Main Sources Of Exergy Destruction Research Articles

Thermodynamic analysis of a novel solar water heating system during low sun radiation in Iran

This paper reports a plenary thermodynamic model of a novel solar system for water heating in buildings. Energy and exergy analyses are used to characterize the exergy destruction rate in any component and calculate system overall efficiency. The system consists of a solar evaporator, a heat exchanger to produce hot water, and an auxiliary pump. A computer simulation program using EES software is developed to model the solar water heating system. The system provides hot water during the hours of low sun radiation. Thermodynamic analysis involves the designation of effects of heat exchanger pinch point and ambient temperatures on the energetic and exergetic performance of the solar water heating system. The performance parameters computed are exergy destruction, and energetic and exergetic efficiencies. The result showed that the main source of exergy destruction is the solar evaporator. In the solar evaporator, 92.85% of the input exergy was destroyed. The other main source of exergy destruction is the heat exchanger, at 4.15%. The overall energetic and exergetic efficiencies of the solar water heating system were approximately 60.17% and 3.002% respectively.

Multi-objective optimization and exergoeconomic analysis of waste heat recovery from Tehran's waste-to-energy plant integrated with an ORC unit

Recovery of waste heat in large industrial plants is nowadays an important topic of thermal optimization. In the present study, energy, exergy, and exergoeconomic analysis of an integrated system, Tehran's waste-to-energy power plant coupled with an organic Rankine cycle (ORC), is analyzed. Parametric study of essential parameters (moisture content, pinch point temperature differences of the HROG, steam generator's superheat temperature difference, and steam turbine inlet pressure) is performed thermodynamically. The best system performance achieved using R123 as the working fluid of ORC. After implementation of the waste-heat-recovery system into the WtE plant, with R123 the energy and exergy efficiencies increase from 17.27% to 19.51% and 14.49%–16.36%, respectively. Exergy analysis reveals that the gasifier and steam generator are the main source of exergy destruction in the overall system. Additionally, the results of single-objective optimization based on maximum exergy efficiency and minimum total product unit cost were calculated. Furthermore, multi-objective optimization based on genetic algorithm using MATLAB software is implemented to find the optimum point with respect to exergy efficiency and total product unit cost as the objective functions. The exergy efficiency and total product unit cost at the optimum point, considering multi-objective optimization, are 19.61% and 24.65 $/GJ, respectively.

Energetic, Exergetic, and Economic Analysis of MED-TVC Water Desalination Plant with and without Preheating

Desalination is the sole proven technique that can provide the necessary fresh water in arid and semi-arid countries in sufficient quantities and meet the modern needs of a growing world population. Multi effect desalination with thermal vapour compression (MED-TVC) is one of most common applications of thermal desalination technologies. The present paper presents a comprehensive thermodynamic model of a 24 million litres per day thermal desalination plant, using specialised software packages. The proposed model was validated against a real data set for a large-scale desalination plant, and showed good agreement. The performance of the MED-TVC unit was investigated using different loads, entrained vapour, seawater temperature, salinity and number of effects in two configurations. The first configuration was the MED-TVC unit without preheating system, and the second integrated the MED-TVC unit with a preheating system. The study confirmed that the thermo-compressor and its effects are the main sources of exergy destruction in these desalination plants, at about 40% and 35% respectively. The desalination plant performance with preheating mode performs well due to high feed water temperature leading to the production of more distillate water. The seawater salinity was proportional to the fuel exergy and minimum separation work. High seawater salinity results in high exergy efficiency, which is not the case with membrane technology. The plant performance of the proposed system was enhanced by using a large number of effects due to greater utilisation of energy input and higher generation level. From an economic perspective, both indicators show that using a preheating system is more economically attractive.

