Fault Analysis of Spray Dryers

Even a successful design cannot guarantee fault-free operation during use, as malfunctions may occur due to climatic or seasonal variations. Consequently, numerous variables influence operational performance. An experienced operator must swiftly identify and resolve system anomalies to minimise downtime. Regardless of scale, any failure that cannot be promptly diagnosed constitutes a major fault. Common production issues include:

1. Material Adhesion to Walls

Sudden adhesion during production primarily results from poorly coordinated operational parameter adjustments, potentially linked to:

A. Fluctuations in airflow volume

B. Changes in airflow direction when regulating fan output

C. Inadequate atomisation causing material to stick

2. Excessive Product Moisture Content

Excessive product moisture primarily relates to air velocity and temperature. Additionally, ambient relative humidity contributes to moisture overrun. Increasing air intake or appropriately adjusting inlet/exhaust temperatures resolves this. Experienced operators should adapt conditions to climatic or material variations, maintaining optimal system efficiency. Continuous monitoring of system status is essential; anomalies require swift, accurate diagnosis for rapid fault rectification.

3. Product Overheating

Particularly for heat-sensitive materials, quality degradation due to overheating is the most common fault. This arises primarily from two causes: firstly, excessively low gas velocity within the drying chamber. During spray drying, droplets on the outer periphery of the spray cloud dry first. As the initial velocity of the atomised droplets significantly exceeds the gas velocity, an upward vortex forms, drawing the dried powder into the high-temperature zone. Exposure to these elevated temperatures causes degradation and other adverse effects. The primary solution is to appropriately increase the gas velocity. Most spray drying units are equipped with sight glasses; observation through these indicates normal gas flow when no upward vortex is present. Numerous operational examples recommend maintaining this velocity around 0.5 m/s. Another contributing factor is excessively high exhaust gas temperature. Many spray-dried products are carried away with the exhaust gas before separation, meaning exhaust gas temperature directly influences product temperature. A relative temperature differential exists between the two, with exhaust gas typically being 10–30°C higher than the product temperature. Should the exhaust gas temperature be elevated, the product temperature will inevitably rise. Exceeding the product's heat resistance threshold may cause overheating and degradation. The solution lies in controlling the exhaust gas outlet temperature. This is achieved by either reducing the inlet temperature of the hot air or increasing the atomised liquid flow rate. This establishes a thermal equilibrium within the system that satisfies the exhaust gas outlet temperature requirements, thereby ensuring the product remains within its specified temperature parameters.