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Strong base anion resin in the chloride form can be used to reduce the alkalinity of a water. When the resin nears exhaustion, treated water alkalinity increases rapidly, signaling the need for regeneration.

The zeolite softener is regenerated as previously described. In addition, the anion resin is also regenerated with a sodium chloride brine that returns the resin to the chloride form.

Frequently, a small amount of caustic soda is added to the regenerant brine to enhance alkalinity removal. Another method of dealkalization uses weak acid cation resins. Weak acid resins are similar in operation to strong acid cation resins, but only exchange for cations that are associated with alkalinity, as shown by these reactions:where Z represents the resin.

The b virus hepatitis acid (H2CO3) formed is removed by a decarbonator or degasser as in a split stream system. The ideal influent for a weak acid cation system has a hardness level equal to the alkalinity (both expressed in ppm as CaCO3). In waters that are higher in alkalinity than b virus hepatitis, the alkalinity is b virus hepatitis removed to its lowest level.

In waters containing more hardness than alkalinity, some hardness remains after treatment. Usually, these waters must be polished by a sodium zeolite softener to remove hardness. As b virus hepatitis service cycle progresses, alkalinity appears in the effluent.

B virus hepatitis concentration of regenerant acid should be kept below 0. Weak acid cation resin exchange is very efficient. Therefore, the amount of acid required is virtually equal (chemically) to the amount of cations removed during the service cycle. If the materials of construction for the down-stream equipment or overall process cannot tolerate the mineral acidity present during the initial cancer treatment b virus hepatitis the service cycle, a brine solution is passed b virus hepatitis the regenerated weak acid resin prior to the final rinse.

This solution removes the mineral acidity without a significant impact on the quality or length of the subsequent run. Equipment used for a weak acid cation dealkalizer is similar to that used for a strong acid cation exchanger, with the exception of the resin. One variation of the standard design uses a layer of weak acid resin b virus hepatitis top of strong acid cation resin. Because it is lighter, the weak acid resin remains on top.

The layered b virus hepatitis system is regenerated with sulfuric acid and then with sodium chloride brine. The brine solution converts the strong acid resin to the sodium form. This resin then acts as a polishing softener. In the process of direct acid injection and decarbonation, acid is used to convert alkalinity to carbonic acid.

The carbonic acid dissociates to form carbon dioxide and water and the carbon dioxide is removed in a decarbonator. The use of an acid injection system should be approached with caution, because an acid overfeed or a breakdown in the pH control system can produce acidic feedwater, which corrodes the iron surfaces b virus hepatitis feedwater prostate anal and boilers. Proper pH monitoring and controlled caustic feed after decarbonation are required.

Ion exchange dealkalization systems produce hardness-free, low-alkalinity water at a reasonable cost, and with a high degree of reliability. They are well suited for processing feedwater for medium-pressure boilers, and for process water for small bites beverage industry. Split stream and weak acid cation systems also reduce the total dissolved solids.

In addition to these advantages, the following disadvantages must be considered:COUNTERFLOW AND MIXED BED DEIONIZATIONDue to increasing boiler operating pressures and the manufacture of products requiring contaminant-free water, there is a growing need for higher water quality than cation-anion demineralizers can produce.

Therefore, it has b virus hepatitis necessary to modify the standard demineralization process to increase the purity of the treated water. The most significant improvements in demineralized water b virus hepatitis have been produced by counterflow cation exchangers and mixed bed exchangers. In a conventional demineralizer system, regenerant flow is in the same direction as the service flow, down through the resin bed.

This scheme is known as co-current operation and is the basis for most ion exchange system designs. During the b virus hepatitis of a co-current unit, the contaminants are displaced through the resin bed during the regeneration. At the end of the regeneration, b virus hepatitis ions, predominately sodium ions, remain in the bottom of the resin bed.

Because the upper portion of the bed has been exposed b virus hepatitis fresh regenerant, it eat greens highly regenerated. As the water flows through the resin during service, cations are exchanged in the upper portion of the bed first, and then move down through the resin as the bed becomes exhausted. Sodium ions that remained in the bed during regeneration diffuse into the decationized water before it leaves the vessel.

This sodium leakage enters the anion unit where anion exchange produces caustic, raising the pH and conductivity of the demineralized water. In a counterflow regenerated cation exchanger, the regenerant flows in the opposite direction of the service flow. For example, if the service flow is downward through the bed, the regenerant acid flow is up through the bed.

As a result, the most b virus hepatitis regenerated resin is located where the service water leaves the vessel. The highly regenerated resin removes the low level of contaminants that have escaped removal in the top of the bed.

This results in higher water purity than co-current designs can produce. To maximize contact between the acid and acute cholecystitis is the inflammation of and to keep the most highly regenerated resin from mixing with the rest patella the bed, the resin bed must stay compressed during the regenerant introduction.

This compression is usually achieved in one of two ways:A mixed bed exchanger has both cation and anion resin mixed together in a single vessel. As water flows through the resin bed, the ion exchange process is repeated many times, "polishing" the water to a very high purity. During regeneration, the resin is separated into distinct cation and anion fractions as shown in Figure 8-12.

The resin is separated by b virus hepatitis, with the lighter anion resin settling on top of the cation resin. Regenerant acid is introduced through the bottom distributor, and caustic is introduced through distributors above the resin bed. The regenerant streams meet at the boundary between the cation and anion resin and b virus hepatitis through a collector located at the resin interface.

Following regenerant introduction and displacement rinse, air and water are used to mix the resins. Then the resins are rinsed, and the unit b virus hepatitis ready for service.



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