Civil Engineering Reference
In-Depth Information
Fig. 23-22.
Typical method for dewatered cake removal from filter press
minutes. Insufficient residence time may produce premature plating-out of lime on the
filter media and the interior of pipelines.
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Two-stage conditioning systems were demonstrated to be somewhat more econom-
ical than one-stage lime addition. In these systems, only a portion of the lime is added
to the incoming untreated sludge, followed by a small polymer addition. When the
mixture is then allowed to age, an appreciable supernatant is formed, which is decanted
and returned to the head of the plant. After sufficient residence time, the remainder of
the lime is added, and the sludge is then ready for filtration. The total lime addition
is less than that used in a single-phase system.
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Each case should be tested to determine
the effectiveness of the type of conditioning system.
The capacity of a pressure filter is determined by the number of filter plates, the
size of filter plates, and the cake thickness provided for in the filter plate chamber.
Filter cake thickness is critical in the design of a pressure filter; cake thicknesses are
standardized to 0.98, 1.18, and 1.57 inches (25, 30, and 40 mm) thickness.
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Filtration
tests determine the most economical cake thickness for any given application.
The basic components for a filter press system are shown in Figure 23-23 and
include:
Storage and mixing tanks for chemical reagents
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A storage and conditioning tank, to provide a consistent feed to the filter presses
for the duration of the filtration cycle. In this tank, chemical reagents are intro-
duced to improve the filterability characteristics of the sludge. Means for agitation
are provided to prevent segregation of particles and also to prevent size degra-
dation and breakdown in the flocculated feed.
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