Amount of condensate formed of start up 5

[Hurricanes]

Can anyone point me in the right direction on how to calculate the amount of condensate generated on start up of a cold pipeline.

I have superheated steam being piped 800 odd metres. I need to calculate how much condensate is going to be produced on start up assuming a cold pipeline.

Obviously this is going to be a tranisent analysis, but beyond that I am a bit lost as to where to start. I am also a bit scared of how to deal with phase change, superheated to saturated and saturated to condensate.

Any nudges or pointers in the right direction would be greatly appreciated.

 

[Latexman]

Have you looked on the website of the steam trap vendor ya'll use yet? They probably have all kinds of helpful information there.

Good luck,
Latexman

 

[Hurricanes]

Latexman, yes I have. I have Spirax Sarco's book which contains the required calculations for us of their products, but it seems to be limited to steady state, and largely concentrates on saturated steam. I was hoping to find something that deals more with transient conditions.

 

[pmover]

thinking a little differently . . .

how much steam/energy will it take to heat the piping from ambient temp to operating temp or above the condensing temp? because at least (most likely more) that much steam will condense. once the piping is at normal operating temps, then the rate of condensate should diminish.

use caution when warming up cold steam piping.

hope this helps!
-pmover

 

[ione]

Hurricanes,

You've already received a valid tip by pmover.

You might find useful info at the link below.

http://www.galloup.com/ref/Trapping Superheated Steam.pdf

 

[Latexman]

This looks like a good reference:

http://www.spiraxsarco.com/us/resources/calculators/pipes/start-up-and-running-losses.asp

Good luck,
Latexman

 

[psafety]

Recommend you use a warm-up bypass around the larger shut-off valve to limit the rate of steam/condensate. Too much condensate (inadequate removal) can present a problem fast.

 

[rmw]

Remember that you are not only heating the steel pipe material, but you are also heating the insulation that surrounds it. And, yes, while insulation does the job of impeding heat transfer, it too operates at an elevated temperature right up against the hot pipe.

So be conservative in your calculations and don't forget valves or other appurtences in the piping that have to heat up too.

rmw

 

[chicopee]

It would also be a good idea to slightly pitch the steam line to drain off the condensate.

 

[Hurricanes]

Thanks for the replies everyone. I'm working through Ione's link and will try and use Latexman's link to check the calcs. Thanks again.

 

[abeltio]

Also consider that typically, superheated steam is not allowed into the piping until the piping is preheated within 150°F of the superheated steam.

Typically, auxiliary steam is used to pre-heat the piping at very low flows

Letting superheated steam directly into the piping will create such a thermal shock that could easily cause the pipe to break and damage supports and other equipment.

So: check the start-up sequence of the plant, see what steam is used for start up and pre-heating.
Once the system is pre-heated, then superheated steam will be allowed.

There are two completely different condensation rates:
1. pre-heating (aux steam) - high condensation, low flow
2. normal operation (super heated steam) - low condensation, high flow



saludos.
a.

 

[racookpe1978]

When planning or drafting the drain lines for this condensate: on initial startup after maintenance - and always after construction or mods! - plan on blowing off completely the condensate at the drain point themselves rather than returning the dirty water to the condenser or recovery piping. You did remember to slope these drain lines the right direction didn't you 8<)

Large valves will need drain points themselves - I've often seen these blended in with the bypass piping. Example: you warm up the piping upstream of MS-1 (between the boiler outlet and the turbine cutout valve) by blowing the condensate out through a drain point in the bypass piping around MS-1. The steam trap for the piping can be at the same tie-in point.

 

[Hurricanes]

Thanks for the advice. This project is only in feasibility so nothing has been designed yet. I've only looked at the most likely route and have done some initial pipeline sizing based on pressure drop.

Abeltio,
Yes, the lines will be preheated, but beyond that, no start up sequence has be determined. Preheat rates and durations are yet to be worked out. I guess I am just trying to get a rough idea of how much condensate could form in the line for preliminary steam trap design.