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The drying process
In general the process of drying solids more or less evolve according to a similar route. In the early phase of the drying process there might be an excess of liquid and the solid particles will be separated from each other by the liquid phase. During the drying process the amount of liquid decreases and the particles tend to move towards each other as there is less room in their liquid environment. As long as there is free liquid or liquid on the outside of the particle the drying rate will be largely determined by the amount of heat put into the system. The greater the amount of heat that can be put into the system the faster the drying rate will be. This phase of the drying process is often called the constant rate drying. If the process conditions maintain constant the drying rate will remain constant.
As soon as the free liquid is evaporated the particles are kept together by liquid bridges. These bridges cause capillary forces and some of the remaining moisture can even be absorbed inside the particles. This final amount of liquid is harder to remove and the drying rate will gradually be reduced. Therefore this phase of the drying process is also called the falling rate drying phase. Especially the moisture absorbed inside the solid will be evaporated slowly, sometimes vacuum can help to increase the drying rate.
Drying efficiency: going green!
|Nowadays Industry is obliged to reduce its energy consumption. In fact the scale and nature of most processes must allow for a significant reduction of used energy! Of course this all starts with selecting the proper and most energy efficient equipment. The responsible use of resources and a constant evaluation of energy consuming processes is paramount. In the case of solids dryers the solvent to be evaporated should be removed as much as possible by mechanical means, e.g. filtration, centrifugation or sedimentation. Then the drying process selected should be the one that produces the minimum amount of wasted energy. And finally serious effort should be put in to the recovery of the energy put into the process, e.g. by means of heat pumps, vapor flow recompression, use of superheated steam or some other means of recovery of the exhaust energy by heat exchangers. Hosokawa Micron engineers have extensive experience in helping select your optimal
drying equipment and applications out of a wide
range of energy saving technologies.
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