Bulk discharge system without the hazard
September 1st 2007

Flexicon has provided a bulk discharge system for Brayton Fire Training Field in the USA that is more efficient and eliminates the potential for dusting and the health and safety concerns that arise from this

The USA based Texas A&M University System are famous for their agricultural and engineering programs but less well known is the fact that one of their agencies has the country's largest training facility for firefighters. The 48,560 m2 Brayton Fire Training Field, operated by the Texas Engineering Extension Service (TEEX), includes full-scale buildings, a chemical complex, a petroleum refinery unit, a loading terminal, a ship and an aircraft fuselage that are used for realistic firefighting drills. Each year, TEEX trains more than 80,000 firefighters and emergency response personnel from over 50 countries. In the course of their training, the students have to fight a variety of fires, using various types of equipment such as hand lines (hoses) and hand-held fire extinguishers that contain sodiumbicarbonate- based (NaHCO3) chemical powder. Brayton Fire Training Field (BFTF) is currently in the midst of a £15 million infrastructure upgrade and one of the first projects to be completed was the installation of an improved refilling operation for portable fire extinguishers. NaHCO3 is a fine powder of 5–20 microns, similar to talcum. It is easily airborne when handled or transferred from one container to another, creating a potential dust hazard. The key feature of the redesigned operation was the installation of a sealed system for unloading bulk bags of the chemical powder and filling the canisters. The new system from Flexicon has eliminated the potential for dusting associated with the previous unloading method and is much more efficient, says Ron Peddy, TEEX's program manager for environmental safety and field services. Prior to installing the new system, the powder was received in 180 kg drums. When a drum was needed for the refilling operation, it was hand-rolled to a 4,350 kg hopper that fed the refilling line. A drum tipper was used to empty the drum into a 270 kg capacity hopper, from which the powder was augured up into the large hopper. From the hopper, hoses were used to refill the canisters as they moved along a roller conveyor. Powder was transferred to the hoppers in the open air and the refilling process was performed outside, under an awning, to prevent dust inhalation. In the new configuration, the whole operation has been consolidated indoors in a single building. Chemical powder is received in 1,000 kg bulk bags, which are stored in the building. A bulk bag unloading frame is located above a floor hopper, at the head of the U-shaped roller conveyor. The powder is transferred from the bag to the hopper and into the canisters without being exposed to the environment. Both the bulk-bag unloading frame and the floor hopper were supplied by Flexicon. The Model BFC bulk-bag unloader incorporates a cantilevered Ibeam, electric hoist and trolley. Bags are brought to the unloading frame by a forklift and lifted by the hoist, which has a spreader bar that attaches to the bag's four corner straps. The bag is positioned above the hopper. Powder is discharged from the bulk bag through a patented Spout-Lock clamp ring that creates a dust-tight seal between the spout and the equipment, and a patented Tele-Tube telescoping tube that promotes product flow and complete discharge by exerting continual downward tension on the bag as it empties and elongates. Powder transfer is enhanced by means of Flexicon's Flow-Flexer bag activators. These are two pneumatically driven plates that rhythmically raise and lower opposite bottom edges of the bag to direct material into the outlet spout. As the bag empties, the stroke of the plates increases to form the bottom of the bag into a steep V shape and promote total evacuation. An adjustable timer controls the frequency of the strokes. Canisters are refilled from the floor hopper via hoses, using an air-driven venturi system. This is the same method as was used before, says field-support foreman Donnie Calhoun, who is in charge of the refilling operation. However, a key difference is that the floor hopper has a capacity of only 90 kg versus 4,350 kg for the hopper that was previously used. In the new arrangement, the bulk bag essentially fills the role of the supply hopper, and the floor hopper is a sealed transfer unit that continually feeds the refill line. Besides being dust-free, the new unloading system is more efficient than the previous one, says Calhoun. "It used to take about four hours to fill a hopper from the drums, using the auger," he says. "Now, it takes only about five minutes to set up a bag on the discharge frame and start feeding powder."

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