Cold Experiment Studies On Fluidized Bed Classifiers

In larger-scale circulating fluidized bed (CFB) boilers, cooling capacity for large-size ash in bottom ash coolers is a problem. Arrange fluidized bed classifiers before the bottom ash coolers can solve the problem. But research and development work on the fluidized bed classifiers is still at the preliminary stage. This thesis presents the studies of fluidized bed coolers.A violent-flow fluidized classifier set and a non-violent flow fluidized classifier set were made. Sand with the same density and different sizes was used to simulate bottom ash. The classifying mechanism is the difference of the minimum fluidization velocities. Test results show that fine sand takes a strong role in the entrainment of coarse sand, so it is difficult to apply the mechanism to fluidized bed classifiers.According to experiments with binary components in a CFB cold set, a new classifying mechanism, using the difference of terminal velocities between coarse and fine particles, was proposed. A cold classifier was made. The results show that the mechanism can be used to fluidized bed classifiers, an expanded structure of a large diameter in the upside and a small diameter in the bottom side can further reduce the carried height of coarse sand in the classifier and the classifying performance can be modified.The carried height of coarse sand is an important parameter. Experiments on the influence of superficial velocities, concentration of fine sand, sand sizes, secondary air on the carried height of coarse sand were made. According to the experiments, an optimal operation condition to classifiers is proposed.