Effect of gas properties on particle charging and wall fouling in gas-solids fluidized beds

Electrostatic charge density and the wall coverage of polyethylene and glass particles fluidized by different types of gases (air, nitrogen and argon) were investigated in a transparent acrylic fluidization column via digital image analysis. Compared to other tested gases, argon generated the least degree of wall fouling, indicating that the dielectric breakdown of fluidizing gas is a significant factor that affects the charge buildup on fluidized particles. For polyethylene particles, the degree of wall fouling was strongly correlated to the charge density of the bed particles. However, such a correlation for glass particles is much weaker. Interestingly, the moisture content in the fluidizing gas has a more significant effect on wall fouling for glass particles than that for polyethylene particles, possibly due to the adsorbed water layer on the hydrophilic surface of glass particles. Moreover, the size of particles coated to the wall in all tests was generally smaller than that of the bed particles, indicating that highly charged small particles had a high tendency to attach to the column wall.

Automated summary

The electrostatic charge density and wall coverage of polyethylene and glass particles fluidized by different gases were investigated. Argon caused the least wall fouling, indicating the importance of dielectric breakdown of fluidizing gas on particle charge buildup. For polyethylene particles, wall fouling was strongly correlated with charge density, while for glass particles, the correlation was weaker. Moisture content in the gas had a more significant effect on wall fouling for glass particles, possibly due to adsorbed water layer. Highly charged small particles had a high tendency to attach to the wall.