Direct measurement of particle motion in a large-scale FBC boiler model

One of the difficulties of designing fluidized bed combustion boilers is that motion of fluidized particles is uncertain in a large commercial-scale boiler. The authors constructed a large atmospheric fluidized bed model with mock-up tubes and obstacles that were nearly equivalent in size to a commercial-scale bed. The model was used to measure motion and diffusivity of particles from an inserted nozzle. The model had a length of 2.3m, a width of 1.7m and a total height of 8.2m. The bed height was adjusted to about 4m. Motion of particles was measured by a small cantilever on which strain gauges were attached. Before measurement, strain rate of the cantilever was correlated to particle velocity by a certain experimental formula. In order to measure overall motion of particles, a pipe with this cantilever was inserted into the bed and traversed at certain horizontal levels then these data were converted to particle velocity distributions. In the diffusion experiments, tracer particles were injected from the nozzle for a certain period then fluidizing air was terminated immediately. The baffle plate effect on the diffusivity was examined by measuring the mixing rate of tracer particles. Diffusion of particles was compared with unsteady diffusion calculations. Resultsmore » are summarized as follows: (1) No significant difference was seen in particle velocity distribution when measurement level of the bed was shifted inside a bunch of tubes; (2) Average velocity of particles approximately ranged from {minus}0.02 to 0.02 m/s in the region of the tubes; (3) The vertical diffusion rate of particles was roughly several times higher than their horizontal diffusion rate; and (4) An effect of the baffle plate on particles diffusion was limited. The baffle plate seemed to enhance horizontal diffusion of injected particles only in the vicinity of it.« less