(136b) Powder Electrification Due to Pneumatic Conveying
Electrostatic charging is an unavoidable and in some processes, an undesired phenomenon which occurs during particle handling and processing due to inter-particle and particle-wall collisions. Particle agglomeration, electrostatic discharge, and adhesion of the particles to the wall surface are some of the adverse effects of electrostatic charge generation. Catalytic gas-solid fluidized bed reactors which are used for polyethylene production, are examples in which electrostatic charge buildup has a negative impact on overall process performance. Charged polyethylene and catalyst particles can adhere to the reactor wall, a problem known as "sheeting" which requires regular reactor shut down for cleaning purpose. One source potentially capable of introducing electrostatic effects in gas-solid polymerization fluidized bed reactors is anticipated to be through the catalyst injection into the reactor via pneumatic conveying. Fresh catalyst, which is transferred and fed into the fluidized bed through narrow pneumatic conveying lines, can become highly charged due to continuous collisions among particles and the conveying tube. Upon injection of these highly charged particles into the reactor, image forces could form leading to the particles migration and adhesion on the reactor wall. In an attempt to better understand the charging of powders through pneumatic conveying, this study illustrates the effect of transport tube length, conveying gas velocity and particle size distribution on triboelectrification of fine glass beads as well as a catalyst powder. In addition, the generated electric current over a part of the transport tube as the result of particle movement was measured and compared with the cumulative electrostatic charge of that particle captured in a Faraday cage.