References

Whilst our IBS is most often used to screen sewage, Rand Water of South Africa chose it for raw water canals, in a project jointly engineered by E&M. Rand Water draws the water from the Vaal Dam, supplied by the Katse, Sterkfontein, Grootdraai and Woodstock Dam. It is then filtered and cleaned at two purification plants. The largest of these is Zuikerbosch, which is one of the largest purification plants in the Southern Hemisphere.

Three open canals, each about 3 metres wide, deliver nearly 40m3/second of flow at peak times, at a depth of between 3.5 and 3.7 metres which, apart from the usual debris, is often heavily-laden with “greenery” that needs to be cleared from the channels.

The solution is not always “off the shelf”. At the Simmering plant in Austria, two long screens are installed side by side, but in one channel. They are required to be removable, by crane hoisting. The size and weight of each unit, and the fact that they each sit dangerously close to the other, meant a little extra engineering was required.

In this installation in 2004, one by one, each screen was lowered above the channel opening. In that position, rollers mounted on the screenframe engage with channel-mounted guide rails. In a controlled decent, the equipment is safely lowered into the channel, guided accordingly by the superstructure mounted therein. Inversely, removal is just a repeat of the exercise but in reverse… controlled and safe.

A reliable overload protection device. The E&M IBS is fitted with a unique electro-mechanical overload device. A purely electronic overload system suffers from two major impediments. Firstly, operations staff cannot see that its not working until it is too late i.e. until the screen has been damaged in the event of a jam. As with all computers (which “glitch” from time to time as any user knows), the componentry and circuitry is all hidden from operators’ eyes and the performance and reliability of the system, or not, is only verified when an overload situation exists. Secondly, when the system has to be repaired, or even adjusted, it has to be done by an expert from Telemechanique, which is a logistical hindrance and generally a relatively-expensive exercise.