Chemical Engineering April 2021 - 46

Feature Report
Part 2
Addressing Problems in
Filtration Processes
Careful attention to even the smallest details will help to prevent operational problems
in filtration processes
Jose M.
Sentmanat
Liquid Filtration
Specialist, LLC
F
IN BRIEF
FILTER PAPER
PROBLEMS
ISSUES WITH TEARING
SOLIDS BUILDUP AND
LEAF DAMAGE
DESIGN, TESTING AND
VALIDATION
AUXILIARY EQUIPMENT
iltration operations are widely used to
achieve effective solid-liquid separations
in the chemical process industries
(CPI). Industrial filtration installations
can involve a variety of components,
including paper sheets, wire mesh, filter
cloth and so on. If not properly specified and
installed, even the smallest elements within
a filtration system can lead to serious operational
problems. This article outlines some of
the typical problems encountered in industrial
filtration processes, and how they can
be rectified.
Filter paper problems
In filtration applications, loss of clarity in product
streams occurs when the solids in the
feed liquor bypass filter media and end up in
the filtrate, contaminating the clean filtered
liquor. The contamination resulting from the
bypassed solids will cause problems, and if
not corrected by a trap filter or recycling, it
will allow unwanted solids into downstream
equipment. To handle such contamination,
the liquor must be filtered again either
through a recycling step or by a second filter
that ends up acting as the trap filter. This
not only causes delays in the process, but
FIGURE 2. Formation of tears in the wire mesh that covers the
filter leaves may necessitate mesh replacement
FIGURE 1. Filter paper must be properly placed on the filter plate to ensure
trouble-free operation. Improper placement can lead to loss of clarity
and other problems
46
also added expense if a trap filter must be
installed. Often, loss of clarity occurs when
the solids bypass filter-paper media through
gaps resulting from improper placement of
the filter paper. Filter paper sheets should be
correctly placed on the filter plates to ensure
that the filter paper is providing an effective
seal in between the filter plates. Figure 1
illustrates the placement of the filter paper
on the filter plate, and also some problematic
situations that should be avoided.
Additional problems can arise when the filter
paper becomes folded. Operators should
pay close attention to ensure that the paper
is placed flat on the filter plate. Furthermore,
operational problems occur when the filter
paper is crumpled, also causing contaminant
bypass and loss of clarity.
To avoid issues, operators should
also be aware that filter paper may
swell up when the paper becomes
wet with the liquid to be filtered. As it
swells, the filter paper, if already compressed
by the filter-plate compression
rings, may start forming wrinkles.
Once the filter cake starts forming
within the filter paper's wrinkles, it will
cause cracks in the filter cake and
loss of clarity. This problem may be
avoided by prewetting the filter paper
as it is placed on the filter plate, thus
allowing the filter paper to swell up
before it is compressed in place by
the filter-plate compression rings.
The prewetting of the filter paper may
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Chemical Engineering April 2021

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