Exergy Consumption Research Articles

Theoretical analysis of a solar-powered multi-effect distillation integrated with concentrating photovoltaic/thermal system

A novel concentrated photovoltaic/thermal-multiple effect distillation system is proposed to simultaneously provide electricity, heating and freshwater for satisfying essential demands from isolated islands. Theoretical analysis under nominal condition is evaluated from perspective of energy and exergy and results indicate that electricity and heating are 353.2 and 432.9 kW with related energic and exergic efficiency of 0.2966 and 0.3635, 0.3177 and 0.0064. Produced freshwater is calculated as 0.7107 kg/s with gain output ratio of 6.59. Exergy destruction analysis exhibits detailed scenario of exergy consumption and solar collector field obtains the largest destroyed exergy, followed orderly by multiple effect distillation, heating unit and preheater. Parametric and sensitive analyses are performed to illustrate effects of parameters on system performance. Results indicate operating parameters exert remarkable impact on system efficiency. Efficiency of electricity is most sensitive to photovoltaic cell temperature, while that of heating and freshwater are most sensitive to coolant fluid temperature in comparison to the rest parameters. Primary energy and exergy saving ratio are conducted and results indicate proposed system is superior over individual systems with the same amount of electricity, heating and freshwater. In conclusion, this built system achieves a rational and efficient strategy to the comprehensive utilization of solar energy.

Reducing the impact of wind farms on the electric power system by the use of energy storage

The deployment of wind power is rapidly growing worldwide. Intermittent, unpredictable availability of wind energy destabilizes the work of the whole power system, which causes additional consumption of resources. When fossil fuel power plants are affected by this phenomenon, they are forced to cycle (change their load) more often, which results in higher consumption of fuel. This negative effect, expressed by means of thermo-ecological cost (TEC) can be significant in comparison to the TEC of construction phase of wind turbines. TEC is defined as the cumulative consumption of non-renewable exergy connected with the fabrication of a particular product. Power plant cycling could be minimized by applying an energy storage system responding to variations in wind power availability. In the present work, several scheduling strategies for cooperation of an energy storage system with wind turbines are investigated. The effect is assessed in local and global balance boundaries. Employing energy storage reduces the energy losses in thermal power plants, but at the same time, energy losses appear in the storage itself. However, depending on the strategy of energy storage scheduling, in some cases the overall consumption of primary exergy in the whole system may be lower.

Human body exergy consumption models’ evaluation and their sensitivities towards different environmental conditions

We can use the concept of exergy to analyze a human body as a heat emitter: while generating heat continuously, the body remains at roughly the same temperature through physiological responses such as shivering, sweating, breathing thus raising/decreasing the core and/or skin temperature to maintain effective heat dissipation. Existing literature provides an estimated exergy consumption rate of the human body ranging from 2 to 5W/m2, while nearly unanimously agreeing on a local exergy consumption minima points to potential individual thermal comfort. To clarify the underlying assumptions used in the existing human body exergy models, we analytically and numerically reviewed the terms used for assessing metabolism, radiation, evaporation, and convection exergy changes of the human body in this paper. We observed overestimations of exergy from metabolism, underestimations of exergy change through radiation, and some caveats in the signage of convective exergy losses in the results we obtained. We were also able to propose an improved expression to estimate human body radiation exergy exchanges as well as selecting reference temperatures that are more process-specific. Future studies that provide experimental verification of these models were also deemed necessary.

Thermodynamics analysis of a direct contact membrane distillation with/without heat recovery based on experimental data

The objective of this study is to analyze various performance parameters of a direct contact membrane distillation (DCMD) system using energy and exergy analysis based on experimental data. The effect of recovering the heat of the permeate stream exiting from the spiral wound MD module is investigated. The analysis is based on experimental tests for brackish waters. The results indicate the maximum water recovery ratio can reach 6.5% at feed flow rate and temperature of 300 L/h and 80 °C, respectively. The performance ratio is found to be 0.3 kg/MJ and can be increased to 1.15 kg/MJ when heat recovery is activated. The gain output ratio can reach a maximum of 2.7 at 150 L/h and 80 °C with the aid of heat recovery. The effect of feed temperature and flow rate on the system performance indicators has been also investigated. The feed temperature has a significant positive effect on performance parameters such as recovery ratio, performance ratio and energy efficiency mainly when the heat recovery is included. The impact of the feed flow rates on the system performance is marginal in particular when the heat recovery is included. The specific energy consumption (SEC) was also evaluated for the evaporator and condenser streams and the entire MD system as well and found to fall within the ranges given in the literature. The specific exergy consumption when the heat recovery is enabled can become as small as 12 kWh/m3, indicating that the present system has the potential to operate at high energy efficiency after some adjustments and optimization allowing further reduction of the irreversibility sources.

