Application of Exergy for Research on Increasing the Usefulness of Solar Radiation by Dispersing It into Monochromatic Beams

Energy determines the ability of matter to work. However, in the given environment, the real usefulness to perform work is determined by exergy. This study covers not only solar, but also any monochromatic thermal radiation. The value of such radiation was determined by its exergy and the ratio of its exergy-to-energy. A novelty in this work is to demonstrate by means of exergy that the usefulness of thermal polychromatic radiation can be increased by its dispersion to monochromatic radiation. This effect is the greater, the lower the temperature of the radiation. Analogies of this effect to the exergetic effect of gas separation have been indicated. The effect of the increase in exergy in the process of radiation dispersion was interpreted by means of a cylinder-piston system that explains this effect with the influence of environmental radiation. The concept of quasi-monochromatic and cumulated radiation was introduced into dispersion considerations and the change in the energetic, entropic and environmental components of the exergy of radiation beams was analyzed. Considerations were illustrated with appropriate examples of calculations considering dispersion of high-temperature radiation, such as extraterrestrial solar radiation and dispersion of low-temperature radiation from water vapor.

基于天然气联合循环发电厂CO_(2)捕集与选择性废气再循环的Exergy分析

通过将选择性废气再循环(S-EGR)与联合循环的集成实现CO_(2)的捕集和循环,以获得更高的系统运行效率。基于实际联合循环电厂的运行数据,探究了选择性废气再循环S-EGR集成对实际联合循环和碳捕集系统的影响。结果表明:S-EGR集成后分别提升碳捕集和联合循环Exergy效率6.9%和1.3%;燃烧室是联合循环中Exergy损失最大的部件,占比44.8%,其次是蒸汽轮机、凝汽器和余热锅炉,造成Exergy损失的主要原因是温差;碳捕集单元与联合循环集成后,热效率和Exergy效率都在S-EGR循环比为10%时达到峰值后逐渐降低。

Energy,exergy,economic and environmental comprehensive analysis and multi-objective optimization of a sustainable zero liquid discharge integrated process for fixed-bed coal gasification wastewater

For a long time,China's regional water resource imbalance has restricted the development of coal chemical industry,and it is imperative to achieve zero liquid discharge(ZLD).Therefore,the game relationship between technical indicators,costs and emissions in ZLD process of fixed-bed coal gasification wastewater treatment process should be explored in detail.According to the accurate model,the simulation for ZLD of fixed-bed coal gasification wastewater treatment process is established,and this process is assessed from the perspective of thermodynamics,economy,and environment.The total energy consumption of ZLD process before optimization is 4.032×10^(8)W.The results of exergy analysis show exergy destruction of ZLD process is 94.55%.For economic and environmental results,the total annual cost is 1.892×10^(7)USD·a^(-1)and the total environmental impact is 4.782×10^(-8).The total energy consumption of the optimal six-step ZLD process based on multi-objective optimization is 4.028×10^(8)W.The CO_(2)content in the treated wastewater is 0.1%.This study will have an important role in promoting the establishment of the ZLD process for coal chemistry industry.

Exergy Analysis of Organic Rankine Cycles with Zeotropic Working Fluids

Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines.Instead of wasting the exhaust stream of an energy conversion system into the environment,its residual energy content can be usefully recovered,for example in Organic Rankine Cycles(ORC).This technology has been largely consolidated in stationary power plants but not yet for mobile applications,such as road transport,due to the limitations in the layout and to the constraints on the size and weight of the ORC system.An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated.The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation.The waste thermal power has been considered as heat input for the ORC plant simulation.A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance.The exergy analysis of the ORC was performed comparing different working fluids:R601,R1233zd(E)and two zeotropic blends of the two organic pure fluids.The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.

