Abstract: The top load of the main fractionating column is too small under low load conditions in fluid catalytic cracking unit, resulting in lower oil and gas partial pressure and higher water vapor pressure; and the water vapor is easy to liquefy due to uneven heat transfer, resulting in salt deposition on the top tray and top circulation system of the column. In order to increase the top load of the main fractionating column, crude gasoline was introduced into the riser via the quench oil line. The operation results showed that this measure not only inhibited salt deposition in the column, but also improved product distribution.

Key words: fluid catalytic cracking, low load, salt deposition, crude gasoline, quenching oil, product distribution