Often an overlooked element of the crushing, screening and milling circuit, chute systems are now emerging from their ‘step-child’ status, says Mark Baller, Managing Director of Weba Chute Systems.
A roller crusher discharge chute on a mine in Mpumalanga.
“It is increasingly recognised that chutes are not just standard items of plate-work, but are vital facilitators of smooth plant operations,” states Baller. “Like every other aspect of plant technology, they require focused technical design that creates a fit-for-purpose solution, as no two chute applications are the same.”
He highlights the key role that chutes play in plant reliability and efficiency. For instance, they ensure that the crushers receive the right material at the correct angle, that the screens are optimally loaded, and that the mills are correctly fed for best performance and economical power consumption.
“It is understandable that the focus in many plants is on the ‘big ticket’ items like mills, crushers and conveyors, as this is where most of the capital is invested,” he says. “But this equipment cannot operate efficiently – and with longevity – if the transfer points connecting them are not well-designed. In many ways, the chutes link the whole process together.”
With 30 years of experience in the field, Weba Chute Systems has seen many plant shutdowns caused by incorrect chute design. Feeding material out of specification onto conveyors or into crushing equipment can cause damage such as holes in a screen deck or damaged belts, leading to costly plant downtime.
“By respecting the laws of physics and applying the latest design technology, we create chutes that control the flow of both material and air to best effect,” he says. “The result is a fully engineered transfer point that is suited to the material and application.”
Customers see immediate value in terms of more efficient plant operation and fewer stoppages, meaning that most of these items can pay for themselves in less than 12 months.
Environmental conditions in mineral processing plants is another growing issue that chute design can help to address. As health and safety standards on mines continue to rise and compliance becomes tighter, there is greater pressure on mines to ensure cost effective dust mitigation strategies.
Baller notes that while many service providers offer mines a range of dust suppression ‘add-ons’ or ‘band-aids’, the primary solution lies in good chute design. The company’s research has shown that levels of dust in the working area can be reduced by 70 % or more by scientifically controlling the flow of material and air at the transfer point.
“We begin with understanding that material tends to aerate when it is in free-fall,” he says. “When it comes to an abrupt stop or changes direction suddenly – as occurs when the flow is uncontrolled – that air is forced out, creating dust.”
If a mine limits its dust-reduction strategies at transfer points to only suppressing or extracting dust, he notes, it is missing a key underlying cause of the problem. In fact, where extraction fans are placed without material flow in mind, the result may even exacerbate the prevalence of dust as the induced air flow could be moving counter to the material flow.
“In one recent application, we assisted a power station in Wyoming in the US, where the dust levels at their transfer stations were exceeding the compliance limits set by environmental authorities,” he said. “By redesigning the chutes, we were able to reduce dust levels by 78 %, bringing them well within regulations.”
Such has been the success of Weba Chute Systems’ proprietary design solutions that half of its production is today destined for customers outside of South Africa, including markets as far afield as North America, South America and Russia. The company has supplied over 4 300 chutes into the global market over the decades, of which about 3 500 are still operational.
The chutes from Weba Chute Systems are applied in soft and hard rock applications and handle lump sizes from 1,4 metres weighing about two tonnes, right down to fines or powder. Throughput rates range from as little as 40 to 50 tonnes per hour up to 12 000 tonnes per hour, in all climates and conditions.
