Melt crystallization is typically used in operations where high purity products are required. It also has the potential to reduce energy requirements due to phase change at a much lower latent heat level.
The suspension-based process provides slow growth rates that allow pure crystal formation even in relatively impure melts.
In special wash columns developed by GEA, the mother liquor is effectively removed from the crystals and a product of high purity is obtained.
Key features:
- Typically applied where high purity products are required
- Two-stage option available for maximum yield
- Separation of components with close boiling points and those difficult to distill
- Ability to split the feed into two streams with adjustable purities
- Continuous stable operation
- Low operation temperatures
- Low energy consumption as the product is typically crystallized only once
- Required heat is two to four times lower than for evaporation
- No need for solvents, thus, no need for solvent recovery or waste byproducts
- Compact plant
- Debottlenecking distillation (+25% capacity)
Working Principle
Working Principle of Melt CrystallizationCrude product is cooled in scraped surface crystallizers. These may be exchanger type or vessel type crystallizers depending on the specific application.
The crystallizer produces pure product crystals and thus, concentrates the impurities in the remaining liquid mother liquor. The crystals are then separated from the impurity rich mother liquor producing a pure product stream and a reject stream. The reject contains the concentrated impurities but also valuable product which may be recovered depending on the specific application.
Each individual crystal is suspended in the mother liquor and can grow freely, suspended in the liquid. With billions of crystals per cubic meter the growth surface can reach 5,000 to 10,000 m2 per m3 of volume, this provides ideal growth conditions characteristic of the suspension based system and results in a 100% pure crystal.
All the impurities are concentrated in the mother liquor outside of the crystal mass and it is most important to remove all the liquid. The crystallizer suspension is fed into a wash column where most of the mother liquor is removed via a filter. The pure crystals form a compressed bed which is then washed to remove any remaining mother liquor. The efficient washing action provided in the wash column is unmatched by any other solid/liquid separation device. The pure product crystals are melted and discharged as liquid product from the system.
Suspension based crystallizers inherently produce pure crystals due to the large growth surface available. The impurities are thereby concentrated in the mother liquor. Wash columns can effectively remove all the mother liquor and thereby produce ultra-high purity product.
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Melt Crystallization: The suspension-based process for pure crystal transformation.
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