EFFECT OF PARTICLE-TUBE COLLISION FREQUENCY ON MATERIAL WASTAGE OF IN-BED TUBES IN THE BUBBLING FLUIDIZED-BED COMBUSTOR

The metal wastage mechanisms and rate that occur in 1018 carbon steel used in in-bed tube of the bubbling fluidized bed combustor (BFBC) are discussed with particle-surface collision frequency around the tube. Electrostatic impact probes based on the triboelectric effect of movin g particles were developed and used to measure the particle-surface co llision frequency, which is one of the major parameters characterizing the material wastage of in-bed tubes in the BFBC. The distribution of the particle-surface collision frequency around the tube was affected by the location of the tube and bed height. A series of material wast age tests was carried out using 742 mu m, quartz silica (SiO2) on 1018 steel at elevated temperature (300 degrees C) which occurs in-bed loc ations of BFBC. The morphologies of the specimens were examined and an alyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The eroded surface morphology under high particle velocity (30 m s(-1)) exhibited typical ductile behaviour. The maximum collision frequency around the periphery of the tube was found at 45 degrees, 315 degrees from the bottom centre, 0 degrees, which was corr elated with maximum material wastage rate of the specimens.