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126 Wastewater Solids Incineration Systems
STEAM DRUM
EVAPORATOR
ECONOMIZER
SUPERHEATER
HOOPERS
Water Tube Boiler
FIGURE 6.7 A typical watertube waste heat recovery boiler.
Boiler tubes are arranged horizontally or vertically, with vertical or horizontal gas
flow arranged to allow solids to drop out of the gas stream. At the top, a steam drum
separates the steam from the rising water. The steam drum is fitted with feedwater
inlet and steam outlet connections and other trim. Some boiler designs have one or
more bottom “water drums,” sometimes referred to as “mud drums,” which can be
blown down periodically for cleaning settled solids out of the steam system.
Drums and tubes are supported directly by the casing. Expansion and contrac-
tion have no effect on the insulation of the casing. The casing is externally insulated
and built to withstand the normal operating pressures of the system. It is desirable to
