The lmportance of Conveyíng and Storage Systems ín...

F. Feige, Gemany

The lmportance of Conveyíng and Storage Systems ín Cement Plants

1. lntmductlon The clesSical cement factory operating according to the dry process. from clinker buming in the rotay kiln up to the product re@ fw dspatch and, normalb having its own raw material de- pouns, can essentiaiiy be characterized by the following six process mm:

quarrying and preparafion, raw mat& storage and blending,

raw mesl produciion and storage as weil as homogenization,

dinker prcduction and storage,

iinish grinding and cernent storage,

cament rnlxing and dispatch.

Thls enumeration does not include the production of puiverized fuels, which has k o m e more and more a process stage strongiy depending on the location wRh the increasing utiiizetion of uecondary fuels and their indvidually adapted preparation. Flg. 1 shows the process stages of cernent making in a block dkgram also Mdicating the rnost important utilities required in a cament íactory to ensure its proper opefation, receiving energy

Taking into account these points of view, the individual stages of the rnost important conveying and storage processes wiil be described hereinafter in the above order highlighting the latest deveioprnents in this field. The cement factory being the basis for these reflections corresponds to the state-of-the-arl and, on the whole, its technology is independent of the plant size. ¡.e. it is suitable both for a relatively small capacity of 1,000 Wd and for a large capacity of approx. 3.000 t/d. The fictitious cement factory shall have its own limestone deposit only a few kilometres far from the cement works. This deposit distin- guishes itseif by a limestone with an ideai chemicai composi- tior with only smali concentratioiis of harmful substances, thus obtaining a material with the desired CaCO, content just by blending the low-grade iimestone of the upper bench with the high-grade iimestone of the iower bench. Gypsum, needed as quick-seiting agent for the cernent. is brought in by trucks to be used for finish grinding afier being prepared correspond- ingly. Wet granulated blastfurnace slag. needed as admixture for the production of slag cement, is supplied via rail in self- dumping wagons.

For the sake of simpiification the kiin piant should be fired with pulvenzed brown coa1 that will be supplied by bulk carners ready for firing and be blown into steei silos installec near the kiln to be stored there and water frofn outside as weil as pnmary and secondary raw

matenais and fue. Though ody storage IS msntioned as ~rocess stam, conveyina IS l aso an impoitant procecS usudlj inte- grated in the process of cement making &nd ck&y imkhg the individual process steps as regards the materials. T k equip- meni fw storage and conveying of a cement factory is expectd to be prop&y designed and dirnensiofied

to be highly reiiabie not causing any downtime or stoppage of one of the main pr-r

to compensate ternporary mass va&- tions as weil as a perrnanent throughput increase,

to exclude as far as possible environmental poiluí!on as well as fomation of coating and c#&ng due ta materials and

9 to run wim rnhirnurn powef require- ment.

ür.-lng. FW Feige. Ybeliucweg 8. 0688'2 Ws?au íkmny Td. + Fax: 4 9 (O) 34931 94810

FQ 1: Luock diagm d cement making lrhe production Of pulyenzed hid and me process stages o1 SecOndafy hiel preparation have not been iaken mto accm1 LkWs abouf me M o r on page 69.

