Specific Exergy Destruction Research Articles

Energy and exergoeconomic analyses of parallel cross feed multi effect desalination system driven by twin-screw compressor with water injection

This work proposes the design of a parallel cross-feed multi-effect desalination system with a twin-screw compressor, incorporating water injection to enhance system performance. The improvement is achieved by injecting water during the compression process to increase the isentropic efficiency of compression. The mathematical model is solved using Engineering Equation Solver software, and the resulting mass and energy balance equations are validated against literature data. The system is analyzed and evaluated from energy, exergy, and exergy-economic perspectives, and compared with the performance of the conventional configuration in terms of specific power consumption, exergy efficiency, and cost of produced water. The impact of various operating conditions, such as the number of effects, steam temperature, compressor efficiency, and injection pressure, on specific power consumption, exergy efficiency, exergy destruction, and final product cost, is examined in this study. Additionally, factors like interest rate, plant life expectancy, and electricity cost are investigated for their effect on the final product cost. The study demonstrates that replacing the normal compressor with a twin-screw compressor result in more than a 15 % reduction in specific power consumption, approximately 4 % less exergy destruction (indicating higher exergy efficiency), and a 14 % lower unit cost of freshwater.

Membrane and desublimation integrated hydrogen separation followed by liquefaction process: An energy, exergy, and economic evaluation

H2 has gained global attention owing to its clean energy characteristics. As an energy vector, long-term storage and transportation of H2 in liquid form is essential which requires effective pretreatment. Standalone technologies, such as pressure swing adsorption, membrane, and cryogenic, cannot produce highly pure H2 with high recovery in an energy-efficient manner. The integration of technologies is a promising alternative to overcome these limitations. In this regard, membrane and cryogenic (desublimation) techniques are integrated to separate H2 with high purity and recovery. Purified H2 is liquefied to produce 100% saturated liquid H2 (LH2). The proposed process is designed in Aspen Hysys v11 and evaluated with respect to energy, exergy, and economic considerations. The results have shown that the proposed process resulted in H2 separation with 99.99% purity and 95.87% recovery. The total net energy consumption of the proposed integrated process was 11.53 kWh/kg. Exergy analysis revealed that the liquefaction section had the highest specific exergy destruction (∼92%). Moreover, the detailed economic calculations showed that the total annualized process cost was 671.6 m$/y. In this study, the potential of membrane–cryogenic integration with LH2 production is evaluated and shown to be fundamental in the development of a sustainable H2 economy.

ANALYSIS OF A VAPOUR COMPRESSION REFRIGERATION SYSTEM WORKING WITH R22

Marine refrigeration has to comply with environmental constraints and with efficiency improvement as well. R22 was a refrigerant governing marine refrigeration systems. After 2020, it is legally in use in old systems, relying on recycled supplies, because of its poor environmental properties. In this paper, it is developed a theoretical analysis of a single stage vapour compression system working with R22, on basis of energy and exergy analysis. The thermodynamic analysis consists in the assessment of the influence of evaporator temperature on the performance of the system- by the use of the laws of thermodynamics. The evaporation temperature varies in the range (6.5-9.5) oC, when the ambient temperature is 28oC.The obtained results will show that the Coefficient of Performance will increase together with the evaporator temperature increase, while the specific work consumption and specific total exergy destruction will decrease. For the maximum considered value of the evaporator temperature, COP value increases with 14% in comparison with the value obtained for the minimum evaporator temperature. In addition, the specific work consumed by the compressor will decrease with 5.81%, while for the specific total exergy destruction the decrement is of 2.4%. Seen that for the highest evaporator temperature it is reached the performance improvement, for 9.5oC are also determined the exergy destructions in the main components of the system. It is found that in the compressor, in the evaporator, in the condenser and in the throttling valve, exergy losses are 5%, 36%, 56% and 3%. Exergy analysis reveals that the most inefficient components of the system are the two heat exchangers of the system.

