Specific Exergy Consumption Research Articles

Exploring Geometric Properties and Cycle Design in Packed Bed and Monolith Contactors Using Temperature-Vacuum Swing Adsorption Modeling for Direct Air Capture.

This study presents a comprehensive comparison between the packed bed and monolith contactor configurations for direct air capture (DAC) via process modeling of a temperature-vacuum swing adsorption (TVSA) process. We investigate various design parameters to optimize performance across different contactor geometries, including pellet size, monolith wall thickness, active sorbent content in monoliths, and packed bed structure configurations, considering both a traditional long column (PB40) and multiple shorter columns configured in parallel (PB5). Our parametric analysis assesses specific exergy consumption, sorbent, and volume requirements across different operating conditions of a five-step TVSA cycle. For minimizing sorbent requirements, PB5 and monoliths with over 80% sorbent loading were the best-performing contactor designs with overlapping performance in the low-exergy region. Beyond this region, PB5 faced limitations in reducing sorbent requirements further and was constrained by a maximum velocity at which it is sensible to operate without substantially increasing the exergy demand. In contrast, monoliths decreased sorbent requirements with minimal exergy increase due to reduced mass transfer resistances and lower pressure drop associated with their thin walls. The analysis of volume requirement-specific exergy Pareto fronts revealed that PB5 was less competitive with this metric due to the requirements for additional void space in the contactor configuration. The study also revealed that optimal sorbent loading for reducing volume requirements in monoliths differed from those minimizing sorbent usage, with the most effective loading being below 100%. Thus, the optimal contactor design varies depending on the goals of minimizing sorbent and volume requirements, and the choice and design of the contactor will depend on the relative costs of these factors. Lastly, our findings challenge the assumption that higher velocities are always preferable for direct air capture, suggesting instead that the operating velocity depends on the contactor configuration.

A multi-node thermodynamic model on temperature-vacuum swing adsorption (TVSA) for carbon capture: Process design and performance analysis

The adsorption technology plays a significant role in the carbon capture domain for mitigating the CO2 emissions, whereas the heterogeneous character is presented in practical adsorption process. In this study, a multi-node thermodynamic model is established for temperature-vacuum swing adsorption (TVSA) considering the end non-uniform adsorption. It shows superior performance for the assessment of practical TVSA cycle compared with lumped model. Through the influence analysis of different operation parameters based on multi-node model, specific exergy consumption increases from 41.6 to 62.4 kJ/mol caused by simultaneous drop of heat consumption and lift of work consumption as feed pressure raises from 1.0 to 3.0 bar. Exergy efficiency ranges between 13.8 % and 15.0 % as CO2 concentration increases from 10 % to 20 %. However, those under ppm-level are below 0.86 %, presenting the higher exergy consumption but lower desorption capacity represented for direct air capture. The heat consumption of front half part of adsorption bed is 39.7 % higher than the latter one, proving the potential cascaded desorption of subzone heating is superior for reducing the energy consumption. Furthermore, exergy consumption is lifted due to enhancement of work consumption of vacuum pump as vacuum pressure reduces from 1.0 to 0.02 bar, resulting exergy efficiency drops from 19.6 % to 13.4 %.

A comprehensive assessment of energetic and exergetic performance for the dehumidification system of a processed pistachio production unit

