Swenson Walker Crystallizer is a continuous type crystallizer designed to make the large, uniform crystals .This operation involves both heat and mass transfer. It works on principle of super saturation by cooling.

Introduction:

• Swenson Walker Crystallizer is a continuous type crystallizer. This operation involves both heat and mass transfer. 
• Crystallization is the formation of solid particles within a homogeneous phase. It may   occur   as   the   formation   of   solid   particles   in   a   vapor,   as   in   snow;   as solidification from a liquid melt, as in the manufacture of large single crystals; or as crystallization form liquid solution.
• In the formation of crystals two steps are required:
• Nucleation:  i.e. the birth of a new solute particle
• Crystal growth: i.e. the growth of the nucleus to macroscopic size.

Principle:

• It works on principle of Super saturation by cooling. A very common type of continuous crystallizer using cooling alone to bring about supper saturation is the Swenson-walker crystallizer.

Construction:

• It consists of U- shaped open trough with a semi cylindrical bottom.
• A water jacket welded to the outside of trough.
• A slow speed, long pitch, spiral agitator running at about 7 RPM and set as close to bottom of the trough as possible.
• Water jacket is divided into section so that differential cooling may be used in the various zones.
• The crystallizer is built in units 10ft long and number of units may join together to increase the capacity.
• For still higher capacity, this larger unit may be arranged one above the other such that the solution cascade from one unit to other.

Operation:

• The hot concentrated solution to be crystallized is fed at one end of trough & cooling water usually flows through the jacket in counter current to the solution.
• Sometimes extra amount of water is introduced into certain sections of trough to control crystal size.
• Nucleation may be started by short cold zone followed by gradual cooling.
• Functions of the spiral stirrer are :
• To prevent an accumulation of crystals on the cooling surface.
• To lift the crystal formed & shower them down through the solution so crystal grow uniformly and free from aggregate and inclusion of mother liquor.
• At the end of the crystallizer, there is overflow gate where crystals and mother liquor overflow to drain box.
• From the mixture, mother liquor is returned to the process & wet crystals are fed to centrifuge.

Advantages:

1. Less floor space is required
2. Saving labor
3. Continuous process
4. Crystal of uniform size, free from inclusions/aggregates

Disadvantages :

1. Scrapper may break crystal to the little extent due to agitation.

Currently Available Swenson Crystallizer in Market :

• Swenson Draft Tube Baffle (DTB) crystallizer is the most successful of the crystallizers designed to make the large, uniform crystals required for fertilizer and similar applications where superior filtration, centrifugation, washing, drying, and storage characteristics are required. This design is the result of years of research and development as well as proven plant scale operation in hundreds of installations.

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