Continuous monitoring and mechanism of electrostatic charge of powder in fluidized bed process

Abstract

In a previous paper (Watano et al., J. Soc. Powder Technol. Jpn, 34, 778, 1997), we developed a novel system which could continuously monitor the electrostatic field strength of powder in a fluidized bed process. This paper reports further study related to the electrostatic characteristics of powder. Two novel achievements are described; one is an improvement of the reliability and accuracy of the sensor, and the other is the mechanism and characteristics of the electrostatic charge for different kinds of powder materials. First, the structure of the sensor extremity has been improved to remove the troubles encountered in the previous sensor. By using a double- walled cylinder, the sensor is devised to tolerate severe vibration, high purge air flow and particle sticking. By increasing the sensitivity, the accuracy of measurement can be increased by approximately five times that of the previous sensor. Secondly, the relationship between electrostatic field strength and the electrical charge of the particles has been investigated using various kinds of powder materials. The sensor shows a good linearity between two measurements, proving that the electrostatic characteristics of charged particles could be monitored correctly via the electrostatic field strength. The performance of the system has been confirmed in the fluidized bed granulation/drying processes using different kinds of particles. The mechanism of the electrostatic charge for different kinds of powdered materials are also discussed.