THE WORLD’S LARGESTCEMENT STORAGE DOME

IntroductionCement storage domes are now being constructedlarger and larger. HoInam Inc.'s new 90 000 t capacitydome at its Clarksville, Missouri plant, USA, is currentlythe world's largest.

The Clarksville plant, one of Holnam's most efficientand profitable plants, is located on the MississippiRiver, north of St. Louis (Figure 1). The additionalstorage benefits the Clarksville plant in at least threeways: Firstly, due to the additional capacity offeredby the new storage facilities, the plant is able to usethe winter months to grind clinker and build up a largestockpile of cement to start the peak season eachyear, in readiness for the heavy summer demands.Secondly, grinding through the winter costs less dueto electrical rates being approximately 50% lowerthan summer season rates. Finally, less clinker hasto be stored outside on the ground, reducingenvironmental impact and improving cement quality.

DesignDuring the latter part of 1997, Holnam hired RiverConsulting Inc. to develop a preliminary design andproject budget. The conceptual design was developedin association with Holnam's technical and plantpersonnel. Two basic schemes were considered: eithertwo smaller domes or one larger dome, capable of storingup to 90 000 t. It was understood that this would be thelargest cement storage dome ever constructed.Foundation design was a major issue, since the storagedome was to be constructed over what was then achannel, leading to the plant's retention ponds.

After evaluating all the issues, including filling and thereclaim system options, the recommendation was madeto proceed with a single dome. The dome would be filledusing an existing pneumatic conveying system (Figure2). Cement is withdrawn by a Cambelt mechanicalreclaim system, which feeds a belt conveyor in a tunnelunderneath the floor of the dome (Figure 3). The reclaimconveyor delivers cement

Mike Hunter, DOMTEC International, LLC, USA, and Rex Wood,Cambelt International Corp., USA, describe the construction of a 90 000 t

cement storage dome, the world's largest, at HoInam Inc.'s Clarksville plant, USA.*Additional information supplied by HoInam, Inc., USA, and River Consulting, Inc., USA.

Figure 1. Holnam’s new 90,00 t cement storage dome

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to an airlift which feeds a MODCO pneumatic transportsystem or discharges directly into an auxiliary truckload-out station situated above a truck scale.

River Consulting's study and recommendationsprovided HoInam with the necessary information tomove forward. HoInam then hired the company toprovide detailed engineering and to manage theproject's complete construction, including site andbudget management and qual i ty control .

This design and construction managementapproach had been successfully executed by RiverConsulting at HoInam's import terminal at Reserve,Louisiana, in 1997. This approach allowed theClarksville facility to be completely designed andconstructed within a 12 month schedule. it also gaveHoInam complete control over selection andprocurement of equipment and subcontractors. As aresult, the project was completed in accordance withthe conceptual design, on schedule and within RiverConsulting's original proposed budget.

Concrete storage domesConcrete domes have proven to be effective forstorage of many bulk materials, including cement(Figure 4). The primary advantages of concrete domesinclude:• Superior protection of the stored material.• Strength and durability.• Low cost per ton construction cost.• Excellent environmental control and containment

of dust.• Rapid construction, regardless of weather.

Domtec International was selected to construct thelarge 90 000 t cement storage dome. Beforeconstruction of the dome began, a drilled pierfoundation and sub grade reclaim tunnel were built,and a heavily reinforced concrete slab poured to actas the roof of the tunnel and the floor of the dome.Domtec International's work then began asconstruction equipment and reinforcement bars werestockpiled on the concrete mat. The large dome

shaped air form, made of single ply roofing fabric, wasthen attached to the edge of the concrete foundation andinflated. Once inflated to its near hemispherical shape,polyurethane foam was sprayed to the interior surface.Reinforcement bars were next tied in place as requiredby the structural engineer. Finally, skilled DomtecInternational nozzlemen sprayed shotcrete to properlyembed the rebars and achieve the designed concretethickness.

As the dome neared completion, concrete curbswere formed at the top of the dome to accommodate ahead house and dust filters. Meanwhile, a large drive-indoorway, including a hydraulically operated structuralsteel door, was constructed.

DOME FROM DOME

Successful dome construction requires both properengineering and quality control of the constructionprocess, and Domtec International's technicians havenow been involved with the construction of approximately70% of the world's cement storage domes, including allof the six largest.

With the popularity of domes increasing, prospectiveclients should be aware that not all domes are the same.They can be constructed out of aluminum, steel or, asat Clarksville, reinforced concrete. Metallic domes performmerely as covers, while concrete domes can also performas containers, allowing materials to be piled high againstthe walls. Different storage applications require differentstorage solutions. The performance requirements of eachapplication usually determine which type of dome is mostsuitable.

