1. The end of the service cycle as measured in net gallons may have been exceeded.
2. You may have lost resin in the backwash, thereby shortening the service run length.
3. Note that the leakage should be expressed as the average across the entire service run, not the leakage at the end or the beginning of the service run.
4. You regeneration cycle may be incomplete. Check your acid consumption.
5. The useful life as well as capacity of the resin diminishes over time. How old is the resin. You need to shorten the service run length to complensate.
6. The rinse cycle following regeneration may be incomplete.
7. The water quality may have changed seasonally.
8. You resin may be fouled with an organic material.
You have asked a very general question. If you would like a specific response, please include more information.
Sodium leakage is indicated here by increased effulent PH across the entire run on both trains. Resin is 5-6 years old and at the last test done by our water rep. the resin was at least "good to fair". Our raw water quality changes very little. A very large lake processed to drinking water for a large city, we use carbon units to remove chlorine. These are also a concern. Organics may have fouled the anions because the units are exhausting on silica and not conductivity. Run lengths are decreasing on a downward trend. Regens have been normal except for occasional extended rinse down times, another indication. Are the sodium atoms leaking past the cation and combining with the OH of the anion unit to give us the high PH? I think a salt cleaning may be in order but isn't that done only on the anion unit, and the problem is with the cation?
If the sodium leakage increases, the Na cations associate with the OH anions and cause the pH to increase. If the Na leakage becomes large enough the amount of OH present can be sufficient to eluet SiO2 from the anion resin.
Have you tried a double or triple regen of the cations? Another possiblity is damage to one of the distributers in the cation.
We have tried double and on one occasion triple regens on the anion only and only if the regen doesn't "take" the first time through,(it won't rinse down to acceptable sio2 levels) The distribution pipes have not been ruled out, but I don't believe this is a main problem. The fact about if enough Na leaks through the cation it will cause elevated Sio2 levels I didn't know, do you think a second regen on the cation will help? Could we be looking at the wrong unit as the culpret?
You are approaching the end of the service life of your resins. You should plan on replacing anion resins every 3 years of service, and cation resins every 5-6 years. Unless of course, you are not that concerned about the water quality.
If your service runs have been trending down on a long-term basis, you can blame the resins. If your trending down is a shorter term (weeks), it is probably a different problem.
It is normal that the anion resins exhaust on silica. Anion exchange resins weakly hold silica; therefore, as the exchanger exhausts, silica appears in the effluent well before the ionic contaminants. Silica is poorly ionized and cannot be detected by measuring conductivity; therefore, continuous wet chemical analysis is recommended between the cation and anion beds.
It is normal to have an elevated pH (8-10) after a cation/anion demineralizer. train since the effluent will have traces of NaOH. Na from the cation unit and OH from the anion unit
Do a double regen on the cation. It might be worthwhile to check the dilute acid concentration and make sure that you are getting the right dose of acid to the resin.
Do you have a CCR or packed bed design? If you do and you over run the cation so that the final 3-4" of resin partially exhaust you will get increased Na slip during operation. It is most important that those last few inches of bed polish the effluent rather than run to exhaustion.
When resin samples are taken, do they collect core samples that represent the entire bed from top to bottom or do they scoop samples off the top 12 inches or so?
Is sulfuric acid used to regenerate the cation resin or is it hydrochloric acid? If sulfuric acid is used, does your system introduce sulfuric acid in two-separate stages: first stage low acid dose, second stage high acid dose?
No, you don't want to brine the cation resin. Multiple, sequential brine & caustic cycles (i.e., "sequeezing") of the anion resin can remove organic foulants, but I would be sure that it will be worth the effort by first performing a batch cleaning on a small volume of resin removed from the anion vessel by the core sampling technique. Have your resin analysis lab compare before and after samples to measure the results. Visual monitoring of color in the wastewater alone can be deceptive. I would also troubleshoot the problem with the cation unit first before tackling the possible organic fouling issue. The suggestions offered by Cub3bead and Bimr are excellent places to start.
cub3bead
Thanks, I'll do a double regen on the cation next time. I'm not sure which, CCR or packed bed, what is the difference?
sbush
We take core samples with a long hollow rod, and we use hydrochloric acid not sulfuric. More resin samples for cleaning comparison are in order.
I believe cub3bead meant CCR to be Counter-current Regeneration. CCR can be done without the bed being packed. CCR is the typical term for a standardly loaded vessel to be regenerated counter flow to the service flow. The vessel is to totally fully of resin but is loaded as a standard system would be loaded with the proper amount of freeboard space above the resin bed.
Gary did a very good job of responding to your question.
There are atleast 3 variations of CCR units. One design uses a water blocking flow to hold the bed down during upflow regneration, the downside is it uses about 30% more water than other desings. Another uses a dome of air to hold the bed down. and the third is a split flow where the regenerant is split with about 1/3 of it flowing from the top of the bed down and 2/3 flowing from the bottom up. A mid bed collector extracts the regeneration waste from the vessel.
Purolite's Puropack, Bayer's VWS, Rohm & Haas' Amberpak or Dow's Upcore are commercial examples of packed or fluidized bed designs.
I am curious, I suspect that you have a packed bed installation. Do you have external resin maintenance tanks at your site?
cub3bead,
We have packed bed units here, and not any type of CCR cycle, just the basic stuff, and we do not have any other tanks for maintenance yet. I don't know how they use to do brine washs here in the past, but looking at the numbers of the amount of material used, they didn't have any of it right based on manufacture numbers. I am going to suggest to management to buy tanks and pumps for as needed brine washes in the future.
Thank you as an end user for confirming the need for external resin maintenace tanks. I have always recommended them to my clients. By the time you find out that you really do need them, then there is usually insufficient space left in the facility.
