Demineralisation chain 1

[padovano]

Hello all, I have a demineralisation chain with a production cycle of 300m3 in 12 hours(25m3/hr). The demineralisation unit is made up of a cationic and anionic ion exchangers. We use hydrocloric acid and Sadium hydroxide solutions for regeneration.
Over the past 2 days, we have encountered a sudden increase of the pressure drop across the cationic drum from 1bar to 5bars. This has reduced our feed rate from 25m3/hr to 12m3/hr.
1-What can be the cause of this sudden increase in pressure drop
2- Is there any method of reversing this pressure drop without openning the cationic drum to filter or replace the cationic resins? The anionic drum has no problem. it's pressure drop is about 1bar.

Thanks.

 

[bimr]

That is a very unusual problem.

Does the unit regenerate normally? Have you checked the backwash rate and is the backwash differential pressure high? Have you taken the manhole cover off and inspected the resin?

 

[ashtree]

The questions that bimr is asking are an excellent start.

I will add a couple more.

What is upstream of the demin units?
Has the rise in pressure been preceded by any maintenance or changes to the system or any periods of incorrect operation or malfunction?
Have you performed any checks or inspections on the control valves to check for blockages or faulty operation?
Does the system have a built in flow limiting valve?
Is demineralisation performance other than flow still okay?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[padovano]

bmir,
1- The the unit regenerates normally
2- I intend to remove the manhole cover by the end of the week.

 

[padovano]

ashtree
1- The normal upstream is 3bars. This gives a flowrate between 25- 30 m3/h. Presently, the upstream is 6bars but the flow rate is about 12m3/h
2-No. The rise in pressure has been sudden
3- All the control valves have been checked. No blockage from them either
4-No built in flow limiting valve
5-The quality of the demineralised water is perfect.

 

[ashtree]

Just to follow up on bimr's question.
In the service mode is it upflow or downflow? Upflow units don't actually backwash and therefore need the resin to be withdrawn from the vessel from time to time for cleaning. If its a downflow unit have you actually checked the backwash flow rate?
Is there any form of pre-treatment such as activated carbon before the demin unit?
What is the source of the water?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Is this a conventionally designed demineralizer with approximately 75% freeboard?

Is it possible that there is a downstream blockage, a closed valve, a clogged resin trap (strainer), etc.?

 

[padovano]

dear all, for now all the fingers are pointing towards the state of the cationic resins. the high pressure drop is exclusively on the cationic drum. The anionic drum is OK. we have planned to shut down the cationic drum on thursday and open it for possible sieveing and top up of the resins.Will keep you guys posted

 

[dfmorvan]

Hi
Cationic resins are pretty sturdy stuff.
They can swell if they see too much chlorine, but it takes some time usually and you said that the change was abrupt
It would point out to some ingress of suspended matter.

 

[itsmoked]

Any structure inside that 6bar could've collapsed?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[shahyar]

I am with "itsmoked". Sudden increase in pressure drop generally is associated with mechanical damage inside. One common breakage happens in the distributor.