Correlation Analysis of Wind Turbine Temperature Rise and Exergy Efficiency Based on Field-Path Coupling

To solve the problems of large losses and low productivity of permanent magnet synchronous generators used in wind power systems,the field-circuit coupling method is used to accurately solve the electromagnetic field and temperature field of the generator.The loss distribution of the motor is accurately obtained by considering the influence of external circuit characteristics on its internal physical field.By mapping the losses to the corresponding part of the three-dimensional finite element model of the motor,the temperature field is solved,and the global temperature distribution of the generator,considering the influence of end windings,is obtained.By changing the air gap length,permanent magnet thickness,and winding conductivity,the relationship between the loss,temperature rise,and exergy efficiency can be obtained.By optimizing the air gap length,permanent magnet thickness,and winding conductivity,the best configuration and material properties can improve the efficiency of the motor by up to 4%.

高温气冷堆氦气透平直接循环的Exergy分析

针对100 MW电功率的氦气透平直接循环的设计,对循环各个部件分别进行热力学第一和第二定律分析。给出了各个部件的输入和产出Exergy公式,计算了Exergy损失分布,并与按照传统分析方法获得的分析结果进行了比较。结果表明:一半以上的Exergy损失发生在堆芯部分,而由预冷器、压气机和间冷器组成的压缩系统所占Exergy损失比重比按照第一定律计算的能量损失份额小得多;循环Exergy损失主要原因是能量形式的转换和不可逆换热。系统Exergy效率略高于热效率。

生物质气成分含量变化对燃烧室exergy效率的影响

用富含CO,N2,CO2,H2的燃料模拟生物质气在燃气轮机燃烧室中燃烧,从exergy量不守恒的关系上考查可燃气体成分变化、惰性气体成分变化情况下燃烧室的exergy损失,研究成分对燃烧室exergy效率的影响。结果表明:降低H2在可燃成分中的比例能够提高燃烧室exergy效率,提高N2在惰性气体中的占比,exergy损失持续增大,但exergy效率存在极大值点。

钢铁工业铁前工序的Exergy分析

铁前工序是钢铁工业能源消耗的主要环节,占总能耗的80%。为此,根据铁前工序的生产数据,通过建立物料平衡,建立了Exergy计算模型,获得了各工序的Exergy平衡关系、热力学完善度、Exergy效率、Exergy损失系数。同时结合理论分析,论述了Exergy分析法对铁前工序(焦化、烧结、高炉炼铁)节能分析的优势,并且提出各工序的节能途径。

可降低数据中心热管理能耗的嵌入机柜式冷却方法及其EXERGY分析

随着社会信息化和对高性能计算的需求,全球数据中心的规模和集成度均以较快的速度增长,由此使得数据中心热耗散功率密度不断攀升,冷却成本大幅增加,传统热管理方案很难适应计算机能耗继续增长的需求。文中提出一种旨在降低数据中心能耗的可对机柜内部直接进行冷却的嵌入式热管理方案,并引入exergy分析方法对分别于机柜内的顶端或各计算单元设置制冷机蒸发器两种热管理方案的性能进行了评估。结果显示,两种方案在可优化exergy部分分别较之传统冷却方案高出0.04%和1.05%,表明其在热经济性方面具有优势,可望发展为今后数据中心有前景的热管理方案。

生命周期exergy分析在能源动力工程中的应用

生命周期评价是一种有效的用于诊断和评价清洁生产的工具,其理念已经逐步引入我国,并在诸多领域得到不同程度的应用。为了能够分析具有不同能量形式的产物的能源系统,引入exergy的概念,将exergy作为比较的统一标准,这就是生命周期exergy方法。文章通过实例介绍生命周期评价及生命周期exergy分析在能源动力工程中的应用。

基于Exergy天津市生态经济系统可持续发展度量

城市生态系统是复杂的高度人工化的复合生态系统,其正常的运转动力来自于外界能量的输入,Exergy作为热力学指标是指系统从给定状态到与其周围介质达到热力学平衡所需做的最大功,Exergy概念被生态学家借鉴应用于生态系统的研究,使它有了生物学的含义。在分析能量、能值和Exergy概念的内涵及总结Exergy的研究进展的基础上,通过构建城市尺度的能质账户分析模型,对天津市生态经济系统的能质效率进行了分析。将生态热力学的理论应用区域经济地理学定量研究中,结果表明,天津市总体的能质(exergy)输入从2003年的682.5PJ增加到2010年的1254.2 PJ,系统的总能质输出从1 42.0 PJ增加到299.8 PJ,能源输入总量快速增加,但总体的能质效率增加不大,提高资源和能源的利用效率方面还有较大的提升空间,这与采用其他方法的计算结果相一致,在该指标易于理解,可以为政府决策者在制定经济发展战略时提供有效理论支持。

