Formulas

Heating

Formulas:

MBtu = 1,000Btu (note: MBtu is not commonly used)
MMBtu = 1,000Mbtu or 1,000,000Btu
Btu per Mcf = Btu per Cf divided by 1,000
MMBtu = Mcf times Btu per Cf divided by 1,000 or Mcf times Btu per Mcf

Calculation Examples:

1,000Mcf times 1100 Btu/Cf divided by 1,000 = 1,100MMBtu
1,000Mcf times 1.100 Btu/Mcf = 1,100MMBtu

Dry Versus Saturated

Btu Factors (Heating Values) can be converted from Dry (natural gas not containing a significant amount of water) to Saturated (natural gas containing water) using the following formulas or conversion factors shown in Table 3. The .25636 factor used in the formulas and in the calculation of the table conversion factors is the vapor pressure of water at 60 degrees Fahrenheit as published in GPA Standard 2172-96.

General Rule:

A Btu is a Btu regardless of whether the gas is Dry or Saturated. Since water vapor will not burn or combust, natural gas of a given composition will contain fewer Btu per Cf if it is Saturated than it would contain if it were Dry. Consequently, the Btu Factor for Saturated gas is less than the Btu Factor for the same gas if it were Dry.

Formulas:

Btu/Cf-Sat divided by (1 minus (.25636 divided by Pb) = Btu/Cf-Dry
Btu/Cf-Dry times (1 minus (.25636 divided by Pb) = Btu/Cf-Sat

Dry vs. Saturated Table 3

Conversion factors for converting heating values from Dry to Saturated.

Calculation Examples:

1000 Btu/Cf-Sat @14.65 divided by (1 minus (.25636 divided by 14.65) = 1018 Btu/Cf-Dry @14.65
1000 Btu/Cf-Sat @14.65 divided by .982501 = 1018 Btu/Cf-Dry @14.65

NGL Gallons by Component

A volume of natural gas can be converted to its liquefiable hydrocarbon components (ethane, propane, etc) by using Mol% or GPM from the compositional analysis of the stream of natural gas.

Formula Definitions:

Cf/Mol = number of cubic feet in a Mol (see Note below)
Gal/#Mol = gallons per pound Mol

Note: The number of cubic feet in a Mol is pressure base sensitive. The standard per the Gas Processors Association is 379.49 cubic feet at a pressure base of 14.696. The formula to convert the standard to a different pressure base is as follows:

379.49 times (14.696 divided by PT)

NGL Gallons by Component Table 4
The number of cubic feet per Mol at different pressure bases

NGL Gallons Table 5

The number of gallons per pound Mol by component

Formulas:

Mcf times GPM for the component = Gallons
Mcf times [(Mol% divided by 100) divided by Cf/Mol] times 1000 times Gal/#Mol = Gallons

Calculation Examples:

1,000 Mcf @ 14.73 times 3.0088 GPM C2 = 3,009 Gallons of C2 (Ethane)
1000 Mcf @ 14.73 times [(11.25 Mol% C2 divided by 100) divided by 378.61406] times 1000 times 10.1259=3,009 Gallons of C2 (Ethane)

MoI% to Gallons per Mcf

Compositional analysis of natural gas expressed as mol% can be converted into gallons per Mcf (GPM) factors by using the formulas and conversion factors shown in Tables 7, 8 and 9 below.

General Rule:

A gallon is a gallon regardless of pressure base.

Formula definitions:

Cf/Mol = number of cubic feet in a Mol (see Note below)
Gal/#Mol = gallons per pound Mol
Gal/Mcf = gallons per Mcf
GPM = gallons per Mcf
PF = pressure base to convert from
PT = pressure base to convert to

Note: The number of cubic feet in a Mol is pressure base sensitive. The standard per the Gas Processors Association is 379.49 cubic feet at a pressure base of 14.696. The formula to convert the standard to a different pressure base is as follows:

379.49 times (14.696 divided by PT)

Table 6

The number of cubic feet per Mol at different pressure bases

Table 7

The number of gallons per pound Mol by component

Table 8

The number of gallons per thousand cubic feet (Mcf) at various pressure bases by component