The top cyclone separator is important for second separation of oil vapor and catalyst in FCC disengager, but during the separate process relatively low-temperature oil drip and scrappy catalyst is frequently carried to the outer wall of vortex finder, part of them can be scoured by the gas stream, part of them will be deposited on the outer wall of the vortex finder.As time goes on, the latter is gradually converted to coke and the thickness of the coking matter grows accumulatively.Fig.1 is the illustration of the coking deposit on the outer wall of vortex finder of a top cyclone separator.