25 May 2005
Adding sulfuric acid in several steps of increasing strength, such as 2, 4, 6 percent are
required for sulfonated styrene resins if fouling of the exchange resin with calcium
sulfate is to be avoided.
Equipment Requirements. The hydrogen ion exchanger is much the
same as the sodium ion exchanger, except that all equipment must be made of, or lined
with, acid-resistant material.
Regeneration Cycle. The regeneration cycle is much the same as that for
the sodium ion exchanger, except that sulfuric acid is used instead of salt. To improve
efficiency, regeneration of hydrogen ion exchangers is commonly done counter-
currently. During operation of the hydrogen cycle softener, it is necessary to check the
outlet (softened) water at regular intervals. The hardness of the outlet water should
always be less than 1 ppm. The ion exchange resin must be regenerated if the
hardness exceeds 1 ppm. This check can be performed daily, once per shift, or as
required depending on unit capacity. Available information on safety and first aid should
be reviewed before using sulfuric acid. Chemical handling and safety instructions should
be posted near sulfuric acid equipment. Sulfuric acid is corrosive to skin, eyes, clothing,
and other materials. Hydrochloric acid should be used with the same precautions. See
paragraph 7-4 for chemical safety information.
Troubleshooting. Troubleshooting is much the same as for sodium ion
exchange, although iron fouling does not occur in hydrogen ion exchangers since the
acid removes iron from the resin.
Effluent Water Properties. The hydrogen ion exchange effluent water is
acidic and cannot be used directly. The water can be mixed with the outlet of a sodium
ion exchanger with the result that the acid in the hydrogen ion exchange water will be
neutralized to some degree and, at the same time, the degree of alkalinity in the sodium
ion exchange water will be lessened. The proportion of the effluent waters to be mixed
is dependent upon the analysis of the water being treated, but typically the proportion is
approximately one-to-one (half-and-half). The testing of blended water should be done
prior to blending to assure that the blended water is satisfactory for use in the boiler or
cooling water system. If neutral (pH 7) water is required, a chemical (such as sodium
hydroxide) must be added.
Carbon Dioxide Production. Carbon dioxide is produced during the
hydrogen ion exchange process and is also produced when the effluent water from
hydrogen and sodium ion exchange is mixed. It is removed from the water in a
decarbonator (degasifier or deaerator).
Demineralization. Sodium and hydrogen ion exchangers remove only the
positively charged ions (cation exchange - i.e., calcium, magnesium, and sodium).
Other ion exchange materials have been developed to remove negatively charged ions
(anion exchange - i.e., sulfates, chlorides, and alkalinity). The process of
demineralization uses both cation and anion exchange resins to remove all ions from
the water, thus producing mineral-free water. A typical deionization (demineralizer)