Steam Piping

[CharlieH]

I need to supply steam to a heater and an eductor in a small enclosure (20"x20"x8") that is attached to a vessel nozzle. The steam flow through the eductor will be the motive fluid to create a suction to get our sample from a flue gas stack.

The vendor indicated they'll need between 20-80 psig steam for the eductor. I located a nearby 3/4" 150# steam pipe that ultimately drops down to steam tracing. I intend to tap into this line and run piping about 6' vertically to a deck where I will put a steam reduction station. The 3/4" pipe will be split into two 3/4" branches with each going to a Fisher 95H steam regulator. The steam will be adjusted to the needed pressure then exit each regulator via preinsulated stainless steel tubing. The tubing will travel vertically about 35 feet to the enclosure.

Questions:
1. The operator indicated the line I want to tap into is a 150# steam line. I did find iso's and drawings to agree with this. Which pressure and temperature do I use for calculations since there are no gauges or indicators? Do I assume saturated steam to be conservative or superheated? If I assume saturated, then any heat loss will generate condensate immediately. I do have some data from the plant stating that when designing for the 150# steam system, use the following for utility characterisics:
Process 410 deg F and 150 psig
Mechanical 450 deg F and 170 psig
Considering the tap off the main header could be a long distance from my work area, I'm concerned that I may be using inaccurate data.


2. Where should I install steam traps in this piping? I intended to put one in the common piping upstream of the two regulators. Is this an appropriate location considering I'd have a reverse flow situation. I assume there will be condensate formation at the upstream side of the regulator (is this correct?) If so, that condensate wouldl be flowing against the steam flow to the regulator.

3. Do I need another steam trap before I make the 35' climb in pre-insulated SS tubing?

4. Do you think a 3/4" 150# steam line would be sufficient to supply a constant 20-80 psig stream to the eductor and a branch for a temperature regulated enclosure heater?

I am a new mechanical engineer and work with a firm that is primarily an electrical company, so I have no experienced people to turn to. This adds a bit of complexity to my work, but having you guys is an asset.

Thanks for your time.

 

[krb]

Here is a good place to start answering your questions

http://www.spiraxsarco.com/us/assets/uploads/PDFS/HookUp.pdf

KRB

 

[rmw]

Go to

http://www.graham-mfg.com

and/or google the word(s) vacuum guide or vacuumguide and you should find a lots of reading.

Don't assume anything. Find a way to trace this line back to its source or get some instrumentation (a IR temperature gun for example) and find out what your steam conditions are.

It is critical to your jet operation that the steam conditions be what the jet is designed for within tight tolerances.

Put a moisture separator before the steam jet.

You didn't say whether your vertical runs were upwards, or down, or at least I couldn't understand it.

That ought to give you a couple of places to start with.

rmw

 

[UtilityLouie]

Typically I've seen design and operating conditions on steam piping.

Design conditions: Pressure - where the lowest relief valve settings is set. Temperature - the max temperature expect with the desuperheaters are failed.

Operating conditions: Where you hope to control the temperature and pressure with desuperheaters and reducing valves.

You design the pipe for operating conditions, but make considerations for saturated conditions for trapping the pipe.

My rule of thumb for trapping - trap a line when it rises or else hammering will occur AND trap a line at a location before a control valve or shut off valve to prevent condensate build up and corresponding big condensate slug on start up.

My other suggestion - the cost difference between 3/4" pipe and 1" pipe is nothing - but you didn't mention steam flow to verify pipe sizing. You will have steam flow to an eductor to influence flow. An eductor completely uses all the steam used to circulate the fluid. There should be an amount of steam that will be used. Use this to size your pipe.

This is a great site for sizing steam pipe - just for a quick off the cuff calculation:

http://appserver.ittind.com/software/HSapps/steamcalculators.htm

 

[superpiper]

am i the only person who is alarmed that someone who is new to piping is attempting to pipe live steam as intended without any experience?

write the job requirement spec, and give it to a piping company.

 

[UtilityLouie]

I've seen some installs by that method and........... not always the best.

Everybody has to learn sometime. A combination of reviewing the Spirax manual and having an experienced piper install is something that can help someone learn.

I'll say it again.... everybody has to learn sometime.

If it's a socket welded system and proper NDE is performed and the system is trapped right.

 

[krb]

I'll second Louie's comments and add that CharlieH is asking questions and trying to learn. There is alot of info out there and the best way to learn is to do your homework and ask those who know more about it than you. So far he is on the right track. I would also caution Charlie to make sure he does a thorough job reviewing the applicable codes and standards as well as the engineering requirements of his job.

KRB