Technical question: What is the purpose of backwashing the resin in a dual-bed system?

This post was last edited by cdpulin on 2010-11-28 at 10:00. In ion exchangers that use reverse flow regeneration, during normal regeneration, only the fat layer on the surface of the resin is backwashed, in order to maintain the structure of the resin layers below and achieve a higher regeneration efficiency. However, after long-term operation, the resin at the bottom gradually becomes compacted or forms lumps due to the accumulation of suspended solids, resulting in excessive flow resistance and even flow deviation. This affects the working exchange capacity of the resin, reduces the quality of the effluent, and increases the consumption of regenerants. To this end, after operating for a certain period of time, it is necessary to backwash the entire bed layer, a process known as backwashing. The backwashing cycle is related to the turbidity of the incoming water; generally, backwashing is carried out after 15 to 20 operating cycles. After backwashing, due to the damage to the resin layer, it is necessary to increase the amount of regenerant by 50-100% or employ a method of performing two consecutive regenerations in order to restore the regeneration degree of the lower resin layer. During backwashing, in order to prevent damage to the intermediate drainage device, a low-volume backwash of the fat-binding layer should be carried out prior to backwashing, to loosen the fat-binding layer and remove contaminants. During backwashing, the flow rate must increase from low to high, and air in the resin layer should be removed as much as possible to prevent resin loss. During the backwashing process, it is necessary to pay attention to any signs of flow deviation or channeling. If such phenomena occur, the resin cannot be fully backwashed, and some of the clumped resin settles at the bottom of the exchanger, affecting regeneration and operation in the subsequent cycle. In such cases, enhanced cleaning methods must be employed to remove the clumped resin.

Backwashing involves removing the suspended particles and microorganisms that accumulate on the surface of the resin after it has been in use for a long time, and then putting it back into the ion exchanger to form a bed again. To ensure the regeneration effectiveness and efficiency of the ion exchanger. The best approach is to first scrub with air, then mix air and water for scrubbing, and finally rinse with water. However, such reverse washing should not be done too frequently.

The regeneration process of the mixed-bed involves a two-step regeneration method, specifically including the following steps: backwashing, settling (layering), adding alkali, displacement, backwashing, layering, adding acid, displacement, forward washing, mixing resins, and forward washing. One-step regeneration can also be used, that is, adding acid and base simultaneously. 　　A mixed-bed contains two types of ion exchange resins with different properties that are evenly mixed together; therefore, it is necessary to separate these two types of resins as completely as possible in order to regenerate the cationic and anionic resins separately. The purpose of backwashing is to separate the cation and anion resins. Through backwashing, the resin is evenly relaxed and expanded; when left to rest, it settles freely in water. Since the specific gravity of cationic resin ranges from 1.23 to 1.28, while that of anionic resin ranges from 1.06 to 1.11, the significant difference in their specific gravities makes layering easy to occur. Backwashing can also remove some impurities and foreign substances, ensuring normal operation in the next cycle. Open the lower water inlet valve and the backwash drain valve, and carry out backwashing until the water output is clear. After backwashing, let it stand; then open the upper discharge valve and drain water until it is more than 10 cm above the surface of the resin layer. 　　The regenerants for the mixed ion exchanger are intended to be 30% NaOH and 30% HCl. Since the mixed ion exchanger requires a longer time for regeneration, no separate storage tanks for acids and bases are provided; instead, the acids and bases are supplied directly from metering tanks via injectors for regeneration. The control of regeneration is achieved through a combination of the concentration of the regenerating agent, the regeneration time, and the flow rate of the regeneration liquid; furthermore, the acid and alkali metering tanks as well as the absorber are configured to maintain storage levels in accordance with the specified regulations.

What was asked about was a dual-bed system, not a mixed-bed system. In fact, backwashing is intended to prevent the resin at the bottom from clumping together, which could lead to a decrease in its exchange capacity. Additionally, during the regeneration process, the resin absorbs various impurities and suspended particles; backwashing removes these impurities from the surface of the resin, thereby increasing its exchange surface area and enhancing its water production capacity.

Reactivating deactivated resin is that simple. Make it so complicated. Professors can’t be good engineers.

First, it is necessary to understand the working principle of resins, which is ion exchange. When there are too many other ions in the resin, its exchange capacity decreases, the quality of the water output becomes unsatisfactory, and backwashing is required. That’s all there is to it.

I’m not sure whether the fixed-bed or floating-bed you’re referring to. But regardless of the type of bed layer, the main purpose of backwashing is to remove accumulated impurities and prevent caking of the resin, which could lead to uneven flow. Another purpose is to eliminate broken resin and reduce the pressure difference within the bed layer.

Is it to loosen the resin layer? To prevent the regeneration fluid from flowing in an uneven manner, can some of the impurities between the resins be removed first?

This post was last edited by cdpulin on 2012-4-6 at 09:36. In fact, the main purpose of backwashing the bed with alternating phases is: 1. To loosen the compacted resin layer, thereby facilitating regeneration； 2. Remove the broken resin ； 3. Prevent deviation in current during regeneration ； 4. Remove the impurities attached to the surface of the resin.