Eliminating Dust Dangers in Bulk Bag Handling Operations

April 1, 2001
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15 years ago, bulk bags were mainly used to contain high tonnages of relatively low value products, such as sand or cement. Today, bulk bags are also used for small amounts of valuable materials, such as organic food ingredients or specialty ceramic products, many of which have difficult flow characteristics and are inherently dusty.

To limit product waste and facility hygiene problems, a number of new procedures are being implemented in bulk bag discharging or unloading. Bulk bag handling companies have recognized the need for these options and have designed their equipment around manufacturers’ needs. New options available in the ceramic powder handling industry include spout closure bars, dust control and containment systems, and static control features.

Spout Closure Bars

On some bulk bag handling systems, an interlocked access door enables the operator to pull the bulk bag spout through the opening of the discharge dish in which the bag sits. The pneumatically operated spout-closure pinch bars close off the bag above the tie string. The bag can then be untied without releasing its contents. The access door is closed, allowing the pinch bars to be opened to release product into the integral conveyor chute.

These circular or “yoke”-type pinch bars* are especially useful if only part of a bulk bag needs to be discharged and then retied—which is often the case in ceramic batching applications.

Dust Control During Unloading

Dust control systems can be attached to bulk bag discharging equipment to effectively deal with material, but in these cases, a quantity of air will be displaced and must be vented. The displaced air is usually extracted by an integral dust extraction device or through a vent into a facility-supplied dust extraction system.

To increase the air quality around the bulk bag handling areas, many bulk bag equipment manufacturers now supply an integral dust collection device.

Containing Hazardous and Noxious Powders

A number of products handled in bulk bags are fine, powdery and invasive. The problem is exacerbated when the product is volatile or toxic, or presents an explosion risk. For these materials, total containment during unloading is necessary to prevent contamination of the local atmosphere and health and safety hazards. Other options often include:
  • A sealing device for the bag base spout*
  • Automatic spout stretching*
  • Variable height adjustment for different bulk bag sizes
  • Static grounding and monitoring
As a bulk bag is filled or discharged, a steady accumulation of charge occurs within the product, which is transferred to the walls of the bag. If left unchecked, this static buildup can result in spark discharges from the surface of the bulk bag, or the charging of adjacent isolated conductors, such as people or unearthed metal, by induction. Additionally, in a hazardous environment where toxic or flammable fumes exist, sparks thrown into the atmosphere during the emptying process can cause the product or atmosphere to ignite, resulting in a fire or explosion.

Specially designed features can ensure the safe discharge of bulk bags and eliminate the risk of dust emissions. The outlet spout of the bag can be connected to an inflatable seal that will prevent dust from escaping during the bag discharge process. The sealing device inflates inside the bottom spout and seals it during discharge to eliminate the risk of dust emissions. Additionally, a tensioning device that pneumatically stretches the outlet spout can be used to promote a smooth and cylindrical path for the material to flow directly into the manufacturer’s downstream process, as well as to eliminate the possibility of a crease being formed and holding residual material. This feature is of special value with poor flowing or light products. To further facilitate material flow, a discharger with variable height adjustment can be used, ensuring safe discharge of any size bulk bag.

Depending on the level of product containment required, the bag outlet spout connection can be placed in a containment enclosure connected to a centralized dust extraction system, or it can be fitted with an integral HEPA filter. When operating correctly, these units can achieve containment levels of up to 0.025 micrograms per cubic meter.

Material can still escape when the empty bag is removed, so total discharge of the product from the bag is crucial. This can be achieved by positioning bag massagers at every corner and two at the bag’s base. The bag can also be attached to a pneumatic bag/liner tensioning system.

Ensuring Bulk Bag Safety

No matter what type of bulk bag unloading system is used, most manufacturers have recognized the need for dust containment and static control. Specially designed options in bulk bag handling systems are now making it easier than ever to comply with regulations and ensure operator safety.

For More Information

For more information about bulk bag handling systems, contact Spiroflow Systems, Inc., 2806 Gray Fox Road, Monroe, NC 28110; (704) 291-9595; fax (704) 291-9594; e-mail info@spiroflowsystems.com; or visit http://www.spiroflowsystems.com.

*patented by Spiroflow

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