Management of Material Flows in Closed-Loop Supply Chains

Transcription

1 Management of Materal Flows n Closed-oop Suppl Chans Decson Support Sstem for Electronc Scrap Recclng Companes rof. Dr. Thomas Spengler Braunschweg Unverst of Technolog Department of Busness dmnstraton and roducton Management Katharnenstr. 3 D-3806 Braunschweg, German hone: ; Fax: E-mal: t.spengler@tu-bs.de bstract Due to the latest developments n European envronmental legslaton, producers wll be responsble for collectng, sortng and recclng of dscarded products at the end of ther servce lfe. The wll be charged b the total recclng costs whch leads to hgher lfeccle costs of ther products. Therefore, a close cooperaton wth recclng companes and ther ntegraton n producers suppl chans, e.g. as supplers of spare parts and secondar raw materals, wll be necessar and leads to so called closed-loop suppl chans. cost-effcent management of materal flows between supplers, producers, customers and recclng companes requres an ntegrated nformaton management as well as advanced plannng sstems. The paper focuses on the desgn and mplementaton of a decson support sstem for electronc scrap recclng companes n closed-loop suppl chans. t has been mplemented n a maor German electronc scrap recclng compan and valdated b real data.. ntroducton Hgh nnovaton rates and lastng market expanson n electroncs ndustr have led to a steadl ncreasng number of manufactured electrcal and electronc equpment durng the last few decades. Due to falures and to rapdl changng technolog, t evolves nto waste after a few ears. t s estmated that n the European Unon more than 6 mllon tons of Waste on Electrcal and Electronc Equpment (WEEE) were generated n 998, and t s forecasted that the amount of electronc scrap wll ncrease 3 5 % per ear (European Commsson 2000). These dscarded products should be recovered due to economc and ecologcal reasons. roducers of Electrcal and Electronc Equpment (EEE) wll have the followng oblgatons: Fnancng the collecton, treatment, and envronmentall sound recover of WEEE Settng up sstems for treatment and recover of WEEE Meetng recclng quotas for each devce categor rovdng nformaton for treatment facltes about the composton of ther products to electronc scrap recclng companes n order to adopt these oblgatons economcall, producers have to decde strategcall on the followng questons: How to remanufacture used products b refurbshng/upgradng processes How to reuse parts and complete modules as substtutes for orgnall manufactured equpment and spare parts How to reccle the non-reusable parts and modules, whch consst of a mx of materals, such as heav metals, ferrous and non-ferrous metals, plastcs, wood, glass, etc. The recover of electronc scrap s a multstage process. ogstc ssues concern collecton, gradng, transport and allocaton of dscarded products, reusable parts and modules, as well as of recovered materals. Dsassembl n order to remove hazardous substances and reusable parts s often followed b bulk recclng to gan separated materal fractons that are sent to metal roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

2 recclng facltes or other recclng specalsts (cf. Fgure ). Suppler Manufacturer Metallc raw materals Waste equpment Refurbshng Reuse Granulated lastcs Recclng Fgure. Materal flows n closed-loop suppl chans [] The paper focuses on the desgn and mplementaton of a decson support sstem for electronc scrap recclng companes n closed-loop suppl chans. The decson support sstem conssts of a sophstcated technoeconomc model of the dsassembl and bulk recclng processes. Therefore, a detaled techncal analss of the bulk recclng process s necessar. Based on cooperaton between producers and recclng companes, nformaton on product structures, reusable parts and modules, hazardous substances and recoverable materals wll be avalable for all companes partcpatng n the closed loop suppl chan. Takng nto account detaled nformaton concernng the suppl wth scrapped products and the demand of reusable parts and modules, recclng companes wll be enabled to use the nformaton for the determnaton of an economcall effcent recclng schedule. Due to a low capact utlzaton of recclng plants, nowadas, most recclng companes actvel requre electronc scrap from anonmous markets. Therefore, onl a small percentage of the avalable recclng capact wll be used b scrapped products resultng from long-term contracts wth producers or supplers. Due to hgh uncertantes n the amount and qualt of avalable WEEE, the long term recclng schedule has to be supplemented b a detaled short term schedule at regular ntervals. The recclng compan regularl has to decde on the dal recclng schedule of scrapped products, the levels of dsassembl, the allocaton of reusable parts and modules to producers or supplers and the further recclng process of recoverable materals. 