Demineralising chains

[padovano]

Dear All, I have been running a demineralising chain made up of cationic drum and an anionic drum. During regeneration of these resins, the operators don`t drain the ionic exchangers completely before starting the regeneration. I think that if those ionic exchangers are drained completely from the water they contained, the efficiency of the regeneration will increase. I would like to know if my thinking is right/wrong. Is there any adverse effect of draining the resins ( they will stay dry) before regeneration.

 

[bimr]

It is not customary to drains the tanks prior to regeneaation. The process is a plug flow type and there would be no advantage.

 

[padovano]

Thanks, I have a unit that treats about 300 000m3 before the resines are replaced. I have treated just about 100 000m3. What I have observed is that, during regeneration, the conductivity doesn't go below 3µS/cm in 25 minutes as it does usually. For it to attain the 3µS/cm the chain has to be recycled for about 6 hours instead of 25 minutes. I would like to know if there are any other things I can do to verify the situation. I have already carried out 2 double regenerations and the situation didn't improve.
Thanks.

 

[bimr]

You are going to have to investigate several things:

1. Has the raw water quality changed?

2. Has the regenerant quality changed?

3. Go through the regeneration cycle and confirm that all steps are being completed and all flows, times, and volumes are correct.

4. You may have to call out the service representative of the equipment supplier.

5. Is this a recent change or has this occured over time.

 

[padovano]

1-The water quality, the regenerant quality, or the the different steps of the regeneration process has not changed. The second other demineralising chain, which has treated more water than this chain doesn`t have any problem.
2- The change is about 2 months old.
3- I supervised a regeneration process where I carried out 2 passages of the regenerant solutions. Nothing actually changed as far as the conductivity is concerned. How ever I stopped the recirculation process after an hour when the conductivity was at 29. The quality of the water had a funny behaviour. In the 1st 4 hours the silicates rose from 0.001mg/l to 0.98mg/l. Then later it dropped to 0.1mg/l and completed its 10 hours of production with a silicate breakthrough of 0.01mg/l. The maximum allowable concentration of our demineralise water is 0.2mg/l.
I have an impression the anions are spent. I will need to carry out some analyses to confirm this.

 

[bimr]

How old is the resin?

 

[padovano]

the resin is about one year old

 

[bimr]

What is the source of raw water? Surface water or well water. What is the pretreatment?

Do you have colloids silica in the raw water?

Is this a power plant?

Was resin replaced in both units.

Is this a new installation?

 

[dougarthur42]

We use the rule of thumb, if the demineralizer train breaks through with high conductivity the anion is the problem. If the train breaks on silica the cation is the problem. But try this first, lengthen the rinse on that vessel. let me explain durring regeneration we have a Caustic/acid injection step then a displace rinse which rinses just that vessel. by extending our displace rinse from 22mins to 60 mins our conductivity issue went away. we assume the regenerant was not getting properly rinsed.
Hope it helps

 

[bimr]

dougarthur42,

You have it backward.

We use the rule of thumb, if the demineralizer train breaks through with high conductivity the cation is the problem. If the train breaks on silica the anion is the problem.

Lengthening the rinse will lower the average leakage over the entire service run, but at the expense of efficiency.

 

[padovano]

Answers to bimr questions:
- The source of raw water is well water
- I don`t know what colloid silica is. What I know is that, the silicate concentration rate is between 24 to 31 mg/l.
- The demineralised water is used in a refinery for turbines, stripping, etc.
- The resin of unit 1 is more of age than the resin of unit 2.
- Its an old installation of about 30 yrs old.

To dougarthur:

I would like to understand something. During the regeneration process, after the caustic / acid injection, the anion undergoes a fast rinse period of 8 minutes followed by a slow rinse period of 60 minutes. I would like to know of this rinses I should increase the time? Thanks.

 

[bimr]

Since you state that you have not made any changes except changing the resin, you might doublecheck that you are using the same resin.