by Rex Wood, Vice-president of Marketing, Cambelt International Corp.and Brett Olaveson, Marketing Representative, Domtec International LCC

North Texas Cement’snew import terminal

North Texas Cement Company, a Texas Limited Partnership, composedof Houston-based Pioneer Concrete of America and Kansas-based AshGrove Cement Co, is enjoying early success at its new cement importterminal. The cement handling and storage facility is located on a 2S-acreparcel of ground on the Houston Ship Channel.

The facility's proximity to majorhighways and railroads makesthe Houston Ship Channel adesirable location for the importfacility. North Texas Cement

distr ibutes incoming cement tocustomers throughout the south Texasmarket. Cement is currently beingimported from Greece and Denmark.

North Texas Cement decidedto proceed with a Houston area cementterminal in late 1995. In fact, 14December, 1995 marked the groundbreaking ceremony The first bulk shipwith 30,000t of cement arrived less than12 months later, on 5 December , 1996.The following design requirements wereoriginally outlined by management.• M o d i f y e x i s t i n g d o c k t oaccommodate vessels of 42,000tcapacity.

•Silos with a total storage capacity

of 70,000t of cement to be built nearthe dock, on a narrow site with lowsoil bearing capacity

•Provide a ship unloader with low dustemission, 400st (short tons) per hourrated capacity and capable ofpneumatical ly conveying theunloaded cement to either of two silosfor storage.

•Automated reclaim from storage silosat 400t per hour and transfer to therail and truck load-out day bins on aconveyor with a slope of 16'.

• Double scale with truck load out fortwo types of cement.

•Rail service both inbound andoutbound.

• Barge loading capability.T h e e n g i n e e r i n g a n d

construction team was assembled, onthe basis of their knowledge,experience, commitment to achieving

necessary completion schedules, andability to give full consideration tointerrelated and overall costs. Notableexamples of decisions reflectingrelationships of weight, cost, time andsafety are:•Compressors for pneumaticallyconveying cement from ship unloaderto domes are not mounted on moveablegantry.•The gantry-mounted ship unloader hasonly two pressure conveying vesselsrather than the usual four, in order toreduce weight on the dock structure,which itself is not supported on idealsubgrade material.*The use of one large conveying linefrom the pressure vessel manifold,instead of two small lines with theirextra valves and controls.• Use of the old shallow port dock as aplatform from which to build the newdeep

CEMENT TECHNOLOGY

water dock. The new dock has thecapacity to support moving reactionloads of about five hundred tons.

*Use of pre-cast concrete panels formajor portions of the dock to optimisespeed and safety of its construction.

The ship unloader

A Fuller-Kovako pneumatic shipunloader was chosen, for bothenvironmental and economic reasons(fig 2). The potential use of additionalstorage capacity at an adjacent facilitywas made even more attractive by theflexibility of the fully pneumatic shipunloader. Fuller-Kovako was able tooffer a very economic solution bymounting the vacuum equipment onthe travelling gantry and placing therugged and reliable (although heavy)Fuller sliding vane compressors on theadjacent dock area. FullerKovakodelivered a fully fabricated gantry, alongwith all the process equipment, directlyto the dock in southeast Houston. NorthTexas then completed final assemblyand erection of the ship unloader, on-site, during construction of the terminal.

The first bulk ship with 30,000t ofcement arrived on 5th December 1996.After some start-up adjustments on theterminal dust collection and controlsystems, the FullerKovako shipunloader was commissioned, almostflawlessly. The first unloading went sowell that the commissioning crew andterminal management agreed to attemptperformance tests. During these tests,the Fuller-Kovako commissioning crewaccomplished an unprecedented event:by successful ly completing al lperformance testing during unloadingof the first ship. For the maximum

capacity test, the unloader achieved442tph, and more than 402tph duringthe longer duration "80/80" test, 10 percent and 20 per cent more than theguaranteed values!

Concrete storage domesNorth Texas Cement contracted withDomtec International of Idaho Falls,

Idaho, US, for the supply of the two35,000t cement storage domes, whichwere substantially completed withinsix months of the first civil excavation.

Concrete domes have provedto be effective for storage of many bulkmaterials, including cement. Theprimary advantages

The following engineering and construction firms, directed by their senior representatives workedclosely with the owner to achieve the overall design and construction goals.

