Particle electrification in an apparatus with a draft tube operating in a fast circulating dilute spout-fluid bed regime--颗粒学报PARTICUOLOGY

Ludwig, W. (2019). Particle electrification in an apparatus with a draft tube operating in a fast circulating dilute spout-fluid bed regime. Particuology, 42, 146-153. https://doi.org/10.1016/j.partic.2018.03.008

Particle electrification in an apparatus with a draft tube operating in a fast circulating dilute spout-fluid bed regime

Wojciech Ludwig ^*

Wroclaw University of Science and Technology, Faculty of Chemistry, Department of Chemical Engineering, Norwida 4/6, 50-373 Wroclaw, Poland

10.1016/j.partic.2018.03.008

Volume 42, February 2019, Pages 146-153

Received 28 September 2017, Revised 22 February 2018, Accepted 25 March 2018, Available online 5 September 2018, Version of Record 21 January 2019.

E-mail: wojciech.ludwig@pwr.edu.pl

Highlights

• The values of the electrostatic charge in the modified Wurster apparatus are determined.

• Impact of the process parameters on the electrostatic charge is investigated.

• The electrification of the bed is very intensive.

• The electrostatic charge relatively little depends on tested process variables.

• Such intense electrostatic phenomena can be used in the electrostatic coating process.

Abstract

The intensity of the electrostatic charge accumulated during the flow of Cellets® particles in a modified Wurster apparatus is investigated in terms of the bed mass, and the initial moisture and velocity of the spouting gas. Particle electrification is proportional to the increase in the velocity of the spouting gas, which is connected with a higher velocity of the cores and the strength of their impact on the walls of the device. The presence of moisture in the bed facilitates electrification, but does not affect circulation, since moisture simultaneously lowers the bed resistance and reduces the relaxation time of particles, leading to rapid discharging if brought into contact with the conducting elements of the apparatus. Therefore, with regard to classic dry-powder coating, the velocity of the spouting gas should be minimized to ensure good circulation, with the particle moisture held at the maximum level admissible for a given product. The investigations show that a unique construction of the apparatus, which brings about an intense natural electrification of the cores, makes it suitable for the electrostatic dry-coating process by means of a high-voltage feeder with the controlled charging of coating powder in the spray nozzle.

Graphical abstract

Keywords

Electrification; Electrostatic charge; Spout-fluid bed; Wurster apparatus

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