(170f) Attrition in Submerged Jetting Region in Fluidized Bed

One of major sources of attrition in fluidized bed and circulating fluidized bed is the jets from the gas distributor. Particles are generally picked up by the jet at the gas distributor. They accelerate along with the jet penetration length, and slam into the relatively slow moving particles. This is how attrition occurs at the gas distributor.

Particle attrition in the submerged jetting region depends strongly on orifice velocity and orifice size. Over the years, the attrition works in open literature were mostly concerned with higher gas jet velocities and smaller orifice size than are commonly found in industrial scale equipment. Furthermore, attempts on attrition model development were mainly based on empirical fitting to the experimental data with a limited number of test materials and narrow range of operating conditions. Attrition rates are typically expressed with a power-law dependence for gas jet velocity and hole diameter. A wide range of power indices are reported in open literature; for example, dependence of jet velocity on attrition rate has been reported to vary from 1 to 5.8.

In this work, PSRI conducted a thorough and systematic study of submerged jets in order to assess attrition in the jetting region of a large scale fluidized bed; a commercially relevant grid nozzle design and experimental conditions were used. Grid attrition rate was found to be proportional to the square of shroud velocity.

One of the major new findings was to have a better understanding on the gas jet orientation on attrition. It was generally known that that downwardly directed jets always produced more fines than the upwardly pointed jets. However, this was found to be not always the case. This result will change our knowledge on the effect of gas jet orientation on attrition.