When dealing with unplanned downtime, there are many mechanical and process related reasons for downtime, one of the most common causes of paddle dryer downtime is blockage of cyclones, chamber outlets, conveyor lines and similar equipment; blockages are of two main Cause: Mechanical problems and moisture. Mechanical issues - whether bridging or reducing flow - are easier to deal with than moisture. These problems are dealt with using mechanical devices such as pneumatic hammers, bridge crushers or increased outlet size.
More difficult problems include moisture and condensation. By definition, the air inside a drying process vessel—whether it’s a chamber, cyclone, or baghouse—is moist and warm, while the temperature outside the vessel is cooler. Condensation can occur if the inner surface of the container is allowed to cool below the dew point of the humid air.
For processes with a dryer outlet temperature of 160°-180°F, the dew point can be in the range of 120°-130°F. If the vessel is at 80°F, there is enough temperature difference to cause heat loss and condensation, causing product to plug or bridge. These problems are usually eliminated if the vessel is insulated and jacketed or heated.
Cyclone tip or key component for product export. In a cyclone tip, the rotation of the air is high. Conversely, because the air velocity is high, the air pressure is low. For example, in a high efficiency cyclone with a 6 inches water column pressure differential between the air inlet and outlet, the static pressure in the tip may be -20 inches water column. This low pressure is the same as moving ocean water from sea level to 1,400 feet above sea level. This low pressure in the region of the cyclone tip causes fog or condensation in the air.