Enhanced exergy cost optimization of operating conditions in FCCU main fractionator

Exergy indicates the maximal energy that can do work effectively. Different from optimization of product quality or calculation of generic energy conservation in most previous studies, the application of exergy analysis and exergy cost optimization in petrochemical industry is of great economic and environmental significance. Based on the main fractionator in Jiujiang Petrochemical Complex No. 2 FCCU, an enhanced exergy cost optimization under different operating conditions by adjusting set points of temperature and valves opening degree for flow control is studied in this paper in order to reduce exergy cost and improve the quality of energy. A steadystate optimization algorithm to enhance exergy availability and an objective function comprehensively considering exergy loss are proposed. On the basis of ensuring the quality of petroleum products, the economic benefits can be improved by optimizing the controllable variables due to the fact that exergy cost is decreased.

Effects of working parameters on gasoline engine exergy balance

To improve the energy utilization efficiency of internal combustion （IC） engine, exergy analysis was conducted on a passenger car gasoline engine. According to the thermodynamic theory of IC engine, in-cylinder exergy balance model was built. The working processes of gasoline engine were simulated by using the GT-power. In this way, the required parameters were calculated and then gasoline engine exergy balance was obtained by programming on computer. On this basis, the influences of various parameters on exergy balance were analyzed. Results show that, the proportions of various forms of exergy in gasoline engine from high to low are irreversible loss, effective work, exhaust gas exergy and heat transfer exergy. Effective exergy proportion fluctuates with cylinder volumetric efficiency at full load, while it always increases with break mean effective pressure （BMEP） at part load. Exhaust gas exergy proportion is more sensitive to speed, and it increases with speed increasing except at the highest speed. The lower proportion of heat transfer exergy appears at high speed and high load. Irreversible loss is mainly influenced by load. At part load, higher BMEP results in lower proportion of irreversible loss; at full load, the proportion of irreversible loss changes little except at the highest speed.

Energy and exergy recovery from exhaust hot water using organic Rankine cycle and a retrofitted configuration

Exhaust hot water （EHW） is widely used for various industrial processes. However, the excess heat carried by EHW is typically ignored and discharged into the environment, resulting in heat loss and heat pollution. An organic Rankine cycle （ORC） is an attractive technology to recycle heat from low-temperature energy carriers. Herein, ORC was used to recycle the heat carried by EHW. To investigate the energy and exergy recovery effects of EHW, a mathematical model was developed and a parametric study was conducted. The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa, Rl13 and R123 as the working fluids. The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system. Under given EHW conditions, an optimum evaporation temperature exists corresponding to the highest exergy efficiency. To further use the low-temperature EHW, a configuration retrofitted to the ORC by combining with flash evaporation （FE） was conducted. For an EHW at 120 ~C and 0.2 MPa, the maximum exergy efficiency of the FE-ORC system is 45.91% at a flash pressure of 0.088 MPa. The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.

Exergy Analysis and Retrofitting of Natural Gas-based Acetylene Process

This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program Aspen Plus. The results indicate that the most important destruction of exergy is found to occur in the reactor and water quenching scrubber, amounting to 8.23% and 10.39%, respectively, of the entire system. Based on the results of thermodynamic and exergy analysis, the acetylene reactor has been retrofitted. The improvement ratios of molar 02 to CH4 and molar CO to CN4 are 0.65 and 0.20, respectively. An improvement of the acetylene production system is proposed. Adopting the improvement operation conditions and using oil to realize the reaction heat recovery, the feedstock of natural gas is reduced by 9.88% and the exergy loss in the retrofitting process is decreased by 19.71% compared to the original process.

