District Steam Condensate Return - Flash Stream
hshank
150 State Street, Suite 110
Rochester, NY 14614
(O): 585-546-8890
(C): 585-353-0399
(F): 585-546-6570
Jauch, Carl
In Minneapolis, our preference is to collect the high pressure trap condensate and route it to flash tanks around the system. The flash tanks are located in customer buildings that take steam all year – the flash steam is connected to the building low pressure steam header. Low pressure condensate is pumped back to our boiler plants. We do have one or two instances where we dump the hp trap condensate into our condensate return lines via a sparger but, as I stated, our preference is to route it to flash tanks.
Best regards,
Carl
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Dageforde, Darren
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 the main plant. We have a couple of installation where we flash it back to low pressure steam headers, but you end up with cross connects that can confuse mechanical techs, not a big deal unless you have a lot of turnover. Where we don’t have a close building or easy flash tank location, (manholes, certain tunnels, etc) we simple inject into the bottom of the pumped condensate pipe and it usually works ok with minimal pipe hammering. IF you inject into the top of the pipe as most pipefitter have been taught (which only works in gravity drained systems, not pumped systems) you will destroy the top of the pipe from the inside and have huge hammering issues. As long as you are getting some flow in the condensate and you have reasonably cool condensate, direct injection seems to work.
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MacKellar, George
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 pressure trap could be discharged directly into a pump condensate line without risk of water hammer. The bottom line is, when there is sufficient condensate in the pumped line, this will usually work. A sparge tube to discharge into the condensate line is recommended. In addition, we have also used an eductor to mix condensate from the pumped line with the trap discharge, thereby cooling it, before discharging into the pumped line. This has worked well.
George D. MacKellar, P.E. | Vice President; Senior Mechanical Engineer | 616.464.3819 | www.ftch.com
Fishbeck, Thompson, Carr & Huber, Inc. | Engineers, Scientists, Architects, Constructors
From: distribut...@googlegroups.com [mailto:distribut...@googlegroups.com] On Behalf Of hshank
Sent: Monday, March 10, 2014 4:50 PM
To: distribut...@googlegroups.com
Subject: {Distribution Forum} District Steam Condensate Return - Flash Stream
Hello Everyone,
--
Edward T. Borer Jr.
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.
One point that I haven’t seen in this excellent discussion is that use of traps that produce a steady discharge, i.e., engineered venturi traps, will result in less hammering than traps that have pulse action. Not everyone is in agreement about venturi trap technology and I don’t want to divert this discussion. But Princeton has had success with this approach.
Ted Borer, PE, CEM, LEED AP
Princeton University
Energy Plant Manager
MacMillan Building, Elm Drive
Princeton, NJ 08543-2158
Cell: (609) 731-2327
Home: (609) 466-3322
Learn about our plant on YouTube: http://www.youtube.com/watch?v=xwHhbDvpdS4
Rod Crichton
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 are discharged into the pumped condensate via a sparger on top of the pipe. We use TLV ball float traps which tend to give a smoother discharge of condensate.
For the most part, the system works well. Where we have had issues is with the stainless steel condensate return pipe. Under “perfect storm” conditions, we’ve experienced the stainless steel pipe cracking. A combination of heat, stress, vibration and road salt (winter) on a localized area will cause stress cracking. The original pipe was sch. 10 304 stainless. Repairs are now made with sch. 40 316 stainless.
Also when the system is down for repairs, it is tricky getting it back up and running. Early procedures actually created more stress on the system and caused further leaks. We’re getting better though, we’ve discovered by draining/venting condensate/steam at certain vaults and the customer site, the system can go back in service more smoothly and cause (hopefully) less future (fingers crossed) problems.
Rod
Rod Crichton
Chief Engineer,
Assistant Plant Manager
T: 519-432-5066
London District Energy
Power Division of Veresen Inc.
