contaminated gas

Contaminated gas

All gas comes out of the ground contaminated to an extent. This can be easily dealt with if the level of contamination is low. If the contamination is higher then it gets more difficult. Around one-third of the world’s gas fields are highly contaminated.

Sweet and sour
In the past Shell mainly developed gas fields with low level contamination, but there are fewer of these fields left, so increasingly we are needing to develop the fields with the more highly contaminated gas. Usually the gas is contaminated by H2S (hydrogen sulphide), and CO2, and is known as ‘sour gas’. In addition, sour gas may be contaminated by other sulphur compounds such as COS (carbonyl sulphide), mercaptans and organic sulphides/disulphides. The challenge is redcung the level of contaminants to make the gas ‘sweet’.

The sulphur content makes sour gas highly poisonous, which causes iron to corrode, causing equipment like valves and flow lines to malfunction. Extracting and processing this gas requires sophisticated technology at every point in the production process, and is something our researchers are focused on developing new technologies in. These include technologies such as ADIP, Sulfinol, and SCOT (Shell Claus Off-gas Treating).

The ADIP process removes H2S and CO2 from gas streams. It can also be applied to remove H2S and COS (carbonyl sulphide) from liquefied petroleum gas (LPG) or natural gas liquids (NGL). The ADIP process uses a solvent which is a mixture of water and an amine. The Sulfinol process removes the same compounds as ADIP, but unlike ADIP it also removes organic compounds from the gas. The Sulfinol solvent consists of a mixture of water, amine and sulfolane and is used when the gas contains higher than usual levels of organic contamination.

Acid gas containing H2S from an ADIP or Sulfinol unit is typically being sent to a Claus unit in which about 95% of the H2S is converted into elemental sulphur (the remaining 5% ends up in the atmosphere as SO2). By putting a SCOT unit behind the Claus unit the sulphur recovery efficiency can be further enhanced to levels over 99.8%, which helps to meet the most stringent environmental specifications.

Shell has over 50 years experience of safe contaminated gas activities with operational experience of some 25 significantly contaminated gas fields. We are also one of the world’s leading sulphur traders. Our challenge is to ensure we continue to find ways to recover sour gas, and to utilize and contain the H2S, CO2 and other sulphur compounds that contaminate it.