DEMINERALIZERSDOE-HDBK-1018/2-93Miscellaneous Mechanical ComponentsDuring the regeneration step, it is important to maintain the cation and anion resins at theirproper volume. If this is not done, the resin interface will not occur at the proper place in thevessel, and some resin will be exposed to the wrong regenerating solution. It is also importantto realize that if the ion exchanger has been involved with radioactive materials, both thebackwash and the regenerating solutions may be highly radioactive and must be treated as liquidradioactive waste.The next step is the slow rinse step, shown in Figure 14d, in which the flow of dilution wateris continued, but the caustic and acid supplies are cut off. During this two-direction rinse, thelast of the regenerating solutions are flushed out of the two beds and into the interface drain.Rinsing from two directions at equal flow rates keeps the caustic solution from flowing downinto the cation resin and depleting it.In the vent and partial drain step, illustrated in Figure 14e, the drain valve is opened, and someof the water is drained out of the vessel so that there will be space for the air that is needed tore-mix the resins. In the air mix step, (Figure 14f) air is usually supplied by a blower, whichforces air in through the line entering the bottom of the ion exchanger. The air mixes the resinbeads and then leaves through the vent in the top of the vessel. When the resin is mixed, it isdropped into position by slowly draining the water out of the interface drain while the air mixcontinues.In the final rinse step, shown in Figure 14g, the air is turned off and the vessel is refilled withwater that is pumped in through the top. The resin is rinsed by running water through the vesselfrom top to bottom and out the drain, until a low conductivity reading indicates that the ionexchanger is ready to return to service.ExternalRegenerationSome mixed-bed demineralizers are designed to be regenerated externally, with the resins beingremoved from the vessel, regenerated, and then replaced. With this type of demineralizer, thefirst step is to sluice the mixed bed with water (sometimes assisted by air pressure) to a cationtank in a regeneration facility. The resins are backwashed in this tank to remove suspendedsolids and to separate the resins. The anion resins are then sluiced to an anion tank. The twobatches of separated resins are regenerated by the same techniques used for single-bed ionexchangers. They are then sluiced into a holding tank where air is used to remix them. Themixed, regenerated, resins are then sluiced back to the demineralizer.External regeneration is typically used for groups of condensate demineralizers. Having onecentral regeneration facility reduces the complexity and cost of installing several demineralizers.External regeneration also allows keeping a spare bed of resins in a holding tank. Then, whena demineralizer needs to be regenerated, it is out of service only for the time required to sluiceout the depleted bed and sluice a fresh bed in from the holding tank. A central regenerationfacility may also include an ultrasonic cleaner that can remove the tightly adherent coating ofdirt or iron oxide that often forms on resin beads. This ultrasonic cleaning reduces the need forchemical regeneration.ME-05Rev. 0Page 28
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