Sodium cycle softening

Sodium cycle softening (base-exchange softening) is used primarily to remove the risk of calcium- and magnesium-based crystalline scale formation and deposition. The general reaction is as shown in Figure 9.2. 

A CEDI system can produce up to 18-megohm-cm water at 90-95% water recovery. Recovery by the CEDI system is a function of the total hardness in the feed water to the system. In general, 95% recovery can be realized at a feed water hardness of less than 0.1 ppm as calcium carbonate.16 This is typically attained if the pretreatment to the CEDI consists of either 2-pass RO or sodium-cycle softening followed by RO. Recovery that is achievable is a function of the feed... 

Sodium cycle softeners with co-flow regeneration softened water hardness = 1-3 mg/1. 

These resins have found a wide range of application, being used on the sodium cycle for softening, and on the hydrogen cycle for softening, dealkalization, and demineralization. 

Maximum values of specific conductance are often not achievable without exceeding maximum T alkalinity values, especially in boilers below 900 psig (6.21 MPa) with greater than 20.0% MU water whose alkalinity is >20% of TDS naturally or after pretreatment by lime-soda or sodium cycle ion exchange softening. Actual permissible conductance values to achieve any desired steam purity must be established for each case by careful steam purity measurements. The relationship between conductance and steam purity is affected by too many variables to allow its reduction to a simple list of tabulated values. 

Strong-acid exchangers can be operated in a hydrogen cycle (often used for water demineralization) or in a sodium cycle (used for water softening). These cycles consist of... 

AVT Barg BD BDHR BF BOF BOOM BOP BS W BSI BTA Btu/lb BW BWR BX CA CANDUR CDI CFH CFR CHA CHF CHZ Cl CIP CMC CMC CMC COC All-Volatile treatment bar (pressure), gravity blowdown blowdown and heat recovery system blast furnace basic oxygen furnace boiler build, own, operate, maintain balance of plant basic sediment and water British Standards Institution benzotriazole British thermal unit(s) per pound boiler water boiling water reactor base-exchange water softener cellulose acetate Canadian deuterium reactor continuous deionization critical heat flux Code of Federal Regulations cyclohexylamine critical heat-flux carbohydrazide cast iron boiler clean-in-place carboxymethylcellulose (sodium) carboxy-methylcellulose critical miscelle concentration cycle of concentration... 

Determine the amount of water to be treated per cycle and the amount of hardness to be removed. Softening of water requires use of a cation-exchange resin operated in sodium form to exchange divalent hardness cations for sodium regenerated with aqueous sodium chloride solution. Total amount of water to be treated is (100 gal/min)(60 min/h)(8 h/cycle) = 48,000 gal/cycle (182 m3/ cycle). 

The principles at play in water softeners are the same as those in precipitation reactions. Water is run over a dense material saturated with sodium ions like a gigantic network of salts. The sodium salts are soluble, whereas the calcium analogs of the same salts are not. So the calcium replaces the sodium and becomes trapped on or in the solid. The water, now enriched in sodium instead of calcium, can be used without worry that it will precipitate soap or form the crusty deposits of scale. In the regeneration cycle of the water softener, the solid support is backwashed with water saturated with so much sodium salt that the sodium eventually replaces the calcium on the solid, and the water softener is ready to start softening again. 

Figure 30F-1 Schematic of a home water softener. During the charging cycle, the valves are in the positions shown. Salt water from the storage reservoir passes through the ion-exchange resin to waste. Sodium ions from the salt water exchange with ions on the resin to leave the resin in the sodium form. During water use, the valves switch and hard water passes through the resin where the calcium, magnesium, and iron cations replace the sodium ions attached to the resin.

The significance of these predictions is shown in Table XV. If the nuclear data are adjusted in line with this experimental information, the design calculations show that at least 50% of the BeO, which was included in the core to soften the neutron spectrum and to increase the Doppler coefficient, can be removed and still meet the Doppler and sodium loss criteria of the reference core. The fissile inventory required decreases by about 3%, and the breeding ratio increases from 1.18 to about 1.25. This results in a decrease in the fuel cycle cost of about 0.1 mill/kW-hr. If one assumes a favorable combination of nuclear data within the limits of uncertainties reported by Greebler (5) and, furthermore, if the safety criteria are relaxed to allow a calculated Doppler effect (T dkjdT) of — 0.004 (with sodium out) and a positive total sodium loss reactivity effect between 1 and 2, all of the BeO can be removed... 

Ion exchange resins are used in columns 8 to 10 feet high and 6 to 10 feet in diameter holding between 100 and 300 ft of resin. The resin bed depth is only 2 to 4 feet. Flow rates are rapid (3000-4500 gal/hr), and the cycle is short (8-16 hours). Regeneration is accomplished in the column with a 10 to 15 percent salt solution at 140 to 160°F. The chloride form of a strong anionic resin decolorizes the liquor, and the sodium form of a strong cation resin softens the liquor. The sweet water from the various adsorbent columns are recovered by returning them to the melter. ... 

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