Applications of Dealkalization and Softening Water Treatment

Water softeners, commonly known as sodium ion exchangers, can only remove hardness components (Ca2+, Mg2+) from raw water, but not alkalinity components (HCO3-, etc.). Therefore, water treated by a softener still contains alkalinity. When softened water with excessive alkalinity enters a boiler, under high temperature and pressure, the bicarbonates are concentrated and undergo decomposition and hydrolysis reactions, significantly increasing the concentration of caustic soda (NaOH) in the boiler water. The reactions are as follows:

Na2CO3 → NaOH + CO2

NaHCO3 → NaOH + CO2

This situation not only causes alkaline corrosion in the boiler water system, deteriorates steam quality, and increases blowdown volume, but also causes acid corrosion in the steam and condensate systems. This endangers the safe operation of the boiler, increases operating costs, and shortens the service life of the boiler and piping. Therefore, when the alkalinity of raw water exceeds 2 mmol/L, de-alkali softening treatment is usually required. II. Alkali Removal and Softening Process and Principle

A weakly acidic hydrogen-form cation exchange resin is used in the hydrogen tank to remove carbonate hardness and alkalinity from the influent, converting alkalinity into carbon dioxide.

That is: 2RCOOH + Ca(HCO3)2 → (RCOOH)2Ca + 2H2O + CO2

2RCOOH + Mg(HCO3)2 → (RCOOH)2Mg + 2H2O + CO2

The carbon dioxide generated in the reaction is discharged through a degassing tower. The effluent then passes through a strongly acidic sodium-form cation exchange resin in the sodium tank to remove non-carbonate hardness.

That is: 2RNa + CaSO4 → R2Ca + Na2SO4

2RNa + MgSO4 → R2Mg + Na2SO4