Natural gas is an important fuel source and potent greenhouse gas. It's found mostly associated with other fossil fuel like in coal beds in the form of methane clathrates. It mainly contain methane with 0-20% hydrocarbons. It is also created in bogs, marshes and landfills by methanogenic organisms.
Natural gas is a good source of sulphur. It contains different sulphur compounds which are removed before the processing of gas to use it as fuel. By products of this processing include- elemental sulphur, water vapor, hydrocarbons, carbon dioxide, ethane, butanes, pentanes, propane etc. Also sometimes they contain helium and nitrogen.
The sulphur compounds found in natural gas includes- sulphur, Tetrahydrothiophene (THT), Hydrogen Sulfide (H2S), Dimethyl Sulfide (DMS), Tertiary Butyl Mercaptan (TBM), Methyl Mercaptan (MTM), Normal Propyl Mercaptan, Isopropyl Mercaptan (IPM), Ethyl Mercaptan (ETM) etc.
There are various unit processes followed in processing of natural gas. A general diagram showing complete processing of natural gas into sales gas pipelines to the market of end user, is given below-
First, raw natural gas is acquired from the wells of oil and gas, and processed to remove the water from it. Thereafter gas condensate collected is sent to oil refinery. Raw gas is transported through pipelines to gas processing plants, where acid gases are removed from it like hydrogen sulfide. Amine treating, benfield process, sulfinol process are acid removal processes mostly used. After treatment through such processes acid gas is moved to sulphur recovery unit where hydrogen sulfide contained in acid gas, converted either into sulphuric acid or elemental sulphur. Clause process is the most well known process used for recovery of sulphur. For recovering sulphur acid, WSA process and Contact processes are mainly used.
After recovering of sulphur, remaining gas which is called tail gas is moved to tail gas treatment unit. Here, residual sulphur containing compounds are recovered and recycled to the Claus unit.