SEP’s extensive experience on process and equipment design and innovative ways to utilize it is the key to developing the optimum solution to our Client’s requirements. Our designs strive to combine high plant performance, low capital costs, and simplicity of operation, to achieve the best value of investment cost and productivity.
State of the art evaporation and crystallization technology is available to our Clients: a wide range of evaporator and crystallizer types, each best suited for a specific task or performance criteria can be supplied. The most common types are the following:
evaporators, also known as Natural Circulation Evaporators, or Long-Tube
Vertical (LTV) Evaporators, are the oldest and simplest of the Evaporators used
no moving parts, and have the advantage of very stable and reliable operation.
This type of evaporator is well suited for the concentration of solutions that are
not very close to the point of precipitation of solids, and are low in
viscosity. Due to the low residence time of the product, thermosensitive
products can be handled well by this machine.
However, to obtain natural circulation, fairly high steam-to-process temperature differences are needed, and this limits this Evaporator’s use in some multiple-effect arrangements.
Film Evaporator has gained increasing acceptance over the last few decades, and
is now the most common type of evaporator. It takes its name from the fact that
the liquid to be concentrated cascades down the inside of the heater tube walls
as a film.
employs a pump to circulate some process liquid to the top of the vertical
heating element, to ensure wetting of the tube walls. In some applications,
Falling Film Evaporator units can operate without this recirculation, however.
SEP has extensive experience in designs that minimize the scale formation on the tube walls, and thus extend the operating cycle of the machine.
Circulation Evaporator/Crystallizer (FC) is the workhorse of the
crystallization industry, as it provides a robust operation with predictable
performance for materials that require large amounts of evaporation in order
that crystallization may be achieved.
occasions, FCs are used for non-crystallizing, but severely scaling evaporation
applications, in an effort to prolong the unit’s operating cycle.
The FC provides mechanical (via a pump)
circulation of the slurry through the heating element and back to the
Crystallizer vapour head.
cases, such as in NaCl production, a Salt Leg in is provided on the FC Vapour
head, where the crystals are collected and washed prior to their removal from
the crystallizer, to optimize crystal size and purity. While, in general, a
simple FC unit provides little latitude in crystal size control, poor design
can reduce the crystal size obtained by the crystallizer.
FC operation is usually hampered by the formation of crusts on its internal surfaces, which require stoppage of the unit to clean it. Proper selection of the operating parameters of the FC can, however, minimize this problem and substantially increase its on-stream time.
crystallizer is used when a larger particle size is desired. The crystallizer is
a combination of a clarifier and a mixed tank in a single vessel. The
mixed-tank part of the unit includes a slow-turning, high pumping efficiency
internal circulator located concentrically in a tube (the Draft Tube) that
helps direct the flow and improve the mixing of the slurry. The internal
circulator provides the mixing of the slurry at a very low energy input, which
is improves the growth rate of the crystals, and has low attrition for the crystals
formed. The clarifier section provides the means to selectively remove and
destroy smaller crystals in the mixed-slurry section, thus increasing the
average product size.
destruction of the small particles is achieved either by heating or by diluting
the brine containing these particles. After this has been done, the heated (or
diluted) brine is returned to the crystallizer.
are also used successfully for crystallization from reaction, such as
fertilizers made by the neutralization of an acid with a base, because of their
high level of internal mixing and the ability to introduce the reactants into a
zone of high turbulence.
A simplified variation of the DTB is the Draft Tube (DT) crystallizer, which is a unit that contains only the mixed-slurry feature of the DTB (no baffle, i.e. no clarification zone). The DT is used for some reaction of flash cooling operations, where the main objective is to provide a well-mixed volume.