When choosing a crystallizer, many factors must be considered, such as: the nature of the material system to be processed, the particle size and particle size distribution range of the desired crystal product, the size of the production capacity, equipment and operating costs, and so on. It can be seen that the problem is more complicated, and there are no simple rules to follow. To a large extent, it depends on practical experience. Cost and land size are also important factors to consider. Generally speaking, continuous operation of crystallizer is more economical than batch operation, especially when the yield is high. Evaporative and vacuum crystallizers require considerable headspace, but at the same output, they occupy a much smaller floor space than cooling horizontal crystallizers.
Some simple cooling type crystallizers, especially the open groove type, are relatively cheap to make, but the cost of cooling mechanical crystallizers is quite high, and their maintenance costs are also considerable. On the other hand, mechanical crystallizers do not require expensive equipment to generate vacuum. Another shortcoming of cooling crystallizers is that their heat transfer surface often has crystals agglomerate to form scars on the side in contact with the solution, and the side in contact with the cooling water is prone to scale precipitation. As a result, the cooling efficiency is reduced and the removal is increased. Trouble with scar descaling. Such troublesome problems are also encountered in evaporative crystallizers. As for the vacuum crystallizers, they do not have a heat exchange surface, so there is no such trouble, but they are not suitable for solutions with a much higher boiling point, such as the crystallization of caustic soda solutions.