No more left in the dust

Jack Mallen-Cooper

Chute Technologies technology packages, which are developed from proven installations for alumina, iron and other mineral ores, as well as coal handling facilities at mines, power plants and ports, tackle dust problems at their source rather than attempting to control dust after it has been created and dispersed into the atmosphere.

The same technologies can be applied to inlet, hood, chute, spoon, enclosure and saturation zones to address widespread spillage hazards, with their cost, downtime and safety issues, Chute Technologies Engineer, Dennis Pomfret said: “Good designs such as these – either new or retrofitted – demonstrate that environmentally sensitive production need not necessarily come at a cost to output. In fact, these chute improvement technologies have achieved major increases in production, exceeding 50% and even 80% – in some cases, while solving waste and spillage problems.”

Chute Technologies’ packages combine proven technologies that address dust and spillage issues as problem-solving packages, such as:

• Integrated advanced product flow analysis.
• 3D discrete element method (DEM) design processes.
• Globally proven 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,” said Pomfret. “But now the environmental safety and profit waste issues raised by dust and spillage have placed these issues high on the industry agendas worldwide.”

Transfer control stations

Chute Technologies’ dust and spillage technologies feature dust-minimising transfer control stations on material handling conveyor belts, as a component of energy efficient and water-conserving technology packages for new and retrofit loadout 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 the 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.

The new transfer chute 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 2700 mg/m3 in the transfer station on a 650 tph alumina conveyer in Australia to well within the client’s target of less than 1000 mg/m³.

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

Figures 1 and 2 show identical coal transfer: Figure 1 shows the original condition, whereas Figure 2 illustrates the coal transfer retrofitted with a passive dust control system. The pictures were taken using the same coal, on the same day and with the same ambient air conditions. Coal throughput was more than doubled on the retrofitted transfer.

Figure 1: Coal transfer in original condition.

Figure 2: Coal transfer retrofitted with a passive dust control system.

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

The Chute Technology engineering group targets problems common to many coal and ore plants and loading systems by addressing them with Chute Technologies’ combination of three skill sets, including advanced engineering analysis of flow from Dennis Pomfret Engineering, followed by upscaleable 3D Discrete Element Method (DEM) design processes from chute technologies partners McKajj Services and finally custom manufacturing to individual plant needs by Partner TW Woods.

The combined technologies are complemented by the practical experience of each of the three principal partners in Chute Technology, who have combined experience of more than 80 years in a wide variety of resource industries, including coal, iron ore, alumina and limestone across Australia, the US, South America and South Africa. The technologies are also applicable to gold, nickel and other bulk minerals and ores.

Chute Technologies’ dust reduction and spillage reduction improvements, which are one component of a comprehensive new and retrofit programme available from the partnership, are based on design and installation elements including:

• 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 buildup and blockages.

Design solution

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 redesigned 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 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, Pomfret said. “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 deration chamber. For superfine materials, a deration 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 or retrofits, depending on system needs,” Pomfret explained. “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.”

By strengthening or replacing the weaker links in an existing system – or building the right components into a new facility – Chute Technologies provides time-efficient and cost-efficient solutions to problems that are often long-standing.

“All of the technologies in the packages are current and proven technologies that are the best of their type. Some have been individually available in recent times but were not considered to be a priority until recent years, when production efficiencies and avoidance of problems has become paramount. Now these are technologies whose time has come," concluded Pomfret. "Mining and energy companies, as well as port loadout facilities, may have been able to afford built-in inefficiencies when resource prices were high. But as the emphasis switches to higher production for lower cost, accepting old standards of inefficiency is no longer an option.

Edited by Jonathan Rowland.

About the Author: Jack Mallen-Cooper is a Public Relations Consultant at Whyte Public Relations.

Read the article online at: https://www.worldcoal.com/handling/26082015/no-morw-left-in-the-dust-2783/