Product/ engineering Company Contact

Air belt conveyors BGRS Fritz KronmillerCivil & contract documents PEC CV Flores and Arnold DeAndaConcrete domes Domtec International Mike HunterAutomated reclaim systems Cambelt International Corp Rex Wood and Kelly BodilyDock Shiner Mosely Doug HearneDome foundations, tunnel & tower SCA Engineers Brad CraneElectrical RE Gardner Engineering Bob GardnerFoundation/geophysical Fugro McClelland Joseph CiborPiping Nye Engineers Jim Nye and Walter ShieldProject engineer/manager Patton H. Caldwell, PEMechanical/load out ENDECO Engineers Jim PedisonShip unloader Fuller-Kovako Fred WuerteleSteel silos Besser Appco Lloyd GarciasConstruction superintendent Watkins Engineers Les WhiteDock and dome foundations NBG David Bloehm

D O M E S T O R A G E

Equipment synopsis: Fuller-Kovako model G-400-E gantry/rail mounted ship unloader,consisting of.

• One Fuller-Kovako vacuum arm, 3-section type with rotating base for 200' swing, hydraulic boom and auxiliary jibhoist. Dimensions of arm: 19m + 18m + 5m = 42m total length.

• One 150HP hydraulic control unit with 15HP cooling system• One 50ft x 40ft steel support gantry with 12 standard rail wheels, 4 of which are self-powered by electric motors.

Rail width is 32ø†-IOø†• One superstructure support tower with pedestal• One 18ft dia. filter receiver, model No. 328FR9 (6) TA.• Two 1 Oft dia. 900 of transfer vessels• Three 200HP, model 1228 RAS-J vacuum pump packages.• Three 400 HP Fuller C-608 conveying air compressors• One 50 HP Fuller-Davey Model 50BAQ control air compressor with 140 cf air receiver and twin tower dryer• Two 40ft x 8ft wide enclosures for mounting of MCC, vacuum pumps, control air compressor and office space.• One 1500kW stepdown voltage transformer from 4160 to 460 volt.• One motor control center, 450 VAC• One lot exterior area lighting• One PLC-type control panel, Allen Bradley, non CRT

D O M E S T O R A G E

of concrete domes include:*Superior protection of the storedmaterial *Strength and durability*Low cost-per-ton construction cost*Excellent environmental control andcontainment of dust• Rapid construction regardless ofweather

On-site construction began latein 1995 with placement of the reclaimtunnel and ring beam spread footingsby NBG Contractors of Houston (fig 3).With footings in place, the dome shellswere finished in a little less than fourmonths, after which Trade MarkConstructors poured the dome floors.Then other local contractors constructedthe covered entries and the head housecurbs at the apex of each dome. Designengineering for the tunnel, ring

beam and dome was by SCAConsulting Engineers of Houston,Texas.

In an unexpected turn ofevents, the construct ion si te,surrounded by the waters of the Portof Houston on three sides, did notrequire soil augmentation engineeredfill or driving of piles. This, despite theload to soils associated with pilingcement to a design depth greater than70ft, which represents an interiorvolume utilisation of about 96 per cent.

With a combined capacity of70,000t, the two adjacent North Texasdomes are con- nected by a commonbelow-grade reclaim tunnel which isaccessible from a point between thetwo domes or from either end. Thetunnel, which conveys reclaimedproduct to above ground, for loadingtrucks, railcars, or barges has beendesigned to accommodate possibleexpansion should the owner requirethe addition of further storage capacity.

Likewise, the North TexasCement facility offers flexibility to allowfor fluctuations in future market supplyand demand. Depending on the flowof product into or out of the facility,domes may befilled and unloadedsequentially, toensure completeturnover of storedproduct; or theymay be unloadedsimultaneously,to increase therequ i red to ta lr e c l a i m r a t e .Successful domec o n s t r u c t i o nrequ i res bo thproper engineeringand quality controlof the constructionprocess. Domtec

International's structural consultingengineers are the most experienced inthe world, for dome design. DomtecInternational's technicians haveconstructed many of the world's cementand fly ash storage domes, includingthe two largest: each with a capacity ofat least 60,000t. Shotcreting a dome,by spraying overhead against a flexibleform, is very different from other sprayedconcrete applications. A superior skilllevel is critical to proper domeconstruction and quality.

As each dome nearedcompletion, concrete curbs were placedat the top, to accommodate aheadhouse and dust col lector(fig 4). Each dome also has a largedr ive- in doorway, inc luding ahydraulically operated structural steeldoor, capable of withstanding thepressure from the stored cement.

