Abstract: The coking of butadiene in the bottom reboiler of depropanizer in a deep catalytic cracking (DCC-plus) unit in a company seriously affects the long-term operation of the unit. The comprehensive analysis shows that the high content of butadiene in LPG, the high reboiler heat source temperature, and the high content impurities such as oxygen and alkaline matter cause coking and fouling. By means of optimizing the separation process, transforming reboiler heat source, reducing impurities such as oxygen, strengthening system equipment passivation, injecting the inhibitor, the coking and scaling rates can be greatly reduced, to ensure the long period operation of the unit.

Key words: deep catalytic cracking, depropanizer, butadiene, coking, reboiler