Improved high efficiency third stage separator cyclones for separation of fines from FCC flue gas

摘要

Stairmand type small diameter (0.254 m) multicyclones were cold flow tested for fluid catalytic cracking third stage separator application. The Stairmand cyclones were less efficient in horizontal orientation (versus vertical), suggestingresistance to "uphill" travel by solids at the cyclone outlet. The gas discharge from the cyclone dust outlets into the common collection hopper was found to far exceed the hopper bleed rate (underflow). The discharged gas reentered the cyclone, carryingreentrained dust and lowering collection efficiencies. Vortex "stabilization" using apex cones was unsuccessful whereas a Mobil proprietary cyclone modification was successful in minimizing excess gas discharge and dust reentrainment at the cyclone-hopper boundary. In tests at 700°C, the modified cyclones captured all particles above 4μm. Mobil-Kellogg incorporated the modified cyclones in a new third stage separator design which is targeted for achieving lowest opacity and <50 mg/Nm{sup}3 emissions atthe stack. The first such unit will be commercialized in Mobil's newest catalytic cracker (M.W.Kellogg design) under construction in Altona, Australia in early 1997.