Page 113 - Wastewater Solids Incineration Systems

82 Wastewater Solids Incineration Systems

In the system shown, the waste heat boiler and the wet ESP are optional
depending on the owner’s desire for heat recovery and regulatory requirements.
Also, the afterburner could be located where the waste heat boiler is shown. Heat
recovery and air pollution control are discussed in detail in Chapters 6 and 7.

9.3 Composition and Construction
The shell of the MHF is constructed of welded or bolted steel plate, although older
furnaces have been provided with rivets for joining the steel. The shells are provided
with reinforcing bands at each hearth to support the lateral forces from the refractory
hearths. Openings are provided for several components: access doors; burners; feed
ports; exhaust gas duct; combustion air ports; observation ports; and ports (lance
tubes) for cleaning clinkers and instrumentation. Openings are reinforced as neces-
sary. The exhaust gas outlet is located on the wall of the top hearth and is a rectan-
gular opening with a flanged stub that is refractory lined. The floor is constructed of
steel plate supported on a steel frame with structural steel columns to provide head-
room between the furnace floor and the building floor for the central shaft drive and
to support bearing and the shaft cooling air housing. The furnace floor and frame
support the entire weight of the furnace. The floor includes an opening for the cen-
tral shaft and sand seal and openings for ash discharge. The roof is constructed of
steel plate, reinforced to support the top bearing and sand seal for the central shaft.
An opening is provided for the central shaft, feed ports, and the emergency exhaust.
The shell, floor, and roof are lined internally with refractory. The wall refractory
typically consists of approximately 230 mm (9 in) thick high-heat-duty refractory
brick, backed by approximately 155 mm (4.5 in) thick insulating brick or block. The
shell may be coated with a corrosion-resistant lining. The floor and roof are typically
lined with castable refractory.
9.3.1 Hearths
Each hearth is constructed of high-heat-duty refractory firebrick arranged in succes-
sive rings from the outside to the inside. The outer ring is constructed of a special
firebrick, referred to as a skewback, having an angled internal face for supporting the
hearth. The brick is approximately 300 mm (12 in) square and much heavier than a
single, standard firebrick. This brick also supports the wall refractory between each
hearth. Each ring is constructed with regular and special shapes with angled faces to
form a tight circular structure. Successive inner rings have slightly different angles to
match the planned diameter of the ring. The hearth starts out at the wall approxi-
mately 230 mm (9 in) thick.