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THE COUNTER CURRENT REGENERATION OF RESIN
Many experiences of cocurrent and countercurrent systems have confirmed that introducing
regenerant chemicals into demineralizer resin beds in the direction opposite to
service flow offers tangible advantages. By designing the bed such that the flow
of water being treated and the regenerant flow are in opposite directions (counter-flow),
the treated water leaving the bed during the exhaustion cycle will be contacting the
most highly regenerated section of the resin bed, and extremely low leakage of ions will
be obtained in the treated water.
THE CONTREX PROCESS
During years of experience, Unidro has developed a unique system to perform the
countercurrent regeneration process: THE CONTREX
The CONTREX process is a fixed bed system where the physical retention of the
ion exchange resin bed in its position in the column is obtained by employing a
neutral synthetic material as a compression layer placed above the resin bed.
The compression mass is made of a material which is inert as far as ion exchange
reactions are concerned, resistant to the chemicals employed in the process, and
sufficiently compressible to take up without difficulty the changes in volume of
the resin bed which occur during the regeneration and exhaustion cycles. Moreover,
the material of the compression mass is of low density so that it remains above the
ion exchange bed and it is of relatively large size in order to allow the passage
of fines and any accumulated insoluble matter removed from the bed during regeneration.
With CONTREX system both internal and external regeneration of the resins are applicable.
Should internal backwashing be selected, then the compression bed has to be removed
from the process vessel (generally to the twin process vessel). As the compression
bed material has a specific gravity of less than 1.0, it floats in water and thus
can readily be carried out of the unit by hydraulic flow. After backwashing of the
resin has been completed, the compression bed is returned to the unit by hydraulic
flow and again firmly and uniformly compacts the resin bed, which is then ready
to be regenerated.
Should external backwashing be selected, then the resin (or some portion of it)
has to be removed from the process vessel and transferred to the backwash tank. The
floating compression bed material can be easily left in place within the process vessel
when the resin is transferred and only the resin material be carried out of the unit
by hydraulic flow. After backwashing of the resin has been completed, the resin material
is returned to the unit by hydraulic flow, again firmly and uniformly compacted under
the compression bed and it is then ready to be regenerated.
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