Swenson Technology, Inc.

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Direct contact refilgeration crystallization

     When crystallization occurs at such a low temperature that it is impractical to use surface cooling or when the rapid crystallization of solids on the tube walls would foul a conventional surface-cooled crystallizer, a draft tube baffle crystallizer (or a forced-circulation unit) utilizing the direct contact refrigeration technique can be used.

     In this operation, a refrigerant is mixed with the circulating magma within the crystallizer body where it absorbs heat and is vaporized.  Refrigerant vapor leaves the surface of the crystallizer similar to water vapor in a conventional evaporative crystallizer.  It then must be compressed, condensed and circulated to the crystallizer to maintain continuous operating conditions.  Refrigerants must be relatively insoluble in the solutions processed and have the thermodynamic characteristics to minimize compressor horsepower.

     Examples are the crystallization of caustic dehydrate with Freon or Propane, and that of Paraxylene with liquid Propane refrigerant,
 

Reactive crystallization

     Reactive crystallization, where a solid phase crystalline material results from the reaction of two components, can often be performed more profitably in a crystallizer than in a separate reactor.  An example of reactive crystallization is the production of ammonium sulfate from liquid or gaseous ammonia and concentrated sulfuric acid.

     The draft tube baffle crystallizer is particularly suited for reactive crystallization.  The reactants are mixed in the draft tube of the DTB unit where a large volume of slurry is mixed continuously with the materials to minimize the driving force (supersaturation) created by the reaction.  Removal of the heat produced by the reaction is accomplished by vaporizing water or other solvents as in a conventional evaporative type crystallizer.

     Reactive crystallization can also be performed in a forced-circulation type crystallizer where the reactants are mixed in the circulation piping.

SWENSON DTB Crystallizer

Eight SWENSON DTB units produce Potassium Chloride from Dead Sea brine at a rate of 58 tons per hour

Two DTB Crystallizers used for the production of Potash at Cleveland Potash, England