Standard cubic foot

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A standard cubic foot (scf) is a unit used both in the natural gas industry to represent an amount of natural gas and in other industries where other gases are used.

Video Standard cubic foot

Definitions

For most gases, "A standard cubic foot of gas is defined as a cubic foot at a temperature of 21 °C (70 °F) and a pressure of 101.35 kilopascals [kPa] (14.696 psia)". Other base pressures and temperatures are sometimes used as well.

For natural gas, a standard cubic foot (scf) is the amount of natural gas contained in a cube whose edges are one foot long at standard temperature and pressure (60 °F (15.6 °C) and 14.73 pounds per square inch [psi] (101.6 kPa) in Canada).

A standard cubic foot of natural gas (at 14.73 psi and 60 °F) is equivalent to 0.0283058557 standard cubic meters (at 101.325 kPa and 15 °C).

The standard cubic foot, in keeping with the ideal gas law, thus defines a standard unit of molecular quantity (not volume, as the name suggests). The conversion to quantity (scf to moles) is straightforward; one standard cubic foot represents 1.19804 moles (0.0026412 pound moles).

Since natural gas is a mix of various molecular species, chiefly methane but with varying proportions of other gases, a standard cubic foot of natural gas does not represent a precise unit of mass.

Converting between standard volumes is not always straightforward. For example, converting standard cubic feet to standard cubic meters (SCM) does not use the same ratio as converting cubic feet to cubic meters (1 cubic foot = 0.0283168466 cubic meters) because the standard temperature and pressure used are different. A standard cubic foot (using the convention of 14.73 psi and 60 °F) is equivalent to 0.0283058557 standard cubic meters (using the convention of 101.325 kPa and 15 °C).

In the natural gas industry where quantities are often expressed in standard cubic feet, large multiples of standard cubic feet are generally not expressed with Metric prefix, rather with prefixes based on roman numerals where the s for "standard" is often omitted. Common units of gas volumes include ccf (hundred standard cubic feet), Mcf (thousand standard cubic feet), MMcf (million standard cubic feet). The M refers to the Roman numeral for thousand,two M's would be one thousand thousand, or one million. Bcf (billion standard cubic feet), Tcf (trillion standard cubic feet), Qcf (quadrillion standard cubic feet), etc. are also used.

Maps Standard cubic foot

Converting Actual Volumes to Standard Volumes

An actual volume can be converted to a standard volume using the following equation:

V_s = V_a × F_p × F_t × (F_pv)²

Where,

V_s: Standard Volume

V_a: Actual Volume ( sometimes shown as V_r for Registered Volume )

F_p: Pressure Factor ( sometimes shown as P_m for Pressure Multiplier )

F_p = Absolute Pressure / Standard Pressure = (Line Gauge Pressure + Atmospheric Pressure)/Base Pressure

F_t: Temperature Factor ( sometimes shown as T_m for Temperature Multiplier )

F_t = Absolute Standard Temperature / Absolute Line Temperature = [ 273.15 + Standard Temperature(deg C) ] / [ 273.15 + Line Temperature(deg C) ] or [ 459.67 + Standard Temperature(deg F) ] / [ 459.67 + Line Temperature(deg F) ]

F_pv: Super Compressibility Factor (often omitted or shown as equaling 1)

Example: How many standard cubic feet are in 1 cubic foot of gas at 80 °F and 50 psig? (assuming we have 13.6 psi atmospheric pressure and ignoring super compressibility)

V_s = 1 cu ft * [ ( 13.6 psi + 50 psi ) / 14.73 psi ] * [ ( 60°F + 459.67°F ) / ( 80°F + 459.67°F ) ]

V_s = 4.16 scf

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References

Source of the article : Wikipedia