A priori, the accumulation of crystals on the walls can occur both on the crystallizer body as well as in the exchanger.
In the body, if blocks of crystals form by splashing, this leads to:
- - the agitator becoming unbalanced;
- - the incorrect operation of temperature, pressure and density detectors;
- - blockages when the blocks detach and enter pipes.
In order to decrease the influence of splashes, we must avoid using rough surfaces, onto which drops of supersaturated liquor can stick. Preferably, the material used should be a smooth or polished surface (rubber or enameled steel).
Inside the exchanger, if an internal tube wall becomes lined with crystals (crusting), the power of the thermal transfer is reduced together with the installation’s capacity, and in extreme cases, the tubes may become blocked. For this, there are three categories of solutions:
- - avoiding excessive supersaturations. In case of cooling, we must enter the labile zone and, in case of vaporization, boiling on the exchanger walls is to be avoided;
- - an internal tube diameter of 35 mm rather than 20 mm slows blockages compared with a smaller diameter without altering the thermal transfer;
- - a slurry speed in the order of 2 m.s-1 ensures that any crystals deposited will be reintroduced without causing any erosion on the tube wall.