In order to further fractionate the light components in the atmospheric heavy oil, the heavy oil at the bottom of the Atmospheric pressure column is heated by a Vacuum furnace and then sent to a vacuum distillation column for flash fractionation. The feed to the Vacuum Furnace is heavier than the Atmospheric Furnace, and the oil is heated to about 410 ℃. In the same Atmospheric and vacuum unit, the thermal load of the Vacuum furnace is approximately half that of the Atmospheric furnace.
The Vacuum furnace can be the same furnace type as the Atmospheric furnace. Due to its high heating temperature, heavy oil and easy coking,it is necessary to consider the facilities of air steam scorching, and the radiant furnace tube of chrome molybdenum is used near the exit.
The steam injected into the furnace tube promotes the vaporization of the oil, so that the volume of the medium in the tube becomes larger, the flow rate in the tube is accelerated, and the temperature of the tube is lowered to prevent thermal cracking of the oil and coking in the tube.