AbstractThe present study aims to conduct a comprehensive evaluation of the energetic and exergetic performance of a dehumidification system utilized in the processing of raw pistachios. The assessment involved the application of the first and second laws of thermodynamics to calculate the exergy aspects of each component of the system, including input and output exergy rates, output/input exergy efficiency, product/fuel exergy efficiency, exergy destruction rate, exergy loss rate, exergy improvement potential rate, and specific exergy consumption. Furthermore, the effect of variations in reference state temperature on the exergy parameters was also investigated. The results indicated that the pre‐dryer chamber had the highest input exergy rate among all the components of the dehumidification system. The product/fuel exergy efficiency is specified to be 35.10%, 9.47%, and 60.43%, for the electro‐fan, heater, and pre‐dryer chamber, respectively, while their output/input exergy efficiency are 87.87%, 22.10%, and 56.28%, respectively. The values of the exergy destruction rate of these components are 0.83, 147.14, and 1.12 kW whereas the exergy loss rate values are found to be 0.03, 4.12, and 9.24 kW, respectively. The improvement potential rate values of these components are obtained to be 0.10, 117.83, and 4.53 kW, while the amount of specific exergy consumption for the dehumidification system is determined as 481.85 kJ/kg. The study also reveals that the exergy parameters vary with changes in reference state temperature and that the exergy efficiencies decrease linearly as reference state temperature rises. Therefore, the findings of this investigation demonstrate the potential for using exergy analysis as an effective tool to improve the performance of dehumidification systems in industrial settings, specifically in the production of pistachios.Practical applicationsPistachio nut known as green gold because of its high economical value, is one of the popular nuts over the world. Dehumidification system based on drying technology could be used in food industry with many distinct advantages for processing of particulate crops like pistachios. For a comprehensive assessment of this system, analysis of the first and second laws of thermodynamics is applied. Exergy aspect based on the thermodynamic analysis the is an important stage for designing, modeling, optimizing, and performance assessment of the dehumidification system to produce processed pistachio. The results of this study show that the performance of dehumidification system could be improved by incorporating a steam compressor, a secondary heat exchanger, self‐heat recuperation technology, and a pinch method. It is believed that such a study would contribute to the industrial exploitation of pistachio which can provide insight into decreasing energy consumption and reducing capital costs for engineers and factory owners.

Дослідження впливу основних режимних параметрів на ексергетичний ККД конвективної сушильної установки

Mathematical model is proposed for the numerical study of exergy losses in a chamber convective drying unit and the determination of the Impact of the main mode parameters during convective drying on the exergy coefficient of the useful effect of the convective drying unit. The mathematical model is implemented in the MathCad environment. The SKRR-400 intermittent chamber dryer for drying agricultural products with a one-time load of 400 kg was chosen as the object of the study. The components of exergy losses, which have the greatest influence on the thermodynamic perfection of the drying plant, are determined, and the ways of reducing their specific weight in the exergy balance are indicated. Numerical studies of the effect on the exergetic efficiency coefficient of the dryer of such parameters as the ambient temperature, the temperature of the coolant at the entrance to the drying installation, the temperature of the coolant at the outlet of the drying installation — spent coolant, the temperature of the steam condensate in the heater have been carried out. A numerical experiment showed that with the increase in the initial air temperature, the useful specific exergy consumption for moisture evaporation decreases and the change the prominence of the dryer performance does not affect the total exergy losses. It is established that the energy or exergetic and thermal efficiency factors of the dryer differ significantly . According to the calculations, the exergetic.efficiency of the chamber dryer, which reflects its thermodynamic perfection, does not exceed 14.5 %. Comparison of exergetic.efficiency with the energy or thermal efficiency of SKRR-400 type dryer showed that the thermal efficiency of dryers is significantly higher (50,4 % versus 14,5 %). It is hypothesized that this is due to the fact that thermal efficiency does not take into account the phenomena of irreversibility of heat and mass transfer processes. It was established that losses with waste coolant in the exergy balance make up 8 %, and in the thermal balance — 33,2 %. According to the results of the numerical experiment, it is shown that increasing the efficiency of drying units can be achieved by improving their heating devices and reducing their losses.

Comparative meta-analysis of desalination and atmospheric water harvesting technologies based on the minimum energy of separation

Desalination and atmospheric water harvesting technologies are highly desirable to produce freshwater for daily life activities and alleviate the global water crisis. Efforts to improve these have mostly been based on better engineering or materials design, but a comparison of their energy performance over a theoretical optimum is not well consolidated. This research conducts a meta-analysis that comparatively assesses existing atmospheric water harvesting and desalination technologies by evaluating the energy optimality in terms of the Gibbs free energy principle derived theoretical limit. After a review of the various existing technologies in these two classes, energy optimality, defined as the theoretical minimum specific energy consumption divided by the specific exergy consumption, is used as the metric to make a comprehensive and fair comparison of the various desalination and atmospheric water harvesting technologies. Results show that the vapor compression cycle and hybrid technologies-based atmospheric water harvesters have higher energy optimality of 12%, whereas others have much poorer performances of under 3%. For desalination, reverse osmosis yielded the highest energy optimality of 67.43%. Furthermore, the ideal energy optimality needed by atmospheric water harvesting to become comparable to desalination is at least 89.9%, which is almost impossible to practically achieve.