Conveying and Storage Systems in Cement Plants

2. The most important Conveying and Storage Processes in the individual Stages of Cement Making

2.1 Quarrying and Preparation

Opening up of a quarry and its later exploiiation are preceded by comprehensive pianning and exploration work. üased on the data of the geoiogical expioration. today mainly block models are prepared which in turn are the basis to control Me entire process of quarrying. Due to its suppoced compact structure, the limestone must be ioosened from the quarry face in large quantities by blasting. Corresponding drillc are used to sink the required large-diameter borehok. m e blasted loosened rock should predominantly be taken by imd- ers with loading shovels from 3 to 10 m3 depending on the capacity of the cement factory and the operating time of the quarry. These loaders wili load a fleet of heavy tipping iorries, which handie the rock to the stationary CNshing plant. Dueto a well-organized cycle of the heavy tipping iorries, both grades of limestone are fed to the crusher in a preset ratio so that the mean content of CaCO, of the crushed limestone mix will be below the set point. An alternative to this actuaily conventional quarrying method is the explosive-less quarrying of solid rock using large-scale hydraulic hammers [ l] . Hydraulic hammers have already proved successful and can be a very advantageous soiution predominantly for minor quarrying outputs, of course depending on the rwk. Today many manufactures, among others aiso Copco/Sweden, offer large-=ale hydraulic hammers. It may also be advantageous to use bucket wheel excavators if there is limestone with a mariy structure. Fig. 2 shows a bucket wheel excavator operating in a q u a q of a cement factory in the USA. The excavator dellered by FAM Forderanlagenbau Magdeburg/Gerrnany removes the rnarl up to bench heights of 11 m and has a COWJeying capaciiy of 1,500 m3/h 121. Since the limestone extracted in the quaw will exclusively be used for cement making, it is advantageously CrUshed in asta- tionary double-shafi hammer crusher that is equipDed with grate bonoms to limit the edge lengths of the finished product. The crusher is fed by a buckle-plate apron conveyor of super- heavy design capable of handling iumps of rcck with edge lengths of up to 1.5 m and which. diven by a hydraulic motor, provides maximum torques even in the lower speed range. Fig. 3 shows a design sketch of crusher feeding provided by AUMUND Fordertechnik GmbWGermany [3]. m e limestone leaving the crusher with edge lengths of up to 25 mm is first caught by a short belt conveyor with rubbedined

Fiy, 2: View 01 a bucket wheel excavator with a desbned mining 15W mVh op+?&ng in a marl quarry in the USA

d

Fig. 3: Design sketch 01 CiUSher fssding o1 AUMUND Fordertechnk GmbH in Rhenbery. The feeder iS designe3 as hickle-Diale WrOn CMYBpr Mth leed widths o! up to 3.0 rn Omrating with high-tendle caterpillar traCks.

idlers and then transferred to an efficient long-distance belt conveyor negotiating curves. valleys and ridges without any transfer points. Finally the limestone is fed to the longitudinal belt conveyor of the blending bed arranged on the edge of the works premises.

Fig. 4 shows, as an example. a view of the beit conveyor of a Chinese cement factory supposed to be longest continuws one of the worid 141.

The belt conveyor connects the limestone quany with the cement works at a distance of 16 km and has been designed for a throughput of 1,260 t/h. On its way to the cement factory, the beit conveyor traveis through Bight wrves and negotiates dif- ferences in altitude of more than 150 m. The belt conveya with a belt width of 1,000 mm is dnven by 4 electromotors with a dri- ving power of 600 kW each. The beit conveyor was deiivered by RE1 from France.

Conveying and Storage Syctems in Cement Plants

5.5: T w psraiiei wndng ppe canveyws hom KOCH Trany)wnschnik Gmbn. Wadgassen, W n g in 1te W o ~ power plan1 nem

wilh thw CMsideraMe convqing didance d 2 x 2.2 km

A M conveyor of similar iength was comrnissioned by EEUMER Maschinenfabrik GmbH & Co. KG in South Korea in íke Wm of the last century. However, this belt conveyor system, which also runs through rough terrain, has a special fea- twe, Le. the lower strand is also used for materia handling. The m e n t factory in South Korea supplies cement clinker to a sea- p r t teninal from where it gets adrnixtures supplied by ships.

Amme recent conveying system for continuous bulk handling is the so-called closed-belt conveyor or pipe conveyor. mis type of wnveyor that has already been intrcduced in the cement industry ensurec a dust-tree handling due to its closed design. WIM a gradability of more than 30 degrees and its cuwe-going ebility this handling system will solve any problem of transport.

Fig. 5 shows two pipe conveyors installed in the tippendori power plani near Leipzig. They have a length of 2.2 krn each and wwe supplied by the German Wadgassen-based KOCH Transprttechnlk GmbH [5]. Fig. 6 shows a flow sheet of the p m s s stages of cement making frorn quarrying to raw material storage and blending including the raw material proportioning.