Energy, Exergy and Economic Feasibility Analyses of a 60 MW Conventional Steam Power Plant Integrated with Parabolic Trough Solar Collectors Using Nanofluids

The present study focuses on the detailed technical and cost-effective feasibility analyses of a 60 MWe steam power plant integrated with parabolic trough solar collectors. Aluminum oxide (Al2O3) nanoparticles are mixed with thermal oil to be used as a heat transfer fluid in the collector loops. The electric power is generated using steam Rankine cycle. For this purpose, the steam turbine of 60 MWe production capability of Teknecik power plant located in Northern Cyprus has been analyzed and an integrated solar steam turbine system is presented which generates electric power. Detailed energy and exergy assessment of the solar thermal plant is carried out. The important parameters are examined including overall energy and exergy efficiencies, exergy destruction rate and system performance by varying direct normal irradiation (DNI), mass flow rate of the collector, ambient and inlet temperatures. Furthermore, thermal power available from the solar field at various solar multiples is assessed, and levelized energy cost has been calculated. Results show that turbines are the main source of exergy destruction (63855 kW) followed by feedwater heaters and boiler. Overall energetic and exergetic efficiencies of the system are observed to be 22.64 and 23.83%, respectively. The integration of PTC system with conventional plant results in a reduction in fuel consumption which significantly brings down the CO2 emissions by almost 33%.

Reducing the exergy destruction in the cryogenic heat exchangers of hydrogen liquefaction processes

A present key barrier for implementing large-scale hydrogen liquefaction plants is their high power consumption. The cryogenic heat exchangers are responsible for a significant part of the exergy destruction in these plants and we evaluate in this work strategies to increase their efficiency. A detailed model of a plate-fin heat exchanger is presented that incorporates the geometry of the heat exchanger, nonequilibrium ortho-para conversion and correlations to account for the pressure drop and heat transfer coefficients due to possible boiling/condensation of the refrigerant at the lowest temperatures. Based on available experimental data, a correlation for the ortho-para conversion kinetics is developed, which reproduces available experimental data with an average deviation of 2.2%. In a plate-fin heat exchanger that is used to cool the hydrogen from 47.8 K to 29.3 K with hydrogen as refrigerant, we find that the two main sources of exergy destruction are thermal gradients and ortho-para hydrogen conversion, being responsible for 69% and 29% of the exergy destruction respectively. A route to reduce the exergy destruction from the ortho-para hydrogen conversion is to use a more efficient catalyst, where we find that a doubling of the catalytic activity in comparison to ferric-oxide, as demonstrated by nickel oxide-silica catalyst, reduces the exergy destruction by 9%. A possible route to reduce the exergy destruction from thermal gradients is to employ an evaporating mixture of helium and neon at the cold-side of the heat exchanger, which reduces the exergy destruction by 7%. We find that a combination of hydrogen and helium-neon as refrigerants at high and low temperatures respectively, enables a reduction of the exergy destruction by 35%. A combination of both improved catalyst and the use of hydrogen and helium-neon as refrigerants gives the possibility to reduce the exergy destruction in the cryogenic heat exchangers by 43%. The limited efficiency of the ortho-para catalyst represents a barrier for further improvement of the efficiency.

Exergy Analysis and Optimization of Multi-effect Distillation with Thermal Vapor Compression System of Bandar Abbas Thermal Power Plant Using Genetic Algorithm

Multi-effect distillation desalination system with thermal vapor compression is one of the systems of producing fresh water based on distillation desalination. This type of desalination system is one of the most appropriate and economic types of desalination systems for low to high capacities of seawater and brackish water in which evaporation and distillation have occurred in a vacuum and in temperature below 70 °C. This research provides a mathematical model in the steady-state conditions for multi-effect distillation desalination system with thermal vapor compression in Bandar Abbas thermal power plant in south of Iran. The genetic algorithm is used for maximizing the produced fresh water and minimizing total exergy destruction rate. Exergy analysis shows that the thermo-compressor and effects are the main sources of exergy destruction in the system (more than 80%). The actual operating data in summer and winter were used for the exergy destruction study. The results show that the exergy destruction in winter is more than summer. Parametric analysis for studying the effects of key parameters shows that increasing the top brine temperature leads to increase in the total exergy destruction of the system. The optimization of the system with two-target genetic algorithm causes distillate production to increase by 16.62%, and the total exergy destruction rate decreases by 3.58%.

