A Second Dome for Senegal

A Second Dome for Senegal

Cile Montgomery, Geometrica, USA, provides a case study on the most recent custom storage dome installed at Les Ciments du Sahel’s plant in Senegal.

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Introduction When Senegalese cement production company Les Ciments du Sahel S.A. sought an additional 3600 tpd of output from its facility, it turned to the engineering services company, Cement Engineering S.A. (CESA), who partnered with Geometrica, the storage dome design and manufacturing firm, to create a custom-engineered bulk storage and blending solution. The Les Ciments du Sahel cement production facility is located in Kirène, Senegal, approximately 70 km from Dakar, the capital city of Senegal, which serves as a major regional port and financial centre for the country.

[BMHR 12] Reprinted from worldcement.com

In 2002, CESA commissioned Geometrica to design and build the plant’s first storage and blending dome.

The 2010 effort to increase the cement plant’s production capacity required the addition of a second production line, which included a raw grinding system; a tangential blending silo; a preheater, calcinatory and kiln; a clinker cooler and two cement grinding systems. CESA designed

Perimeter under construction.

Cladding installation.

Finished dome.

Reprinted from worldcement.com [BMHR 12]

the additional production line and ThyssenKrupp Polysius supplied the equipment. In consideration of production needs, as well as stringent quality and environmental standards, a Geometrica bulk storage dome for limestone and clay blending was part of the expansion plan.

A range of solutions for cement processing and storage The Geometrica engineering team uses a unique and efficient design process and strong, corrosion-resistant building components to make custom structures for cement storage. Available solutions include ring stockpile storage for limestone and clay; conical pile storage for potash or cement; as well as free form and longitudinal pile storage for a variety of materials. Domes may span up to 300 m, depending on the conditions and design method. Geometrica domes span large areas without intermediate supports, providing an efficient shape for stockpile enclosure and blending. Custom-designed Geometrica structures are delivered to a job site for assembly by local labour, and may be installed over an operating stockpile.

For CESA, Geometrica’s erection-friendly design was a major factor in its selection of the company to supply the second domed structure for the Sahel plant. The unique and efficient design process requires no welding or sophisticated construction equipment and can be erected quickly with minimal interference to day-to-day plant operations. This, along with the aesthetics and the weight benefits of the structure, helped cement Geometrica as the ideal dome supplier for the plant.

The resulting design was a ring stockpile dome 94 m dia. x 28 m high, anchored to a ringshaped concrete foundation. The dome was designed

by Geometrica in consultation with CESA, and was delivered to the construction site in palletised packages.

Geometrica utilises a computerised manufacturing and delivery process to help facilitate the organised and efficient production of custom components, which are individually labelled and delivered according to the order of assembly.

Choosing a dome type: the basics Ring stockpiles Limestone, clay and many other materials are stored in automated ring piles. A slewing stacker at the centre of the structure stacks the material and creates the pile, while a bridge or a portal rake reclaims the material from the face of the pile.

While diameters of ring stockpiles typically range from 75 m to 100 m, it is possible to support spans up to 300 m.

The diameter of a ring stockpile dome is usually 6 – 12 m more than the diameter of the pile. This additional space allows clearance of the reclaimer and circulation of maintenance personnel and small vehicles. The dome height is typically set at about onethird of the diameter of the dome, but may be modified.

Geodesic domes for ring piles need to clear the reclaimer at its highest point near the perimeter of the stockpile. Instead of using an expensive vertical wall to achieve this, a dome with elliptical or compound parabolic profiles can provide a steep slope near the perimeter.

If the footprint of the pile needs to be constrained, a concrete perimeter wall and foundation can support the perimeter of the dome.

Conical pile storage Conical piles are used to store potash, clinker and other materials, which are reclaimed through underground extraction hoppers and tunnel conveyors.

For these piles, Geometrica creates domes with a profile that closely follows the shape of the pile – often in a parabolic shape. Additionally, the dome may be set on a concrete wall, increasing capacity while realising savings over an all-concrete dome solution.

If the dome sits on the ground, it is important to consider the effect of fines accumulating around the perimeter. The dust is aerated when settling, which adds a small angle of repose. As a result, the pile grows over time. Solutions to this problem include

mounting the dome on a short (1.5 – 2.5 m) concrete wall, or increasing the perimeter so that a small front end loader can remove accumulated dust.

Ideally, the design of the conical pile would include a reclaim tunnel or tunnels that extend across the entire pile diameter, so that dead-load fines may be pushed to the reclaim chute and removed from the dome.

Replaceable breakaway panels may be installed on the bottom portion of the dome in order to prevent damage in the case of accidental lateral overloading.

The shape of a dome covering a conical pile may be adjusted to accommodate the increased load of a conveyor at the apex of the dome. An acute toroidal shape resists an apex load most effectively, and can be designed to carry hundreds of tonnes at its apex.

Longitudinal domes Limestone for cement manufacturing can be stored either at the quarry stockpile, or at the cement plant itself – in circular or longitudinal structures – where the material is stacked and reclaimed in transverse, cross-sectional slices. Blending may also be carried out in circular or longitudinal structures, with the entire stacker/reclaimer system either rotating slowly around the centre of the pile (circular) or moving slowly down a straight line (longitudinal). The type of storage facility depends on the space available for the project and the needs of the plant or quarry.

Geometrica offers longitudinal structures in various cross-sections to suit each project’s conditions. Acute or parabolic geometries are best for large crest loads, circular cross-sections are ideal for large wind loading sites, and bents elevate vertically in order to minimise the building’s footprint.

The ends of any longitudinal enclosure may be left open, or closed with semi-domes or flat walls, depending on the needs of the stockpile or preferred aesthetic.

A custom-designed dome The Les Ciments du Sahel dome, which is lightweight and strong, consists of a geodesic structure of galvanised steel tubes secured by aluminium hubs. The design incorporates Vierendeel geometries, which increase the strength and tension of the dome in an efficient doublelayer design. The dome is built from components of the patented Geometrica structural system: prefabricated galvanised steel tubes and slotted aluminium hubs. The connection between the tubes and hubs is compact, simple and efficient, with no welding required. The 6504 m 2 Les Ciments du Sahel dome incorporates more than 23 500 tubes and 4500 hubs.

The durable dome exterior is clad in galvanised steel panels, with the periodic installation of translucent plastic panels to allow for natural lighting within the interior of the dome. Additional cladding materials included rain gutters, ridge caps and skirt flashings, which are also made of galvanised steel.

The dome was prefabricated and delivered in containers of individually numbered parts, which were organised according to the construction plan. A Geometrica site consultant assisted with the construction process, which was carried out by a Senegal-based contractor and took just over two months. When the structure was complete, it was anchored to the ringshaped foundation by an additional concrete pour. Lastly, the cladding was installed.

Constant monitoring and measurement of quality throughout the design, fabrication and installation of a dome is a critical part of Geometrica business processes.

The company is ISO 9001 certified to ensure that every structure and process is high quality, safe and secure.

The planning and production teams utilise an online, wiki-based workspace to communicate and coordinate

with clients around the world. Additionally, Geometrica is certified to the BS OSHAS 18001 standard for managing occupational health and safety risks.

Designing and building domes for two decades Geometrica, which has facilities in Houston, Texas and Monterrey, Mexico, has designed, manufactured and installed hundreds of domes and space frame structures around the world for the last 20 years.

Industrial applications of Geometrica circular and longitudinal domes and free-form structures include bulk storage and blending for cement and mining, as well as storage and processing for waste-to-energy production facilities.

[BMHR 12] Reprinted from worldcement.com