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{{Short description|Fuels which under ordinary conditions, are gaseous}}
{{Distinguish|gasoline}}
{{Hatnote|Compare [[fuel oil]].}}
<!--yes, this is a stub made from a redirect, but it was requested to begin a top-level general article for the entire subject matter. If possible, please give it time. Date=Feb 2013-->
[[File:Light my fire (2152952690).jpg|thumb|Blue flame of fuel [[gas burner]]s]]
'''Fuel gas''' is one of a number of [[fuel]]s that under ordinary conditions are [[gas]]eous. Most fuel gases are composed of [[hydrocarbon]]s (such as [[methane]] and [[propane]]), [[hydrogen]], [[carbon monoxide]], or mixtures thereof. Such gases are sources of [[energy]] that can be readily transmitted and distributed through pipes.

Fuel gas is contrasted with [[liquid fuel]]s and [[solid fuel]]s, although some fuel gases are [[Liquefaction of gases|liquefied]] for storage or transport (for example, [[autogas]] and [[Liquefied petroleum gas|liquified petroleum gas]]). While their gaseous nature has advantages, avoiding the difficulty of transporting solid fuel and the dangers of spillage inherent in liquid fuels, it also has limitations. It is possible for a fuel gas to be undetected and cause a [[gas explosion]]. For this reason, [[odorizer]]s are added to most fuel gases. The most common type of fuel gas in current use is [[natural gas]].

==Types of fuel gas==
[[File:Chartres Gaslights NOLA.JPG|thumb|19th-century style gas lights in New Orleans]]
There are two broad classes of fuel gases, based not on their chemical composition, but their source and the way they are produced: those found naturally, and those manufactured from other materials.

===Manufactured fuel gas===
{{See also|History of manufactured gas}}
Manufactured fuel gases are those produced by chemical transformations of solids, liquids, or other gases.  When obtained from solids, the conversion is referred to as [[gasification]] and the facility is known as a [[gasworks]].

Manufactured fuel gases include:<ref name=Ullmann>{{cite book |doi=10.1002/14356007.a12_169.pub3|chapter=Gas Production, 1. Introduction |title=[[Ullmann's Encyclopedia of Industrial Chemistry]] |year=2011 |last1=Hiller |first1=Heinz |last2=Reimert |first2=Rainer |last3=Stönner |first3=Hans-Martin |isbn=978-3527306732 }}</ref><ref>{{Cite book |last=Scott Wilson |first=D. |title=The Modern Gas Industry |publisher=Edward Arnold |year=1969 |location=London |pages=6, 11–35}}</ref>
* [[Coal gas]], obtained from pyrolysis of coal
* [[Water gas]], largely obsolete, obtained by passing steam over hot [[Coke (fuel)|coke]]
* [[Producer gas]], largely obsolete, obtained by passing steam and air over hot [[Coke (fuel)|coke]]
* [[Syngas]], major current technology, obtained mainly from [[natural gas]]
* [[Wood gas]], obtained mainly from [[wood]], once was popular and of relevance to [[biofuel]]s
* [[Biogas]], obtained from landfills
* [[Blast furnace gas]]
* [[Hydrogen]] from [[Electrolysis]] or [[Steam reforming]]
The coal gas made by the pyrolysis of coal contains impurities such a tar, [[ammonia]] and [[hydrogen sulfide]]. These must be removed and a substantial amount of plant may be required to do this.<ref name=":0">{{Cite book |last=Williams |first=Trevor |title=A history of the British gas industry |publisher=Oxford University Press |year=1981 |isbn=0198581572 |location=Oxford |pages=15–18, 182}}</ref>

===Well or mine extracted fuel gases===
{{See also|fossil fuel}}
In the 20th century, [[natural gas]], composed primarily of [[methane]], became the dominant source of fuel gas, as instead of having to be manufactured in various processes, it could be extracted from deposits in the earth. Natural gas may be combined with hydrogen to form a mixture known as [[HCNG]].

Additional fuel gases obtained from natural gas or [[petroleum]]:
* [[Propane]]
* [[Butane]]
* Regasified [[liquefied petroleum gas]]
The composition of natural gas varies widely, but the table shows a typical composition.<ref>{{Cite book |last=Cassidy |first=Richard |title=Gas: Natural Energy. |publisher=Frederick Muller Limited |year=1979 |location=London |pages=14}}</ref>
{| class="wikitable"
|+Composition of natural gas
!Component
!Volume %
|-
|[[Methane]]
|93.63
|-
|[[Ethane]]
|3.25
|-
|[[Propane]]
|0.69
|-
|[[Butane]]
|0.27
|-
|Other hydrocarbons
|0.20
|-
|[[Nitrogen]]
|1.78
|-
|[[Carbon dioxide]]
|0.13
|-
|[[Helium]]
|0.05
|}
Natural gas is produced with water and gas condensate. These liquids have to be removed before the gas can be used as fuel. Even after treatment the gas will be saturated and liable to condense as liquid in the pipework. This can be reduced by superheating the fuel gas.<ref name=":1">{{Cite book |last=Gas Processors Suppliers Association |title=Engineering Data Book |publisher=GPSA |year=2004 |location=Tulsa |pages=18–9}}</ref>