Propane-isobutane mixtures in heat pumps with higher temperature lift: An experimental investigation

The shift towards renewable energies leads to an increased interest in heat pumps, not only for floor heating at temperatures around 40 °C, but also for providing hot water at higher temperatures (>60 °C). To reach the goal of a climate neutral process, it is important to use working fluids with a low global warming potential (GWP). Zeotropic mixtures are discussed to potentially increase the coefficient of performance (COP) of a heat pump compared to pure fluids. The present work experimentally analyses a compression heat pump process of such fluids; five mixtures of propane (R290) and isobutane (R600a) are investigated here. The influence of composition, compressor frequency, inlet temperature of the working fluid into the evaporator and the inlet temperature of the secondary fluid water into the condenser are researched. Besides the COP, the destroyed exergy in the components are evaluated, to find the most relevant losses. It is shown that the COP for a temperature lift of 33 K are above 3 for the mixtures, while at a higher temperature lift of 53 K the COP is around 2. Furthermore, a strong impact of the overall compressor efficiency on the process was found. The results show that the advantage of the zeotropic mixture within the heat exchangers is often limited by their low contribution to the total specific exergy destruction compared to the compressor. The compressor efficiency changes with the composition, due to composition dependent pressure and density variations. The often-neglected changes in electro-mechanical losses get important, when the pressure ratios are changing with composition, as shown experimentally.

The second law analysis of a humidification-dehumidification desalination system using M-cycle

Humidification-dehumidification desalination (HDD) systems offer a feasible approach for the production of fresh water in inaccessible areas as they can be operational using renewable energy and require little maintenance. Various studies are being carried out to boost the system performance. In this paper, an open air open water HDD system is proposed that exploits the enhanced evaporation and condensation processes by implementing with the Maisotsenko cycle (M-cycle). The system utilizes solar energy as the energy input to heat the saline water. A thermodynamic model is formulated under steady-state conditions, considering the first and second law of thermodynamics. The energetic and exergetic performance of the system is studied. The model is first validated with the experimental data and a good agreement is found where the maximum discrepancy is about 6.0 %. Effects of different operating conditions on key performance parameters such as the Gain Output Ratio (GOR), specific energy consumption (SEC), exergy destruction, and exergy efficiency are analyzed. An improvement is observed in the GOR when the inlet air temperature is raised at constant humidity ratio. The system exhibits better performance in dry air environment when compared with humid air environment. The analysis shows a maximum mass flow rate of desalinated water of 22.3 kg/h, recovery ratio (RR) of 0.223, GOR of 3, SEC of 0.23 kWh/kg and an exergy efficiency of 43.21 %.

Characterisation of the effect of water content on the methanol spray combustion

The methanol spray combustion in a laboratory-scale combustor was experimentally studied in the present study, especially for the effect of the water content in methanol on the flame phenomena. The results showed that as the water content in the fuel mixture was less than 10%, and the flames can be sustained stably. The appearance of the flames was not significantly different for various water contents in the fuel mixture. However, the flame length was reduced by increasing water contents, but there was no apparent change in the flame lift-off height. The exergy efficiency was in the range of 18%-21%. In addition, near flame extinction, the increase of specific exergy destruction can be found. As the water content in the fuel mixtures was increased by 10%, the exergy efficiency reasonably decreased by 9.98%, but the thermal efficiency reduced by 26.61%.

Using synthesis gas heat to produce work via an externally fired gas power cycle

Synthesis gas production requires significant amounts of energy. Efficiency improvements and introduction of renewable or non-carbon energy sources are needed to reduce carbon dioxide emissions. Downgrading of high level heat in synthesis gas cooling trains contributes significantly to exergy losses. Recently, turbine expansion of synthesis gas was investigated by various authors, as one method to reduce exergy losses. However, using synthesis gas as a working fluid poses risks to rotating machinery. Thus an externally fired gas power cycle is proposed, which also allows flexibility to incorporate various types of renewable energy sources. In this study helium is the working fluid and nuclear energy the heat source. A helium-steam combined cycle arrangement is simulated and analysed using energy, exergy and cost analysis. Hot synthesis gas is used to provide additional heat to the helium-steam combined cycle via indirect heat exchange, thereby allowing a close match between the temperatures. Further cooling of the synthesis gas via steam generation is also employed. The work output of the integrated system versus a standalone case was increased by at least 19%. The specific exergy destruction in kW/MW work output was reduced by 38% and the specific equipment cost in $/MW work output increased by 22%.