Exergy and ecological modelling of lake environment

The thermodynamic theories and ecological theories can be integrated effectively by exergy(biogeochemical energy of the system) to study the environmental problems of the lakes and reservoirs. In this paper, the applications of exergy in the ecological modelling of lake environment were reviewed. Results showed that exergy can be used as a goal function to estimate the parameters of the ecological model for lakes and reservoirs and to develop the structural dynamic models accounting for the changes in lake ecosystems, and as an ecological indicators for the development and evolution of lake ecosystems.

Synthesis of indirect work exchange networks considering both isothermal and adiabatic process together with exergy analysis

In this paper, an efficient methodology for synthesizing the indirect work exchange networks(WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In contrast with superstructure method, the transshipment model is easier to obtain the minimum utility consumption taken as the objective function and more convenient for us to attain the optimal network configuration for further minimizing the number of units. Different from division of temperature intervals in heat exchange networks,different pressure intervals are gained according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and the characteristics of no pressure constraints for stream matches. The presented approach for WEN synthesis is a linear programming model applied to the isothermal process, but for indirect work exchange networks with adiabatic process, a nonlinear programming model needs establishing. Additionally, temperatures should be regarded as decision variables limited to the range between inlet and outlet temperatures in each sub-network. The constructed transshipment model can be solved first to get the minimum utility consumption and further to determine the minimum number of units by merging the adjacent pressure intervals on the basis of the proposed merging methods, which is proved to be effective through exergy analysis at the level of units structures. Finally, two cases are calculated to confirm it is dramatically feasible and effective that the optimal WEN configuration can be gained by the proposed method.

Exergy Analysis and Thermal Optimization of a Double-Turbine Regeneration System in a Ultra-Supercritical Double-Reheat Unit

Improving the primary steam parameters is one of the most direct ways to improve the cycle efficiency of a powergeneration system. In the present study, the typical problem connected to the excessively high superheat degree ofextraction steam in an ultra-supercritical (USC) double-reheat unit is considered. Using a 1000 MW power plantas an example, two systems (case 1 and case 2) are proposed, both working in combination with a regenerativesteam turbine. The thermal performances of these two systems are compared with that of the original systemthrough a heat balance method and an exergy balance strategy. The results reveal that the two coupled systemscan significantly reduce the superheat degree of extraction steam, turbine heat rate, and coal consumption of theunit and improve the energy utilization efficiency. These results will provide useful theoretical guidance to futureinvestigators wishing to address the general problem relating to energy conservation and modelling of the coupledextraction steam regenerative system of USC double-reheat units.

Energy Analysis and Exergy Utilization in the Residential Sector of Cameroon

In this paper, we present an analysis of energy and exergy utilization in the residential sector of Cameroon by considering the sectoral energy and exergy flows for the years of 2001-2010. Exergy analysis of Cameroon residential sector utilisation indicates a less efficient picture than that obtained by the energy analysis. Cooking stands out as the most inefficient end use in the Cameroon’s residential sector. In 2010, the energy and exergy efficiency are determined and were respectively 58.74% and 22.63%. Energy and exergy flows diagrams for the overall efficiencies of Cameroon residential sector are illustrated and a comparison with the residential sector of other countries is also done. To carry out this study, a survey of 250 households was conducted and the sharing of the end uses of energy was done and data were gathered.

Exergy Analysis of a Double-Effect Solar Absorption Refrigeration System in Ngaoundere

Solar energy is replacing more and more traditional sources of energy because of the fact that it’s also fighting about global warming. This study is based on exergy analysis of a double-effect series flow absorption refrigeration system powered by solar energy in Ngaoundere. The simulation is done on the basis of a half hourly analysis for the first time, from 6.30 AM to 6.30 PM, using water-lithium bromide as working pair. The main parameters for the performance of an absorption cycle, which are the COP and the ECOP, have been analyzed and the results show that this two parameters increase while increasing the temperature of the main generator. The exergy loss of each component of the system and the total exergy loss of the system have been analyzed and their effectiveness calculated, using the first and second law of thermodynamics. The highest exergy loss occurs in the main generator GI and in the absorber, making these components more important in an absorption cycle. This analysis is based on a mathematical model using FORTRAN?language. The results obtained may be useful for the optimization of solar absorption refrigeration systems.