Electrostatic hazards of polypropylene powders in the fluidized bed reactor

This paper reports on electrostatic hazards related to a powder fluidized bed reactor. The electric field and the space charge density were monitored over the fluidizing time. We also investigated the minimum ignition energy of sample powders with a Hartman vertical-tube apparatus. A batch-type fluidized bed system containing 1 kg of commercial grade polypropylene resin powder was used in the experiments. The superficial air velocity with zero relative humidity was in the range of 0.2 to 0.32 m/s. Results obtained from the experiments show that the bi-polar charging existed in the reactor during operation. As the superficial air velocity increased, the space charge density in the lower column increased, whereas, the space charge density decreased in the upper column. The electric field generated from charged powders reached a maximum of 250 V/cm, safe level for incendiary electrostatic discharge from charged powders. The powders in the upper column section can be more easily ignited by electrostatic discharges compared to powders in the lower column.