×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Design of Main Steam Header for Intermittent Service

Design of Main Steam Header for Intermittent Service

Design of Main Steam Header for Intermittent Service

(OP)
Hi guys.  Looking for design suggestions here.  I have the Spirax manuals and the Babcock Bible but I thought I'd ask here also.

I am designing a main steam header to intermittently carry 120,000 lb/hr of 65% quality steam at 600 psig.  Line length is 3500 ft and it goes cross-country, up and down, across hill and dale.  The line size we are using is 10" which will keep flow in the annular/mist flow regime.  We design these lines to run in this flow regime because it prevents phase disengagement.

The problem with this particular line is that it will be in service (under full load) for only about 30 minutes out of every 24-hr period.  The rest of the day the line sits idle.  So, the short answer is, I need to drain the condensate from the line at the low points during the periods when the line is idle to prevent it from rocking and rolling when it's started back up.  

My first thought is to use a pair of properly-sized thermodynamic traps at each low point in the line, one trap online and one standby, with the traps feeding a condensate receiver.  Tricky part will be sizing the traps properly - we don't care if the condensate is removed or not while the line is in operation. I just need to drain the condensate when flow stops to ensure the line is empty when it's ready to be placed back in service.

What say ye?  Any suggestions/ideas/brainstorming/insults/ comments of a generally obnoxious nature are welcome.  smile  Thanks guys!! Pete

RE: Design of Main Steam Header for Intermittent Service

Suggestions:

1) Find the actual steam flowrate at the destination based on the heat loss of your insulation system. Consider what will happen as the insulation degrades.

2) Perform a flexibility evaluation (computer based stress analysis) of the design.

3) Summarize and evaluate the capital cost of 3500 ft of piping, supports, traps etc....add the cost of maintenance and the cost of the energy and condensate lost over the life of the facility versus the cost of installing a 120,000 lb/hr (possibly used) boiler at the destination. You may be surprised at the present value of many years of energy loss.

4)Ask many questions and use well the fine and helpful people at Spirax Sarco.

My opinion only

-MJC
 

   

RE: Design of Main Steam Header for Intermittent Service

Basically, you will have to drain the line at zero pressure so:
The traps MUST have gravity drain only.  Condensate receiver must be atmospheric and physically below trap, which is also below the steam line.

If this is in the north, you may have freezing problems.  There are drain valves available that open when the internal water temp reaches below 40F, you can use these also.

You may have to add vacuum breakers and air vents to the line. When the steam condenses it may draw a vacuum preventing the condensate to drain.  The vacuum breaker will add air to the line and allow drainage, but then you must get rid of the air for proper steam temp/flow when you start-up again.

Final advice, think gravity.

RE: Design of Main Steam Header for Intermittent Service

Be careful with those drain valves that open at cool temperatures; if you use them, provide proper drains.  If you just dump them to pad, they have the potential to make wonderful skating rinks.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources