Abstract: The causes of catalyst deposits in flue gas expander of a 3.5 Mt/a RFCC unit were analyzed. It was found that with the increase of catalyst fines in flue gas, heavy deposition of catalyst in cyclone separation system and flue gas expander could be happened. In order to avoid increasing catalyst fines in flue gas, keeping the catalyst discharge of cyclones in good conditions, evading overloading and keeping balance loading of individual pipe for the third cyclone separator were essential. By optimizing the design of cyclone separator to smoothly discharge of catalyst and to increase the recovery rate of catalyst fines, the flue gas expander was kept running in good conditions for three years. Besides, some monitoring and control measures in daily operation were also introduced.

Key words: catalytic cracking, cyclone separator, flue gas expander, deposit, particle size distribution