Systematic energy and exergy assessment of a hydropurification process: Theoretical and practical insights

Improvement of process efficiency and reduction of operation costs are of significant importance in industrial chemical plants. In this study, an effective approach is proposed to analyze a hydropurification process, focusing on energy utilization, operating costs, environmental impact (e.g., CO2 emissions), and exergy performance. The hydropurification process includes heat exchangers, pumps, crystallizers, reactor, and furnace. This process is operated under high pressures and temperatures; it is prone to high consumption of energy and considerable loss of work quality. The vital operating parameters affecting the system performance are chosen by employing Taguchi method. The process simulation and/or thermodynamic modeling are carried out using Aspen Plus® software, and by writing codes for the exergy calculation in MATLAB software environment. The results are in acceptable agreement with the industrial data. The optimal conditions lead to 15% reduction in the process exergy destruction. The optimal operation can be established by implementing lower minimum approach temperature (ΔTmin) of the reaction system feed preheaters (e.g., 5 °C), setting a higher operating pressure in the heat exchangers of the feed preparation section (e.g., 96 bar), and enhancing the performance of heat exchangers using oil as heat transfer medium (optimizing furnace operating conditions). Furthermore, the performance of the fourth and sixth heat exchangers can be enhanced by 33.3%; the performance of the fourth crystallizer can be improved up to 18.7%. The furnace, which utilizes the expensive Therminol® 66 (as the heat transfer fluid), experiences a significant exergy destruction due to significant fluctuations in temperature and thermodynamic irreversibility in the combustion process. Implementation of the proposed optimal conditions can lower the operation costs and carbon tax by 9.96% ($20.5/h) and 14.75% ($14.54/h), respectively; and the CO2 emission rate can be decreased by 0.582 t/h. A decrease in ΔTmin of the heat exchangers improves the process specific energy consumption and exergy destruction. Moreover, effective control of the plant and avoidance of high fluctuations in the process parameters can lead to exergy destruction reduction.

Understanding the transient behavior of the dew point evaporative cooler from the first and second law of thermodynamics

Owing to its high energy efficiency without using greenhouse gases, dew point evaporative cooling offers a desired solution for thermal management of electronic and electrical devices. This paper elucidates the transient behavior of a dew point evaporative cooler and its significant influence on the dynamic cooling performance. A large time constant (400 s) of the product air temperature was observed under a zero-state response, leading to a pronounced deviation of the time-average cooling performance below its steady state by 13.8%–26.4% over a long period (2500 s). To capture this phenomenon, a modified transient lumped parameter model and a new partial differential exergy model were developed. An air mixing process in the dry channel was identified to account for the slow cooler’s transient responses. A detailed exergy analysis revealed that the specific exergy destruction at the dry channel entrance was above 400 W/kg, owing to the air mixing. This finding demonstrates that the transient behavior should be judiciously considered in the cooler design and optimization, together with the steady-state performance. Accordingly, a detailed sensitivity analysis of the cooler’s objective variables is proposed to gain insights into the future improvement of the dew point evaporative cooler.

Black Hole-Inspired Optimal Design of Biomethane Liquefaction Process for Small-Scale Applications

