Particle motion at fluidized bed tube surfaces

Abstract

Metal loss from in-bed heat transfer tubes in fluidized bed combustors is recognized as a problem that is affecting the commercialization of FBC technology for coal utilization. A program has been initiated to address the erosion aspect of the wastage problem. Objectives were: (1) to develop a method for measuring the particle impact velocities and mass flux at a fluidized bed tube surface, (2) to obtain wear data from test tubes in an operating cold flow model, and (3) to correlate the results. An instrumented probe was develop during Phase I that could be used to obtain the three orthogonal velocity components and mass flux at a fluidized bed tube surface. The sensors were contained in a 2 inch diameter schedule 40 pipe that can be installed in the cold flow model in place of one of the test tubes. This arrangement allows measurements to be made non-intrusively. The velocity measuring portion used a Laser Doppler Velocimeter (LDV) for obtaining the resultant impact velocity and impact angle of the bed particles at the immersed tube surface. Mass flux was derived from the output of a high speed force transducer that measured the individual particle impact momentum signals. The above systemmore » was used successfully to measure particle impact velocities and momentum during a limited test program. Test were run in a 1 ft {times} 2 ft ambient temperature fluidized bed test facility using sand and acrylic test tubes. Measurements were taken in the center of the bed at eight circumferential location, by rotating the probe to the desired tube angle. Tube erosion data were also taken at locations corresponding to the above measurement points. The instrumentation provided a wealth of information about the internal hydrodynamics of the fluidized bed. 3 refs., 49 figs., 17 tabs.« less