Method of separating and transferring ion-exchange resin

Abstract

A method for separating and transferring an ion-exchange resin having the lower specific gravity from an ion-exchange resin having the higher specific gravity in an ion-exchange resin separating tank that is indispensable to a pure or ultrapure water producing plant and which is packed with a mixed bed of ion-exchange resins having different specific gravities is disclosed. This method contains the following essential steps: (1) a first step in which the mixed resin bed is separated into two layers by backwashing and the greater part of the ion-exchange resin (SBR) having the lower specific gravity is transferred by means of a perforated sluicing pipe that is disposed below the interface between the separated resin layers and a resin transfer pipe that is disposed above said sluicing pipe; (2) a second step in which SBR that is left untransferred in the first step is separated to be situated above the layer of the ion-exchange resin (SAR) having the higher specific gravity; and (3) a third step in which sluicing water is introduced into the tank at high flow rate through the sluicing pipe so that the particles of SBR are lifted in the water in the freeboard above the resin layer, while pressurized water is introduced from the top of the tank so as to transfer the residual SBR through the resin transfer pipe. According to the process of the present invention, substantially complete separation and transfer of SBR can be accomplished by operations in a fully automatic and unattended way, with the volume of SAR being held constant at all times after the transfer of SBR. If the process is applied to the condensate demineralizing system in a PWR power plant which requires stricter control of water quality that a thermal power plant, the sequence of the second and third steps may be repeated after the third step so as to reduce the total level of residual SBR to 0.05% of the total anion resin and below.