Atmospheric and Vacuum Distillation

Atmospheric and Vacuum Distillation

1. Raw materials: Crude oil etc.

2. Products: Naphtha, gas oil, residual oil, asphalt, minus one line.

3. Basic concepts: Atmospheric and vacuum distillation is a combination of atmospheric distillation and vacuum distillation, which is basically a physical process: feedstock is divided into oils with different boiling point ranges (called fractions) according to the evaporation capacity in the distillation column, and some of these oils are blended. After adding additives, it leaves the factory in the form of products, and a considerable part is feedstock for subsequent processing devices.

Atmospheric and vacuum distillation is the first process of petroleum processing in refineries, which is called primary processing of crude oil, including three processes:

a. Desalting and dehydration of crude oil;

b. Atmospheric distillation;

c. Vacuum distillation.

4. Production process:

Crude oil generally contains salt and water, which can lead to corrosion of equipment. Therefore, before entering atmospheric pressure, crude oil is first subjected to desalination and dehydration pretreatment, usually adding demulsifier and water. The crude oil passes through the flow meter, the heat exchange part, and the distillation tower to form two parts. 

One part forms the top oil, passing through the cooler, the flow meter, and finally enters the tank area. This part is chemical light oil (called naphtha);

One part forms the bottom oil, and then passes through the heat exchange part, entering the atmospheric furnace and the atmospheric tower, forming three parts, one part diesel oil, one part wax oil, and one part tower bottom oil;

The remaining bottom oil is further processed through a vacuum furnace and a vacuum tower to generate reduced line, wax oil, residual oil and asphalt.

The respective yields: naphtha (light gasoline or chemical light oil) accounts for about 1%, diesel accounts for about 20%, wax oil accounts for about 30%, residual oil and asphalt account for about 42%, and minus one line accounts for about 5%.

The atmospheric and vacuum process does not produce gasoline products, in which the wax oil and residual oil enter the catalytic cracking process to produce gasoline, diesel, kerosene and other refined oils; The naphtha is directly sold by other small enterprises to produce solvent oil or enter the next step of deep processing. Generally, they will produce solvent oil or extract extractive compounds by catalytic reforming. Minus one line can be directly adjusted into lubricating oil.

5. Production equipment:

The atmospheric and vacuum unit is a distillation unit for primary processing of crude oil.

It is a processing device that fractionates crude oil into gasoline, kerosene, diesel oil, wax oil, residual oil and other components.

Crude distillation generally includes two parts: atmospheric distillation and vacuum distillation. 

a. Atmospheric distillation column

The so-called atmospheric distillation of crude oil is the distillation of crude oil at atmospheric pressure (or slightly higher than atmospheric pressure). The distillation equipment used is called crude oil atmospheric distillation column (or atmospheric column).

The heavy oil components left by atmospheric distillation have large molecular weight and high boiling point, and are easily decomposed at high temperature, which will deteriorate the distilled product and produce coke, destroying normal production. Therefore, in order to extract more light components, the boiling point range of the distilled feedstock oil is often reduced by reducing the distillation pressure. This distillation process under reduced pressure is called vacuum distillation. 

b. Vacuum distillation column

 Vacuum distillation is a distillation process carried out under a negative pressure state with a pressure lower than 100KPa.The core equipment of vacuum distillation is the vacuum column and its vacuum system.

The vacuum equipment of the decompression tower is usually a steam ejector (also called a steam suction jet pump) or a mechanical vacuum pump. Among them, mechanical vacuum pumps are only used in some dry vacuum distillation columns and vacuum columns in small oil refineries, while steam ejectors are widely used.