The project at the Trekkopje desalination plant follows other recent successes by WEG in supplying motors and systems to desalination projects in Algeria and Dubai, and also the HNSS Project in Andhra Pradesh, India, one of the largest irrigation projects in the world. The plant is the largest of its kind in sub-Saharan Africa and is a vital water supply asset in a country where 98% of the land is considered arid or semi arid. The WEG motors, ranging from 18.5kW to 750kW, drive pumps that are considered crucial to the plant’s reliable operation.
Designed and built by specialist water treatment firm, Keyplan, part of the Aveng Group, the Trekkopje plant converts sea water from the Atlantic Ocean into potable water for use at the large Trekkopje opencast uranium mine.
The desalination process entails abstracting salt water via pipes that are placed one kilometre out to sea. The sea water is then pumped to the plant where screening and ultra filtration prepares it for reverse osmosis, a process where a membrane selectively retains the salt, allowing the desalted water to pass through.
Keyplan considered a number of companies for the supply of the pump motors. However, the Zest WEG Group was chosen because of its technical expertise and the proven quality of WEG motors. “It is important that the motors complement the application and ensure maximum productivity coupled with minimal maintenance and downtime," said Gavin Lee, Keyplan Projects Director.
While competitive pricing played a role in the decision making process, the value added service that the Zest WEG Group was able to offer was infinitely more important to the customer.
"This was especially pertinent in terms of the company's ability to work closely with other suppliers to ensure a perfect product match as well as meet the deliveries according to scheduled timeframes," said Mr Lee.
The Zest WEG’ Group’s scope of work included providing technical advice and supplying 62 WEG self- monitoring motors, ranging from 18.5kW to 750kW. “Keyplan required Zest WEG to calculate the run up times for those third party pumps that were deemed critical to the plant operation,” said Russell Finch, Project Manager at the Zest WEG Group.
The 750 kW motors were fitted with soft starters while the remainder of the motors were combined with variable speed drives. All motors were supplied with anti-corrosion coating because of the corrosive nature of the environment. In addition, because the ambient air is very moist due to omnipresent fog, the installation of anti-condensation heaters in every motor was imperative to keep the motors heated and thus eliminate any moisture build-up and ingress.
Fresh water is scarce in the world. Although two- thirds of the planet is made up of water, only around 3% is fresh water suitable for consumption, irrigation or for use in industry. However, seawater is plentiful. For many countries, the only policy is to make large investments in technology to desalinate sea water and use the resulting liquid for consumption.
There are approximately 14,000 desalination plants worldwide, most of them in the Middle East. According to data from the International Desalination Association, they produce today over 59.9 billion litres of water per day.
The desalination of water is achieved through a process known as Reverse Osmosis. High pressure pumps draw the solution making it pass through semi-permeable membranes, which are like filters. The salt is retained in these membranes and what comes out on the other side is a “pure” water solution.
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