Page 199 - Wastewater Solids Incineration Systems

166 Wastewater Solids Incineration Systems

• The unit uses relatively small quantities of water for irrigating and flushing
the collection tubes.
• Power consumption by the unit is relatively modest in comparison with the
fan or blower power that a Venturi scrubber would require to achieve compa-
rable particulate removal efficiency.

Disadvantages of the wet ESP are as follows:
• The unit works best when it is lightly loaded with particulate matter, essen-
tially acting as a final control device after a Venturi scrubber or other device
has removed the bulk of the particulate matter.
• If a wet ESP is exposed to heavy particulate loadings, collection surfaces can
build up particulate matter and choke the flow of exhaust gas through the unit.
• If the surface of the collecting tubes becomes dry from an upset in the condi-
tion of the flue gas or interruption of the fine mist generating system, particu-
late matter will adhere to the dry section of the collection tubes and can cause
a buildup.
• The unit collects the particulate matter in liquid form, which may require sep-
arate clarification to remove the particles from the flushing water.

2.7.3 Operation and Maintenance
Similar to the dry ESP, the wet ESP requires little operator attention because the
voltage and current across the electrodes and collection tubes are controlled automat-
ically to achieve a given particulate removal efficiency. Periodic checking of voltage
drops is necessary to ensure that no dry spots or particulate buildups are occurring.
If these conditions do occur, more frequent flushing of the collection surfaces or an
adjustment of the mist generating system may be required. If the design voltage drop
between the electrodes and the collection tubes cannot be attained, realignment of the
electrodes so that they are precisely positioned in the center of the collection tubes
should be performed.

2.8 Fabric Filters
Fabric filters, or baghouses, have been increasingly used on power plants, refuse
incinerators, and other emission sources where the absolute maximum level of par-
ticulate control is required. Fabric filters are large structures that house an array of
long cylindrical cloth or fabric bags. Inside each bag is a rigid wire cage that keeps