2. General roblem Descrpton Smeltng egend: Current materal flow otentals to close loops n materal flow Uncoordnated materal flow Decson problems of electronc scrap recclng companes refer to the tasks suppl, dsassembl and bulk recclng. Other stages lke transport, smeltng or marketng of reusable parts often are excluded snce the are accomplshed b external servces. The materal flow throughout a tpcal recclng compan s shown n Fgure 2. ong-term contracts for ncurrng scrap collected b publc and ndustral collectors contrbute less than 0% of the recovered mass. Thus, the actve acquston of electronc scrap s a necessar task. Snce the nput storage of recclng enterprses often s a separated proft centre that ma acqure and sell scrap on the market, the delver of scrap to the recover works s assessed wth a gven transfer prce that s dependent on the scrap market. Therefore, the recover works manager faces the acquston decson whch products from the storage have to be taken and recovered n the consdered dal plannng perod as seen at pont (*) n Fgure 2. The frst recover step dsassembl s composed of manual or partl-automated processes. Mechancal assstance concerns onl transport and lftng tasks. lannng the dsassembl step, the recover works manager has to determne the dsassembl level at pont (**) n Fgure 2, takng nto account that some products do not have to be dsassembled at all, that the reusable part demand as well as prces change dal and that some dsassembl operatons are mandator n order to elmnate hazardous substances. The second step bulk recclng s desgned to gan precous fractons such as ferrous and non-ferrous metals from mxed electronc scrap, usng unt operatons lke crushng and separaton steps. When plannng the bulk recclng step, the recover works manager has to decde whch scrap tpes are to be reccled nternall or are to be marketed externall as seen at pont (***) n Fgure 2. Decsons of recover works management: (*) acquston decson (**) dsassembl level decson (***) nternal/external recclng decson Tube Glass Recclng Tube Glass,68 % cture Tubes 0,3 % cture Tubes,38 % lastcs Recclng lastcs 0,27 % lastcs 0,27 % Functon test arts 2,89 % arts Re-Use arts 2,89 % ght products 2,9% Fractons Marketng cquston (*) Bulk recclng Heav products 47,20% Scrap 30,6 % (**) (***) ght scrap Heav scrap dsassembl dsassembl (**) (**) (***) (***) Scrap components 4,7 % Scrap components,92 %,0 % Ferrous metals,35 % Non-ferrous metals 0,57 % Hazardous substances,85 % Waste 0,58 % Cable 48,86 % Fe-Metals 2,03 % Waste 23,02 % Metals,59 % Cable 0,66 % Hazardous substances 3,82 % Ferrous Metals 0,8 % Non-ferrous Metals 0,09 % Hazardous Substances 0,29 % Waste,0 % Cable 43,95 % Ferrous Metals 20,86 % Non-ferrous metals 8,89 % Waste Fgure 2. Materal flow of a tpcal electronc scrap reccler [2] Ths s a complex problem due to the fact that bottlenecks can appear n dfferent unts. Snce the long-term capact of each unt s calculated on the bass of an expected specfc nput composton, varatons from ths composton can lead to bottlenecks n the subsequent unts f the components that should be separated n the roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

3 precedng unts of the faclt, e.g. ferrous metals, are underrepresented n the feed. Thus, a recclng enterprse can beneft from the blended composton of the bulk recclng nput adusted b the feed of dfferent scrap tpes. The output of the recclng centre s taken to smeltng plants (70% metals), chemcal ndustr (>% plastcs), glass ndustr (>2% tube glass), part traders (3% reusable parts) and waste dsposal (22% waste and hazardous substances). detaled analss of the dsassembl and bulk recclng operatons and the relevant plannng data s gven n chapter terature Revew General revews of plannng problems n a product lfe ccle are gven b [3], [4] and [5]. ccordng to the chosen sstem boundar the followng lterature revew s restrcted to dsassembl levellng and bulk recclng plannng problems that occur n the product recover stage. enev and de Ron [6] descrbe a statc cost comparson tool to determne an economc dsassembl level and sequence of a sngle product. Krkke et al. [7] use a method on a tactcal management level to determne a good product