Study on the biomass-based integrated gasification combined cycle with negative CO2 emissions under different temperatures and pressures

To reduce the carbon emissions in power sector, a biomass-based integrated gasification combined cycle (BIGCC) with oxy-fuel combustion is proposed. The syngas generated from biomass gasification is burned under oxy-fuel atmosphere for power generation, and CO2 in the flue gas is captured by merely cooling. Thus, the negative CO2 emissions are realized considering the carbon neutral character of biomass. The effects of gasification temperature and pressure on syngas composition and system performance are investigated. The results show that rising pressure and temperature lead to lower H2 and CO production, while CO2 and CH4 generation are enhanced with higher pressure and lower temperature. The system efficiency increases with the pressure rise, while it fluctuates with the temperature variation. The optimum temperature and pressure of gasification is 1000 °C and 3.5 MPa. The corresponding energy and exergy efficiency is 35.41% and 31.21%. The thermodynamic analysis is carried out for each subsystem. The energy loss and exergy destruction is 76.2% and 55.4% for gasifier and 21.8% and 31.3% for HRSG. Considering the unavoidable energy and exergy consumption in gasification, the system optimization can be concentrated on HRSG. The efficient power generation and significant carbon emissions reduction are achieved in the proposed system.

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

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

Thermal analysis of sinter vertical cooler based on waste heat recovery

Sinter vertical cooler, as a new type of sinter waste heat efficient recycling device, is facing great potential and rare opportunities for development. The structural and operating parameters greatly affect the subsequent utilization of waste heat. In the present work, the 3-D model has been improved, and the novelty is that a convection term is added to the energy equation of the solid phase to achieve the steady-state heat transfer condition in gas solid state. The reliability of the mathematical model was verified by the experimental data. Four main parameters were investigated based on exergy, energy consumption and dimensionless exergy consumption. The results show that, when the other parameters are constant, the optimal cooling gas mass flow rate is 85 kg/s based on the maximum exergy. The greatest impact on dimensionless exergy consumption is cooling section diameter, followed by cooling gas mass flow rate, cooling section height and sinter mass flow rate. The structural and operating parameters have a monotonous effect not only on the exergy but also the energy consumption. These results should be helpful for understanding the flow and heat transfer process in the sinter vertical cooler for waste heat recovery engineering.

An urbanization algorithm for districts with minimized emissions based on urban planning and embodied energy towards net-zero exergy targets

The realization of net-zero exergy districts can be supported by urbanization options for district density and building characteristics. This research work formulates an urbanization algorithm to minimize the carbon dioxide emissions responsibility of districts based on energy usage and aspects of embodied energy to tackle multiple drivers of urban emissions. The combined method is implemented to scenarios that contribute to a net-zero exergy district target with 6 options for district density and the selection of building materials. Based on a comparison of scenarios for a case study in the province of Ankara, Turkey, the scenario in which on-site exergy production is about 9.5% of the annual exergy consumption will be responsible for about 13,731 ktonnes of carbon dioxide emissions in a timeframe of 30 years. Conversely, a near net-zero exergy district in which on-site exergy production is 75% of the annual exergy consumption will have about 2967 ktonnes of carbon dioxide emissions during the same timeframe, including embodied energy in buildings. The sensitivity analysis with 9 different combinations provides differences in trade-offs based on timeframes and scenarios. The research work has ramifications for local decision-making to avoid locking-in of carbon dioxide emissions by prioritizing an integrated approach to urban energy solutions on the supply and demand sides, district density, and building materials while reaching net-zero targets in the future.

Improving the performance of a heating system through energy management by using exergy parameters

Energy management systems are used to analyze the efficiency of energy systems and identify any problem areas to lower costs and save energy, typically using energy based performance measurements. Our aim was to use exergy parameters, instead, to see if more accurate information could be obtained about which ener?gy saving application would result in greater energy savings. Exergy analysis is based on the Second law of thermodynamics and focuses on the environment and the quality of the energy. Implementing an exergetic approach to analyze a steam heating system, we examined data related to exergy flows and exergy losses, and ultimately improved the performance of the system through this energy management model. The following seven energy saving applications were identified and ranked according to their improvement potentials: adjusting the air to fuel ratio ? 1, preventing steam leaks ? 2, installing an automatic blow down system ? 3, insulating the pipes ? 4, insulating valves and flanges ?5, insulating fuel tank ?6, and recovering heat loss from the waste condensate ?7. The optimum ranking obtained through the exergy analysis was 3-1-2-5-7-6-4. A reduction of 15.918 kW in exergy consumption was achieved by installing an automatic blowdown system. This meant a total reduction of 1779.03 kg per year in total fuel consumption, $1458.81 per year of cost reduction and the total cost reduction achieved was $1829.25 per year. Making improvements to the seven selected areas in the system, 38.4% of the energy loss was recovered while the recovery in the exergy consumption was 44.5%.

