Natural gas can frequently contain a large number of different types of impurities. Sour gas is a type of natural gas that contains large amounts of hydrogen sulfide. Also known as H2S, hydrogen sulfide is dissolvable in water, which can lead to a number of problems. Such problems can include the formation of a type of acid that can be corrosive to meters, valves, pipes, and other equipment.
Typically, gas is considered to be sour if it contains more than 5.7 milligrams of hydrogen sulfide per cubic meter of natural gas. This is equivalent to about 4 ppm by volume. When natural gas does not contain any significant amount of H2S, it is known as sweet gas.
Therefore, H2S removal techniques are known as sweetening methods. Amine treatment processes are commonly used for such purposes. Once H2S is removed, it is typically converted to a by-product in a Claus process. In some instances, it may also be treated in a WSA Process unit in order to produce a sulfuric acid by-product. While sour gas can be problematic, proper sweetening processes can eliminate this impurity and make it easier and more profitable to bring natural gas to market.