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Application example drying
Contact dryers are often used for the evaporation of explosive solvents.
If the product comes from upstream units such as centrifuges, filter presses and suction filters, the material is often still moist and therefore does not flow freely. For this purpose, forced paddle dryers or forced spiral dryers are used, in which the product is constantly shoveled by the mixer during the drying process.
However, this creates a source of ignition: either a controlled atmosphere must be created or the speed must be reduced.
It is generally valid that there is no risk of explosion at peripheral mixer speeds of <1 m / sec, but most products cannot be dried under economical conditions at these peripheral speeds: It takes too long and the product forms agglomerates that can no longer be destroyed.
So it makes sense to cover the product space with pure nitrogen in order to ATEX1)2)-being compliant. For applications in the pharmaceutical and fine chemical industries, it is best to assign nitrogen generators to a specific drying system.
Before starting the contact drying system, it is flushed with pure nitrogen so that the product can then be introduced. During the drying process, the product is also covered with a nitrogen curtain between 5 and 30 m³ / h, depending on the application. As a result of this superposition, drying also takes place faster, since the gas serves as a carrier for the moisture.
- Example of a fully automatic nitrogen system