Staking a claimin the stockyard

stackers, reclaimers andother stockyard equipment

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As part of its ongoing expansion and development programmeCementownia Warta of Poland is installing a new limestonestorage facility including automated stacking, blending andreclaim equipment by Schade (Aumund Group).

The name of Gustav Schade has been synonymous with thehigh quality chain scraper reclaimer design for over 50 years,with some of the original machines delivered to the Germanpower industry still operating reliably today... 24/7.

The illustration bottom right shows an early design withcantilevered reclaimer boom installed in a power plant alongwith a travelling stacker shown in the background.

Since those early days Schade has developed substantially andnow offers a comprehensive range of designs with reclaim ratesto 5,000tph (tonnes per hour).

Now part of the internationally renowned Aumund Groupsince 2001, the Schade Company has expanded its previousdiversifications into the cement industry offering efficientsolutions for the storage and reclaim of raw materials, additionsmaterials and solid fuels.

A new project for Cementownia Warta draws on Schade’sexperience in particular in handling difficult materials underarduous conditions with, in this case, a nominal stacking rate of2,000tph and a reclaiming rate at 700tph.

With moisture content of up to 18%, limestone can beextremely sticky and difficult to handle. To achieve ahomogeneous output, effective blending was considered essential.

For this purpose a travelling and luffing stacker was specified.The stacker (typical example illustrated on p44) is supplied withan integral tripper car to raise the material from the low leveltroughed belt yard conveyor to the stacker boom feed boot.

For enclosed designs the travelling stacker solution is ideal inthat no loads are applied to the building structure and thereforean economical space frame design may be employed, as shown.

The stacker boom is mounted to a sub-chassis with pivotshaft coincident with the feed point allowing the boom to raiseand lower whilst maintaining a controlled flow from the trippercar to the boom feed boot thus minimizing the risk of spillage

Schade supplies limestone stacking and reclaim system to Polish cement plant

Early cantilevered boom reclaimer.

Louise Dodds-Ely

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and belt alignment problems.By integrating the tripper car and stacker in this way the

result is an economical, efficient and compact design with veryefficient use of available space.

Using the hydraulically operated luffing system the stackingboom discharge level may be accurately set to minimize thematerial free fall from the boom head to the stockpile. Whilstdust generation is not an issue with the Warta project, in manysituations this is an important factor along with materialdegradation and noise level all of which are mitigated byreducing the material free fall.

In this project the major benefit of the travelling and luffingstacker solution is its ability to achieve a layered stockpile withmultiple stockpile level increments.

When using the Chevron method, the stockpile is alwaysgenerated in layers by travelling the stacker along the length ofthe stockpile zone and raising the boom only a small incrementafter each pass.

In this manner the material is spread over the full length ofthe live stockpile avoiding the likelihood of similar materialsbeing deposited in the same zone. Since the material moisturecontent in particular, but also the general materialcharacteristics, vary according to the location within thequarry from which it is extracted day by day, this method ofstockpiling provides uniformity of blending when the stockpileis reclaimed.

Also, when stockpiling materials of varying lump size thelarger lumps always run to the outside of the stockpile andthe fines always accumulate in the centre. If the stockpilewere generated with a single pass then not only would theblending effect be compromised but also the larger lumpswould be effectively concentrated in specific sections of thestockpile along its length thus creating an imbalance inmaterial lump size uniformity when the stockpile is reclaimedalso.

Using multiple thin layers generated by a continuouslymoving stacker all material types, moisture content and lumpsizes are evenly distributed and therefore the reclaimedmaterial represents an effective blend of all sources both inrespect of characteristics and granulometry.

The preparation of a homogenous layered stockpile is only anadvantage if the material may be reclaimed in such a manner thatmaterial is taken from each layer in the stockpile uniformlyensuring the output contains elements of every layer andtherefore every material type delivered to the stockpile with nobias to any particular source or type or lump size.

The Schade ‘Bridge’ reclaimer with reciprocating harrow isthe ideal solution and was selected by Cementownia Warta for

this project.A classic design of double side reclaimer is shown on p43

with the reciprocating harrows arranged to follow the materialrepose angle and by moving back and forth across the full face ofthe stockpile elements of every layer are dislodgedsimultaneously and flow down to the reclaim scraper conveyorrunning across the base of the stockpile.

The harrow is supplied with multiple adjustable tines coveringthe entire face of the ‘A’ frame structure, formed in round barssharpened to enter the stockpile face.

The tine pitch varies over the full height of the harrow and isat its greatest near the base where the material flow is at itspeak.

To accommodate the difficult material handling characteristicsassociated with a very high moisture content a special extralarge harrow design was employed ensuring full coverage of thestockpile face to ensure effective and reliable flow down to thereclaim conveyor below.

Illustrated below; the adjustable sharpened tines fitted to theharrow structure bring material down to the lateral chainscraper reclaim conveyor below.

The complete harrow assembly is mounted to wheelsrunning on rails fitted to the reclaimer bridge structure andhydraulic cylinders are employed to achieve the 3.0 metre lateralreciprocating movement.

For free flowing materials the chain scraper reclaim conveyormay be designed with a raised section at the discharge to lift thematerial onto the receiving conveyor.

However, for handling cohesive materials the preferred

Travelling and luffing boom stacker. Boom stacker and tripping car.

Reciprocating harrowwith tines.

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design, as supplied to Cementownia Warta, has a simplifiedstraight reclaim conveyor which conveys the material directlyacross an inclined bed and off the concrete wharf side.

As illustrated above, the straight pattern reclaim conveyorallows direct discharge with minimum risk of blockage andreduced chain tension and drive torque demand.

