Swenson Technology, Inc.

 Page 1

SWENSON two-stage forced-circulation evaporative crystallizer at Armour Agricultural Chemical Company

Crystallization: An industrial process for producing high-purity compounds from impure solutions with low energy input.

     Crystallization is the process by which a chemical is separated from solution as a high-purity, definitively shaped solid. 
     A crystal may be defined as a solid composed of atoms arranged in an orderly, repetitive array. The inter-atomic distances in a crystal of any definite material are constant and characteristic of that material. Crystals are, in short, high-purity products with consistent shape and size, good appearance, high-bulk density and good handling characteristics. 
     Because the pattern or arrangement of the atoms is repeated in all directions, there are definite limitations on the shapes which crystals may assume. For each chemical compound, there are unique physical properties differentiating that material from others, so the formation of a crystalline material from its solution, or mother liquor, is accompanied by unique growth and nucleation characteristics. 
     While crystallization is a unit operation embracing well known concepts of heat and mass transfer, it is nevertheless strongly influenced by the individual characteristics of each material handled. Therefore, each crystallization plant requires many unique features based upon well established general principles. Each application must be evaluated on an individual basis to achieve optimum results. 
     The mechanical design of the crystallizer has a significant influence on the nucleation rate due to contact nucleation (that which is caused by contact of the crystals with each other and with the pump impeller, or propeller, when suspended in a supersaturated solution). This phenomenon yields varying rates of nucleation in scale up, and differences in the nucleation rates when the same equipment is used with different materials. 
     It is important in performing pilot plant tests that designs are used in which both the small- and large-scale characteristics are well known, and that the testing is performed by highly experienced personnel. 

Swenson Crystallization experience

     The Swenson Evaporator Company, was formed in 1889 to build sugar evaporation and crystallization equipment. Since that time, Swenson has become a recognized force in the market and has broadened its capabilities to include the manufacture of a wide range of crystallization equipment, including evaporative, surface-, vacuum- and refiigerant-cooled crystallizers ranging in size from pilot plant equipment to units over 40' in diameter. 
     Swenson has long maintained a fully staffed, fully equipped laboratory for development and feasibility testing. The facilities include a rising film and falling film evaporator, a forced-circulation evaporative crystallizer, two draft tube baffle crystallizers, and a small glass unit capable of handling about three liters of slurry. Operation is typically "around the clock" and tests with centrifuges, filters and dryers can be made so that the laboratory product will resemble the