Sour gas is a term used to refer to gas which contains hydrogen sulfide in concentrations greater than four parts per million. The term “sour gas” is usually used with reference to natural gas, although it can be used to discuss other gases as well. Gas with impurities such as hydrogen sulfide needs to be treated before it can be safely used. The gas refining process includes a step known as “sweetening” to remove hydrogen sulfide and other materials.
When natural gas is initially accessed in the field, it usually contains an assortment of impurities, which can depend on where natural gas drilling sites are located. These impurities must be removed at a refinery to ensure that the gas performs in a stable and predictable way when it is used. In the case of sour gas, the hydrogen sulfide gives the gas a distinctively strong odour which makes it easy to identify, and the sweetening process removes much of the odour.
As sour gas is drilled and transported to a refinery for processing, care must be taken, because the hydrogen sulfide can be corrosive. Specialized pipes and equipment are needed to avoid adverse reactions during transport which could pose a safety risk. Once sour gas arrives at the refinery, it can be put through a series of processes to sweeten it. Typically, hydrogen sulfide isn’t the only impurity in the gas, with sour gas often containing carbon dioxide as well.