Hydroskimming is one of the simplest types of refinery used in the

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

industry and still represents a large proportion of refining facilities, particularly in developing countries. A hydroskimming refinery is defined as a refinery equipped with atmospheric

distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

, naphtha reforming and necessary treating processes. A hydroskimming refinery is therefore more complex than a ''topping refinery'' (which just separates the crude into its constituent petroleum products by distillation, known as atmospheric distillation, and produces naphtha but no gasoline) and it produces gasoline. The addition of catalytic reformer enables a hydroskimming refinery to generate higher octane reformate;

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...

, and

xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...

; and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

for hydrotreating units. However, a hydroskimming refinery produces a surplus of fuel with a relatively unattractive price and demand. Most refineries, therefore, add vacuum distillation and catalytic cracking, which adds one more level of complexity by reducing fuel oil by conversion to light distillates and middle distillates. A ''coking refinery'' adds further complexity to the cracking refinery by high conversion of fuel oil into distillates and petroleum coke. Catalytic cracking, coking and other such conversion units are referred to as secondary processing units. The

Nelson Complexity Index The Nelson complexity index (NCI) is a measure to compare the secondary conversion capacity of a petroleum refinery with the primary distillation capacity. The index provides an easy metric for quantifying and ranking the complexity of various re ...

, captures the proportion of the secondary conversion unit capacities relative to the primary distillation or topping capacity. The Nelson Complexity Index typically varies from about 2 for hydroskimming refineries, to about 5 for the Cracking refineries and over 9 for the Coking refineries.Info from

Reliance Industries Reliance Industries Limited is an Indian multinational conglomerate company, headquartered in Mumbai. It has diverse businesses including energy, petrochemicals, natural gas, retail, telecommunications, mass media, and textiles. Reliance is ...

Notes and references

Oil refineries {{technology-stub