Exergy analysis on eco-industrial systems Exergy analysis on eco-industrial systems

Exergy analysis on eco-industrial systems

  • 期刊名字:中国科学B辑(英文版)
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  • 论文作者:YANG Li,HU Shanying,CHEN Dingj
  • 作者单位:Center for Industrial Ecology
  • 更新时间:2020-12-06
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Science in China: Series B Chemistry 2006 Vol.49 No.3 281- -288281DOI: 10.1007/s11426-006-0281-0Exergy analysis on eco-industrial systemsYANG Li, HU Shanying, CHEN Dingjiang & ZHANG DaweiCenter for Industrial Ecology, Tsinghua University, Beijing 100084, ChinaCorrespondence should be addressed to Hu Shanying (email: hxr-dce@mail.tsinghua.edu.cn)Received July 8, 2004; accepted August 22, 2005Abstract Exergy analysis of eco-industrial systems reflects the thermodynamic characteristics ofresource utilization by studying complicated material flow patterns to an industrial system. Differentindicators based on exergy analysis are presented, such as system exergy depletion index, cyclingratio of material exergy, etc. which can be used to evaluate the efficiency of resource utilization andthe environmental potential effect. The interrelations of these exergy indicators and their interpretationon industrial ecology are further discussed. Finally, the result of case study suggests effectiveness ofexergy analysis methods and practicability of these exergy estimate indices.Keywords: eco-industrial system, exergy, analysis.1 Introductionmodes and their effects on eco-industrial systems withEcological industry is to realize the harmony de-industrial ecology and thermodynamics theories, thenanalyzing essential characteristics in resource utiliza-velopment between economy and environment bytion of eco-industrial systems is an important issue.planning industrial systems according to material cy-The second law of thermodynamics indicates thatcle in the natural ecological system. It got grown rap-1o process is possible which consists solely in theidly both in theories and practices since the 190sl-.21.transfer of heat from one temperature level to a higherMany countries including China have applied indus-one. It reveals the essence of an industrial process intrial ecology to industrial practices. It is deeply recog-which raw materials (fosil fuels, metal ore, etc.) withnized that developing ecological industry and advanc-“lower entropy” are consumed and wastes or pollut-ing on a new industrialization mode is an importantants with“high entropy”are discharged. Exergy as anway to realize sustainable development in China.analysis and evaluation function of eco-industrial sys-An industrial symbiosis net could be formed by ex-tems is proposed based on the second law, because itchanging by-products and wastes, cascading utiliza-can be used to denote material and energy both quan-tion of energy and waste water, and sharing infra-titatively and qualitatively. So it is reasonable to bestructure among system units. Different processesused to judge and compare whether resources arecorrelate each other with material flows, energy flows,made full use or not in different production processes.money flows and information flows. An eco-industrialExergy analysis is taken to analyze the utilization de-system has more complicated resource utilizationgree of mass and energy in eco-industrial systems inmodels and more closed interrelationship in compari-this paper. Exergy analysis and evaluation indicatorsson with a common industrial system. Studying dif- are proposed中国煤化工leristics of re-ferent kinds of complex energy and material utilizationsource utiliCNMHGIimpact ofwww. scichina.comwww.springerlink.com282Science in China: Series B Chemistryeco-industrial systems are studied according to ther-trial processes in utilization of renewable resources,modynamic principles.and compared the utilization efficiency between re-newable and nonrenewable resources with exergy2 Review of research on exergy analysis for eco-analysis°. Rosen discussed the interrelationship be-industrial systemstween exergy and process environmental impact, andthe potential effect of industrial processes to environ-Exergy is the maximum amount of useful work thatment can be calculated'.can be extracted from a physical system by exchang-On the basis of these researches, it is possible tong matter and energy with large reservoirs throughdrive studies on eco-industrial