Results Of Exergy Analysis Research Articles

Optimization of Operating Parameters of a Solar Ejector Refrigeration System on Exergy Analysis

Exergy analysis is used as a tool to analyze the performance of a refrigeration system. In this paper, it is based on the following conditions: the solar radiation is set as 750 W/m2, the refrigerating capacity is 10 kW, R141b is fixed as the refrigerant in the refrigeration cycle and ambient temperature to be the reference temperature is 31°C. The exergy analysis results of the solar ejector refrigeration system shows that irreversible loss comes from all components and depends on the operating temperatures. The exergy efficiency increases with the condensation temperature’s decrease or the evaporation temperature’s increase. In the specific evaporation temperature and condensation temperature, the optimum generating temperature can be get when the system exergy efficiency is at its maximum. For the operating conditions in this paper, the optimum generating temperature is 95°C.

Analysis of Exergy and Energy of Gasifier Systems for Coal-to-Fuel

The purpose of this study is to investigate the performance features of coal-to-fuel systems based on different gasification technologies. The target products are the Fischer–Tropsch synthetic crude and synthetic natural gas. Two types of entrained-flow gasifierbased coal-to-fuel systems are simulated and their performance features are discussed. One is a single-stage water quench cooling entrained-flow gasifier, and another one is a two-stage syngas cooling entrained-flow gasifier. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) for the systems are both investigated. The results of exergy analysis provide insights about the potential targets for technology improvement. The features of different gasifier-based coal-to-fuel systems are discussed. The results provide information about the research and development priorities in future.

J112 熱・エネルギーシステムのエクセルギー評価の重要性(一般講演(1))

By tight supply of power after the Great East Japan Earthquake, the use of renewable energy and unused energy has attracted attention. In this situation, opinion such as "a large amount of heat is thrown away to sea water in thermal power plants. You should use more of this low-temperature waste heat" is seen here and there. Cause of such misunderstandings would be a lack of knowledge about exergy. In this paper, the results of exergy analysis and that of enthalpy analysis are compared to show the effectiveness of exergy analysis.

Life cycle assessment of CO 2 sequestration in magnesium silicate rock – A comparative study

This paper addresses the energy and environmental implications of sequestrating CO 2 from a coal power plant using magnesium silicate rock. An accounting type life cycle assessment (LCA) of the mineralization method under development at Åbo Akademi University (ÅAU), Finland, is presented and the results are compared with the process developed at the National Energy Technology Laboratory (NETL), formerly Albany Research Council (ARC) in the US. The ÅAU process is a multi-staged route where CO 2 is sequestered via a process that first produces magnesium hydroxide, Mg(OH) 2 from Mg silicate. The Mg(OH) 2 produced is later reacted with CO 2 in a high temperature gas/solid pressurized fluidized bed (FB) reactor, forming pure, stable and environmentally benign MgCO 3 product. This study addresses the following important issues; (a) the material and energy requirements of sequestering 1 ton of CO 2 (t-CO 2) in mineral silicate, (b) the overall environmental burdens associated with CO 2 sequestration using serpentinite mineral, (c) the priorities and opportunities for reduction of energy requirements and environmental impacts associated with mineralizing CO 2, and (d) comparison of LCA results of the ÅAU mineralization process route with that of the mineralization process developed by NETL. Exergy calculations show that with heat recovery mineralizing 1 t-CO 2 using the ÅAU process requires 3.6 GJ/t-CO 2 while that of the NETL needs 3.4 GJ/t-CO 2. Applying results of exergy analysis in the life cycle inventory (LCI) models of the ÅAU and the NETL processes leads to 517 kg CO 2e and 683 kg CO 2e of greenhouse gas emissions (in CO 2 equivalents) respectively, for every ton of CO 2 mineralized in serpentinite.

Analysis of exergy and energy of sugar production process in sugar plant

Abstract In this paper, the energy and exergy analysis results of sugar production processes were presented by using operational system data from the Kayseri sugar plant, Turkey. All sugar production processes were thought as a steady state open thermodynamics system and employed the energy and exergy analyses, based on the first and second laws of thermodynamics. The best values of the energy and exergy efficiencies were obtained as 95·1% for the juice production process and 74·3% for the juice concentration process respectively. Moreover, the location of the energy degradation and the irreversibility were determined during the whole sugar production processes. Consequently, it has been pointed out that the energy and exergy efficiencies can be improved if the rates of the energy degradation and irreversibility in the sugar production processes are reduced.

