Dust collector for pneumatic conveying systems : overview

Pneumatic conveying aims at moving powders and other solids with air. The mixture air + product must then be separated at the end of the conveying. It is done thanks to a dust collector equipped with a filter.

1. Material collection then discharge to equipment

The simplest way to separate material and air at the end of a pneumatic conveying line is to install a material collection hopper equipped with a filter. The air stream is typically entering the hopper just below the filters. The material and air thus separate in the bottom of the hopper where the material accumulates and the air goes up to the filters, carrying dust. The dust is then filtrated and retained on the filters (there are different levels of efficiency depending on the filter media). When the cleaning system is activated (typically a pulse jet system), then the dust cake falls back to the product stream (repeating those cycles should allow the fine dusts to somehow agglomerate and be taken out via the product stream at the end of the hopper.

The outlet of  the hopper will depend how is operated the conveying line. If the conveying is continuous, if the discharge must be done to a vessel with a higher pressure, or if required as a dust explosion safety measured, the hopper must be connected to an airlock rotary valve.

If the conveying is done by batch, which allows the content of the hopper to be discharged in between 2 conveying, a simple butterfly valve can be used.

An alternative, to reduce the load of materials to the filter, is 1st to install a cyclone, then have the dust filter downstream. Both equipment are discharging to the next unit operation.

In order to combine the advantages of both systems, a tangential inlet is often used to enter the materials to the receiving hopper.

2. Dust collection directly on a process equipment

The dedusting filter can be located directly on a process equipment to have quick loading, for example of a dry mixer, or a larger hopper. This system is however less and less used to the profit of having a well defined equipment separating bulk solids and air.

3. Different kinds of inlets

The most common situation is to have the inlet of material below the filters and use the free area below the filters to disengage most of the powder and reduce the load to the filters. However, in certain situations, it is possible to foresee the inlet of material at other levels :

• Inlet on top of the filters
• Vertical inlets

In both cases, some precautions must be taken to avoid a direct contact in between the incoming material and the filters and it would wear then create very early dust leakages. Some free areas must be implemented around the filters for this purpose.