Large cold-model experiment on heat transfer and hydrodynamics of an FCC external catalyst cooler

In order to obtain deeper insights on the heat transfer properties and hydrodynamics of FCC external catalyst cooler, a large cold fluidized-bed model (φ500 mm×3.0 m) with 9 vertical finned heat exchange tubes was established. With a similar heat transfer mechanism adopted in commercial units, the heat transfer coefficient changes of heat exchange tube was measured and analyzed based on the bed density changes along axial and radial direction. The experimental results indicated that, as superficial gas velocity increased, the heat transfer coefficient first increased and then decreased at 0.4 m/s, which is related to the flow regime transition from bubbling to turbulent regime. In industrial design, the predicted onset turbulent velocity can be adopted as the optimum operating gas velocity. Due to stronger bubble and particle movement, the heat transfer coefficient of heat exchange tube in the central bed was higher than that in the side bed, which agreed with the measured radial bed density profiles. As heat transfer coefficient decreased monotonously with the decrease of bed height, changing bed height can be an effective measure to change the heat removal load of an industrial external catalyst cooler.