3 replies to this topic

[Javed Mateen]

We have 04 LM 6000 PC Engines in our Power Plant rated at 48 MW each.We are located in karachi Pakistan.The gas turbine control system measures natural gas in pounds (lbs).Natural gas is injected at 640 PSIG at 147 F I need to get the density of the natural gas at this temperature and pressure so as to get the consumption in Standard Cubic Feet(SCF)

Compressibility factor is 0.95

[breizh]

Hi ,

Standard condition are defined at 60F and 14.7 PSIa .

To transform actual condition (1) to standard condition (2) consider the equation :
P1*V1/T1 = P2*V2/T2 or V2 = P1*V1/T1 *T2/P2 with T1 & T2 in Kelvin T1 =337 K ;T2 = 288.7 K

V1 , V2 are volumic values ( m3 , Ft3,....) , P1 and P2 are absolute pressure 654.7 PSia and 14.7 PSia .

To get access to flow rate , you need to get access to density . P*V=Z*R*T and density = Mw / V with Mw = 16 g/mol for CH4.
With the proper units , you will get density # 26 kg/m3 .
To convert density to lb/m3 you have to multiply density per 2.6792 then to convert the mass flowrate lb /unit time to m3/ unit time you have to divide the flowrate (lb/unit time) / density (lb/m3) .
Finally you will get a volumetric flowrate at (T,P)actual condition to convert at (T0,P0) standard condition using the 1rst equation above .

Hope it helps
Breizh

[S.AHMAD]

We have 04 LM 6000 PC Engines in our Power Plant rated at 48 MW each.We are located in karachi Pakistan.The gas turbine control system measures natural gas in pounds (lbs).Natural gas is injected at 640 PSIG at 147 F I need to get the density of the natural gas at this temperature and pressure so as to get the consumption in Standard Cubic Feet(SCF)

Compressibility factor is 0.95

Hi,
The easiest method is to obtain the molecular weight of the gas. The lbs of NG divided by the mol weight to get lb-mole then multiply by 379.48 to get the SCF. Then multiply by compressibility factor to account for non-ideality.

Note: 1 lb-mol of an ideal gas occupies 379.48 ft3 at 60F and 1 atm (14.696 psia).
The compressibility factor mentioned above is for gas at 60F and 1 atm not at the operating conditions. The compressibility factor of 0.95 is too low at that standard conditions it should be very close to 1.0, please check.

Edited by S.AHMAD, 11 February 2010 - 01:45 AM.

[JMW]

Of course, gas quality can vary dependent on your source and any applicable regulations.
In critical applications PTZ calculation may not be accurate enough e.g. at higher pressures, and if the cost justifies it then inline/online gas density meters are used to determine the density.
Online relative density analysers may also be used to help determine quality relative to a reference gas. Many flow computers are available to privide all the necessary calculations.
The operating manual for Emerson gas density, gas relative density and flow computers (gas flow) can be found on their website, and you will find the various relevant equation detailed in the manuals.
Gas Specific Gravity (Relative density): http://www2.emersonp...ages/index.aspx
Gas Density: http://www2.emersonp...ages/index.aspx
Flow Computers: (Signal converters actually): http://www2.emersonp...ages/index.aspx