Page 196 - Wastewater Solids Incineration Systems

Emission Control and Monitoring 163

temperature, and flow distribution through the unit, particulate removal efficien-
cies of 99% and greater are achievable.

2.6.2 Advantages and Disadvantages
Dry ESPs have certain advantages over other types of APC devices. For example,
because they do not use water, there is no requirement to supply clean water or to
treat processed water. Compared with a medium or high pressure drop Venturi
scrubber, dry ESPs use much less electric power.
There are also several disadvantages to dry ESPs. The inlet gas to the precipitator
must be cooled to less than 316°C (600°F) to prevent warping of the plates. This
requires use of a heat removal device, such as a waste heat boiler. In addition,
exhaust gas must be relatively free of VOCs to prevent particulate matter from
sticking to the plates. This is not a problem for a fluid bed incinerator, but application
on an MHF would require an afterburner. Also, a flue gas with high moisture can
promote discharging of the electrical charge between electrodes and plates which
will prevent a high charge buildup on the particles.
Operation of the unit depends greatly on the characteristics of the fly ash and
may limit the use of certain chemicals (such as ferric chloride, alum, lime, or
methanol) in liquid processes at the WWTP. The dry ESP also has no effect on
gaseous pollutants and, therefore, must be followed by other APC devices. Another
disadvantage of dry ESPs is their relatively high capital cost.
2.6.3 Operation and Maintenance
The operation of a dry ESP does not require significant effort by the operator because
voltage from electrodes to plates is automatically controlled by automatic voltage
controllers. Occasional observation of the voltages and measurements of various
plates and fields is all that is required to ensure effective particulate removal. Correct
alignment of the electrode in the center of the collection field is important to
achieving a highest voltage potential across the gap from discharge electrode to col-
lection plate. In general, the greater the voltage potential, the greater the particulate
removal efficiency. In time, if the voltage and current measurements indicate a
buildup of particulate and degradation of performance, manual cleaning of the plates
and electrodes will be required. A dry ESP, particularly one located outdoors, should
be well insulated because cold spots on the ESP housing will cause condensation of
the moist gas on the inside, causing corrosion of the steel housing. This problem is
particularly severe during cold startup of the unit when warm moist flue gas enters.
Provisions for preheating the unit before entry of the exhaust gas can greatly mitigate