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  1. #1
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    Fundamental question (air in the NH3-system)


    This is me frist Thread!
    Fundamental question (air in the system)
    Where are collect the air in the a NH3-Refrigeration-System

    -45°C Booster and -20°C Compressor, Tc = 32° to 40°C
    Collect the air for itself in the condenser or in the receiver tank, and why?
    We have to same NH3-Refigeration plant on the world, only small differences in the thermo-siphon installation.
    In one plant, we find the air in the receiver tank, drain out be gas purge.
    In the other plant, we find the air in the condenser, here we can not drain out the air and we have trouble with oil temperatures is much to height.
    Thank you !



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    Re: Fundamental question (air in the NH3-system)

    The most common location for finding air is in the receiver or condenser(s). Ideally you want to purge both of these locations on a regular basis.

    Air usually collects in the bottom of an evaporative condenser coil (during operation) as this is the coolest location in the condenser. Air flows into the receiver when the pipe traps in the condenser drain line loose their liquid seal. When the liquid seal in the pipe trap disappears the air flows into the drain line and then to the receiver.

    On thermosiphon receivers this can be another location where purging is required for the same reason as stated above.

    Quote Originally Posted by NH3-Coolman
    In the other plant, we find the air in the condenser, here we can not drain out the air and we have trouble with oil temperatures is much to height.
    This may be caused by problems that prevent sufficient liquid flowing to the oil coolers also. Or another possibility is if the liquid lines are exposed to air warmer than the liquid refrigerant temperature in the pipes.
    Last edited by US Iceman; 30-08-2007 at 07:44 PM. Reason: fixed spelling
    If all else fails, ask for help.


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    Re: Fundamental question (air in the NH3-system)

    Dear US Iceman
    Thank your for your answer, I am 100% accordant with your answer!

    I am work more then 20 years as master in one of the greats Central NH3-Refrigeration-Supply in world, 75 MW refrigerating capacity, turbo and screw compressors.

    In the new pant, I think the piping is bad.
    Receiver location is too height (8m), the reason, is the thermosyphon oil cooler works badly.
    The Condensers outlet piping has long way (7m horizontally) to receiver.
    The hot gas form oil cooler block (pressure equalization pipe is present) the drain from NH3- liquid and the air too. That means higher discharge pressure, which means higher oil temp. etc.

    And that everything because one didn't listen to our experience

    We need answer from person they stand not in the forest

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    Re: Fundamental question (air in the NH3-system)

    Hi NH3-Coolman,

    It seems you have the common problems found on thermosiphon systems.

    The equalizing line from the receiver back to the discharge line must be sized properly. If it is too small the receiver cannot vent the pressure from the receiver. This can impose a higher pressure on the thermosiphon and cause the refrigerant boiling temperature to increase. This can have very bad effects on the oil coolers. This can also prevent the condensers from properly draining too.

    The 24 m height of the receiver adds a lot of static pressure to the liquid ammonia. This increases the saturation temperature of the liquid ammonia and also reduces the oil cooler capability.

    Does your oil cooling system work better when the weather is cooler outside?

    I understand your comment about the forest! Condenser and thermosiphon piping is not very simple, but people think it is just piping.

    I have worked on a system that was close to your capacity. These are certainly not a common system to find, and do require a lot of thinking before rushing to fix something.
    If all else fails, ask for help.


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    Re: Fundamental question (air in the NH3-system)

    Dear US Iceman

    The size of the pressure equalization pipe is DN150
    I work normally in Germany and the new plant is on the other side on the world,
    And the new plant now becomes widen on 4-fold size, same compressor 4 “Frick RWB II 856
    Technical compete and start up 2008 middle of the year.

    For more Info not over this way!
    --------------------------------------------------------------------------------------
    For fix or correction we need 1 or ˝ year preparation for a system it running 24 hours on 365 day in the year, is will never stopped.

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    Re: Fundamental question (air in the NH3-system)

    Dear NH3-Coolman,

    A DN150 pipe for an equalizing line may seem large, but it depends on the TOTAL volume of gas that flows through the pipe at full capacity (and the desired minimum pressure loss).

    The allowable pressure loss through the equalizing pipe is much lower than a normal refrigeration pipe (although the allowed pressure loss is similar to that used for say a -40°C suction line---- very low!)

