Page 194 - Wastewater Solids Incineration Systems

Emission Control and Monitoring 161

FIGURE 7.11 A tray scrubber with a P trap.

least one installation, in Canada. On these installations, the earlier fluid bed incinera-
tors, built in the 1980s and early 1990s, had single field ESPs; whereas, plants built
after 1995 have two to three field ESPs, which typically form the first stage of the flue
gas treatment process. On these installations the exhaust gas is first cooled in a waste
heat boiler before the dry ESP.
In a dry ESP, as shown in Figure 7.12, the exhaust gases pass through a large
chamber where electrodes impart a negative charge to the particulate matter in the
exhaust gas stream. The electrodes are negatively charged and are provided with a
direct current from 20 to 100 kV. Plates with a positive electrical charge run parallel
to the flow of gases through the chamber. The negatively charged particles are
attracted by the positive electrical force to the plates. Periodically, buildup of particu-
late matter on the plates is removed by rapping the plates, which causes it to fall to
the bottom of the chamber for removal.