Exergy analysis of C2 recovery plants refrigeration cycles

This paper provides an exergy analysis of the multistage refrigeration cycle used for Ethane and heavier hydrocarbons (C₂⁺) recovery plant. The behavior of an industrial refrigeration cycle with propane refrigerant has been investigated by the exergy method. The equations of exergy destruction and exergetic efficiency for the main cycle components such as evaporators, condensers, compressors, and expansion valves are developed. The relations for the total exergy destruction in the cycle and the cycle exergetic efficiency are obtained. An ethane recovery unit with its refrigeration cycle has been simulated to prepare the exergy analysis. Using a typical actual work input value; the exergetic efficiency of the refrigeration cycle is determined to be 43.45% indicating a great potential for improvements. The simulation results reveal that the exergetic efficiencies of the heat exchanger and expansion sections get the lowest rank among the other compartments of refrigeration cycle. Refrigeration calculations have been carried out through the analysis of temperature-entropy (T-S) and pressure-enthalpy (P-H) diagrams where coefficient of performance (COP) was obtained as 1.87. The novelty of this article includes the effect and sensitivity analysis of pressure drop and temperature on the exergy efficiency and coefficient of performance of the cycle.     

Factorial design of experiment (DOE) for parametric exergetic investigation of a steam methane reforming process for hydrogen production

Hydrogen is expected to play a significant role in future energy systems. The efficient production of hydrogen at a minimum cost and in an environmentally acceptable manner is crucial for the development of a hydrogen-including economy. The exergy analysis is a powerful tool to quantify sustainable development potential. An important aspect of sustainable development is minimizing irreversibility. The purpose of this study is to perform the exergy analysis of a steam methane reforming (SMR) process for hydrogen production. As a first step, an exergy analysis of an existing process is shown to be an efficient tool to critically examine the process energy use and to test for possible savings in primary energy consumption. The results of this investigation prove that the exergetic efficiency of the SMR process is 65.47%, and the majority of destroyed exergy is localized in the reformer with a 65.81% contribution to the whole process destroyed exergy. Next, an exergetic parametric study of the SMR has been carried out with a factorial design of experiment (DOE) method. The influence of the reformer operating temperature and pressure and of the steam to carbon ratio (S/C) on the process exergetic efficiency has been studied. A second-order polynomial mathematical model has been obtained through correlating the exergetic efficiencies with the reformer operating parameters. The results of this study show that the rational choice of these parameters can improve the process exergetic performance.     

Performance Assessment of a Potato Crisp Frying Process

Frying is a common and popular cooking method, which has been widely used in food manufacturing, though it is a very energy-intensive process. Energy analysis has been commonly used to assess the performance of fryers. In this study, we attempted to exergetically assess the performance of a potato crisp frying system, which consists of three main components, a combustor, a heat exchanger, and a fryer. In the analysis, we utilized the actual operational data obtained from the literature. We determined exergy destruction in each system component and the whole system. We calculated universal and functional exergy efficiency values for the system components and compared them with each other. We also undertook a parametric study to investigate how the overall cycle performance was affected by changing the reference environment temperature and some operating conditions. We illustrated the exergy results through the Grassmann (exergy loss and flow) diagram. We calculated the universal exergetic efficiency values of 58, 82, and 77% for the combustor, heat exchanger, and fryer, respectively, with a universal exergetic efficiency value of 4% for the whole frying system. We found that the fryer had the highest functional exergetic efficiency value of 74%, followed by the heat exchanger with 47% and the combustor with 0.08%.     

Evaluation of the effects of fuel and combustion-related processes on exergetic efficiency

The fuel used in combustion applications has significant influence on irreversibility generation and hence the exergetic efficiency of the system. This work discusses a method of estimating the availability destructions and exergetic efficiencies of combustion for different classes of fuels viz. hydrogen, hydrocarbons, alcohols and biodiesel surrogates. A ranking of these fuels is presented based on their exergetic efficiencies during isobaric and isochoric combustion. It is observed that availability destruction is greater for heavier hydrocarbon fuels and oxygenated fuels with higher oxygen fraction. Though unsaturated hydrocarbon fuels are associated with lower availability destruction, they result in poor exergetic efficiency as a significant fraction of the fuel availability is lost in the products. Hydrogen and acetylene are identified as the fuels with maximum and minimum exergetic efficiencies respectively. Optimum exergetic efficiency is obtained for reactant mixtures on the leaner side of fuel-air stoichiometry. Availability destruction increases with exhaust gas recirculation (EGR) and decreases with oxygen enrichment of the supplied air. However, oxygen enrichment entails significant chemical availability losses and lowers exergetic efficiency. Preheating the reactants is found to be effective in mitigating availability destruction.     

