Process Applications

Environmental engineers base their selection of the proper process for a water treatment on criteria mentioned previously. Their flow sheet is based on resin properties. Resins are used in the following processes:

Softening Dealkalization Desilicizing Organic scavenging Deionization Metal waste treatment

The characteristics of the functional group determine the application in the process.

Generally, the ion-exchange process involves a colum-nal contact of the liquids being treated. The design of ionexchange process equipment provides good distribution under design conditions, but environmental engineers must be careful in situations where the flow is decreased or increased beyond design conditions. The flow direction for service and regeneration is an important consideration. Two designs are offered: cocurrent and countercurrent. Generally, cocurrent is practiced when service and regenerant flows are in the same direction, usually downward.

Countercurrent normally services downflow and regeneration upflow. For example, the performance of a two-bed system is closely related to the way the cation exchange resin is regenerated. Alkalinity and sodium control are also closely associated with leakage. The advantages and disadvantages of these process steps can be summarized as follows:

Strong-acid-cation-exchange resin—Removes all cations regardless of with which anion they are associated. This resin has moderate capacity and requires a strong acid regenerant such as hydrochloric or sulfuric acid.

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