Thermodynamic and thermal comfort optimisation of a coastal social house considering the influence of the thermal breeze

Tropical coastal areas are characterised by high levels of wind and solar resources with large potentials to be utilised for low-energy building design. This paper presents a multi-objective optimisation framework capable of evaluating cost-efficient and low-exergy coastal building designs considering the influence of the thermal breeze. An integrated dynamic simulation tool has been enhanced to consider the impacts of the sea-land breeze effect, aiming at potentiating natural cross-ventilation to improve occupant's thermal comfort and reduce cooling energy demand. Furthermore, the technological database considers a wide range of active and passive energy conservation measures. As a case study, a two-storey/two-flat detached social house located in the North-Pacific coast of Mexico has been investigated. The optimisation problem has considered the minimisation of: i. annual exergy consumption, ii. life cycle cost, and iii. thermal discomfort. Optimisation results have shown that adequate building orientation and window opening control to optimise the effects of the thermal breeze, combined with other passive and active strategies such as solar shading devices, an improved envelope's physical characteristics, and solar assisted air source heat pumps have provided the best performance under a limited budget. Compared to the baseline design, the closest to utopia design has increased thermal comfort by 93.8% and reduced exergy consumption by 10.3% whilst increasing the life cycle cost over the next 50 years by 18.5% (from US$39,864 to US$47,246). The importance of renewable generation incentives is further discussed as a counter effect measure for capital cost increase as well as unlocking currently high-cost low-exergy technologies.

Exergy Analysis of Directional Solvent Extraction Desalination Process.

This paper presents an exergy analysis to evaluate the performance of a continuous directional solvent extraction (DSE) desalination process using octanoic acid. The flow of exergy was calculated for each thermodynamic state and balanced for different components of the system to quantify the inefficiencies in the process. A parametric study was performed to evaluate the impact of three critical design variables on exergy consumption. The parametric study reveals that the total exergy input decreases significantly with an increase in heat exchanger effectiveness. The results also indicate that the heat exchangers account for the highest exergy destruction. The total exergy consumption, however, has a slightly declining trend as the recovery-ratio increases. There is a small variation in the total exergy consumption, within the uncertainty of the calculation, as the highest process temperature increases. When compared to conventional desalination processes, the exergy consumption of the DSE, with heat recovery of 90%, is comparable to those of multi-stage flashing (MSF), but much higher than reverse osmosis (RO). Octanoic acid, which has low product water yield, is identified as the primary factor negatively impacting the exergy consumptions. To exploit the low-grade and low-temperature heat source feature of the DSE process, directional solvents with higher yield should be identified or designed to enable its full implementation.

Expanding exergy analysis for the sustainability assessment of SJ-type oil shale retorting process

A framework based on the conventional exergy analysis and expanding exergy analysis is constructed for the sustainability assessment of an energy conversion system. Based on the cumulative exergy consumption and abatement exergy consumption methods, the resource utilization efficiency indicator and the environmental impact factor are defined to evaluate the exergetic sustainability of resource and the environmental sustainability of pollutant throughout the whole life cycle, respectively. Besides, the SJ-type oil shale retorting process is considered as the case study to display the application of the constructed framework.The simulated results are properly consistent with the actual data of the shale oil production process in Yaojie. In the processing capacity of 100 kg/s lump oil shale, 8.15 kg/s shale oil is produced. The total exergetic efficiency (εtot) of the study system is 45.16%. The power generation subunit has the largest exergy destruction (49.69 MJ), which accounts for 54.12% of the total exergy destruction in the overall system. Also important from an exergy destruction point of view is the recycle retorting gas burning subunit (19.89 MJ). The power generation subunit has the lowest value of resource utilization efficiency indicator (23.36%) and the largest value of environmental impact factor (43.49%), followed by oil shale retorting, recycle retorting gas burning and semi-coke cooling subunits. Improvement strategies are proposed to improve the sustainability of the whole system.