2.2

Due to the relativeiy large distance between the limestone quarry and the cement factory. the raw rnix consisting of the high-grade and low-grade limestone is not piled in the quarry it- seii but in a longitudinai blending bed inside the cernent factory accwding to the Chevron method. A stacker shouid form the stockpile of the limestone rnix while a bridge scraper effects re- ciaiming. The tasks of the latter are either to feed the proportioning bin between the blending bed and the grinding plant so that it will be perrnanently filled for the raw meal production orto directly fe& the mil1 via a rneasurement of the rnass flow and speed control. Fig. 7 shows a circular blending bed in the Polish cernent works of Kuyawi delivered by Polysius AG from BeckuWGemany [SI. This blending bed arrangement with a storage capacity of 27,000 t of limestone has a circular rail di- arneter of 82 m. Today blending beds will very rarely be installed in the open air for reasons of environmental protection. There- fore. very light and, from the architectural point of view, aes- thetic constructions have been developed for both longitudinal and circular blending heds. The iirnestone mix discharged frorn the stcchastic two-component blending bed still has to be cor- rected bydosing high-grade limestone. which is also stored in a longitudinal shed together with gypsum. It is brought in by trucks, durnped into a pit bin. discharged by a heavy armoured chain mveyor and finaliy vertically lifted to the store by a so- called corrugated-edge conveyor. Limestone and gypsurn are reclaimed by porta scrapers. Bin discharge conveyors and also portal reclairning scrapers are offered by AUMUND Forderiech- nik GmbH. Corrugated-edge conveyors are supplied by Anla- gen- und Fordertechnik Arthur Loibl GmbH at Straubing/Ger- many. The granulated blastfurnace slag is discharged into particulariy long pit bins from self-dumping wagons and is stored there until it is discharged for fine grinding. Before the cement raw materials are prepared to becorne raw rneal they are conveyed from the individual stores to a proportioning plant where the desired raw materia mix is composec by rneans of the so-called raw rneal mix control loop. The weighing equip-

Raw Material Storage and Blending

blending beds

I imeStOne 1 + 2


Fig. 7: Vew inside lhe circuiar biending bed siore 01 Me ArgentMBn Loma Negra cernent w o i b with a storage capacm, ot 60 m0 l o1 limestone to feed a kiln line with a lhmughput of 5 15OVd

rnent withdrawing the material from the level-controiled proportioning bins are either the traditional weigh-belt feeders, e.g. from Schenck Process GmbH, DarmstadffGermany, or fuily enclosed devices as they are offered today by Pfister GmbH irom

high-capacity bucket elevator handling them to the raw meal storage silo. The raw mea stwage silo has to fulfil two tasks: to provide a stock of raw meal for a kln opefation of one to iwo days and, to render a certain homogenizing e W due to its central bottom cone leading lo a vmex formation dunng discharge to smooth residual pfoperty vanatis of the raw meai stiil exist- ing. An annuler area et the cone base with a certain inclination to- wards the silo mis is permanently aaated dunng discharge so that the raw rneal is put into a flowable state in the bottom range. Then the raw meal is discharged at 4 lo 6 points of the central cone via adjustable rotary drum feeders and airslides and is passed to a downstream proportioning bin that is directly connected to a weighing systern for proportioned feeding of the preheater. The raw meal is discharged from the silo via the lwei measurernent of the proportioning bin. Each rotafy drum feeder is preceded by a quick-acting shut-off device to be able to close the silo quickiy and safeiy in case of a discharge stop. Today al1 major suppliers of equipment for the cement industry offer silo designs inciuding the corresponding technical equiprnent. l3AU Harnburg and BMH Ciaudius Peters AG at BuxtehuddGermany come first as regards these suppliers. The rotor weighfeeder from Pfister is the ideal weighing equipment for kiln meai proportioning due to its fuliy enclosed design. The raw meai feed of the preheater has fundamentelly changed. In the past the raw meai was aimost exclusively fed by pneurnatic conveyors, the airiii or screw pumps. Today. for reasons of energy saving, with rare ex- ceotions. onlv hiah-caDacitv bucket elevators are used. Fa. 9 .

A-gsDdg/Germany (F g. 8) Tne welgn.ng eqLiPmen1 OftW Pro pon oning p.an1 ha5 a very n gn mponance as regards CiuaJW ln

snohs ine nen K TI nc: 01 -5 500 I a ut Lohgn Cemmt's Uñion 0, uue LJ dnt r ) Marvario -SA omna cons1mc:K)n Iwo of tne

the process of cement making. This should always be taken into account when selecting the corresponding equiprnent.

