Crystallization technology

Oslo Crystallizers

Since 1924, today a GEA staple. Able to grow the largest crystals in a fluidized bed without mechanical circulation methods.

Invented by F. Jeremiassen of Krystall A/S in Oslo, Norway in 1924, it took the name of the city in which it was originally designed. It is also referred to as “growth-“, “fluid bed-“ and “Krystal-“ crystallizer.

GEA is Davy Powergas' and A.W. Bamforth's crystallization technology successor and as such, owns all the documentation of OSLO installations built by them. This background, added to GEA's own extensive experience, makes the primary designer of OSLO crystallizers of the world out of GEA.

The primary advantage of the OSLO Crystallizer until today is the ability to grow crystals in a fluidized bed, which is not subject to mechanical circulation methods. A crystal in an OSLO unit will grow unhindered to the size that its residence time in the fluid bed will allow. 

The result is that an OSLO crystallizer will grow the largest crystals in comparison to other crystallizer types. The slurry is removed from the crystallizer's fluidized bed and sent to typical centrifugation sections. Clear liquor may also be purged from the crystallizer's clarification zone, if necessary.

Particular features:

  • Large crystals of up to 6mm
  • No internal circulation pump
  • Negligible secondary nucleation rate
  • High supersaturation 
  • Efficient fines destruction
  • Large retention time in the fluid bed 
  • Long production cycle between cleanings

Working Principle

Working Principle of Oslo Crystallizers

The OSLO Crystallizer consists of five basic components:

  • The crystallizer vessel. Provides most of the active volume dictated by the residence time requirements and enables a proper disengagement of process vapors.
  • The baffle. Controls the crystal population by separating fine crystals (to be dissolved by heating or dilution) from coarse crystals (to further growth). 
  • The circulation pump. Provides sufficient circulation rate to operate the crystallizer under optimal supersaturation and superheating conditions. Typically, axial-flow propeller pumps are used.
  • The heat exchanger. Supplies the required thermal energy to the crystallizer for the desired evaporation rate.
  • The fluidized bed. Bed of crystals fluidized by the circulating brine releasing its supersaturation to the suspended crystals.

In a similar way that with a DTB Crystallizer, a clarified solution containing fine crystals of a specific size, is withdrawn from the baffle zone. By superheating the solution within the external heat exchanger, the fines are dissolved. This superheating is relieved through the evaporation of a solvent which is either conduced to the subsequent process steps or is internally reused by applying a recompression system of choice.

The supersaturated solution is then guided down the draft tube, gently fluidizing a crystal bed where the supersaturation is relieved to the suspended crystals through crystal growth.


Heating options for thermal separation plants

Traditionally, an evaporator or crystallizer is heated by live steam, but waste heat can be used as energy source as well, as long as the amount of energy required for the thermal separation process is given.

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