Feed water treatment methods include internal treatment processes like zeolite treatment and demineralization, and external treatment processes like mechanical and chemical treatment. Demineralization, or ion exchange, involves removing ionic substances from water using cation and anion exchange resins to produce essentially distilled water. In the demineralization process, raw water first passes through a cation exchanger to remove bicarbonates and is then passed through an anion exchanger to remove chlorides, sulfates, and nitrates, exchanging them for hydrogen and hydroxyl ions. The treated water is then passed through a degasifier tower to remove carbon dioxide by contacting the water with low pressure air.

1. Subject: Power Plant Engineering (2171910)
Topic: Feed Water Treatment

2. Feed water treatment
Methods of
water treatment
Internal
Treatment
External
treatment
Mechanical Chemical
Zeolite
treatment
Demineralization
Process
Thermal
Deaeration Evaporation

3. Demineralization or ion exchange process
Purpose
Removal of ionic substances
Reduction of conductivity
Control of pH
Any process which results in the reversible exchange of ions contained in
a fluid with those contained on a solid without a permanent change in the
solid structure.
Water is treated with an ion exchange resin.
 The mineral content of water may be removed by evaporation or by series of cat ion
and anion exchangers to produce essentially distilled water .
Demineralization is often the most economical method of producing make – up water
for high pressure boiler.
 The functional groups are molecules with exchangeable ions such
as H+ or OH-, that can be safely released into the system.
Cat ion resins :
Exchange positively charged functional groups, for undesirable positive ions. With
their functional groups in the hydrogen form, R – H, “R” represents the
exchange resin and “H” represents the attached hydrogen ion.

4. Anion resins :
• Exchange negatively charged functional groups for any undesirable negative ion.
• The hydroxyl ion, OH- (R—OH) is commonly used as the functional group in an anion
resin.
Process:
In this system , raw water is first passed through a weak acid cat ion exchanger to remove
the bicarbonates. Water coming out contains dilute carbonic acid , hydrochloric acid and
sulphuric acid .
The demineralizer system consists of one or more ion exchange resin columns, including a
strong cat ion unit and a strong anion unit. The cat ion resins exchange hydrogen for raw
water cat ions as shown below:

5. the water coming out of cat ion exchanger is passed through anion exchanger.
In anion exchanger such as chlorides , sulphates and nitrates are removed from water with
certain resinous material (RCOз). anion exchanger also exchanges acid radicals .
The anion resins exchange hydroxyl for raw water anions.
The water coming out from anion exchanger is passed through a degasifier tower . Which is
filled with porcelain packing. Water is distributed over very large surface area provided by
the packing as it flows downward through the tower .
Water comes in contact with low pressure air blown in at bottom , CO2 is liberated and is
vented from the top of the tower .

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