Collection Electrodes

Most U.S. precipitators use plate collection electrodes because these units treat large gas volumes and are designed to achieve high collection efficiency. The plates are generally made of carbon steel. However, plates are occasionally made of stainless steel or alloy steel for special flue-gas stream conditions where corrosion of carbon steel plates would occur. The plates range from 0.05 to 0.2 cm (0.02 to 0.08 in.) in thickness. For ESPs with wire discharge electrodes, plates are spaced from 15 to 30 cm apart (6 to 12 in.). Normal spacing for high-efficiency ESPs (using wires) is 20 to 23 cm (8 to 9 in.). For ESPs using rigid-frame or plate discharge electrodes, collection plates are typically spaced 30 to 38 cm (12 to 15 inches) apart. Plates are usually between 6 and 12 m (20 to 40 ft) high.

Collection plates are constructed in various shapes, as shown in Figure 1. These plates are solid sheets that are sometimes reinforced with structural stiffeners to increase plate strength. In some cases, the stiffeners act as baffles to help reduce particle reentrainment losses. This design minimizes the amount of excess rapping energy required to dislodge the dust from the collection plates, because the energy is distributed evenly throughout the plate. The baffles also provide a "quiet zone" for the dislodged dust to fall while minimizing dust reentrainment.   

Tubes are also used as collection electrodes, but not nearly as often. Tubes are typically used to collect sticky particles and when liquid sprays are used to remove the collected particles.

   Figure 1 -Typical collection plates