There are generally three categories of technological processes of atmospheric and vacuum distillation units:

1) Electric desalination---atmospheric pressure tower---decompression tower

2) Electric desalination---flash tower---atmospheric pressure tower---decompression tower

The advantages are that the load of the heating furnace is low, the recovery rate of light hydrocarbons is high, and the one-time investment is relatively low.

3) Electric desalination---preliminary distillation tower---atmospheric pressure tower---decompression tower

The advantages are that it can pre-dehydrate, remove hydrogen sulfide, prevent atmospheric towers from being overrun, etc., and the operation is also more flexible, and can share the load of atmospheric towers; the disadvantages are that the process is more complicated and the investment is high (setting up light hydrocarbon recovery can save part of the investment), The arsenic content of the initial naphtha was higher.

Electrodesalination

Conventional electric desalination systems usually only design first-level electric desalination tanks. However, with the rapid decline of global crude oil production, if the production of crude oil is to be increased, a large amount of auxiliary agents are required for extraction, which increases the salt content in crude oil. . Affected by this, most newly designed atmospheric and vacuum distillation units have to use two-stage electric desalination tanks to reduce the salt content of processed crude oil. The main factors affecting the operation of electric desalination are the choice of demulsifier, the control of crude oil residence time, the control of water injection, temperature and pressure, etc.

Preliminary distillation column

After the crude oil passes through the electric desalination system, it passes through the heat exchanger for heat exchange and enters the initial distillation tower. Part of the naphtha extracted from the top of the tower is cooled and separated, and the light naphtha is used as the chemical raw material, and the heavy naphtha is used as the reforming raw material. The bottom part of the tower continues to pass through the heat exchanger, and then enters the atmospheric furnace for heating and heating, and then is sent to the atmospheric tower for fraction cutting and separation. The main products of the initial distillation tower are light naphtha, heavy naphtha, and initial top gas (recovery of light hydrocarbons).

Atmospheric pressure tower

The bottom oil of the initial distillation tower is heated to 360-380 ° C through heat exchange and heating furnace, and enters the atmospheric tower for cutting and separation. The general atmospheric tower is equipped with three middle-stage refluxes, which are the normal top oil circulation, the normal one-middle circulation, and the normal two-middle circulation.

The main products of the atmospheric tower are constant top gas, constant top oil (naphtha), constant first line (jet fuel), constant second and third line (diesel) and constant bottom oil (wax oil and residual oil mixture, such as North Refinery) The plant processing light crude oil can directly enter the catalytic cracking unit, such as Changqing Petrochemical).

Decompression tower

After the normal bottom oil is boosted by the normal bottom oil pump, it enters the decompression furnace and is heated to 380-410°C, and then enters the decompression tower for cutting and separation. The general decompression and pressure tower is equipped with three mid-section reflux, which are minus one-line circulation, minus two-line circulation, minus three-line circulation. The main products of the vacuum tower are reduced overhead gas, reduced overhead oil and reduced first line (diesel), reduced second and third lines (wax oil), and vacuum residue (also known as asphalt).