Does the resin flow out during the backwashing of mixed ion exchange resin?
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RT, when regenerating mixed ion exchange resin, backwashing is required first – will the resin flow out with the water?
As long as the flow rate is not too high, it won’t be backwashed out. Generally, the backwash flow rate does not exceed 10 m/h. The backwash efficiency of a proper mixed-bed system is 100%, and resin leakage is usually not an issue; if it does occur, an appropriate amount of anionic resin can be added. The resin used for running is basically an anionic resin. There’s a slightly higher amount of anionic resin, but it’s no big problem. However, cation resins cannot be added arbitrarily, as too much of them will make it difficult for the effluent to meet the standards.
1. The backwash flow rate for mixed-bed resins should not be too high; the backwash expansion rate should be 100%. During backwashing, the resin layer should not extend above the upper part of the upper viewing hole, so that the resin layer remains visible. If resin is used for an excessively long time, it can become broken; therefore, it is normal for broken resin to be washed out during backwashing and layer separation. However, it is important to check whether the size of the resin particles washed out is normal. 2. Generally, manufacturers install stainless steel filters on the backwash drain pipes of mixed-bed systems to prevent resin from leaking during backwashing, but it is important to choose the right mesh size for these filters; either too large or too small a mesh size is not suitable.
What does the backwash expansion ratio mean? I couldn’t find it online. . . Could you recommend any books on this topic?
The purpose of backwashing a mixed-bed is to spread out the resin and separate it into layers by taking advantage of the different specific gravities of the anionic and cationic resins. The expansion rate of the resin can be understood as the ratio of the increase in the height of the resin within the mixed-bed unit after it becomes loose. For example, in a normal mixed-bed unit, the height of the cationic resin is 500 mm and that of the anionic resin is 1000 mm, giving a total height of 1500 mm. An expansion rate of 100% means that the height of the resin increases by 1500 mm; this is done to ensure that the resin expands sufficiently so that stratification can occur.
The last edit to this post was made by Red-Blue Phoenix on 2016-8-31 at 21:40. Does the expansion rate refer to the height measured after the washing process is complete, after waiting a few minutes for the resin to settle? What is the meaning of the expansion rate – to see how good the stratification effect is? Why, after I did the backwashing and let it sit for a while, layers formed, but it seems like the height didn’t increase? During backwashing, the expansion rate is based on the height to which the resin rises; thus, the meaning of the expansion rate is to guide us on when to stop backwashing
The significance of the expansion rate is to allow the anionic and cationic resins to separate fully, providing sufficient space for them to divide based on their difference in specific gravity, thereby achieving an excellent layering effect. During backwashing and layer separation, it is necessary to maintain a high resin expansion rate for a period of time, usually 15 to 30 minutes, so that the anion and cation resins can be fully separated. Moreover, after the backwashing is completed, the backwashing flow rate should be reduced gradually until it is completely shut off, allowing the resin to settle naturally to ensure proper stratification. The steps for regenerating mixed-bed resins are available online; you can look them up. I hope this helps you.
I have used resin before. First, the flow rate needs to be controlled, especially during the backwashing stage; the valve should be opened to half its capacity, otherwise the resin will flow out. Second, it is recommended not to perform backwashing immediately after replacing the resin, as this will cause a large amount of resin to flow out. Third, when rinsing, observe the drain outlet.
I have used resin before. First, the flow rate needs to be controlled, especially during the backwashing stage; the valve should be opened to half its capacity, otherwise the resin will flow out. Second, it is recommended not to perform backwashing immediately after replacing the resin, as this will cause a large amount of resin to flow out. Third, when rinsing, observe the drain outlet.