Analysis of Causes and Countermeasures for Abnormal Operation of Flash Dryers

Flash dryers are continuous drying equipment integrating drying, pulverising and screening functions, widely employed in the processing of high-viscosity, heat-sensitive materials across chemical, food, pharmaceutical and environmental protection industries. However, operational anomalies may occasionally occur during use. Below, we shall conduct a detailed analysis of these issues and their corresponding solutions.

1. Bottom Material Blockage (Most Common Fault)

· Symptoms: Accumulation of wet material at the bottom of the drying chamber, causing agitator rotation difficulties or complete stalling, accompanied by excessive current alarms from the main unit.

· Root Cause Analysis:

· Excessive feed rate or volume: Overloads the dryer's instantaneous evaporation capacity, leading to wet material accumulation.

· Insufficient hot air temperature: Inadequate thermal input prevents rapid moisture evaporation.

· Insufficient hot air volume/pressure: Fails to lift material, preventing normal ‘flash drying’ fluidisation.

· Worn or damaged agitator teeth: Reduced crushing capacity prevents disintegration of large lumps.

· Excessively high initial moisture content or viscosity: Material properties exceed equipment design parameters.

· Remedial Actions:

1. Adjust operations: Reduce feed frequency, adopting the principle of ‘start equipment first, then feed material; stop feeding first, then shut down equipment’ to ensure stable hot air operation.

2. Inspect heat source: Verify steam pressure and gas/fuel supply integrity. Clean heater fins to elevate hot air temperature.

3. Inspect air system: Clean air intake filters, check for fan belt slippage, adjust damper openings to ensure airflow volume and pressure meet specifications.

4. Inspect and maintain agitator teeth: Regularly assess wear on agitator teeth, replace or repair promptly to maintain crushing efficiency.

5. Pre-treat material: For excessively moist or viscous materials, perform preliminary dehydration (e.g., filter pressing) or blend with dry material.

2. Excessive final moisture content in product (incomplete drying)

· Symptom: Discharged product remains damp, failing to meet drying specifications.

· Root causes:

· Insufficient hot air temperature: Primary factor, indicating inadequate heat input.

· High exhaust humidity/insufficient airflow: Moist air cannot be expelled promptly, reducing drying driving force.

· Unstable or excessive feed rate: Insufficient residence time within the drying chamber.

· Excessive clearance in the grading ring (material retention ring): Wet particles are carried out by the airflow before complete drying.

· Countermeasures:

1. Increase hot air temperature: The most direct and effective method.

2. Inspect the exhaust system: Ensure the exhaust fan operates normally, the bag filter is not clogged, and regular cleaning is performed to maintain unobstructed airflow.

3. Stabilise and optimise feed rate: Maintain a uniform, steady feed rate matched to hot air conditions.

4. Adjust grading rings: Appropriately reduce clearance between grading rings and main shaft to prolong residence time for coarse particles, ensuring only dry fine powder is discharged.

3. Product over-drying or degradation

· Symptoms: Product coking, discolouration, or loss of activity.

· Root causes:

· Excessive hot air temperature: Supplies excessive heat.

· Prolonged residence time: Potentially due to insufficient airflow or overly fine material causing prolonged circulation within the drying chamber.

· Remedial actions:

1. Appropriately reduce hot air temperature.

2. Increase system airflow to accelerate post-drying material conveyance, minimising residence time in high-temperature zones.

4. Significant Drop in Output

· Phenomenon: Reduced output per unit time under identical parameters.

· Cause Analysis:

· All causes leading to high moisture content or material blockage as mentioned above.

· Material accumulation within the system: Agglomerates adhering to drying chamber walls, ducts, cyclone separators, etc., reducing effective flow area.

· Baghouse filter blockage: Increased system resistance reduces overall airflow.

· Inadequate equipment sealing causing significant air leakage: Particularly at the drying chamber base, infiltrating cold air lowers bottom temperatures and impairs drying efficiency.

· Countermeasures:

1. Address material blockage and incomplete drying per the aforementioned methods.

2. Regular cleaning: Thoroughly remove accumulated material and scale from the equipment interior after shutdown.

3. Clean or replace filter bags: Verify proper functioning of the compressed air pulse cleaning system.

4. Seal inspection: Focus on seals at manhole doors, sight glasses, and connecting flanges; promptly replace aged gaskets.

5. Abnormal Vibration and Noise

· Symptoms: Severe vibration or piercing noise during equipment operation.

· Cause Analysis:

· Imbalance in agitator shaft: Uneven wear or fracture of agitator teeth compromises dynamic balance.

· Bearing failure: Main shaft bearings damaged due to inadequate lubrication or end-of-life.