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Unidro has developed a wide experience with up-to-date technologies for
the brine purification in the chloralcali industry All the steps required
to produce saturated brine at the purity standard necessary for the most
demanding membrane manufacturers are available.
Anthracite filters
This has been the most applied technology for the filtration of the brine,
combining the advantage of a simple and reliable system with a reasonable cost
and an acceptable performance.
UNIDRO anthracite filters for brine purification are automatic pressure filters,
whose unique internal design allows an even distribution of the influent brine,
while a thorough wash of the filtering layer (surface wash and upflow backwash)
assure the best performances which can be obtained with this kind of filter.
Depending on the flowrates to be treated, the filters can be vertical or horizontal type.
Precoat candle filters
When the performances of the filtration unit have to be such that virtually
all the suspended solids be removed from the brine, then precoat candle filters
are the mandatory choice for this step. UNIDRO candle precoat filters use special
porous carbon filter elements which are specifically designed for this application
and whose reliability is confirmed by a world-wide successful application in this field.
Chelating resin units
Multivalent ions including Ca, Mg, Sr, Ba, Fe, Pb, Ni, Mu, Cr are responsible for the
fouling of ion exchange membranes and therefore for their shorter life. The removal of
such ions down to the required limits is done by passing the brine on beds of selective
resins called chelating resins.
The very high treated brine quality which is to be achieved in the secondary brine
purification units makes the design of the equipment very critical, especially in
respect to the prevention of any by-passing or channelling phenomena in the resin
bed which would lower the resin's effective capacity (hardness leakage). This applies
equally to the operation and regenerating sequences.
All the above considerations lead to the conclusion that the hydraulics of the
resin towers, the positioning of distributors, the selection of flow rates, require
good margins of flexibility and a very accurate and complicate engineering design.
Finally, it has to be underlined that the extremely low leakage of divalent
ions can be obtained at any time only by a two columns system operating in
the lead-polisher mode. When the design throughput of the lead column (first column)
is reached, the column is put out of service and the regeneration sequence is
initiated. Upon completion of the regeneration cycle, the column is put again
into service in the polishing position (second column).
When the quality of the treated brine is very strict and the size of the unit requires
a severe control of the chemical consumption, the most effective arrangement is a
three columns system, operating in the so called merry-go-round mode.
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