Oil shale gas (also:retort gas orretorting gas) is a synthetic non-condensable gas mixture (syngas) produced byoil shale thermal processing (pyrolysis). Although often referred to as shale gas, it differs from thenatural gas produced from shale, which is also known as shale gas.[1]
Oil shale gas is produced byretorting (pyrolysis) of oil shale. In the pyrolysis process, oil shale is heated until itskerogendecomposes intovapors of apetroleum-likecondensableshale oil, non-condensablecombustible oil shale gas, andspent shale—a solid residue.[2] The process is the same as theshale oil extraction and oil shale gas usually occurs as a byproduct of shale oil production. The ratio of oil shale gas toshale oil depends on retorting temperature and as a rule, increases by the rise of temperature.[2]
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 usuallymethane,hydrogen,carbon monoxide,carbon dioxide,nitrogen, and differenthydrocarbons likeethylene. It may also consist ofhydrogen sulfide and other impurities.[2][3]
Oil shale gas has served as a substitute fornatural gas.[4] In the 19th century and in the beginning of the 20th century oil shale gas was used as illuminating gas. In the 1920s, gas plants inTallinn andTartu produced oil shale gas as atown gas.[3] Since 1948, Estonian-produced oil shale gas was used inLeningrad and the cities in North Estonia.[5][6][7] For this purpose, 276 gas generators were operational inKohtla-Järve until 1987.[8]
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.[2]