Even concrete domes are not all the same. For example,two concrete domes of identical dimensions could beconstructed using substantially different quantities ofConcrete and rebar, depending primarily on the structuraldesign. HoInam's Clarksville dome was designed andconstructed in accordance with established, provenengineering standards which have been used for themajority of the world's cement storage domes.

Figure 2 (left). Load in pneumatic conveying systemand auxiliary truck load out station.

Figure 3 (below). Load out belt conveyor located intunnel.

Automated reclaim system

The dome was installed with Cambelt InternationalCorporation's automated mechanical system, of whichthere are now approximately 20 systems operating inthe cement industry. This system allows the volume ofthe dome to be more efficiently utilised, as the reclaimsystem can be buried within the cement storage pile.The marriage of the dome and reclaimer provide thefollowing advantages:• Superior protect ion of stored materials.• Major cost savings compared to other storage

and reclaim systems.• Maximum utilisation of the storage space inside

the dome.• Virtually 100% reclaim of the stored materials.• High reclaim rates.• Reduced operating and maintenance costs.• No personnel working inside the dome: a major

safety feature.• Excellent environmental control.The Cambelt reclaiming system consists of the followingcomponents (Figure 5):• A mechanical load-in conveyor system.• A centre column support base.• A rotating centre column.• A support bridge and rotating screw reclaimer.• A cable hoist for raising and lowering the bridge.• An observation and maintenance platform.• Headhouse column drive equipment.• Controlled discharge and mechanical load-out.• Emergency discharge hoppers.Automated reclaim of the cement is initiated by activatingthe fluidised bin bottom at the base of the rotatingcentre column. During the first phase, the reclaim cycle,cement flows to a rat hole by gravity, without the needfor a reclaim screw (Figure 6). During the second phase,cement is reclaimed using a combination of gravity and

screw reclaim. Only during the third phase does themechanical screw pull the remaining cement to thedischarge. The reclaimer column support base is mountedin beam pockets built into the tunnel walls. On its top side,the support base carries the entire load of the heavyreclaimer, while from below, it also supports the controlleddischarge equipment.

Figure 5. Automated reclaim system.

Figure 6. Typical dome loading and gravity reclaimig (phase 1)

Figure 7. Bridge truss, reclaim screw, and rotating centre column.

Rotation of the centre column is achieved by a driveassembly located inside the headhouse at the top of thedome. The drive equipment includes a large gear boxsupplied by Falk. The bridge truss supports an openreclaimer screw and is attached to the rotating centrecolumn with a pin connection. The entire bridge screwdrive and reclaim screw were fully assembled and aligned,then disassembled for shipment (Figure 7).

An observation and maintenance platform was installedjust below the headhouse at the top of the rotating centrecolumn. Access is through a hatchway in the driveassembly platform in the headhouse f loor.

Utilising the services of Trimax Systems Inc., Cambeltincluded a fully automated central control. A ModiconPLC is used to control the Cambelt reclaimer. The PLCis interfaced with an IBM compatible PC, using the'Wonderware InTouch' graphical man-machine interface,graphics control package (Figure 8).

The programmable logic controller, processing datareceived from sensors, automatically provides the required

flow of material to the centre discharge. This isaccomplished by adjusting the rotational speed of thecolumn and the depth of the screw's cut into the cementpile. Modem support is provided, including the capabilityfor 24 hr per day support, on-line training andtroubleshooting.

Although the Cambelt reclaimer is designed to reclaimvirtually 100% of the stored material, additional emergencydischarge openings are designed into each reclaimsystem as a precautionary maintenance feature. Theseallow partial reclaim by gravity, facilitating access to thescrew through the large drive-in door (Figure 9).

Pre-assembly of the steel structures and preparation forinstallation of reclaim equipment took place outsideduring the final stages of construction. Installation thentook place within a matter of weeks.

Cambelt's mechanical reclaimer will remove all the storedcement to within a few inches of the dome floor uponcommand. Each dome discharge cycle is predictably thesame as the previous one. The operation of the reclaimer

is not affected by the tendency of stored cementto compact into a cohesive mass as a reactionto pile pressures, humidity and time.

Summary

HoInam's new Clarksville dome is anenvironmentally friendly storage solution (Figure4) providing HoInam increased capacity forimproved plant efficiency, better quality andservice for its clients. Design and constructionmanagement of the complete facility wasperformed by River Consulting, incorporatinga high quality Domtec concrete dome and stateof the art material handling equipment. Thisincluded Cambelt's mechanical reclaim systemand other components selected not only foreconomic advantages but also for versatilityand proven track record of effectiveperformance in bulk cement handling.

Figure 8. Typical terminal computer control screen.

Enquiry no: 7