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On Behalf Of hshank
Sent: March-10-14 4:50 PM
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Subject: {Distribution Forum} District Steam Condensate Return - Flash Stream
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Ontiveros, Juan M
Hendrik,
Most of our high-pressure traps discharge directly into the condensate return piping since most of the high-pressure traps are in the tunnel. There is one high-pressure trap in each building with steam and this goes back to the condensate return piping since we do not charge the building for any of the steam consumption on the high-pressure side. We try to only meter the steam downstream of the PRV station. Right or wrong, this way the buildings do not pay for any of the transmission losses.
Leonard Friesenhahn, P. E.
Associate Director - Mechanical Distribution
The University of Texas at Austin – Utilities and Energy Management
Murray, Michael M [FPM]
We are similar to Darren. It was surprising to learn how many building mechanics do not understand what a flash tank is or how it is supposed to work. In buildings where pipe is labelled with flow arrows, you will often find the steam line connected to a flash tank shown as flowing towards the flash tank. This has created problems during attempts at shutting down building steam.
In tunnels we have mainly gravity flow pipes and we dump traps into the line above the condensate flow.
In most direct buried systems with flooded condensate lines we inject traps into the flooded main using sparge tubes. We have had little hammering problem, but have had a problem with the flash steam driving oxygen out of cold condensate from low use buildings, resulting in oxygen pitting.
In some direct buried systems with fiberglass condensate lines, we have vented condensate pumps in the steam vaults just for the traps. These have been horrendously high maintenance.
Mike Murray P.E.
Chief Mechanical Engineer, Utilities
Facilities Planning & Management
Power Plant Building, Ames, Iowa 50011-4023
Telephone: 515-294-8751
mimu...@iastate.edu
Making Commitments, Keeping Commitments
Molnar, John
At Penn State we run the HPS traps to a “accumulator” tank which is a 8” pipe, 48” long which stands vertical and is bolted to the manhole wall. The trap discharges into the upper portion of the tank so the carry over steam and flash steam accumulates at the top of the tank then cools back into condensate and discharges out a lower tap to the main return. We do this for several reasons,
· We do not have anywhere to use the flashed steam
· It eliminates water hammer in the condensate return
· It transferred the flashing corrosion leak point from a hard to isolate main line to a simple to isolate tank.
· Eliminated vented condensate pumps
Bullets 3 & 4 have greatly reduced maintenance problems.
John Molnar
Supervisor Steam Distribution
The Pennsylvania State University
Office; 814-865-5434
Cell; 814-215-7397
Email; jf...@psu.edu
Fax; 814-865-2282
Kim Nixon
Darren,
At the university of Oklahoma we deliver two different steam pressures to campus, medium pressure at (100 psi) and low pressure at (7 psi). We trap the medium pressure steam line into the low pressure steam line using it as the flash tank, some of the condensate flashes to steam increasing the steam production in the low pressure line, the low pressure steam line is trapped into the main condensate return line, this allows us to keep as much heat in the system as possible.
If there is anything else I could help with please feel free to call or email.
Kim Nixon
Power Plant Manager
Corix Utilities
University of Oklahoma
405-325-4601 office
405-325-5462 fax
405-640-6683 cell
Manning, Robert
John,
Do you insulate the vertical pipe tank you describe below? I’m curious about the tradeoff between cooling off the flash steam and adding too much heat into the manhole
Regarding original question: The answer is basically all of the above.
We have traps piped into vented receivers in buildings, we use intermediate trap lines, and we have traps discharging directly into the condensate main where other methods are not feasible/practical. We did have some significant condensate hammering at one direct conect location and we added a radiator to the trap discharge to pull some heat out of it and it seemed to work.
Bob Manning
Harvard University
.
Molnar, John
We do not insulate the tank so it has to add some heat to the manhole. It does not have fins so only the pipe surface offers up the heat exchange which isn't as much. I haven checked the actual rise in temperature of the manhole but my crew has not said anything about the manholes being hotter. I will take some temperature reading of some with the tanks and some without and see if there is much of a difference.
John
Sent: Wednesday, March 12, 2014 5:30 PM