SPECIALIST EQUIPMENT
South America and South Africa. T e technologies are also applicable to gold, nickel and other bulk minerals and ores.
Design solution T e main design solution elements, varying from project to project, include improvements in a number of areas. First is in the inlet area. T e approach to dust abatement in this area is a headchute enclosure to limit the infl ow of entrained air by the use of overlapped curtains. Next is the hood and intermediate chute. T is area is redesigned to ensure material trajectory is at an optimal angle, with respect to impact forces and material fl ow (wall friction is used to retard the fl ow speed). T e sides of the hood are shaped in to contain the accelerating material and
thereby minimise the expansion eff ect caused by free fall. Design improvements can also be made in the spoon area. Redesign of chute spoons focuses on more smoothly turning material into the direction of the receiving belt, while more closely matching the speed of the exiting material to that of the receiving belt. “Changing the particle dynamics in this area is important because, when a vertically falling particle lands on to a moving surface – i.e. the belt – a motive force is suddenly applied to one side of the particle,” says Pomfret. “T e inertia of the particle resists acceleration in the direction of the belt. Instead, it generates a rotation in the particle, which may have a tangential velocity that is faster than the speed of the belt. Consequently, the particle ‘bounces’ in the opposite direction to the belt travel.
“T is counter rotation motion of material in the loading zone generates a highly agitated – and therefore highly aerated – product. T e action leads to dust otherwise bonded to being expelled into the free air.” Material is guided so that it is
not fl owing sideways into load zone skirtboards – wearing them and prompting seal failures – but rather running parallel with them. With regard to the spoon deration
chamber, for superfi ne materials, a deration chamber to allow reconsolidation of the material to normal density from the low density developed during free fall. Meanwhile the chute recirculation
enclosure is designed to minimise the entry of new air into the transfer by eliminating the need for low pressure zones to draw air into the system. T is pressure diff erentiation eff ect is overcome, where required, by connecting the high pressure zone to the low pressure zone and setting up a recirculating air path. T e fi nal element to consider is the
load zone enclosure. Here, a long chute extension with soft seal skirtboards and overlapped internal curtains to allow entrained dust laden air to resettle on the outgoing material stream. “Any or all of these elements can be incorporated into new or retrofi ts, depending on system needs,” says Pomfret. “Sometimes we fi nd that a total redesign of existing systems isn’t required, because just two or three components of the transfer are mainly responsible for creating the dust load. “Mining and energy companies,
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www.engineerlive.com A multidirectional chute
from Chute Technology
as well as port loadout facilities, may have been able to aff ord built-in ineffi ciencies when resource prices were high. But as the emphasis switches to higher production for lower cost, accepting old standards of ineffi ciency is no longer an option.” ●
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