(84g) Experimental Investigation of Granular Electrostatics and Ignition Hazard in a Pneumatic Conveying System

As granules are transported in a pneumatic conveying system, electrostatic charges will be accumulated both on granules made of high resistivity material and the insulating walls. As charges accumulate to a certain level, they may be discharged in the form of a spark and thus present possible ignition hazards. In our present pneumatic conveying system, spark discharge was observed at a pipe bend and brush discharge at the horizontal pipe section. In order to characterize the electrostatic properties of the granular flow, three instruments referred to as the electrometer, modular parametric current transformer and Faraday Cage were used to obtain the induced current and charge density. The effects of operating conditions of the system such as air flow rate, solid flow rate, particle velocity and others on electrostatics were investigated. Similarly, the influences of environmental factors such as ambient temperature, relative humidity and transportation distance on spark generation were also studied. Based on energy analyses, the critical conditions required for spark discharging to occur could be obtained. With a better understanding of electrostatic charging characteristics of granular flows, it would be possible to maintain safe operation of granular handling processes such as by regulating operating conditions in pneumatic conveying systems.