Exergetic and engineering analyses of sulphuric acid decomposition process

The purpose of this study was to evaluate the exergetic efficiency of the sulphuric acid decomposition process, which occurs in hydrogen producing thermochemical cycles and chemical energy storage systems. It is a process in which sulphuric acid is decomposed to a gaseous mixture consisting of water, sulphur dioxide and oxygen, using high temperature thermal energy, oxygen as a vector and mostly adiabatic equipment. Parts of the basic process with excessive exergy losses have been identified and a modified flow sheet has been developed and analyzed from thermodynamic and engineering points of view. Thermodynamic analysis of the modified flow sheet indicates that the overall exergetic efficiency of the decomposition process is 79.86%, which represents an improvement of 14.17% over the basic process. Engineering analysis of a plant producing 10⁶ mol of SO₂ per hour shows that the typical levelized cost of chemical exergy production was $ 2.25/GJ exergy from the basic process and $ 1.79/GJ exergy from the modified process.     

Performance analysis of activated carbon + HFC-134a adsorption coolers

The purpose of this paper is to present the results of performance analysis of a heat driven continuous vapor adsorption refrigerator with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC-134a) as the refrigerant. A set of four adsorption cells takes on the role of the mechanical compressor in the conventional vapor compression refrigeration (VCR) system. Three specimens of activated charcoal under various packing densities were investigated. A parametric analysis was carried out with several evaporating, condensing/adsorbing and desorbing temperatures which are typical operating conditions catered to by HFC-134a. A new integrated relative performance evaluation scheme is proposed. It uses the maximum cycle uptake difference as a factor against which the coefficient of performance (COP) and exergetic efficiency are evaluated. It is shown that there is an optimal set of operating conditions wherein the exergetic efficiency is the maximum. A major part of the thermal energy input is for sensible heating of the compressor body.     

Industrial-scale fixed-bed coal gasification: modeling,simulation and thermodynamic analysis

We have developed a process model to simulate the behavior of an industrial-scale pressurized Lurgi fixed-bed coal gasifier using Aspen Plus and General Algebraic Modeling System （GAMS）. Reaction characteristics in the fixed-bed gasifier comprising four sequential reaction zones-drying, pyrolysis, combustion and gasification are respectively modeled. A non-linear programming （NLP） model is developed for the pyrolysis zone to estimate the products composition which includes char, coal gases and distillable liquids. A four-stage model with restricted equilibrium temperature is used to study the thermodynamic equilibrium characteristics and calculate the composi-tion of syngas in the combustion and gasification zones. The thermodynamic analysis shows that the exergetic effi-ciency of the fixed-bed gasifier is mainly determined by the oxygen/coal ratio. The exergetic efficiency of the proc-ess will reach an optimum value of 78.3%when the oxygen/coal and steam/coal mass ratios are 0.14 and 0.80, re-spectively.     

Enhancing the exergetic performance of a pilot-scale convective dryer by exhaust air recirculation

Abstract

In this study, an air recirculating pilot-scale convective dryer operating at various exhaust air recycle fractions was exergetically investigated in detail. Two drying air temperatures (55–70?°C), two air volume flow rates (360–450?m³/h), and six exhaust air recycle fractions (0–100%) were considered for drying of poplar wood chips. The effects of drying variables were studied on the exergetic efficiencies of drying system and drying chamber. The total exergy of air exhausting from drying chamber was also fractionated into thermophysical and wet exergies for further evaluating the effect of recycle fraction. The universal exergetic efficiency of drying chamber ranged from 41.84% to 98.07%, while the average overall functional exergetic efficiency of drying system varied from 1.32% to 4.01%. Exhaust air recirculation profoundly improved the overall functional exergetic efficiency of drying system as a decision-making parameter up to over two times. Although the recycle fraction of 100% showed the highest improvement in the overall functional exergetic efficiency of drying system, the drying time drastically increased at this condition as expected. Overall, a compromise should be made between drying time and exergetic improvement in order to select a proper recycle fraction for recovering exergy from outflow air.     