2.3

The raw rneal shall be produced in a vertical rdler mil1 operatlng interconnected with the kiln plant. The exit gas of the 5-stage preheater passes through the mili for drying the raw mk, whidi should have a quarry misture of 5% as annuai mean. me material is fed to the mil1 either via a well sealed gate system or via a pressure-tight armoured chain conveyor. Fdlowing ihe current trend, the cement raw meal discharged together with me gas flow is separated in an ESP without precleaning. Aiter passing a system of airslides. the raw meal. together with the klln dust continuously discharged vie the preheater exit gas, is fed to a

Raw Meal Production, Storage and Homogenisation

Fig. 8: Pfisier mtor weighteeda iype TRW cuitable lar mili teedlng

Conveying and Storage Systems in Cernent Plants

Rg. 1 0 Hwh-c-l) Mi buckel &miar fm raw med fasd o1 ihe kih line al Jalaptalhan m t piant in Shailand, erected by AUMUND

hghest high-performance belt bucket elevators with a cenlre distance of 131.5 m and a designed conveying capacity of 550 tih each have been installed there by BEUMER Maschinenfabrik I7]. AUMUND erected 2 belt buckel elevators with a centre distance of 137 m at the Kodinar plan1 of Gujarat Ambuja Cernent in india.

Fig. 11 shows a flow sheet with the individual process stages of m t making, from raw meal production to the clinker pro- ductin and storage.

2.4 Clinker Production and Storage

climker 1s produced in a rotary kiln supported by two canying roller stations. h e kiln plant comprises an upstream calciner and a 5-stage cyclone preheater. Taking into account the &ve statements conceming the throughput. the preheater is designed as single-flow unl. h e clinker 1s cooled in a mcdem reciprocat- mg grate cooier wkh a rolbrgrate at the outiet for limiting the grain cize of ciinkef to rnax. s 25 rnm. Then the clinker is transported upwards by an inciined deep-pan apron conveyor and dis-

into two reinforced concrete siioc arranged one behind the other. The deep pans of the deep-pan apron conveyor. which has to handle the abrasive clinker leaving the reciprmting grate codw with a temperature of approx. 75"C, are expected to have a high acwracy of fit and tightness. in particular at the ddection pants. BEUMER Maschinenfabrik and AUMUND F6rdertechnik as well as the ltalian company GAMBAROlTA from Trento are well-known rnanuíacturers of thoose conveyors.

The kiln plant is fired with brown-coa1 dust supplied ready for firing. lt is proportioned and pneumatically handled to the finng points of the rotary kiln and calciner by the explosion-proof rotor weighfeeder frorn PFISTER, type DRW. which is a proven solu- t i ¡ . The kiln exit gas and the exhaust air from the grate cwler are dedusted in ESP plants. While the kiln exit gases, which at first flow thrwgh a conditioning tower after the preheater, are uti- l ~ e d for combined drying and grinding in the vertical roller mil1 in interconnected operation around the clock. the grate cooler exhaust air is either blown into the open air without being utiiized or used for drying of the granulated blastfurnace slag in the finish grlnding plant. The dust is handlec below the two ESP plants by efiicient wntinuous-flow conveyors.

Clinker can be stored in the most different ways. It can be stored in a blending bed, in high-capacity silos rnade of steel or rainforced concrete, in normal tower silos of reiniorced con-

- Conveying and Storage Systems in Cement Plants

crete. in enclosed conical, circular stores and. recentiy also in dome silos which are very similar to high-capacity silos as regards their heighvdiarneter ratio. Longitudinal stores with open sides cannot be found any longer in nodem carneni faciories for economic and particularly envirwimental m n s .

As regards tower silos, soii bearing capaciiy is an important fea- ture. The rnajor load is of course the ciinker pile spread over a more or less large surface. depending on the iype of storage fa- cility. Cylindncal silos require a high so¡¡ bear¡~ capaciiy whereas covered stockpiles rnay be buik on a ground with a poor soil beanng capacity provided their diameter does not r e quire a central coiurnn to support the roofing stnicture. If this is the case, piling underneath the wiumn rnay have to be taken into consideration. The available space is a further item to be added to the above considerations and influences the individual, piant specific decision which storage type to choose.

