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Suction Gas Flow Transmitters

problem suction flow suction flow transmitter process oil and gas turbine suction suction flow process gas flow transmitter

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#1 Sarah_Process_engineer

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Posted 18 January 2017 - 06:44 AM

Hello everybody.

 

in the plant where I work, we are experiencing a wierd issue with our suction gas flow transmitters of the boosters.

 

we have to compressors working in parallele, one on mode: Suction and the other one in mode Speed.

 

The problem is that the flow transmitter often blocks in its maximum range. And we need to stop the machine to purge it.

 

at the beginning, this was happening only with the first booster. So we thought it's the transmitter that disconnects. So we replaced it.

 

But, the problem still happens again.

 

So we thought it was a problem of water condensation in the transmitter's capillaries so we installed pots of condensations to recover any water droplets.

 

after that, we launched the machine with total recycling of the gas (ASV is 100% open).

 

The thing is that problem is now occuring to the second booster.

 

Now, I assume it's not the transmitter that makes all this mess. But still dont know where the problem comes from !!!!!!

 

 

can someone please help me?! Anyone that faced this problem before?!Attached File  IMG_20170120_072208.jpg   243.43KB   2 downloads

Attached Files


Edited by Sarah_Process_engineer, 20 January 2017 - 09:58 AM.


#2 Bobby Strain

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Posted 18 January 2017 - 09:20 PM

Sarah,

     We need more information to help you. Installation details (a sketch with proper elevations). Transmitter range and normal/maximum flow. And some information about the gas; temperature, pressure, composition, source, etc., and about the compressors. Otherwise you will get only guesses.

 

Bobby



#3 Sarah_Process_engineer

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Posted 19 January 2017 - 01:30 AM

we have a three phase separation unit, followed by two boosters on parallele ( pressure from 42 to 82 bars, and temperature from 41°c  to 97°c   but gets cooled again to 45°c  )

 

transmitter range : 0 - 2750 mmH2O

normal flow: 1750 mmH2O approximately ( to each booster)

compressors are driven by turbines: one booster is put on speed mode, the other on suction mode ( for any perturbation on the flow in the entrance, the suction mode machine will absorb the perturbations)

 

the gas composition : mainly CH4 (84 %) , C2H6, C3H8 and CO2 (8%)

 

 

(( the transmitter always gets blocked at night ; 3 - 5 am)



#4 Bobby Strain

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Posted 19 January 2017 - 10:55 AM

Maybe you should keep it in the light. But, more seriously, you didn't respond with requested information about the installation. Is the gas water saturated? What is the ambient temperature? What is the source of the gas? Did this problem just appear whenever it got cold?

 

Bobby



#5 Saml

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Posted 19 January 2017 - 12:31 PM

You come saturated from a 3 phase separator at 41°C. So it is saturated with both hydrocarbon and water at 41 °C.

At night (unless you are in a horribly hot spot), temperature will drop well below 41°C and condensation may occur in the instrument piping. However, since we don't know your configuration it is only a guess. I will assume that you are working with an orifice plate or nozzle.

You have several installation options:

- Mounting higher than the orifice plate with slope towards the element.

- Mounting with remote seals

- Adding tracing to the tubing

- Filling the instrument legs with appropriate non volatile fluid. 



#6 pavanayi

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Posted 19 January 2017 - 01:01 PM

Since it is a compressor suction line, most likely you have a ventury flow meter. I would imagine the tappings would have been specified in a way that no condensate can enter. (physically the tappings would be located at the top of the pipe).
If not, maybe that is a likely reason. Please provide the information already requested by other members as without it, everything is a guessing game.

#7 Sarah_Process_engineer

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Posted 19 January 2017 - 01:58 PM

Maybe you should keep it in the light. But, more seriously, you didn't respond with requested information about the installation. Is the gas water saturated? What is the ambient temperature? What is the source of the gas? Did this problem just appear whenever it got cold?