    I have worked on a large R-22 system with thermosiphon oil cooling and a very large high-pressure storage receiver (a separate receiver from the one used for the thermosiphon). The equalizing line for that system was equivalent to a DN250 while the system capacity was only +/- 9MW.

    It was over sized with a small margin, but the pipe size used was based on the actual requirement. In this system the equalizing pipe was sized for both the thermosiphon and storage receiver below.

    Do you have two equalizing lines (one for the thermosiphon and one for the storage receiver) or, are you using a single equalizing line for both?

    A Frick RWB II 856 is a very large screw compressor!

    Can you send me a private message with the location of the facility please? I am curious to know where this will be installed.

    Quote Originally Posted by NH3-Coolman
    For fix or correction we need 1 or ˝ year preparation for a system it running 24 hours on 365 day in the year, is will never stopped.
    I understand. With a system this size nothing is easy.
    Last edited by US Iceman; 31-08-2007 at 07:30 PM. Reason: edit
    If all else fails, ask for help.


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    Thumbs up Re: Fundamental question (air in the NH3-system)

    Hi,
    I have send you private Info, US Iceman.

    I think we, one-few of topic strayed.
    But I think also that the air problenmaik (the air doesn't gather in the receiver) is interconnected with the bad thermo-siphon function and the badly drain piping from the condenser to receiver.

    Here Info

    Design Oil cooler by full load an max. design comperssor.

    Oil cooler 750KW
    Inlet line DN50, out line DN 80 to receiver.
    Flow 2400kg/h = 4,2m3/h
    Gas back to receiver (if it all gas, 100%)195m3/h

    BR! NH3-Coolman

    **And sorry for me bad English

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    Re: Fundamental question (air in the NH3-system)

    Hi NH3-Coolman,

    I think your problems are related to the thermosiphon and condenser piping. If the piping is not installed correctly or if the piping is not correctly sized this can cause the discharge pressure to be higher than what you may expect.

    In some installations it may be difficult to find the cause of the high discharge pressure. The problem may appear to be caused by air in the system, but this problem could also be caused by the condensers not draining properly too.

    You do not have to apologize for your English. You are doing just fine.
    If all else fails, ask for help.


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    Re: Fundamental question (air in the NH3-system)

    Quote Originally Posted by US Iceman View Post
    The most common location for finding air is in the receiver or condenser(s). Ideally you want to purge both of these locations on a regular basis.

    Air usually collects in the bottom of an evaporative condenser coil (during operation) as this is the coolest location in the condenser. Air flows into the receiver when the pipe traps in the condenser drain line loose their liquid seal. When the liquid seal in the pipe trap disappears the air flows into the drain line and then to the receiver.

    On thermosiphon receivers this can be another location where purging is required for the same reason as stated above.



    This may be caused by problems that prevent sufficient liquid flowing to the oil coolers also. Or another possibility is if the liquid lines are exposed to air warmer than the liquid refrigerant temperature in the pipes.
    I don't agree that the bottom of the coil is the coolest location of the condenser. Usually, we have saturated liquid at this point. Liquid seal is the reason of air at the bottom of the coil. Air just stuck at this seal.
    Do we need to purge air from high pressure receiver and from thermosiphon receiver? Certainly, thermosiphon receiver shouldn't be purger. It continuously vented to discharge pipe. For condensers with liquid seal. Sometimes some air can present in high pressure receiver but it doesn't have influence on condensing pressure. Sooner or later this air will go to condensers and can be purged from them.

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    Re: Fundamental question (air in the NH3-system)

    Hi

    Now become it interestingly

    Info the high pressure receiver and the thermosiphon receiver is same *tank


    At the physics’ attribute point of view
    We can never find Air in the Condenser


    The density of NH3 gas is 0,77 kg/m3
    The density of Air is 1,29kg/m3 (O2 = 1,42 + N2 =1,25)


    - Is the piping good and we has no liquid seal, the air will collect his self in the *receiver
    - Is the piping badly with liquid seal (no way for the air), the air will take condensing surface and the pressure will increase,
    - We can see it if the water inlet and outlet temperatures different to small.


