13 replies to this topic

[gourav.agrawal]

Please tell me how to convert gas flow rate from nm3/hr to kg/hr for compressor systems at any pressure and temperature

[Saml]

 It does not depends on pressure and temperature 

[breizh]

Hi ,

Use the search engine in this forum , you will find the answer . One important point is to define "normal condition".

 

http://www.cheresour...and-normal-t-p/

 

Good luck

Breizh

Edited by breizh, 30 August 2016 - 09:34 PM.

[Bobby Strain]

If you use what you learned, you can use the volume definition for a Kg-Mole. And you won't be far off. After all, it's only an exercise.

 

Bobby

[Mahdi1980]

Hi,

The ideal gas law demonstrates that: PV=nRT in which n=m/M 

n= mole number

m= mass or mass flow (kg/h)

V= volume or volumetric flow (m3/hr) 

M= molecular weight of the gas for example Molecular weight of nitrogen (N2) =28 kg/kgmole

In Normal conditions according to the latest SI definition P=100 kpa and T=0 C or 273.15 K

R = gas constant =8.314 pa.m3/mol.K

So, PV=(m/M)*R*T or    m(kg/h) = (P*V*M)/(R*T)

at Normal conditions then we have: 

                                                     m(kg/h) = M* 100* V (Nm3/h) / (8.314*273.15)   or

                                                     m(kg/h) = 0.044 M* V (Nm3/h)

example:                       20 Nm3/h of Nitrogen is equal to:

                                                     m = 0.044* 28 (molecular weight) * 20 (Nm3/h) 

                                                     m = 7 kg/h

 

Hope it is clarified.

Edited by Mahdi1980, 30 August 2016 - 04:09 PM.

[Bobby Strain]

The hooker is that there is no universally accepted value for Normal conditions. All contracts include the definition for normal conditions.

 

Bobby

[gourav.agrawal]

One more question how to convert specific gravity of gas like methnae, ethane, propane into density.

[Profe]

Hi Gourav Agrawal

If you have Volume in Nm³/h and gas composition by gas cromatography, you can use the attached file in Excel for calculate mass gas flowrate. Review  the spreadsheet and the calculations for obtain the requires answer. I use for our mass balance for gases from FCC unit to Gas concentration Unit.

 

It uses definition of Gas Specific gravity related of air. And air density for Kg/Nm³.

Also Normal conditions are: 1 atm and 273,15 K. The transformation no depends of pressure and temperatura. But for calculate of volumen its necesary the Process conditions.

Good luck

Fausto

Attached Files

•  Vol Nm3 to mass.xlsx   15.76KB   1147 downloads

[Mahdi1980]

Agrawal

 

Are you kidding us ? This forum is not a place to ask such elementary questions. search the conversion factors on the net.

[amad]

agrawal

 

as mahdi said, for simple conversion unit you can using 'grandpa' google for seaching to answer it. But, I will answer it.

specific gravity is formula between fluid density to air or water density. For gas fluid, like methane:

SG = fluid density/air density.

From this formula you will get answer of your question.

cmiiw

Edited by amad, 01 September 2016 - 08:33 PM.

[Profe]

Hi Agrawal.

Not, not, not...

For gases if you review the Spreadsheet I attached and for definition

Specific graviti for gases is: MW of gas/MW of Air

Average Mol Weigth of air = 28,96247 Source: Flow Measurement Engineering Handbook - R W Miller p 2-28

then SG_gas = MWgas/28,96247

MW_gas = 23,16822

SG_gas = 23,16822/28,96247 = 0,799939 (adimentional)

I think this little bit clarify...

 

Good luck

Edited by Profe, 02 September 2016 - 03:39 PM.

[SAN15]

For ideal gas

1 mole of gas equivalent to volume of 22.414 litre at STP

Example 

Flow rate of N2 = 1 kg/hr

Molecular weight of N2 = 28

 

volume flow rate for N2 = 1/28*22.414 

                                      = 0.8 M3/hr at STP

Temperature and pressure correction factor to be provided to get flow at desired condition.

 

Hope this is usefull

[benabed]

sudip Rokde

 

At STP 1 kgmol=23.645 Sm3 and not 22.414 which is the molal volume at normal conditions

[Art Montemayor]

To all contributors to this thread:

 

Please, for my sake and the sake of all experienced chemical engineers, STATE THE SPECIFIC TEMPERATURE AND PRESSURE OF YOUR "STP" (Standard Temperature & Pressure).  Failure to do so only creates more chaos and controversy.  The issue of so-called "standard conditions" has been discussed, argued, and thoroughly defined in many previous threads in our Forums for the last 15 years.  As Bobby Strain has correctly inferred, failing to define your STPs can only lead to mistakes, wrong conclusions, and (in some cases) legal problems.