 

Bobby

yeah indeed, the gas is water saturated ( did not yet pass through the dehydration unit) the ambiant temperature in winter is varying from 4°c at night to 16-19°C in the day!!

about the source of the gas? I don't really know what you mean : it is a natural gas that passes through a three-phase separation unit after that it is compressed in the boosters unit.

It appears only at night !! coincidence ? I don't know.

 

if you wanna further information, please tell me ! 



#8 Bobby Strain

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Posted 19 January 2017 - 04:20 PM

Sarah,

     Without installation details available,  I can only guess it is likely that hydrate is forming in the tubing at the low nighttime temperature. So, trace and insulate the tubing as suggested above. If the transmitter is installed properly, the transmitter will be located above the meter. And the meter should have instrument taps on the top, not the bottom. A sketch of the meter and transmitter installation, or a photograph, can tell us a lot. Since you mentioned that you installed water catch pots, it suggests that the installation is such that the taps are on the bottom of the meter, which is poor practice. But if this is the case, trace and insulate everything between the meter taps and the transmitter.

 

Bobby



#9 Sarah_Process_engineer

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Posted 20 January 2017 - 09:48 AM

Sarah,

     Without installation details available,  I can only guess it is likely that hydrate is forming in the tubing at the low nighttime temperature. So, trace and insulate the tubing as suggested above. If the transmitter is installed properly, the transmitter will be located above the meter. And the meter should have instrument taps on the top, not the bottom. A sketch of the meter and transmitter installation, or a photograph, can tell us a lot. Since you mentioned that you installed water catch pots, it suggests that the installation is such that the taps are on the bottom of the meter, which is poor practice. But if this is the case, trace and insulate everything between the meter taps and the transmitter.

 

Bobby

When we purge the transmitter, no water droplets are noticed.

for the moment being, we installed only the water catch pots, no problems with transmitter so far ! !

if the problem occurs again, i suggested we insulate the capillaries.

I took a photograph of the system! please check it above



#10 Sarah_Process_engineer

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Posted 26 January 2017 - 06:54 AM

Since it is a compressor suction line, most likely you have a ventury flow meter. I would imagine the tappings would have been specified in a way that no condensate can enter. (physically the tappings would be located at the top of the pipe).
If not, maybe that is a likely reason. Please provide the information already requested by other members as without it, everything is a guessing game.

The tappings are taken from the top of the pipe, and yeah indeed it is a venturyflow meter.

 

I've added more details to the questions. please check them!



#11 Bobby Strain

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Posted 26 January 2017 - 04:47 PM

I can't find any details you mention.

 

Bobby



#12 pavanayi

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Posted 27 January 2017 - 05:05 AM

Looking at the pictures, I can't seem to find any fault in the installation. I don't think you would physically see any water droplets if you drain the catch-pot and/or the transmitter itself as the flash is from 42 bar to atmospheric. Assuming you are based in the northern hemisphere and your post is in winter season, my natural conclusion is that for some reason there is condensation in the tubing, so the tracing advice given above still holds, as from your picture, the tubing is open to the elements . Maybe there is a composition change to the gas and one of those cold spells has tipped it over the edge. (Confirmed by the fact that once you drain the capillaries, even though you don't see anything, the problem disappears).

 

 

Attached Files



#13 Sarah_Process_engineer

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Posted 27 January 2017 - 06:53 AM

I can't find any details you mention.

 

Bobby

please check again, I uploaded pictures of the system to the question text !

 

Thank you



#14 PRO_ING

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Posted 27 January 2017 - 10:39 AM

Attached File  Pages from M04.pdf   107KB   14 downloadsHi sarah,
You may find an answer for your query in the attached file.

Regards 



#15 breizh

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Posted 28 January 2017 - 01:49 AM

Hi ,

My experience with Ammonia liquified storage tank and level measurement based on Delta P is to use sensor sealed equipped with capillar and liquid not subject to change due to temperature .

Let you contact big names like E&H, Rosemount and others .

Hope this helps .

 

Breizh






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