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Sunday, August 23, 2020

Principle,construction,working,and uses of Swenson walker Crystallizer


Principle of Swenson Walker Crystallizer

 

Crystallization is induced by passing the cold water in a direction opposite to the flow of hot concentrated solution . This results in supersaturation and subsequent deposition of crystals are deposited . agitation prevents the accumulation of crystals on the cooling surface The crystals are simultaneously separated from the mother liquor and therefore it can be used as a continuous process 

 

 Construction of Swenson Walker crystallizer :  

 

1. It is a linear type and consists of long open . trough about 0.6 metres wide and 3 metres long with a semi-cylindrical bottom . The trough is welded with a water, jacket externally.


2. Long pitch spiral scrapper is fixed as close to the bottom of the trough as possible.


3. Spiral scrapper rotates on its own-axis with the help of a motor. For higher capacity, maximum of four such units are joined together. For still higher capacities, several such sets are placed one above the other. In this arrangement, the solution flows from one set to its below set. 


Swenson-walker-crystallizer-diagram
fig: Swenson walker crystallizer


Working of Swenson Walker Crystallizer


1.The hot concentrated solution to be crystallized is fed at left side of the trough. Cooling water enters through (other end) right side in the jacket. Due to cooling of the hot solution, supersaturation is achieved and crystals begin to form.


2. If necessary, the size of crystals can be controlled by injecting an extra amount of cooling water into the selected sections. 


3.Spiral scrapper rotates on its own-axis at a speed of 7 revolutions per minute. It helps in agitating the mixture and conveying of the crystals, It also prevents the accumulation of crystals on the cooling surfaces by lifting them.


4. This results in a suspension, which allows the crystals to grow individually. Thus aggregation is prevented.


5. Draining table is attached to one end of the crystallizer. Mother liquor and crystals together over flows into the draining table. While crystals are retained, the mother liquor is sent back to crystallizer. The wet crystals are conveyed to a centrifuge. 

 

6.A screw conveyor can also be used in place of the draining table. Screw conveyor with a slight inclination lifts the crystals from solution and delivers to a centrifuge. Mother liquor overflows at a convenient point. 


Advantages of Swenson Walker Crystallizer


1.saving in floor space, material and labour costs can be achieved in Swenson Walker crystallizer. 


(2) It is a continuous process. 


(3) Crystals of uniform size and free from inclusions or aggregations can be obtained. 


Disadvantage of Swenson Walker Crystallizer


The scrapper may break the crystals to a little extent, while agitating the suspension.


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