Recently, we’ve received a series of questions from an array of customers about the amount of powder build-up or chamber deposits that they are seeing on the walls of their spray dryer drying chambers. They want to achieve less.
Build-up or deposits on the drying chamber walls can cause a multitude of potential problems starting with fire safety issues, especially if auto-ignition reactions are a potential related to Maillard reactions. Discolored specks in the finished powder are a quality issue. Avalanches of powder that block a fluid bed or product outlet are a reliability issue. Microbiological growth is another quality issue. Even if you don’t have these problems, it may just cause you to CIP more frequently, have CIP take a longer duration or use more water and chemicals during CIP. In this case it also increases wastewater loading.
For a well designed spray dryer in the dairy or food industry, it is typical to have the sidewalls of the drying chamber remain clean and free from significant deposits for one week to several months, depending on the nature of the product produced.
Of course, if your spray dryer was originally designed for a different product, or you’ve pushed the production level beyond the original specification, then the drying chamber may suffer from more build-up.
The characteristics of the product are also a factor in drying chamber wall deposits. Particle characteristics like glass-transition temperature (stickiness) need to be understood to have the full context when analyzing a specific dryer or issue.
Check the Air Disperser and Airflow
You need evenly distributed airflow through the air disperser at the original design velocity to prevent certain issues.
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Although it’s unlikely, there have been cases where the air disperser on top of the drying chamber may become partially blocked with debris. We’ve seen fragments of filters blocking airflow, as well as other debris. This should be checked annually.
Many air dispersers have multiple guide vanes inside of them. These guide vanes are often adjustable and may come loose and get out of alignment. An annual check of these parts can eliminate issues.
If the airflow is operating at 80 percent or less of the original design OR is running at 120 percent or above the original design, then the air disperser may not be doing its job correctly. Too low of airflow and the air becomes ’lazy’ and doesn’t go laminarly straight down the drying chamber. Too high of airflow and the air may be pushed too hard through the air disperser and the air is pushed towards the wall. Either case can lead to wall build-up. The solutions for this are to modify an air disperser for higher or lower levels of airflow.
Evaluate the Atomization System
Most spray dryers have high pressure nozzle atomization. There are many reputable nozzle brands (Spraying Systems, Delavan, Bete and others). There will be a correct nozzle, orifice and core/swirl chamber specifications that will be specific to your equipment:
- The atomization pressure at which you operate to produce your required particle size distribution for your feed flowrate
- The correct spray cone angle to efficiently dry while keeping the product from reaching the walls of the drying chamber before the powder is dry and causing build-up or deposits.
If you have a rotary atomizer, similar issues can occur when the feed solids have changed or the rotary atomizer is operating at a non-optimum speed (RPM) for your specific product.
Both of these issues can be evaluated and are generally easy to correct with a site visit from a spray drying process engineer and some parts and adjustments.
Need Assistance With Chamber Deposits?
Are you experiencing problems with your spray dryer system? Caloris can provide service support for units from many manufacturers. Call us at 410-822-6900 or problem.solved@caloris.com to arrange for a process assessment at your facility.
