Abstract: It is one of the most important hidden troubles to threaten the long-term stable operation of catalytic cracking unit that the coke blocks on the outer wall of the vortex finder of the cyclone separator on the top of the settler (top-cyclone). To solve this problem, a new prevention and cure scheme was put forward, which was to set up a network coke trap in the ash bucket of the top cyclone to intercept the large coke falling off and avoid the clogging of the dipleg. The separation efficiency, pressure drop and flow field changes of the cyclone separator with different structures of the ash bucket were investigated in a comparative study with the methods of experiment and numerical simulation. The results showed that the pressure drop of the cyclone separator was not obvious, but the separation efficiency dropped about 0.21~0.91 percentage point after adding coke trap and intercepting coke block in the ash bucket. The maximum tangential velocity of the fluid in the separation space and ash bucket decreased by 0.4% and 41.2%, respectively. At the same time, the upward region of the axial inner swirl increased, resulting in the increase of particle entailing, the increase of particle backmixing escape rate and the decrease of separation efficiency. Increasing the height of the ash bucket can reduce the escape rate and entrainment of particles, restore or even improve the separation efficiency. So, it can be realized to prevent and control the hidden danger of coke blocking the dipleg by installing a coke trap and increasing the height of ash bucket.

Key words: cyclone separator, coke blocks, coke trap, separation efficiency, pressure drop, flow field