Dust Control & Environment

7 design solutions for less dusty transfers

Dust and spillage are perennial problems for many mine and plant operators.

ABHR spoke to Dennis Pomfret, one of three partners behind engineering business Chute Technologies, which is combining advanced analysis, DEM modelling, and manufacturing to minimise dust and spillage around chutes and transfers.

ABHR has previously reported on the ‘dream team’ behind Chute Technologies.

The organisation harnesses the diverse skills of three experienced engineers: Tom Woods of TW Woods is an experienced manufacturer; Dennis Pomfret of Dennis Pomfret Engineering adds broad engineering and technology experience; while Gary Telford of McKajj Services contributes project management, engineering and drafting experience.

According to Pomfret, Chute Technology aims to tackle dust problems at their source rather than attempt to control dust after it has been created and dispersed into the atmosphere.

He says the firm’s technologies can be applied to inlet, hood, chute, spoon, enclosure and saturation zones to address widespread spillage hazards.

“Good designs, either new or retrofitted, demonstrate that environmentally sensitive production need not necessarily come at a cost to output,” explained Pomfret.

“In fact, these chute improvement technologies have achieved major increases in production, exceeding 50 and even 80 per cent in some cases, while solving waste and spillage problems.

“Chute Technology’s problem-solving packages combine integrated advanced product flow analysis, Discrete Element Method (DEM) design processes, and manufacturing services.

“The packages, which apply to completely new plants and problem areas within existing plants, deploy technologies whose availability and application may have been too fragmented or unmanageable and put into the too-hard basket.”

 

Transfer control stations

Chute Technology’s dust and spillage control technologies feature dust-minimising transfer control stations on conveyor belts, as a component of technology packages for new and retrofit load-out facility projects.

The new transfer stations and associated downstream technology minimise the amount of dust created in the first place, reducing water needs as well as energy required for dust collection fans and filter houses. They contain whatever dust is created within the transfer point, minimising harm to the surrounding environment.

 

One example of Chute Technologies' transfer station designs.
One example of Chute Technologies’ transfer station designs.

 

The new transfer technologies also curtail spillage and optimise conveyor belt width loading potentials by eliminating the disruptive steep drops and turns in conventional chutes that cause dust, blockages, spillage and wear.

“Instead of having huge energy-sucking extraction installations to collect up dust that escapes conventional chute designs, we cost-effectively engineer new transfer stations based on passive dust control principles with de-aeration chambers,” said Pomfret.

In-service examples of the technology have cut dust emissions from 2700mg/m3 in the transfer station on a 650tph alumina conveyer in Australia to well within the client’s target of less than 1000mg/m3.

In addition, the heavily reduced dust load was contained within the transfer station, rather than allowed to be able to escape to the atmosphere and onto surrounding valuable arable land.

Good results have also been achieved on ore and coal installations, including a power station coal feeder in the US where new chute systems, engineered and modelled to achieve design flow rates of 1000 tph, increased throughput nearly 50 per cent while reducing spillage and dusting in the yard by 98 per cent.

Chute Technology’s design principals are based around:

  • Reduction of induced and entrained air
  • Elimination of free-fall and impact problems
  • Curtailment of agitation and disturbance of conveyed material
  • Removal of water spray issues, including situations where water sprays cause material to become sticky resulting in build-up and blockages.

Design solutions

Design solution elements, varying from project to project, include improvements in the following areas:

  1. Inlet area. The approach to dust abatement in this area is a headchute enclosure to limit the inflow of entrained air by the use of overlapped curtains.
  2. Hood and intermediate chute. This area is re-designed to ensure material trajectory is at an optimal angle, with respect to impact forces and material flow (wall friction is used to retard the flow speed). The sides of the hood are shaped in to contain the accelerating material and thereby minimise the expansion effect caused by free fall.
  3. Spoon. 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,” said Dennis Pomfret.
    “The 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.
    “This counter rotation motion of material in the loading zone generates a highly agitated, and therefore highly aerated, product. The action leads to dust otherwise bonded to being expelled into the free air.”
    Material is guided so that it is not flowing sideways into load zone skirtboards, wearing them and prompting seal failures, but rather running parallel with them.
  4. Spoon de-aeration chamber. For superfine materials, a de-aeration chamber to allow reconsolidation of the material to normal density from the low density developed during free fall.
  5. Chute recirculation enclosure. The 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. This pressure differentiation effect is overcome, where required, by connecting the high pressure zone to the low pressure zone and setting up a recirculating air path.
  6. Load zone enclosure. 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.
  7. Secondary dust scrubbing zones. In rare cases where super fine dust is generated a localised air filter is located at the exit to the load zone chamber.

 

“Any or all of these elements can be incorporated into new transfers or retrofits, depending on system needs,” concluded Pomfret, who holds patents on materials handling technologies.

“Sometimes we find 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. We can strength or replace the weaker links in an existing system, or build the right components into a new facility.”

Contact: Tom Woods, email – tom@twwoods.com.au

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