recover and dsposal polc of one product tpe takng nto account techncal, economc and ecologcal crtera. For ths purpose a two-phased dnamc programmng algorthm s presented. Spengler et al. [8] develop a mxed-nteger lnear programmng model based on lnear actvt analss for ntegrated dsmantlng and recclng of buldngs. The purpose of the model s to obtan optmal dsmantlng strateges but also an optmal assgnment of components and parts to recclng technques. ambert [9] develops a lnear optmsaton model for an optmal dsassembl of complex products. detaled revew of dsassembl sequencng approaches s gven n [0]. Sodh and Remers [] descrbe an ntegrated dsassembl and materal recover model for dscarded electronc products. n addton to other works the presented model ncludes the process stage of metal smeltng. Onl a few papers refer to operatons research models for the economc assessment of bulk recclng operatons. und et al. [2] use lnear programmng n order to analse the desgn and the operaton of muncpal waste materal-recover-facltes. Sodh et al. [3] present a dnamc programmng model for the determnaton of the operatons sequence for float-snk materals separaton b denst. Stuart and u [4], [5] offer decson support for processng and reprocessng optons n electronc scrap bulk recclng centres. Rudolph [6] provdes an ntegrated model for dsassembl and bulk recclng plannng wthout gvng a practcable bulk recclng descrpton. The recent publcatons that deal wth the applcaton of operatons research n recover plannng focus on dsassembl and bulk recclng aspects. n ntegrated model of the acquston, dsassembl and bulk recclng problem s not avalable untl now. Therefore, the development of an ntegrated model for decson support n the three mentoned questons seems to be necessar. 4. lannng Data and Operatons nalss The applcaton of sophstcated recover plannng models s often obstructed b the lack of data. n ths paper, we assume that nformaton s provded b a database that contans product and operatons data. Snce the composton of dscarded electronc products show sgnfcant varatons, the avalablt of recclngrelevant nformaton for all partners n the closed-loop suppl chan s a complex problem that should be solved b producton enterprses and ther supplers, referrng to the forthcomng drectve of the EU on Waste on Electrc and Electronc Equpment [7]. Fgure 3. Sheet of a recclng passport [5] practcal concept seems to be the recclng passport of the Belgan-German equpment producer GF-Gevaert G that contans data about hazardous substances, composton and reusable parts [8] as shown n Fgure 3. t can be used to plan recover operatons and to estmate dsassembl tmes. Nowadas, recclng passports exst onl as prnted versons for selected products, but a possble scenaro for the future s the webbased provson of the nformaton from the manufactures to the recclng companes on two dfferent levels. Frst, the generated recclng passports wll be made avalable n the nternet. Thereb t s mportant to use a format that can not be changed or modfed and to permt searchprocesses to fnd the recclng passport of a specfc devce. Ths level allows the manufacturers to meet the legall requred nformaton dutes. The second level of nformaton provson goes further and tends to support decson and plannng processes wthn cooperaton between manufacturers and recclng companes. Ths permts the realzaton of hgh grade recclng processes roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

4 lke reuse and refurbshng strateges. Thus, t s necessar that a hgh level of securt can be guaranteed snce now detaled nformaton wll be provded. Wth support of the nternet technolog the recclng companes wll be enabled to access relevant nformaton b the use of retreval functons. The recclng compan`s browser connects to a web-server and a request form can be flled n. The web-server wll then access the recclng data base of the manufacturer b usng predefned logcs. The requested nformaton wll be extracted from ths data base and provded to the recclng compan b the nternet. n example of the dsassembl operatons structure s depcted n Fgure 4. personal computer (=3) chosen from the dscarded products range (= 6) must be opened and the harmful part batter (=7) has to be removed (dsassembl actvt =3). The resultng b-products are ferrous metals (=29) from casngs, whch can be reccled n the steel ndustr and the personal computer wthout batter (=2). The dsassembl opton to gan spare parts (dsassembl actvt =4) can be exercsed f there s a market for the resultng parts CD-drve (=), dsk-drve (=4), prnted crcut board (=22) and personal computer wthout drves and boards (=3). Dsassembl output has to be drected towards external or nternal treatment. n case of external treatment, the output s collected n boxes and marketed externall, e.g. as spare parts or n order to be treated b recclng specalsts. lternatvel, the dsassembled parts can be reccled nternall n a bulk recclng faclt where the are mxed wth other products and parts. The flowsheet of the bulk recclng step s shown n Fgure 5 (a). Fgure 5 (b) wll be explaned n chapter 5. valable products T-Set = deo recorder =2 ersonal computer =3 Telephone =4 Telecommun - catons swtchboard =5 =3 C batter re moval Output of frst dsassembl actvt Batter = ersonal computer wthout batter =2 Ferrous metals =29 Output of second dsassembl actvt Dsk-drve =4 rnted crcut board (standard) =22 =4 ersonal computer wthout Bulk drves and boards recclng =3 CD-drve = C parts ganng Bulk recclng fractons Copper l= lumnum l=2 Ferrous metals l=3 rocess waste l=4 Cell phone =6 Fgure 4. Example of the dsassembl operatons of a personal computer a) Flowsheet b) Model Shredder Dust 2l 2 Magnet Fe-Recclng 3 Edd current separaton l-recclng Crusher l 2 3l 3 4l u 4 u 23 u Magnet 2 Edd current separaton 2 Fe-Recclng l-recclng Dsposal 4 5l u 4l r separaton Cu-Recclng 5 6l u Crusher 2 6 7l 7 Screen Dsposal 7 u 74 8l 8 Cu-Recclng Denst separaton Dsposal 8 u 8 l Fgure 5. Flowsheet (a) and model (b) of the bulk recclng process roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

5 The bulk recclng process conssts of sze-reducton and separaton unts. The sze-reducton n order to solate and concentrate the valuable materals s accomplshed b several totall automated shreddng and crushng unts and has decsve mportance for the success of the separaton. Ferrous metals represent a huge share of the bulk recclng nput. Ther removal b magnetc separators takes place after the frst shreddng step snce the sze-reducton of ferrous metals s ver energ- and wear-ntensve. Other valuable materals lke alumnum and copper are ganed b electro- and denst-separaton processes and classfng stages. The range of materal components n the nput of the unts as well as of separated materal fractons n the output of the unts s ndcated wth the ndex l. Relevant cost drvers n bulk recclng are mantenance, energ consumpton and labour [9]. Dscarded product composton Dsassembl operatons Bulk recclng operatons Recover market data and restrctons ntegrated dsassembl and bulk recclng plannng sstem Fgure 6. Structure of the consdered dal plannng problem The structure of the consdered dal plannng problem of the recover works manager s shown n Fgure 6. Takng nto account the avalable scrapped products, the feasble dsassembl and bulk recclng operatons and costs, the market prces of reusable parts and secondar materals as well as capact and market constrants, the recover works manager has to determne an optmal short term recclng program and an optmal allocaton of dsassembl and bulk recclng operatons. 5. Formulaton of a M-Model Maxmal total achevable margnalncome Short term recclng program Optmal allocatonof recover operatons: Dsassembl Bulk recclng The model formulaton s based on the lnear actvt analss [20] that permts a ver smple and approprate model formulaton of recover plannng problems [2], [22]. The modellng approach of the dsassembl sector corresponds to the optmsaton model that s gven b Spengler et al. [8]. The ntegraton of the bulk recclng plannng problem and the development of an ntegrated dsassembl and recclng model for short term plannng problems s descrbed n [2] and [23]. The actvt analss based model descrpton s shown n Fgure 7. ntal state masses Fgure 7. ctvt analss based model descrpton t s assumed that a number of dfferent dscarded products, parts and materals =,, are avalable n the storage at a gven negatve or postve transfer prce. These scrap tpes can be dsassembled b the applcaton of =,, dfferent dsassembl actvtes and can be processed b a bulk recclng plant usng k=,,k process unts. s seen n fgure 5b all bulk recclng nput masses (l= ) are allocated to the shredder (k=). Therefore the can be modelled b the T vector (... ) gven n Fgure 7. The followng ndces, parameters, coeffcents, lmts and varables are used: ndces : ndex of scrap tpes: products, parts, materals {,..., } : ndex of dsassembl actvt,..., { } k : ndex of unt operaton k {,..., K} l : ndex of materal l {,..., } a l : c k z c Dsassembl actvtes + = x v nternal recclng Dsassembl output masses D D n n nternall reccled masses External recclng Blendng Ex Ex Externall reccled masses Bulk recclng nput masses Bulk recclng K arameters and Coeffcents Materal fracton masses K Composton factor that dsposes scrap tpe composton to materal component l [kg/kg] ( 0 a l ) Bulk recclng cost factor for unt k [ /kg] Dsassembl labour cost factor [ /h] roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

