TL;DR
Outlet temperature is the primary product quality control parameter in spray drying. Verify sensor calibration, then check feed rate and inlet temperature before adjusting setpoints.
What you might see
- outlet temperature rising above setpoint
- product moisture content out of specification
- inlet air temperature sensor reading erratic
- product darkening or off-color
Likely causes
Feed rate lower than setpoint causing reduced evaporative cooling
Inlet heater malfunction delivering inconsistent inlet temperature
Temperature sensor drift or fouling at the outlet probe
Exhaust fan speed reduction decreasing airflow and drying capacity
Required tools
- Reference thermometer or calibrated RTD probe
- Multimeter (for heater element resistance check)
- Moisture analyzer
- LOTO kit (if accessing heater element)
Safety first
- The heater section operates at high voltage AC. Lock out and tag out the heater before inspecting heater elements.
- Spray-dried pharmaceutical powder can be explosive in suspension at high concentration. Follow the site ATEX procedures when working inside the chamber or cyclone.
- Hot inlet air above 150 degrees C is present at startup. Confirm the system is cooled before opening inspection ports.
Procedure
- 1
Check the current feed rate on the feed pump controller. Confirm it matches the process order setpoint.[1]
- 2
Check the inlet air temperature reading. If the inlet temperature is low, inspect the heater output.[1]
- 3
Inspect the outlet temperature sensor probe for product buildup or physical damage.
- 4
Calibrate the outlet temperature sensor against a reference thermometer at a known temperature point. Sensor drift above 2 degrees C requires recalibration.
- 5
Check the exhaust fan speed and compare to the setpoint. Low fan speed reduces airflow and raises outlet temperature.
- 6
If the heater is not reaching setpoint, check the heater element resistance and the temperature controller output.
- 7
After corrections, allow the dryer to stabilize for 10 minutes before sampling product for moisture content.
Sources
GEA Niro GEA Niro PSD / Mobile Minor Spray Dryer general technical documentation, GEA Niro
GEA Niro PSD / Mobile Minor spray dryer general temperature control and sensor maintenance procedures (general)
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