systems from generalcomplete reversible process (heat transfer process,description to quantitative expression by combiningmass transfer process, chemical reaction etc.) in a ref-exergy analysis and ecological models' 10. Evaluationerence state. It is the maximum amount of work poten-for eco-industrial systems can be realized with exergytial of matter or energy on the basis of a given refer-analysis. Rivero proposed exergoecologic improve-ence statel'. As a thermodynamic parameter, it isment potential index. The larger the index is, theproposed in 1956 by Rant.severer environmental pollution is. Rosen improvedExergy analysis for an ecosystem at first appearedeco-industrial systems with exergy analysis in an at-in a research on the natural ecosystem. Jorgenson et al.tempt to raise utilization efficiency of raw materialsused exergy as an objective function to analyze theand energyt. Wang et al. made further study on theevolution of the natural ecosystem and presented ex-traditional exergy analysist'! Combining with theergy storage hypothesis*. Marques et al. applied theenvironmental factor, they considered two aspects ofstructural dynamic model of the natural ecosystem andresource utilization and environmental impact in aadopted exergy index as an objective function to studyprocess. Li introduced exergy parameters into resourcea river ecosystem suffering from different eutrophica- physics proposed by Tsuchida Atsushi and developedtion'. They made useful exploration to exergy analy-a more effective method for evaluation and utilizationsis for ecosystems.of resource. They considered both resource utilizationExergy analysis is applied to eco-industrial systemsand pollution prevention in industrial processes basedfrom a research on the relationship between exergyon the proposed ecological cost coefficient and de-parameters and environmental impact of industrialstruction indexl4.systems. Ayres introduced exergy parameters intoIn total, though some useful studies have been ful-economics analysis', which revealed economicfilled about exergy parameters on eco-industrial sys-meaning of the second law of thermodynamics. Andtems as above mentioned, there are still some draw-he indicated that exergy could be taken as an indicator backs. For instance, some study only considered howto express both quantity and quality of input and outto reduce environmental pollution by decreasing dis-put material and energy in a production process, andcharge of wastes, but did not consider degree of re-could be used to make comparison of resource utiliza-source utilization. Some of them took resource utiliza-tion efficiency in different industrial processes. As-tion and environmental impact in a system as asume environmental condition as a standard of exergymulti-objective optimization problem, but it is difficultparameter and judge the differences between a systemto be modeled and solved because of complexity of theor a material flow and environment. So if appropriatesystem. The application range of exergy parameters isreference criterion is determined, not only energy orextended in some research. Many factors such asresource utilization but also environmental pollutioncapital, information, labor, material and energy etc. arecaused by discharged wastes can be measured. Ste- all placed in the category of exergy, which decreasedpanov finished an analysis on environmental impactthe veracity and practicability of the analysis model.caused by discharge pollutants from industrial proc-By referring中国煤 化Timing to theiresses, especially chemical processes' . Konoreos et al.problems, inYHCN M H Garce uilizationanalyzed environmental impact resulting from indus- and environnculas puluai licl. Indicators an.Exergy analysis on eco- industrial systems283models of these two evaluation objectives are proutilization to diminish the effect of resource utilizationposed based on exergy parameters. Then resource on environment. One is to cut down the amount ofutilization and environmental impact in eco-industrialwaste discharged from industrial systems, and thesystems can be comprehensively analyzed and evalu- other is to lower demand to raw materials by puttingated.wastes or products to their best use. From thermody-namics, cascading utilization means wastes or prod-3 Exergy analysis for eco-industrial systemsucts which with low exergy value are used by the fol-lowing production