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Boiler feed water
Ion exchange is an effective, versatile means of conditioning boiler feedwater.
The term “ion exchange" describes the process : as water flows through a bed of ion exchange material, undesirable ions are removed and replaced with less objectionable ones.
For example, in softening processes, calcium and magnesium ions ( hardness ) are exchanged for sodium ions.
In dealkalization, the ions contributing to alkalinity ( carbonate, bicarbonate, etc. ) are removed and replaced with chloride ions.
Other dealkalization processes utilizing weak acid cation resin or strong acid cation resin in a split stream process, exchange cations with hydrogen.
This forms carbonic acid which can be removed in a decarbonator tower.
Demineralisation is simply replacing all cations with hydrogen ions ( H+ ) and all anions with hydroxide ions ( OH- ).
Ion exchange materials are like storage batteries; they must be recharged ( regenerated ) periodically to restore their exchange capacity.
With proper design and operation, ion exchange processes are capable of removing selected ions almost completely ( in some cases to a fraction of a part per million ).