Measurement of Local Frequencies of Filter Regeneration and their Effect on Successive Operating Cycles Page: 2 of 7
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drop increase gets steeper, the lower the regeneration efficiency becomes. This results in a reduction of
filter cycle duration with decreasing regeneration efficiency. In case of only a single regenerated surface
area the residual pressure drop also increases with decreasing regeneration efficiency (Dittler and
Kasper, 1999). The results shown in figure 2 describe the pressure drop curve after removal of parts of
a uniform dust layer. Therefore they describe the pressure drop curve in the second filtration cycle (after
the first regeneration of the filter medium) theoretically.
In order to describe the transient development of filter cycle duration and residual pressure drop
over a multitude of filtration cycles, two boundary cases of transient filter regeneration will be discussed.
In the first case the filter medium is always regenerated at the same filter positions after every filtration
cycle with a constant regeneration efficiency of f = 20%. In the second case the filter surface is
regenerated also by 20%, but the positions in with the filter surface is regenerated are randomly
distributed. Figure 3 shows the geometrical arrangements of both boundary cases of transient filter
regeneration addressed. In case the filter element is always regenerated with a constant regeneration
efficiency in the same positions the residual dust cake grows continuously as schematically shown in
figure 4 (left). In case the 20% of the surface is regenerated randomly after every filtration cycle it is
almost unlikely, that parts of the filter surface remain uncleaned after a certain number of filtration cycles.
Pressure drop curves calculated for both boundary cases of transient filter regeneration are shown in
figure 4. In case the filter medium is always regenerated at the same positions the pressure drop curves
change their character from cycle to cycle. They get steeper resulting in a reduction of filter cycle
duration with increasing number of filtration cycles. The filtration process is instable over a multitude of
filtration cycles in terms of development of filter cycle duration, but filter cycle duration reaches a
constant level after a multitude of filtration cycles.
In case the filter is regenerated randomly with respect to the cleaned filter regions the pressure drop
curves have the same shape. Therefore residual pressure drop and filter cycle duration remain at a
constant level from the second filtration cycle onwards, resulting in a stable filter operation.
Criteria for Stability of a Filtration Cycle - Definition of Successive Filtration Cycles
Defining stable filter operation and with this a successive filtration cycle through constant residual
pressure drop after regeneration and constant filter cycle duration, different regeneration characteristics
can be assigned to a stable or instable filter operation (Dittler, 2001):
" Stable filter operation
In terms of the above definition stable filter operation occurs according to the model calculations
performed and displayed schematically in figure 5 in case of:
1. Completely regenerated filter surface
2. Partially regenerated surface with randomly regenerated surface areas
" Instable filter operation
Instable filter operation is the result of partially regenerated filter media as illustrated in figure 6 in
case of:
1. Partially regenerated filter surface - decreasing regeneration efficiency from cycle to cycle
2. Partially regenerated filter surface - filter surface always regenerated at the same positions
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Dittler, A. & Kasper, G. Measurement of Local Frequencies of Filter Regeneration and their Effect on Successive Operating Cycles, article, September 19, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc784931/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.