4 CSTR tanks in series agitator problem

[erdyne]

Dear Colleagues,

In one part of the plant (phosphoric acid) I am working as a process engineer, we have 4 CSTR crystallization tanks in series and the slurry is flowing as overflow from one to another and from 4th tank to filtration section by slurry pump. For a long time, we have been having issue with the agitators. Every 5-6 months, the agitator shaft of any of the crystallization tanks is raptured so we are required to empty the tank and repair and put it bak into the operation. It makes a huge impact on our process. I follow up the specs of the slurry and it does not change that much and physically everything looks ok. What can be the reason of that problem? Please help me out with possible reasons I should be concentrated on.

 

[Dhurjati Sen]

Dear erdyne,

With the limited info you have provided the following could be done:

Re-check / modify the design of the shafts (by your design section or by the vendor himself).

Replace the shafts instead of repairing.

Regards.


DHURJATI SEN
Kolkata, India

 

[LittleInch]

"Slurry" is a very vague term and its consistency and impact on agitators can vary a lot.

If your shafts are breaking then they appear to be too small.

Any sort of shock loading will shorten the life of your agitator.

How are they breaking? Torsion? End connection? Fatigue?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jari001]

I follow up the specs of the slurry and it does not change that much...

How much is it changing? Did you check all the properties, or only the ones for releasing the product (I'm assuming there is a difference in what's tested, correct me if I'm wrong).

 

[geesamand]

I have a few questions, if you're still tuning in.

First, know that 5-6 months (or 1-2 years per agitator) is unacceptably low life. If your supplier has no feedback on the failure causes, they might be viewing you as a revenue stream.

1) Are these agitator shafts made from hollow pipe? What material? Is the OEM supplying the replacements?
2) Are the agitators ever stopped and solids allowed to settle around or below the impellers?
3) Do they fracture in the same place each time?

Thanks, David