Clinker storage in a tower silo (Fig. 11) is an economic and espe- ciaily "clean" altemative. These silos of reinforced concrete have the only disadvantage to maintain the ternperature of the ciinker discharged from the cooler for days and days. However. since the clinker exit temperatures today have to be guaranteed by the suppliers and are norrnaily below 1M)'C when using a recipro- cating grate Cooler, there is no danger for the durabilty of the concrete. As a rule. the clinker is discharged by granty tom the silos via square openings in the silo bottom without any discharge equiprnent. Then it is transported by troughed bek mveyors or apron conveyors to the ievel-contrdled proportioning bins (Fig. 12).

To achieve a higher live capacity, the optirnurn rato of stored and reclaimed volume and thus proñtabiliiy of ciinker storage. the gravity discharge must be assisted by adáitional rnechanid reclaim for automatic operation. An autornized clinker discharge system such as MOLMTM deveioped by Aumund (Rg. 13), a- lows to reclaim in auiornatic operation. With this system the major clinker quantity is discharged by graviiy through t h ~ cer-


tral opening. Automatic operation ts started when discharge by gravity ts no longer possibie.

2.5

Since tha Wment factory shouid al= produce slag cement and blast fumace cement. cement clinker and granulated blastfurnace siag are separately ground in a modern vertical roller mili (Fig. 14 (previous page)). Compared with the tube ball mili, the vertical rdier mili has the advantage that it is relatively easy to switch írom one mil1 feed to another, tn addition to the better energy utilmtion. For a better adaptation to the material being ground. the mil1 should be equipped with a speed-controliabie drive of the gnnding table. m e combined mechanical-pneumatic material circulation is another possibility to save energy, which si- mukaneousiy is to influence the granulometric composition of the finished prcduct. An efficient bucket elevator is used for mechanical material handling. The finished product is separated in a large fabric separator. While the predominantiy produced Pon- land cement is stored in two cyiindrical silos of reinforced concrete arranged ona behind the other, the ground granulated blasifumace slag is passed to a siio compartment of the nearby mixing plant. The two cement siios are predominantly fed by a high-capacity bucket elevator operating either with a central chaln oi a stee-reinforced belt. The silo bottoms again have the shape of a central cone and are approached from k l o w by bulk carriers to bf? filled with bulk cement. Today cement dispatch is íuliy automatic. Sophisticated autornatic systems are offered in the market for this field. An economic alternative to the cyiindrical silo of reinforced concrete is the storage dome, in particular for veiy large storage capacities. Fig. 15 shows such a silo of Ash Grove Cernent at Durkee in OregonIUSA. The dome of 0 44.2 m x 28.2 m has a capacity to store 45.000 t of cement [a]. It was set up by the Dome Technoiogy Inc. hom ldaho Falls/USA and was wmrnissioned in spring 1999. Depending on the level. the silo will first be discharged by gravtty only, then by gravity and mechanical reclaiming and. in the last stage. by mechanical discharge devices oniy. The material is mechanicaliy dlscharged by a screw reclaimer that can be iiíted and iowered on a rotating central column. Fig. 16 shows the pressure relief chamber and aerated discharge Roor of a storage dome with purely pneumatic material discharge. This dome silo with the dimensions 0 42 m x 34.1 m was erected by IBAU Harnburg for Lehigh Cement in Gienn Fails/ USA and has a storage capacity of 44.000 tons of cement [9].

Finish Grinding and Cement Storage

2.6

About 1 O years ago the development of blended cements was started, based on the increased diversity of grades, the increasing portion of composite cements and the demands of the rnarket for quicker and more flexible supplies. Today almost every modern cement factory has a mixing and dispatch plant in which. in addition to cements usuai in the trade, the separately prepared components of a composite cernent. such as granulated blastfurnace slag, limestone rneal. fly ash or por- zoiana are storeá, discharged in corresponding proportions, weighed and mixed to be finally dispatched as bulk cement or bagged and palletised. The types of mixing plants can be very different. Fig. 12 shows a mixing plant in the imrnediate vicinity of the cement silos. It comprises 8 cylindrical steel silos. A rnix- ing pient of this type has the advantage that it can be extended in a modular way any time. Fig. 17 shows the mixing and dispatch plant at dornburger zement. 6 of totally 8 steel silos are used to store components and 2 silos to store the finish product. The heart of the piant is a single-shait positive mixer from IBAU, type iEM8000, with a net mixing volume of 6,600 iitres. Fig. 18 shows this mixer in three-dimensional representation for which a mixing capacity of 150 t/h had been guaranteed