== Specification ==
In addition to  chemical composition fuel gas may need to comply with parameters such as [[calorific value]], Wobbe index, dewpoint, etc. The following specification is for the British National Transmission System.<ref>{{Cite web |title=Gas Safety (Management) Regulations 1996 |url=https://www.legislation.gov.uk/uksi/1996/551/contents/made}}</ref>
{| class="wikitable"
|+Specification of fuel gas
!Content or characteristic
!Value
|-
|[[Heat of combustion|Gross calorific value]]
|37.0 – 44.5 MJ/m<sup>3</sup>
|-
|[[Wobbe index|Wobbe number*]]
|47.2 – 51.41 MJ/m<sup>3</sup>
|-
|Water dewpoint
|<-10 °C @ 85barg
|-
|[[Hydrocarbon dew point|Hydrocarbon dewpoint]]
|<-2 °C
|-
|Hydrogen sulphide content*
|≤5 mg/m<sup>3</sup>
|-
|Total sulphur content (including H<sub>2</sub>S)*
|≤50 mg/m<sup>3</sup>
|-
|Hydrogen content*
|≤0.1% (molar)
|-
|Oxygen content*
|≤0.2% (molar)
|-
|Carbon dioxide content
|≤2.0% (molar)
|-
|Nitrogen content
|<5.0% (molar)
|-
|Total inerts
|<7.0%
|-
|Incomplete combustion factor*
|≤0.48
|-
|Soot index*
|≤0.60
|}
'''Incomplete Combustion Factor''' (ICF) – an empirical index that relates the composition of a gas to its tendency to burn incompletely in a gas appliance.<ref name=":2">{{Cite web |title=Material comparators for end-of-waste decisions Fuels: natural gas |url=https://assets.publishing.service.gov.uk/media/5a80f4b9ed915d74e6231655/Material_comparators_for_fuels_-_natural_gas.pdf |access-date=15 November 2023}}</ref> Dutton defined the ICF as: ICF = 0.64 × (W − 50.73 + 0.03 × PN) where W is the Wobbe index, MJ/m<sup>3</sup>; PN is the volumetric percentage of C<sub>3</sub>H<sub>8</sub> plus N<sub>2</sub> in a three-component mixture.<ref>{{Cite journal |last=Duan |date=2019 |title=Experimental Study of the Influence of Natural Gas Constituents on CO Emission from Chinese Gas Cooker |journal=Energies |volume=12 |issue=20 |pages=3997|doi=10.3390/en12203997 |doi-access=free }}</ref> 

'''Soot Index''' (SI) – an empirical index that relates the composition of a gas to its tendency to produce soot during combustion in a gas appliance.<ref name=":2" />

The calorific value of manufactured gas is around 500 Btu per cubic foot (18,629 kJ/m<sup>3</sup>). Whereas, the calorific value of natural gas is twice that at around 1000 Btu per cubic foot (37,259 kJ/m<sup>3</sup>).<ref name=":0" /> For a given amount of heat only half the volume of natural gas is required.  

==Uses of fuel gas==
One of the earliest uses was [[gas lighting]], which enabled the widespread adoption of [[streetlamp]]s and the illumination of buildings in towns. Fuel gas was also used in [[gas burner]]s, in particular the [[Bunsen burner]] used in laboratories. It may also be used [[gas heater]]s, camping stoves, and even to power vehicles, as they have a high calorific value.

Fuel gas is widely used by industrial, commercial and domestic users. Industry uses fuel gas for heating furnaces, kilns, boilers and ovens and for space heating and drying . The electricity industry uses fuel gas to power gas turbines to generate electricity. The specification of fuel gas for gas turbines may be quite stringent.<ref name=":1" /> Fuel gas may also be used as a feedstock for chemical processes.

Fuel gas in the commercial sector is used for heating, cooking, baking and drying, and in the domestic sector for heating and cooking.  

Currently, fuel gases, especially syngas, are used heavily for the production of ammonia for fertilizers and for the preparation of many detergents and specialty chemicals.<ref name=Ullmann/>

On an industrial plant fuel gas may be used to purge pipework and vessels to prevent the ingress of air. Any fuel gas surplus to needs may be disposed of by burning in the plant [[gas flare]] system.

For users that burn gas directly fuel gas is supplied at a pressure of about 15 psi (1 barg). Gas turbines need a supply pressure  of 250-350 psi (17-24 barg).

==References==
{{Reflist}}

{{Fuel gas}}
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{{DEFAULTSORT:Fuel Gas}}
[[Category:Fuel gas| ]]
[[Category:Industrial gases]]
[[Category:Synthetic fuel technologies]]
[[Category:Combustion]]