ERV facing frequent chocking by process crystallization 4

[Mussha]

In our storage tanks Biphenyl Product tan & Terphenyl Product tank, there is problem in Emergency Vent cover for frequent chocking.

The Emergency vent cover pops up within 100 mmWC while its set pressure is 150 mmWC and while overhauling we observed the process crystalizes due to which it causes continues passing.

To prevent the crystallization of process in the valve seats during operation, we provided electrical heat tracing cable over the valve bodies. But not effective.

Attached photographs.

 

[LittleInch]

Your file is missing a .jpg so won't download. Please try again.

Your best point of contact is really the vendor and what they recommend for fouling service.

But you seem to be normalising failure here. The "emergency" vent should NOT OPEN in normal operation, so fix the process first so that the valve doesn't open and worry about the valve not reseating second. If it keeps happening even at 150mm WC, then there is something wrong in your design which you need to fix.

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

 

[Mussha]

Thanks for your reply Mr. LittleInch. i am attaching photo for reference.

Operation side, we checked N2 blanketing is within the PCV limit. Electrical heat tracing applied externally to ERV that also working fine.

 

[LittleInch]

That's not good, but you're ignoring my point that these shouldn't be lifting.

Any lift of an EMERGENCY valve should be investigated and treated as a failure of the system.

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

 

[Mussha]

Yes, any lift is a risk, which we already raised to process safety dept to take care. But as integrity we are checking how to overcome. Thanks for your support.

 

[Latexman]

P&ID or pic. of the installation?

Was insulation over the ERV and tracing? Is N2 injected just below ERV inlet and flows into tank to keep vapors/solids away from ERV?

Biphenyl has a relatively high sublimation pressure.

Good Luck,
Latexman

 

[Mussha]

@Mr. Latexman,
Thanks for your interest, pls find below:

Was insulation over the ERV and tracing?
---There is insulation and EHT around the ERV and EHT around the PVRV. The EHT number of turns are provided to the maximum we can without affecting the instrument moving parts integrity.

Is N2 injected just below ERV inlet and flows into tank to keep vapors/solids away from ERV?
----As per the P&ID and GA drawing the nitrogen is injected into “N7” which is not below ERV. We have a newly installed nitrogen supply for the PVRV line which is just below the PVRV, but we are still seeing BP crystals after we removed it.

 

[pierreick]

Hi,
Please check with your process engineer.
EDIT:

https://webbook.nist.gov/cgi/cbook.cgi?ID=C92524&Mask=4

Below 70C risk of crystallization.
Note: For Terphenyl the melting point is much higher :212-214 C.
How do you keep warm the tanks?
What about other PVRV's? risk of tanks collapsing because safety reliefs ineffective.
Btw share with us the PID of your storage tank to get a good understanding of your operation. If you use N2 blanketing, this could be the local point for crystallization. You may need to warm the N2 prior to enter the tanks.
Good luck.
Pierre

 

[Latexman]

The P&ID and GA drawing did not make it.
What temperature do you keep/control the liquid in the tank?


Good Luck,
Latexman

 

[LittleInch]

Musha,

your file is just called P and won't download. Please try again and include a.pdf or whatever.

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

 

[Mussha]

@Latexman
The P&ID and GA drawing did not make it.
- sorry for that, i am trying to upload, it is showing same what i did before.
What temperature do you keep/control the liquid in the tank?
- 90degC as steam coil is there inside the tank.

@LittleInch
first time i uploaded in pdf format only, but i think that was also not opening.

 

[Mussha]

@Latexman pls check this P&ID, might it will open.

 

[LittleInch]

Same thing. file is just called P

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

 

[Latexman]

No idea why the file is not uploading. Maybe use "Contact Us" for help.

Biphenyl melts at 70[sup]o[/sup] C. You'll probably reduce the problem by getting closer to 70[sup]o[/sup] C, but I understand the need for a safety margin. Do you have experience with this? Maybe a low power agitator or gentle recirculation and 75 or 80[sup]o[/sup] C?

Good Luck,
Latexman

 

[Latexman]

When I went to close Chrome, it said, "still downloading". This was 10-15 minutes after I tried to see the P&ID. That may be a hint to why the P&ID is not being available.

Good Luck,
Latexman

 

[georgeverghese]

What is
a)design pressure of this tank - lower and upper design
b)N2 injection pressure regulator setpoint

N2 injection below PVRV assembly may not work unless there is a constant flow of N2 at injection point to enable downward flow of N2. To make this happen, inbreathing N2 PCV setting should be HIGHER than that of outbreathing PCV, and this will mean a lot of N2 loss. What do you have? P&ID or some sketch required with settings for PCVs'.

 

[Mussha]

Thanks ALL gentlemen and for your patience to my reply:

@pierreick
How do you keep warm the tanks?--- steam coil inside the tank maintaining at 90degC.
What about other PVRV's? risk of tanks collapsing because safety reliefs ineffective.----PVRV also have issue but not that ------ Noted, already raised this concern to Process Safety.
Btw share with us the PID of your storage tank to get a good understanding of your operation. If you use N2 blanketing, this could be the local point for crystallization. You may need to warm the N2 prior to enter the tanks.
----I am trying to attaché in another format pls check now.

@Latexman
No idea why the file is not uploading. Maybe use "Contact Us" for help.

Biphenyl melts at 70o C. You'll probably reduce the problem by getting closer to 70o C, but I understand the need for a safety margin. Do you have experience with this? Maybe a low power agitator or gentle recirculation and 75 or 80o C?-------- No experience & no agitator. We will discuss this option with our internal team.


@LittleInch
Same thing. file is just called P----I am trying to attaché in another format pls check now.


@georgeverghese
I will reply to you soon, pls bear with me.

 

[Mussha]

Gents,
Some more info. in attached file.

 

[Mussha]

Gents,
Some more info. in attached file for tank venting design data.

 

[Mussha]

@georgeverghese

a) design pressure of this tank - lower and upper design---------- (0.0175/-0.004) kg/cm2g
b) N2 injection pressure regulator setpoint--------- (0.0080) kg/cm2g

N2 injection below PVRV assembly may not work unless there is a constant flow of N2 at injection point to enable downward flow of N2. To make this happen, inbreathing N2 PCV setting should be HIGHER than that of outbreathing PCV, and this will mean a lot of N2 loss. What do you have?----------(Correct, this is our current setup)