Steel Awards 2012

Medupi Power Station takes gold

Steel Awards 2012
Steel Awards 2012

The giant chimneys at the Medupi Power Station in Limpopo have won the “overall” prize the “Mining and Industrial” category prize at the Steel Awards 2012.

 
Hosted on September 6th 2012 by the Southern African Institute of Steel Construction (SAISC) with the Aveng Group as main sponsor, the Steel Awards 2012 were held simultaneously at Emperor’s Palace in Gauteng, Durban Botanical Gardens in KwaZulu-Natal and Kirstenbosch in the Western Cape.
 
SAISC executive director, Dr Hennie de Clercq praised the use of steel at Medupi. “One may question whether or not anybody should build a coal-fired power station in this day and age, but once somebody has decided to do so, the least that can be done is to use the greenest possible materials and construction processes. Steel then becomes the logical material for several reasons.

Firstly, relatively little of it is used in comparison with what would have been required if other materials were used. This cuts down on all sorts of ‘downstream’ energy costs such as transportation.
Secondly, the steel in the project can be used again or recycled at the life-end of the project. Thirdly, steel construction creates jobs and thus has a positive social impact. Fourthly, steel construction has a highly beneficial effect on the economy at large. Steel also has a relatively small carbon footprint which has been reduced by 40% in the last 50 years,” he concluded.
 
The project team for Medupi submitted two entries. The first was the platform steelwork designed to give access for future maintenance, to assist in overall erection inside the concrete chimney, and to support the hanging mass of three 9m-diameter ceramic-lined flues and a concrete roof to the chimneys.
 
The second entry was the actual steel cans that make up the flues. However, because they were integrally linked in the end product, the judges decided to treat the entries as one.
 
Platforms
The platforms surrounding the three 9-m diameter cans led to a conceptual layout that relied on three radial beams, each 17m long, joined together in a “central three-way jointing connection fabrication”. The outer ends of these three radial beams connect to three across-the- arc beams to carry the loads back to and on top of three relatively short beams. These shorter ‘corbel beams’, which allowed for construction tolerance to marry the steel and concrete together, are supported on concrete corbels built into the concrete chimney walls. Once this main spine and support system has been resolved, the secondary beams are framed into these main girders providing support for the grating floors that are shaped to accommodate the circular openings to allow the cans to pass through the floors. These complicated girders were built to meet the stringent straightness of web and flange tolerances.
 
Cans
Each can is 9m in diameter and made from stiffened 8mm thick plates. The 18 uppermost cans are made of stainless steel because of its corrosion resistance properties, as they will be exposed to acid corrosion. Once the decision to make the cans site-bolted and seal-welded was reached, the next decision was to make the sub-cans into 9m lengths (based on 3m-wide plates) with bolted flanges. Joining 3 plates made up the circumferential length.
 
Assembly Line
Perhaps the most remarkable aspect of the process came next. Every plate then had to be cut to size, their edges prepared for welding requirements and rolled to the right radius. Thereafter the work becomes an’ assembly line’ – flanges drilled to ensure that every can could fit every other one; holes aligned and bolted; circumferential welding completed. Analysts remarked that this is a “first in ‘plate work’ fabrication, changing traditional methods that have been employed for decades into a carefully thought-out, highly effective ‘assembly line’ production method”.
 
Safety issues
In both the fabrication shops and in the chimneys, or on the site of the chimneys, safety procedures were diligently and intelligently applied. The judges remarked that as a visitor to the site it is reassuring that there was “safety at work” in the work place.
 
The judges concluded by saying that this project was “a truly excellent alternative design followed by a detail design and implementation process, for what must surely be the first assembly lines for flue cans. “All this, together with such a complicated platform steelwork make this a truly deserving Overall Winner of Steel Awards 2012.”
 
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