How does the refinery work?

Refineries use appropriate extraction methods and chemical reactions to convert crude oil into products with commercial value, which can be made into various valuable fuels and lubricants, and can also produce many downstream chemical raw materials. The basic function of an oil refinery is batch processing. In this process, crude oil is distilled and converted into various fractions, from the lightest liquefied petroleum gas to naphtha with different densities, to the heaviest fraction of asphalt and residual oil. Distilled fractions are further processed and upgraded to petroleum products with great commercial value, such as hydrodesulfurization to produce fuel with little sulfur content, and cracking technology to produce lighter gasoline, diesel oil and kerosene. In petroleum products, this part accounts for a large proportion, and the octane number of gasoline can be improved by improving technology. The model of a refinery depends on the density range of crude oil it processes and the structure of the designed final product. The environmental protection law prohibits factories from discharging harmful substances, and the improvement of fuel composition promotes the upgrading of factories and sets new standards for newly-built refineries.

Although "light and sweet" (low viscosity and low sulfur content) oil can be directly used as fuel for heating steam boilers, on the whole, unprocessed crude oil mined from underground is useless. Lighter components can form explosive vapor in the fuel tank, so it is very dangerous. For other purposes, it is necessary to divide oil into different components, such as fuel oil and lubricating oil. In addition to fuel oil and lubricating oil, some by-products can be obtained, such as plastic, fuel, solvent, synthetic rubber, nylon and polyester fiber (polyester) and other chemical fiber products. As a fossil fuel, petroleum can be used in ships, automobiles and aero-engines. Different hydrocarbons have different boiling points, which means that they can be separated by distillation. Due to the huge demand for lighter liquid components that can be used in internal combustion engines, modern refineries can convert heavy hydrocarbons and heavier gas components into lighter and more valuable products through complex processing technologies.

The following figure is the flow chart of a standard refinery, showing the flow chart of conversion between crude oil input and final product. The figure only abstractly represents hundreds of refineries of a certain type, and does not include the auxiliary equipment of refineries, such as steam production, cooling water, power guarantee system, crude oil batching tanks, intermediate products and final products. The actual refinery composition is far more than that shown in this figure. For example, distillate oil produced by vacuum distillation unit can be processed into lubricating oil, such as spindle oil, light mechanical oil, engine oil and cylinder oil used in textile industry. In the coke tower, the residue can be processed into petroleum coke.

Legend of the whole oil refining process in the standard oil refining flow chart-from the injection of crude oil to the end of the final product. Source: Shell and Total, 2008.

Petroleum refining begins with distillation, which divides oil into different hydrocarbon components (about 84% of crude oil is carbon).

"Refining is a magical process. Refined petrochemical products have been stored in refineries before being transported to natural gas stations, airports and chemical plants. In addition, in order to produce petroleum-related products on the spot, the refinery must also treat the waste generated in the refining process with the minimum air and water pollution costs. "

Generally speaking, crude oil is composed of the following elements or chemical components. Source: Total and Shell Companies, 2008.

Carbon: 84% hydrogen: 14%

Sulfur (hydride, sulfate, disulfide and elemental sulfur): 1% ~ 3% nitrogen: < 1%.

Oxygen (existing in organic components, such as carbon dioxide, phenol, ketone and carboxylic acid): < 1%.

Metals (nickel, iron, vanadium, copper): < 1%

Salts (sodium chloride, magnesium chloride and calcium chloride): < 1%

The final product of oil refining is directly related to the composition characteristics of crude oil. Most distillation products are deeply processed by cracking, upgrading and other conversion measures, which changes the size and structure of hydrocarbon molecules and thus transforms them into more useful products. Then, these conversion products are separated from the lightest to the heaviest through various processing and separation treatments. Such as extraction, hydrogenation and desulfurization, to remove unwanted components and improve product quality. But comprehensive refining, transformation, processing, modulation combined with fractionation are also petrochemical processing technologies.