6 Ex e Cost (-) or prce (+) factor for scrap tpe to external recclng [ /kg] e e m z t u v cceptance cost (-) or prce (+) factor for scrap tpe [ /kg] Recclng materal sale cost (-) or prce (+) factor of solated materal fracton l separated b separaton unt k [ /kg] Mass of one pece of scrap tpe [kg] ( m > 0) Dsassembl tme needed for one applcaton of actvt [h/act] Transformaton coeffcent for unt operaton k and materal l [kg/kg] ( 0 u ) Dsassembl actvt coeffcent for the nput (-) or output (+) masses of scrap tpe caused b one applcaton of actvt [kg/act] mts max T mt for dsassembl labour tme [h],max mt for masses of scrap tpe that s avalable to be taken [kg] Ex,max mt for sale capact of scrap tpe to external recclng [kg],max k mt for equpment capact of separaton unt k [kg] mt for sale capact of solated x,max D materal fracton l separated b separaton unt k [kg] arables nteger Decson varable for the number of applcatons of dsassembl actvt Decson arable for the mass of scrap tpe to be taken for recclng [kg] arable for the mass of scrap tpe after dsassembl [kg] Ex arable for the mass of scrap tpe to external recclng [kg] Decson arable for the mass of n scrap tpe to nternal recclng [kg] arable for the mass of materal component l n the mxture that s treated n separaton unt k [kg] arable for the mass of solated materal fracton l separated b separaton unt k [kg] The obectve functon () maxmses the total achevable margnal ncome subect to mass balance equatons and capact restrctons. The three short term decson questons are depcted b the decson varables mass of scrap tpe to be taken ( ), number of applcatons of dsassembl actvt ( x ) and mass of scrap tpe drected to nternal recclng ( ). The values of the other varables are determned b the constrants. The total achevable margnal ncome results from acceptance revenues/costs, dsassembl output revenues/costs, bulk recclng output revenues/costs, varable dsassembl costs and varable process costs. ccepted and externall marketed products, parts or materals are accounted wth a gven prce. cceptance prces n e for delvered materal as well as dsassembl output sales prces e Ex and bulk recclng output sales prces e refer to the transferred masses. Operatons are assessed wth a factor representng varable costs. The dsassembl cost factor z c represents labour. The bulk recclng cost factors c k for the unt operatons k nclude mantenance, energ, labour and mantenance costs, f not consdered as overheads. MX,..., ; x,..., x ; n n ;...; = ( e + Ex e Ex K Z Z x t c = k= c ) + k K k= l= l= e n realt the fracton ma be polluted. That would lead to a prce that depends on the composton of these fractons and thus to a prce as a functon of the decson varables. n the model, these non-lnear effects are neglected and constant prces are assumed. () roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

7 The chosen products, parts and materals can be depcted b an ntal state vector = [ ] that contans the masses of ever taken scrap tpe. For ever scrap tpe the materal flow throughout the recover enterprse can be descrbed. Dsassembl operatons are modelled wth lnear nput-output coeffcents v that represent the nput and output masses of ever scrap tpe n one dsassembl actvt and the number of applcatons of the dsassembl of ths actvt x (2). The coeffcents v are gven b the nput-output-relatonshps of the dsassembl actvtes. D = = + x v =,..., (2) D The obtaned dsassembl output has to be drected ether to external or to nternal treatment (3). D Ex n = + =,..., (3) The removal of hazardous substances n dsassembl s mandator before the treatment n bulk recclng. n ths n model, ths can be acheved b the settng = 0 ntatng external treatment f a scrap tpe that contans hazardous substances s not dsassembled (4). n = 0 0 f contans hazardous substances else =,..., (4) t s assumed that dsassembl output to nternal treatment s completel processed n the bulk n recclng unts. The nput of the bulk recclng process s blended b a mxture of dsassembl output parts and/or dscarded products n the feed of the process. n the frst unt, the nput masses result from the n composton of. t the moment