Specific Exergy Destruction Research Articles

Syngas production with thermo-chemically recuperated gas expansion systems: An exergy analysis and energy integration study

In spite of the large degree of energy integration in the modern syngas production units, the highly endothermic reactions of steam methane reforming and the combined steam and power generation still require a huge amount of energy that is typically supplied by an expensive natural gas-fired furnace at very high temperatures. Since normally only half of the energy supplied by the furnace is used to carry out the reforming reactions, the remaining heat recovery must be performed in a separate convection train (HRCT). Additionally, the high temperature effluent of the secondary reformer is generally cooled down by producing low temperature steam, increasing the process irreversibility and the losses associated to the excessive amount of condensate. Thus, in this paper, the advantages of introducing a chemically recuperated gas turbine (CRGT) concept to simultaneously carry out the endothermic chemical reactions and recover the exergy available from the autothermal reformer effluent are discussed. In this way, higher temperatures and higher conversions can be attained with lower driving forces. The power required by the air compression as well as other ancillary systems (e.g. air separation unit, carbon capture system, boiler feedwater pumps and recompressor) can also be supplied, while the exergy of the exhaust gases from the turbine is used more efficiently than in typical steam generation systems. Thus, more compact and integrated syngas production plants can be envisaged. Moreover, by introducing more advanced cogeneration features such as air enrichment, process gas reheating and incremental levels of pressures in the reaction-driven components, energy savings together with drastically reduced atmospheric CO2 emissions and irreversibility can be achieved in the frontend syngas production section. As a result, the average specific exergy destruction and exergy fuel consumption of the proposed CRGT-based configurations are, respectively, 12.0% and 2.7% lower, whereas the specific atmospheric CO2 emissions are cut down up to 25%, when compared to the conventional syngas production process.

Performance assessment of a marine freshwater generator through exergetic optimization

The objective of this study is to examine the effect of operating parameters on the freshwater generation capacity of a vacuum type and low-temperature single-stage freshwater generator and the exergy destruction of the condenser and evaporator sections. Evaporator and condenser, which are plate type heat exchangers, are modeled using the ε-NTU method. Energy and exergy analyses were applied to the control volume enclosing the condenser and evaporator to find the freshwater production rate and to investigate the system performance. A parametric study was performed to assess the effects of the jacket water mass flow rate, the seawater salinity, and the seawater temperature on the output parameters (fresh water production rate and specific exergy destruction). In addition, an optimization study was performed using the Taguchi method to maximize the freshwater production rate and minimize the exergy destruction rates of the condenser and evaporator. The results derived from the parametric study showed that the seawater temperature of 31.88 °C and jacket water mass flow rate of 72,000 kg/h are the required values to obtain the maximum freshwater generation capacity (30 m3/day). When the salinity increases from 3 g/kg to 41 g/kg (3000 to 41,000 ppm), the freshwater production rate increases by 2.18% and 5.06% under the constant seawater temperature (23 °C) and the jacket water mass flow rate (58,500 kg/h), respectively. The optimization results revealed the conditions to obtain the maximum fresh water production rate and the minimum exergy destruction.

Exergy and thermo-economic analysis of ghee production plant in dairy industry

The India’s annual milk and ghee production are approximately estimated as 160 MT and 1.72 MT respectively. India has the largest production of Ghee in the dairy Industry worldwide. Ghee consumption in India is 28% annually after fluid milk i.e. 44% due to high consumer demand. The butter churner, butter melter, ghee boiler and ghee clarifier are the key subunits of ghee production plant. The dairy industry is characterised by high energy consumption for production of Ghee and Butter in the country. The thermo-economic analysis and thermodynamic derivatives calculated in this study. The value of the universal exergy efficiency and specific exergy destruction of the plant was found as 34.21% and 438.61 kJ/kg respectively. The cost rate of exergy destruction for the entire plant was calculated as 3270.68 R/H; 39% of which was contributed by boiler for ghee production (ghee boiler). The highest value of percentage relative cost difference was associated with butter melter (97.29%) followed by butter churner (96.73%). The thermo-economic factor butter churner (8.00%) and ghee boiler (1.09%) revealed that impact of capital investment was more influential in former while exergetic degradation appeared to be more noticeable in latter.

