Within the past two years, three dome silostorage systems handling cement wereplaced into operation. The systems areunique since the dome structure hadpreviously not been used for storage ofcement. Materials normally stored withinthe domes are fertilizer, grain, coal and salt.The dome now provides an alternatemethod of silo storage to the cementindustry.

Two of the three cement storage domeswere constructed for Independent CementCorporation as the result of a companysearch for cost-effective ways to expand itsstorage capacity. One of the domes wasbuilt at Independent's Everett,Massachusetts terminal and an identical onewas built at their Providence, Rhode Islandterminal. Both of these dome structures are122 ft inside diameter, 85 ft tall and willstore up to 25,000 tons of cement.According to Scott Horton, TerminalOperations Manager for the Everett andProvidence facilities, project cost for eachdome was about US$ 4 million ,approximately one-third (1/3) the cost ofbuilding conventional silos with the samestorage space (Fig. 1).

The third dome storage system was built forDelta Cement Corporation in Georgetown,South Carolina. Tom Darrah, formerPresident of Delta Cement Corporation, alsostated substantial savings in constructioncost were realized for this terminal. SanteePortland Cement Corporation of Holly Hillbought the facility in May, 1989 from DeltaCement Corporation while it was underconstruction.

The Delta Cement dome is 92 ft insidediameter. 112 ft high with a 20,000-tonstorage capacity. A 26 ft wide arched truckdrive-thru is at the base of the silo. Trucks areloaded at the center of the silo.

All of the concrete placement for the shelltakes place inside the air-supported fabric,or airform, so weather is no problem. Noconstruction dirt or dust is released to theatmosphere. Crews can work around-the-clock inside. The PVC coated airformprotects the dome from leaks, whileproviding a form for attaching rebars for thestructural concrete shell.

The contractor for the projects DomeSystems Corporation, a Division of PorterGrain Systems, Inc. of Rensselaer, Indiana,used two (2) 12-hour crews to construct thedome once the base was prepared. The shellthickness for the 122 ft diameter domevaries from 18 inches at the bottom to 6inches at the top. The 92 ft diameter domeshell thickness varies from 24 inches to 6inches.

All three domes have piling foundationswith the circular concrete footing for thedome perimeter and the pile caps creating acontinuous concrete floor slab for the dome. The airform is placed on the center of theslab with a crane. Workers unravel the hugefabric and then they roll the membrane backfar enough to allow stockpiling of all rebarsrequired for the job on the slab, position thecrane on the slab, and drape the membrane

back over the equipment and materials. Tohold the fabric while it is being inflated, a1/4 inch x 2 inch steel girdle is positionedaround the perimeter of the footing withanchor bolts. Below this girdle, the excessportion of the airform is wrapped around aone-inch diameter rope, forming a relativelythick bead to prevent the fabric fromslipping loose. The airform is inflated in lessthan two hours. Electric motor operatedblowers are backed up with diesel drivenunits in case of a power failure. With theairform fully inflated, workers can enter andexit the interior via an airlock - a double-door entry which prevents air loss - andproceed to cover the interior of the airformwith 2 inches of urethane insulation. Metalhangers are embedded in the urethaneinsulation to position the rebars. Highstrength ready mix shotcrete is sprayed onthe interior structure.

Reclaim from these large diameter domespresented a challenge to Fuller. The concernwas to be able to effectively withdraw thecement to obtain maximum storageutilization of the essentially flat bottomdome storage silo. Fuller's experiencewith reclaim of cement from largediameter cement storage silos pointed to

E.T. Mitman, USA

Dome SiloStorage Systems

Volume 11, Number 1, March 1991

Mr. Edward T. Mitman, Senior Applications Engineer,

Pneumatic Conveying Dept., Fuller Company, 2040 Avenue

C, Bethlehem, PA 18017, USA

Fig. 1: Dome Silo Storage installation at Everett and Providence Terminal. An identical dome is at Everett.

two possible solutions. One solution was touse multiple outlets on the periphery of thesilo. The second solution was to use acentral inverted cone with multiple outlets.Both solutions required the silo floor to besloped toward the outlets and the floor tobe covered with Fuller open type Airslide airgravity conveyors. It was decided to use thecentral inverted cone with multiple outletsfor all three of the dome silo storage systemspresently in operation.