Biomethane is regarded as a promising renewable energy source, with great potential to satisfy the growth of energy demands and to reduce greenhouse gas emissions. Liquefaction is a suitable approach for long distances and overseas transportation of biomethane; however, it is energy-intensive due to its cryogenic working condition. The major challenge is to design a high-energy efficiency liquefaction process with simple operation and configuration. A single mixed refrigerant biomethane liquefaction process adopting the cryogenic liquid turbine for small-scale production has been proposed in this study to address this issue. The optimal design corresponding to minimal energy consumption was obtained through the black-hole-based optimization algorithm. The effect of the minimum internal temperature approach (MITA) in the main cryogenic heat exchanger on the biomethane liquefaction process performance was investigated. The study results indicated that the specific energy consumption of modified case 2 with MITA of 2°C was 0.3228 kWh/kg with 21.01% reduction compared to the published base case. When the MITA decreased to 1°C, the specific power of modified case 1 reduced to 0.3162 kWh/kg, which was 24.96% lower than the base case. In terms of exergy analysis, the total exergy destruction of the modified cases 1, 2, and 3 was 31.28%, 22.27%, and 17.51% lower than the base case, respectively. This study’s findings suggested that introducing the cryogenic liquid turbine to the single mixed refrigerant-based biomethane liquefaction process could reduce the specific energy consumption and total exergy destruction significantly. Therefore, this study could provide a viable path for designing and improving the small-scale biomethane liquefaction process.

A comprehensive energy, exergy and enviroeconomic (3-E) analysis with carbon mitigation for multistage evaporation assisted milk powder production unit

The global annual milk powder trade was estimated to be of 851.84 Million Metric Tons whereas; its Indian counterpart was recorded as 196.18 Million Metric Tons in the year 2019. The world’s annual milk powder production has registered a growth of 50% in the last three decades. In view of high thermal and electrical energy consumption; the present work focus upon energy, exergy and enviroeconomic assessments for comprehensive powder production wherein, the value of exergy efficiency, specific exergy destruction and specific exergy improvement potential. The exergetic performances of triple effect evaporator and single stage spray dryer unit were computed as 56.62% and 66.11% respectively. Additionally, involvement of economic approach with total saving in uniform yearly cost through electricity from PV panels will be approximately calculated as 979,006$ and 874,319$ at an interest rates of 4.5% and 7.5% respectively. Similarly, the investment on PV panels will be recovered after 8 and 11 years of operation for the respective rates of interests. On the basis environmental evaluation, it was found that adoption of clean energy solution (PV panels); could assist in mitigation of approximately 17,670 Tonnes of CO2 during its lifetime with securing a revenue of 256,215$/lifetime.

Energy quality factor and exergy destruction processes analysis for chemical looping hydrogen generation by coal

SummaryChemical looping hydrogen generation (CLHG) is a hydrogen production process with broad prospects for its advantages of not requiring H2 purification process and direct CO2 capture. Presently, the research on the integrated system of CLHG focuses on the impact of integrated processes and operating variables on the overall energy efficiency and exergy efficiency of the system. However, the research on the matching relationship between quantity and quality in the process of energy conversion is insufficient, and the flow direction of exergy and the specific exergy destruction process for equipment are not clear. The integrated system of coal gasification (CG) and three reactors CLHG was established in this paper with a hydrogen production efficiency of 42.55% and system exergy efficiency of 52.98%. This paper studied the exergy flow direction and efficiency of the equipment in the system, providing the improved direction for the amelioration of the system; a detailed description was present on the change process of energy quality in each equipment with energy quality factor, and the concept of energy quality factor ratio was proposed as an evaluation tool for matching the quantity and quality of energy in the system. It is calculated that the ratio of energy quality factor of the integrated system of CG and CLHG is 0.944. By comparing with the energy quality ratio of the traditional CG hydrogen production system (0.896), it can be concluded that the integrated system of CG and CLHG has a better energy matching relationship.

Exergoeconomic optimization of a forward feed multi-effect desalination system with and without energy recovery

The escalating freshwater demand is stimulating the researchers to optimize the performance of desalination technologies. The current study presents the exergoeconomic optimization of a forward feed multi-effect desalination (FF-MED) system under two configurations i.e., conventional MED and MED with energy recovery (MED-ER). A detailed numerical model concerning energy, exergy, and a component-based exergoeconomic analysis is employed to estimate the energy consumption, exergy destruction, and water production cost. Thereafter, the FF-MED-ER system is optimized using a Genetic Algorithm for four different objective functions i.e., maximum gain output ratio (GOR), and minimum specific energy consumption (SEC), exergy destruction, and water production cost. The constraint variables included steam temperature, brine salinity, and the last effect brine temperature. The analysis showed that the incorporation of an energy recovery section increased GOR by 17.9% and decreased SEC and water production cost by 14%, and 10.5%, respectively. Moreover, the optimization improved GOR by 9.26%, decreased SEC by 12.86%, exergy destruction by 12.59%, and the water production cost by 8.25% compared to the standard nonoptimal system.

