Technologies for Controlling Conveyor Dust and Carryback
Controlling dust, carryback and material accumulation is an essential element of bulk material handling by conveyor, as well as bulk storage. If accumulation gets bad enough in chutes and storage vessels, it can force unplanned system outages and cause major disruptions in production to clear blockages.
Innovative Belt Cleaner Design
Unlike conventional belt cleaners that are mounted at a 90-degree angle to the belt, the CleanScrape Cleaner is installed diagonally across the discharge pulley, forming a three-dimensional curve beneath the discharge area that conforms to the pulley's shape.
The unique design incorporates a matrix of tungsten carbide scrapers and is tensioned lightly against the belt to prevent damage to the belt or splices. Despite extremely low contact pressure between belt and cleaner, it has been shown to remove as much as 95 per cent of potential carryback material. The novel approach has been effective in saving on belt cleaning costs and maintenance time.
The innovative belt cleaning system received the Australian Bulk Handling Award in the 'Innovative Technology' category for its design and potential benefits, which include low belt wear, extended service life, reduced maintenance and improved safety, ultimately delivering lower cost of ownership. With its compact size, the design is an excellent solution for areas with restricted space. It can be located either inside or outside of the transfer chute, and the installation typically requires less than two hours.
'Smart' Air Cannons
Air cannons have proven to be an effective flow aid over 40+ years of use in cement manufacturing, coal and ash handling, rock crushing and other applications. Also known as air blasters, the technology helps improve throughput and reduce material build-up with a powerful discharge of air, dislodging accumulation that impacts process efficiency and raises maintenance expenses.
There have been a number of improvements to air cannon designs. Among the upgrades is a high-speed valve design that can be mounted on a smaller air reservoir, delivering higher discharge forces than less efficient valves on larger tanks. The new generation of valves produces about twice the blast force output of the designs introduced just a decade ago, allowing users to save energy by using about half the compressed air volume.
Another energy-saving development is the piston return reservoir. During the air cannon's firing sequence, the pressure in the return reservoir approaches that of the tank, but the fast-acting valve closes when about 50 per cent of the tank's original pressure remains. The peak force output remains the same, but air consumption is dramatically reduced, easing the demand on plant air supply and reducing cost.
Air cannons have also become safer in recent years, with new positive-firing valves that respond to an air pressure surge delivered by a solenoid valve. A cannon equipped with this new type of valve will not discharge accidentally in response to a drop in pressure, so an interruption in air supply or broken line cannot trigger it. There has also been significant advancement in nozzle technology for air cannons over the last few years, such as a 360º retractable design that extends into the material stream only during the firing cycle to protect itself from extreme temperatures and abrasion. Further, the retractable nozzle can be serviced from outside the vessel, reducing service time and risk of injury.
The benefits include significantly reduced damage to refractory brick and drastically shorter nozzle service times. It also allows system operators to add air cannons to an existing process during a brief shutdown, without completely cooling down the entire system to allow entry into the interior of a vessel.
Cleaner Air, Smaller Footprint
While central 'baghouse' air cleaning systems have been in use for decades, they present a number of challenges, not the least of which is their cost. An alternative to the central collector is the integrated air cleaner system, which contains a suction blower, filtering elements and a filter cleaning system. Instead of a centrally located unit connected to dust generation points via ductwork, this type of cleaner is incorporated into the dust generation point itself. The particles are not extracted, but are instead collected within the enclosure and periodically discharged back into the material stream.
Unlike central systems, the integrated approach employs a series of smaller, independently operating units, one at each dust generation point. This decentralised approach allows the air cleaners to be incorporated into a maintenance cycle, and no single unit requires a complete system outage for maintenance. The nature of the integrated air cleaner design eliminates many of the disadvantages of a central dust collector, often while providing superior effectiveness.
Among recent advancements in air cleaning technology is a new integrated design that features improved filtering and a smaller footprint, helping bulk material handlers minimise airborne dust at belt conveyor loading and transfer points. The Martin® Insertable Air Cleaner is an automatic, self-cleaning unit designed to remove dust from the air in conveyor loading and transfer points, silo vents, bucket elevators and screens.
The collector design employs filter elements that are approximately one-eighth the size of filter envelopes in preceding systems. The smaller filter elements allow a significant reduction in the dust collector's 'footprint,' so it can be placed in locations where tight quarters complicate the installation of other systems. The mesh-like material filters better and lasts longer ' while consuming less energy 'than conventional filter bags. The new filters also allow a reduction in fan size to move air through the elements, helping to reduce the overall power consumption of the collection system.
For more information, visit www.martin-eng.com or call (309) 852-2384. Global representatives for Martin Engineering can be found at www.martin-eng.com/rep-finder.