CFD SIMULATION OF A TWO STAGE MULTI-ENTRY CYCLONE OPERATED AT HIGH LOADING RATIOS

摘要

Demand for a short and exact contact time, a high catalyst/oil ratio in order to produce more light olefins and a reduction in dust emissions, has led to the NExCC process, which utilizes multi-entry cyclones (Figure 1). A multi-entry cyclone is more efficient than conventional cyclones in handling high catalyst loading ratios with low entrance velocities and a low pressure drop. The novel cyclone design enables deeper process unit integration in several applications. Catalyst attrition is the main reason for dust emissions. High velocities, especially in the feed nozzles and in the cyclones, tend to grind catalyst particles down into micron sized dust. Dust escaping from the catalyst regenerator into the atmosphere is one of the environmental problems associated with conventional FCC technology. Fortum Oyj developed multi-entry cyclone technology using cold and hot model tests. Novel CFD tools have been successfully utilized for designing and analyzing the multi-entry cyclones in different process development phases. This paper presents simulations carried out to test different designs of the two-stage multi-entry cyclone. The effects of both downward and upward gas outlet pipes on the operation of the multi-entry cyclone are presented. Also, the use of CFD in the development of attrition and erosion analysis is pointed out. The general differences in the performance between the multi-entry and conventional cyclones are shown.