Demag South Africa national product and sales manager Wynand Andeweg points out that this comprehensive turnkey solutions offering also includes the commissioning and automation of the crane equipment, the long travel rails and the flocculation system for two sedimentation tanks.

“Demag’s machinery will form an integral part in the process of converting water from the Vaal Dam and River into potable water, as flocculators mix incoming water with flocculent that attracts suspended solids, and a resultant sludge then settles at the bottom of the tank,” he explains.

According to Andeweg, the automated desludging bridge will scour the 10,000m2 floor to remove this sludge layer. “In total, 200-million litres of water are expected to flow through this system of tanks and 16-million litres of sludge will be pumped out by the bridges each day, thereby ensuring that the quality of the water is at the right level for the next stage of cleansing.”

Each bridge spans 40m, and is fitted with six pantograph hoists to guide the pumps to sludge level. The bridges travel at 0.7-metres-per-minute during automatic operation and 20m-per-minute during transfer operation. The pumping capacity of each bridge is eight-million-litres-per-day.

Andeweg admits that any failure of the system will result in filter blockages, which is a major concern. “To minimise this risk, the desludging bridges are fully-automated and they communicate with the Rand Water control room on a regular basis, thereby ensuring smooth and seamless operation at all times,” he continues.

Owing to the unique nature of this project, a number of challenges were encountered and efficiently overcome. “Our cranes have never been designed to handle water, and we had a limited timeframe to learn the technical aspects of pumps and hydrodynamics,” adds Andeweg.

The pantograph was also a new concept proposed by Demag as a more robust and reliable solution, compared to industry-standard sludge bridges. Andeweg continues: “This required extra engineering effort to ensure first time success. Logistics was another concern, as the cranes each weigh 60 tons and are 40m long and 8m wide. A partnership with a trusted transport company solved this challenge.”

Bearing in mind the complexities of this project, Andeweg highlights the fact that Demag stood out from the rest of the competition thanks to its unrivalled 59 years of experience in developing advanced crane technologies, together with its 40,000m2 under roof manufacturing facility.

“This competitive edge ensured that we were able to fully manufacture, assemble and test the machinery in-house before transporting the completed machines in three parts, with the main structures and auxiliary equipment transported in one piece. This is a major achievement. In the past, all desludging bridges were delivered to Rand Water in parts, with final manufacturing on site.”

Demag has been working on the project for a total of 21 months, including delivery of all components on site. The estimated commissioning date for the project is June 2015 once power has been installed at the site. “To facilitate this handover, Demag’s dedicated service team will train Rand Water personnel on the operation and basic maintenance of the machinery,” adds Andeweg.

 The operational lifespan of the bridges is 20 years, but with regular maintenance and servicing, they could last more than 30 years. Although these bridges are prototypes, Andeweg is confident that this new type of concept will set a new standard in the local industry, creating the potential for export to burgeoning international markets too. “This will be a proudly South African contribution, owing to the fact that the local content of this project is an impressive 80%, which creates the potential for sustainable job creation and skills development in the foreseeable future,” he concludes.

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