Thermodynamic viability of a new three step high temperature Cu-Cl cycle for hydrogen production

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.

Co-production of Hydrogen and Copper from Copper Waste Using a Thermochemical Cu–Cl Cycle

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...

Energy and, exergy analysis of a CCHP-ORC system based on MGT - ORC and absorption chiller

A CCHP-ORC system consisting of a MGT, an ORC and an absorption refrigeration chiller was proposed in this study. A verified simulation model based on specific mass, energy conservation and exergy destruction was built. Thermodynamic analysis was applied to the system. A parametric study was carried out to investigate the impacts of the ORC's evaporating temperature and, turbine efficiency, and the ARC's generating temperature on the system's performance. Six different organic working fluids (R141b, Toluene, D4, n-Octane, n-Heptane and MM) were selected in this study, and their impact on the system's performance was also analyzed. The results showed that the CCHP-ORC system's primary energy efficiency and exergy efficiency could reach a maximum of 76.89% and 54.95% respectively, with toluene as the organic working fluid. The MGT accounted for a large part of exergy destruction in both the CCHP-ORC and reference system. Compared to the reference system, the total exergy destruction of the CCHP-ORC system decreased, for all six organic working fluids. The main exergy reduction occurred in the GEN, ABS and DHW. A T-Q diagram method was conducted to analyse the heat transfer process in the CCHP-ORC and reference system. The results showed that the CCHP-ORC system can significantly reduce the mean heat transfer temperature difference in the heat transfer process, which helps to decrease the exergy destruction in GEN, and improves the system's exergy efficiency. Hence, it is beneficial for the system's efficiency and exergy destruction to introduce ORC as a middle cycle into the CCHP system. © 2017 American Institute of Chemical Engineers Environ Prog, 2017

Exergetic performance analysis of an ice-cream manufacturing plant: A comprehensive survey

In this study, a comprehensive exergetic performance analysis of an ice-cream manufacturing plant was conducted in order to pinpoint the locations of thermodynamic inefficiencies. Exergetic performance parameters of each subunit of the plant were determined and illustrated individually through writing and solving energy and exergy balance equations on the basis of real operational data. The required data were acquired from a local ice-cream factory located in Tehran, Iran. The plant included three main subsystems including water steam generator, refrigeration system, and ice-cream production line. An attempt was also made to quantify the specific exergy destruction of the ice-cream manufacturing process. The functional exergetic efficiency of the water steam generator, refrigeration system, and ice-cream production line was determined at 17.45%, 25.52%, and 5.71%, respectively. The overall functional exergetic efficiency of the process was found to be 2.15%, while the specific exergy destruction was calculated as 719.80 kJ/kg. In general, exergy analysis and its derivatives could provide invaluable information over the conventional energy analysis, suggesting potential locations for the plant performance improvement.

Application of exergy analysis to the dairy industry: A case study of yogurt drink production plant

This work was aimed at undertaking a detailed exergy analysis of an industrial-scale yogurt drink production plant using actual operational data. Exergy efficiency and exergy destruction rate of each subcomponent of four main subsystems of the plant, including steam generation, above-zero refrigeration, milk reception, pasteurization, and standardization, and yogurt drink production lines were derived independently. This analysis was performed to quantify thermodynamic inefficiencies of all subcomponents of the plant in order to identify the breakthrough points for further energy savings. An effort was also made to compute the quantity of exergy destruction in processing a given amount of pasteurized yogurt drink. The results indicated that the highest exergy destruction rate occurred in the boiler & compressor combination of steam generator, followed by ice-water tank & agitator combination in the above zero refrigeration system. The specific exergy destruction of pasteurized yogurt drink was determined as 442kJ/kg according to the mass allocation method. The steam generator had the highest contribution to the specific exergy destruction of pasteurized yogurt drink, followed by yogurt drink production, above-zero refrigeration, and milk reception, pasteurization, and standardization lines, respectively. In general, the current survey can be an important step for future improvements of dairy processing plants from the sustainability and productivity viewpoints. This study clearly showed the effectiveness of exergy analysis for determining irreversibilities and losses occurring in dairy processing plants in order to improve their thermodynamic performances.

