Is Green Gas Flammable? (A Comprehensive Overview)

Is Green Gas Flammable?

Yes, green gases are flammable. The green gases denomination is attributed to gases that were obtained from renewable sources and can be used in place of fossil fuels. 

When obtained from renewable sources the following fuels can be considered green gases:

  • Methane (CH4)
  • Propane (C3H8)
  • Butane (C4H10)
  • Hydrogen (H2)

Methane and propane may be called biomethane and bio-propane if they were obtained from biological processes such as from bacteria metabolism. Also, in some contexts, green gases may be called renewable gases instead.

The composition of a green gas may or may not be exactly the same as the fossil counterpart. In trace amounts there may be differences in their composition but this difference would be too small to significantly influence their flammability..

Since a green gas must be able to exert the same function as fossil fuels, green gases are all necessarily capable of undergoing combustion releasing a significant amount of energy (heat). In the vast majority of cases this indicates they will be flammable.

Methane Fire Related Properties

Methane is extremely flammable, according to the U.S. National Fire Protection Association (NFPA) methane has a flammability degree of 4, the highest degree in this classification. Methane is also toxic if inhaled. Burning methane releases carbon monoxide.

Methane gas can travel significant distances, possibly contacting distant ignition sources. Methane can react violently with oxidizing substances such as peroxides and perchlorates, chlorine (Cl2), fluorine (F2), bromine (Br2), and many others.

Liquefied methane boils on water.

In case of a fire generated by burning methane the gas flow should be stopped.

Methane is a colorless and odorless gas under ordinary temperatures and pressures. 

Below are some physical and chemical data on methane.

Boiling point-162 ºC (259 ºF) at 1 atm
Melting point-182 °C (-296 °F) at 1 atm
Flash point-188 °C (-306 °F)
Autoignition temperature537 °C (999 °F)
Explosive limits4 to 17% (percentage in volume in air)

Propane Fire Hazards

Propane is a very flammable and explosive gas, its flammability degree of propane is also 4. In the event of a propane tank fire, there is always the potential for a type of explosion known as boiling liquid expanding vapor explosion (also known as BLEVE).

Propane is a colorless and odorless gas at ordinary temperatures and pressures. Some important data on propane is represented in the table below.

Boiling point-42 to -42 °C (-44 to -44 °F) at 1 atm
Melting point-188 °C (-306 °F) at 1 atm
Flash point-104 °C (-155 °F)
Autoignition temperature470 °C (878 °F)
Explosive limits2 to 9% (percentage in volume in air)

Butane Fire Hazards

Butane (n-butane) is used in gasoline blending and as a fuel in many different applications. It is colorless and odorless, in some applications as fuel it is mixed with a mercaptan (a substance containing the functional group C-SH) to provide an easily detectable odor.

Butane and its isomer, iso-butane, are extremely flammable and explosive.

In the table below some important physical properties of butane.

Boiling point-1 to -1 °C (-30 to -34 °F) at 1 atm
Melting point-140 to -134 °C (-220 to -209 °F) at 1 atm
Flash point-60 °C (-76 °F)
Autoignition temperature405 °C (761 °F)
Explosive limits2 to 8% (percentage in volume in air)

Hydrogen Gas Fire Hazards

Hydrogen gas is extremely flammable and explosive, its flammability degree according to NFPA is 4. Its explosive limits in air have a wide range of 4 to 74%, Pure hydrogen flame is not visible to the human eye as the flame emits only in the ultraviolet radiation.

When hydrogen undergoes a combustion reaction with oxygen gas, water is the only substance formed. Hydrogen is also flammable in the presence of chlorine gas even in the absence of oxygen.

Boiling point-253 °C, ​(-423 °F) at 1 atm
Melting point-259 °C, ​(-434 °F) at 1 atm
Flash pointNo data
Autoignition temperature500 °C (932 °F)
Explosive limits4 to 74% (percentage in volume in air)

How Are Green Gases Obtained?

Green gases are all obtained from renewable sources. In other words, biomass, waste material, renewable sources of power such as wind.

Four examples, the most common, will be discussed in greater details below:

Methane from Renewable Sources, Renewable Natural Gas or Biomethane

It is composed of nearly pure methane mostly obtained by one of two types of processes. From gasification of solid biomass followed by methanation or by removing carbon dioxide and other contaminants from biogas.

Thermal gasification of solid biomass followed by methanation:

Woody biomass (woody material from trees and shrubs) is put under high temperatures and pressures in a space with a low concentration of oxygen (O2). From this process, syngas is obtained (a mixture of carbon monoxide (CO), hydrogen gas and methane).

The syngas is subjected to initial purification steps to remove possible acidic and corrosive substances from the gas mixture.

Next, the methanation process takes place using a catalyzed chemical reaction to turn hydrogen and carbon monoxide or hydrogen and carbon dioxide into methane. At the end of this process the remaining carbon dioxide and water are removed from the gas mixture (which is mostly methane at this point).

As of 2019, about 90% of the biomethane produced worldwide is obtained by the the process called: upgrading biogas.

