Steam Line Losses

[Jeter316]

I'm trying to calculate the thermal losses in a steam line. For example, I have a 4" steam line that is roughly 1000ft long and there is roughly 2000 lbs/hr of 150psi steam flowing through it. I'm trying to calculate the loss in the line in lbs/hr so that I can have an estimate to the actual steam load of the facility minus the line loss. All the pipe is above ground with 3" insulation and an aluminum jacket. Thanks for any help.

 

[Latexman]

I'd use U = 1 Btu/hr/ft²/^oF to estimate it. That's for an insulated line with about 200 ^oC driving force across it.

Good luck,
Latexman

 

[rneill]

There is a variety of software out there for calculating heat losses from piping. One common one is NAIMA 3E Plus which I believe is a free download. Alternatively, it is pretty easy to setup a spreadsheet but I've gone ahead and loaded the spreadsheet I put together for calculation glycol tracing loads. This will calculate pipe heat loss for you if you fill in the appropriate data.

I provide no warranty with regards to the accuracy and/or acceptability of this spreadsheet and suggest that you validate its results against known data before using if for anything other than preliminary estimates.

Note: this spreadsheet assumes calcium silicate insulation.

ttp://files.engineering.com/getfile.aspx?folder=09e9584a-b6f4-4dcb-8b6b-acfaee82989e&file=Glycol_Tracing_&_Heat_Loss.xls

 

[Jeter316]

Latexman - I don't follow your approach, could you elaborate?

rneil - I tried to download your spreadsheet but nothing happens. I click on the "Glycol Tracing" link and it opens another window but nothing else happens. Any ideas?

Thanks

 

[rneill]

I'll try again

http://files.engineering.com/getfil...806d26efc&file=Glycol_Tracing_-_Heat_Loss.xls

 

[ione]

I’d use U = 0.75 Btu/(hr ft^2°F) that is a value a bit less pessimistic than that suggested by Latexman.

You can use this calculator from Spirax

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

Or the following diagrams

http://www.engineeringtoolbox.com/heat-loss-insulated-pipes-d_1152.html

 

[steamdog]

Don't forget to add the losses in the piping to the steam traps, and sometimes a % loss through the traps is added as well.

 

[Latexman]

Q = UA[Δ]T

U - overall heat transfer coefficient
A - heat transfer area (outside area of insulated pipe)
[Δ]T - temperature difference (steam - ambient)

Use consistant units.


Good luck,
Latexman

 

[Jeter316]

how would I account for the losses in the system due to the traps, assuming no leakage?

 

[steamdog]

The traps add additional piping. If the trap is working, then the piping to the trap, the drip leg, etc are all thermal losses of the system. Some traps, depending upon the type, use a bit of steam all the time. All traps will fail eventually.

 

[ione]

Jeter316,

You can find some guidelines in the link below

http://www.spiraxsarco.com/resource...eam-trapping/energy-losses-in-steam-traps.asp

 

[Jeter316]

my overall heat transfer coefficient seems too low... U=.25 btu/hr ft F... One of my assumptions is that I can neglect radiation. Can I neglect radiation heat transfer? If not, how do I account for the radiation loss? Thanks!

 

[ione]

The radiative part of the heat loss can be accounted for using the Stefan-Boltzmann law
Q = ?*? *(Ts^4 – Tamb^4)*A
where:
? = emissivity of the surface (values are tabulated)
? = Stephen-Boltzmann constant 5.67 *10-8 W/(m^2* K^4)
Ts = Surface temperature [K]
Tamb = Ambient temperature [K]
A = Area of the emitting surface [m^2]

I also suggest you to take a look at the link below

http://www.cheresources.com/insulationzz.shtml