Common ion exchange demineralized treatment system, weak acid positive resin and strong acid positive resin, or weak alkaline negative resin and strong alkaline negative resin are set in the same exchanger, that is, set into a bunk bed or two-compartment bunk bed exchanger.
1.
Bunk bed exchanger is the use of weak acid (or weak base) resin density than strong acid (or strong base) resin density is smaller, so that the weak resin in the upper part of the strong resin, running water top-down, first through the weak resin exchange, and then the strong resin exchange; In the regeneration process, the regeneration liquid is bottom-up, and the strong resin is regenerated first, and then the weak resin is regenerated.
2.
The double-chamber double-layer exchanger is divided into the upper and lower chambers with a porous partition in the exchanger, and the weak resin and the strong resin are separately filled to form a double-chamber bunk bed or a double-chamber floating bed (the strong resin is in the upper chamber, the weak resin is in the lower chamber, the water is bottom-up when running, and the regeneration liquid is from top to bottom when regenerating).
The advantages of bunk beds and double-chamber bunk beds are that, without increasing the equipment, the advantages of weak resin exchange capacity and easy regeneration are used to improve the effectiveness of the exchanger and reduce the consumption of regenerant. In particular, the cation exchange bunk bed has obvious advantages.
For anion-exchange bunk beds and two-compartment bunk beds, although there are the above advantages, there are also obvious disadvantages, that is, it is easy to cause colloidal silicon contamination of the resin. This is because when regenerating strong negative resin and weak negative resin in the same exchanger, the regeneration waste liquid discharged from the strong negative resin contains higher silicon compounds. When flowing through the weak negative resin, the weak negative resin is easy to absorb OH-, reducing the pH value in the regeneration liquid, so that the silicon compounds are easy to form colloidal silicic acid and deposited in the resin. Especially when the temperature is low, it is often difficult to clean after regeneration, and because the resin is contaminated by colloidal silicon, the silicon content of the effluent is high, affecting the water quality and periodic water production.
Measures to prevent colloidal silicon contamination:
1. Step-by-step regeneration
With 1%NaOH regeneration solution at a faster flow rate, the resin can be initially regenerated, and the amount of silicic acid exchanged at this time is not much, but the weak negative resin can be initially regenerated, and the resin layer is alkaline. Then, 3%-4% NaOH is used for regeneration at a lower flow rate, which can avoid the precipitation of colloidal silicic acid due to the decrease of pH value.
2. Appropriately increase the temperature of the regenerated liquid
The temperature of NaOH regenerated liquid can be increased to about 50℃ by adding a heater or using condensate to configure the regenerated liquid, so as to improve the regeneration effect.