of destructon n the frst unt shredder, the composton coeffcents a l dspose the scrap tpes to a materal component l. The nput masses of the other unts can be calculated b the followng mass balance equatons for each unt (5) (see Fgure 5b). n al f k = = = ( k ) l ( k ) l f k = 2,..., K l =,..., (5) The transformatons n the separaton unts throughout the flowsheet as seen n Fgure 5a are descrbed b lnear coeffcents u for the nput-outputtransformatons n separaton step k as shown n Fgure 5b. The coeffcent u represents the share of the avalable materal l n the nput of the unt k that s drected n materal fracton l of ths unt (6). t s determned b emprcal data taken from the process dar of the enterprse referred to. The effect of adustments of the techncal shreddng and separaton parameters n order to mprove the process stablt s neglected because the range of consequences for the separaton coeffcents s ver small. Due to the avalablt of emprcal data the unts Crusher, Magnet 2 and Edd current separator are depcted b ust one unt (k=4) n the model. = u k =,..., K l =,..., (6) The values of u as well as prce factors e for the separated fractons are have to be determned emprcall. mass-rato of 0,75 from the component ferrous metals (l=3) that has gone nto the unt operaton Magnet (k=2) can be found n the separated ferrous metals fracton of the unt. Ths rato s based on the share of ferrous metals that has been lberated n the prevous sze-reducton step. n ths unt, onl one fracton s ganed, but n other unts more fractons ma be separated as shown n Fgure 5. Capact restrctons represent nput suppl capact (7) as well as output sales capact (8), (9). Bottlenecks n bulk recclng can appear n ever unt due to varatons n feed composton. Thus, capact constrants must be depcted b lmts for ever unt, too (0). The dsassembl capact restrcton refers to a maxmum of labour tme of the avalable workers ().,max =,..., (7) Ex Ex, Max =,..., (8),max k =,..., K l =,..., (9) l= = x t Z, max k,..., K k T max = (0) () Dsassembl actvtes as well as the number of dscarded products and parts are modelled as nteger varables (2)(3), snce the dsmantlng of a dscarded product can not be splt. Ex ; N m m 0 =,..., (2) x N 0 =,..., (3) Wth the gven product range that s shown n Fgure 4, the M conssts of 70 nteger arables, 226 Non- roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

8 nteger arables and 328 Constrants. t can be solved b the applcaton of varous knds of soluton procedures for combnatoral optmsaton problems. lthough mxed-nteger lnear problems often are Nhard and lead to exponentall growng soluton tme due to the complext of the calculated problem, standard optmsaton software packages usng Branchand-Bound Technques provde a quck soluton n case of the gven problem complext. Therefore, the presented decson support sstem has been mplemented on a personal computer (entum / 600 MHz) referrng to EXCE-spreadsheets that contan the data sets and usng commercal solver NGO optmsaton calculatons. Usng these standard software tools, one takes advantage of ther publc avalablt and the absence of addtonal mplementaton costs [23]. 6. Results and nterpretaton The presented decson support sstem has been appled to a tpcal plannng stuaton of electronc scrap recclng companes. detaled descrpton of the plannng data, scenaros and senstvt analss s gven n [23]. n the followng, onl a few aspects of the applcaton are mentoned (see Fgure 4). ll avalable T-sets (=) are taken and dsassembl (=) s enforced. The subsequent parts lke pcture tubes (=0), housng parts (=6) and cheap crcut boards (=2) are marketed externall. share of the obtaned mxed parts (=5) s treated nternall, another share of them s treated externall due to the capact restrctons n the bulk recclng unts. deo recorders (=2), whch are accepted altogether, are sent to bulk recclng drectl. ust a share of avalable personal computers (=3) s taken. The number s lmted b the market restrcton for CDdrves (=). Mandator dsassembl (=3) s done and the batter (=7) has to be sent to a recclng specalst. The resultng parts of the operaton spare part ganng (=4) dsk-drves (=4), CD-drves (=) and standard crcut boards (=22) - are marketed externall. Telephones (=4) are accepted n toto and sent to bulk recclng drectl (=5). ll Telecommuncaton swtchboards (=5) are taken and dsassembled (=6,7) to gan precous crcut boards (=20) for sale. The accumulators (=9) of taken cell phones (=6) need to be removed (=9) and treated b specalsts. Further dsassembl (=0) of cell phones s not