Energy and exergy analysis of air-film cooled gas turbine cycle: Effect of radiative heat transfer on blade coolant requirement

Gas turbine blade cooling is critical to continuous reliable operation of gas turbines. Literature suggests that air-film cooling is one of the most widely used blade cooling techniques. This paper compares previously developed blade cooling models which are relevant to film cooling technique and it also proposes a gas turbine blade cooling model for the estimation of blade coolant mass fraction, considering radiative heat transfer from hot combustion gases to gas turbine blade surface. The proposed model gives an enhanced coolant mass fraction (≈5–6% over a wide range of TIT) as compared to previously developed models while analyzing gas turbine cycle. Gas turbine cycle performance has been evaluated based on two blade cooling models to compare blade coolant flow mass fraction, gas turbine plant specific work which are function of both compressor-pressure ratio and turbine inlet temperature. Both the blade cooling models closely follow each other with radiative cooling model. For the proposed blade cooling model, gas turbine specific work is around 417.39 kJ/kg (rpc = 22 and TIT = 1650 K) and gas turbine thermal cycle efficiency has been found to be 41.25% at (rpc = 22 and TIT = 1550 K). Exergy analysis of gas turbine cycle has also been done which shows combustor to be main source of exergy destruction (≈29%).

Thermodynamic studies and parametric effects on exergetic performance of a steam power plant

ABSTRACTA comprehensive thermodynamic analysis is conducted for an existing 82 MW steam power plant. A detailed assessment on energy loss and exergy destruction for individual components of plants (including boiler sub-parts) is reported. A code is built in EES to evaluate the energy loss, energy efficiency, physical and chemical exergies, exergy efficiency and exergy destruction for each part of plant by considering the real values’ range of operating parameters. Analysis pointed out that the main sources of exergy destruction are boilers followed by the turbines, deaerators and then condensers. In boiler, combustor contributes about 50% in total exergy destruction. The maximum energy loss is reported in boilers followed by condensers, in piping, due to friction and in turbines. The exergy efficiency procured about 42% for boilers, 84% for turbines, 38% for condenser, and 60% for deaerators, respectively. The effects of crucial working parameters on plant performance are analysed.

Thermodynamic evaluation of a rice husk fired integrated steam and hot air generation unit for rice parboiling

This paper presents a simplified energy improvement system using agricultural waste for local rice processing. An integrated steam and hot air production unit using rice husk energy was evaluated thermodynamically. Besides characteristics of steam and hot air, temperature effectiveness of the fluid streams, energy and exergy flow within system components were also studied. Effect of input operating parameters on steam production and drying air temperature together with their correlation have been shown. Overall system energy and exergy efficiencies were found to be 47.81% and 10.93%, respectively. Although, the combustor showed the highest temperature, energy and exergy efficiencies, it was the main source of exergy destruction contributing more than 60%.

Exergy and energy analysis of a regenerative organic Rankine cycle based on flat plate solar collectors

In current study, a low temperature organic Rankine cycle (ORC) based on flat plate solar collectors with storage tank is considered. Due to low cost applications, water at ambient pressure is used in both the tank and collectors. Also, the cooling is done by water in ambient temperature. Energy and exergy analysis is used to evaluate the performance of the system under various conditions to find the main sources of exergy destruction and the potential to improve them. Some parameters including exergetic efficiency, thermal efficiency, exergy destruction rate, fuel depletion ratio and irreversibility ratio are investigated. Exergy efficiency and exergy destruction ratio are calculated for the overall system according to the second law of thermodynamics based on daily efficiency. Exergy analysis of each sub-system leads to the choice of the optimum physical parameters for minimum local exergy destruction ratios. Four different working fluids are considered including R245fa, R134a, pentane and toluene to evaluate the system. Results show that the solar collector, thermal storage tank and the vapor generator are the main sources of exergy destruction respectively. Also a parametric study shows that there is an optimum daily exergy efficiency based on turbine inlet temperature. Under the same load, pentane has the best performance followed by R245fa, toluene and R134a. The corresponding daily exergy efficiencies are 24.08%, 22.53%, 22.09% and 21.76%.

