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  1. #1
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    Very long suction line question



    Have seen a plant with very long dry suction line, about 300 metres, on large liquid overfeed vessel, -40 C
    Vessel is well oversize for job, so very low risk of high level.
    Dry suction from vessel has a few low area's in it, as it follows roof line across buildings.

    At plant room before compressor suction is a slop pot/trap, with boil off coil in it.
    Can anyone see that this vessel would be useful?
    Changes in suction pressure, could you condense liquid in dry cold suction line & get slugs of liquid?
    Thanks for any replies



  2. #2
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    Re: Very long suction line question

    I don't think that ammonia will condense in suction line. However, if mentioned vessel will trip on high level(leaking solenoid) and will be started too fast some liquid can fly into suction line, but 300m length will evaporate this liquid. What type of compressors do they have? Reciprocating compressors very sensitive to the liquid, but screw compressors not so much.

  3. #3
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    Re: Very long suction line question

    Segei,
    This is a screw compressor plant with horizontal accumulator that from operating level, to high level would be approximately 5 tonne of ammonia.
    Hard to get a high level, but of course anything possible.
    Another company suggested it & installed trap, which have never seen before in this scenario.

  4. #4
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    Re: Very long suction line question

    Hi Ranger
    I wouldn't think you would get ammonia condensing in the suction. There may have been a problem with liquid in the separators and it was assumed it came from the suction and therefore they installed the suction trap. As you know sometimes a band aid measure is used instead of fixing the problem.
    I have seen liquid sit in a suction line and get drawn back to the compressors but this was from a very small vessels on flooded evaps.

    Regards
    Paul
    Born to fish, forced to work

  5. #5
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    Re: Very long suction line question

    Hi
    during of running system you shouldn't have liquid in suction line .
    only when your system is off for long time your suction pressuer goes up and during day and night time the ambient temperature were Change at that time might you having liquid in suction line .
    To have suction separator is a good idea.
    Last edited by mbc; 13-10-2017 at 05:55 AM.

  6. #6
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    Re: Very long suction line question

    Hi Ranger.
    An intreaging one this!
    Do you know why the slop pot was suggested.
    Ie. Do you have historic site knowledge?
    Has liquid carry over been an issue before?
    As you point out my concern would be the working levels being maintained and the ramp rate of the suction on comp startup.

    Is the heater coil on some kind of float switch?
    Basically I am assuming that under normal running the pot is no more than a large bore pipe.

    Like you I would question its effectiveness and check the comp heaters.
    Is oil carry over an issue on the site?

    Lots of questions but hey no real issues.
    Cheers grizzly
    Despite the High Cost of Living it still remains Popular!

  7. #7
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    Re: Very long suction line question

    Quote Originally Posted by Grizzly View Post
    Hi Ranger.
    An intreaging one this!
    Do you know why the slop pot was suggested.
    Ie. Do you have historic site knowledge?
    Has liquid carry over been an issue before?
    As you point out my concern would be the working levels being maintained and the ramp rate of the suction on comp startup.

    Is the heater coil on some kind of float switch?
    Basically I am assuming that under normal running the pot is no more than a large bore pipe.

    Like you I would question its effectiveness and check the comp heaters.
    Is oil carry over an issue on the site?

    Lots of questions but hey no real issues.
    Cheers grizzly
    Grizzly,
    Large ammonia plant with new plate freezers installed.
    Accumulator as well as plate freezers is in remote area from main plant.
    Accumulator & plate freezers hold 20 tonne of ammonia.
    Accumulator requires probably another 10 tonne to get high level, unless some plates are turned off.
    Would say near impossible to get high level.
    This system in new & never run as need to be connected to main plant.
    Dry suction several hundred metres long with pockets due to old buildings landscape etc.
    Another company runs new dry suction back to main plant & installs a new compressor.
    They insist it requires a slop pot approx 3 m diameter x 4 m high with boil off cool in it.
    Appears to. E an expensive slop pot for suction line condensate.
    Wont hurt, but is it necassary, as unusual to me.
    Plant runs continuously, rarely stops.

    Thanks for input.

  8. #8
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    Re: Very long suction line question

    Quote Originally Posted by mbc View Post
    Hi
    during of running system you shouldn't have liquid in suction line .
    only when your system is off for long time your suction pressuer goes up and during day and night time the ambient temperature were Change at that time might you having liquid in suction line .
    To have suction separator is a good idea.
    Fair enough, but is it absolutely necessary, or luxury $100k slop pot.
    Would be interesting to trend if it ever gets a level in it.

  9. #9
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    Re: Very long suction line question

    Hi
    actually I was in hospital to look after my father in law and I got time to look for this site
    it is late to reply.
    sorry
    Last edited by mbc; 13-10-2017 at 02:00 PM.

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