    That is my Think


    BR! NH3-Coolman

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    Re: Fundamental question (air in the NH3-system)

    Quote Originally Posted by NH3-Coolman View Post
    Hi

    Now become it interestingly

    Info the high pressure receiver and the thermosiphon receiver is same *tank


    At the physics’ attribute point of view
    We can never find Air in the Condenser


    The density of NH3 gas is 0,77 kg/m3
    The density of Air is 1,29kg/m3 (O2 = 1,42 + N2 =1,25)


    - Is the piping good and we has no liquid seal, the air will collect his self in the *receiver
    - Is the piping badly with liquid seal (no way for the air), the air will take condensing surface and the pressure will increase,
    - We can see it if the water inlet and outlet temperatures different to small.


    That is my Think


    BR! NH3-Coolman
    Some plants have two-in-one(high pressure receiver+thermosiphon) vessel, others plants have two separate vessels.
    We can talk about density if we have natural convection. No natural convection in condenser. Air just blown by moving gas to the point where it stuck(liquid seal).
    Evaporative condensers in parallel operation should have liquid seals. Only single condenser doesn't require liquid seal.

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    Re: Fundamental question (air in the NH3-system)

    Nh3 - coolman
    You can go to BAC site and download there handbook this will give you the lay outs for condenser pipework.
    As this is where your problem will lie.
    Also check the hansen technoliges site about the cost of air in R717 systems.
    It shows where air collects usually the coolest point and low velocity as suggested by US Iceman and also like sergei suggest the problem will lie in the lack of liquid seal.
    The Frick compressors are they single stage or two stage,and what conditions
    You should proceed down the line of pipework issuses if you know all components are sized right.
    Inlet line DN50, out line DN 80 to receiver for 750Kw is this correct.
    Please let us know where the plant is.

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    Re: Fundamental question (air in the NH3-system)

    Dear RWF II

    Sorry! What means "BAC"
    Yes Line DN50, DN80 750KW is correct!

    Thanks you all for your show an interest!

    NH3-Coolman

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    Re: Fundamental question (air in the NH3-system)

    Hi NH3-Coolman,

    BAC means Baltimore Air Coil. They are a manufacturer of evaporative condensers, cooling towers, and evaporators. They are a USA based manufacturer but have plants all over the world.

    Here is a link to the European website for the condenser engineering brochure.
    http://www.baltimoreaircoil.be/BAC/E...Condensers.pdf

    There are some pages that show some different piping arrangements for condensers. Please be careful as these pictures are only suggestions. They may not account for all possible conditions.
    If all else fails, ask for help.


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    Re: Fundamental question (air in the NH3-system)

    Hi NH3-Coolman,

    My thoughts abouts Non Condensables Gases
    • They are a mixture of gases and they are running through the systems.They fill all the space where they are (Boyle)
    • They do not separated nither by gravety , for diferente density nor low velocity or other mecanical medio as does water and oil
    • Just we have to create spot where they are richer .Its concetration is higher.These spots could be in any point where exists a dead zone (zone whithout flow).
    • A good place to create a dead zone and richer non-condensable zone is at the outlet of the condenser. So you make an inverted siphon to crate a ammoniac liquid seal or you can go with a manifold benneth the thermosiphon creanting again a seal
    • Finally you should cold down this mixture of gasses trapped to condese the ammonia and get rid out the Non condensables gases. The temperature to cold down will depend of the amount of the Non condensables gases in the mixture. it should be as lower as possible
    I also like to point out (as the collegues have said) the higt pressure in the sistem could be for many problems.For instance.
    The distane between the oulet and the seal in a condenser is very import. A shorter distance could make the condenser flooded and you lost the heat transfer area increasing the condenser presure.It happen when you have an existing installation and you add condenser differente side ,diferente brand ,differente place.
    Some time the discharge pipe is not tild correctly and some oil sack and liquid are build incrasing pressure drop

    Hope this thought can help
    Regards
    Gwapa

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    Re: Fundamental question (air in the NH3-system)

    Daer all
    I will answer your all, at the moment I am busy
    I will give you few drawing (PowerPoint), then we can discussed.

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    Re: Fundamental question (air in the NH3-system)

    Dear gwapa,
    Dear all user of this Thread

    Thanks for your detailed answer

    I probably employed myself a little awkwardly during the question.

    Naturally, it is a gas mixture and naturally, the inert gases can collect themselves only in a rest area and be drain is out with gas purge.