Selection of a Waste Heat Recovery System for a Marine Diesel Engine Based on Exergy Analysis

Highly increased fuel prices and the need for greenhouse emissions reduction from diesel engines used in marine engines in compliance with International Maritime Organization (IMO) on the strict regulations and guidelines for the Energy Efficiency Design Index (EEDI) make diesel engine exhaust gas heat recovery technologies attractive. The recovery and utilization of waste heat not only conserves fuel, but also reduces the amount of waste heat and greenhouse gases dumped to the environment .The present paper deals with the use of exergy as an efficient tool to measure the quantity and quality of energy extracted from waste heat exhaust gases in a marine diesel engine. This analysis is utilized to identify the sources of losses in useful energy within the components of the system for three different configurations of waste heat recovery system considered. The second law efficiency and the exergy destroyed of the components are investigated to show the performance of the system in order to select the most efficient waste heat recovery system. The effects of ambient temperature are also investigated in order to see how the system performance changes with the change of ambient temperature. The results of the analysis show that in all of the three different cases the boiler is the main source of exergy destruction and the site of dominant irreversibility in the whole system it accounts alone for (31-52%) of losses in the system followed by steam turbine and gas turbine each accounting for 13.5-27.5% and 5.5-15% respectively. Case 1 waste heat recovery system has the highest exergetic efficiency and case 3 has the least exergetic efficiency.

Thermodynamic comparison and efficiency enhancement mechanism of coal to alternative fuel systems

Coal to alternative fuels is an important path to enforce energy security and to provide clean energy. In this paper, we use exergy analysis and energy utilization diagram (EUD) methods to disclose the internal reasons for performance differences in typical coal to alternative fuel processes. ASPEN plus software is used to simulate the coal-based energy systems, and the simulation results are verified with engineering data. Results show that coal to substitute natural gas (SNG) process has a higher exergy efficiency of 56.56%, while the exergy efficiency of traditional coal to methanol process is 48.65%. It is indicated that three key factors impact the performance enhancement of coal to alternative fuel process: (1) whether the fuel is distillated, (2) the synthesis temperature and the amount of heat release from reactions, and (3) whether the chemical purge gases from synthesis and distillation units are recovered.Distillation unit is not recommended and synthesis at high temperature and with large heat release is preferable for coal to alternative fuel systems. Gasification is identified as the main source of exergy destruction, and thereby how to decrease its destruction is the key direction of plant efficiency improvement in the future. Also, decreasing the power consumption in air separation unit by seeking for advanced technologies, i.e. membrane, or using another kind of oxidant is another direction to improve plant performance.

Exergy Performance Analysis and Optimization of a Desiccant Wheel System

This paper focused on the exergy analysis and optimization of a dehumidification desiccant wheel (DW) system. A two-dimensional unsteady state numerical model was developed for simulation of the heat and mass transfer phenomena in a representative channel of a DW matrix. The DW mathematical model was validated using a series of experimental data and parametric studies were conducted to investigate the effects of operating parameters on the DW system performance. Exergy parameters were also studied and adopted to predict the total inlet–outlet exergy and exergy destruction, as well as exergy effectivenesses. Furthermore, a new exergy effectiveness parameter was introduced based on the concept of dehumidification. Parametric studies were carried out to characterize the optimal performance of the overall system regarding exergy destruction and exergy dehumidification effectivenesses. The results demonstrate that electrical power consumption, regeneration heat, and heat and mass transfer between air and desiccant are the main sources of exergy destruction. The optimization calculation shows that at the lowest process air velocity (up = 0.2 m/s), lowest DW rotational speed (NDW = 4 Rph), highest regeneration air temperature (Ta,r,in = 140 °C), and moderate regeneration air velocity (ur = 1.7 m/s), minimum exergy destruction occurs. The optimal value of the parameters proves that, when exergy destruction effectiveness is selected as the objective function, the only regeneration air velocity is decision variable of optimization and operational limits impose on the other parameters.

