Our evaporators and crystallizers are implemented
for zero liquid discharge applications among other
convert dilute or concentrated salt containing water streams into solid salt
crystals and clean water. Crystallization is a solid-liquid
separation technique in which solid crystals are
formed from a liquid solution. Crystallizers can eliminate
liquid wastes to create zero liquid discharge (ZLD).
Crystallization is divided into two stages: primary
nucleation and secondary nucleation. Primary nucleation
involves the growth of new crystals. Secondary nucleation
perpetuates growth and is the main stage that causes the
mass production of crystals. There are three types of
crystallization processes: concentration, cooling
(under vacuum or with a heat exchanger), or by reaction or
Selecting crystallizers requires an
analysis of application requirements. For example, a brine
crystallizer processes wastewater and produces both solid
salt crystals and clean water. A resin crystallizer allows
for the crystallization of flake or amorphous resin pellets.
A vertical continuous cooling crystallizer (VCCC) is used to
crystallize highly viscous and extremely slowly
crystallizing fill masses. Other application-specific
crystallizers are also available.
Crystallizers can either stand alone or
be combined with other technologies, such as a brine
concentrator or evaporator. Steam-driven evaporators remove
water from a solution or slurry, but the discharge is still
in liquid and not crystal form. During evaporation, a
product is concentrated by boiling off the solvent, generally
water. A brine concentrator is a specific type of evaporator
used to turn waste-saturated industrial wastewater into
distilled water for reuse. A typical brine concentrator can
recover 95 to 99% of wastewater for reuse. Evaporators and
crystallizers often replace steam hosts when a plant’s
original host is lost.
Brine crystallizers are suitable for recovering
salts from waste water that can then be used or sold. In
this way, a crystallizer maximizes waste stream usage and
helps plants meet zero liquid discharge (ZLD) requirements.
Crystallizers are used in manufacturing, chemical
processing, mining, petrochemical refining, and electrical
component manufacturing applications.
In the design and manufacturing of
crystallizers, our work focuses on the
crystallization of solutions and not on the melt
crystallization. Our expertise covers the three types of
We possess the know-how and expertise for
all of the following types of crystallization equipment: with total or
partial classification, involving the recirculation of the
magma, with or without settling zones.
Forced Circulation Crystallizer
Oslo Type Crystallizer
DTB crystallizer (draft - tube -
Induced Circulation Crystallizer
An "active volume", designed case by
case, to get both required residence time for crystal
growth and mother liquor desuper saturation
A given agitation (recirculation
rate) rated to control the extent of super saturation
arising from the evaporation, and to keep the
temperature difference in the heat exchanger within
A special design of the liquid-vapor
separation area to minimize the carry over losses and
avoid the formation of an excessive amount of fines,
which is highly detrimental to crystal growth.
Continuous Forced Circulation
Crystallizer: depending upon specific process requirements,
additional devices for our Crystallizers can be provided.
Internal baffles, used mainly for
excess mother liquor overflow and /or withdrawal of
fines when crystal growth is slow or disturbed by
impurities build-up (see Figure 2)
Elutriation leg, to improve product
purity and to deliver a narrow crystal size distribution
An internal scrubbing section to
reduce to very low value the carry over losses, or even
to provide stripping or absorption devices when a
volatile compound must be recovered
Continuous Forced Circulation
Forced circulation crystallizers are of
the (Mixed Suspension Mixed
Product Removal) MSMPR type and operate either on controlled
or "natural" slurry density depending upon process
requirements and/or unit material balance.
These crystallization systems can be either single or
multiple effects and the vapor recompression concept (either
thermal or mechanical) is often applied. Usually, these
operate from low vacuum to atmospheric pressure.
As a rule, these crystallization units are used for high
evaporation rates and when crystal size is not of the utmost
importance or if crystals grow at a fair rate.
Almost any material of construction can
be considered for the fabrication of these crystallizers.
It is worth bearing in mind that the
heating element is omitted for vacuum cooling crystallizers.
Typical products produced with these
When the problem of scaling impedes the
process of concentration, a crystallizer design similar to the one
described above is proposed. This applies for CaSO4
saturated solutions, like fertilizer grade phosphoric acid,
demineralization effluents, vinasses.
The Oslo type crystallizer also called
classified-suspension crystallizer is the oldest
developed for the production of large, coarse crystals.
