Downstream (petroleum industry)
The oil and gas industry is usually divided into three major sectors: upstream, midstream and downstream. The downstream sector commonly refers to the refining of petroleum crude oil and the processing and purifying of raw natural gas, as well as the marketing and distribution of products derived from crude oil and natural gas. The downstream sector reaches consumers through products such as gasoline or petrol, kerosene, jet fuel, diesel oil, heating oil, fuel oils, lubricants, waxes, asphalt, natural gas, and liquefied petroleum gas (LPG) as well as hundreds of petrochemicals.
Midstream operations are often included in the downstream category and considered to be a part of the downstream sector.
Crude oil is a mixture of many varieties of hydrocarbons and most usually have many sulphur-containing compounds. The oil refining process commonly includes hydrodesulphurization which converts most of that sulphur into gaseous hydrogen sulphide. Raw natural gas also may contain gaseous hydrogen sulphide and sulphur-containing mercaptans, which are removed in natural gas processing plants before the gas is distributed to consumers.
The hydrogen sulphide removed in the refining and processing of crude oil and natural gas is subsequently converted into byproduct elemental sulphur. In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulphur from refineries and natural gas processing plants.