Electrostatics and Gas Phase Fluidized Bed Polymerization Reactor Wall Sheeting

The presence of electrostatic charges in gas phase fluidized bed polyethylene reactors can significantly impact reactor operation. Electrostatic charges are known to influence fluidized bed hydrodynamics, including bubble size and shape, particle mixing rate, and fines elutriation. If the electrostatic charge on particles in a fluidized bed exceeds a critical value, the resultant electrostatic force causes the particles to adhere to the reactor wall. If the particles reside on the reactor wall long enough in a reactive environment, they can overheat and fuse together or melt due to the exothermic heat of reaction. Polymer particles that have fused or melted together on a reactor wall are called “sheets”.
Significant reactor wall sheeting often causes plugging of the reactor product discharge system or loss of fluidization. Either consequence typically causes reactor down time to remove the sheets from the reactor. The reactor operator incurs significant economic impact each time the reactor is shut down, both in lost production and in additional maintenance costs to clean the reactor. Thus there is significant economic incentive to prevent reactor wall sheet formation.
Despite the negative consequences of excess electrostatic charge accumulation, the electrostatic charge generation, dissipation, and mitigation mechanisms and the relationship between the electrostatic charge level and incipient reactor wall sheet formation are poorly understood. This paper reviews the relationship between reactor wall sheeting and the presence of excess electrostatic charges.
A description of reactor wall sheeting is first provided to explain the consequences of excess electrostatic charging. The mechanism of reactor wall sheet formation is then provided to relate sheet formation to electrostatic charge accumulation. After that, various aspects of electrostatic charge generation, electrostatic forces, electrostatic charge dissipation, and mitigation techniques are discussed....