Product Challenges: Dusting & Dust Containment

by James Podevyn

Product Challenges: Dusting & Dust Containment

In this blog series, we are discussing the common bulk conveying challenges many of our clients face. Today’s blog topic is dedicated to the issue of dusting and dust containment.

Many of our customers have some kind of issue with dust containment when conveying their product and this can lead to a number of very serious issues, from fire and explosive hazards to unexpected downtime and cleanability problems. Containing the dust can lead to increased efficiency in manual handling and help the bottom line as you will lose less of your product into the air. With all of this in mind, we offer dust collection systems as an optional extra on all relevant equipment.

Dust is a Health & Safety Issue

The immediate effects of dust in the workplace can cause irritation to the eyes, headaches, coughing & sneezing. Poor indoor air quality can lower employee performance and cause prolonged absences and even cause long-term serious effects. Employers have a duty to ensure all staff and visitors are not exposed to dust. Using dust tight conveying and bulk bagging equipment is a step towards improving air quality if your product has dusting challenges.

What Causes Dust Containment Issues?

Bulk Bag Design

Most of the issues around dusting come from the dry bulk product itself and how this is stored, filled and unloaded into the bulk bags. A bulk bag must be specifically designed to contain the fines present in a given product, particles can sift through the fabric of the bag.  This looks like smoke escaping from the bag as it is being handled and emptied.  Depending on the number of fines present in the product, the particle size, and its shape, a coated fabric may be all that is required to contain the dust.  However, in some cases, polyethylene liners are required to prevent product sifting.

Large group of bulk bags

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 and dust extraction 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.

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 re-tied 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.

How Can We Overcome these Dust Containment Issues?

Material Testing

Have the supplier test your product in the bulk bag unloader being considered to verify the suitability, and specifically dust control and containment capabilities, of the equipment for your application.

Our test facilities are fully equipped with flexible screw, aero mechanical and tubular drag conveyors, as well as bulk bag fillers and bulk bag unloaders, so we can advise without bias on the right type of solution for your particular product, application and layout restraints. Wherever possible, we simulate your site conditions in terms of conveyor length, flow rate and angle of lift. For more information on Spiroflow’s testing facilities click here. 

Spiroflow materials testing facilities

Bulk Bag Design

Proper bulk bag selection is one of the most important considerations for dust containment in a bulk bag unloading system.  The bulk bag must contain the fines present in your product or particles can sift through the bag fabric.  Depending on the amount of fines present in the product, the particle size, and its shape, a coated fabric may be all that is required to contain the dust.  If coated fabric doesn’t contain the product fines, polyethylene bulk bag liners can be used to prevent product sifting.  Inlet spouted bags, not open top bags, should always be used for dusty materials.

Integral Dust Collection

Bulk bag unloaders can be configured with an integral dust collection system.  This is an important option for discharging dusty materials.  Bulk bag unloaders can also be designed with a port to tie into a plant-wide dust collection system.

Dust Tight Bag Seating

Pay attention to how a full bulk bag is installed within the frame of the bulk bag unloader, as this can be a source of unwanted material dusting.  Often a dust-tight docking seal built within the base of the bulk bag unloader can significantly help mitigate dusting.

Bulk Bag Tensioning

Make sure your bulk bag unloaders are designed to properly tension the bulk bag, and any associated liner so that the complete contents of each bag is discharged.  Residual material trapped in bag creases and folds can potentially increase dusting and spillage during bag removal.

Enclosed Access Chamber

Nearly half of all spillage and dusting occurs during the bag spout untying process.  Controlling dust becomes a much bigger challenge in cases where the product is free-flowing.  Look for a bulk bag unloader design where the bag spout access chamber is enclosed and kept under a slight negative pressure to minimize dusting issues and contain spillage.  For hazardous material applications a glove box arrangement, instead of access chamber doors, should be considered to prevent operator exposure.

Sanitary Spout Docking

Positive spout docking arrangements can ensure complete product containment and allow for efficient bag stretching at the end of the discharge cycle.  Consider this design option with or without the access chamber.  Efficiently docking a spout can require some dexterity and performing this operation in an enclosed area can compensate for operator errors.

‘Empty’ Bulk Bag Removal

Dusting can often occur during the ’empty’ bag removal cycle. It is imperative to tie off the bag spout tightly prior to bag removal.  Consider adding a ‘bag collapsing’ feature that utilizes a dust collector to evacuate the bag and rid the environment of suspended dust.  Again, an enclosed access chamber facilitates the capture of any fugitive dust during this step in your operation.

Manually dumping small bags into a dust tight unloader

Read our Case Study on how we installed a bulk bag unloader for an adhesives company to help reduce dust emissions – Case Study 3015 

Downstream Process Optimization

Allowing sufficient time for the operator to perform each of the necessary steps in the bulk bag unloading process is essential.  Planning for strategic time buffers throughout the process can eliminate downtime and allow the operator to properly perform all the necessary operations for a dust-free bulk bag unloading operation!

Read our Case Study on how Spiroflow helped to eliminate dust ad increase productivity for a pharmaceuticals company: Case Study 6001 – Resin Flakes

Other Equipment

As well as adding these dust contol options to equipment all our mechanical conveyors are dust tight. The tubular drag conveyors, aero-mechanical conveyors and flexible screw conveyors are all great choices when considering a dust tight container. If you are looking to move a product which is particularly dusty take a look at our mechanical conveyor comparison chart to work out which conveyor will best suit your application. Or get in touch with us to discuss conveying your product. We also offer dust hoods, dust collector and glove boxes to help contain the dust and comply to hygiene and saftey standards.

Dust tight flexible screw conveyor

Read our Case study on how we installed a flexible screw conveyor to reduce dust issues for a company conveying flour: Case Study 1016 -Flour