ecosystems through recognizing, quantifying, and appraising resources depleted and released within the environment. This study aims to apply the thermodynamic approach to maximize the decision-making information on the environmental impacts of energy consumption in the apple production process. In this case, two different scenarios of energy and exergy flow during the apple production process are assessed thermodynamically and the environmental effects of these scenarios are evaluated. The first scenario is based on conventional agriculture carried out by using almost no renewable energy source, while in the second scenario, renewable energy sources including hydroelectricity, biodiesel, and microbial fertilizers are employed. The results indicated that in the second scenario, the Cumulative Exergy Consumption (CECx) and exergy loss are decreased by more than 93% and 74%, respectively (584.5 and 3023 MJ.ton−1), while the Cumulative Degree of Perfection (CDP) and Renewability Index (RI) are increased by 6.01 and 0.83, respectively. Additionally, in this scenario, the Cumulative Carbon Dioxide emission (CCO2) was decreased to 11.23 kg.ton−1. The results also indicated that the application of microbial fertilizers along with improving the irrigation system can decrease the total energy-exergy loss and total input costs of the apple production process. The results of the present study pointed a direction for the invention and development of new technologies or methodologies in agricultural productions to improve the energy-exergy flow and mitigate CO2 emission in the future.

Exergy analysis in the assessment of hydrogen production from UCG

The demand for H2 increases rapidly with the gradual recognition of the potential of H2 as an important secondary energy. At present, coal gasification is the main way to obtain hydrogen on a large scale and at a low cost in China. The underground coal gasification (UCG), as a kind of in-situ utilization technology that can exploit the unreachable deep coal resources, could become an alternative H2 production pathway. This paper presents comparative study of energy utilization and resource consumption in H2 production by UCG and typical surface coal gasification (SCG) technology, namely Lurgi fixed bed gasification, with 1.2 billion Nm3/a throughput of H2 as example, to offer corresponding data support. The efficiency and the amount of resources consumed in constructing and operating each coal-to-hydrogen system under different conditions have been researched from exergetic point of view, which is not reported in existing literatures. In this paper, the exergy efficiency is calculated to be 40.48% and 40.98% for hydrogen production using UCG and SCG. The result indicates the competitiveness of UCG in the field of hydrogen production comparing with widely used coal gasification technology. The resource consumption is measured by cumulative exergy consumption (CExC), which is 8.17E+10 MJ and 6.57E+10 MJ for H2 production from UCG and SCG. The result shows that although the H2 production from UCG has higher CExC, it can significantly reduce the resource consumption of equipment comparing with H2 production from SCG, indicating its advantage in total investment. It is found that the exergy efficiency increases with the rise in H2O-to-O2 and O2-to-CO2 ratio, while the value of CExC decreases with the appreciation of H2O-to-O2 ratio yet increases as the O2-to-CO2 ratio rises. In addition, the sensitivity analysis of production capacity reveals that the exergy efficiency gap and CExC gap between hydrogen production by UCG and SCG diminishes at smaller scale production capacities, showing that UCG is more suitable for small-scale hydrogen production.

Modelling Grid Constraints in a Multi-Energy Municipal Energy System Using Cumulative Exergy Consumption Minimisation

Efficiency measures and the integration of renewable energy sources are key to achieving a sustainable society. The cumulative exergy consumption describes the resource consumption of a product from the raw material to the final utilisation. It includes the exergy expenses for energy infrastructure as well as the imported energy. Since consumers and renewable potentials are usually in different locations, grid restrictions and energy flows have a significant impact on the optimal energy system design. In this paper we will use cumulative exergy minimisation together with load flow calculations to determine the optimal system design of a multi-cell municipal energy system. Two different load flow representations are compared. The network flow model uses transmission efficiencies for heat, gas and electricity flows. The power flow representation uses a linear DC approximated load flow for electricity flows and a MILP (mixed integer linear programming) representation for heat and gas flows to account for the nonlinear pressure loss relation. Although both representations provide comparable overall results, the installed capacities in the individual cells differ significantly. The differences are greatest in well meshed cells, while they are small in stub lines.

Energetic assessment of the agricultural production system. A review

Energy holds a key role in farm systems. Cultivation is based on the conversion of solar energy into biomass of interest. Fossil energy allows mechanized and high-yield agricultural production system, but has a strong impact on climate change, and its supply is compromised in the next decades. Energy flows stand between two worlds: while energy is a strategic component of the economy, it is also a thermodynamic state variable for describing ecosystems. This situation reemphasizes the need for energy flow analysis in farm systems. There is a great variety in the approaches used to compute energy flows at farm scales. Yet, their main characteristics and the ways they handle farm sustainability issues need to be clarified. This review identifies ten kinds of energetic approaches, i.e., (i) conventional energy analysis, (ii) pluri-energy analysis, (iii) agroecological energy analysis, (iv) exergy analysis, (v) cumulative exergy consumption, (vi) extended exergy account, (vii) cumulative exergy extraction from the natural environment, (viii) eco-exergy, (ix) cosmic exergy analysis, and (x) emergy assessment. These approaches are analyzed through key features to discuss their ability to address resources’ efficiency issues and identify promising outcomes for energy assessment of farms. This analysis emphasizes the lack of clear definition of system boundaries in farm-scale studies. In addition, most of the studies mainly focus on socio-economic flows through a sectoral perspective. Yet, internal biomass flows that play a role in maintaining agroecosystem functionality can also be considered according to a circular/systemic perspective. Then, integration of soil organic matter in the energy balance leads to significant changes in energy efficiency evaluation playing a function of biotic energy storage in the farm system. Hence, some recommendations are provided to perform an exhaustive energetic assessment of farm systems as well as future lines of research to be investigated.

