Distillation in the oil & gas industry

After desalting, the crude oil is further heated to around 375oC in a furnace. From here it flows into the bottom of an atmospheric distillation column, actually at slightly above atmospheric pressure. As the oil vapours rise up the column and cool, various fractions with different boiling temperatures condense into liquids, and are removed from the side of the column. These liquid fractions are known as sidecuts, and include naphtha, kerosene, light gas oil etc, as shown on the diagram. The liquids are cooled and process efficiency improved by exchanging their heat with the incoming oil feedstock. The gas remaining at the top of the column comprises the lightest fractions of the crude oil, those with the lowest boiling points. Typically the distillation column will be run in a continuous steady state, controlled by crude oil distillation instrumentation: here flow measurement and the consequent balancing of the fractions is important for control.

The residual oil that comes out of the bottom of this column, the ‘atmospheric bottoms’, has a boiling point above 375oC, and is fed into the subsequent vacuum distillation column. The vacuum conditions effectively lower the boiling points for these heavy fractions, avoiding any further increase in temperature, which could cause plugging, due to coke formation.

KROHNE has a range of atmospheric and vacuum distillation measurement solutions suitable for these harsh conditions. Special high temperature ultrasonic and Coriolis flowmeters and distillation column level transmitters have been developed for this duty. In addition KROHNE manufactures gas vortex and variable area flowmeters that are used for fuel gas, off gas and gas injection flow measurement and control.