Many operations leaders who are responsible for spray dryers find that maintaining trouble-free operation of their baghouse to be a challenge. If you are experiencing baghouse problems in your spray dryer, here is a list of items to check to diagnose the issue.

Going back to basics, remember that a baghouse is a filter. Its purpose is to capture the product and meet emissions requirements, while allowing your spray dryer to run continuously. It’s the filter media (the bag in the baghouse) that will be particularly important to this discussion of baghouse problems. The baghouse (the stainless steel vessel) is simply a filter housing

Keep in mind that what makes a baghouse on a spray dryer unique from other baghouse and nuisance dust collectors, is that inside the baghouse can be a relatively high moisture environment. If there are carbohydrates or sugars in your product, the air in the baghouse is often at or at least it is near the sticky point, technically the glass transition temperature, of the product. If there are fats in your product, it might be that the temperatures in your baghouse are near the melting point.

A standard filter bag for a food or dairy spray dryer is often a 16 oz polyester felt. There are other materials and fabric weights, but this is most common. There are many coatings and surface finishes available, but often a standard bag will work fine. Beware of additives you may have in your product, for instance Lecithin that may be added in an external fluid bed to instantize and solubilize your product, as additives need to be considered in regards to correct baghouse functioning.

Watch out when buying your baghouse bags because not all are of the same quality — beware of less expensive bags, especially the less-expensive version of bags with surface coatings. These may be fine for standard environments, but problems will often arise when they are applied to the challenging environment of a hot and moist spray dryer.

Potential Baghouse Problems….(All Seen from Experience)

High Pressure Drop
If you are experiencing a high pressure drop, investigate the following:

• Is the instrument reading correctly? Is the product sensor plugged?
• Compressed air for reverse jet pulsing
  • Moisture in compressed air
  • Solenoid maintenance
  • Timing sequence (time on and space between pulses)
• Increase in spray dryer air flow
• Additives – As mentioned above, lecithin can quickly blind over bags

Emissions
Baghouse problems dealing with emissions could be mechanical or process in nature.

• Mechanical Causes
  • Is the filter bag sealing correctly to the tubesheet?
  • Filter bag durability
• Process
  • Filter bag fabric — are the emissions going through or around the bag ?

Product particle size is key. If you make more small particles, you will have more emissions. It’s important to know your particle size distribution, feed material (viscosity), feed solids and spray pressure.

The seal of the bag to the tubesheet is critical to prevent powder bypass. If you suspect problems with the bag sealing to the tubesheet, investigate the following:

• Do the roundness and size of the tubesheet holes match?
• Check the felt fabric (cuff, durability)
• The bag’s diameter — is it correct?

Get to know your bag fabric really well.

• Ask for data from the manufacturer
• Ask for feedback on how their product will interact with yours
• Have your emissions guarantees with your local authorities handy for these discussions.

Caloris is Here to Help

If you need assistance diagnosing and correcting baghouse problems in your spray dryer, contact Caloris anytime. Give us a call at 410-822-6900 or send email to problem.solved@caloris.com to be connected with a spray dryer specialist.

For more information, you may want to check out “Industrial Gas Cleaning,” International Series of Chemical Engineering, Volume 8.