Extended exergy accounting for a typical cement industry in China

Abstract The cement production is one of the most energy-intensive industries with huge amount of CO2 emissions. In this paper, extended exergy analysis is employed to explore a typical cement production chain in China. The cumulative exergy consumption ( C E x C ) , capital and labor exergy, and environmental remediation exergy are calculated to quantify the real ecological cost of cement production and the specific sectors with exergy losses are identified. Moreover, three scenarios including carbide slag substitution, corn straw substitution and waste heat recovery are set up to examine the potential improvement of the traditional cement production with detailed comparison of extended exergy components. In the carbide slag substitution scenario with three substitution percentages, the total extended exergy, C E x C conversion efficiency and exergy loses change little. In the corn straw substitution scenario under three substitution scenarios, the C E x C conversion rates are slightly improved while the exergy loses are notably decreased. The C E x C conversion efficiency of the waste heat recovery scenario is almost the same due to the extra capital investments on kilns and power generation units. The results may provide useful suggestions for upgrade of cement industry in an integrated perspective of energy efficiency and socio-economic and environmental costs.

Local exergy cost analysis of cullet glass heating by microwaves

In this paper, the analysis of the local exergy costs of a cullet glass heated by microwaves in a cubical cavity activated by a susceptor is presented. The analysis is based on a previously validated 3-D electromagnetic model, but goes further by applying the concepts of local exergy efficiency and local unit exergy consumption, what enables a local analysis (in time and space) of the process efficiency. Furthermore, local exergy cost quantifies in detail the path of the exergy cost formation during microwave heating, which is determined by the local irreversibilities taking place in this transient process.Four different susceptor positions have been also compared, in order to find out not only which one is the most efficient but also to justify in detail this result by the time and space evolution of efficiency, unit exergy consumption (both external microwave power and conduction contributions) and unit exergy cost. The best conclusion of the paper is that the local exergy cost approach can contribute to the design of more efficient energy conversion systems, as it could be noted in its application to a complex process like this 3-D example of microwave cullet heating.

Ecological cumulative exergy consumption analysis of organic Rankine cycle for waste heat power generation

Effective energy saving and environmental protection are the global topics. Organic Rankine cycle (ORC) that efficiently converts the waste heat into electricity has drawn widespread attention. The sustainability assessment of ORC can explicitly reveal its contribution to mitigating the ecosystem degradation. Meanwhile, the ecological cumulative exergy consumption (ECEC) analysis is generally used to evaluate the sustainability of industrial activities. Therefore, we established the ORC-ECEC model based on the ecological life cycle assessment involving three fundamental aspects, the resource consumption, economic capital and the environmental impact. Particle swarm optimization algorithm was adopted to optimize the system parameters. The working fluid, R134a, is used in ORC to illustrate the features of proposed framework and conduct the comparison with coal-fired power generation system. Further, systems using working fluids of different hydrogen fluoride olefins (HFOs) are selected to investigate the effect of working fluid on ORC sustainability. The results showed that the economic capital exhibited the largest ECEC during the life-time of ORC, followed by environmental impact and resource consumption. The ECEC of system using R134a was about 1.89E+10 sej/kWh, which was much smaller than that of coal-fired power plant, 1.41E+12 sej/kWh. In addition, the ECEC analysis of systems using different HFOs indicated that ORC using R1336mzz as working fluid was significantly superior compared to systems using other working fluids from the point of view of the sustainable development.

Energy and Exergy Based Performance Analysis of Westinghouse AP1000 Nuclear Power Plant

Energy and exergy analyses of the performance of the Westinghouse Advanced Passive 1000-MWe Nuclear Plant (AP1000) was conducted with the primary objectives to identify and quantify the operational locations having the largest energy and exergy losses under normal operating conditions. The energy and exergy losses in the reactor units were determined from formulations of the energy and exergy rate balances based on the Gouy-Stodola theorem. The performance of the overall AP1000 plant was estimated by component wise modeling and detailed break-up of energy and exergy losses in the various plant sections. Operating at maximum core power of 3400 MW, the AP1000 reactor core experienced moderately small thermal loss of 125.1 MW and very substantial exergy consumption of 1814.8 MW achieving energy and exergy efficiencies of 96.3% and 46.6% respectively. For the entire AP1000 plant, energy losses occurred mainly in the condenser where 1849.8 MW was lost to the environment. Exergy analysis, however, revealed lost energy in the condenser was thermodynamically insignificant due to the low quality and that irreversible losses of 1868.4 MW in the reactor and steam generator assembly were the major source of irreversibilities in the plant. The study confirmed that the major heat transfer inefficiencies occurring in nuclear reactor plants resided in the reactor cores and efforts to increase the efficiency of the plant should concentrate on the design of the core components.