Recycle effect on the relative exergy array

Since the eco-efficiencies of all industrial processes/plants have become more and more important, engineers need to find a way to integrate process design, process control and measurements of eco-efficiency. The thermodynamic concept of Exergy can be used to analyze a process in terms of its efficiency. The Relative Exergy Array (REA) that measures both the relative exergetic efficiency and the controllability of a process has been proposed by Montelongo-Luna et al. (2011). The REA can be used for quick comparison between several process/control structure candidates. It is very common that the industrial unit/process includes some recycle loops. The recycle effect on REA is investigated in this paper through two process case studies. Simulation results show that the REA without consideration of the recycle loop may mislead the selection of control configuration. Recycle loop should be considered for selection of control configuration.     

影响增强聚丙烯雾化测试结果的因素

雾化重量法是衡量汽车内饰材料挥发物中的有害成分对人体健康的影响程度的测试.因此,为了合理控制挥发性物质的产生,降低车内环境污染,对用于汽车内饰的材料进行雾化测试是十分必要的.通过控制变量研究样品状态、加工工艺、测试温度、测试时间、平衡时间对雾化重量法进行测试,分别测试了内饰材料增强聚丙烯系列的长玻璃纤维增强材料和短玻璃...     

EXERGY ANALYSIS OF A DELAYED COKER UNIT

ＥＸＥＲＧＹＡＮＡＬＹＳＩＳＯＦＡＤＥＬＡＹＥＤＣＯＫＥＲＵＮＩＴＹａｎｇＸｉａｎｇｐｉｎｇ（ＵｎｉｖｅｒｓｉｔｙｏｆＰｅｔｒｏｌｅｕｍ，Ｄｏｎｇｙｉｎｇ，Ｓｈａｎｄｏｎｇ２５７０６２，Ｃｈｉｎａ）Ａｂｓｔｒａｃｔ：Ｏｎｔｅｓｔｉｎｇｔｈｅｕｓｅｄｅ...     

Exergetic criteria in process optimisation and process synthesis: Opportunities and limitations

The exergy concept is a well established way to express the quality of any kind of process stream, be it energy or matter. Thus detailed exergy analysis of chemical processes can in general be performed and several such applications have been reported in the literature. However, systematic methods for exergetic process optimisation only exist for the comparably less complex area of power systems. For chemical processes a solid optimisation approach based on exergy analysis has yet to be derived. This paper presents a thorough investigation of opportunities and limitations of the exergy concept in both process optimisation and process synthesis. The two tasks are treated separately since their specific requirements and solution strategies are different. As a result of the presented evaluation, concepts for the efficient use of exergetic criteria are proposed.     

室温磁制冷机性能评测及能效分析

为建立磁制冷机能效统一评价指标,弥补采用温跨和制冷量作为磁制冷系统性能评价标准的不足,在现有评价方法的基础上提出了新的室温磁制冷样机能效指标-(火用)效率。为了验证新评价指标的可行性,分别对2011年维多利亚大学公布的样机数据和2012年丹麦理工大学公布的样机数据进行分析计算,将以温跨-热源温度和温跨-制冷量形式给出的测试数据统一转换为温跨-冷量(火用)的形式,以实现对不同样机的能效进行客观评价;同时搭建测试平台对四川大学旋转式室温磁制冷样机在25、27及30℃工况下进行冷量(火用)、(火用)效率指标测试。实验结果表明,该室温磁制冷样机在25℃工况下,磁制冷机转速6 r·min^-1时,制冷量为240 W,最大冷量(火用)为3.26 W。在剔除电机损失、机械损失、磁滞损失及涡流损失等因素的影响后,最大(火用)效率为0.039。     

Das Zerstäuben als Grundverfahren

Atomization as a unit process. Liquid atomization can be classified by three successive steps: disintegration; multiphase flow in the spray; and impact of droplets on the substrate. The most important process parameter is the size distribution of the droplets. By means of this parameter the liquid disintegration process can be related to the different transport phenomena in the spray or to the impacting process. The size distribution of the droplets is not a static parameter but an evolving result of local changes depending on sifting effects, on strand formation, on coalescence, on evaporation, on drying or chemical reaction processes. It is thus essential, for further analysis, to start from local instead of integral size distributions. This will be possible because of the efficiency of new particle sizing instruments with high spatial or temporal resolution. This opens the possibility for differential instead of integral balance. From this one can derive, for the future, higher precision of apparatus design and improved optimization procedures for process design. Finally, appropriate measuring techniques are discussed with regard to their special applicability to liquid atomization analysis.     

