Oil shale gas (also: retort gas or retorting gas) is a synthetic non-condensable gas mixture ( syngas) produced by

oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...

thermal processing (

pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''pyr ...

). Although often referred to as shale gas, it differs from the natural gas produced from shale, which is also known as shale gas.

Process

Oil shale gas is produced by retorting (pyrolysis) of oil shale. In the pyrolysis process, oil shale is heated until its kerogen decomposes into

vapor In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...

s of a

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

-like condensable

shale oil Shale oil is an unconventional oil produced from oil shale rock fragments by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock (kerogen) into synthetic oil and gas. The resulting oil c ...

, non-condensible

combustible A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

oil shale gas, and

spent shale Spent shale or spent oil shale (also known as retorted shale) is a solid residue from the shale oil extraction process of producing synthetic shale oil from oil shale. It consists of inorganic compounds (minerals) and remaining organic matter kno ...

—a solid residue. The process is the same as the shale oil extraction and oil shale gas usually occurs as a byproduct of shale oil production. The ratio of oil shale gas to

depends on retorting temperature and as a rule, increases by the rise of temperature.

Composition

There is no exact formula of oil shale gas. Compositions of oil shale gas depends on the retorted oil shale and exploited technology. Typical components of oil shale gas are usually

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxi ...

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simp ...

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is tr ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...

, and different

hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or e ...

ethylene Ethylene ( IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

. It may also consist of hydrogen sulfide and other impurities.

Use

Oil shale gas has served as a substitute for

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon di ...

. In the 19th century and in the beginning of the 20th century oil shale gas was used as illuminating gas. In 1920s, gas plants in

Tallinn Tallinn () is the most populous and capital city of Estonia. Situated on a bay in north Estonia, on the shore of the Gulf of Finland of the Baltic Sea, Tallinn has a population of 437,811 (as of 2022) and administratively lies in the Harju ' ...

and

Tartu Tartu is the second largest city in Estonia after the Northern European country's political and financial capital, Tallinn. Tartu has a population of 91,407 (as of 2021). It is southeast of Tallinn and 245 kilometres (152 miles) northeast o ...

produced oil shale gas as a

town gas Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...

. Since 1948, Estonian-produced oil shale gas was used in

Leningrad Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...

and the cities in North Estonia. For this purpose, 276 gas generators were operational in

Kohtla-Järve Kohtla-Järve is a city and municipality in northeastern Estonia, founded in 1924 and incorporated as a town in 1946. The city is highly industrial, and is both a processor of oil shales and is a large producer of various petrochemical products ...

until 1987. As oil shale gas often occurs as a byproduct of shale oil extraction, depending on the processing technology, it may be used for heating the pyrolysis process.

References

{{Reflist, 2 Oil shale Synthetic fuels Fuel gas Unconventional gas