Giant Dome Controls Dust at Cement Plant
By T.V.S. Chidambaram, Star Cement Co. LLC, and F. Castano, Geometrica, Inc.
Ras Al Khaimah, in the UAE, holds the distinction of being the largest cement producer in the country. For a long time this emirate, often referred to as RAK, has provided high-quality construction materials to its more famous siblings, Dubai and Abu Dhabi, helping build the country's infrastructure and fuel its remarkable growth. To continue this growth, Star Cement, a company of the ETA group, built a new, world-class cement plant in RAK. The new plant has a capacity of 7000 tons per day of clinker and is now working.
Early in the design stage, Star Cement decided to allocate a significant portion of the total investment to ensure that the new plant would be built with the utmost respect for the surrounding environment. A key ‘green decision’ was that all conveying and storing of bulk materials would be done under cover.
The biggest challenge was the limestone stockpile: A week’s worth of limestone – the raw material for cement production – amounts to 34,000 tons and has a diameter of 92 meters. Star Cement's civil and structural consultant, FLSmidth Designs Pvt Ltd, India, drafted a performance specification that included all dimensional and loading requirements for the stockpile cover. It would have to allow ample clearance for the stacker-reclaimer system; provide an opening for the incoming conveyor as well as four entrances for off-road vehicles; and include space for a traffic lane inside the dome around the ring rail of the reclaimer.
Cover System Selection
During the supplier selection process, Star Cement considered various alternatives for the stockpile cover: Conventional A-frames arranged radially, aluminum dome, and Geometrica's galvanized steel dome. The table below compares the short-listed alternatives.
As may be seen from the above table, the quantum of total on shore work in a conventional steel structured dome is nearly 3.7 times than that of a galvanized steel dome. This results in reduced investment cost as well as speedy construction at site.
The Geometrica Dome
The Geometrica galvanized steel dome was selected for various reasons:
Both initial and lifetime costs were most competitive,
The dome could be installed at the same time as the stacker reclaimer, which would simplify the schedule and save time; and
The galvanized finish would provide years of maintenance-free use.
The galvanized steel solution combines the cost advantage of conventional steel with a corrosion resistance comparable to that of aluminum. These advantages made the galvanized solution compelling.
The dome was prefabricated in Geometrica's plant located in Monterrey, Mexico in an exacting computer-controlled process. The modules were packaged into 2-ton crates, then containerized and shipped to site. Remarkably, the weight of the dome – including cladding – is less than 30 kg/m2 over the covered area, and its chord-to-chord thickness is less than three-thousandths of its span. The resulting slender structure is beautiful and efficient.
Before the prefabricated dome sections arrived, a simple concrete ring was poured to form the perimeter of the building. Stirrup steel bars were left exposed by this first pour, and the first ring of the dome was assembled under these reinforcing bars to lock the dome to the ground. Dome construction proceeded upwards and towards the center.
The length of the galvanized steel tubes used in this dome was approximately 1.7m, with slight variances to achieve the dome’s curvature. Great structural strength was achieved by using two layers of geodesic lattice separated by 300-millimeter Vierendeel spacers.
Assembly was carried out entirely by a local labor contractor, with direction and assistance from a Geometrica site-consultant. The dome was self-supporting during construction, and no scaffolding, central towers or cranes were required. No welding was required either, as the struts were joined with Geometrica's efficient mechanical hubs.
Crucial to the schedule was the fact that the dome could be installed concurrently with the stacker-reclaimer and the conveyor gallery. Because of this, dome assembly activity was never on the critical path for the whole plant, and was carried out at a leisurely pace. Once the structure was complete, the second pour of the concrete edge beam was completed and the cladding installed. The cladding used for this structure consists of simple rectangular panels of “Star Cement Blue” laid out in a 12-sided arrangement. Translucent fiber-reinforced plastic panels form chevron-shaped skylights that make interior artificial light unnecessary during daylight hours.
The teams at Star Cement, FLS, Geometrica and the labor contractor worked closely together throughout the project's development. This teamwork approach insured a very successful implementation. The new dome is now a new landmark in the country, one witnessed by people from around the world when they come to visit Ras Al Khaimah.
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