Exergy analysis of single effect absorption refrigeration systems: The heat exchange aspect

The main limitation of conventional energy analysis for the thermal performance of energy systems is that this approach does not consider the quality of energy. On the other hand, exergy analysis not only provides information about the systems performance, but also it can specify the locations and magnitudes of losses. A number of studies investigated the effect of parameters such as the component temperature, and heat transfer fluid (HTF) temperature and mass flow rate on the exergetic performance of the same absorption refrigeration system; thus, reported different coefficient of performance (COP) values. However, in this study, the system COP was considered to remain constant during the investigation. This means comparing systems with different heat exchanger designs (based on HTF mass flow rate and temperature) having the same COP value. The effect of HTF mass flow rate and inlet temperature of the cooling water, chilled water and heat source on the outlet specific exergy and exergy destruction rate of each component was investigated. It was found that the lower HTF mass flow rate decreased exergy destruction of the corresponding component. Moreover, the lower temperature of heat source and chilled water inlet increased the system exergetic efficiency. That was also the case for the higher cooling water inlet temperature. Based on the analysis, since the absorber and condenser accounted for a large portion of the total exergy destruction, cooling tower modification with lower cooling water mass flow rate is recommended. Furthermore, increasing the cooling water temperature is also recommended as long as the cooling tower can meet the cooling load.

Exergy analysis of an industrial-scale ultrafiltrated (UF) cheese production plant: a detailed survey

In this study, a detailed exergy analysis of an industrial-scale ultrafiltrated (UF) cheese production plant was conducted based on actual operational data in order to provide more comprehensive insights into the performance of the whole plant and its main subcomponents. The plant included four main subsystems, i.e., steam generator (I), above-zero refrigeration system (II), Bactocatch-assisted pasteurization line (III), and UF cheese production line (IV). In addition, this analysis was aimed at quantifying the exergy destroyed in processing a known quantity of the UF cheese using the mass allocation method. The specific exergy destruction of the UF cheese production was determined at 2330.42 kJ/kg. The contributions of the subsystems I, II, III, and IV to the specific exergy destruction of the UF cheese production were computed as 1337.67, 386.18, 283.05, and 323.51 kJ/kg, respectively. Additionally, it was observed through the analysis that the steam generation system had the largest contribution to the thermodynamic inefficiency of the UF cheese production, accounting for 57.40 % of the specific exergy destruction. Generally, the outcomes of this survey further manifested the benefits of applying exergy analysis for design, analysis, and optimization of industrial-scale dairy processing plants to achieve the most cost-effective and environmentally-benign production strategies.

Exergetic performance assessment of a long-life milk processing plant: a comprehensive survey

The aim of this study was to carry out a comprehensive exergy analysis of an industrial-scale long-life milk processing plant for the first time. The plant consisted of four main lines including steam generator, above-zero refrigeration system, milk reception, pasteurization, and standardization line, and ultra-high-temperature (UHT) milk processing unit. This survey was performed to obtain more in-depth information about the exergy destroyed in the whole plant and its main subcomponents. In addition, an attempt was made to quantify the exergy destroyed for processing a given amount of the long-life milk using the mass allocation method. The results indicated that the largest exergy destruction rate occurred in the compressor and boiler combination of the steam generation system, accounting for 89% of the total exergy destruction of the system. More specifically, the specific exergy destruction of the long-life milk processing was determined as 345.50 kJ kg−1. The steam generation system had the greatest contribution to the specific exergy destruction of the long-life milk processing followed by above-zero refrigeration system, UHT milk processing unit, and milk reception, pasteurization, and standardization line, respectively. Hence, a small improvement in the exergetic performance of the steam generator could profoundly lower the specific exergy destruction of the long-life milk processing. According to the outcomes of the current study, the performance and sustainability parameters of dairy processing plants can be best-evaluated and improved using exergy analysis.

