Standard cubic foot

Source: Wikipedia, the free encyclopedia.

A standard cubic foot (scf) is a

cubic meter at different reference conditions.[1]
The reference conditions depend on the type of gas and differ from other
standard temperature and pressure conditions
.

Usage

The scf and the scm are units of

temperature
, each definition fixes base values for pressure and temperature.

Natural gas

Since natural gas is an imprecise 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, but a molecular quantity, expressed in moles.

For petroleum gases, the standard cubic foot (scf) is defined as one cubic foot of gas at 60 °F (288.7 K; 15.56 °C) and at normal sea level air pressure. The pressure definition differs between sources, but are all close to normal sea level air pressure.

The standard cubic meter of gas (scm) is used in the context of the

meter at a temperature of 15 °C (288.150 K; 59.000 °F) and a pressure of 101.325 kilopascals (1.0000 atm; 14.696 psi).[1]

Converting volume units between the standard cubic foot and the standard cubic meter is not exact, as the base temperature and pressure used are different, but for most practical situations the difference can be ignored. Comparing the same volume between the 15 °C (288.15 K) and 101.325 kPa standard cubic meter versus the 60 °F (288.71 K) and 14.73 psi (101.56 kPa) standard cubic foot gives an error of 0.04%. A standard cubic foot in the US Customary System is approximately equivalent to 0.02833 standard cubic meters in the SI system.

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 prefixes, but 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), and MMcf (million standard cubic feet).[3]
The "M" refers to the Roman numeral for thousand, while a double "M" ("MM") represent one thousand thousands, or one million. Bcf (billion standard cubic feet), Tcf (trillion standard cubic feet), Qcf (quadrillion standard cubic feet), etc., are also used.

Compressed or liquefied gases in refillable cylinders

The National Conference on Weights and Measures, a US-based non-profit organization working in cooperation with the US National Institute of Standards and Technology, has defined a set of standards in a regulation entitled the "Uniform Regulation for the Method of Sale of Commodities".[4] This regulation defines a standard cubic foot, for compressed or liquefied gases in refillable cylinders other than LPG by, "A standard cubic foot of gas is defined as a cubic foot at a temperature of 21 °C (70 °F) and a pressure of 101.325 kilopascals [kPa] (14.696 psia)".[4]

Industrial gases

Yet other definitions are in use for

psia
(101.325 kPa), while in Canada, a standard cubic meter for industrial gas use is defined at 15 °C (59 °F) and 101.325 kPa (14.696 psia).

Converting actual volumes to standard volumes

An actual volume can be converted to a standard volume using the following equation:[6][7]

Vs = Va × Fp × Ft × (Fpv)2

Where,

Vs: standard volume
Va: actual volume (sometimes shown as Vr for registered volume)
Fp: pressure factor (sometimes shown as Pm for pressure multiplier)
Fp: absolute pressure / standard pressure = (line gauge pressure + atmospheric pressure)/base pressure
Ft: temperature factor (sometimes shown as Tm for temperature multiplier)
Ft: absolute standard temperature / absolute line temperature = [273.15 + standard temperature (°C)] / [273.15 + line temperature (°C)] or [459.67 + standard temperature (°F)] / [459.67 + line temperature (°F)]
Fpv: 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 gauge pressure 50 psi? (assuming that there is 13.6 psi atmospheric pressure and ignoring super compressibility)

Vs = 1 cu ft × [(13.6 psi + 50 psi) / 14.73 psi] × [(60 °F + 459.67 °F) / (80 °F + 459.67 °F)]
Vs = 4.16 scf

See also

References

  1. ^
    ISBN 978-0-12-800000-7
    .
  2. ^ a b "Uniform Laws and Regulation" (PDF). National Institute of Standards and Technology. 2019. pp. 129, 132. Retrieved 8 December 2019.
  3. ^ "Category:Glossary". PetroWiki. SPE International. Retrieved 21 November 2017.
  4. ^
    doi:10.6028/NIST.HB.130-2017
    . Retrieved 21 November 2017.
  5. ISBN 9781461306733
    . Retrieved 17 Nov 2017.
  6. ^ "PART VIII: Provisions Specific to Gas". Electricity and Gas Inspection Regulations. Government of Canada. Retrieved 18 July 2014. {{cite book}}: |website= ignored (help)
  7. ^ "Introduction to Gas Metering" (PDF). Introduction to Gas Measurement. Barchard Engineering. Retrieved 18 July 2014.
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