process. The whole cascading3.1I Environmental effect indicator based on exergyutilization is just a linear reduction process in whichanalysisexergy value changes from high to low. RecyclingDischarged wastes by a system have differentutilization is to form self-closed or semiclosed mate-components with different chemical properties (toxic-rial cycle utilization net. Even materials with lowerity, green house effect, photochemistry effect, strato-exergy value can be used to other production proc-sphere Ozone loss effect, acid rain effect, etc.), whichesses by raising material quality. Recycling is moremay cause different harm to environment. This mustefficient than cascading utilization of materials ibe considered while calculating exergy loss of wastesthermodynamics.but not simple addition. Coefficient of harm is intro-In order to reflect thermodynamic characteristics ofduced to indicate difference in damage of those com-material utilization in eco-industrial systems, a newponents to environment. Environment Negative Effect,indicator, Cycling Ratio of Material Exergy (CME), isENEl'5), is introduced as an indicator to evaluate en-proposed and used to evaluate degree of resourceutilization,vironmental impact:ENE= 2 B,Exi,(1CME= _ exergy reycle to pocss(3)exergy consumed in resourcewhere Ex; denotes chemical exergy and physical ex-(i) Process exergy efficiency. Materials and en-ergy of component i in wastes of the system, kW; B; isergy are carriers of exergy. Resource utilization effi-its effect coefficient to environment.ciency in any processes can be measured with exergyIn order to compare different environmental imtransform efficiency because the essence of material orpacts of eco-industrial systems we defined an envi-energy utilization is its exergy consumed.ronment negative effect factor, ENEF, as an evaluationThere is an exergy loss in practical operation proc-indicator. Its expression isesses because of its ireversibility. In a given produc-_ENEtion or consumption process, the amount of exergyENEF =(2)loss reflects thermodynamic efficiency of the process.ExinIn addition, there is still some exterior exergy loss inwhere Exin is input exergy.practical processes, such as exergy discharged into3.2 Resource utilization indicators based on exergyenvironment with material flows and work loss etc.For measuring extent of resource utilization and ther-(i) Cycling ratio of material exergy. It is generallymodynamic characteristics of a process, process ex-believed that cascading utilization and recycling utili-ergy efficiency (t) as an evaluation indicator for de-zation could be taken for the purpose of reducing re-gree of exergy utilization is defined:source consumption, but they are different in essenceeffective exergy obtained(4)on the basis of thermodynamics. Cascading utilizationof materials means that products or wastes produced in(ili) Renewable exergy efficiency. There are twoone or more resource consumption processes are usedsources of exS existing or中国煤化工as raw materials by the next step until all resources arethe earth anc_ming from themade full use. Two measures are adopted by cascadingsun. In fact,YHCN M H G solar exery..284Science in China: Series B ChemistrySolar exergy flow is defined as renewable exergy infrom thermodynamics in an industrial system andthis paper.could be used as a quantitative indicator to evaluateThe problem of resource utilization cannot besustainability of exergy. .solved thoroughly by approaches of industrial ecologyat present, which only reduce resource consumption to4 Case studya certain extent. Only if all exergy losses are suppliedAn eco-industrial system, Lubei eco-industrial park,by renewable exergy flows in eco-industrial systems,could zero consumption of resource become true, thatis studied with exergy analysis and evaluation in thisis an ideal resource model. Renewable exergy effi-section.ciency, L2, is defined to show the ideal extent of re-4.I Exergy analysis and evaluation on Lubei eco-source utilization in industrial systems:industrial systemQ=renewable exergy obtained(5Lubei Group, in Shandong Province, is a large scaleexergy consumed in resourceenterprise of inorganic chemicals in China. It has three(iv) Exergy depletion index. The above definedhighly symbiosed industrial chains, which are ammo-indicators can effectively reflect different aspects ofnium phosphate sulfuric acid-cement (PSC) poly-resource utilization in industrial systems. Based ongeneration industrial chain, seawater industrial chainthese indicators, a composite thermodynamic indicator,and salt-alkali-power industrial chain. They formed anexergy depletion index, Yop, is proposed to show theeco-industrial system as in Fig. 2.overall result of energy utilization of a system:In Lubei eco-industrial system, nodes are connected4op=together so that by-products and wastes can be suffI-exergy depletion in whole industrial systemciently used. The proposed exergy analysis method isefctive exergy obtained in productin and consumption processPbp embodies exergy consumed in production, con-applied to Lubei eco-industrial system. Three subcases,sumption and all relevant processes of a system. Acorresponding to three separate industrial chains, PSCresource recycling model is established to ilustratepolygeneration industrial chain and symbiosis systemconnections between 4bp and CME, τ, L2 etc. It con-of industrial chains respectively, are studied and com-sists of production or consumption process C, rawpared.material utilization process V and resource recycling4.2 Subcase 1: Three separate industrial chainsutilization process R (Fig. 1).According to definitions of proposed indicators, in-According to the definition of indicators, the fol-dicators for singular ammonium phosphate plant, sul-lowing expression can be derived:furic acid plant and cement plant are calculated re-1-2 \1-2RYp =(1- CME)x-F-+CMEX(7)spectively, as shown in Table 1.where Ybp is function of CME, T and A. As a composite4.3 Subcase 2: PSC polygeneration industrial chainindicator, Yp shows extent of resource utilizationCorresponding V-C-R model is built based on the :ey 1eusec. tosneCR_gRCeR loes einpuR中国煤化工Fig. 1. V_C-R model on resource consumptionIHCNMHG.Exergy analysis on eco- industrial systems285Scawater industrial chainSeawater.AIA5B12-15Be24B26.5Beittern..... ScaA7 SaltplasterA8Crude C2 Chlor-.AquaculureBromine plantFisherylodized salt12 NaOl | Rsitm sueSO,(L) Sal-plasterMagnesium chlordePSCH2SO4。Cementindustrnal'PhosphorileBIHSO, plant so (G)Cement plantSl-alkali-powerindusrial chainAi1A_ CITbemal售”SlagCoul -BI: Ammonium phosphate plantFig. 2. Lubei eco-industrial system.Table 1 Values of exergy analysis indicators for the separate industrial chainIndicatorENEFCMEAmmonium phosphate plant0.08034.41%02.91Sulfuric acid plant0.08434.18%2.930.4844.90% .2.23PSC polygeneration industrial chain, where process CThere are two main circling processes in Fig. 4. Therepresents ammonium phosphate and phosphogypsum;first one is from phosphogypsum to cement, and gasprocess V generates phosphoric acid from the reactionSO2 to sulfuric acid, at last sulfuric acid becoming asof sulfuric acid on phosphorite, which is a process tothe raw material of ammonium phosphate. This proc-consume raw materials; process R corresponds to theess is set as R1 in the V-C-R model. The second circleindustrial chain which produces cement with pho-is that liquid SO2 flows into the seawater industrialsphogypsum and sulfuric acid subsequently. Recyclingchain to extract bromine, and salt-plaster produced inof resource is completed in this step (Fig. 3). Values ofseawater industrial returns to the PSC chain as the rawexergy analysis indicators for Subcase 2 are listed inmaterial of cement. This is set as R2. V in sec. 4.3 isset as VI, and the process producing power and steamTable 2.in thermal power plant in the seawater industrial chain4.4 Subcase 3: Symbiosis system of industrial chainsis set as V2. Process C is not changed. Then a nestedA complicated V-C-R model with the symbiosisV-C-R model is obtained. Values of exergy analysisindicators for Subcase 3 are listed in Table 3.system of multi industrial chains is formed based onLubei eco-industrial system. The PSC polygenerationindustrial chain is the main object analyzed, and sea-5 Analysis and disussinn.中国煤化工water industrial chain and salt-alkali-power industrialTable 4.The aboveHCNMH G'ted together inchain are also combined, as shown in Fig. 4..286Science in China: Series B ChemistryTable 2 Values of exergy analysis indicators for the PSC polygeneration industrial chainIndicatorENEFCME4s2VPSC chain0.07145.50%63.13%54.30%24.32%12.82%1.38CAmmoniumAmmonium phosphatephosphate。production seriesPhosphorite、Ammonium phosphate_plant十Phosphogypsum-H.SO,Sulfuric acid plant一SO, (G)- Cement plant.