Summer, and its accompanying humidity, is almost upon us. Are your spray drying systems ready for the extra moisture in the air?

If you’re not dehumidifying your drying air, then you need to be ready to adjust processing parameters (dryer outlet temperature) to account for the extra humidity and prevent excess moisture in the final powder, or at its worst, stickiness that creates clumping in the powder or plugging of the equipment.

If you are dehumidifying the air for all or some portions of your spray dryer, then you should prep the spray dryer for the extra duty it will perform during the summer season. The following problems with dehumidifying air handlers are common when humidity rises:

1. Getting to a dewpoint around 45F in the cooling section
2. Blocked drains under the droplet catcher or demister … or not having a droplet catcher at all
3. Not reheating the air to an adequate temperature above the dewpoint

• A pre-filter to prevent large dust and particles from getting in to the system.
• A dehumidification coil, generally with chilled glycol, should cool the air to a dewpoint of 45F.
  • Bonus Tips
    • Make sure the glycol supply system valves are working correctly
    • These coils should be cleaned annually with a foaming machine to remove any particulate or microbiological growth
• The cooling coil should be followed with a demister (ideally chevron configuration). This collects the condensation from the cooling coil. Correct drainage design is important.
  • Bonus Tips
    • Demisters are very velocity dependent. Too slow of airflow and the small water droplets pass through. Too high a velocity and the condensation carries through. 
    • There needs to be effective drainage from the demister section. The drains are often found blocked or plugged so that the condensation does not drain ourt completely. 
    • The drain needs to have an effective barometric leg so that a drain trap (like under a sink) works correctly for the air pressure inside the air handling unit. This is another area that is often not correct.
    • The demister should be a slide-out design and should be part of an annual cleaning program for equipment. 
• The best most recent innovation in the last 20 years is to add UV lights to the section after the demister to sanitize the damp surface downstream of the demister. Alternatively, these are sometimes installed after the reheat coil. Only about 10% of the systems provided contain UV lights. 
• A reheat coil—the air needs to be reheated such that the relative humidity drops from 100% (dewpoint) to 80% or less. This prevents humidity being absorbed by the powder and adding to the powder moisture. Reheating with a steam coil to 65-68F is needed. There is no harm in heating to higher temperatures if the process requires it.
  • Bonus Tips
    • We often find that these coils aren’t getting to the correct temperature
    • Make sure the valves supplying hot water or steam are working correctly
• A final filter—whether 95% ASHRAE final filters to meet USDA, or some degree of HEPA filtration, the maintenance and correct sealing of the final filters is important to the final product quality. 

Need Assistance Before Humidity Sets In?

Contact us at 410-822-6900 or problem.solved@caloris.com to arrange a service visit at your facility. We can also look for other ways to achieve an efficiency improvement for your equipment.