Convert lb/hr to SCFM
Convert lb/hr to SCFM
(OP)
I need the formula to convert lb/hr of 20.07 mole weight gas to scfm.
J. D. Jackson B.S. M.E. & B.S. E.E.
TransContinental Engineering





RE: Convert lb/hr to SCFM
(359.05 std cu ft/1 lb-mole) = 0.2982 std cu ft/min
1 lb/hr = 0.2982 std cu ft/min
STP = 492 degrees R and 14.696 psia
Good luck,
Latexman
RE: Convert lb/hr to SCFM
I am trying to convert 19,640 lbs/hr of 20.07 mole weight gas at a temperature of 43 degrees F to SCFM.
Do I need to incorporate the temperature into the equation for a more accurate SCFM equation? Somehow logic tells me the temperature was used in a previous equation to determine the lbs/ft3 thus resulting in the flowrate of the lbs/hr. Am I correct about the temperature?
J. D. Jackson B.S. M.E. & B.S. E.E.
TransContinental Engineering
RE: Convert lb/hr to SCFM
V = nRT/P
V = 1 x 10.732 x 491.67 / 14.696 = 359.05 (I hope you can figure the units)
Now, once you know the definition of the STP you need, you can figure out the V.
Good luck,
Latexman
RE: Convert lb/hr to SCFM
1.0 lbmole of gas occupies 379.49 cu.ft. @ 14.696 psia and 60 oF
This definition, I believe, is where JDJACKSON is getting his number of 379. I never discuss Scfm or other standard gas conditions without knowing the basis for it: the LB MOLES FLOW RATE. You can't go wrong with moles because they are the real "stuff" of which gas volume is made.
So the equation should be:
Scf/time @ 14.696 psia & 60 oF = [(lb/time)/MW]*379.49
You can conver to another pressure and temperature base by using the gas law, as Latexman points out. This is probably why they call Chemical Engineers "Mole Chasers".
Art Montemayor
Spring, TX
RE: Convert lb/hr to SCFM
J. D. Jackson B.S. M.E. & B.S. E.E.
TransContinental Engineering
RE: Convert lb/hr to SCFM
However, to convert moles to volume units you indeed need determine both, as cleary explained by Montemayor and Latexman.
As a small digression: ideal gas molecules are considered by the kinetic theory to be of zero volume non-interacting point particles, and the formula brought by Latexman applies.
Real gas molecules take up space and collide, and when they are close a weak electrical attractive force named the van der Waals force, plays a role. When molecules move apart they do work to overcome this force, and as a result the molecular kinetic energy drops. Thus, a rarified real gas, i.e, with low particle densities n/V, approaches ideality.
But this is another issue for another thread.