Exergy-based thermodynamic analysis of solar driven Organic Rankine Cycle

In this paper thermodynamic modeling of organic Rankine cycle (ORC) driven by parabolic trough solar collectors is presented. Eight working fluids for the ORC were examined. The effect of turbine inlet temperature on main energetic and exergetic performance parameters were studied. The influences of turbine inlet temperature on turbine size parameter, turbine outlet volume flow rate and expansion ratio were also investigated. Important exergetic parameters including irreversibility ratio and total exergy destruction rate were also included in the analysis and evaluated. The study reveals that increasing the turbine inlet temperature results in increasing the net electric efficiency, net power output, exergy efficiency and expansion ratio while the total exergy destruction rate and turbine size parameter are reduced. From the considered working fluids, o-xylene gives the best energetic and exergetic performance. The results of the study also show that the main source of exergy destruction occurs in the solar collector where 74.9% of the total exergy loss is destructed. Next to collectors, 18.2% of the total destructed exergy occurs in the condenser

Exergetic study of catalytic steam reforming of bio-ethanol over Pd–Rh/CeO2 with hydrogen purification in a membrane reactor

An exergy analysis of the ethanol steam reforming process using a Pd–Rh catalyst supported on ceria in a Pd–Ag membrane reactor has been performed based on experimental data. Both chemical and physical exergy for chemical species together with thermodynamic loss calculations have been considered to evaluate the exergy efficiency of the process. The system has been studied under different operational conditions in terms of temperature (873–923 K), pressure (4–12 bar), and feed flow rate using a water–ethanol mixture of 50–50% volume (S/C = 1.6). A significant exergy efficiency dependency on the fuel flow rate and pressure has been encountered when considering the heat loss from the reactor. The best results regarding the exergetic and thermal efficiency have been obtained at high flow rates and 8–12 bar, which has been attributed to the higher hydrogen permeation through the membrane. The chemical reactions involved in the reforming process and the heat losses are the main sources of exergy destruction.

Exergy analysis of parabolic trough solar collectors integrated with combined steam and organic Rankine cycles

In this paper, detailed exergy analysis of selected thermal power systems driven by parabolic trough solar collectors (PTSCs) is presented. The power is produced using either a steam Rankine cycle (SRC) or a combined cycle, in which the SRC is the topping cycle and an organic Rankine cycle (ORC) is the bottoming cycle. Seven refrigerants for the ORC were examined: R134a, R152a, R290, R407c, R600, R600a, and ammonia. Key exergetic parameters were examined: exergetic efficiency, exergy destruction rate, fuel depletion ratio, irreversibility ratio, and improvement potential. For all the cases considered it was revealed that as the solar irradiation increases, the exergetic efficiency increases. Among the combined cycles examined, the R134a combined cycle demonstrates the best exergetic performance with a maximum exergetic efficiency of 26% followed by the R152a combined cycle with an exergetic efficiency of 25%. Alternatively, the R600a combined cycle has the lowest exergetic efficiency, 20–21%. This study reveals that the main source of exergy destruction is the solar collector where more than 50% of inlet exergy is destructed, or in other words more than 70% of the total destructed exergy. In addition, more than 13% of the inlet exergy is destructed in the evaporator which is equivalent to around 19% of the destructed exergy. Finally, this study reveals that there is an exergetic improvement potential of 75% in the systems considered.