Exergy analysis of electrodialysis for water desalination: Influence of irreversibility sources

The increasing freshwater demand is pushing the development and adoption of desalination technologies. In this framework, electrodialysis has a consolidated role in brackish water desalination, but to make it competitive with other technologies for the desalination of more concentrated solutions (e.g., seawater), the specific energy consumption should be reduced. Exergy analysis provides a useful tool for determining the contribution of each thermodynamic inefficiencies on the process efficiency and the specific energy consumption. In this regard, this paper presents an exergy analysis of the electrodialysis process. A 1-D model is used for evaluating the performance of industrial-scale systems, consisting of a single or a double-stage configuration, and fed by brackish water, concentrated brackish water, or seawater. The analysis is devoted to quantifying the effects of irreversibility sources, focusing especially on the non-ideal membrane behavior. Results highlight that the ohmic resistance of solutions and membranes along with undesired transport phenomena play a major role. More specifically, passing from an “ideal” to a “real” process, the maximum value of the exergy efficiency decreases by about 6% in the case of brackish water and 16% in the case of seawater. Besides, results reveal that the water permeability of membranes is detrimental to the exergy efficiency, leading to an 8% reduction in the case of seawater desalination. The development of improved membranes with low resistances slightly enhances the exergy efficiency with negligible influence on the performance of the system. The adoption of the double-stage strongly reduces the specific exergy consumption, and in the second stage, the exergy destruction due to uncontrolled mixing phenomena becomes more important than the one caused by the membrane resistance. The results shed a light on the main actions to be undertaken by industries and engineers for improving the performance of electrodialysis systems.

Thermo-economical and environmental analyses of a Direct Contact Membrane Distillation (DCMD) performance

As a promising desalination technology, membrane distillation is expected to be developed continuously due to its wide application and low sensitivity to salt concentration in the feed stream. The performance of a direct contact membrane distillation (DCMD) has been investigated based on energy, exergy, economic and environmental analyses in the current study. Performance evaluation of a DCMD unit is comprehensively carried out in terms of the operating parameters, including gained output ratio (GOR), specific energy consumption (SEC), concentration polarization coefficient, temperature polarization coefficient, recovery ratio, exergy efficiency, specific exergy consumption, carbon cost, and cost of water. This study presents one of the most comprehensive investigations on DCMD behavior performed in the available literature by developing a robust computational code in MATLAB software. In addition to pervasive energy and exergy analyses, a complete economic study for freshwater production plants with different capacities based on heat extracted through geothermal energy and wasted heat, and investigation of the environmental effects of using heat recovery MD cycle to reduce greenhouse gas emissions, are presented. The results showed that the utilization of heat recovery heat exchangers significantly improves the system's operating conditions. The exergy efficiency of the DCMD module with and without heat recovery is 38.23% and 56.71%, respectively, indicating a 48.34% improvement in exergy efficiency. Finally, the economic and environmental analyses showed that for a 15000 m3/day desalination unit, recovering the wasted heat could reduce the distillate water production cost down to 1.31 $/m3 while CO2 emissions and energy consumption also decreased by 59%.

Exergy-based Energy Efficiency Evaluation Model for Machine Tools Considering Thermal Stability

Machine tools, as the extensively used basic equipment of manufacturing industry, are characterized by intensive and inefficient energy consumption. With the launch and implementation of ISO 14955-1, energy efficiency has become an important criterion for machine tool evaluation. However, most ongoing research on energy efficiency evaluation of machine tools emphasizes on workpiece material removal energy efficiency and rarely considers energy consumption needed to ensure machining accuracy and accuracy consistency, especially energy consumption for thermal stability control of machine tools. In light of this, an exergy analysis based approach is presented to assess the comprehensive energy efficiency of machine tools, including energy consumption for material removal and thermal stability control. The key performance indexes of exergy efficiency, exergy destruction, and specific exergy consumption are analyzed. The feasibility of the proposed approach was demonstrated by a case study, in which the comprehensive energy efficiency of a machine tool was found to be 21.57% instead of 14.38% of material removal energy efficiency. The proposed method is more effective to evaluate the comprehensive energy efficiency, to support designers to design high-efficient machine tool and users to operate machine tool for green and precision machining.

