Decrease in the fluidization quality of fluidized beds containing binary mixtures of different catalyst particles

• Fluidization quality drastically decreased when mixing catalyst and FCC particles.
• Gas channeling and irregularly-shaped voids were observed for mixed particles.
• The bed behavior was quite similar to that of Geldart's Group C particles.
• The collisions between the different types of particles caused the bipolar charging.
• The fluidization quality was reduced by the increase in cohesiveness.

Good fluidization was generally established when fine and light catalyst particles were fluidized. However, a large decrease in the fluidization quality was observed when two types of particles composed of different materials were mixed and fluidized, even though good fluidization was established with each type of particle alones. Formation of gas channeling was observed for binary mixtures of particles in a two-dimensional (2D) fluidized bed. In a three-dimensional (3D) bed, measurement of the pressure fluctuation showed that abnormal fluidization occurred due to mixing of the particles. In addition, measurements of the minimum fluidization velocity and emulsion phase expansion indicated that particle agglomeration occurred. The phenomena observed in the fluidized bed with the mixture of particles are quite similar to those observed for Group C particles. On the basis of the direction of the electrostatic charge, the particles were separated using electrodes installed above the fluidized bed surface. It was confirmed that one type of particle was positively charged and the other was negatively charged. Thus, it was concluded from these results that the bipolar charging caused by the difference in chemical composition of the particles induced the agglomeration phenomena and poor fluidization.

Figure optionsDownload high-quality image (181 K)Download as PowerPoint slide