Crystallizer technology

Forced Circulation Crystallizers

The most widely used crystallizer thanks to its simple and robust design as well as the easy operation. Its high mechanical energy input and high secondary nucleation rate make it the best solution when large crystals are not required.

The Forced Circulation Crystallizer is the most common type of crystallizer. Simple in design and easy to operate, it is usually employed in evaporative crystallization of relatively flat or inverse solubility products in rather viscous media and when scaling is a major issue. Its highly mechanical energy input and high secondary nucleation rate make it the best solution when large crystals are not required.

Particular Features:

  • MSMPR (mixed suspension, mixed product removal) crystallizer
  • Suitable for products with relatively flat or inverse solubility curve
  • Limited crystal size (<0.8mm) due to elevated secondary nucleation rate
  • Single loop or double loop installation for large capacities
  • Central pipe or tangential inlets 
  • Scaling and down-time minimization by surface treatment and reliable flushing concepts
  • Auxiliary equipment
    • Demister (internal or external) for condensate quality control
    • Integrated salt leg for elevated product purity
    • Baffle zones (internal or at circulation pipe)

Working Principle

Working Principle of Forced Circulation Crystallizers

The Forced Circulation Crystallizer is made of four 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 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.
  • Interconnecting piping. Connects the components of the crystallizer.

 

Slurry of a desired solid density is circulated from the crystallizer vessel through the heat exchanger, gets superheated and is returned to the evaporation chamber. The superheating is relieved by means of evaporation and the evolving supersaturation is leading to growth of the suspended crystals. The evaporated solvent is conducted to the subsequent process steps or is internally re-used by applying any re-compression system.

forced-circulation-crystallizer-diagram
evaporation-type-01

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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