Pressure drop modeling and performance optimization of a humidification–dehumidification desalination system

In this study, the thermodynamic and pressure drop models of the humidification–dehumidification (HDH) system are developed and verified by the experimental results. The effect of operating parameters on the system performance is investigated. The parametric analysis indicates that the optimum point of the energy efficiency may appear in some cases. The pressure drop in the system increases with the air and liquid mass flow rates and the liquid top temperature. The influence of electric consumption on the system overall performance is evaluated from the different point of view (energy and exergy). In terms of energy consumption, the proportion of electric consumption in the total energy consumption is small with an average of 9.9%. The effect of electric energy consumption is negligible in many cases. In terms of exergy consumption, the average proportion of electric consumption is 29.4%, and the highest is 40.6%. The electric energy consumption has significant influences on the overall energy efficiency. Furthermore, numerical optimization is performed to achieve the minimum specific exergy consumption (SEXC). It can be concluded that, in the performance optimization of the HDH system, the priority is to adjust the liquid mass flow rate and liquid top temperature. The minimum values of the optimized SEXC are 222.0 kJ/kg.

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.

Comprehensive exergy analysis of a commercial tomato paste plant with a double-effect evaporator

In this study, a detailed exergy evaluation of a commercial tomato paste plant with a double-effect evaporator was conducted in order to provide information on the system thermodynamic inefficiencies. Using energy and exergy balance equations, all components of the plant were analyzed individually and their exergetic parameters were calculated on the basis of actual operational data. The required data were obtained from Nazchin tomato paste factory located in Tehran, Iran. In addition, it was attempted to quantify the exergy utilized for processing a given amount of the tomato paste. The results showed that over 82% of the total destroyed exergy in the plant occurred in the boiler combination as the main component wasting exergy. Furthermore, exergy analysis introduced this combination as the main equipment rejecting exergy to the ambient where 4.79% of its total exergy input was lost. The rational exergy efficiency of the first- and second-effect evaporative units was found to be 65.33% and 56.60%, respectively. The specific exergy consumption of the tomato paste production was also determined as 16.83 MJ/kg. Generally, exergy concept and its extensions could be served as a powerful assessment technique to optimize the design and performance of multiple-effect evaporation systems employed in food industry.

Specific exergy consumption as an index for steam extraction scheme selection for CO2capture systems in coal-fired power plants

In coal-fired power plants, steam is extracted from steam turbine to supply the regeneration heat for chemical absorption carbon capture. This research analyses the steam and heat consumption of a CO2 capture system for different extracted steam, as well as the influences of different extracted steam on electricity production and power plant electric efficiency. Results show that specific steam consumption and specific heat consumption, which only reveal the quantity of the steam consumption, could not be used for evaluating the true energy savings of different steam extraction methods. Specific exergy consumption of the extracted steam (SEXCS), which focuses on both the quantity and quality of energy, is proposed and used as a main comprehensive evaluation index in the CO2 capture system. Compared with specific steam consumption and specific heat consumption, SEXCS can better evaluate the true energy saving of the different extracted steam. Compared with plant electric efficiency and specific primary energy consumption for carbon avoided (SPECCA), SEXCS is both simple in calculation and easy in acquiring the required data. SEXCS is thus recommended to be used as an important index for selection of steam extraction schemes for CO2 capture systems. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Comprehensive exergy analysis of an industrial-scale yogurt production plant

In this study, a comprehensive and detailed exergy analysis was carried out to investigate an industrial-scale pasteurized yogurt production plant located in the north-west of Iran, West Azarbaijan province. For this goal, the plant was subdivided into four main subsystems, including steam generation, above-zero refrigeration, milk standardization and pasteurization, and yogurt production lines. Accordingly, exergetic efficiency and exergy destruction rate were defined and computed for each component of the four lines individually. Moreover, this analysis was conducted to find the amount of exergy consumed in producing a given amount of the pasteurized yogurt. The main contributors to the exergy destruction of the entire plant were in descending order of importance: boiler & air compressor combination of the steam generator (12484.88 kW), ice-water tank & agitator combination of the above-zero refrigeration system (2900.59 kW), and pressure reducer #2 of the steam generator (731.82 kW). Moreover, the specific exergy consumption of the pasteurized yogurt was found to be 841.34 kJ/kg based on the mass allocation concept. More specifically, the percentile contributions of the steam generation, above-zero refrigeration, milk standardization and pasteurization, and yogurt production lines to the specific exergy consumption were determined as 82.62%, 9.36%, 2.80%, and 5.21%, respectively.

