Onecoin 150423004844 Conversion Gate02 150425020546 Conversion Gate01
Conversion
Transcript of Conversion
Smart questionsSmart answers Smart people
Go Find A Forum Go
� Join � Directory � Search � Tell A Friend
� Whitepapers � Jobs
Home > Forums > Chemical Engineers > Activities > Chemical process engineering Forum
Convert lb/hr to SCFM thread798-72789
JDJACKSON (Mechanical) 26
Sep
03
19:57
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
Latexman (Chemical) 26
Sep
03
20:11
1 lb/hr x (1 hr/60 min) x (1 lb-mole/20.07 lb) x
(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
JDJACKSON (Mechanical) 26
Sep
03
22:13
Latexman, thanks for your help. Isn't there 379 lb/moles per standard cubic foot?
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
Latexman (Chemical) 26
Sep
03
23:45
It depends on the definition of STP (standard temperature and pressure). Most conventions agree on the P part, i.e. 1 atm or 14.696 psia. The T
part is usually where differences come in. At the University, it was usually 0 C (273 K) or 32 F (492 R). Different industries use different T's. 60 F
(520 R) is quite common in North America. So, it depends on where you are and what you use it for. It all comes from the ideal gas law, PV =
nRT. The number I used above is derived as follows:
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
Online Engineering Degree
Get Online Engineering Degree in 15 days from the Top University in KSA AccreditedLifeexperienceDegrees.com
Share This
Page 1 of 2Chemical process engineering - Convert lb/hr to SCFM
2/19/2012http://www.eng-tips.com/viewthread.cfm?qid=72789
Join | Jobs | Advertise | About Us | Contact Us | Site Policies
Copyright © 1998-2012 Tecumseh Group, Inc. All rights reserved. Unauthorized reproduction or linking forbidden without express written permission.
Montemayor (Chemical) 27
Sep
03
20:28
The problem that one always encounters with other engineers is the failure to state the basis for "standard" conditions up front. That is why I always
have used the GPSA's definition:
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
JDJACKSON (Mechanical) 28
Sep
03
2:22
Thanks Art, As you can see I am an M.E. and E.E. and got stuck with a problem while I am out of town rebuilding a gas processing liquid separation
terminal in Louisiana. I guess I am going to have to go back to school when I get back to Deer Park, Texas and take some ChemE courses. I
appreciate the help this forum has given me with this problem.
J. D. Jackson B.S. M.E. & B.S. E.E.
TransContinental Engineering
25362 (Chemical) 28
Sep
03
3:43
To convert mass to moles, via molecular mass, you don't need to know the temperature or the pressure.
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.
Analyse-it for Excel
Easy to use statistical software for Microsoft Excel. Free trial! www.analyse-it.com
Page 2 of 2Chemical process engineering - Convert lb/hr to SCFM
2/19/2012http://www.eng-tips.com/viewthread.cfm?qid=72789