Northern Engineering Industries Plc

James R Emmett

A high degree of water purity is obtained from a mixed-bed deionization process by minimization of cross-contamination of the cation and anion materials. After service, the materials are classified into superimposed uppermost, intermediate and lowermost layers above a perforate barrier in a separator vessel. The vessel has an elongate conduit having an inlet adjacent the barrier and an outlet outside the vessel. At least a major proportion of the material of the lowermost layer is passed through the outlet of the conduit and an interface between materials is detected. Thereupon, the conduit outlet is isolated from the conduit inlet so as to segregate in the conduit material from the intermediate layer. The ion exchange materials are then regenerated and re-mixed. The segregated material is independently removed from the conduit before the next regeneration cycle starts. For example, the material may be kept in the conduit, or transferred to and kept in a separate container while the rest of the materials are being regenerated.

Regeneration of ion exchange materials

In a method of regenerating mixed ion exchange materials, the materials are classified into layers. The lower layer is then transferred from the separator vessel. The transfer is controlled by detecting an interface between materials. The separated materials are then regenerated after which the anion material is reclassified to allow any contaminant cation material to settle to the bottom thereof. Material is then removed from the bottom of the anion layer to remove settled contaminant cation material. The removed material is isolated from the regenerated materials which are then remixed. The method reduces the cross-contamination of materials that occurs during the separation of classified materials and, particularly, reduces the amount of cation material in the sodium form (following regeneration of the anion material) that is eventually returned to service.

In mixed bed ion exchange resin regeneration processes, transfer of resin after classification is controlled by detecting a change in a parameter of transfer water dependent on ion concentration, e.g. conductivity. The process includes increasing the ion concentration of the transfer water. The increased ion concentration ensures that large percentage uncontrolled fluctuations in the conductivity of the water do not mask the change required to be detected. The ion concentration can be increased by adding, for example, decationized water to the transfer water.

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Brewood, United Kingdom

James R Emmett