Packaging any dry bulk solid material involves the transfer of product from the end of the process/storage/conveying system to the package. At that transition point, depending on the material and other factors, dust emissions can occur. How do you ensure that your bulk bag filling system doesn’t emit dust and become a productivity and profit drain?
Controlling dust in your packaging operation involves careful bulk bag design as well as expert bulk bag filling equipment design.
Bulk Bag Design #1: Unless a bulk bag has been specifically designed to contain the fines present in your product, particles can sift through the bag fabric as the bag is being filled. This looks like smoke escaping from the bag seams and/or fabric as the product enters the bag. Depending on the amount of fines present in the product, the particle size and its shape, coated fabric may be all that is required to contain the dust. However, in some cases polyethylene liners are required to prevent product sifting.
Bulk Bag Design #2: Bulk bags come in many styles. Most have a top panel where a cylindrical inlet spout is sewn. Others have duffle style tops that expose the entire top of the bag to the atmosphere. Easily aerated products should never be filled into open top bulk bags. While there are ‘area extraction’ dust collection systems that are designed to work in relatively close proximity to a source of dust emissions, they are virtually never consistently effective. Rule of thumb: use inlet spouted bags for dusty product.
Connecting the Bulk Bag to the Upstream Process: The connection between the bulk bag’s inlet spout and the tube or cylinder through which product flows must be secure and dust tight. While there are a few workable systems where the inlet spout is strapped to the tube with a bungee cord or some variation of a circular clamp, often this solution results in the inlet spout being bunched up around the tube thereby creating channels for air – and dust – to escape. Use a fill tube with an inflatable collar that expands to securely hold the inlet spout and in so doing provides a seamless, dust tight, connection.
What happens to the air? An empty bulk bag contains air in an amount equal to the volume of the bag. Your 50 ft3 bulk bag that is now rigged and ready to be filled contains 50 ft3 of air. What happens to that air as the bag is being filled? For every increment of product volume that enters the bag, an equal volume of air leaves, or is displaced, from the bag. If that air contains dust particles there is a constant stream of dust laden air that must find its way out of the bulk bag as it is being filled. Where does it go? Unless your system is specifically designed to deal with displaced air it will still escape but not in a good way. The choices for trapped air are to filter out of the bag itself (see sifting above) or to otherwise find an opening in the upstream connections to the atmosphere. To properly contain dust your bulk bag filler MUST have a twin-tube bulk bag fill head that features an inner cylinder where product flows into the bag and an outer, concentric, cylinder that forms an open ring or annular gap around the inner tube. The outer tube has a dust vent that is connected to a dust collection system that provides the required amount of vacuum to extract the dust laden, displaced air through the annular gap.
What happens when the bag is filled? Your bulk bag is filled to its target weight and you are ready to disconnect the bag’s inlet from the fill tube. Home free? Maybe not. If your product is a health or explosion hazard dust particles may be emitted from the inner surface of the fill tube and the inlet spout as the bag is disengaged and the inlet spout is tied must be contained. In this case a specialized dust containment chamber that encloses the fill tube and inlet spout area of the bag, maintained under negative pressure relative to the atmosphere, can be incorporated. The operator accesses the interior of the chamber through flexible ‘letter’ slots. As the spout is released from the fill tube and tied by the operator within the chamber, any dust particles emitted are extracted. This provides an extremely high level of dust containment.