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Automatic mixed bed

1     Introduction
The mixed bed is the abbreviation of the mixed ion exchange column, which is also a device designed for ion exchange technology. The so-called mixed bed is that a certain proportion of cation and anion exchange resins are mixed and loaded in the same column to exchange and remove ions in the fluid.Because the specific gravity of cation resin is bigger than that of anion resin, in the mixed bed, the anion resin is on the top while the cation resin is below. Generally,the filling ratio of cation resin and anion resin is 1:2, and there are also filling ratios of 1:1.5, which can be selected according to different resins.The mixed bed includes two types: internal synchronous regeneration mixed bed and external regeneration mixed bed. The whole operation and regeneration process of the synchronous regeneration mixed bed are carried out in the mixed bed. In other words, the resin does not need to be removed from the equipment during regeneration, and the cation and anion resins are regenerated at the same time,so the auxiliary equipment required is less and the operation is simple. OMZ provides the internal synchronous regeneration type.

2     Structure


FIG 2-1  The structure of the mixed bed

The structure of the mixed bed is shown in the FIG 2-1, including spray device, middle sewage discharge, etc. Now we describe its structure and functions in a specific work environment. For example, mixed bed is used to produce maltose.

First of all, the preparatory work before operation shall be completed according to the steps, then open the corresponding valve and the maltose enter the mixed bed through the feed inlet, and the internal rinsing water is discharged out of the body gradually. When the concentration of maltose reaches the requirement of discharging, the feeding valve and the discharging valve open simultaneously. After the completion of production, the remaining liquid in the mixed bed is discharged out of the body with the help of compressed air and condensed water, and then the mixed bed is cleaned, specifically including top washing, air washing, to wash away the protein and other impurities adhering to the top, with a time of about 5 min.Then, the column is backwashed with condensed water at a large flow rate. Under the condition that the normal resin particles are not discharged with the water flow, the resin is divided into two layers. At this point, the mixed bed enters the regeneration stage. The acid solution of a certain concentration enters the mixed bed through the outlet to regenerate the cation resin, and the alkali enters through the inlet to regenerate the anion resin. If the exchange capacity of the resin decreases, cross regeneration is needed. The cation resin is treated by alkali and acid, and the anion by acid first and then alkali. The sewage in resin regeneration is discharged through the middle sewage discharge.The regenerated resin is washed at a low flow rate and then mixed again. The rinsing water enters the mixing bed through the feed inlet port, while the top wash water enters through the spray device that can forms a water flow wash the column top.

3     Advantages of mixed bed

1)  Compared with the common ion exchange column, the mixed bed is equipped with both cation resin and anion resin, so the mixed bed is equivalent to the multi-stage composite bed with numerous anion and cation exchange resins. Moreover, the anion and cation exchange reactions are almost carried out at the same time. The H + and OH - will not accumulate, almost eliminating the influence of anti ion, and the reaction was done more thoroughly.

2)  Compared with peers, the mixed bed of OMZ is fully automatic controlled. The control screen is shown in FIG. 3-1. The pH and conductance of materials are monitored online in real time. The mixed bed system is usually designed as one for use, one for standby, so that the process of ion exchange can be carried out continuously.


FIG. 3-1  The control screen of mixed bed

At present, the full-automatic mixed bed ion exchange system has been widely used in the refining process of various starch sugars and organics. 

 

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