Internal Microclimate: Cumulative Exergy Consumption in a Sandcrete and a Burnt Brick- Walled Structure

Current practices of planning and designing of buildings in Nigeria do not consider the thermal comfort, the building energy and exergy demand. There is a need for better understanding of exergy analysis to improve the quality match between building energy demand and supply. The aim of this study is to estimate the exergy consumption value for a hollow sandcrete and a burnt brick-walled structure in a tropical sub-region. The properties of the building were assessed, eQuest software was used to estimate the energy demand of the respective buildings and the exergy analysis was conducted using the exergetic factor of electricity. The cumulative exergy consumptions of the existing sandcrete-walled building, the modelled sandcrete and the burnt brick-walled building were found to be 246,074.4 MJ/year, 128,646 MJ/year, and 128,595.6 MJ/year respectively. The modelled sandcrete-walled building, as well as the burnt brick-walled building, were found to be 48% more energy efficient than the existingbuilding as a result of improving the airtightness of the building, reducing the solar heat gain, and utilizing extremely efficient systems. However, the exergy analysis suggested that the hollow burnt brick-walled building perform better than the hollow sandcrete-walled building.
 Keywords: Building, electricity, energy, eQuest, exergy, sandcrete.

Extended exergy analysis (EAA) of two canola farming systems in Khorramabad, Iran

Extended exergy analysis (EEA) is a novel method in evaluation of agricultural ecosystems. In this study, a comprehensive analysis of the sustainability of an agricultural system was carried out using this method. Specifically, we looked for sustainable patterns of canola production by performing EEAs of two canola production systems, commercial and traditional, located in Khorramabd, Iran using data from the 2017–2018 crop year. The EEA of these two systems showed that the exergy of the environmental remediation cost (EEE) for the traditional system was less than that of the commercial system by 2.69 × 104 MJ ha−1. Accordingly, the ecological sustainability of the traditional system was found to be two times higher than the commercial system. In contrast, the values of thermodynamic indicators such as the capital conversion factor of the annual monetary value of product sales (KcapEEA), the extended exergy efficiency (ŊEEA), and the cumulative degree of perfection (CDP), respectively, indicate the higher economic value, the higher thermodynamic efficiency, and the greater optimality of the commercial system compared to the traditional system. The high consumption of inputs led to increased cumulative exergy consumption (CExC) in the traditional system. The high amount of CExC in the traditional system caused its thermodynamic indices to decrease. On the other hand, the high consumption of resources such as chemical fertilizers caused the EEE of the commercial system to increase. Therefore, based on the results of the EEAs performed in this study, we recommend designing new patterns for managing agricultural production systems, whereby through choosing the appropriate type and amount of inputs for each production system and by employing the required knowledge and technology for optimum production, the costs of environmental remediation will be reduced, and the thermodynamic-economic indexes will be improved.

Optimal Municipal Energy System Design and Operation Using Cumulative Exergy Consumption Minimisation

In developed countries like Austria the renewable energy potential might outpace the demand. This requires primary energy efficiency measures as well as an energy system design that enables the integration of variable renewable energy sources. Municipal energy systems, which supply customers with heat and electricity, will play an important role in this task. The cumulative exergy consumption methodology considers resource consumption from the raw material to the final product. It includes the exergetic expenses for imported energy as well as for building the energy infrastructure. In this paper, we determine the exergy optimal energy system design of an exemplary municipal energy system by using cumulative exergy consumption minimisation. The results of a case study show that well a linked electricity and heat system using heat pumps, combined heat power plants and battery and thermal storages is necessary. This enables an efficient supply and also provides the necessary flexibilities for integrating variable renewable energy sources.

Application of cumulative exergy consumption approach to assess the sustainability of rapeseed production in two different farming systems

The study aimed to assess the sustainability of mechanised production system (MPS) and semi-mechanised production system (SMPS) in the rapeseed agroecosystem in northern Iran. The study was conducted through the cumulative exergy consumption (CExC) approach, including the two sustainability indices of cumulative degree of perfection (CDP) and renewability index (RI). The CDP was higher in the MPS (4.36) than SMPS (4.29). The RI was determined to be 0.712 for MPS and 0.731 for SMPS. The results highlighted that CDP and RI could significantly be improved through the consumption of renewable-based energy resources, including biofuel and solar energy.