Sodium softeners exchange

A sodium ion-exchange water softener is required for all boiler plants operating at an MAWP of over 15 psig. 

Carbonate and phosphate control is vital. If a minimum carbonate alkalinity of 250 mg/1 expressed in terms of CaC03 is consistently maintained when carbonate control or sodium ion exchange softening is used, a residual of soluble phosphate need not be maintained. A residual of soluble hardness up to 5 mg/1 expressed in terms of CaC03 is then usually found in the BW, but scale formation may be minimized by phosphate or carbonate conditioning treatment. 

The most widely used techniques for removing dissolved inorganic solids are boiling, addition of washing soda, lime-soda softening, complexation, sodium ion exchange, demineralization, reverse osmosis, electrodialysis, adsorption onto suspended solids, and aeration. 

Sodium ion exchange. Sodium ion exchange on zeolites (Section 7.3) or on synthetic organic cation-exchange resins such as Dowex-50 (a sulfonated polystyrene Fig. 14.1), in most circumstances, is superior to the above softening methods.13 The exchange process favors binding of Ca2+ or Mg2+ over Na+ in the solid resin phase ... 

Sodium Cation Exchanger (Zeolite) Process. This is the most widely used water-softening process in industrial, commercial, institutional and household applications. Hard water is softened by flowing it, usually downward, through a bed (2 feet to over 8 feet in thickness) of a granular... 

Sodium softeners are used to treated RO influent water to remove soluble hardness (calcium, magnesium, barium, and strontium) that can form scale on RO membranes. Once known as sodium zeolite softeners, zeolites have been replaced with synthetic plastic resin beads. For sodium softeners, these resin beads are strongly acidic cation (SAC) polystyrene resin in the sodium form. The active group is benzene sulfonic acid, in the sodium, not free acid, form. Figure 8.12 shows styrene-divinylbenzene gel cation resin. Equation 8.4 shows the softening reaction for calcium exchange ... 

Figure 8.13 Sodium softening reaction for calcium exchange.

In addition to sodium ion exchange for softening water, other cation and anion exchangers are used in series and combination (mixed-bed ion exchange) to reduce the concentrations of all dissolved solids, and thus increase the water purity. The terms demineralization and deion-... 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

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