Energy and Exergy Analysis of Gasifier-Based Coal-to-Fuel Systems

National energy security concerns related to liquid transportation fuels have revived interests in alternative liquid fuel sources. Coal-to-fuel technologies feature high efficiency energy conversion and environmental advantages. While a number of factors are driving coal-to-fuel projects forward, there are several barriers to wide commercialization of these technologies such as financial, construction, operation, and technical risks. The purpose of this study is to investigate the performance features of coal-to-fuel systems based on different gasification technologies. The target products are the Fischer–Tropsch synthetic crude and synthetic natural gas. Two types of entrained-flow gasifier-based coal-to-fuel systems are simulated and their performance features are discussed. One is a single-stage water quench cooling entrained-flow gasifier, and another one is a two-stage syngas cooling entrained-flow gasifier. The conservation of energy (first law of thermodynamics) and the quality of energy (second law of thermodynamics) for the systems are both investigated. The results of exergy analysis provide insights about the potential targets for technology improvement. The features of different gasifier-based coal-to-fuel systems are discussed. The results provide information about the research and development priorities in future.

Exergy analysis of ice storage air-conditioning system with heat pipe during charging period

The ice storage air-conditioning system with heat pipe was presented, and analytical model relating to the exergy loss amount and loss rate was developed in each component of the ice storage air-conditioning system. Exergy analysis results of the ice storage air-conditioning system with heat pipe were compared with those of the ice storage air-conditioning system with ice-on-coil. The energy saving and exergy loss reduction possibilities were also analyzed and discussed. The results indicated that the exergy efficiency of the ice storage air-conditioning system with heat pipe is 9.55% higher than that of the ice storage air-conditioning system with ice-on-coil. The exergy loss in the condenser can be reduced by reducing thermal resistance and the temperature difference of heat transfer or utilizing exergy of heat rejected by the condenser. The exergy loss in the expansion valve is reduced through increasing supercooling temperature of the refrigerant before entering into the expansion valve or decreasing pressure difference between the condensing pressure and the evaporating pressure.

Analysis on exergy consumption patterns for space heating in Slovenian buildings

Problem of high energy use for heating in Slovenian buildings is analyzed with exergy and energy analysis. Results of both are compared and discussed. Three cases of exterior building walls are located in three climatic zones in winter conditions. Results of energy analyses show that the highest heating energy demand appears in the case with less thermal insulation, especially in colder climate. If the comparison is made only on the energy supply and exergy supply, the results of exergy analysis are the same as those of energy analysis. The main difference appears, if the whole chain of supply and demand is taken into consideration. Exergy calculations enable us to analyze how much exergy is consumed in which part, from boiler to building envelope. They also reveal how much energy is supplied for the purpose of heating. Results show that insulation has much bigger effect than effect of boiler efficiency. However, the most effective solution is to improve building envelope together with boiler efficiency. Better thermal insulation also makes an important contribution to the improvement of thermal comfort conditions. It causes higher surface temperatures resulting in a larger warm radiant exergy emission rate and consequently better thermal comfort.

Hydrogen enrichment effects on the second law analysis of a lean burn natural gas engine

This paper presents a computational work aimed at investigating the effects of hydrogen addition on the exergy (or availability) balance in a lean burn natural gas spark ignition (SI) engine. A thermodynamic engine cycle simulation was extended to perform the exergy analysis. A zero dimensional, two-zone computational model of the engine operation was used for the closed part of the cycle. The results of the model were compared with experimental data to demonstrate the validation of the model. Exergetic terms, such as exergy transfer with heat, exergy transfer with work, irreversibilities, fuel chemical exergy, and total exergy, were computed based on principles of the second law. The exergetic (the second law) efficiency was also calculated. The results of exergy analysis show that increasing hydrogen content and lean burn have considerably affected the exergy transfers, irreversibilities and second law efficiency. With increasing hydrogen content, the irreversibility produced during combustion decreases, and the second-law efficiency sharply increases at near the lean limit.

