Primary processing is the process of separating crude oil into light and heavy fractions by distillation, which is usually called crude oil distillation, including crude oil pretreatment, atmospheric distillation and vacuum distillation. Primary processed products can be roughly divided into: ① light distillate oil (see light oil), which refers to distillate oil with boiling point below 370℃, such as crude gasoline, crude kerosene and crude diesel oil. ② Heavy distillate oil (see heavy oil) refers to heavy distillate oil with a boiling point of about 370 ~ 540℃, such as heavy diesel oil, various lubricating oil fractions, cracking raw materials, etc. ③ Residual oil (also called residual oil). Traditionally, the bottom oil obtained by atmospheric distillation of crude oil is called heavy oil (also known as atmospheric residue, semi-residue, topping oil, etc.). ).

The second process is the reprocessing of the products from the first process. It mainly refers to the process of cracking heavy distillate oil and residual oil to produce light oil, including catalytic cracking, thermal cracking, petroleum coking, hydrocracking and so on. Among them, petroleum coking is essentially thermal cracking, but it is completely converted thermal cracking, and the products include petroleum coke in addition to light oil. Secondary processing sometimes includes catalytic reforming and petroleum product refining. The former is to change the molecular structure of gasoline to improve the octane number of gasoline or prepare light aromatic hydrocarbon (benzene, toluene and xylene); The latter is to refine various light oil products such as gasoline and diesel oil, or to make distillate lubricating oil from heavy distillate oil, or to make residual lubricating oil from residual oil.

Tertiary processing mainly refers to the process of further processing various gases produced by secondary processing (refinery gas processing) to produce high octane gasoline components and various chemicals, including petroleum hydrocarbon alkylation, olefin superposition, petroleum hydrocarbon isomerization and so on.

Crude oil processing flow is a combination of various processing processes, also known as the general flow of refinery. According to the nature of crude oil and market demand, the processing process that constitutes the refinery has different forms, which can be complex or simple. For example, crude oil processed in western European countries contains a lot of light components, while coal resources are few and heavy fuels are insufficient. Sometimes only atmospheric distillation and catalytic reforming of crude oil are used to obtain high octane gasoline and heavy oil (atmospheric residue), which is used as fuel oil. This treatment process is called shallow treatment. In order to make full use of crude oil resources and process heavy crude oil, countries tend to develop in the direction of deep processing, that is, using catalytic cracking, hydrocracking, petroleum coking and other processes to obtain more light oil products from crude oil.

In production, different processing processes also constitute a typical process of producing different types of products, including fuel, fuel lubricating oil and fuel chemical products (see refinery).