    Here the story
    • Forwards approx. 17 years we exchanged all condensers, gradually all condensers the same design, same capacity (shell-tube-condensers, 6500KW) the same pipe installation to the receiver tanks, see Pictures.
    • All lines without liquid seal (all liquid seals removed), thus free liquid drain to the receiver tank.
    • Afterwards we could determine an improved capacity with small pressure „Pc “on to cost the NH3 sup-cooling (Tcu = 0,5-1K) as we it expecting.
    • Moreover, the gas purge work since that simply perfectly, if inert gases find in the system (no smell), see pictures.
    • herefore, we built before an in NH3-liquid pressure-increase-station with sup-cooler.
    The drive costs saved thereby are enormously high, with a plant (75MW) of this order of magnitude!

    We have the same installation kind then with an extension of the system with two screw compressors (2 times 5MW, -5°C) and Thermo-siphon repeat. The plant works perfectly also at air removal.

    This screw compressor plant has built as a copy now, in another world (2 times 2,8MW -21°C and 2 times 450KW -45°C).

    The air does not collect itself in the receiver tank (but in condenser) and we has a very badly working Thermo-siphon (the problem was found, here are we thereby changes).

    The master problem is the Thermo siphon (too much thermionics, equal movement) and the bad tubing achievement installation!!
    • If the changes do not help, we will try your suggestion!
    Originally Posted by: Gwapa
    A good place to create a dead zone and richer non-condensable zone is at the outlet of the condenser. So you make an inverted siphon to crate a ammoniac liquid seal or you can go with a manifold benneth the thermosiphon creanting again a seal
    BR! NH3-Coolmann
    Attached Files Attached Files

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    Re: Fundamental question (air in the NH3-system)

    Coolman

    If what I assume is the compressor are the same size if this is the case at the lower condition the oil cooling load would have increased. which would mean the pipe sizing would be to small. and if your drawing is correct or as I read it. The vent from the reciever to condensor is only 50mm this is very small and also unless the liquid drain form the condenser is massively oversized, meaning the actual thermosyphon reurn line is limited to the 50mm vent line.
    Why dont you let us know the compressor type and speed and conditions and we can check thermo line size etc.
    regards
    RWF II

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    Re: Fundamental question (air in the NH3-system)

    Dear RWF II

    The second Pictures with the line 50 DN, condenser to receiver the plant without thermo-siphon oil cooler (oil cooler with water-cooling) see title, Sorry for misunderstood.

    Only the first Pictures are tow pants one in Germany (-5°) good working and one in China (-20°C) bad working. With the same compressor, “Frik RWB II 856” the size from the oil cooler to receiver is DN 80 and form receiver to condensers DN 150/100.


    I Think it is an multi problem!
    Attached Files Attached Files

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    Re: Fundamental question (air in the NH3-system)

    Dear Coolman

    According to your flow diagram I would install NC gases purger at top of the condenser . Let me attached the Anstrong recomendations

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    Re: Fundamental question (air in the NH3-system)

    Dear Coolman
    Sorry I couldn´t send the complet file. Please see

    www.armstrong.com.br/bind/produtos/purgador_gas/purger.pdf

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    Re: Fundamental question (air in the NH3-system)

    Dear gwapa

    Thank you for this interesting Web page from Armstrong, I will now study the PDF-document from the air purging.

    However, I can say now an industry shell-tube-condenser with a diameter size form 2.20m and a length from more as 6 m is not inside so easy manufactured.

    Inside the condenser are a lot of baffle plate for an optimal flow and working.
    On the top of this kind of condensers we can in operating mode not drain the air out.

    BR! NH3-Coolman

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    Re: Fundamental question (air in the NH3-system)

    Coolman

    Do I have this correct

    50Hz 2950rpm

    -5 Deg C @ +35 Deg C condensing
    -21 Deg C @ + 35 Deg C condensing

    This is a oil cooling load of:
    -5 = 1634 Kbtu
    -21 = 2056 Kbtu

    Pipe size should be:
    -5 80 mm supply and 125mm return
    -21 100mm supply and 125mm return

    50mm & 80mm would possibly do the low load but if I,m reading all correctly you have pipe size issue with the compressor operating at -21.

    Regards
    RWF II


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