CEMENT TECHNOLOGY North Texas Cement s new import terminal by Rex Wood, Vice-president of Marketing, Cambelt International Corp. and Brett Olaveson, Marketing Representative, Domtec International LCC North Texas Cement Company, a Texas Limited Partnership, composed of Houston-based Pioneer Concrete of America and Kansas-based Ash Grove Cement Co, is enjoying early success at its new cement import terminal. The cement handling and storage facility is located on a 2S-acre parcel of ground on the Houston Ship Channel. The facility's proximity to major highways and railroads makes the Houston Ship Channel a desirable location for the import facility. North Texas Cement distributes incoming cement to customers throughout the south Texas market. Cement is currently being imported from Greece and Denmark. North Texas Cement decided to proceed with a Houston area cement terminal in late 1995. In fact, 14 December, 1995 marked the ground breaking ceremony The first bulk ship with 30,000t of cement arrived less than 12 months later, on 5 December, 1996. The following design requirements were originally outlined by management. Modify existing dock to accommodate vessels of 42,000t capacity. Silos with a total storage capacity of 70,000t of cement to be built near the dock, on a narrow site with low soil bearing capacity Provide a ship unloader with low dust emission, 400st (short tons) per hour rated capacity and capable of pneumatically conveying the unloaded cement to either of two silos for storage. Automated reclaim from storage silos at 400t per hour and transfer to the rail and truck load-out day bins on a conveyor with a slope of 16'. Double scale with truck load out for two types of cement. Rail service both inbound and outbound. Barge loading capability. The engineering and construction team was assembled, on the basis of their knowledge, experience, commitment to achieving necessary completion schedules, and ability to give full consideration to interrelated and overall costs. Notable examples of decisions reflecting relationships of weight, cost, time and safety are: Compressors for pneumatically conveying cement from ship unloader to domes are not mounted on moveable gantry. The gantry-mounted ship unloader has only two pressure conveying vessels rather than the usual four, in order to reduce weight on the dock structure, which itself is not supported on ideal subgrade material. *The use of one large conveying line from the pressure vessel manifold, instead of two small lines with their extra valves and controls. Use of the old shallow port dock as a platform from which to build the new deep
D O M E S T O R A G E The following engineering and construction firms, directed by their senior representatives worked closely with the owner to achieve the overall design and construction goals. Product/ engineering Company Contact Air belt conveyors BGRS Fritz Kronmiller Civil & contract documents PEC CV Flores and Arnold DeAnda Concrete domes Domtec International Mike Hunter Automated reclaim systems Cambelt International Corp Rex Wood and Kelly Bodily Dock Shiner Mosely Doug Hearne Dome foundations, tunnel & tower SCA Engineers Brad Crane Electrical RE Gardner Engineering Bob Gardner Foundation/geophysical Fugro McClelland Joseph Cibor Piping Nye Engineers Jim Nye and Walter Shield Project engineer/manager Patton H. Caldwell, PE Mechanical/load out ENDECO Engineers Jim Pedison Ship unloader Fuller-Kovako Fred Wuertele Steel silos Besser Appco Lloyd Garcias Construction superintendent Watkins Engineers Les White Dock and dome foundations NBG David Bloehm water dock. The new dock has the capacity to support moving reaction loads of about five hundred tons. *Use of pre-cast concrete panels for major portions of the dock to optimise speed and safety of its construction. The ship unloader A Fuller-Kovako pneumatic ship unloader was chosen, for both environmental and economic reasons (fig 2). The potential use of additional storage capacity at an adjacent facility was made even more attractive by the flexibility of the fully pneumatic ship unloader. Fuller-Kovako was able to offer a very economic solution by mounting the vacuum equipment on the travelling gantry and placing the rugged and reliable (although heavy) Fuller sliding vane compressors on the adjacent dock area. FullerKovako delivered a fully fabricated gantry, along with all the process equipment, directly to the dock in southeast Houston. North Texas then completed final assembly and erection of the ship unloader, onsite, during construction of the terminal. The first bulk ship with 30,000t of cement arrived on 5th December 1996. After some start-up adjustments on the terminal dust collection and control systems, the FullerKovako ship unloader was commissioned, almost flawlessly. The first unloading went so well that the commissioning crew and terminal management agreed to attempt performance tests. During these tests, the Fuller-Kovako commissioning crew accomplished an unprecedented event: by successfully completing all performance testing during unloading of the first ship. For the maximum capacity test, the unloader achieved 442tph, and more than 402tph during the longer duration "80/80" test, 10 per cent and 20 per cent more than the guaranteed values! Concrete storage domes North Texas Cement contracted with Domtec International of Idaho Falls, Idaho, US, for the supply of the two 35,000t cement storage domes, which were substantially completed within six months of the first civil excavation. Concrete domes have proved to be effective for storage of many bulk materials, including cement. The primary advantages
