Selection of pumps for drying processes

Fundamentally, we must distinguish between short-term drying and drying processes that can require several hours or even days. Independently of the duration of drying, all drying processes proceed approximately as in Section 2.24 

As an example of an application, the drying of salt (short-term drying) is described, this being an already well-proven drying process. 

400 kg of finely divided salt with a water content of about 8 % by mass is to be dried in the shortest possible time (about 1 h) until the water content is less than 1 % by mass. The expected water evolution amounts to about 28 kg. The salt in the chamber is continuously agitated during the drying process and heated to about 80 °C. The vacuum system is schematically drawn in Fig. 2.78. 

If the pumps are to be of the correct size for a longer process run, it is expedient fo break down the process run into characteristic sections. As an example, paper drying is explained in the following where the paper has an initial moisture content of 8 %, and the vessel has the volume V. 

The backing pump must be suitably rated with regard to the volume of the vessel and the desired pump-down time. This pump-down time is arranged according to the desired process duration if the process is to be finished after 12 -15 h, the pump-down time should not last longer than 1 h. The size of the backing pump may be easily calculated according to Section 2.3.1. 

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