Abstract: Based on the Reynolds Stress Model, the three-dimensional gas-phase flow fields of two kinds of the fourth stage separation systems in FCCU were simulated. The characteristics of gas flow fields in the two systems were especially analyzed. The results show that in the material storage tank of the traditional structure, the gas flows upward at some areas, which is not conducive to particle sedimentation. Reverse flow exists in the dipleg. Bias flow happens in the cyclone separator, by which particle transportation is affected. The unreasonable structure design is the main reason for particle plugging. However, in the improved one, the air flow is relatively slow, favorable to particle sedimentation. In the dipleg, the pneumatic transportation is influenced by the periodic secondary vortex that can wear the wall. The flow field in the cyclone separator is stable enough for particle separation. Particle plugging can be avoided effectively in the improved structure. The comparison of the gas flow field in the two structures provides valuable guidance for designing efficient fourth stage separation system.

Key words: FCCU, the fourth stage separation system, gas flow field, numerical simulation