Considering the material cohesiveness both the harrow andreclaimer conveyor drives were up rated for this project toensure reliable operation with a design reclaim rate of 700tphadjustable by varying the long travel speed.

Illustrated below on another similar project with a bridgereclaimer the long travel drive bogies include guiding wheelsmounted to vertical axles and running on the rail edge providingaccurate alignment of the bridge structure relative to the railswithout the need for electronic compensation systems.

For this purpose specific rail sections are required and specialfoundation clamp mountings (chairs) for the reclaimer specificallyare necessary to accommodate the horizontal forces. Thesefixings are generally used for large gantry cranes and are

extremely robust compared with traditional solutions.For the Cementownia Warta project the rail centre distance

is 42 metres and each of the two travel bogies are fitted withfour wheels two of which are driven each side using invertervariable speed control giving a working speed range from 0.5 to5 metres per hour but with a dual range function allowing atraversing speed of 12 metres per minute.

The very wide speed range is achieved using an invertercontrolled drive with reduction gear for the working range. Inthe traversing mode the slow speed drive is electricallydisengaged and a direct coupled squirrel cage fixed speed motorengaged to provide for the traversing speed to minimize losttime positioning the equipment.

Clearly in the working mode by varying the travel speed therate of reclaim may also be varied since it is this factor alonethat controls the rate at which the harrows recover materialfrom the stockpile.

Of all the mechanical components probably the conveyorchain (illustrated above) has the greatest impact on the system

Discharge to troughed belt conveyor.

Long travel drive and guidance.

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reliability. For the Cementownia Wartaproject special outboard bearing rollerchains are supplied with integral ballbearings and labyrinth seals to reduce therunning friction and noise generation andprovide significantly extended chain lifeparticular when handling difficult andabrasive materials.

Schade uses only its own design ofconveyor chain, developed over many yearsand each specified to achieve maximumservice life and selected to suit the uniquerequirements of each application individually.

In addition to the outboard bearingroller chains every other scraper shovel issupplied with a central guide roller toaccommodate horizontal loadings.

Illustrated above right, the heavyfabricated steel conveyor shovels are boltedto the conveyor chain extended link platesand supported by the chain rollers running in guides formed intothe bridge structure.

With a bridge reclaimer in particular all of the materialenters the reclaim conveyor from one side at a time, never bothsides simultaneously, and therefore off centre unbalanced loadsare inevitable.

With a dual harrow design these off centre loads cannot becompensated and therefore the entire lateral loading must beabsorbed by the central shovel guide rollers.

For the Cementownia Warta project the shovel width is 1.75metres although for even higher outputs shovels are available upto 3 metres for the very largest portal reclaimer designs withoutput to 5,000tph.

Combining the travelling/luffing stacker with a bridge typereclaimer as described for this project at Cementownia Wartagives the greatest benefit in terms of material blendingpresenting a homogeneous mix to the ongoing process plant.

However, the mechanical equipment is not the end of thestory... effective automated control of the complete installation iscritical to achieving the required blending and systemperformance as a whole.

Schade supplies all the necessary field instrumentationsystems, level and positional sensors plus safety equipment andbackup systems for the effective control of the stacker andreclaimer.

Integrated control systems using programmable logiccontrollers may be provided along with all necessary switchingand motor control gear.

These control systems may be linked to a central processcontrol installation or may be automated locally depending uponthe client’s requirements.

Generally the equipment will operate continuously since thebuffer storage between the reclaim stockpile and the kiln islimited to a few hours production at best.

This clearly puts heavy pressure on the reclaimer to delivermaximum availability under all operating conditions even thoughthere may be backup systems.

Whilst the reclaim must continue 24/7, often the stackingsection can only operate on a reduced shift, say ten hours perday and therefore the relatively high stacking rate compared toreclaim set for this project at 2,000tph and 700tph respectively.

Therefore the option for simultaneous stacking and reclaim isessential. For Cementownia Warta the stockpile length is 102

metres with a base width of 38 metres and height of 16 metresgiving two stockpile zones each of 32,800 tonnes capacity forlimestone of density 1.45 tonnes per cubic metre and staticrepose angle 38°.

The system will be arranged to make one stockpile whilst theother is being reclaimed and effective interlocks are included toeliminate the risk of stacker and reclaimer collision.

In a typical cement plant the limestone blend will betransferred to the raw meal grinding station silos and furtherblended with other material before grinding to form the rawmeal for introduction to the kiln.

Reliability of this blend is essential if the kiln chemistry andtherefore clinker quality it to be maintained and since limestoneis generally 80% or more of the raw meal mix the quality andrepeatability of the limestone blend delivered to the raw mealsilos is critical.

Achieving this quality is not only a question of delivering theright combination of machinery and maintaining its performanceand reliability but also the effective control of the stockpilingprocess as a whole.

Schade has very wide experience in this market and hasamassed a wealth of knowledge in stockpiling and reclaimingsystems working in almost every conceivable environmenthandling almost every conceivable material type.

For the Cementownia Warta project the limestone is inertand invariable wet, and therefore dust generation andenvironmental pollution is not an issue. In this situationlongitudinal external stockpiles are an excellent solution.

However, there are many applications where externalstockpiles are not acceptable for environmental reasons.

In these applications there is an option to enclose thelongitudinal stockpile but generally the most economical answerfor enclosed systems is a circular storage.

Circular storage can include a radial boom stacker with acircular bridge type reclaimer all mounted within a dome designlight weight enclosure.

There are many alternatives of stockpile design and reclaimerspecification each with its own attributes. The final election ofstockpile solution depends not only on the material, blendingdemands and site layout but also on the environmentalperformance.

In all these areas Schade has the experience and know-howto deliver world class-solutions for a client’s individual project.

Shovels with central guidance.

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