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 jib hoist. 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 of concrete domes include: *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 On-site construction began late in 1995 with placement of the reclaim tunnel and ring beam spread footings by NBG Contractors of Houston (fig 3). With footings in place, the dome shells were finished in a little less than four months, after which Trade Mark Constructors poured the dome floors. Then other local contractors constructed the covered entries and the head house curbs at the apex of each dome. Design engineering for the tunnel, ring beam and dome was by SCA Consulting Engineers of Houston, Texas. In an unexpected turn of events, the construction site, surrounded by the waters of the Port of Houston on three sides, did not require soil augmentation engineered fill or driving of piles. This, despite the load to soils associated with piling cement to a design depth greater than 70ft, which represents an interior volume utilisation of about 96 per cent. With a combined capacity of 70,000t, the two adjacent North Texas domes are con- nected by a common below-grade reclaim tunnel which is accessible from a point between the two domes or from either end. The tunnel, which conveys reclaimed product to above ground, for loading trucks, railcars, or barges has been designed to accommodate possible expansion should the owner require the addition of further storage capacity. Likewise, the North Texas Cement facility offers flexibility to allow for fluctuations in future market supply and demand. Depending on the flow of product into or out of the facility, domes may be filled and unloaded sequentially, to ensure complete turnover of stored product; or they may be unloaded simultaneously, to increase the required total reclaim rate. Successful dome construction requires both proper engineering and quality control of the construction process. Domtec International's structural consulting engineers are the most experienced in the world, for dome design. Domtec International's technicians have constructed many of the world's cement and fly ash storage domes, including the two largest: each with a capacity of at least 60,000t. Shotcreting a dome, by spraying overhead against a flexible form, is very different from other sprayed concrete applications. A superior skill level is critical to proper dome construction and quality. As each dome neared completion, concrete curbs were placed at the top, to accommodate a headhouse and dust collector (fig 4). Each dome also has a large drive-in doorway, including a hydraulically operated structural steel door, capable of withstanding the pressure from the stored cement. The automated reclaim system Automated reclaiming systems (fig 5), as manufactured by Cambelt International Corporation, have been installed in the two 35,000t storage domes. The Cambelt reclaim system allows the dome and its superior
strength to be most efficiently utilised. The marriage of the dome and reclaimer provide the following advantages at the North Texas Cement bulk handling facility. Superior protection of stored materials Major capital cost savings compared to other storage and reclaim systems Maximurn 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 following 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 Figure 5 A Cambelt reclaimer in Horizontal position, dome empty. D O M E S T O R A G E Figure 6: TYPICAL RECLAIM SYSTEM The automated reclaiming equipment normally consists of (1) Mechanical or pneumatic load-in; (2)Headhouse column drive equipment; (3) Rotating screw reclaimer;and (4) controlled discharge and mechanical or pneumatic load out. An equipment mounting platform Headhouse column drive equipment Controlled discharge and mechanical load-out Emergency discharge hoppers Automated reclaim of the cement is initiated by activating the fluidised bin bottom at the base of the rotating centre column. During phase I of the reclaim cycle, material flows to a "rathole", by gravity, without the use of the reclaim screw (fig 7). During phase 2, the material is reclaimed using a combination of gravity and screw reclaim. Only during phase 3 does the mechanical screw, by itself, pull the remaining material to the reclaim opening. The reclaimer column support base is mounted in beam pockets built into tunnel walls. On its top side, the support base carries the entire load of the reclaimer; while from below, it also supports the controlled discharge equipment. Rotation of the centre column is achieved by a drive assembly located inside the head house at the top of the dome. The drive equipment includes a large gear box system, manufactured by Falk. The bridge truss supports an open reclaimer screw. The bridge truss is attached to the rotating centre column by a massive pin connection. The entire bridge screw drive, and reclaim screw were fully assembled and aligned in Cambelt International's production facility, then disassembled for shipment. An observation and maintenance platform is installed just below the headhouse at the top of the rotating centre column. Access is through a hatchway in the drive assembly platform (headhouse floor). A programmable logic controller automatically provides the required flow of material to the centre discharge. This is done by sensors throughout the system that provide data to the PLC, which adjusts the column's rotational speed and the depth of the screw's cut into the cement pile. The graphical manmachine interface software provides an easy-to-operate control system. Modem-based technical support is provided, including the capability for 24 hour on-line training and trouble shooting Ȧlthough the Cambelt reclaimer is designed to reclaim virtually 100 per cent of the stored material, additional emergency discharge openings are designed into each reclaim system, as a precautionary maintenance feature. These allow partial reclaim, by gravity, allowing access to the screw, through the dome's large drive-in door.
Load-Out Conveyor North Texas Cement purchased the AirBelt air -supported load-out belt conveyor because the belt conveyor is located outdoors and must protect the product from weather. It must contain dust, require minimal maintenance, and consume a minimum amount of energy The totally enclosed radiussed 16' inclined conveyor, 36 inches wide by 500 feet long, transports cement from under a dome to hoppers about 250 feet away (fig. 8). It is fabricated of painted carbon steel and conveys 445 tons per hour of cement at 60 pounds per cubic foot at a belt speed of 380 feet per minute, with a 75 HP motor. The air supported belt has no troughing idlers except in the loading sections. Summary The recently completed North Texas Cement import terminal, located on the Houston Ship Channel is exceeding original operational goals. Design of the complete facility incorporated state-ofthe-art components, selected not only for economy, but also for their versatility and proven track record of effective performance in bulk cement. Figure 7: The reclaiming phases. Phase 1 - Gravity Reclaiming Phase 2 - Gravity and Screw Reclaiming Authors: Rex Wood, Vice President of Marketing, Cambelt International Corp. Salt Lake City, Utah, United States. Fax: +1801972 5522 Brett Olaveson, Marketing Representative, Domtec International LLC Idaho Falls, Idaho, United States Fax: +1208 522 5344 Phase 3 - Screw Reclaiming to Dome Floor Alternate Loading and Unloading System used for storing materials that are not free flowing. Figure 8 Shows the loadout system.