Safety first. Powder deposits in a hot dryer can smoulder and ignite. Follow your site procedure for fire and explosion protection. Never open the chamber or enter it before it is shut down, cooled, isolated and cleared for entry.
Symptoms
- Powder deposits growing on the chamber wall, roof or cone.
- Brown or scorched particles in the product.
- Rising pressure drop over the cyclones or bag filter.
- Higher moisture in the powder, or lumps from the outlet.
Likely causes
- Outlet temperature too low or too high. Too low leaves wet, sticky particles. Too high can make some products soften. Both lead to deposits.
- Atomisation. A worn or blocked nozzle, or an atomiser wheel with damaged vanes or wrong speed, gives large droplets that hit the wall before they are dry.
- Feed changes. Higher solids, higher viscosity, a different recipe or a lower feed temperature changes how droplets form and dry.
- Air flow and distribution. A blocked air disperser, a wrong damper setting or a change in exhaust fan speed lets wet droplets reach the wall.
- Hammers, sweepers and cone air. If wall hammers, air brooms or sweep air are not working, normal small deposits are not removed and keep growing.
- Product stickiness. Products high in sugar or fat become sticky above a certain temperature, so a setting that suits one product can fail on another.
What to check, in order
- Compare inlet and outlet temperatures, feed rate and feed solids with the values from a good production run.
- Check where the deposit is. A ring at nozzle or wheel height points to atomisation. Deposits in the cone point to drying or cone air.
- Inspect the nozzle or atomiser wheel for wear, blockage and correct speed or pressure.
- Check the air disperser, dampers and fan speeds against your service documentation.
- Confirm that wall hammers, sweep air or cone air are running as set.
- Ask whether the recipe, raw material or concentrate solids changed before the problem started.
When to call a TPS engineer
Call a TPS engineer if deposits keep returning after settings are back to normal, if you see scorched or smouldering powder, or before you change the drying profile for a new product.
Ask LiveAccess
Ask with your inlet and outlet temperatures, feed rate and product type, and a photo of where the deposit forms. In the app you can also find a spray drying expert in the Expert Network and chat or call them.
This guide gives general checks. Settings, limits and procedures differ between machines: always use the values in your service documentation and your site procedures.
