Study On Residence Time Distribution Of Large Cylindrical Heavy Object In A Fluidized Bed

Large objects in municipal solid waste fluidized bed incinerator affect fluidization, which is bad for safe and stable operation. They should be discharged as soon as possible. Study on motion behaviors in incinerator give a theoretical reference for slag-off design of fluidized beds. The residence time(RTD) of single large objects in fluidized bed is animportantindicator of slag-offcharacteristics.In this thesis, factors which influence RTD were studied usingElectrical Capacitance Tomography(ECT) tracer experiments and mechanical analysis, and the RTD model suit for large objects in fluidized bed was established.The influences of superficial gas velocity, size, length-diameter ratio and density of large objects on RTD of large cylindrical objects were investigated on a cold fluidized bed equipped with a 5°inclined air distributor and orientation air cups. The difference of RTD between cylindricaland spherical objects was also sdudied. Results show that: the RTD of a single large cylindrical objectis positive-skewedand has a positive-skewedtailing.The RTD is flater when the mean residence timeis longer. There is a positive correlation between the degree of dispersion and mean residence time. With increasing fluidization velocity, the mean residence time is reduced sharply at beginning, then the reduction slows down. Finally the residence time tends to be minimum value.With decreasing fluidization velocity, the mean residence time increasesslowly at beginning, then increasesrapidly. Finally the large objectcan’t arrivethe low side wall of inclined air distributor.With the increase of density or size of large object, the mean resident time were decreased first and then increased. These results are consistent with the large spherical object studied before.But the residence time of large spherical object is apparentlylonger than the same diameter cylinder object. In the range of the experimental conditions, large objectwasclose to the air distributor.According to the mechanical analysis, the mechanical balance equation was established for the movement of large object on air distributor.The mechanical condition to start moving from static was also given.Considered with the characteristics of flow field force, these equations explainthe reaons for influence of changing of fluidization velocity, size and density of large object on residence time.RTD is described using the shift of the log-normal distribution model, Gamma distribution model with time delay, the single parameter axial dipersion model and the normal distribution model.results show that the shift of the log-normal distribution model is the better than the other models. It can accurately describe the peak height, peak position andpositive-skewed tailing ofthe residence time distribution.This research results can be a theoretical reference ofthe slag-off design of fluidized bed.