Conversion 1

[ukd]

Hi,

How to calulate standard flowrate from the mass flow rate for HC gas? Available data density at actual condition and pressure is given? Mass flowrate : 194773 Kg/hr and Density 84 kg/m3 at 94 bar? Please anybody can help me out.

 

[ngb23]

Rho divided by rho is unitless. Multiplying M by a unitless number leaves the units in a mass flow rate basis.

Standard cubic foot is based On 1 cubic foot @ 60F and @ 14.7 psia.

Here is the formula to convert cubic feet to standard cubic feet:

AT = Actual Temp + 460 = Temp. Rankin
AP = Actual Pressure + Atmospheric (14.7 @ sea level)

520/AT = Temp Correction Factor
AP/14.7 = Pressure Factor

CF x Temp Factor x Pressure Factor = SCF

Example:
1 cf of gas @ 29.4 psia & 200F you would have:

29.4/14.7 = 2 (pressure factor)
200+460 = 660 (temperature conversion to Rankin)
520/560 = .7878 (temperature factor)

(1 cf of gas) x (2) x (.7878) = 1.5756 scf

Hope that helps.

NGB

 

[ngb23]

But if all you have is actual density, convert to cubic feet, then convert to standard cubic feet.

 

[mbeychok]

ukd:

The standard cubic foot defined by ngb23 is only one of many, many different definitions of "Standard" or "Normal" gas volumes. There simply is no universally accepted definition of Standard or Normal gas volumes.

Read this article in the online Citizendium encyclopedia:

click ==> Reference conditions of gas temperature and pressure

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

 

[TD2K]

What is the level of accuracy you need?

As said, you can correct the flowing volume to standard conditions (with Milton's caution what are the standard conditions).

I'd include one comment to NGB23's comment and that would be to include the compressibility factor at flowing P and T (essentially your 84 kg/m3) to the compressibility factor at standard conditions. At 94 bar that could be a significant factor.

Do you have a molecular weight? You then know the molar flow and can calculate the volumetric flow at standard conditions using the ideal gas law (and compressibility factor at standard conditions if needed)

 

[mbeychok]

TD2K:

If the origninal poster (ukd) knows both the temperature and pressure of his given density value, then the molecular weight can be can calculated from this version of the ideal gas law (corrected by the compressibility):

M = (d[•]Z[•]R[•]T) / P

where:
M = molecular weight
d = density
Z = compressibility factor
R = universal gas law constant (also known as the molar gas constant)
T = absolute temperature
P = absolute pressure



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

 

[PaoloPemi]

basically once you define a flow at some "standard conditions" you specify the flow in terms of "mass" as the quantity (mass) of gas contained in the specified "standard" volume at some specified "standard" pressure and temperature is constant, the problems being:
a) there are many different "standard" conditions, here in Europe we use normal, standard and normalized cubic meters, specified at different reference temperatures and pressures, reference temperature (or pressure) may change in different countries
b) you need an accurate value for the gas density at your "standard" conditions in order to conver from mass to "standard" volume flow

for hydrocarbons with critical temperature far from usual "standard" temperatures (as for CH4) compressibility differs from unity at the usual "standard" condition, you may use an equation of state or equivalent method to obtain an accurate value, once you have the value for density at your "standard" conditions converting to or from mass flows it's immediate

As said in a different thread I use Excel with the free version of Prode Properties (

http://www.prode.com)

for this kind of calc's but I think that any other good tool can do the work.