When choosing the crystallizer, many factors should be taken into consideration, such as: the nature of the system to be treated, the particle size and distribution range of the crystal product, the size of the production capacity, the cost of equipment and operation, etc. It can be seen that the problem is relatively complex, there are no simple rules to follow, and to a large extent, it depends on practical experience. Cost and land occupation are also important factors to consider. Generally speaking, continuous operation of the mold is more economical than batch operation, especially when the production rate is high. Evaporating and vacuum crystallizers need considerable top space, but at the same output, they occupy much less ground than cooling horizontal crystallizers.
Some simple cooled crystallizers, especially those with open grooves, are relatively cheap, but the cost of cooled mechanical crystallizers is quite high, and their maintenance costs are considerable. On the other hand, mechanical crystallizers do not need expensive equipment to produce vacuum. Another disadvantage of cooled crystallizers is that their heat transfer surfaces often have crystal scabs on the contact side with the solution, and on the contact side with the cooling water, there are scale deposits easily. The result is to reduce the cooling efficiency and increase the trouble of scale removal. This kind of trouble can also be encountered in the evaporative mould. As for the vacuum crystallizer, they have no heat exchange surface, so there is no such trouble, but they are not suitable for the solution with much higher boiling point, such as the crystallization of caustic soda solution.