Problem rinsing cation/anion stream online

[Thumpick]

System is: cation anion, co-flow, co-flow regeneration with sulphuric and sodium hydroxide. Fixed volume regeneration not pumped. We have two identical cation/anion streams. The problem is on both streams.

We changed our cation and anon resin sometime last year with an equivalent resin. The only difference was the cation is a slightly larger particle size but chemically identical. The anion is exactly the same. The volumes of resin are identical.

The issue is, upon regeneration, the stream won't rinse online. The conductivity must drop below 10 microS/cm to allow online. However it does not drop below around 20 microS/cm. this has been confirmed as sodium. The way to solve the problem is by back washing the cation for around 20 mins. This normally allows the bed online. Occasionally not and the anion has been backwashed.

The regent process looks fine. Acid strength and contact as it always has been.

Any ideas on what our issue could be. I don't think it's mechanical as it is occurring on both streams.

Thanks

 

[bimr]

You do not provide enough information to arrive at any conclusion.

Have you had the manufacturer's service people visit?

Why don't you try to rinse longer instead of backwashing?

Are you backwashing with DI water?

Does the new resin have the same regenerant requirements as the old resin?

Have you evaluated the resin?

Where did you buy the resin? Maybe it was not new.

Do you have a graph showing the conductivity over the service cycle?

 

[Thumpick]

Hi,

The manufacturer has offered suggestions but no site visit.

Rinsing for longer does not solve the problem. The conductivity settles at around 20 microS/cm. We use DI water to rinse. The new cation resin is a direct replacement from the same manufacturer. It has a different name but has the same functional groups. It wad new and had the same regen requirements. I do have a graph of conductivity over the rinse but can't download it.

We never had this issue with the old resin. All of the evidence points to not enough acid to fully regen the cation? A double regen allows the bed to rinse online.

 

[bimr]

It may be a bad resin batch. Suggest you take a sample and send it back to the resin supplier for testing.

Make a pdf of the chart and "upload your file to ENGINEERING.com" as shown at the bottom of the post area.

 

[sbush]

I've experienced what you're seeing and doing. The likely culprit is poor liquid distribution and/or collection. If the regenerant distributor and/or under drain collector was never inspected, tested (hydraulically) or cleaned prior to the resin replacement, "hideout" could be occurring. The second backwash redistributes the unregenerated beads back into a new flow path where final rinsing is allowed to occur.

Sometimes the regeneration flow rate is too low. If you are introducing regenerant at below 0.25 gpm/cf of cation resin, try increasing that flow rate to 0.50 or 0.75 gpm/cf.

If increasing regen flow rate doesn't fix the problem, consider removing and saving the resin in a suitable container then checking the under drains for blockages (wedge wire & wire cloth screens can become clogged by debris such as fractured beads). The saved resin can be reinstalled. If you do this, consider installing a support bed of anthracite to a depth that would raise the cation resin bed approximately 4 - 6 inches above the under drain collectors.

S. Bush

http://www.water-eg.com