Measurement of dynamic forces in fluidized bed systems

Conference Dates

May 22-27, 2016


The internals in fluidized bed systems such as heat exchanger tube bundles and baffles trays are subject to dynamic buffeting forces caused by rising bubbles and particle motion. Understanding the nature of these forces are industrially important in the structural design since excessive vibrations in tubes can eventually lead to their failure. To quantify these forces, a piezoelectric force sensor, which has a high response time and a constant sensitivity over a wide range of temperatures and pressures was mounted in a 2-D fluidized bed (12-in X 1-in) containing fluid catalytic cracking catalyst and glass beads for a visual depiction of the phenomenon where a single bubble was injected at a certain time interval. The motion of the bubble was synchronized in real time with the response from the initial thrust of the bed, the bubble roof and the bubble wake as shown in Figure 1. Tests were also done to quantify the forces during the startup of the bed and due to subsequent fluidization. The glass beads, which were bigger in size, moving with a greater momentum, generated greater force when they came in contact with the base of the sensor. There were also a couple of events, which produced enormous dynamic forces, close to 25 psi at the center of the bed. The magnitude of these forces and pockets of bed which are unstable due to excessive vibrations caused by fast moving bubbles are important in the design of fluidized bed systems to mitigate internal structural damage.

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