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Water Softning Plant

Water Softener

Water Softening Plant

We call water "hard" if it contains a lot of calcium or magnesium dissolved in it.

A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous

iron ion concentration in hard water.

These "hardness ions" cause three major kinds of undesired effects.

Most visibly, metal ions react with soaps and calcium-sensitive detergents, hindering their ability to lather

and forming a precipitate-the familiar "bathtub ring". Presence of "hardness ions" also inhibits the

cleaning effect of detergent formulations

Second, calcium and magnesium carbonates tend to precipitate out as hard deposits to the surfaces of

pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate

ions but also happens to some extent even in the absence of such ions. The resulting build-up of scale

can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat

into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a

pressurized system, this can lead to failure of the boiler.

Third, the presence of ions in an electrolyte, in this case, hard Water, can also lead to galvanic corrosion,

in which one metal will preferentially corrode when in contact with another type of metal, when both are

in contact with an electrolyte. However the sodium (or potassium) ions released during conventional

Water softening are much more electrolytic ally active than the calcium or magnesium ions that they

replace and galvanic corrosion would be expected to be substantially increased by water softening and

not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more

plumbo-solvent than hard water

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Ion-exchange resin devices

Conventional Water-softening devices intended for household use depend on an ion-exchange resin in

which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionic

functional groups of the polymeric resin. A class of minerals called zeolites also exhibits ion-exchange

properties; these minerals were widely used in earlier water softeners. Water softeners may be desirable

when the source of water is a well, whether municipal or private.

How it works?

The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind

metal ions, which are positively charged. The resins initially contain univalent hydrogen, sodium or

potassium ions, which exchange with divalent calcium and magnesium ions in the water. As the water

passes through the resin column, the hardness ions replace the hydrogen, sodium or potassium ions

which are released into the water. The "harder" the water, the more hydrogen, sodium or potassium ions

are released from the resin and into the water.

Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and

hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.

Regeneration

As these resins become loaded with undesirable captions and anions they gradually lose their

effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium

ions) then regeneration is usually effected by passing concentrated brine, usually of sodium chloride or

potassium chloride, or hydrochloric acid solution through them.

For anionic resins a solution of sodium or potassium hydroxide (lye) is used. If potassium chloride is used

the same exchange process takes place except that potassium is exchanged for the calcium, magnesium

and iron instead of sodium. This is a more expensive option and may be unsuited for people on

potassium-restricted diets.

In mixed-bed deionizers the caution-exchange and anion-exchange resins are intimately mixed and

contained in a single pressure vessel. The thorough mixture of caution-exchangers and anion-exchangers

in a single column makes a mixed-bed deionizer equivalent to a lengthy series of two-bed plants. As a

result, the water quality obtained from a mixed-bed deionizer is appreciably higher than that produced by

a two-bed plant.

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Although more efficient in purifying the incoming feed water, mixed-bed plants are more sensitive to

impurities in the water supply and involve a more complicated regeneration process. Mixed-bed

deionizers are normally used to 'polish' the water to higher levels of purity after it has been initially

treated by either a two-bed deionizer or a reverse osmosis unit.

Applications

Boiler Feed

Cooling Systems

Foundries

Distilleries

Pharmaceutical companies

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