Atmospheric and vacuum distillation unit is the basic unit of oil refining enterprises, the first working procedure of crude oil processing, and plays a very important role in oil refining. Its technological process is the process of separating crude oil into oil products or semi-finished products with different boiling points by heating distillation and repeated condensation and vaporization. The main separated products are: reforming raw materials, gasoline components, aviation kerosene, diesel oil, secondary processing raw materials (lubricating oil, catalytic cracking raw materials, etc. ) and residual oil (reforming and coking, asphalt raw materials).

In the atmospheric tower, crude oil is rectified, so that the heat exchange and mass exchange between gas and liquid can be fully realized. Under the conditions that reflux is provided at the top of the tower and the bottom of the tower is purged, gasoline with lower boiling point is fractionated from the top of the tower, and heavy oil with higher boiling point is fractionated from the bottom of the tower, and by-products are kerosene, diesel oil, heavy wood and wax oil. , is extracted from the middle of the tower. The residual heavy oil components after atmospheric distillation have large molecular weight and are easy to decompose at high temperature. In order to separate various high boiling point lubricating oil components from atmospheric heavy oil, vacuum distillation was used in vacuum tower. The heated atmospheric heavy oil is fractionated under negative pressure, so that the high-boiling components are distilled out in turn at the corresponding temperature to become lubricating oil. Many technical measures are often adopted in vacuum distillation of atmospheric and vacuum distillation unit, such as crude oil transfer line, large tower diameter, high efficiency structured packing (GEMPAK) and so on. Realize low furnace temperature, high vacuum, narrow fraction and light color decompression operation, and improve the quality of lubricating oil.

Second, the control scheme

Atmospheric and vacuum distillation units are usually dominated by traditional single-loop control, supplemented by some complex controls, such as cascade, uniformity and switching.

1. Differential pressure adjustment of desalting tank, fixed value control of water injection flow and fixed value control of drainage flow in electric desalting part.

2. Initial distillation section

★ Tower top temperature control: control the tower top temperature by adjusting the amount of reflux oil at the tower top, automatically record the reflux flow and observe the reflux change.

★ Liquid level control at the bottom of the tower: differential pressure level gauge is used at the bottom of the primary distillation tower, and indoor indication and acousto-optic alarm are provided at the same time to prevent the flushing tower or the bottom pump from being evacuated.

★ Tower top pressure control: In order to ensure the fractionation effect of the fractionating tower, a pressure transmitter is generally installed at the tower top and monitored and recorded indoors.

★ Control of liquid level and boundary of reflux tank: the reflux tank is equipped with an automatic liquid level regulator to control the flow of the oil outlet device at the top of the tower to ensure full reflux; At the same time, the oil-water interface is kept constant through the interface regulator (the regulator is installed on the drain pipe).

★ Control of steam side tower: In order to reduce the load of atmospheric furnace and improve throughput, a steam side tower is added beside the primary distillation tower. The liquid level of the steam side tower needs to be automatically controlled (the regulating valve is installed on the distillation outlet of the primary distillation tower), and a flow regulator is equipped to control the flow into the atmospheric tower.

3. Atmospheric pressure part

Key control:

★ Feed flow control of the heating furnace: In order to keep the outlet temperature of the atmospheric heating furnace, four feed lines of the heating furnace are equipped with flow regulators to adjust the flow of the heating furnace.

★ Outlet temperature control of heating furnace: the outlet temperature of atmospheric heating furnace is kept constant by adjusting the amount of fuel oil and fuel gas (fuel gas can be switched between low-pressure gas fuel gas, self-produced gas fuel gas and high-pressure gas fuel gas).

★ Atmospheric tower top outlet temperature control: keep the atmospheric tower top outlet temperature constant by adjusting the reflux into the tower; If the atmospheric first line is a plan to produce aviation kerosene, the atmospheric first line temperature can be used to control the reflux flow into the tower and record the reflux flow.

★ Control of liquid level and battery limit of reflux tank: In order to ensure the amount of reflux oil at the atmospheric tower top, a liquid level regulator is installed at the upper part of reflux tank to adjust the amount of gasoline discharged from the atmospheric tower top. An interface regulator is installed below it to maintain a certain oil-water interface (the regulator is installed on the drainage pipeline).

★ Pressure adjustment of atmospheric tower: generally, a pressure transmitter is installed indoors and recorded for reference when controlling product quality; A pressure regulator can also be installed in the reflux tank to adjust the amount of gas released.

★ Adjustment of the liquid level at the bottom of atmospheric tower: In order to ensure the stability of the liquid level at the bottom of atmospheric tower, the feed pumps of the washing tower and vacuum heating furnace are in the tower without evacuation.

The bottom is equipped with differential pressure liquid level transmitter, liquid level record and acousto-optic alarm to facilitate accident analysis. In order to save energy, some devices have a frequency converter at the bottom of the tower, and the liquid level at the bottom of the tower is controlled by switching between the regulating valve and the frequency converter.

★ Adjustment of liquid level and flow rate of stripper: In order to control the quality of side-line products, automatic liquid level regulators are installed in each side-line stripper of atmospheric tower to adjust the oil quantity from the distillation outlet of atmospheric tower to the side-line stripper. When the finished product of each side line leaves the device, there is a flow regulator, which is installed on the outlet pipeline of each fraction extraction pump.

4. Decompression part

Key control:

★ Temperature adjustment at the top of vacuum tower: In order to ensure a certain temperature at the top of vacuum tower and avoid oil and gas loss, a temperature regulator is installed on the outlet pipeline of the top of the tower to adjust the amount of reflux oil at the top of the tower.

★ Tower top product flow regulation: In order to improve the light oil yield, a flow regulator is set on the pipeline of the tower top light oil outlet device. The vacuum pipeline is also equipped with a temperature regulator to control the oil return. The flow regulator is also installed on the pipeline of the vacuum pipeline outlet device.

★ Side-line reflux flow adjustment: In order to take away the heat of the vacuum tower and ensure the quality of side-line products, there are two-line and three-line reflux reduction devices. At the same time, in order to ensure a certain return flow, a flow regulator is installed on the oil return pipe after entering the tower.

★ Liquid level adjustment at the bottom of vacuum tower: In order to ensure the stability of liquid level at the bottom of vacuum tower, a liquid level regulator is set at the bottom of vacuum tower to adjust the oil quantity of residual oil at the bottom of vacuum tower. In order to save energy, some devices have a frequency converter at the bottom of the tower, and the liquid level at the bottom of the tower is controlled by switching between the regulating valve and the frequency converter.

★ Record of vacuum degree at the top of the vacuum tower: In order to ensure the fractionation effect of the vacuum tower, a vacuum pressure transmitter is installed at the top of the vacuum tower to record the vacuum degree of the vacuum tower.