A Novel Air Liquefaction Process by Using LNG Cold Energy

Since imported LNG is increasing gradually in China, the research of LNG cold energy utilization becomes quite urgent. A novel air liquefaction process with LNG cold energy utilization is proposed in this paper. With the Aspen plus software, this paper builds the simulation model of the air liquefaction process by using LNG cold exergy and analyzes the effects of the key parameters on the performance of the process. The results show that the power requirement to produce liquid air with LNG cold energy utilization is 142.9kWh/t, lower by 67.4％than that for the conventional air liquefaction process, and the specific exergy consumption of liquid air production is 310.3kWh/t. With LNG cold energy utilization, the energy cost of liquid air production in this proposed process is 48.7% lower than that of conventional process. The optimal conditions are reached through the analysis of economic effectiveness.

Flash evaporation and thermal vapor compression aided energy saving CO2 capture systems in coal-fired power plant

In this paper, flash evaporation and thermal vapor compression are used to reduce heat consumption of CO2 capture processes and two improved capture systems are proposed. One is the flash evaporator (FE) and thermal vapor compressor (TVC)-aided system, the other is the heated flash evaporator (HFE) and thermal vapor compressor (TVC)-aided system. Analyses are carried out to verify their effectiveness in reducing heat consumption. Compared with the base CO2 capture system of 108.76t/h CO2 capture capacity from a 660 MW coal-fired power unit, the FE-TVC-aided capture system reduces the specific heat consumption from 4.421GJ/tCO2 to 4.161GJ/tCO2, and the specific exergy consumption from 1.368GJ/tCO2 to 1.275GJ/tCO2, the corresponding energy saving and exergy saving are 10.3%, and the plant electric efficiency penalty is decreased from 11.83% to 11.02%, on condition that the CO2 recovery ratio is set at 90%. Compared with the base CO2 capture system, the HFE-TVC-aided capture system reduces the heat consumption from 4.421GJ/tCO2 to 4.057GJ/tCO2, and the specific exergy consumption from 1.368GJ/tCO2 to 1.243GJ/tCO2, the corresponding energy saving and exergy saving are 12.5%, and the plant electric efficiency penalty is decreased from 11.83% to 10.80%.

EXERGY CONSUMPTION MITIGATION IN THE ELECTRODIALYSIS OF THE AMMONIUM SULFATE AQUEOUS SOLUTIONS

A mathematical model was derived to describe the specific exergy consumption for the ammonium sulfate recovery by electrodialysis (ED) from diluted solutions. The model includes two new equations established on the basis of experimental data: the equation of the solution conductivity and the equation of the concentration vs. time. A TetraCon 196-1.5 conductivity cell was employed to measure the conductivity. A laboratory- scale ED unit type TS 2-5 from Eurodia/Tokuyama was used to generate the kinetic curves concentration vs. time. The equations of the mathematical model were numerically solved for different constant operating parameters. The voltage applied exerts the most important influence. At 303 K, 100 L/h flow rate, 1980 s ED time, and a voltage of 10 V the specific energetically consumption was of 2.25 kWh/kg ammonium sulfate separated. This is closed to that reported by other researchers for lactate separation in similar conditions.

Exergonomics of an EOR (OCDOPUS) project

The combined production of power, carbon dioxide, process steam, hot water, and compressed nitrogen for EOR is considered. Exergy-flow diagrams are used to evaluate plant efficiency. The exergy efficiency of the plant is defined as the sum of the exergy outputs divided by the exergy of the consumed fuel. Estimations of the invested exergy, net exergy coefficient and the sum of the specific exergy consumption are presented.

Exergonomics of the OCDOPUS project

The project of combined production of power, carbon dioxide, process steam, hot water and compressed nitrogen for oil recovery enhancement is considered. The exergy analysis to evaluate effectiveness of the plant is used. As the main tool the exergy flow diagrams are developed. Exergy efficiency of the plant is defined as a relation of the sum of delivered exergy flows to the exergy of consumed fuel. At attempt to guess the invested exergy, net-exergy coefficient and the sum of specific exergy consumption (exergonomic criterion) is presented.