Companies around the world transport and handle large volumes of materials in bulk bags but unloading bulk bags can be a dusty mess if not managed properly. Let’s examine what causes dust emissions.
Bulk Bag Design: Unless a bulk bag has been specifically designed to contain the fines present in a given product, particles can sift through the bag fabric. This looks like smoke escaping from the bag as it is being handled and emptied. 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.
Onset of Product Flow: The point in time when the operator releases the outlet spout tie and product begins to flow can be a significant contributor to dust emissions. If the product is flowable, when the outlet spout is released a down rush of product can occur. You must be sure that your bulk bag unloader is designed to handle the down rush that can occur the bulk bag unloader is closed. The rapid drop of product causes an updraft of dust laden air that must be extracted properly or it will result in a cloud of dust being emitted into the atmosphere. Look closely at how your bulk bag unloading equipment is designed to prevent this.
Product Flow: Your bulk bag unloader must provide suitable dust containment while product is moving out of the bulk bag. While this seems obvious, make sure your equipment can’t lose its ability to extract dust during the discharge cycle while the bag empties. You don’t want the bulk bag to move in such a way that alters the integrity of the ‘seal’ required to maintain proper dust containment.
End of the Discharge Cycle: As the final pounds of product empty from a bulk bag it may cause the bulk bag unloader’s dust containment/extraction features to lose their ability to control dust. This can result from the bag breaking its seal with the equipment as it loses its shape near the end of the discharging cycle.
Empty Bulk Bag Removal: Dusting can still occur even when the bag is ’empty.’ When a dusty product has been discharged from the bulk bag, the bulk bag is still full of dust laden air. If the bag is removed from the bulk bag unloader without re-tying its outlet spout the dust laden air will exit the bag in transit from the discharger and spread throughout the immediate plant area. Even if the outlet spout is retied prior to removing the empty bag, care must be taken in how it is handled when it reaches the disposal area – a bulk bag can’t be folded or compressed without doing something with the dust laden air it contains. Determine the best Standard Operating Procedure for your situation and ensure that your bulk bag unloader supports it. It may be necessary to use purpose-built bulk bag folders to make this step of the process dust free.