Simulation and exergetic evaluation of CO2 capture in a solid-oxide fuel-cell combined-cycle power plant

The incorporation of fuel cells into power plants can enhance the operational efficiency and facilitate the separation and capture of emissions. In this paper a fuel-cell unit, consisting of solid-oxide fuel-cell stacks, a pre-reformer, and an afterburner is incorporated into a combined-cycle power plant with CO2 capture. The thermodynamic performance of the plant is examined using an exergetic analysis and it is compared with a conventional combined-cycle power plant (reference plant) without CO2 capture, as well as with other plants with CO2 capture.The inefficiencies of the chemical reactions taking place in the fuel-cell unit are found to be the main source of exergy destruction among the plant components. However, the additional power generated in the fuel-cell stacks and the afterburner enhances the overall efficiency and compensates for the energy needed for the capture and compression of the carbon dioxide. When compared with the reference plant and with alternative capture technologies, the solid-oxide fuel-cell plant with CO2 capture operates more efficiently and appears to be a thermodynamically promising approach for carbon capture.

Investigating the effect of several thermodynamic parameters on exergy destruction in components of a tri-generation cycle

Multiple energy generating cycles such as tri-generation cycles, which produce heat and cold in addition to power through burning of a primary fuel, have increasingly been used in recent decades. On the other hand, advanced exergy analysis of thermodynamic systems by splitting exergy destruction into endogenous and exogenous parts identifies internal irreversibilities of each of the components and the effect of these irreversibilities on the performance of other components. Therefore, main sources of exergy destruction in cycles can be highlighted and useful recommendations in order to improve the performance of thermodynamic cycles can be presented. In the present work, a tri-generation cycle with 100 MW power production, 70 MW heat and 9 MW cooling capacity is considered. For this tri-generation cycle, effects of various thermodynamic parameters on the amount of endogenous and exogenous exergy destructions, exergy loss and the amount of fuel consumption, are investigated. The results indicate that, increasing compressor pressure ratio, pre-heater outlet temperature and excess air leads to better combustion and lower exergy loss and fuel consumption. Increasing the mass flow rate of steam generator, while keeping the cycle outlet temperature constant and considering cooling capacity variable, lead to increase the first- and second-law efficiencies of the cycle.

Exergy and energy analysis of an AC steel electric arc furnace under actual conditions

The energy and exergy analyses of an existing steel Electric Arc Furnace (EAF) are performed to estimate the potential for increasing the furnace efficiency. To obtain realistic results, the effect of air infiltration into the furnace was taken into account. The results of the analyses revealed that the energy and exergy efficiencies of the furnace are low and should be increased. The main sources of energy waste are stack gases followed by heat transfer to the cooling water, while the main sources of exergy destruction are combustion and heat transfer. Hot stack gases contain 18.3% and 12.2% of the total input energy and exergy, respectively. Increasing the air infiltration reduces the energy and exergy efficiencies of the EAF. By using the energy of flue gas to preheat the sponge iron, the electrical energy consumption of the furnace can be reduced by 89 GJ, dictating a 21.4% reduction in electrical energy consumption and a 13.6% increase in steel production.

Exergy analysis of gas turbine – solid oxide fuel cell-based combined cycle power plant

Fuel cell technology is one of the promising systems for cleaner and competitive alternate power generation systems. When the high temperature fuel cells like solid oxide fuel cell and molten carbon fuel cell are integrated with the gas turbines, the total thermal efficiency of the combined cycle can be obtained greater than 60%. In the present work, thermodynamic analysis of SOFC-GT combined system (3MW) has been carried out for the fuel methane to evaluate the energy efficiency, exergy efficiency and exergy destruction of each component and compared with other fuels like coal gas and ethanol. The effect of compression ratio, turbine inlet temperature and ambient temperature of air on the performance of the system has been analysed. The outcome of the system modelling reveals that SOFC and combustion chamber are the main sources of exergy destruction. At the optimum compression ratio 9 and at the turbine inlet temperature 1,250 K, the total thermal efficiency and the exergy efficiency are found to be 63.3% and 60.85% respectively.