Sour gas
Encyclopedia
Sour gas is natural gas
or any other gas containing significant amounts of hydrogen sulfide
(H2S). Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm
by volume. On the other hand, natural gas
that does not contain significant amounts of hydrogen sulfide
is called "sweet gas."
Although the terms acid gas
and sour gas are sometimes used interchangeably, strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts, whereas an acid gas
is any gas that contains significant amounts of acid
ic gases such as carbon dioxide
(CO2) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being toxic, hydrogen sulfide in the presence of water also damages piping
and other equipment handling sour gas by sulfide stress cracking. Natural gas can contain several ppm of volatile sulfur compounds, but gas from some wells have been known to contain 90% hydrogen sulfide.
process. The removed H2S is most often subsequently converted to by-product elemental sulfur
in a Claus process
or it can be treated in a WSA Process unit where the by-product is sulfuric acid
. Alternatively, the highly H2S concentrated gas, the by-product of the amine treatment plant, can be recompressed by compressor units specifically designed to handle highly toxic gas and injected in the reservoir.
Within oil refineries or natural gas processing plants, the removal of organosulfur compounds
and hydrogen sulfide is referred to as "sweetening". The sweetened products lacks the sour, foul odors of mercaptans
and hydrogen sulfide. Another product removed in sweetening is carbonyl sulfide
.
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
or any other gas containing significant amounts of hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
(H2S). Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...
by volume. On the other hand, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
that does not contain significant amounts of hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
is called "sweet gas."
Although the terms acid gas
Acid gas
Acid gas is natural gas or any other gas mixture which contains significant amounts of hydrogen sulfide , carbon dioxide , or similar contaminants. The terms acid gas and sour gas are often incorrectly treated as synonyms...
and sour gas are sometimes used interchangeably, strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts, whereas an acid gas
Acid gas
Acid gas is natural gas or any other gas mixture which contains significant amounts of hydrogen sulfide , carbon dioxide , or similar contaminants. The terms acid gas and sour gas are often incorrectly treated as synonyms...
is any gas that contains significant amounts of acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
ic gases such as carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being toxic, hydrogen sulfide in the presence of water also damages piping
Piping
Within industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid....
and other equipment handling sour gas by sulfide stress cracking. Natural gas can contain several ppm of volatile sulfur compounds, but gas from some wells have been known to contain 90% hydrogen sulfide.
Methods for sweetening
Before a raw natural gas containing hydrogen sulfide or carbon dioxide can be used, the raw gas must be treated to remove those impurities to acceptable levels, commonly by an amine gas treatingAmine gas treating
Amine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines to remove hydrogen sulfide and carbon dioxide from gases...
process. The removed H2S is most often subsequently converted to by-product elemental sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
in a Claus process
Claus process
The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the scientist Carl Friedrich Claus, the Claus process has become the industry standard....
or it can be treated in a WSA Process unit where the by-product is sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. Alternatively, the highly H2S concentrated gas, the by-product of the amine treatment plant, can be recompressed by compressor units specifically designed to handle highly toxic gas and injected in the reservoir.
Within oil refineries or natural gas processing plants, the removal of organosulfur compounds
Organosulfur compounds
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odours, but many of the sweetest compounds known are organosulfur derivatives. Nature abounds with organosulfur compounds—sulfur is essential for life. Two of the 20 common amino acids are...
and hydrogen sulfide is referred to as "sweetening". The sweetened products lacks the sour, foul odors of mercaptans
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
and hydrogen sulfide. Another product removed in sweetening is carbonyl sulfide
Carbonyl sulfide
Carbonyl sulfide is the chemical compound with the formula OCS. Commonly written as COS, it is a colourless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom...
.
See also
- Natural gas processingNatural gas processingNatural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas.-Background:...
- Oil refineryOil refineryAn oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...
- RectisolRectisolRectisol is the trade name for an acid gas removal process that uses methanol as a solvent to separate acid gases such as hydrogen sulfide and carbon dioxide from valuable feed gas streams. By doing so, the feed gas is made more suitable for combustion and/or further processing...
- SelexolSelexolSelexol is the trade name for an acid gas removal solvent that can separate acid gases such as hydrogen sulfide and carbon dioxide from feed gas streams such as synthesis gas produced by gasification of coal, coke, or heavy hydrocarbon oils...
- WSA Process