Draft tube crystallizers are for superior control over crystal size and characteristics.
For superior control over particle size when excessive fine crystals are present, the Swenson draft tube baffle (DTB) crystallizer has been proven highly effective. This type of crystallizer is used primarily in the production of a variety of large-size crystalline materials such as ammonium sulfate, potassium chloride and diammonium phosphate for the fertilizer industry.
The DTB crystallizer is built in both the adiabatic cooling and evaporative types and consists of a body in which growing crystals are circulated from the lower portion to the boiling surface by means of a large, slow-moving propeller circulator. Surrounding the suspended magma is an annular settling zone from which a stream of mother liquor bearing fine crystals can be removed. These fines are separated from the growing suspension of crystals by gravitational settling in the annular baffle zone.
A solution of 28% Na 2 SO 4 is to be crystallized to yield Glauber's salt in a four-section Swenson-Walker crystallizer. It is fed to the unit at 100 o F and is cooled with 50 o F water flowing countercurrently. The crystallizer has a cooling surface of 3ft 2 /ft, and each section is 10ft long. The crystallizer operates with an overall coefficient of heat transfer of 20 BTU/hr-ft 2-o F across. This invention relates to vacuum crystallizers and method of crystallizing. The invention has particular relation to the method of and apparatus for crystallizing disclosed In my prior Patent 1,865,614 issued July 5, 1932, according to which crystallization is effected by subjecting the solution to a vacuum whereby the solution is cooled to the temperature at which crystals deposit. The Swenson-Walker crystallizer. Oae of the commonest types of continuous crystallizers (with cooling only) used in the United States is the Swenson-Walker crystallizer, shown in Fig. It consists of an open trough A, 24 in. Wide, with a semicylindrical bottom, a water. The Computer-Aided Design ('CAD') files and all associated content posted to this website are created, uploaded, managed and owned by third party users.
Fines leaving the baffle zone are sent to a following stage, settler, or heat exchanger in the case of an evaporative DTB crystallizer. The mother liquor is returned to the suction of the propeller circulator after the fines have been destroyed by heating or mixing with dilute feed or water, depending on the flowsheet.
Low temperature rise at low power input
In the case of adiabatic cooling or evaporative crystallizers, the temperature rise in the circulated magma caused by the mixing of the incoming feed or heated mother liquor at the eye of the propeller is approximately 1°F and thereby limits the supersaturation rate to very low values. The boiling action is concentrated in the center of the vessel and is well distributed across the surface by means of the vertical draft tube inlet.
Crystallizers of this type typically operate with a suspension of solids ranging from 25-50% apparent settled volume. The low temperature drop at the boiling surface and the uniform distribution of boiling created by the circulation pattern minimizes crystallization buildup on the walls of the unit and extends the operating cycle. There are no close clearances where salt buildup can produce a large reduction in the rate of circulation as in other crystallizer designs.
Baffling allows slurry density control
Swenson DTB crystallizers are especially useful in multiple stage cooling crystallizer applications where cooling of the feed solution in each stage limits the natural slurry density to a few percent. By means of the baffled zone, the operating slurry density within the crystallizer can be regulated at any desired value by controlling the slurry underflow rate and removing the remaining mother liquor from the baffle section.
Organic and inorganic chemicals produced by the Swenson draft tube baffle crystallizer include: hypochlorite, Epsom salt, potassium sulfate, monosodium glutamate, borax, sodium carbonate decahydrate, trisodium phosphate, sodium chlorate, boric acid, MAP, urea, YPS, etc.
Basic Principles of the Swenson DTB Crystallizer:
Swenson Walker Crystallizer Pdf Download
Growing crystals are brought to the boiling surface where supersaturation is most intense and growth is most rapid.
The baffle permits separation of unwanted fine crystals from the suspension of growing crystals, thereby affecting control of the product size.
Sufficient seed surface is maintained at the boiling surface to minimize harmful salt deposits on the equipment surfaces.
Low head loss in the internal circulation paths makes large flows at low power requirements feasible.
Swenson Walker Crystallizer Pdf Online
Advantages of the Swenson DTB Crystallizer:
Capable of producing large singular crystals
Lower operating costs
Minimum space requirements, single support elevation
Adaptable to most corrosion resistant materials of construction
Can be easily instrument controlled
Simplicity of operation, start-up and shutdown
Produces a narrow crystal size distribution for easier drying and less caking
Product size varies only slightly with large changes in production