The interior of the 122 ft diameter domes atProvidence and Everett are identical. Thecentral inverted cone base is octagonshaped having a 26'-6" dimension acrossflats on the interior of the dome. There areeight outlets at the base of the cone. The silofloor is segmented into eight sections witheight radial 24 inch wide (active width) opentype Airslide air gravity conveyors extendingfrom the outlet to the exterior wall andinclined at 10" slope toward the outlet.Feed open type Airslide air gravity conveyorswere installed on both sides perpendicularto the radial Airslide conveyor. The feedsections are also inclined at a 10" slopetoward the radial sections and arepredominantly 24 inch size.

Approximately, 3,800 ft of open typeAirslide conveyor was installed in one week.The active fabric area coverage isapproximately 65%, which is about as tightas the Airslide conveyors can be installed.

The open type Airslide conveyors haveplenum piping to facilitate the piping ininstallation. In addition, the aeration air tothe feed sections is zoned to minimize theair volume and power requirements forfluidizing during normal withdrawal.Multiple blowers permit several modes offluidization depending on the level ofmaterial in the silo. Power consumption forwithdrawal can be as low as 0.1 - 0.2 kWhper ton.

Withdrawal can be from one or moreoutlets simultaneously depending on plantrequirements. The Everett terminal has oneFuller-Kinyon pump located in the octagonroom. Withdrawal is from one outlet at atime and sequenced to each of the eightoutlets on a timed cycle. Provisions include afuture pump. The Providence terminal, hastwo Fuller ModuDense pressure tankconveying systems which can operateindependently or simultaneously.Withdrawal from the dome silo is from oneoutlet at a time when one ModuDenseconveying system is in operation. Whenboth conveying systems are in operation,withdrawal is from two outlets.

Each outlet is equipped with an air operatedrotary flow control valve and a manualemergency cut-off gate. The cut-off gate isequipped With an access cover downstreamof the guillotine type gate for inspection andremoval of lumps. Lumps are a commonproblem when receiving cement in bulkcarriers. Frequently, the ship hatches are nottight enough and have not been sealedsufficiently to prevent formation of lumps.Preferably lumps should be removed prior tostorage.

The transfer of cement from the dome siloto loadout silos is performed underautomatic control. The control cabinethouses a programmable controller anddevices necessary for automatic control ofthe withdrawal and conveying operation.The automatic control system sequences theequipment into operation. Each startingstep is performed automatically in anadjustable time duration and in apredetermined sequence. Automaticoperation continues until the operator stopsit or a situation arises which causes ashutdown. Each shutdown step is alsoperformed automatically.

The room under the converted cone

contains the withdrawal equipment, aircontrol valves for silo operation and awithdrawal dust collector. The four 300 ftModuDense tanks were buried to minimizehead room requirements.

Virtually total cleanout has beenexperienced. The 122 ft inside diameterdome silo had a residue of less than 300 t.

The 92 ft inside diameter dome silo atGeorgetown has six outlets with Airslideconveyors delivering to a central bulkloading spout for loading trucks. In this case,19 inches open type Airslide conveyors wereused to aid in withdrawal of the cement.The radial Airslide conveyors are also at a 10slope toward the outlet. The feed Airslideconveyors are at a 10 slope toward theradial Airslide conveyors.

The open type Airslide conveyors haveplenum piping to facilitate the pipinginstallation. In addition, the aeration air tothe open type Airslide is zoned to minimizethe air volume and power requirements forfluidizing during normal withdrawal.Multiple blowers permit several modes offluidization depending on the level ofmaterial in the silo.

Withdrawal is from one outlet at a time andsequenced to each of the six outlets on atimed cycle.

The withdrawal system is designed to load25 ton trucks in five minutes. The bulkloading spout and dust collector arecentrally located under the central invertedcone. The truck scale is located in the 26 ftwide x 14 ft 6 inch high drive-thru. Flowcontrol valves are three (3) position rotarytype to permit full flow, dribble flow andfinal cut-off from appropriate weightsignals.

In the cases cited, the dome silo providedthe most economical solution for the totalproject. It must also be noted that the domesilo will not always be the most economicalchoice. Cost estimates for the total projectshould be compared using bothconventional slip form silos and dome silosbefore making the final decision.

On the other hand, when reclaim from largediameter silos is required, the scheme aspresented proved to be invaluable. Thecentral inverted cone with controlled flowfrom multiple outlets provides: High reliability due to more outlets Virtually total cleanout Side discharge arrangement to minimize

headroom requirements Simple equipment installation Easy and secure maintenance access Low power consumption Usable space under the cone for dust

collection equipment

Volume 11, Number 1, March 1991Dome Silo Systems

Fig. 2: Interior of storage facility showing Fullers open type Airslide conveyors

TM

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