Electrical precipitators corona

T" s minimum potential required for the start of corona discharge in an electrical precipitator V... 

When corona occurs, current starts to flow in the secondary circuit and some dust particles are precipitated. As potential is increased, current flow and electric field strength increase until, with increasing potential, a spark jumps the gap between the discharge wire and the collecting surface. If this "sparkover" is permitted to occur excessively, destmction of the precipitator s internal parts can result. Precipitator efficiency increases with increase in potential and current flow the maximum efficiency is achieved at a potential just short of heavy sparking. 

Current Flow Corona discharge is accompanied by a relatively small flow of electric current, typically 0.1 to 0.5 mA/m" of collecting-electrode area (projected, rather than actual area). Sparking usually involves a considerably larger flow of current which cannot be tolerated except for occasional periods of a fraction of a second duration, and then only when smtable electrical controls are provided to hmit the current. However, when suitable controls are provided, precipitators have been operated continuously with a small amount of sparking... 

Fig. 4.3. Schematic of dry rod and plate electrostatic precipitator (after Oglesby and Nichols, 1978). The rods have sharp horizontal protrusions (nails) which promote corona formation. Dusty gas flows between the plates and around the rods. A large electrical potential (60 000 V) is applied between the rods and plates. This negatively charges the dust particles - causing them to approach and adhere to the positive collection plates. The dust is gathered by periodically rapping the plates, causing sheets of dust to fall into dust bins below, Fig. 4.4. Table 4.2 gives industrial precipitation data.

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