DEMINERALISATION
INTRODUCTION
For removal of raw water dissolved salts, to make water free from soluble salts of Calcium, Magnesium & Sodium, water demineralisation plants are advisable. Raw water which contains chlorides, sulphates & carbonates of Calcium, Magnesium & Sodium make water unfit for use in the pharmaceutical, chemical & battery manufacturer industries and for high pressure boilers. The units can be different types depending on feed water quality and required treated water quality. The process of demineralization defined as under:
- SAC – SBA
- SAC – SBA — MB
- SAC – DG – SBA
- SAC – DG – SBA – MB
- SAC – DG – WBA – SBA
- SAC – DG – WBA – SBA – MB
CATION EXCHANGE
In demineralising, the cation exchange resin is used in the hydrogen form (RH). The ions in the water re actually freely moving but for the purposes of simplicity then may be identified as definite pairs.
INLET WATER QUALITY
Because an ion exchange resin must be kept clean to function efficiently, the inlet water or raw water must be cold, clean and colourless. The water should be free of suspended matters, organic matter, oil, algae, slime and heavy metals such as iron, aluminum. These impurities would collect on or within the resin particle and reduce their capacity for removal of the ions. Hence waters may require coagulation and filtration prior to being fed into the deionizer. The ion exchange resin particles can act as filters but their deionising ability and capacity will suffer and the resin bed may then require frequent cleaning or replacement.
CAPACITY BETWEEN REGENERATIONS
The capacity of the deionizer between regenerations depends on the type and quantity of ion exchange resins used in the columns, the quantity of acid and alkali used per regeneration of each respective column and the dissolved ionic content of the raw water. An economical quantity of regeneration chemical has been specified in the technical data sheet.
ANION EXCHANGE
There are several types of anion exchange resins which differ in basicity. Commonly used are the strong base (SB) anion exchange resins such as type-I or Type-II. The strong base resins are completely ionized throughout the complete pH range and can remove all acids – strong acids such as hydrochloric and sulphuric acids and weak acids such as silica and carbonic acid. Weak base resins are ionized only at a low pH and can, therefore, remove only the strong acid. Weak acids pass through the resin unaffected.
In demineralising, the anion exchange resin is used in the basic or hydroxide form. If the treated water from the cation exchange resin is passed through the anion exchange resin, the acids are removed.
MIXED BED UNIT
Mixed bed demineraliser plant embodies a single column of strong acid cation exchange resin and strong base anion exchange resin, material mixed intimately together. Water passing through the column comes repeatedly in contact with these resins and is thus in effect subjected to an almost infinite number of demineralising stages. Demineralised water of extreme purity is produced – purity that cannot be equaled by any other commercial method. Mixed bed demineralisers are regenerated with acid and alkali but the ion exchange resin must be separated before this can be done. Bed separation is accomplished by back-washing-this carries the lighter anion resin sinks to the bottom. Two completely separated and super imposed layers are thus formed.
TECHNICAL DATA OF TWO BED D.M. PLANTS
Sr.
Nos.
Model
DIA MM
H.O.SMM
Thickness
Frontal
Piping
( mm)
Max. Flow Rate m3/hr.
Resin Qty.
C A
HCl (100%) Kgs.
NaoH (100%) Kgs.
AMT
(mm)
CDT
(mm)
Remarks
Shell
Dish End
1.
ENVIROX
CAU-200
200
900
5
5
25
1.0
28
28
3.0
3.0
300 x 700
300 x 700
M.S.R.L.
2.
ENVIROX
CAU-250
250
900
5
5
25
2.0
40
40
4.5
4.5
300 x 900
300 x 900
M.S.R.L.
3.
ENVIROX
CAU-300
300
1500
5
5
32
3.0
102
102
12.0
12.0
400 x 900
400 x 900
M.S.R.L.
4.
ENVIROX
CAU-400
400
1500
5
5
32
4.5
160
160
18.0
18.0
500 x 900
500 x 900
M.S.R.L.
5.
ENVIROX
CAU-500
500
1500
5
6
40
7.5
280
280
32.0
32.0
700 x 900
700 x 900
M.S.R.L.
5.
ENVIROX
CAU-600
600
1500
5
6
50
11.0
410
410
48.0
48.0
800 x 900
800 x 900
M.S.R.L.
5.
ENVIROX
CAU-800
800
1500
5
6
65
20.0
720
720
85.0
85.0
900 x 900
900 x 900
M.S.R.L.
5.
ENVIROX
CAU-900
900
1500
5
6
80
25.0
920
920
110.0
110.0
1200 x900
1200 x 900
M.S.R.L.
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