Cost optimization of a combined power and water desalination plant with exergetic,environment and reliability consideration

The present study deals with the multi-objective optimization for designing a combined gas turbine and multi stage flash desalination plant. In optimization approach, the exergetic, economic and environmental aspects have been considered, simultaneously. In order to achieve the optimal design, Multi-objective genetic algorithm (MOGA) is applied as a suitable optimization technique. The thermoenvironomic objective function is obtained by integrating the environmental impacts and thermoeconomic objective. By applying the optimization approach, this objective function is minimized, whereas system exergy efficiency is maximized. Moreover, equipment reliability using the state-space and the continuous Markov method is incorporated in optimization results to improve the products' cost values. The optimization results show that the cost of products and environmental cost impact are reduced by 13.4% and 53.4%, respectively, whereas a 14.8% increase happens in total exergy efficiency. Therefore, improvement in all objectives has been achieved using the optimization process, although the power and water productions have not changed much. Additionally, the sensitivity analysis shows the relationship between the fuel cost, pollution damage cost and the objective functions.     

雾化器结构参数对循环流化床锅炉SNCR脱硝性能影响研究

还原剂雾化质量对循环流化床锅炉旋风分离器SNCR脱硝效率具有重要影响,为研究空气雾化喷嘴结构参数对雾化质量及脱硝效率的影响,采用数值模拟的方法对喷嘴的4个结构参数即撞击件长度、出口直径、混合室长度和气液入口交角,进行单因素分析和正交数值试验,结果表明影响旋风分离器烟气脱硝效率的主要因素是喷嘴出口直径,次要因素是撞击件长...     

Exergetic optimisation of a production process of Fischer–Tropsch fuels from biomass

An exergy analysis of Biomass Integrated Gasification-Fischer–Tropsch process is presented. The process combines an air-blown, atmospheric gasifier, using sawdust as feedstock, with a Fischer–Tropsch reactor and a steam-Rankine cycle for electricity generation from the Fischer–Tropsch tail gas. Results show that the rational (exergetic) efficiency is 36.4%, consisting of 34.5% efficiency to Fischer–Tropsch diesel and wax, and 1.9% efficiency to electricity. The largest exergy losses take place in biomass gasification and in generation of electricity from the Fischer–Tropsch tail gas. Recommendations are given for process improvements, which increase the rational efficiency to 46.2%.     

Exergetic,economic and environmental analyses and multi-objective optimization of an SOFC-gas turbine hybrid cycle coupled with an MSF desalination system

The present study presents thermodynamic, economic and environmental (emissions cost) modeling of a solid oxide fuel cell–gas turbine (SOFC–GT) hybrid system integrated with a multi stage flash (MSF) desalination unit. A heuristic optimization method, namely, multi-objective genetic algorithm (MOGA) is employed afterwards to obtain the optimal design parameters of the plant. The exergetic efficiency and the total cost rate of the system are considered as the objective functions of the optimization procedure; where, the total cost rate of the system (including the cost rate of environmental impact) is minimized while the exergetic efficiency is maximized. Applying the optimization method, a set of optimal solutions is achieved and the final selected optimal design leads to an exergetic efficiency of 46.7%, and a total cost of 3.76 million USD/year. The payback time of the selected design is also determined to be about 9 years. Although the determined value for the payback period seems to be relatively high for the proposed plant (due to the high capital cost of the SOFC system), this integrated technology is expected to be promising in the near future as the capital costs of SOFCs are decreasing and their operational lifetimes are increasing.     

Energetic and exergetic analysis of a triple-effect distiller driven by solar energy

This paper relates to the energetic and exergetic analysis of single-, double- and triple-effect distiller driven by solar energy. Energetic analysis makes it possible to define an applicable zone of operation according to the following criteria: water rejection limit to 50%, maximum salinity limit to 5.5%, and minimum energy consumption. This analysis also makes it possible to quantify energies: energy necessary for the vapour condensation and the power consumption per unit mass of pure water. Exergetic analysis makes it possible to show that the most significant exergy losses are condenser losses and water alimentation losses and that the condenser losses decrease with the number of effects. The exergetic efficiencies have also been found. They are located between 19 and 26% for a triple-effect system, between 17 and 20% for a double-effect system, and less than 4% for the single-effect system. Consequently, it seems interesting to implement a double- or triple-effect system.