Thermodynamic Performance Indicators for Offshore Oil and Gas Processing: Application to Four North Sea Facilities

Well-defined performance indicators can motivate optimal operation of offshore oil and gas platforms. We evaluate several thermodynamic performance indicators presented in the literature according to three criteria: Thermodynamic performance indicators should evaluate the use of technically achievable potential, they should evaluate the use of theoretical potential, and they should evaluate the total use of energy resources. The performance indicators are tested on four North Sea facilities, and the results are discussed. We recommend the use of a set of indicators for a thorough evaluation of oil and gas platforms--the best-available-technology efficiency on an exergy basis, a task exergy efficiency, and the specific exergy destruction.

Exergy analysis of a novel configuration of desiccant based evaporative air conditioning system

In this work, a process is developed for exergy analyses of a novel configuration of desiccant based an evaporative air conditioning system. The exergy transfer and destruction between the components of the system are defined for the average measured variables obtained from the experimental results. The exergy formulations are carried out to the experimental system using the data collected during a typical operation of the system. The exergy output, specific flow exergy, exergy destruction, exergy input and exergy efficiency are determined. Furthermore, the sustainability assessment and relative irreversibility of components are obtained. It is found that the exergy efficiency of the entire experimental unit is 40.7% at a reference temperature of 15°C. It is also observed that the exergy efficiencies of the entire system varies between 56% and 25% for reference temperature of 0–30°C, respectively. The effects of reference temperature on the performance of the studied system are investigated. Based on the investigation, it is seen that an exergy analysis can provide beneficial knowledge with respect to the theoretical upper limit of the system performance.

Second law and sensitivity analysis of large ME-TVC desalination units

Large number of low temperature multi-effect thermal vapor compression (ME-TVC) desalination units have been installed recently in most of the GCC countries. The new trend of combining ME-TVC with conventional multi-effect led to tremendous increase in the unit size more than eight times during a very short period. The unit size capacity of this technology is currently available with 10 million imperial gallons per day (MIGD), and research studies are expected to increase this unit capacity up to 15 MIGD in the near future. Hence, this technology becomes highly attractive and competitive against multi stage flash desalination system. A mathematical model of ME-TVC desalination system is developed in this paper, using Engineering Equation Solver Software. This model is used to evaluate and improve the system performance of some new commercial ME-TVC units with capacities of 2.4, 3.8, and 6.5 MIGD using energy and exergy analysis. A sensitivity analysis is also presented in this paper to investigate the system performance of Al-Jubail ME-TVC unit in KSA, which is considered as the largest ME-TVC desalination plant in the world. Results showed that the first effect was found to be responsible for about 31% of the total effects exergy destruction in Al-Jubail, compared to 46% in ALBA and 36% in Umm Al-Nar. Results also showed that the specific exergy destruction is reduced significantly by increasing the number of effects as well as working at lower top brine temperatures.

Thermodynamic analysis of a cogeneration gas turbine and desalination plant

This work deals with a thermodynamic analysis of the performance of a cogeneration gas turbine and thermal desalination plant. A heat recovery steam generator links the two units together. The analysis is based on the application of mass, energy and exergy balances on the whole cogeneration plant as well as on each of its components. The analysis is also based on an accurate evaluation of the seawater properties, which leads to correct calculations of the flow exergy and exergy efficiency of any component of the desalination plant. The main results of the study concern the influence of the pressure ratio of the compressor and the turbine inlet temperature on the exergy efficiency of the gas turbine and the whole combined system. It was found in particular that as the performance ratio of the desalination plant increases the specific exergy destruction rate decreases.