他R↓CementFig. 3. V-C-R model of the PSC polygeneration industrial chain.Table 3 Values of exergy analysis indicators for the symbiosis system of industrial chains2CME .RQYSymbiosis system0.06552 .88%52.71%20.73%16.01%1.55Seawater industrial chain| sO(L)R Lalphasere- →CementPhosphorite mmonium phosphatcSulfuric acid< -SO,(G)Cement plant -lantplant↑Power↑↑↑. Steam:SlayCoal-Thermal powePhosphogypsum-production seriesFig. 4. V-C-R model of the symbiosis system of industrial chains.5.1 Exergy analysis and evaluation on environ- and weighted sum of tbree nlants. it shows that themental impact of eco-industrial systemsformer is muc中国煤化工e reason is thatthere are no (HCNMHGelttersothatMaking a comparison of ENEF between Subcase 2by-products are dischargea as wastes, which causes.Exergy analysis on eco- industrial systems287Table4 Exergy analysis and evaluation on industrial system02 (%)SubcaseENEFCME (%)"bpQRammonium phosphate plant0.08034.412.91cement plant0.48244.902.23Subcase 1sulfuric acid plant0.08434.182.93weighted sum of three plants0.30940.312.48Subcase 20.07163.1354.3024.321.38Subcase 30.06545.5052.8852.7120.7316.011.55potential harm to environment. In addition, consump-lower in circulate processes and an amount of exergytion of raw materials (exergy) in Subcase 1 is moreis consumed in upgrading utilization of wastes duringthan that in Subcase 2, which makes Ex.mn bigger and process C, it is not better to improve CME than toENEF smaller. This partly reduced the potential effectutilize raw material offering to process C. Whenof Subcase 1 to environment. In fact, based on thethere is no difference no mattersame output of ammonium phosphate, sulfuric acidand cement, the ENEF in Subcase 1443.6X10 kJ/h, iswhether CME is improved.6.19 times as much as that in Subcase 2, 72.09X 10°Secondly, get the partial derivative to τ from eq.kJ/h. This shows that a polygeneration process is su-(7), to obtain the following expression:perior to several separate production processes on en-dψ |vironmental impact. In terms of ENEF, that Subcase 3is more effective than Subcase 2 is further evidence.=-(1- CME)x(1-s2V)- CMEx(1-s*)/≤0.Therefore, it can be concluded that development of(9eco-industrial systems could provide an effective wayBecause eq. (9) is less than or equal to zero, an im-to solve more and more severe industrial pollution.provement of τ can increase the whole exergy effi-5.2Exergy analysis and evaluation on resourceciency of the system. In eq. (9), τ。is the total exergyutilization efficiency of eco-industrial systemstransformation efficiency and can be calculated fromComposite evaluation indicator Ybp reflects overallτn =τV x(1-CME)+ τR xCME.(10)effect of resource utilization in an industrial system.In terms of eq. (10), there are two ways to raise τn:Its value is decided by indicators of CME, τ and 2,(1) improving τv and tr; (2) when τY ≠τR, adjust-etc.Firstly, get the partial derivative to CME from eq.ing CME to raise the ratio of those processes withhigher exergy transformation efficiency.(7):Thirdly, get the partial derivative to Q from eq. (7):dψ(8JψaCMEτ,R|&*=QV =It is usually believed that increasing circulate ratio of(11)material is beneficial to improve its utilization degree,(1- CME)X+ CMExτR≤0.but eq. (8) shows that_dψdetermined by theJCMEConsidering that eq. (11) is always not greater thanprocess R is not always greater than zero. When ther-zero, the increase of Qn is helpful for raising exergymodynamic weight of process C is higher than that ofefficiency of the whole system, where 2。is overallprocess R, exergy efficiency of the system can be im-utilized exergy of renewable resources, and can beexpressed as eau (12):proved by raising CME because of中国煤化工、E:ME.(12)HCNMHG.and vice versa. When thermodynamic efficiency is Similarly as I, uir uJU wuys W siseQn: (1) in-.288Science in China: Series B Chemistrycreasing n~ and s2x in process V and process R re-Acknowledgements This work was supported by the Na-spectively; (2) when sV≠s2R, adjusting CME totional Natural Science Foundation of China (Grant No.20436040).raise Q nAnalysis on中DP shows that indicator values forReferencesPSC ploygeneration industrial chain, symbiosis systemof industrial chains and separate industrial chains areErkman S. Industrial ecology: An historical view. J Cleaner Prod,better, good and worse respectively. 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