The lower heating value (LHV) of biomethane is around 36,000,000 Joules per cubic meter. In this sense it is the same as natural gas and so it can be used without the need for any changes in transmission and distribution infrastructure.

Biogas

Biogas consists of a mixture of methane (typically ranging from 45 to 75%), carbon dioxide (typically ranging from 55 to 25%) and small quantities of other gases produced by bacterial anaerobic metabolism of organic matter in an environment with no oxygen.

The exact composition of biogas depends on how it was produced and on the type of material it was obtained from. Two common types of production methods are:

  • Biodigesters: containers in which organic material, diluted in water, is broken down by naturally occurring micro‑organisms.
  • Landfill gas recovery systems: decomposition of municipal solid waste under anaerobic conditions at landfill sites.

The LHV of biogas usually stays between 16,000,000 and 28,000,000 joules per cubic meter.

Propane From Renewable Sources

Propane can be obtained from agricultural waste products, cooking oil and meat fats. Additionally, propane is produced as a co-product in biodiesel production.

All the processes utilized to produce propane from the above mentioned source require somewhat complex processes, all of which involve a step of hydrogenation to guarantee the purity of the obtained propane.

Butane From Renewable Sources

Differently from methane and propane methods to produce butane in large amounts is more scarce. An example of a method which is being researched is by means of bacteria culture of waste volatile fatty acids.

According to the study by Scrutton and collaborators in 2020 butane and propane can be obtained from fatty acids derived from biomass or industrial waste via a photo catalyticalyzed process by bioengineered strains of E. coli and Halomonas.

Hydrogen Gas From Renewable Sources (Power)

Hydrogen is more easily obtained from renewable power than from renewable feedstocks. Examples of renewable power include: wind, solar, geothermal and electricity.

Water can undergo an electrochemical process by which hydrogen and oxygen are obtained. This process requires substantial energy and is commonly performed consuming electrical energy (electricity). There are commercially available tools for this process.

Conclusion

Green gases are flammable, explosive and sometimes novel to humans or the environment the same as their fossil fuel counterparts. However green gases can serve as an important alternative to fossil fuels given that the former is possibly less harmful to the longevity of society.

Frequently Asked Questions (FAQ): Is Green Gas Flammable?

Is green gas explosive?

That will depend on what the specific green gas is made of, but all well known green gases at this moment (methane, propane, buane, hydrogen) are highly explosive and flammable.

Is propane the same as green gas?

Green gas is a broad denomination, which includes propane that was obtained from a renewable source. However, green gas may refer to other fuels such as methane or hydrogen.

Can green gas explode in the heat?

That depends on the specific composition of the green gas. Green gases may have very different compositions and which have their own specific thermal properties. All the well known green gases will catch on fire if a ignition source is applied to them in an ambient with oxygen gas such as any open air area.

What is green gas used for?

Green gas can be used the same way as fossil fuels as long as they have the same composition. What makes green gas different from fossil fuels is not their composition but their means of production.

Can airsoft guns explode?

The most commonly used airsoft gun gas is propane. Propane is extremely flammable and explosive, so yes airsoft guns can explode if heated or in contact with an ignition source.

Can you use CO2 in a green gas gun?

Yes it can be used.

References

https://www.greengas.org.uk/green-gas (Accessed June 10th, 2022)

https://www.iea.org/reports/outlook-for-biogas-and-biomethane-prospects-for-organic-growth/an-introduction-to-biogas-and-biomethane (Accessed June 10th, 2022)

https://www.epa.gov/lmop/renewable-natural-gas (accessed June 13th, 2022)

Scientific review on catalyzed methanation from hydrogen and carbon dioxide:

Xiong Su, Jinghua Xu, Binglian Liang, Hongmin Duan, Baolin Hou, Yanqiang Huang, Catalytic carbon dioxide hydrogenation to methane: A review of recent studies, Journal of Energy Chemistry, Volume 25, Issue 4, 2016, Pages 553-565, ISSN 2095-4956, https://doi.org/10.1016/j.jechem.2016.03.009.

Methane safety data sheet:

https://nj.gov/health/eoh/rtkweb/documents/fs/1202.pdf (Accessed June 13th, 2022)

https://www.cdc.gov/niosh/docs/99-129/default.html (Accessed June 14th, 2022)

Patnaik, P. A Comprehensive Guide to the Hazardous Properties of Chemical Substances. Wiley-Interscience. 2007.

https://propane.com/environment/stories/renewable-propane-a-cleaner-energy-source/ (Accessed June 14th, 2022)

Mohamed Amer, Emilia Z. Wojcik, Chenhao Sun, Robin Hoeven, John M. X. Hughes, Matthew Faulkner, Ian Sofian Yunus, Shirley Tait, Linus O. Johannissen, Samantha J. O. Hardman, Derren J. Heyes, Guo-Qiang Chen, Michael H. Smith, Patrik R. Jones, Helen S. Toogood, Nigel S. Scrutton. Energy Environ. Sci., 2020,13, 1818-1831. https://doi.org/10.1039/D0EE00095G

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