Exergy analysis of synthetic natural gas production method from biomass

The paper presents the results of exergy analysis for a biomass-to-synthetic natural gas (SNG) conversion process. The presented study is based on wood gasification, which is analysed for different gasification conditions like temperature and/or pressure. The analysed temperature was varied in the range from 650 to 800 °C and the pressure range was from 1 to 15 bar. The main process units of biomass-to-SNG conversion technology are gasifier, gas cleaning, synthesis gas compression, CH4 synthesis and final SNG conditioning. The results showed that the largest exergy losses take place in the biomass gasifier, CH4 synthesis part and CO2 capture unit. The overall exergetic efficiency of the biomass-to-SNG process was estimated in the range of about 69.5–71.8%.

Effect of Internal Heat Recovery in Ammonia-Water Absorption Cooling Cycles: Exergy and Structural Analysis

First and second law analysis have been conducted for three low temperature driven ammonia-water absorption cooling cycles with increasing internal heat recovery. Based on the results of exergy analysis the structural analysis has been achieved. The obtained Coefficients of Structural Bonds (CSB) consider how the irreversibility of the whole cycle is affected by a change in the irreversibility related to an efficiency improvement of a single component. Trends for the different configurations are similar, while quantitative differences among the main heat exchangers are considerable. The highest values of the CSB are found for the refrigerant heat exchanger. Also the evaporator, the condenser, the generator and the absorber show values higher than unity. The lowest CSB’s are obtained in the solution heat exchanger. In general, CSB’s decrease with increasing efficiency. That means that for very efficient heat exchangers, a further improvement looks less attractive. The dephlegmator is an exception as it shows a singularity of the CSB value due to its complex interactions with the other components. Once the CSB’s are obtained for the main components, they can be used in the structural method of the thermoeconomic optimisation. This method enables us to find the optimum design of a component in a straightforward calculation.

Comparison of low temperature mixed refrigerant cycles for separation systems

Numerous mixed refrigerant cycles (MRCs) were developed in the past several decades in different applications. In this paper, two sets of low temperature MRCs are developed and simulated for a typical olefin plant utilizing a mixture of methane, ethane, propane and nitrogen as cycle working fluid to replace the pure ethylene refrigeration cycle that is used in conjunction with propylene refrigeration cycle in conventional plants. The key parameters of the cycles including mixture compositions and operating pressure levels are optimized to meet the objective of minimum shaftwork in compressor. The results show that different cycle configuration has different optimal mixture composition and low and high operating pressures. The results of exergy analysis reveal that the main location of the exergy loss in the cycles is the heat exchanger system. Also, the Carnot factor versus heat flow diagram is provided to identify the distribution of inefficiencies in the heat exchangers for each cycle. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system using the optimal working fluid mixture composition, optimal high and low operating pressures and optimal arrangement of the cycle components. Copyright © 2008 John Wiley & Sons, Ltd.

Mathematical analysis of spark ignition engine operation via the combination of the first and second laws of thermodynamics

This study aims at the theoretical exergetic evaluation of spark ignition engine operation. For this purpose, a two-zone quasi-dimensional cycle model was installed, not considering the complex calculation of fluid motions. The cycle simulation consists of compression, combustion and expansion processes. The combustion phase is simulated as a turbulent flame propagation process. Intake and exhaust processes are also computed by a simple approximation method. The results of the model were compared with experimental data to demonstrate the validation of the model. Principles of the second law are applied to the model to perform the exergy (or availability) analysis. In the exergy analysis, the effects of various operational parameters, i.e. fuel–air equivalence ratio, engine speed and spark timing on exergetic terms have been investigated. The results of exergy analysis show that variations of operational parameters examined have considerably affected the exergy transfers, irreversibilities and efficiencies. For instance, an increase in equivalence ratio causes an increase in irreversibilities, while it decreases the first and also the second law efficiencies. The irreversibilities have minimum values for the specified engine speed and optimum spark timing, while the first and second law efficiencies reach a maximum at the same engine speed and optimum spark timing.

