Crude Oil low boiling fractions usually vaporize below 400°C at Atmospheric Pressure without Cracking the Hydrocarbon Compounds.

Therefore, all the Low Boiling Fractions of Crude Oil are separated by Atmospheric Distillation. A Crude Distillation Unit (CDU) consists of Pre-Flash Distillation Column. The vapors from the top of the column are a mixture of Hydrocarbon Gases (e.g., Methane, Ethane, Propane, Butane) and Naphtha vapors, at a Temperature of 120 °C - 130 °C. A few Plates below the Top Plate, the Kerosene is obtained as product at a Temperature of 190 °C - 200 °C. A few Plates below the Kerosene Draw Plate, the Diesel fraction is obtained at a Temperature of 280 °C - 300 °C. Residual oil present at the bottom of the Column is known as Reduced Crude Oil (RCO). The Temperature of the stream at the bottom is 340 °C - 350 °C, which is below the Cracking Temperature of Oil.