Exergy analysis of the valorisation of rice straw for energy purposes with a life cycle approach: rice production in Cuba

In this paper, the exergy analysis methodology is used to analyse four alternatives for the valorisation of rice straw for energy purposes in Cuba. The exergy input and output of the product (%), the exergy destroyed (MJ) and the exergetic efficiency (%) are calculated. The exergetic efficiency increases in the three alternatives where rice straw is valorised for energetic purposes. In alternative 4, where it is considered the production of biomethane (to replace 60% of the diesel fuel for harvesting and transportation of products) and electricity via biogas, the exergetic efficiency reaches values of 66.6%. The exergy flow contained in the product increases from 13.2% to 21.9%. The increase in exergy flow in the final product also represents a reduction in greenhouse gas emissions as emissions are avoided by generating the same amount of electricity in a thermal power plant. Alternative 4 also achieves the highest sustainability index (2.994). The cumulative exergy consumption in greenhouse gases (CExCGEI), a new indicator that considers the accumulated exergy that is destroyed in greenhouse gases, is proposed.

Sustainable management and conservation of resources for different wheat production processes; cumulative exergy consumption approach

One of the new methods for evaluate the exergy-energy and share of agricultural productions, is cumulative exergy consumption (CEXC) analysis. CExC approach ensures that crop production processes can evaluate in the context of sustainable management and conservation of resources. In this research, wheat production processes (dry and wet) was investigated by CEXC approach. Cumulative degree of perfection (CDP) calculated 2.9 and 6.48 for wet and dry wheat production, respectively. The Renewability Indicator (RI) in this research were obtained 0.65 and 0.84 for wet and dry wheat production, respectively. In this research, electricity and diesel fuel had the highest consumption in all wheat production process. For a new case, it was assumed that the electricity and diesel fuel are produced by solar energy and biodiesel, respectively. In the new case, the CDP factor of wet and dry wheat production were 16.70 and 13.92 and RI values were 0.94 and 0.92, respectively.

Exergy analysis of the valorisation of rice straw for energy purposes with a life cycle approach: rice production in Cuba

In this paper, the exergy analysis methodology is used to analyse four alternatives for the valorisation of rice straw for energy purposes in Cuba. The exergy input and output of the product (%), the exergy destroyed (MJ) and the exergetic efficiency (%) are calculated. The exergetic efficiency increases in the three alternatives where rice straw is valorised for energetic purposes. In alternative 4, where it is considered the production of biomethane (to replace 60% of the diesel fuel for harvesting and transportation of products) and electricity via biogas, the exergetic efficiency reaches values of 66.6%. The exergy flow contained in the product increases from 13.2% to 21.9%. The increase in exergy flow in the final product also represents a reduction in greenhouse gas emissions as emissions are avoided by generating the same amount of electricity in a thermal power plant. Alternative 4 also achieves the highest sustainability index (2.994). The cumulative exergy consumption in greenhouse gases (CExCGEI), a new indicator that considers the accumulated exergy that is destroyed in greenhouse gases, is proposed.

Thermoconomic analysis of cogeneration installation (cgam) based on theory of the exergetic cost

Modern cogeneration systems are complex energy-technology complexes with a high degree of energy recovery. Pre-design analysis of these systems must take into account both the economic and thermodynamic components of the process of energy conversion. The most scientifically grounded basis for the development of recommendations for the design of aggregates of the cogeneration system is the modern method of thermoeconomic analysis. On the basis of the theory of exergetic cost, a thermoelectric model of a cogeneration unit is constructed, which takes into account the nonequivalence of exergy losses, which is related to the structural-topological features of the technological scheme. The thermoeconomic model has a hierarchical structure, which is a thermodynamic model, which is necessary for the determination of exergy flows, as well as an exergo-topological model that establishes, by means of flow graphs, the interconnections between exergetic flows in the installation. For visualization of the thermoelectric model, a functional exegetic flow diagram of a cogeneration unit is proposed, which helps to perform the separation of flows for a qualitative sign "fuel" - "product" of the element. In order to further coherent assessment of the exergetic and economic indicators of the system to the general thermoelectric model, the functions of the capital cost of the elements can be involved.On the basis of the numerical implementation of the thermoelectric model in the technological scheme of the installation areas are identified that have an excessive specific consumption of exergy, anomalies and dysfunctions for each element of the scheme. With the involvement of methods of the theory of experiment planning, regression models of the exergy efficiency of the installation were constructed depending on the determining factors, the factor analysis was performed and the interrelated influence of them on the exergy efficiency of the installation was determined.