advsable. The obectve functon represents a value of about 3000 per dal plannng perod. The man contrbuton to the obectve value results from acceptance fee revenues. The dsassembl tme capact restrcton as well as bulk recclng capact restrctons are reached. s a result, the feed composton of the bulk recclng plant s adusted conscousl through the choce of taken products and marketed parts. detaled senstvt analss has been carred out [23] and as a result the acceptance prces on the one hand and the metal prces on the other hand have been dentfed as most mportant. Furthermore, the result of the presented case stud depend on the avalablt of necessar nformaton concernng the product structure, hazardous substances and reusable parts. The choce of a representatve product can onl be recommended, f not real product data are avalable. n order to pont out the benefts of the optmsaton model, the calculated result should be compared wth basc concepts to determne short term recclng programs that alread have been used n the past. The frst concept Re-Use ams at hgh dsassembl output revenues and demands the choce and dsassembl of products that contan parts wth postve market value, e.g. computers wth CD-drves. Dsassembl s contnued untl all parts wth a postve value are lberated. arts that contan no hazardous substances and that have a negatve value are reccled nternall. f dsassembl and equpment capact constrants are not reached ths wa, addtonall the products wth the hghest acceptance prces are treated, n order to maxmze the total achevable margnal ncome. Ths concept leads to an obectve value of about 2400 per dal plannng perod. The second concept cceptance fees determnes the choce of dscarded products n sequence of acceptance prces. Onl mandator dsassembl s done untl the constrants are met. arts that contan no hazardous substances and that have a negatve value are reccled nternall. Ths concept s assessed wth an obectve value of about The success of ths concept s mpared b lower bulk recclng output revenues whch s caused b the treatment of less valuable scrap from T-sets (=) and telephones (=4) n the bulk recclng unts. These ntutve strateges have been compared to the optmsaton calculaton concernng other datasets. Bascall, a beneft of at least 0% can be obtaned usng the optmsaton calculaton. 7. Conclusons n ths paper, an ntegrated short term recclng plannng problem for electronc scrap has been analsed and formulated as mxed-nteger lnear programmng model, based on the lnear actvt analss. The purpose of ths dal operatonal management task s to get an optmal choce of recovered products for dsassembl and bulk recclng as well as an optmal allocaton of dsassembl operatons. Compared wth the models found n the lterature, the presented model has mportant specfc characterstcs: The actvt analss based modellng of materal flows throughout the dsassembl and mul-stage bulk roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

9 recclng unts, the ntegraton of the acquston, dsassembl and bulk recclng plannng problem nto one mxed-nteger lnear programmng model and the onlne-avalablt of relevant product data va recclng passports. The materal wth the help of the decson support sstem, electronc scrap recclers wll be enabled to appl advanced plannng sstems, whch have been mplemented n varous ndustral branches durng the last ears.. Though the plannng tool refers to electronc scrap recover, t can also be appled to other recover plannng problems wth bulk recclng processes. The nteger constrants n the present model formulaton are not essental, but ustfed b the precse depcton of the realt and the short soluton tme for the gven complext. The error of the obectve value caused b an -relaxaton of the model s less the % n the consdered case stud. The possble use of standard senstvt analss for lnear programs s a strong argument for a relaxaton of the nteger varables. The presented model provdes practcable decson support concernng the amount and tpes of dscarded products as well as dsassembl and bulk recclng actvtes for recover facltes. Compared wth basc short term recclng programs used n the examned recclng enterprse, a beneft of at least 0% can be obtaned. When we model a multstage electronc scrap recover faclt centred on dsassembl and bulk recclng, t becomes obvous that dsassembl s onl advsable f hazardous or ver precous parts are removed. Dsassembl n order to gan materals leads to hgh varable costs. Therefore, rough data are suffcent for a model of scrap recclng f there s no functonal value n