Producing Demineralized water from Ion-exchange resins

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Hi every one

I hope you are all well and healthy.

We planned to make Demin water out of municipal drinking water (Tap water), with a total hardness of 450 ppm, pH=7 by using the Ion-Exchange resin method. For this process, the Strong Acid Cation (SAC) resin,  PUROLITE C100 H, and   Strong base Anion  (SBA) resin PUROLITEA400 OH was used as Ion-Exchange media. The ion-Exchange was filed in an FRP Tank. (25 lit Cation and 50 lit Anoin resin). The desired ammount  of water was 300 liters in 8 hrs (M`=0.0375 M3/hr)

First, the inlet water runs through PP and activated carbon cartridges and enters to Cation stage first, and then goes to the Anion, and after all, 2 mix bed cartridges with around 2.5 Lit of PUROLITE MB-400 resin.

The TDS of outcoming water is around 40 ppm but the problem was that the pH of water is 9 to 10 !!!

Then we added a Degasser tank after the cation stage,(a high 500 lit vertical tank with permanent air stream inside it, injected by a big bubble diffuser) the result was almost the same.

I was thinking if we use (CATION > ANION >CATION > ANION > MIX BED) system, without degasser. But I don`t have any sense that what would be the result.

Please help me how can I fix the pH.

Thanks a million. 

A.Reyhan

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7 Answers

  1. It is possible to reduce the pH by injecting a small amount of CO2 through a diffuser

  3. To check the feed water quality between design and actual including BV/hr design vs actual for Twin Bed and MBP. The main ion exchange activity is done at Twin Bed. while the residual anion and cation ion will be exchange at MBP. By analyzing the feed water quality, you will be able to know ionic loading to Anion and Cation exchanger of Twin Bed. On the top of that, you will also evaluate the resin volume and chemical is sufficient for regen. Need to check all above before you plan to change to other technology or install additional equipment.

  4. Is the flow rate continuous at 0.04 cm/hr?  If so you are likely to have poor distribution in the mineral bed.  Based on the volume of resin you mentioned a more typical flow rate would be about 10X (5 LPM).  I would try a small recirculating pump to recirculate 5 LPM from the MB outlet to the cation inlet.

     

    That might also improve the water quality.  40 ppm from this system is about 10X what I would expect from this system.

    1 Comment

    1. Hi dear Mr.Averbeck.

      The problem was solved with increasing the flow rate, the amount of water with less than one micro simence conductivity was 7.5 m3 totall and now it needs to be regen. I am changing the design for the recycling system advice.

      Thanks again for your time and consideration.

  5. A single-bed  demineralizer  contains either  cation  or  anion  resin beads. In most cases, there are two, single-bed  ion  exchangers in series; the  first  is a  cation  bed and the second is an  anion  bed. Impurities in plant water are replaced with hydrogen ions in the  cation  bed and hydroxyl ions in the  anion  bed.  You always run through strong acid resin (action removal) first.  No need to do the above.  Cation>Anion>Mixed bed.  Rinses and back washes are imperative for all to get the proper reveal without slippage or channeling.  Read up on this basic configuration for a demin system.  You can take loading off and probably save money with a zeolite softener upstream to remove hardness.  This will also prevent calcium sulfate formation in your action bed.  It happens when you have a poor regeneration sequence and your purge of the rinse is incomplete.  Test your beds for conductivity before you put them in service after the regeneration to ensure no acid is left.  Using hydrochloric helps, but you vessels need to be lined or otherwise protected from corrosion by HCl.  These are the basics, but you can fine tune with a dilution study to get your optimum testing standards to move forward in each step until it is second nature.  This will also lay the ground work for potential fouling challenges later.  Dilution study once a year and resin clean every 24 months minimum.  Enjoy the carnage.  Fun subject though.  Best, Sean

  6. For the volumes you are using try RO, then DI

  7. Good Morning  Alireza,

    Aquathin produces an RODI UF process for high purity applications.  Your pH issues will be resolved accordingly.  See attachments.

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