Problem with ion-exchange resins efficiency

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Problem with ion-exchange resins efficiency

David Averbeck Sean Roop 

Hi everyone.

I made a set-up for ion-exchange resin demineralization. The water analysis is attached. the feed water is slightly sore municipal water, and the  feed debi is 200 liters per hour,  measured by a flowmeter. The cycle is getting less. in the beginning, it was around 3 m3 per cycle. It was not okay at the beginning, I thought maybe it was because of the regeneration material dilution, first, it was 20 lit HCl in 200 lit Water and 20 Kg of NaOH in 200 lit water. (The valves are automated.) I changed the volume of the regenerants as follows., but got worset. I have 3 main problems: 

1-The cycle is not 6m3 as we expected.

2- pH varies  between 3 to 14

3- Since I don't know when to stop the final rinsing sequence, I will waste the capacity of the deionizer. How can I understand when to stop rinsing?

The system Details As follows:

Cation Exchange: (Total Cation: 23.611 meq/L)

Resin: Purolite C100H ( Capacity:2.0 eq/L ) / Vol: 125 Liters / Regen by 20 liter HCl (No water added)

Vessel : FRP 12X52

Cation Exchange: (Total Cation: 23.609 meq/L)

Resin: Purolite A400OH ( Capacity: 1.3 eq/L ) / Vol: 175 Liters / Regen by 10 Kg dry NaOH in 40 lit. of water)

Vessel : FRP 14X62

 

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6 Answers

  1. Refer resin technical data sheet for rinse volumes. Normally cation resin is regenerated with 5 % HCl and Anion with 5% NaOH. Regeneration level also available in resin data sheet. If the ionic load is more than the designed the unit will give less output. Enough free boards should be available for cation and anion vessels during backwash/bed expansion.

  2. Good Afternoon Alireza,

    Respectfully, send Purolite's Tech Support pictures of the installation along with full parameters of source water and strength of regenerates so they can advise how their resins are specified to operate.

    Warmest regards,

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  3. I'm confused please check the Cation vessel I get by 12x52 only around 95 lts in the cylinder. normally you should have a freeboard of min. 10%, how you bring inside 125 liners of resin?.

    Btw regeneration is in same flow than raw water? That eats more regenerants. Or it's counterflow?

    Volume of Anion is OK, but freeboard could be a little bit better you should rinse wit DI water down to 10 micS. see the comment from Ed. Also I found by Lanxess program this system eats itself.

  4. The anion resin will exhaust after 25 bed volumes. 25BVx175l = 4 400l then the anion resin will be exhausted and the pH will start dropping, conductivity goes up, yes? If you are using 10 bed volumes to rinse, you have already half exhausted the resin.

    2 Comments

    1. Hi. Thanks for your kind answer. The pH is Alkaline at the beginning but it gets Acidic. I think this shows that the Anion is fully exhausted. Do you mean that I should reduce the Velocity of Regeneration?

      How can I measure or control the velocity of water entering the system while the regen. process. There is a flowmeter but how can I measure it??

      1 Comment reply

      1. The velocity of regeneration should be about 5m/h and the concentration about 5%. That isn't the most important bit, if these figures differ slightly. The rinse water is what is exhausting your resin. velocity is flow rate divided by the cross-sectional area of you column.

    2. Dear Ed. Thanks. if I change the rinsing water to Soft water, then can the product water be better or the anion matters too much?

      1 Comment reply

      1. Soft water still contains chloride so will exhaust the anion resin. Do an elution curve: measure the pH and conductivity of the water coming out of the anion unit during a regeneration and rinse every 5 minutes. Send me your email and I'll give you some information on how to measure this.

  5. Hi Alireza, first with this high TDS (conductivity) the water isn't good to desalinate by IEX. Better RO and then IEX. For bigger Demineralization plants we find out that IEX is economical up to 160 micS inlet water conductivity vs RO systems.  Other point: If that is municipal water tan the NH4+ is drastically to high harms the humans later I will check by IEX program how it is. For me are the concentrations of regeneration chemicals to high too. Normally around 5% weight is OK.. Best regards Dieter

    1 Comment

    1. Hi. Thanks for your kind answer. I have attached the water analysis, but I can't see it here now. About using RO, since we have a water shortage in that area, and we are not allowed to use one, I had to go for IEX. About Cation I made a mistake, the Vol is 75 Lit. of Cation Resin. I am really confused with regen materials. Software (WAVE) says: "100 gr/Lit. HCl 32%" and in another place said "Dose Fraction 100%" I suppose that the Lit is for a liter of Resin but I don't get the dose Fraction thing. As Mr. @Ed Hardwick said, I put the recycling system for the DI-system. If there is a way I could have contacted you I appreciate it so much.  

  6. Recycle the rinse water back to your feed tank when the conductivity drops below the municipal water conductivity.