Energy and exergy investigation of two modified single mixed refrigerant processes for natural gas liquefaction

Liquefaction processes consume a high amount of energy, and any attempt to achieve lower energy consumption and higher exergy efficiency would lead to a remarkable enhancement in the process efficiency. In the present study, two mini-scale modified single mixed refrigerant processes for natural gas liquefaction are simulated. The specific power consumption and total exergy destruction rate are optimized using the genetic algorithm tool. As a result of the energy optimization of the base case process, the specific energy consumption and the total exergy destruction rate are reduced by 19.4% and 25.4%, respectively. On the other hand, the maximum total exergy efficiency of 47.51 % is obtained through the exergy optimization of the process. The results related to the process configuration with a pump shows a higher exergy efficiency. Moreover, the minimum specific power consumption of 0.221 kWh/kg LNG is obtained through the optimization of the exergy destruction rate function.

Analysis of displacing natural gas boiler units in district heating systems by using multi-objective optimization and different taxing approaches

District heating systems are proven to be effective way of increasing energy efficiency, reducing environmental impact and achieving higher exergy efficiency. In research papers, district heating multi-objective optimization usually takes into account minimization of the total discounted cost and environmental impact, while exergetic objective function is rarely introduced. Most of the times, economic and ecological objective functions are studied as a single objective optimization problem through internalization of the cost related to carbon dioxide emissions tax. This paper presents novel approach since additional tax, related to exergy destruction, has been introduced. The influence of these two taxing systems on a single and multi-objective optimization results of district heating system has been carried out. Two approaches have been proposed. In the first one, multi-objective optimization has been used where objective functions were defined as economic and ecological or exergetic. In the second approach, single-objective optimization has been used where cost function also includes both carbon and exergy destruction tax. It has been shown that inclusion of carbon tax causes convergence of Pareto fronts after specific exergy destruction has been reached. On the other hand, if all technologies are available, increase of exergy tax doesn’t reduce carbon dioxide emissions. The most important outcome of this paper is analysis of the impact of exergy tax on natural gas consumption in heat-only boilers. Acquired results show that exergy, together with carbon tax, can effectively reduce natural gas consumption in heat-only boilers. If there are no back-pressure CHP technologies available, these taxing systems can completely push out its consumption. Finally, the analyses with carbon emissions allocation in CHP units has also been carried out. Acquired results have shown that with increase of carbon tax, exergy efficiency of the system could be increased.

Estimation of thermodynamic characteristics for comprehensive dairy food processing plant: An energetic and exergetic approach

India produces and consumes an array of traditional and modern dairy products. The value added milk derivatives such as cream, butter, ghee, yogurt, ice cream and other condensed forms of milks etc, forms 54% of the total dairy consumption with an annual energy consumption of 0.4 Mtoe in the year 2018. In view of 3.6% annual growth of this sector, the exergetic estimation of comprehensive dairy processing plant which primarily includes milk pasteurisation, cream pasteurisation and ghee manufacturing units are highly imperative for better utilization of energy resource. The present study determined first and second law performances, exergy destruction and exergy improvement potential in specific values for complete dairy processing plant consisting of aforementioned units; as 90%, 82.13%, 612.77 kJ/kg and 410.12 kJ/kg respectively. The highest contribution to specific exergy destruction was found at ghee production unit (410.10 kJ/kg) followed by cream pasteurisation unit (117.68 kJ/kg). Similarly specific exergy improvement potential was reported to be highest in ghee production unit (291.14 kJ/kg) followed by cream pasteurisation unit (74.31 kJ/kg). The total amount of electrical and thermal energy consumption was ascertained to be 322.25 kW and 171.64 kW respectively.

