Feed is concentrated into solid crystals and pure water using crystallizers. Solid crystals are produced from a liquid solution through crystallization, a solid-liquid separation method. Liquid waste may be eliminated by crystallizers, resulting in zero liquid discharge (ZLD). Primary nucleation and secondary nucleation are the two phases in the crystallization process. The development of new crystals is called primary nucleation. Secondary nucleation is the key stage in the mass creation of crystals, and this is where they grow. Evaporative crystallization and cooling crystallization are two different types of crystallization.
A crystallizer is a device
that feeds a heated saturated solution to a lagged, closed vessel that is kept
under a vacuum; the solution evaporates and cools adiabatically, resulting in
crystallization. The solution temperature is progressively lowered by flashing
the solution in a vacuum. Crystallization occurs as the salt's solubility is
reduced. Preheating can be done with the resulted vapor stream. Alaqua is a
vacuum crystallizer supplier in USA
that also supplies other processing equipment to meet various industrial
demands.
Process of Vacuum Cooling Crystallization
Vacuum cooling
crystallization is mostly utilized for salts that lose solubility as the
temperature drops. The multi-stage vacuum crystallizer K1-4 is fed a warm,
virtually saturated solution. The pressure is progressively lowered in this
scenario, allowing the solvent (water) to evaporate and the solution to cool to
the boiling point. Salt crystallizes when you reduce the temperature. Air drawn
in at the bottom of the crystallizer (air agitation) keeps this in suspension
and transports it to the exit. The suspension is then pushed by the suspension
pump SP to the cyclone ZY for thickening. In centrifuge Z, the liquid is
separated again. In dryer T, the salt is dried. The resultant vapor steam can
be condensed with cooling water in the mixing condenser MK or utilized to warm
the mother liquor in the bath condenser BK. The use of steam jet pump D can
lower the stage pressure and therefore the solution temperature even more. A
vacuum pump VP is used to remove the inert gases.
Some of the advantages of Vacuum Crystallization are mentioned
below:
- Crystallization under control
- Crystals are larger and more uniform
- Fines are reduced
- The color formation is reduced
- Crystal yield is high
Characteristics of Vacuum Cooling
Crystallization
- Cooling surface incrustation (fouling)
does not occur since no cooling surfaces in the form of heat exchangers
are required for evaporation. As a consequence, the duration between cleaning
processes is increased to the maximum.
- After salt separation, heat can be
recovered by reheating the draining solution.
- It is feasible to operate with partial
loads in a flexible manner.
- It can be used in different manners.
- Impeller with a hydrodynamic design.
- Calandria has a smooth bottom and a low
head for better circulation
- Seeding material is mixed quickly.
Variants of Vacuum Cooling
Crystallization
- In order to optimize heat recovery, the
number of steps should be increased.
- With or without separation of salt.
- Horizontal crystallizers with air agitation, an external circulation
circuit (Forced Circulation, FC), or vertical crystallizers with draught
tube and bottom flange stirrer (Draft Tube Baffled, DTB).
- Vacuum generators are created using
vacuum pumps and/or steam jet pumps.
- By using acid condensation or
refrigerating equipment and refrigerants, the pressures and therefore the
discharge temperature of the solution/suspension is reduced.
- In mixing or surface condensers, the
vapor from the last step is condensed.
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