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Flash tank needed?

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jacobsond
jacobsond Member Posts: 92
in Strictly Steam

We are having a new system installed on campus. The current setup is on an 85 psi steam supply.The supply goes to a heat exchange for a hot water heating system. The contractor has piped the out of the exchanger through a trap right to the condensate tank.. When the exchanger is in operation with a 50psi input live steam comes out of the vent on the condensate tank. This is not right. Should there be a flash or buffer tank before it gets to the condensate tank? Contractor is currently checking out what needs to be done. I am trying to get information so when they come up with a solution I can be satisfied with the fix. My steam experience is mostly self taught 10yrs read everything I can.I think there should be a flash tank installed because of the super-heated condensate leaving the exchanger.

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Comments

  • Intplm.
    Intplm. Member Posts: 2,835
    edited 7:35PM

    When you say steam system? Do you mean a new boiler? Commonly, a system would be the piping. This is helpful for discussion purposes.

    You mention some very high steam pressures. 85 and 50 psi. Why so high? Often, steam would be 0-15 psi and theoretically considered low pressure. Medium pressure is at times and theoretically, 16-80psi and high pressure is above 80 psi. What is this "system" doing? Is there a pressure-reducing station?

    From your description, a "flash tank" would be necessary, but I'm unsure of its design/location.

  • Pumpguy
    Pumpguy Member Posts: 783

    I don't know anything about this system, but in a large campus setting, the steam would come from a central steam plant at a high pressure; in this case 85 PSI. Typically, this would go through a pressure reducing station at each building, and then into the building rads.

    In this case, the steam is supplying HX for a hot water heating system. It may be that this HX is sized for steam at that pressure; around 325*F.

    If not, then the steam pressure should be reduced to provide the steam temperature the HX was sized for.

    The need for the flash tank would depend on the temperature of the outgoing condensate.

    Another question is what is to be done with the steam that resulted when that high temperature condensate flashed back to steam in the flash tank?

    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • jacobsond
    jacobsond Member Posts: 92

    This is a steam system at a college. The pressure on the main line is 85. A contractor installed in a new building a so called high pressure heat exchanger. They said no PRV will be needed. I kind of questioned that decision at the time,but what do I know. Now when the heat exchanger is under full load its running at 50psi. Just one little steam trap. If I had to guess the condensate coming out of the trap is superheated well over 212. Probably closer to 230 or more. When it hits the 0 psi condensate return the stuff turns to steam. I believe it needs a buffer or flash tank to get that temp down. We have tanks like that all over campus before the PRVs on the drip traps. Im waiting on their engineer for the fix. The condenstate needs to be less than 210 coming into the condensate tank/pump. This will be the only building on campus without a PRV.

    There was an error rendering this rich post.

  • pecmsg
    pecmsg Member Posts: 6,787

    At MSG our HW generatorwas 15# steam. 85 sounds high.
    find and review the original design specs.

  • Pumpguy
    Pumpguy Member Posts: 783
    https://forum.heatinghelp.com/discussion/comment/1879979#Comment_1879979

    I would tend to agree. I'm still curious what is to be done with the steam we now have in the flash tank? Can it be put to use somewhere?

    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,632
    Sarco Book.pdf
    Sarco Steam Utilization.pdf

    I don't know who sized the HX but normally the 85 psi pressure is required for distribution and then a PRV is used to drop the pressure before the HX. The other reason is that 85 PSi is usually too high of a pressure for the control valve feeding the HX. It can't control the temp.

    But as @Pumpguy said maybe your process requires that temp or pressure. I would get a copy of the submittal for the HX and see what it says. You need to find out what it was designed for. This is a "built up" system. There are rules to follow but we would need the design.

    As far as the condensate goes for most general use condensate pumps temp that high will ruin the pumps.

    A flash tank takes in condensate and flash steam. The flash steam goes out the vent to outdoors and is wasted (unless piped for another use) and the condensate has to be cooled if dumped down a drain max tepm to a sewer is about 120 I think.

    See the attached Sarco books for help.

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