Thermodynamic analysis of theoretical dolomite formation from seawater and captured carbon dioxide

In this study, an integrated system is proposed to form dolomite chemically from seawater and carbon dioxide. The system contains three main chemical processes: formation of magnesium hydroxide and calcium hydroxide, the reaction of magnesium hydroxide and calcium hydroxide with carbon dioxide, and the formation of dolomite. Based on the fundamental thermodynamic laws, energy and exergy analyses, and performance assessment of the proposed system is carried out. Furthermore, the effects of varying temperatures of each process on various energy and exergy efficiencies are assessed through parametric studies. The results show that formation of dolomite is favorable at temperature ranges of 313–470 K based on the thermodynamic study. The exergy efficiency of dolomite formation is found to be about 23.8% and the results reveal that the dolomite formation process has the specific exergy destruction value of 29.6 kJ/mol among other sub-processes. The results suggest that the proposed system may provide enhanced options for low-temperature dolomite formation using seawater and captured carbon dioxide once the reaction kinetics is favored.

Exergy analysis of marine steam turbine labyrinth (gland) seals

The paper presents an exergy analysis of marine steam turbine labyrinth (gland) seals - an inevitable component of any marine steam turbine cylinder, in three different operating regimes. Throughout labyrinth seals, steam specific enthalpy can be considered as a constant because the results obtained by this assumption do not deviate significantly from the results of complex numerical models. Changes in labyrinth seals exergy efficiency and specific exergy destruction are reverse proportional. The analyzed labyrinth seals have high exergy efficiencies in each observed operating regime at the ambient temperature of 298 K (above 92%), what indicates seals proper operation. An increase in the ambient temperature resulted with a decrease in labyrinth seals exergy efficiency, but even at the highest observed ambient temperature of 318 K, seals exergy efficiency did not fall below 90.5% in each observed operating regime.

Comparative analyses on a batch-type heat pump dryer using low GWP refrigerants

The simulation of batch type open cycle heat pump dryer has been performed to study the system performances and food quality using promising low GWP refrigerants (R290, R600a, R32, R152a and R1234yf) as a substitute of R134a for carrot and banana drying. The experimentation with heat pump dryer test facility using R134a has been performed for model validation. Effects of drying time and material moisture content on the coefficient of performance, moisture extraction rate, specific moisture extraction rate, specific energy consumption, drying efficiency, exergy destruction, exergy efficiency and product water activity have been investigated. Results show that moisture extraction rate is maximum for R32, specific moisture extraction rate is maximum for R152a, specific energy consumption is minimum for R152a, drying efficiency is maximum for R152a (average value is 29.74%) and exergy destruction is minimum for R152a for the same air inlet velocity of 2m/s, respectively. The present study reveals that R152a may be a potential option for heat pump dryer by considering performances, environmental safety (low GWP) and personal safety (low flammability).

Energetic and exergetic performance simulation of open-type heat pump dryer with next-generation refrigerants

A batch-type open cycle heat pump dryer has been numerically simulated to study the energy and exergy performances using various low-GWP refrigerants (R290, R600, R600a, R32, R152a, R1234yf, R1234ze(E)) as a substitute of R134a. Effects of air inlet conditions, drying time, and material moisture content on the coefficient of performance, moisture extraction rate, specific moisture extraction rate, specific energy consumption, drying efficiency, exergy destruction, and exergy efficiency have been discussed. Results show that moisture extraction rate is maximum for R32, specific moisture extraction rate is maximum for R1234ze(E), specific energy consumption is minimum for R152a, drying efficiency is maximum for R152a (average value is 29.74%), and total exergy destruction is minimum for R1234ze(E) for the same total energy input and air inlet velocity of 2 kW and 2 m/s, respectively. Specific moisture extraction rate increases with air inlet velocity. The present study reveals that R152a may be a potential substitute of R134a for heat pump dryer by considering performances as well as environmental and personal safeties.