Atmospheric and vacuum distillation unit is the general name of two devices, atmospheric distillation and vacuum distillation, because the two devices are usually together, so they are called atmospheric and vacuum distillation units. It mainly consists of three processes: desalting and dehydration of crude oil, atmospheric distillation and vacuum distillation. The crude oil sent from the oil field to the refinery often contains salt (mainly oxide) with water (dissolved in oil or emulsified), which can cause corrosion of the equipment, scale the inner wall of the equipment and affect the composition of the finished oil, and it needs to be removed before processing.