The basic crystallizer design criteria are two fold:
Desuper saturation of the mother
liquor by contact with the largest crystals present in
the crystallization chamber
Keeping most of the crystals in
suspension without contact by a stirring device, thus
enabling the production of large crystals of narrow size
classifying crystallization chamber is the lower part of the
crystallization unit. The upper part is the liquor-vapor separation area
where super saturation is developed by the removal of the
solvent (water for most applications). The slightly
supersaturated liquor flows down through a central pipe and
the super saturation is relieved by contact with the
fluidized bed of crystals. The desuper saturation occurs
progressively as the circulating mother liquor moves upwards
through the classifying bed before being collected in the
top part of the chamber. Then it leaves via the circulating
pipe and after addition of the fresh feed, it passes through
the heat exchanger where heat make-up is provided. It is
then recycled to the upper part.
Additional devices, such as described for
the forced circulation crystallizer, are of course
It is worth bearing in mind that the
operating costs of the Oslo type crystallizer unit are much
lower than with any other type when both large and coarse
crystals are required. Since crystals are not in contact
with any agitation device, the amount of fines to be
destroyed is lower and so is the corresponding energy
This Oslo type crystallizer (classified -
suspension crystallizer) allows long cycles of production
between washing periods.
In addition to usual process operations,
the Oslo type crystallizer has also found a number of
interesting applications, e.g. for reaction-crystallization
and for separation-crystallization when several chemical
species are involved.
Most of the Oslo type crystallization
units are of the "close type." However, the "open" type
(refer to Figure 2) is worth to be considered when very
large settling areas are required or when the vessel must be
fabricated out of high cost alloys or metals.
Typical crystallizer products are:
The Draft Tube Baffle Crystallizer is an
elaborated Mixed Suspension Mixed Product Removal (MSMPR)
design, which has proven to be well suited for vacuum
cooling and for processes exhibiting a moderate evaporation
rate. The concept is such that if no (or little) heat
make-up is required, it results in a rather compact
arrangement; therefore the initial investment is minimized.
a rule, these units operate with a rather low
super saturation, which is sometimes a limitation to crystal
growth, so that very large crystals can be produced only by
providing extensive and costly dissolving of fines.
The Draft Tube Baffle unit (Figure 1)
includes a baffled area (settling zone), peripheral to the
active volume, from where excess of mother liquor and/or
fines are removed for further processing. The necessary
agitation of the suspension mixed with the incoming feed
solution is provided by a bottom entry agitation at moderate
Draft Tube Baffle crystallizers are often
equipped with an elutriation leg below the body to classify
When destruction of fines not needed or
wanted, baffles are omitted and the internal circulation
rate is set to have the minimum nucleating influence on the
suspension (Draft Tube design, draft-tube crystallizer).
When large evaporation rates are
required, an external heating loop must be provided, making
the arrangement less competitive from an initial cost
The Draft Tube Baffle Crystallizer, which
can be considered when crystallization can be achieved with
natural suspension, has proven to be well suited to many
applications such as:
induced circulation crystallizer design has been recently
developed to provide additional agitation of the active
volume of forced circulation crystallizers with the use of
only one pump, it operates similarly to a Draft Tube Baffle
crystallizer but without the internal agitation device. The
main applications are for evaporative crystallization cases.
The unit also operates according to the Mixed Suspension
Mixed Product Removal (MSMPR) principle and all options
described for the other designs are of course available for
this concept. The equipment is able to produce a narrow
crystal size distribution. Like other designs, it can be
fabricated in almost any material of construction.
Performances and product quality are equivalent to those of
a Draft Tube Baffle unit designed to the same specification,
but appear to be limited to non-viscous solutions as the
induced flow would be quite limited when the mother liquor
exhibits a high viscosity.
We have completed over 40 crystallizer installations for evaporating and crystallizing
organic and inorganic compounds including: ammonium sulfate, ammonium
chloride, ammonium hydroxide, ammonium nitrate, sodium
sulfate, sodium carbonate, urea, calcium acetate, calcium
chloride, lithium chloride, chromium trioxide, cupric
sulfate (blue vitriol), ferric chloride, barium chloride,
sodium chloride, sugar, MSG, boric acid, adipic acid, MgSO4,
KCl, silver nitrate, zinc sulfate, caprolactam, acetic acid,
lactose, sodium cyanide, etc. Some of the larger units
furnished: Dupont: Crystallizers for caprolactam sulfate and
Allied Chemical: (NH4)2SO4, adipic
acid and caprolactam sulfate.
Ames Goldsmith: 100 T/d silver
J. Huber: MVR evaporator for Na2SO4
Kalium Corp: KCl
Pacific Coast Borax: KCl
Monsanto: Boric acid evaporator
Sherrit Gordon Mines: 2x 300 T/d
(NH4)2SO4 classifying growth crystallizer.
American Potash: Evaporators and
crystallizers for – soda ash Na2CO3, 1,000 T/d potash
KCl, 1,000 T/d K2SO4, boric acid and Na2SO4 salt cake.
National Lead: Sodium fluoride
American Cyanamid: Sodium cyanide
concentration and salt cake crystallization.