Page 265 - Wastewater Solids Incineration Systems

Incinerator Operations 227

induced draft fan. The operator can control the amount of air drawn into the incin-
erator by using the dampers located around the incinerator. These dampers provide
the quickest response to control the combustion reaction and may be operated
either manually or automatically.
The dampers located on the same hearth all allow equal volumes of air into the
incinerator. Air introduced at the lower hearth dampers will be heated more than air
introduced at the dampers located on the upper hearths. If oxygen is needed to
increase the combustion process, air should be drawn from the dampers located on
the lower hearths. However, if the temperature in the incinerator must be decreased
rapidly, air should be drawn from the dampers located on the upper hearths. During
stable operations, the percent of each damper open generally increases through the
lower hearths of the incinerator.

2.6.3 Burnouts
Uncontrolled burnouts occur when temperatures within the incinerator rise rapidly
and resist returning to normal by ordinary operational controls. The operator should
record the cause of the high temperature in the log and any corrective action taken.
An uncontrolled burnout can be brought under control by using one or more of the
following techniques:
• Open air sources. This increases the air passing through the incinerator and
provides convective cooling to the combustion process. However, adding too
much air to the incinerator can cause overpressurization and result in the
emergency bypass stack damper opening.

• Reduce the center shaft speed. This reduces the speed at which the rabble
arms turn over the burning cake solids and expose new fuel to oxygen, thus
reducing the rate of combustion.

• If the incinerator temperatures continue to increase, the center shaft may be
stopped for short periods of time. Shutting off the center shaft for 30 seconds
out of every one minute slows down the combustion by reducing the feed
cake surface area exposed to the hot gases.
• Add water to the feed by decreasing the solids content in the dewatered cake.

However, this requires changes in the operation of the dewatering units.
The operator should note that all of these actions result in a larger volume of moist
feed cake on the top hearth, additional heat for evaporation, and a lower temperature