Calculating Superheated steam press drops in pipes

[PaulDix]

I'm searching for a useful formula to calculate pressure drops in pipes with superheated steam. I've tried using the original Babcock formula, but this doesn't seem to work for high pressure superheat steam. The pipe in question is DN150, 90 metres (with numerous elbows and valves) and the steam is at 83 bara (initial), 525 degC, 15.41 kg/s.

Can anyone point me in the right direction.

Cheers

 

[hacksaw]

The pressure drop formula is is only as good as details of your piping configuration. even with the best of data you can only expect 20% accurracy, if that.

What degree of accurracy are you shooting for?

 

[TD2K]

If you can get hold of a copy of Crane's technical paper 410, that has the formulas in it.

 

[PaulDix]

I'm not after good accurracy. 20% will be okay.

This superheated pipe feeds a power steam turbine. I already know the pressure drop from plant instrumentation. I want to know what the pressure drop would be if the pipe was a bigger diameter, then I can carry out a feasibility study of bigger pipe increase against increased steam turbine output. The accurracy of the calculation is not essential, 20% will give me a good idea.

 

[athomas236]

Hello PaulDix,

Your could try the following formula

DP=(8.10569E+6*W^2*SV/D^4)*((F*L*1000/D)+K)

Where
DP= pressure drop in bar
W= flow rate kg/s
SV= specific volume m^3/kg
D= pipe bore mm
L= pipe length m

F= friction factor = 0.015 to 0.02 for DN150 depending on Reynolds number and pipe thickness

K= sum of loss factors for bends etc

typical values are
entrance = 0.5
exit = 1.0
3D bend = 0.18
globe valve = 5.1

Hope this helps

athomas236

 

[hacksaw]

we've been down that road.

change out of HP steam piping is a practical impossibility unless you are putting new boilers on-line.

with existing boilers and TG's, the degree of superheat is the big player.

the best improvements are insulation and making certain the SH's are working at peak efficiency. We got an extra 2% just bringing the steam temperature up to design.

if you are running CS pipe you have some specific steam temperature limitations to consider so you cannot just arbitrarily increase superheat.

good luck,

 

[TD2K]

Rule of thumb is that pressure drop is proportional to the ratio of the diameters to the 5th power.

 

[quark]

TD2K!

Why can't you contribute in this thread

thread507-29593

 

[davefitz]

there is a simple answer and a more difficult /exact answer.

If the steam is flowing at less then 0.2 Mach no, then an incompressible flow procedure will work.
A simple method is
DP ( psi) = (nVh) * Vh
nVh = number of velocity heads lost = Sum ( fL/d), including pipe straight length, bends, inlet , exit, valves, etc.
Vh ( psi)= (sv/12) * (W/1E5/A) **2
where sv= spec vol. ft3/lbm
W= lb/hr
A= pipe flow area , ft2


If you prefer a more acurate European approach, I believe they use the Gnielinski model on that side of the pond.