The 'entropy-cycle' method for thermodynamic analysis of energy intensive systems

In the design and operation of energy intensive systems, the possibility of improving the system's efficiency is very important to explore. The main way of improving efficiency is through thermodynamic analysis and optimisation. One of the more representative thermodynamic characteristics of system are exergy efficiency and exergy losses. As it is known the exergy losses can be calculate on the base of Gui-Stodola equation (method of entropy generation) as well as in result of exergy balances. In this paper is made the comparative thermodynamic analysis of Air Refrigerator (AR) based on 'entropy-cycle' method and on exergetic methods. It is shown that both approaches are thermodynamically objective and for this reason give the same results. On the other hand, the exergetic approach is more simple in application abut the 'entropy-cycle' method gives better possibility for graphical illustration of the exergy losses in any process in AR cycle. Illustrative example and numerical results of exergy analysis of AR are given.

Simulation, exergy analysis and application of diabatic distillation to a tertiary amyl methyl ether production unit of a crude oil refinery

This paper presents the results of a detailed exergy analysis of a tertiary amyl methyl ether (TAME) unit of a crude oil refinery and the application of diabatic distillation to the depentanizer tower of the unit. Diabatic distillation is a separation process in which heat is not only supplied to the reboiler and extracted from the condenser [as in a conventional (adiabatic) distillation column], but is also transferred inside the column. The process enables operation to approach equilibrium conditions, thus reducing exergy losses and increasing exergy effectiveness. In a TAME unit of a refinery, isoamylenes are converted to TAME. Before transforming the isoamylenes in the reactors, it is necessary to recover them from a catalytic gasoline stream by a depentanization process. The exergy losses of this depentanization process represent about 70% of the total exergy losses of the unit. The results of the exergy analysis of the TAME unit are presented and a detailed exergy analysis of the conventional adiabatic depentanizer column is conducted for comparison purposes. Then, the application of diabatic distillation to the system is evaluated by using cooling water circulating in series from tray to tray in the rectification section and by making the steam emanating from the reboiler circulate in series from tray to tray in the stripping section. The results in terms of the reduction of exergy losses, heating and cooling media flow rates, and cost effectiveness of the diabatic option for the depentanizer section of the plant are compared to the original adiabatic system, and the effect of the diabatization on the overall exergy performance parameters of the depentanizer section and on the whole TAME unit, are presented in this paper.

Simulation and thermodynamic analysis of conventional and oxygen permeable CPO reactors

A one-dimensional steady-state heterogeneous model has been used to simulate the conventional CPO reactor. With the mechanism of O 2 permeable membrane, the model has been developed to simulate O 2 membrane reactor. The output temperature and the mole flow rates of different species in the tube side and the shell side can be calculated. They are the basis for the exergy analysis of the conventional CPO reactor with air, the conventional CPO reactor with pure O 2, and the O 2 permeable membrane CPO reactor. The simulation and exergy analysis results indicate that when the inlet conditions are the same, for a given methane conversion, the exergy efficiencies η 2 and η 1 of conventional CPO reactor with pure oxygen is lowest among the three reactors, because of the large amount of accumulative exergy required for obtaining pure oxygen. The exergy efficiencies η 1 and η 2 of membrane reactor are comparable with conventional CPO reactor with air and much higher than conventional CPO reactor with pure oxygen. As the membrane reactors can carry out simultaneous separation and reaction, in the mean time, removal of nitrogen from the product stream can be accomplished; the membrane reactor has advantages compared to other types of reactors. The operation of the membrane CPO reactor is more favourable when the inlet temperature is increased and the operation pressure is decreased from a thermodynamic point of view.

焼成および非焼成ペレットを使用した還元鉄製造プロセスのエクセルギー評価

In order to make a clear evaluation of overall energy requirement for the production system of directly reduced iron through pellet from iron ore powders, exergy analysis was applied to the two systems. The first one consists of pelletizing, firing and reduction processes (Fired pellets method) and the second one includes pellets curing process instead of firing process (Cement bonded pellets method).Being compared with enthalpy balance, exergy analysis has two advantages in that the exergy expresses the quality of energy and evaluates different kinds of energy like chemical, thermal, pressure, mixing energies and so on by a unified measure.As a result of exergy analysis, fired pellets lose less exergy than cement bonded pellets in the reduction process in a shaft furnace. As the overall system, however, exergy requirement in the cement bonded pellets method is about 50% of that in the fired pellets method. This marked difference is caused by the large exergy loss in the firing process. Furthermore, exergy loss in the production of cement bonded pellets will be decreased by decreasing the amount of cement added as binder.