Does crude oil need to be pretreated before entering the atmospheric distillation unit? If so, which pretreatment is required?

The atmospheric distillation unit is the first processing unit in a refinery, and its primary function is to separate crude oil into different fractions based on their boiling points. These fractions include gases, gasoline, naphtha, kerosene, diesel, and atmospheric gas oil, among others.

Crude oil is a mixture of hydrocarbons, and it contains various impurities such as water, salts, sulfur, and heavy metals. These impurities can cause problems in the atmospheric distillation unit and other downstream processes if not removed before entering the unit.

Feeding crude oil directly into the atmospheric distillation unit without pretreatment can lead to different issues, such as: 1. Corrosion of equipment due to the presence of salts (e.g., sodium chloride) and water. 2. Formation of undesirable compounds, such as hydrogen sulfide (H2S), due to sulfur-containing compounds and water having a negative impact on the process and product qualities. 3. Fouling and plugging of heat exchangers, pipes, and distillation trays due to the presence of heavy metals and other impurities. 4. Negative impact on catalyst performance in the downstream refinery processes.

Based on the issues mentioned above with untreated crude oil, the following pretreatment steps are required before crude oil enters the atmospheric distillation unit: 1. Desalting: The removal of salts (e.g., sodium chloride) and water from the crude oil using an electrostatic coalescer and wash water. 2. Dehydration: Reduction of the water content in the crude oil, usually achieved during the desalting process. 3. Degassing: Removal of dissolved gases (e.g., H2S) from the crude oil to prevent corrosion and improve process safety. 4. Preliminary treatment, such as sedimentation or filtration, may be applied to remove heavy solids and other impurities if necessary. In conclusion, crude oil must undergo a pretreatment process consisting of desalting, dehydration, and degassing before entering the atmospheric distillation unit to ensure efficient separation, prevent equipment corrosion, fouling, and plugging, and ensure the product's quality and the sustainability of downstream processes.