Sizing Expansion Steam Header
Sizing Expansion Steam Header
(OP)
Hi,
Can some of the more knowledgable folks please point me in the correct direction.
I would like to size a steam header to reduce the pressure of the recovered process steam (saturated condition) at 600psig to 20psig where it is returned to the deaerator.
The 600psig steam are from 3 separate, but identical lines which will feed into a common header. The 20psig steam is returned to the DA. The total steam flow rate is 3x 6,000lbs/hour.
The steam had been used to do heat up combustion air for a process plant.
What approach should I use to size the steam header?
Thanks.
Can some of the more knowledgable folks please point me in the correct direction.
I would like to size a steam header to reduce the pressure of the recovered process steam (saturated condition) at 600psig to 20psig where it is returned to the deaerator.
The 600psig steam are from 3 separate, but identical lines which will feed into a common header. The 20psig steam is returned to the DA. The total steam flow rate is 3x 6,000lbs/hour.
The steam had been used to do heat up combustion air for a process plant.
What approach should I use to size the steam header?
Thanks.





RE: Sizing Expansion Steam Header
A velocity that is too high will give you problems with noise and/or erosion. A velocity that is too low will make the pipe expensive. Check the piping handbooks for recommended maximum velocities for your steam conditions - especially the quality (entrained water) of the steam.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Sizing Expansion Steam Header
The max velocity in the outlet section of the transfer pipe ( inlet of valve) should not exceed 250 fps for sat steam, and if the steam is wet, then it may be neccesary to use a lower velocity or upgrade the pipe alloy to P11, for erosion concerns.
RE: Sizing Expansion Steam Header
What size is the inlet to the DA ?
I would prefer a thicked wall for this "extended nozzle"
-MJC
RE: Sizing Expansion Steam Header
The 3x6,000lbs/hr lines are provided with 2" or 3" pipes to have a reasonable velocity.
I plan to use either 16" or 20" pipe as the common expansion header, but cannot decide on its volume (and hence its length). The header will be horizontal with two end pipe caps.
A 6" line will carry the LP 20psig steam to the DA which has also a 6" nozzle. The reason of using the common header and line is to minimize the number of openings on the DA and also because the common header will be located closer to the air heaters.
Do I consider the steam specific volumes, flashing of steam and residence time to size the volume? My concern is sizing the volume too small.
RE: Sizing Expansion Steam Header
I2I
RE: Sizing Expansion Steam Header
RE: Sizing Expansion Steam Header
Insult2Injury's question of whether you have steam or condensate, plus your comments on required volumes and residence times, made me realize that your question is not as simple as you first stated it.
It now seems to me that you have 600 psig steam being fed to 3 process air heaters, and what you are trying to do is to recover the flash steam from the condensate exiting those heaters, and to direct the flash steam to your deaerator. If this is the case then you must disregard what I (and davefitz and MJCronin) said before.
Each process air heater must have its own steam trap, or other means of maintaining the pressure in the heater. The condensate from the heaters should be piped to a properly sized condensate collection vessel which can also be your flash vessel. This flash vessel will be sized to disengage the 20 psig flash steam from the condensate and your questions on volumes and residence times become more relevant here. It is actually the superficial velocity of the steam in the flash drum that you should be concerned with.
In this situation your main design problem (apart from sizing the flash vessel) is the sizing of the condensate lines from the heaters to the collection vessel. When you flash 600 psig condensate down to 20 psig you will convert approximately 25% of your condensate to steam. This flash will start to happen in the piping from the traps to the collection vessel. Sizing of these lines is not a trivial exercise and in addition to the flowrates you need to consider the length, changes in elevation and actual routing. It is a problem that should be given to an experienced piping engineer. I would not be surprised if these lines need to be 4" or even 6" diameter. It is not a problem to be solved in a forum such as this. You can get tips here (it is called eng-tips after all!) but detailed designs must be done by competent engineers who have all the information available.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Sizing Expansion Steam Header
I know the steam will start flashing along the pipe. I also wonder about the possible errosion, etc of the pipes in the future due to the high two phase flow velocity in the pipes and the subsequent impingement onto the header. But this is the design we are adopting for the plants that we have. So will tackle the process problems (if any) probably a few years down the road.
Thanks for advices above.
RE: Sizing Expansion Steam Header
I2I
RE: Sizing Expansion Steam Header
The process connections to the deaerator are: the boiler feed water, the deaeration steam which is bled from the turbine LP bleed (75psig), demin water makeup and vent.
The process connections to the feed water tank are: the return pipe from the header discussed above, 3 min flow lines from the BFW pumps, and 3 other 2" condensate return lines operating at 75psi.
The DA operates at 20psig, and the equipment are part of a waste heat recovery plant with steam turbine generator.
RE: Sizing Expansion Steam Header
katmar: you are of course to the point, giving you a star for saving me many words, and most important for an engineer: knowing when to call in expertice.
Code1: Being no expert myself, and in addition, as katmar says, drawings and full layout is necessary; one suggestion would be for youto contact your local representative from one of the world-wide suppliers of complete steam accessories.
For instance will both Spirax Sarco and Gestra (Tyco) have available layot suggestion and dimensioning tables for different parts mentioned in your question. Both will in addition have available technical papers and manuals for steam equipment.
http://spiraxsarco.com/ http://www.gestra.com/
RE: Sizing Expansion Steam Header
gerhardl: I believe gestra is a flowserve company.
I2I
RE: Sizing Expansion Steam Header
insult2injury: you are indeed correct about Gestra, as the link clearly gives. Thank you for the correction!
RE: Sizing Expansion Steam Header
I2I
RE: Sizing Expansion Steam Header
You need to stand up to your bosses because it is NOT simply a question of "will tackle the process problems (if any) probably a few years down the road." Industrial accidents are most unpleasant. People die. Other people are held accountable. Correctly so. Don't let it be you.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Sizing Expansion Steam Header
I2I