Abstract: The composition and crystal phase of the scaling sample of FCC expander was characterized. Based on the results, the formation condition of scaling was analyzed and checked by calculating. The cause and precaution measures were thus proposed. The scaling procedure is as follows: Very few drops of raw oil was not fully vaporized but deposited on the catalyst to become coke；few coke solids entered the flue,the combustion continues to reach the melting temperature of fine coke powder, which was converted into liquid viscous substance; the smoke with trace high-temperature molten dust is subjected to high-speed centrifugation at the three-screw feeding mouth, the blade of the smoke expander and other parts, and adheres to the parts that are easy to form scale, forming unshaped scale. Scaling of expander could be reduced by improving atomization effect of feed oil nozzle, adjusting appropriate ratio of catalyst to oil and fine powder content in the reaction-regeneration system.

Key words: catalytic cracking, flue gas expander, scaling, melting