The so-called atmospheric distillation of crude oil refers to the distillation of crude oil under the condition of constant pressure (or higher than constant pressure). The distillation equipment used is called crude oil atmospheric distillation tower (referred to as atmospheric tower). As the raw material and product of the crude oil atmospheric distillation tower are different from the ordinary rectification tower, it has the following technological characteristics:

1. The raw material and product of the atmospheric tower are mixture of complex composition

Crude oil is obtained through the atmospheric distillation of gasoline, kerosene, diesel and other light distillate and atmospheric heavy oil. These products are different from the general distillation tower products, and they are also complex mixtures. The quality is controlled by some quality standards. Fractionation accuracy requirements for each product are not very high, which means that the precise separation of crude oil, a complex mixture, is not required.

2. Atmospheric tower is a composite tower structure

The general waste oil distillation tower usually uses one tower only to get two products from the top of the tower and the bottom of the tower. While the crude oil distillation tower open a number of lines in the side of the tower to get a number of products, which likes a few towers stacked together, so they are called compound tower or complex tower.

3. The lower part of the atmospheric tower with stripping section, and the measuring line product with stripping tower

Above the gasification section of the general distillation tower is called rectification section and a part of the products in the top tower after cooling and condensing return to the tower top as liquid reflux; under the feed section is called stripping section and a part of the bottom products is vaporized by the reboiler and then return to the bottom of the column as a vapor phase reflux.

4. Atmospheric tower is often equipped with middle loop reflux

In the crude oil distillation tower, in addition to the use of top tower reflux, it is usually equipped with one or two middle loop refluxes, that is, a portion of the liquid phase hot oil ( or line products) was withdrawn from the upper part of the rectifier distillation section. After exchanging heat with other cold flow or cooling, it returns to the tower. The return port is usually 2-3 layers higher than the extraction port.

The function of the middle loop reflux is to remove the excess heat in the distillation tower under the premise of ensuring separation effect of every part. The advantages of adopting middle circulation flow are: it can reduce the tower diameter under the same treatment capacity or it can improve the treatment capacity of the tower under the same tower diameter; it also recycle the heat source with higher temperature.