CONTINUOUS MONITORING AND MECHANISM OF ELECTROSTATIC CHARGE OF POWDERIN FLUIDIZED-BED PROCESS

In a previous paper (Watano ef RI., J. Sec. Powder Technol. Jpn, 34, 7 78, 1997), we developed a novel system which could continuously monito r the electrostatic field strength of powder in a fluidized bed proces s. This paper reports further study related to the electrostatic chara cteristics of powder Two novel achievements are described; one is an i mprovement of the reliability and accuracy of the sensor, and the othe r is the mechanism and characteristics of the electrostatic charge for different kinds of powder materials. First, the structure of the sens or extremity has been improved to remove the troubles encountered in t he previous sensor. By using a double-walled cylinder, the sensor is d evised to tolerate severe vibration, high purge air flow and particle sticking. By increasing the sensitivity, the accuracy of measurement c an be increased by approximately five times that of the previous senso r. Secondly the relationship between electrostatic field strength and the electrical charge of the particles has been investigated using var ious kinds of powder materials. The sensor shows a good linearity betw een two measurements, proving that the electrostatic characteristics o f charged particles could be monitored correctly via the electrostatic field strength. The performance of the system has been confirmed in t he fluidized bed granulation/drying processes using different kinds of particles. The mechanism of the electrostatic charge for different ki nds of powdered materials are also discussed.