the reccled parts. n the future, muncpal collecton sstems wth specfc scrap categores are expected to be realsed n order to compl wth regulatons lke the forthcomng drectve on WEEE [7]. The offers on the scrap market and thus the decsons of recover enterprses wll be ruled b ths classfcaton. Thus, the adaptaton of these scrap categores n the plannng model wll be necessar. ong-term cooperaton between producers of equpment and recclng enterprses wll attan an ncreasng relevance due to the expected benefts for both sdes. Two basc strategc postons for recclng enterprses have been presented: on the one hand concentratng on acceptance fee revenues wthn the scope of mplementng take back and recclng-sstems and on the other hand ntensfng efforts to recover reusable parts whch wll fnd a read market through producers and supplers of the tradtonal suppl chan. Especall the last strateg wll lead to closed loop suppl chans. Future research s necessar n order to balance demand and suppl of the reusable parts and n order to coordnate producers or supplers demand plannng and the recclng program plannng of the recclng enterprses. References [] Hesselbach,., Spengler, T., Graf, R., loog, M., 200, Materalkresläufe schleßen, D Umwelt 4/5, [2] loog, M., Spengler, T., 2002, ntegrated lannng of Electronc Scrap Dsassembl and Bulk Recclng, roceedngs of the EEE nternatonal Smposum on Electroncs and the Envronment, San Francsco, [3] Gungor,., Gupta, S. M., 999, ssues n envronmentall conscous manufacturng and product recover: a surve. Computers & ndustral Engneerng 36, [4] Spengler, T., Schröter, M., 200, Ensatz von Operatons Research m produktbezogenen Umweltschutz Stand und erspektven. Betrebswrtschaftlche Forschung und raxs (Bfu), 53, [5] Fleschmann, M., 2000, Quanttatve models for reverse logstcs (Berln etc: Sprnger). [6] enev, K.D., De Ron,.., 996, Determnaton of a dsassembl strateg. nternatonal ournal of roducton Research 34 (2), [7] Krkke, H.R., an Harten,., Schuur,.C.,998, On a medum term product recover and dsposal strateg for durabl assembl products. nternatonal ournal of roducton Research, No., -39. [8] Spengler, T., üchert, H., enkuhn, T., Rentz O., 997, Envronmental ntegrated producton and recclng management. European ournal of Operatonal Research, 97, [9] ambert,..d., 997, Optmal dssambl of complex products. nternatonal ournal of roducton Research, 35: [0] ambert,..d., 2002, Dssambl sequencng: a revew, nternatonal ournal of roducton Research, Specal ssue on roduct Recover, forthcomng [] Sodh, M.S., Remers, B., 200, Models for recclng electroncs end-of-lfe products, OR Spektrum 23, [2] und,. R., Tchobanoglous, G., nex, R.., awer, R.., 994, near programmng for analss of materal recclng facltes. ournal of Envronmental Engneerng, 5, [3] Sodh, M. S., Young,., Knght, W.., 999, Modellng materal separaton processes n bulk recclng. nternatonal ournal of roducton Research, 37, [4] Stuart,.., u, Q., 2000a, Model for Dscrete rocessng Decsons for Bulk Recclng Of roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE

10 Electroncs Equpment. EEE Transactons on Electroncs ackagng Manufacturng, 4, [5] Stuart,.., u, Q., 2000b, Refne-or-Sell Decson Model for a Staton wth Contnuous Reprocessng Optons n an Electroncs Recclng Center. EEE Transactons on Electroncs ackagng Manufacturng, 4, [6] Rudolph,., 999, ltproduktentsorgung aus betrebswrtschaftlcher Scht (Hedelberg: hsca-erlag). [7] European Commsson, 2000, roposal for a Drectve of the European arlament and of the Councl on waste electrcal and electronc equpment. Brussels, Commsson proposals, Document 500C0347(0). [8] eren Deutscher ngeneure, 2000, Recclngorenterte roduktentwcung, D- Rchtlne 2243 Blatt Entwurf, Düsseldorf. [9] Meer-Staude, R., Mersmann,., 997, Cost- Structure and Cost Factors for Mechancal rocessng of Electro-Scrap. ufberetungstechnk, 6, [20] Koopmans, T.C., 95, Effcent llocaton of Resources, Econometrca 9, [2] Souren, R., 996, Theore betreblcher Redukton: Grundlagen, Modellerung und Optmerungsansätze stofflcher Entsorgungsprozesse (Hedelberg: hsca- erlag). [22] Spengler, T., 998, ndustrelles Stoffstrommanagement, Betrebswrtschaftlche lanung und Steuerung von Stoff- und Energeströmen n roduktonsunternehmen (Berln: Erch-Schmdt-erlag). [23] Spengler, T., loog, M., Schröter, M., 2002, Methodcal lannng of ntegrated Recover rocesses: Case Stud on Electronc Scrap Recclng. nternatonal ournal of roducton Research, forthcomng. roceedngs of the 36th Hawa nternatonal Conference on Sstem Scences (HCSS 03) /03 $ EEE