World Largest Cement Storage Dome
Original Print Article Below
Mike Hunter, WORLD DOMES LLC, USA and Rex Wood Cambelt International Copr., USA, describe the construction of a 90,000 ton cement storage dome, the world's largest, at Holnam Inc's Clarksville plant, USA.
Introduction
Cement storage domes are now being constructed larger and larger. HoInam Inc.’s new 90 000 t capacity dome at its Clarksville, Missouri plant, USA, is currently the world’s largest.
The Clarksville plant, one of Holnam’s most efficient and profitable plants, is located on the Mississippi River, north of St. Louis. The additional storage benefits the Clarksville plant in at least three ways: Firstly, due to the additional capacity offered by the new storage facilities, the plant is able to use the winter months to grind clinker and build up a large stockpile of cement to start the peak season each year, in readiness for the heavy summer demands. Secondly, grinding through the winter costs less due to electrical rates being approximately 50% lower than summer season rates. Finally, less clinker has to be stored outside on the ground, reducing environmental impact and improving cement quality.
Design
During the latter part of 1997, Holnam hired River Consulting Inc. to develop a preliminary design and project budget. The conceptual design was developed in association with Holnam’s technical and plant personnel. Two basic schemes were considered: either two smaller domes or one larger dome, capable of storing up to 90 000 t. It was understood that this would be the largest cement storage dome ever constructed. Foundation design was a major issue, since the storage dome was to be constructed over what was then a channel, leading to the plant’s retention ponds.
After evaluating all the issues, including filling and the reclaim system options, the recommendation was made to proceed with a single dome. The dome would be filled using an existing pneumatic conveying system. Cement is withdrawn by a Cambelt mechanical reclaim system, which feeds a belt conveyor in a tunnel underneath the floor of the dome. The reclaim conveyor delivers cement o an airlift which feeds a MODCO pneumatic transport system or discharges directly into an auxiliary truck load-out station situated above a truck scale.
River Consulting’s study and recommendations provided HoInam with the necessary information to move forward. HoInam then hired the company to provide detailed engineering and to manage the project’s complete construction, including site and budget management and quality control.
This design and construction management approach had been successfully executed by River Consulting at HoInam’s import terminal at Reserve, Louisiana, in 1997. This approach allowed the Clarksville facility to be completely designed and constructed within a 12 month schedule. it also gave HoInam complete control over selection and procurement of equipment and subcontractors. As a result, the project was completed in accordance with the conceptual design, on schedule and within River Consulting’s original proposed budget.
Concrete Storage Domes
Concrete domes have proven to be effective for storage of many bulk materials, including cement. The primary advantages 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.
World Domes was selected to construct the large 90,000 t cement storage dome. Before construction of the dome began, a drilled pier foundation and sub grade reclaim tunnel were built, and a heavily reinforced concrete slab poured to act as the roof of the tunnel and the floor of the dome. World Domes International’s work then began as construction equipment and reinforcement bars were stockpiled on the concrete mat. The large dome shaped air form, made of single ply roofing fabric, was then attached to the edge of the concrete foundation and inflated. Once inflated to its near hemispherical shape, polyurethane foam was sprayed to the interior surface. Reinforcement bars were next tied in place as required by the structural engineer. Finally, skilled Domtec International nozzlemen sprayed shotcrete to properly embed the rebars and achieve the designed concrete thickness.
As the dome neared completion, concrete curbs were formed at the top of the dome to accommodate a head house and dust filters. Meanwhile, a large drive-in doorway, including a hydraulically operated structural steel door, was constructed.
Automated Reclaim System
The dome was installed with Cambelt International Corporation’s automated mechanical system, of which there are now approximately 20 systems operating in the cement industry. This system allows the volume of the dome to be more efficiently utilised, as the reclaim system can be buried within the cement storage pile. The marriage of the dome and reclaimer provide the following advantages:
• Superior protection 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 following components
• 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.
Rotation of the centre column is achieved by a drive assembly located inside the headhouse at the top of the dome. The drive equipment includes a large gear box supplied by Falk. The bridge truss supports an open reclaimer screw and is attached to the rotating centre column with a pin connection. The entire bridge screw drive and reclaim screw were fully assembled and aligned, then disassembled for shipment.
An observation and maintenance platform was installed just below the headhouse at the top of the rotating centre column. Access is through a hatchway in the drive assembly platform in the headhouse floor.
Utilising the services of Trimax Systems Inc., Cambelt included a fully automated central control. A Modicon PLC is used to control the Cambelt reclaimer. The PLC is interfaced with an IBM compatible PC, using the ‘Wonderware InTouch’ graphical man-machine interface, graphics control package.
The programmable logic controller, processing data received from sensors, automatically provides the required flow of material to the centre discharge. This is accomplished by adjusting the rotational speed of the column and the depth of the screw’s cut into the cement pile. Modem support is provided, including the capability for 24 hr per day support, on-line training and troubleshooting.
Although the Cambelt reclaimer is designed to reclaim virtually 100% 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, facilitating access to the screw through the large drive-in door.
Pre-assembly of the steel structures and preparation for installation of reclaim equipment took place outside during the final stages of construction. Installation then took place within a matter of weeks.
Cambelt’s mechanical reclaimer will remove all the stored cement to within a few inches of the dome floor upon command. Each dome discharge cycle is predictably the same as the previous one. The operation of the reclaimer is not affected by the tendency of stored cement to compact into a cohesive mass as a reaction to pile pressures, humidity and time.
Summary
HoInam’s new Clarksville dome is an environmentally friendly storage solution providing HoInam increased capacity for improved plant efficiency, better quality and service for its clients. Design and construction management of the complete facility was performed by River Consulting, incorporating a high quality Domtec concrete dome and state of the art material handling equipment. This included Cambelt’s mechanical reclaim system and other components selected not only for economic advantages but also for versatility and proven track record of effective performance in bulk cement handling.
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