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.

 

[pierreick]

Hi,
What is really missing is your PID, PDF format is the best.
How the solution is mixed? Coil is definitely not the best equipment to heat up your tank, do you have tracer in place on the shell, on the top of the tank?
What is the temperature of N2 entering the tank? This could be an issue and promote crystallization, if below 70 C.
Pierre

 

[Mussha]

Hi Mr. Pierreick,
pls check now P&ID in pdf format. N2 entering at ambient temperature.

 

[Mussha]

Hi Mr. Pierreick,
What is really missing is your PID, PDF format is the best.------------- i attached but i don't know why it is showing P while download, i raised query to eng-tips.com Contact Us also. Lets wait.
How the solution is mixed--------- Mixing not required, this is product tank, solution is coming after mixing by piping(externally EHT with insulation).
Coil is definitely not the best equipment to heat up your tank, do you have tracer in place on the shell, on the top of the tank?--------It is designed like that. No traces on shell or top of the roof.
What is the temperature of N2 entering the tank? This could be an issue and promote crystallization, if below 70 C.---------N2 entering at ambient temperature.

Thanks once again.

 

[Jon]

Apologies for this problem. I have corrected the filenames so they will now open and let the original poster know how to avoid this issue in the future.

Thanks, Jon

 

[Mussha]

Thanks Jon,

Gents,
@pierreick, @Latexman and @LittleInch
Now pdf attached file is opening.

 

[Latexman]

It looks like liquid biphenyl is sprayed at the cone top. I assume this is to wash/melt the "whiskers" off from time to time. Could liquid be sprayed underneath the ERV from time to time to do the same?

Good Luck,
Latexman

 

[pierreick]

Hi,
Thanks, we got the PID.
Regarding your tank, I'm also worried about solid accumulation on the ceiling, in other words the integrity of the roof.
You need to pay attention to every cold spot (below 70c).
Pierre

 

[georgeverghese]

re P&I D uploaded: Some have notes in them, some dont. One has tank data on titlehead, others dont. All are poor resolution, difficult to read everything.

 

[3DDave]

"&" is not a character the download software handles.

The upload software really should do the filename cleaning.

 

[hacksaw]

All the files download just fine.

The photos showing the solids buildup, suggest the entire vessel top and the RV require insulation and heat tracing to avoid solids build up.

Basically you are dealing with an unsafe vessel design.

 

[georgeverghese]

Since process drawings loaded are all poor resolution, I cannot see the details on N2 inbreathing / outbreathing controls, and other related design info also not clear.
Off hand, you can install a rupture disc upstream of safety valve to stop the safety valve from contacting biphenyl in normal operation. See API and other guidelines for installation and design details on rupture disc in series with PSV combination ( rupture detection, sizing of PSV etc). For better reliability, use a reverse buckling type RD.

 

[Mussha]

@hacksaw Thanks for your reply, actually its Tank and on above the Tank there is PVRV & ERV which are already insulated and in between insulation there is electrical wires for heating which is acting as heat tracing.

@georgeverghese Thanks Sir, N2 inbreathing / outbreathing controls are provided which is working fine & it is confirmed by inlet/outlet PCV & N2 injection pressure regulator setpoint is 0.0080kg/cm2g. Regarding RD we will discuss with our team. Thanks for suggestion. Pls refer photos for process design data of ERV.

 

[pierreick]

Hi George,
There is no guarantee that the RD will not be coated with solid.
To me there is a huge risk that the ceiling of the tank is also coated, no prevention in place to prevent cold spots.
It should be traced and insulated.
Pierre

 

[georgeverghese]

@pierre,
Am not an expert on RDs', but these are in the API for polymerisation or fouling or corrosive applications ( at least when I saw these in the API many years ago), so I presume these RDs' will still burst the same as in clean service.
Agreed, purging of the RV nozzle neck on constant flow control will also help to keep biphenyl off the RD / RV.
Pls check with RD manufacturer.

 

[pierreick]

Hi,
25 years ago, manufacturing latex in SE Asia, I found several times RD coated with latex on SB reactors. What was supposed to protect from runaway reaction was ineffective.
Pierre

 

[georgeverghese]

https://my.fike.com/_fike_docs/Pres...ulletins/TB8105_Best_Practices_for_RD_PRV.pdf