For companies handling large volumes of bulk materials it is increasingly important to reclaim efficiently from large stockpiles. From Halley & Mellowes P/L, the latest vibratory drawdown hopper and flow control device provides an effective system which is simple to install, operate and maintain.
The recovery of coal and other materials from large stockpiles these days demands greater efficiency and reliability. The reclaim system selected must be economical, easy to install and maintain. Ideally it must be able to handle large as well as low tonnages accurately, and must reclaim from several selected areas of a stockpile when blending.
The reclaim system described below is proving effective and popular, and uses the Carmen vibratory drawdown hopper in combination with the Picor low headroom flow control gate.
This system can handle more than 7000t/hr or as little as 300t/hr while maintaining excellent control and it is suitable for blending.
The vibrating feeder has been used for many years and has proven a reliable method for lower reclaim rates (Figure 2).
“Swing hopper” flow control gate
With the requirement for larger reclaim rates, other systems were developed. The Halley & Mellowes “swing hopper” flow control gate was designed to enable large flow rates of up to 6000t/hr to be controlled. With only one moving component, this system will allow variable discharge rates by position adjustment of a pivoted swing hopper against a stationary curved floor.
When adjusting the swing hopper away from the curved floor, an open area is created to allow material flow. The volume of material discharged varies depending on gate position. The system has been installed in a large number of locations in Australia and overseas, and has been operating reliably for some 20 years.
Low headroom flow control gate
The latest development to regulate material flow is the low headroom flow control gate. This gate is a heavy-duty bi-parting slide gate designed by Picor, and it incorporates a range of unique design features. The gate was introduced in Australia a few years ago by Halley & Mellowes in response to a call for lower headroom in reclaim tunnels. The benefits of this gate are several:
Reduced reclaim chamber head right (by more than two metres). This reduces excavation and concrete structure costs.
Reduced capital cost by half
Non-stop infinite modulating control. A hydraulic power source allows instant flow rate change in response to weigh scale signals. (No time delay due to excess number of starts per hour for electric motors).
Easy low maintenance (no rollers). This gate uses low friction HD polymer blocks with long lifespan.
Fail-safe close. A hydraulic accumulator immediately closes the flow control gate in the event of power failure, ready for restart.
The low headroom flow control gate has been installed in a number of recent Australian projects and is performing reliably as it has done overseas in the past.
Control of the reclaim system involves both the drawdown hopper and flow control gate.
The drawdown hopper is designed for cyclic operation. When flow is required, the drawdown will commence its cycling, typically 10 to 15 seconds “on” and five to six minutes “off”. This conserves energy and increases the drive components’ life. Cycling also reduces the likelihood of consolidation of the stockpile.
The flow control gate uses hydraulic actuation of the two blades. The automatic operation of the gate is acting in response to the downstream belt scale. This can also be adapted to modulate in accordance with changing surge bin levels, control systems operate both the drawdown hoppers and the flow control gates c/w hydraulic power plant, and they typically include other tunnel equipment such as sump pumps, ventilation fans and conveyor. Where required control systems also control PLS precision train loading systems in a fully integrated package.
Causes of material spillage are readily identified and designed out. Several new belt loading designs and features are available suited to different applications. The latest designs have shown that it is possible to contain all material on the belt at varying flow rates and material consistencies, and to eliminate spillage altogether.
Complete stockpile modelling is now available to quantify available reclaim from any given stockpile. This allows for easy and quick determination of optimum stockpile configuration and expected live reclaim.
The stockpile drawdown reclaim system is a proven performer amongst the various reclaim systems available for reclaiming bulk materials. Using gravity to do most of the work the system can now handle 7000t/hr with an installed power requirement of 30kW operating on a cyclic basis. The technical advances provide a cost effective powerful stockpile reclaim, fine modulating control, safe and clean facilities and full integration with supply to plant, ship or train.