Cement Mixing Plant and Dispatch


FiQ. 1R SinQle-shaH PUSitlYe mixer, Wpe IB - M8W. hom IBAU

[l O]. One of the biggest mixing and dispatch plants of the worid was set up by Lafarge Zernent at their Karsdorf works. Fig. 19 shows this plant essentially consisting of a multi-compartment silo. The silo of reinforced concrete wiih the dimensions of 0 24 m x 71 m has altogether 22 silo cornparirnents of different sizes in two levels. The individual components are directly fed from the grinding plants into the silo wmpariments via a systern of airsiides or also pneumatically from bulk con- tainer vehicles. The civil design of the plant was executed by Peter und Lochner Consulting Civil Engineers, StutigarVGer- many. A modern rotary packer provides bagged cement for dispatch. As leading rnanufacturer of bag packers, it was HAVER .% BOECKER, Oelde/Gernany, who introduced the seai technoiogy and succeeded in a herrnetically sealed cernent bag for the first time in the world (Fig. 20). The following palletising and packing is carrled out autornatialiy. Fig. 21 shows an autornatic palletizer frorn Maschinenfabrik M6llefs GmbH u. Co., BeckurnIGermany.

Fig. 19 View af the rnulti~compaitmsnl silo 01 the mking md dspalch plml at the Karsdori works 01 Lafarge Zernsnt

Rg. 21: Autmatic pdelizer frorn MMim

3. Conclusion It is not exaggerated to say that the stabie prcduction pracess of a cement factory also vitaliy depends on the relime and safe operation of its conveying and storage equiprnent. Frequent

Conveying and Storage Systems in Cernent Plants

breakdowns and unforeseen faüures of these technical installa- tions rnay lead to sefious dangers as regards maintaining the production process and may also be connected with severe econornlc impacts. If, for instance, lirnestone handling frorn the quariy to the &meni factory is interrupted. because iurnps of Masted rock, whih are tw large. have darnaged the apron conveyw fw crusher feeding or if the long-distance belt conveyor fails due to an unforeseen heay darnage - then there is high state of aieri so lo speak. Clogged silos rnay also have a dwruptive effect or the production process. Clogging rnight be caused, fw exarnple. by hydrated cernent or a senous break- down of the aerated bottomc.

In Mew of the fact that today rnost of the cernent rnanufacturers pursue the concept of an in-line Operation of the cernent factory withwit exaggerated storage capacitiies and stand-by equipment, mainly for ecoromic reasons, the right choice and design of the conveying equiprnent and storage processes are of great irnportance.

References [l] BAUTECHNIK report Spscial: "Sprengstofflose Fest-

gesteinsgewinnumg". Kmpp Berco Bautechnik. October 2000.

'New minig system frorn FAM at Hoily Hili - Holcirn (US) Inc." ZKG INTERNATIONAL 55 (2002) No. 11, pp. 35-36.

[Z]

[3] Brochure: Y3unkerabzugsforderer", AUMUND Forderiech- nik GrnbH, May 1997.

141 XJnhi, K. Rver".ZKG kTERbAIOluAL 54 12001, No 10 DD 54C

hen 6400 1 d cernent pan1 il ! re i'ang!¿e

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'Sauber und sicher auf engstern Raurn: KOCH Pipe Con- veyor beim Bau des Lotschberg-Basistunnel". Schüttgut 8 (2002) No. 6, pp. 550 - 551

DJSON& M.: "The new kiln line for Lafarge Cernent Polska at the Kujawy plant". ZKG INTERNATIONAL 54 (2001) No. 11, pp. 602 - 608.

BOATE, F.E.: von der Wroge, H.: "High-performance bucket elevator sets new records at Lehigh Cernent Union Bridge". ZKG INTERNATIONAL 55 (2002) No. 10, pp. 48 - 53.

[E] HUNER, M.: "Alsen's flyash storage dome - a case study." Bulk Sdids Handling (1999) No. 2

p ] &?JE~MANN. J.: "Pneurnatic discharge systern for large dome silos". ZKG INTERNATIONAL 55 (2002) No. 3, pp. 46 - 53.

[lo] THEUERWIUF, H.: "New blending piant for binders at dornburger zement - buiit entirely of steel". ZKG INTERNA- TiONAL 53 (2000) No. 7, pp. 388 - 393.

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