conversion required for kg/hr to mmscfd 2

[opstech]

hello, i am in need of a conversion factor from kg/hr to mmscfd - have no eng. textsbooks on the plant to look up, i need this to see how much our flash gas compressors are putting through our dew point plant - none of our meters are working yet - plant has just been commisioned. Thanks for your help - lowly tech here, nt an engineer !

 

[mbeychok]

opstech:

scf/day = (kg/hr)(2.204 lb/kg)(lb-mol/lb)(379.48 scf/lb-mol)(24 hr/day)

Since lb-mol/lb = 1/MW :

scf/day = (kg/hr)(2.204 lb/kg)(1/MW)(379.48 scf/lb-mol)

where:
MW = molecular weight of the gas
scf = standard cubic feet at 60 degrees F and 1 atmosphere

Divide scf/day by 1,000,000 to get mmscfd

Milton Beychok
(Contact me at www.air-dispersion.com)
.

 

[IFRs]

Converting kg/hr to mmscfd requires a density of the gas. Using air density as 0.00256 slugs/ft^3, you would multiply Kg/Hr by 642 to get Ft^3 per day. Using 1.25x10^-3 gm/cm^3 yields a multiplier of 657.

 

[mbeychok]

opstech:

The second equation in my response omitted the 24 hr/d term and it should read:

scf/d = (kg/hr)(2.204 lb/kg)(1/MW)(379.48 scf/lb-mol)(24 hr/d)

Please excuse my typographical error.


Milton Beychok
(Contact me at www.air-dispersion.com)
.

 

[mbeychok]

IFRs:

Don't forget that opstech asked for mmscfd (i.e., millions of scfd) ... your multipliers still have to be divided by 1,000,000. You should also tell him the reference temperature and pressure applicable for your density look-ups.

Milton Beychok
(Contact me at www.air-dispersion.com)
.

 

[opstech]

Thanks guys - it took me a half hour of puzzling in front of a calculator, but we are getting around 20mmsfd from the MP/LP seps as flash gas. Cheers once again.

... i may need to glue a calculator to the panel now though ... ;D

 

[JimCasey]

>>
... i may need to glue a calculator to the panel now though ... <<

If it's really a consideration, consolidate all your constants and lay out a really simple equation, or even better: tape an excel spreadsheet to the wall.

 

[katmar]

If you are looking for a calculator to do this, there is one built into my freeware units conversion program, Uconeer. Unfortunately it does not include mmscfd, but it will take the conversion as far as scfm and you will have to apply a factor (0.00144) to convert the output from scfm to mmscfd.

You can download this free program from

http://www.katmarsoftware.com

I deliberately delayed posting this link because I believe it is important that you first understand how the calculation is done, and thanks to Milton Beychok you now know how to do it ;-)

 

[TD2K]

You don't need a density to convert from kg/hr to MMscfd.

convert kg/hr to lb/hr

Convert lb/hr to lbmole/hr using the MW

1 lbmole occupies 379.6 scf

 

[25362]

This has already being treated in past threads.
It all depends on what "standard" P,T conditions selected for the ideal gas:

System T P V

SI 273.15K 101.325 kPa 22.415 m³/kgmol
Universal scientific 0^oC 760 mm Hg 22.415 L/g mol
Nat. gas industry 60^oC 14.696 psia 379.4 ft³/lb mol
American engineering 32^oF 1 atm 359.05 ft³/lb mol

 

[25362]

A typing error: it should be 60^oF not 60^oC

 

[zdas04]

25362,
From 15 years in natural gas measurement, that industry uses 14.73 psia as "standard" for the Natural Gas Industry (see API 14.3). I don't know where it came from, but that is the number they use. As long as everyone in a given transaction uses the same value it doesn't much matter.

TD2K,
Your technique implicitly determines density at "STP". I recently worked through a mass balance on a compressor station using density (at actual conditions) and got exactly the same numbers as another engineer who did the job last time using MW, moles, and actual pressures/temperatures. Neither calculation was particularly more difficult than the other, but each of us was more comfortable with our technique.

David

 

[25362]

To zdas04,

I believe this strange pressure (762 mm Hg = 14.734 psia) used by AGA, stems from selecting a standard "round" value of 30 inches of mercury, instead of the more common 29.92, as used, for example, in air conditioning.

 

[zdas04]

25362,
Thanks, that makes more sense than any of the other explainations that I've heard over the years.

Now, maybe you can tell me why New Mexico (average elevation in the north around 5,500 ft, call atmospheric pressure 12.01 psia) uses 15.025 psia as the "standard" pressure for calculating volumes reported to the state?

David

 

[25362]

I"ll try.

The standard average atmospheric pressure is taken at 14.4 psia (at about 100 ft elevation).
Then you add 10 oz/in² to correct for sea level.

10 oz/in² = 0.625 psi​

14.4 + 0.625 = 15.025 psi​

QED.

 

[zdas04]

ADD??????????????? Must be a government thing. Thanks for the chuckle.

David

 

[25362]

Considering the pressure changes with elevation, I should have said 500-600 ft, not 100 ft. Nevertheless, the explanation stands.

 

[TD2K]

Zdas, good point.

I should have remembered there's been more than a coupleof threads here which have shown if you want to start a debate, ask a group of engineers to define 'standard' conditions

 

[ColourfulFigsnDiags]

Ignoring 25362's little typo in the above post (you might want to subtract mate ) I can't believe you calculate things like that in imperial units ... so much easier to do in SI and convert back to imperial if you must (mind you I wish imeprial would vanish from the face of the planet!)

Read the Eng-Tips Site Policies at FAQ731-376

 

[25362]

To ColourfulFigsnDiags and Zdas, no error: as you go down (ie, lower elevation as at sea level) atmospheric pressure increases.

Thus, add 10 oz/in² to the average 14.4 psia at an average elevation above sea level, not substract.