The automated reclaim systemAutomated reclaiming systems (fig 5),as manufactured by Cambel tInternational Corporation, have beeninstalled in the two 35,000t storagedomes. The Cambelt reclaim systemallows the dome and its superior

D O M E S T O R A G Estrength to be most efficientlyutilised. The marriage of thedome and reclaimer providethe following advantages atthe North Texas Cement bulkhandling facility.• Superior protection of

stored materials• Major capital cost

savings compared toother storageand reclaim systems

• Maximurn utilisation ofthe storage space insidethe 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

controlThe Cambelt reclaiming

system consists of thefollowing components (fig 6).• 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

• An equipment mounting platform• Headhouse column drive equipment• Controlled discharge and

mechanical load-out• Emergency discharge hoppers

Automated reclaim of thecement is initiated by activatingthe fluidised bin bottom at thebase of the rotating centre column.During phase I of the reclaimcycle, material flows to a "rat-hole", by gravity, without the useof the reclaim screw (fig 7). Duringphase 2, the material is reclaimedusing a combination of gravity andscrew reclaim. Only during phase3 does the mechanical screw, byitself, pull the remaining materialto the reclaim opening. Thereclaimer column support base ismounted in beam pockets builtinto tunnel walls. On its top side,the support base carries the entireload of the reclaimer; while frombelow, it also supports thecontrolled discharge equipment.

Rotation of the centrecolumn is achieved by a driveassembly located inside the headhouse at the top of the dome. Thedrive equipment includes a largegear box system, manufacturedby Falk. The bridge truss supportsan open reclaimer screw. Thebridge truss is attached to therotating centre column by amassive pin connection. Theentire bridge screw drive, and

reclaim screw were fully assembledand aligned in Cambelt International'sproduction facility, then disassembledfor shipment.

A n o b s e r v a t i o n a n dmaintenance platform is installed justbelow the headhouse at the top ofthe rotating centre column. Access isthrough a hatchway in the driveassembly platform (headhouse floor).

A programmable logiccontroller automatically provides therequired flow of material to the centredischarge. This is done by sensorsthroughout the system that providedata to the PLC, which adjusts thecolumn's rotational speed and thedepth of the screw's cut into thecement pile. The graphical man-machine interface software providesan easy-to-operate control system.Modem-based technical support isprovided, including the capability for24 hour on-line training and troubleshooting.

Al though the Cambeltreclaimer is designed to reclaimvirtually 100 per cent of the storedmaterial, additional emergencydischarge openings are designed intoeach rec la im system, as aprecautionary maintenance feature.These allow partial reclaim, by gravity,allowing access to the screw, throughthe dome's large drive-in door.

Figure 5 A Cambeltreclaimer in Horizontalposition, dome empty.

Figure 6: TYPICAL RECLAIM SYSTEMThe automated reclaiming equipment normally consists of (1) Mechanical or pneumatic load-in;

(2)Headhouse column drive equipment; (3) Rotating screw reclaimer;and (4) controlled dischargeand mechanical or pneumatic load out.

Load-Out ConveyorNorth Texas Cement purchased theAirBelt air -supported load-out beltconveyor because the belt conveyor islocated outdoors and must protect theproduct from weather. It must containdust, require minimal maintenance, andconsume a minimum amount of energy

The totally enclosed radiussed 16'inclined conveyor, 36 inches wide by 500feet long, transports cement from undera dome to hoppers about 250 feet away(fig. 8). It is fabricated of painted carbonsteel and conveys 445 tons per hour ofcement at 60 pounds per cubic foot at abelt speed of 380 feet per minute, witha 75 HP motor. The air supported belthas no troughing idlers except in theloading sections.

SummaryThe recently completed North TexasCement import terminal, located on theHouston Ship Channel is exceedingoriginal operational goals. Design of thecomplete facility incorporated state-of-the-art components, selected not onlyfor economy, but also for their versatilityand proven track record of effectiveperformance in bulk cement.

Authors:

Rex Wood, Vice President of Marketing, CambeltInternational Corp.Salt Lake City, Utah, United States.Fax: +1801972 5522Brett Olaveson, Marketing Representative, DomtecInternational LLCIdaho Falls, Idaho, United StatesFax: +1208 522 5344

Figure 8 Shows the load-out system.

Phase 1 - Gravity Reclaiming

Phase 2 - Gravity and Screw Reclaiming

Phase 3 - Screw Reclaiming to Dome FloorAlternate Loading and Unloading System usedfor storing materials that are not free flowing.

Figure 7: The reclaiming phases.