RE: {Distribution Forum} Abridged summary of distribution-forum@googlegroups.com - 4 Messages in 1 Topic
wayne kirsner
For John M at Penn State from Wayne Kirsner
John--Assuming the vertical tank is uninsulated, is it just acting like a heat exchanger dispensing heat into the manhole in order to condense the flash steam before it is injected into the condensate return? If so, how do you know all the steam is condensing? Couldn’t the high pressure from the trap discharge push all the water from the tank into the condensate return and then follow it with un-flashed steam?
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Sent: Wednesday, March 12, 2014
12:16 PM
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Subject: {Distribution Forum}
Abridged summary of distribut...@googlegroups.com - 4 Messages in 1 Topic
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§ District Steam Condensate Return - Flash Stream [4 Updates]
"Dageforde, Darren" <ddag...@unmc.edu> Mar 11 09:09PM
At the University of Nebraska Medical center, we too try to take high pressure
end of main drips to building mechanical rooms where we can hit a flash tank
and safely vent it before we pump it back to ...more
"MacKellar, George"
<gdmac...@ftch.com> Mar 11 08:31AM -0400
Hendrik,
There was an excellent discussion of this led by Wayne Kirsner at the recent
Distribution Workshop in Atlanta.
Wayne described
a means to determine how much condensate from a high ...more
"Edward T. Borer Jr." <etb...@Princeton.EDU> Mar 11 09:22PM
Princeton tries to use flash tanks and
hotwells in buildings for discharge from steam lines above 15 PSIG. Below 15
PSIG it is common to find trap discharge routed to the condensate line.
...more
Rod Crichton
<rcri...@londondistrictenergy.ca> Mar 12 12:46PM
Hi Hendrik,
Here in London,
we have a high pressure (190psi) steam customer approximately 3km away in which
we pump the condensate back from. Located in steam vaults, the high pressure
line traps ...more
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Molnar, John
Wayne
The tank acts as a heat exchanger cooling the flash steam. If the traps are operating as design (even blowing through) the amount of discharge to the tank mixes with the already cooled condensate already in the tank and tempers the condensate temperature below the flash point. If a blowing trap generates more heat than the tank can cool through surface heat exchange and mixing with the volume of condensate in the tank the steam could the flash in the condensate main. Our traps discharge rate must not reach this point because we have not found this occurring in our system which is operating at 150 Lbs. @ 365 degrees. If this did occur the tank could be make bigger for larger exchange area and more tempering capacity.
John
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wayne kirsner
John--I guess the tank would be full of liquid condensate. My reasoning is that when the trap last cycled off (assuming it’s an on/off trap like a inverted bucket), the tank would be mostly full of flash steam. As the flash steam condensed due to heat loss thru the vessel’s walls, it’s pressure would fall below that of the condensate return so condensate would push back into the tank and fill it (assuming no check valve between the tank and CR line). When the trap next discharged, it would be putting flash steam into the condensate from above the condensate. I agree this will not hammer, especially if condensate has not had time to subcool.
I guess the bottom line is—Does it work, meaning specifically, did it end waterhammer in the condensate return where you had it before?
And, since the tank is effectively a condensate cooler, do you think it’s more cost effective than mounting a finned tube heat changer on the wall of the manhole and running the trap’s discharge thru it?
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Molnar, John
Wayne
The bottom line answer yes it works very well. We have not found any signs of flashing steam in the tank or the return line. They have eliminated the corrosion leaks at the traps discharge connecting point on the return line. We have not had any of those leaks since we installed these tanks the last 5 – 7 years.
John
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wayne kirsner
In the article I wrote for Chemical Engineering Magazine and the speech I gave at the Feb. 2014 Distribution Conference, THE POINT was—schemes to blend high pressure condensate into pumped condensate return lines DO NOT WORK to prevent waterhammer if:
Pumped condensate flow AND subcooling in the PCR line are
insufficient to continually condense all the flash from the high pressure trap
discharge as it enters the PCR. It does not matter whether your
system uses a sparger to break up the flash steam bubbles or any other type of
blender if the heat capacity of the condensate mass flow cannot condense all
the steam as it enters the PCR.
