What are the reasons for the formation of crystalline scale on the inner wall of the crystallizer, and how can it be resolved?
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This post was last edited by slayerstar on 2011-2-19 at 14:05. When a crystallizer is cooled using a cooling water jacket, a thick layer of crystalline scale forms on the inner wall of the crystallizer. It affects heat transfer and can cause pipe blockages. There is no other way but to use vacuum evaporation for cooling. However, the efficiency is low; the crystallizer temperature fluctuates due to variations in vacuum level, and the cooling capacity is limited to around 40 degrees. The concentration of the mother liquor is approximately 40%. May I ask, why does scaling occur? How to solve it?
Change the mixing mechanism, add multiple cooling stages to reduce temperature differences, and change the type of crystallizer
Scaling is a common phenomenon during the crystallization process; serious consequences can be avoided as long as the crystallization process is well controlled. The scaling phenomenon in general crystallization processes is mainly caused by nucleation and growth during crystallization, which is reflected on the surface as a temperature difference, that is, the level of supersaturation. To avoid severe scaling, it is necessary to prevent the outbreak of nucleation and the continued growth of nuclei, as well as to stop growth on those nuclei. Generally, it is important to maintain a good flow condition in order to avoid dead zones of supersaturation; another key reason is the elimination of supersaturation. If necessary, we can communicate again.
Coil heat exchange can be considered, along with appropriate stirring.
The problem of crystallization and scaling, which is common in chemical and petrochemical production, is mainly caused by two factors: one is an excessive temperature drive for crystal nucleation； The other issue is that the concentration driving force for crystal nucleation is too high. As long as you choose the right temperature and appropriate concentration, you can completely avoid the problem of crystallization and scaling!
1) Improve mixing to prevent the formation of mixing dead zones； 2) Control the temperature to prevent excessive release of supersaturation ；
We strongly support this key point; that’s exactly what we do
It is a common problem in industry; the main reason for it is excessive supersaturation, which leads to crystalline scars. Everything said upstairs is correct. If large changes are not desired, some devices that promote nucleation can be added to the crystallizer, so that crystals can grow on these substances; for example, rough materials can be attached to the inner wall of the crystallizer, such as placing some ropes there, haha.
This phenomenon is quite common. In my opinion, the first approach is to use external water for steady cooling. Second: Find the crystallization temperature, maintain the temperature at this point for a period of time, and then lower it. Third: Add seeding at the crystallization point and appropriately increase the stirring speed.
1. First, cool it down to room temperature using circulating water at a constant rate, and then further cool it using chilled water at around zero degrees. 2. The stirring speed should not be too slow; an optimal rotation speed is around 60 revolutions per minute. 3. Find the crystallization temperature, maintain the temperature at this point for a period of time, about an hour, and then lower the temperature. 4. It is sufficient to keep the reaction mixture at zero degrees for 1 hour.