WORKING PRINCIPAL OF MIX BED DEIONISER IN D.M PLANT:-

Mixed Bed Deionizer is very important water treatment equipment for any industries for treated boiler water. Mix bed deionizer or mixed bed polisher are typically installed where water quality is less then 1 micro ohm conductivity is required.  Mix Bed Deionizer is a single shell unit and contain with strongly acid cation and strongly basic anion mixed with proper ratio . mixed bed shell contain strong acid cation (SAC) resin and strong base Anion (SAB) resin combined to a ratio of approximately 40% cation resin and strong base Anion (SBA) resin. Mixed bed  deionizer  is used to polish water at higher purity level it has been initially treated by either a two-be deionizer or a reverse osmosis unit.

After passing water through cation and anion exchangers water interned into mix bed unit where both of resin available when water is passing through it effluent water get contact with thasound of cation/anion exchangers resulting good quality of water in output. Internally resin bed contains a rubber lining inside where a good space for resin expansion when back wash is conducted through it.
In addition to the usual distributors, a mixed bed is fitted with a centre distribution and collection system. When backwash is conducted through mix bed unit the heaviest cation resin settled down and lighter anion resin are lift up.

After some time when back wash is stopped the resins settle without upsetting the separation. There is a well defined interface between the cation and anion resin bed and that interface is just at the level of center distributors.

Passing a solution of sodium Hydroxides ( caustic Soda ) then regeneration the anion resin and passing a solution of hydrochloric Acid regenerate the cation resin. Then the columns are rinsed individually and finally remixed again, by passing of 5 psi. Thus the unit become ready for another cycle of operation to produced pure Deionized water of electrical conductivity less then 0.5 us/cm equivalent to approximately 0.5 ppm of dissolved solids in D.M water. Reaction taking place in a mixed bed unit are similar to that of taking place in cation & anion exchanger.

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*WORKING PRINCIPAL OF MIX BED DEIONISER IN D.M PLANT

General reaction taking place in cation exchanger

R-H+CaCo3→HCO3+R-Ca

General reaction taking place during regeneration of cation exchanger is :-
R-Ca +HCL→CaCl2+R-H

general reaction take place in anion exchanger

R-OH+HCO3→H-OH+R-CO3

general reaction taking place during regeneration of anion exchanger is

R-CO3 +NaOH →Na2Co3+R-OH

Hence the final composition of water after mix bed is
H+OH→H2O
(De-mieralized water )

Defect ,causes and remedies for mixed bed operation

Defect :- mixed bed quality not good

Causes: –
– resin not separated during backwash properly.
– air mix not properly.
– final rinse not proper
– some valves may be leakage & contaminated the treated water.
Remedies:-
– give extended backwash
– repeat the process
– repeat the process
– check & examine

Defect :– unit rinse takes long time

Causes :- –
– flow rate too low
– unit exhausted
– backwash valve passing
– anion resin originally fouled
– mixed bed air mixes not satisfactory
– Acid/ alkali pockets formation in unit

Remedies :-

– Increase flow rate
_ regeneration unit check and rectify.

Defect :- resin being lost
Causes :-
-Excessive backwash pressure
-Faulty collecting system
-Inlet strainer damaged

Remedies:-
– check inlets pressure and reduced if necessary

– examine it for breakage
Check and replaced

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