- This means any heat extraction device from the high pressure condensate before it enters the PCR line (like a tank or finned tube heat exchanger) is going to reduce the flash steam and lesson or eliminate the surviving flash steam bubbles in the PCR.
- It also means that if there aren’t a lot of blowing HP steam traps directly into the PCR so that the temperature of the returning condensate stays low enough to condense all flash steam entering the PCR from HP traps, there will be no hammering. This implies that a temperature and pressure gauge in the condensate return are important trouble shooting tools ( the pressure gauge is important because it’s actually the subccoling of the condensate in the PCR that’s important to condensing the incoming flash steam from HP Traps)
- There’s a lot of money wasted on mixing or blending devices like a sparger or ejector that can help, but only in a limited way. (Why they can help is implied in the magazine article where I explain the marginal effect of incomplete mixing).
Waterhammer due to flash steam bubbles
surviving in the PCR line is going to happen, if it happens, when one of these
events triggers it:
- Another PCR branch with subcooled condensate joins the main PCR and has enough additional cool condensate to condense the surviving bubbles in the Main line. The waterhammer will occur at the junction of the lines in the Main.
- A large condensate pump cycles on that significantly increases the subcooled flow in the PCR so flash steam bubbles that formerly survived are suddenly condensed in condensation induced waterhammers (this is what happened in the magazine article)
- A large steam trap cycles off changing the balance between condensate subcooling and entering flash steam, although I think this would be rare.
The magazine article features a busted check valve that did not survive a waterhammer even though flash steam from the high pressure trap it was associated with was delivered into the PCR thru a carefully designed sparger assembly.
What I would like to know is: Have others experienced waterhammer in their pumped condensate return lines (PCR) where high pressure traps discharge into the PCR, and, did the hammer go away when:
- They removed flash steam from numerous blowing traps entering the PCR, or
- They installed heat removal devices in Vaults to reduce the flash steam before in entered the PCR.
Alternately, did waterhammer not go away when they installed spargers or some other blending device in the HP trap assemblies entry to the PCR?
Write me a reply if you applied some fix for waterhammer in your PCR, and IT EITHER STOPPED WATERHAMMERING that was occurring before the fix, OR it did not stop the waterhammer that it was supposed to prevent. I’m trying to confirm that what I think is going on is actually what’s going on.
From: wayne kirsner
[mailto:kir...@kirsner.org]
Sent: Thursday, March 13, 2014
10:40 PM
To: 'Molnar, John';
'distribut...@googlegroups.com'
Cc: 'Len Phillips'
Subject: RE: {Distribution Forum}
Abridged summary of distribut...@googlegroups.com - 4 Messages in 1 Topic
John--I guess the tank would be full of liquid condensate. My reasoning is that when the trap last cycled off (assuming it’s an on/off trap like a inverted bucket), the tank would be mostly full of flash steam. As the flash steam condensed due to heat loss thru the vessel’s walls, it’s pressure would fall below that of the condensate return so condensate would push back into the tank and fill it (assuming no check valve between the tank and CR line). When the trap next discharged, it would be putting flash steam into the condensate from above the condensate. I agree this will not hammer, especially if condensate has not had time to subcool.
I guess the bottom line is—Does it work, meaning specifically, did it end waterhammer in the condensate return where you had it before?
And, since the tank is effectively a condensate cooler, do you think it’s more cost effective than mounting a finned tube heat changer on the wall of the manhole and running the trap’s discharge thru it?
Wayne Kirsner, P.E.
kirsner consulting engineering, inc.
From: Molnar, John [mailto:jf...@psu.edu]
Sent: Thursday, March 13, 2014
1:12 PM
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