(611j) Influence of Pressure on Gas-Solid Fluid Bed Electrification

Generation of electrostatic charges in gas-solid fluidized beds in some cases could result in challenges such as particle agglomeration and reactor wall coating. Gas-phase polymerization of ethylene to produce polyethylene is an example of such case where bed electrification results in reactor wall fouling.  In order to better understand the charging behaviour of fluidizing particles, it is important to investigate the impact of fluidization operating conditions such as gas velocity, operating pressure, etc. This work aimed at studying the effect of pressure on the extent of fluidizing particles charging and their tendency to foul on the column wall. Experiments were conducted in a high-pressure pilot-scale gas-solid fluidization system consisting of a stainless steel column, 0.15 m in diameter and 4.5 m in height. Linear low density polyethylene resin (mean particle diameter of 710 microns) was used as the fluidizing particles while the fluidization was conducted in the bubbling flow regime (1.5U_mf) for one hour. The degree of fouling and the particles charge-to-mass ratio within the bulk of the bed and those fouled on the column wall were determined for various operating pressures (0, 5, 10, 15, 20, and 25 barg). Results showed that the degree of wall coating increased at elevated pressures while the particles charge density did not significantly vary from pressures of 5 to 25 barg. However, the bipolar charging behaviour of the particle layer coating the column wall was different between atmospheric and high pressure trials where at atmospheric conditions the majority of the wall layer was occupied by negatively charged particles while the opposite was found for pressures of 5 barg and higher.