Pressure drop and flow calcs

[mgithens]

We stumbled upon one of those inconslusives... so I was wondering what people are doing to "guesstimate" capacities.

Existing 8" line flowing in excess 10 MMSCFD nat gas @ 1050 psi, with a 1/2" tap we are attempting to pull off 2.5 MMSCFD. No this is not by design, but we wish to minimize downtime and cost, the 1/2" tap is already there.

We are modeling the capacity of flow as if it were an excessively long 1/2" choke bean. We are shooting for a 25 to 50psi pressure drop. We intend to flow less than 1 foot of 1/2" pipe/tubing.

Any input would be great...

 

[jmw]

The Crane handbooks are very useful. In metric and imperial units they are full of useful help on headloss and flow calculations. Try

http://www.cranevalve.com/bookstor.htm

Other useful sites may be

http://www.pipingnews.com/memberpipingne/pipe_sizing.htm

or

http://www.epin.ncsu.edu/apti/ol_2000/module2/rate/rate.htm,

though i haven't visited them for a while so no guarentees.

 

[TD2K]

Doing a quick check, assuming a 17.4 MW NG at 60F with a Z of 0.83 (from the GPSA general curves) and 1/2" sch 80 pipe, I estimate you'd need about 20 psi drop to move that 2.5 MMscfd (entrance loss of 0.5 K was used).

If you assume the 1/2" is sch 160, you'll need closer to a 50 psi dP across that foot of 1/2" pipe.

As JMW suggested, the Crane books are very good, I've made a spreadsheet based on them so it's a quick calc.

 

[ChasBean1]

MMSCFD is Millimeters of Standard Cubic Feet per Day? Micromanometers of Swedish Czechoslovakian Fathoms per Decade?

My point is that you eliminate half of the best engineers available to answer your question by assuming that they speak in the exact language you broadcast.

By better defining your problem, you will get better answers. (Note that I may have just killed my legitimacy in the natural gas world). But odds are I'd have the right answer for you if you spoke in universal terms.

Choke Bean?... is that when you inhale a baked bean by accident?

 

[MortenA]

Chasbean1

I actually dont know what a choke bean is but i think that ost ppl. who work with pressuredrop for gas line know what mmSCFD is.

Best Regards

Morten

 

[mgithens]

by sticking to the lingo, it does eliminate people who might not know what I am referring to...

FYI = MMSCFD is the oil field term for Million Standard Cubic Feet per Day.. the M's refer to the roman numeral for 1000... so it is technically 1000 1000 standard cubic feet per day... this is because of the mode of sales is measured in 1000's per day, whereas we typically calculate in millions due to the amount that must be produced to show profit...

Choke Bean = the actual insert that is located inside of a choke device, the typical increments is in 1/64ths, and because of the nature of critical flow, it is quite possible to choke about any upstream pressure to any downstream pressure... the only requirement is a limit in fluxuation in the supply...

Your point is well taken, but I am truly looking for someone who has this experience to provide this answer, I don't think that the suggestions provided by someone who reads a 2 minute brochure on the subject would be able to make a usuable suggestion... we have some experienced facility engineers here in the office and this is a stumper, I was seeking help from anyone that might have previously encountered and maybe modeled or tested their theory.

 

[TD2K]

mgithens, if the tap is into the 8" line is similar to a sockolet with about a 1 of 1/2" piping attached to it, then my post should give you an idea of the dP you'll need.

If there is something in that 1/2" tap or line that significantly affects the flow, let us know the details.

 

[jmw]

Some useful spreadsheets at this site:

http://chemengineer.about.com/gi/dy...ue&site=http://www.mnsi.net/~pas/brochure.htm