Exergy analysis of a high-temperature-steam-driven, varied-pressure, humidification–dehumidification system coupled with reverse osmosis

In this study, exergy analysis of a novel desalination system is presented and discussed. The water desalination is carried out using combined humidification–dehumidification and reverse osmosis technologies. Six system performance parameters are examined: overall exergetic efficiency, equivalent electricity consumption, specific exergy destruction, specific exergy lost, and total true specific exergy lost, as well as the exergy destruction ratios of the main components. The total true specific exergy lost is a new parameter presented in this study. It is a function of summation of total the exergy destruction rate and loss per total mass flow rate of the total pure water produced. This parameter is found to be a useful parameter to assess the exergetic performance of the system considered. By contrast, use of overall exergetic efficiency as an assessment tool can result in misleading conclusions for such a desalination system and, hence, is not recommended. Furthermore, this study reveals that the highest exergy destruction occurs in the thermal vapor compressor, which accounts for 50% of the total exergy destruction of the system considered. This study, in addition, demonstrates that the specific exergy destruction of the dehumidifier and TVC are the parameters that most strongly affect the performance of the system.

Exergetic and sustainability performance comparison of novel and conventional air cooling systems for building applications

This study presents energy and exergy analyses and sustainability assessment of one novel and three conventional types of air cooling systems for building applications. First, effectivenesses of the systems are determined using energy analysis method. Second, exergy aspects of the systems are investigated for twelve different dead state temperatures varying from −5°C to 50°C with a temperature interval of 5°C. The specific exergy flows of humid air, dry air and water, exergy efficiency, and specific exergy destruction are then calculated. Sustainability index is also used to define and discuss the systems’ sustainability aspects. Finally, the results obtained here show that at the dead state temperatures of higher than 23°C (comfort temperature), exergy efficiency and sustainability of the novel system, which is based on the novel Maisotsenko cycle (M-Cycle), is higher than those of the conventional systems. At a dead state temperature of 50°C, novel cooling system's exergy efficiency can reach 60.329% as the maximum, while the minimum exergy efficiency of other conventional cooling systems becomes as low as 35.866%, respectively.

The effect of stage temperature drop on MVC thermal performance

The aim of this research is to study the thermal performance of MVC desalination system. A hybrid MSF–MVC desalination system is proposed in this study, and a parametric study was carried out to study the effects of MVC brine temperature and temperature drop across MVC stage on system performance in terms of specific power consumption, pressure ratio, feed to distillate ratio, specific heat transfer area, distillate product and exergy destruction. The analysis was performed using steady state mathematical model for hybrid MSF–MVC system; the model is based on first and second laws of thermodynamics. Results showed that as temperature drop across the stage increases, the specific power consumption increases, and distillate water production decreases. On the other side as MVC brine temperature increases, the specific heat transfer area decreases. Results showed that the increase in the temperature drop across stage causes an increase in exergy destruction.

Thermodynamic bounds for food deep chilling tray tunnel operation

In this paper a thermodynamically guided intensification method on tray tunnels for food deep chilling is presented. Two indicators of the performance of the system are used: the exergy power and the destruction of specific exergy. The objective function corresponds to the maximization of the exergy power and the minimization of the specific exergy destruction. Exergy has the main advantage to take into consideration both the food mass flow rate and its output temperature level. The food mass flow rate stands for its quantity whereas the temperature level represents its quality. An endoreversible model is also presented in conjunction with a simple mathematical description of the refrigeration cycle internal irreversibilities. A numerical investigation against operation variables permits to find the so-called intensification zone that defines bounds for food mass flow rate and output temperature as well as for the refrigeration cycle evaporator temperature.