5. Make-up water treatment and boiler water conditioning

5.1 External treatments or pre-treatments

• Softening

  Softening consists in replacing the alkaline-earth cations (calcium and magnesium) with the sodium cation. This replacement eliminates the risk of carbonate scale precipitation, as sodium carbonate is soluble, unlike calcium carbonate. This operation is carried out by passing the water through a strong cation exchange resin, regenerated in sodium form.

  The water produced has a residual total hardness (TH) of less than 0.5 °f.

  $$\text{R}\text{−}{\text{Na}}_2+{\text{Ca}}^{\text{+}\text{+}}\to \text{CaR}+2\text{Na}$$