Comparison Of Flash Column Scheme And Initial Distillation Scheme

1. There are several schemes in the process design of atmospheric and vacuum distillation unit:
(1) Conventional electric desalting → atmospheric tower → vacuum tower process.
(2) Electric desalting → flash tower → atmospheric tower → vacuum tower process.
(3) Electric desalting → primary distillation tower → atmospheric tower → vacuum tower process.

In order to recover light hydrocarbon, after the atmospheric and vacuum distillation process, the process is divided into compressor scheme and primary distillation tower pressurization scheme (without compressor scheme).

2. Scheme comparison
The first is the pressurization scheme of the primary distillation tower, which is the process of electric desalting → primary distillation tower → atmospheric tower → stabilizer, and the operating pressure of the primary distillation tower is 0.2MPa, so the compressor in front of the stabilizer is canceled.
c4 flash column chromatography
The second is the flash column scheme, which is set with the flash column, that is, the process of electric desalting → flash column → atmospheric tower → pressure reducing tower → stabilizer. The flash tower is operated under atmospheric pressure, and a compressor is set in front of the stabilizer.

In order to increase the adaptability and flexibility of the unit, especially the adaptability of the unit to sulfur-containing light oil, there are basically two options for the atmospheric and vacuum distillation process. One is to use the pressure lifting scheme of the primary distillation tower to make the light hydrocarbon in the crude oil dissolve in the primary top oil as much as possible under the condition of slight pressure. The primary top oil is pumped to the stabilization tower to recover the light hydrocarbon.

The advantage of this scheme is that there is no compressor in the whole process, which reduces the amount of mechanical maintenance, but this scheme also has its disadvantages.

For example, a small part of light hydrocarbon will be taken to the flash column to lose from the overhead gas, and a complete set of reflux cooling system will be added to the initial top, which makes the process more complex.

Second, the flash tower is adopted. In this scheme, the light components of crude oil flash out of the flash tower and enter a suitable part of the atmospheric tower, making the heat exchange of flash bottom oil more reasonable, reducing the material flow into the atmospheric furnace to save energy, adding a compressor on the top of the atmospheric tower to compress and boost the overhead non condensable gas, and the overhead oil uses the pump to boost and the overhead gas after boosting to recover light hydrocarbon in the stabilization tower, Due to high pressure, the non condensable gas on the top of the stabilizer can be sent to the desulfurization system of the whole plant for desulfurization treatment.

The advantage of this scheme is that the flash tower is adopted, the process is simple, the non condensable gas of the unit can be desulfurized, and the environment can be protected. The disadvantage of this scheme is that the compressor needs to be set, and the maintenance is a little difficult. It is understood that at present, most of the foreign processing of high sulfur light crude oil adopts flash tank and constant top gas compressor scheme. The comparison of this project’s plans focuses on the advantages and disadvantages of these two plans.