3
Subsequently, 60 kPa was chosen as the pressure differ-
ence (–60 kPa vacuum) for further laboratory testing.
Different types of vacuum filters and different suppliers
use different filter settings. In order to be able to compare
these settings, Figure 3 shows the cake moisture plotted ver-
sus the dewatering ratio which is defined as the quotient of
the cake drying time divided by the cake formation time.
Modern vacuum disc filters are designed for maximum
solids throughput and run with slurry levels of up to 50 %.
This means that half of the filtration area is used for cake
formation and the other half for cake drying. This results
in a dewatering ratio of 1. Standard vacuum disc filters are
designed to minimize manufacturing cost and run with
slurry levels of up to 35 %.This means that a quarter of the
filtration area is used for cake formation and about half for
cake drying. This results in a dewatering ratio of 2. Figure 3
shows that any dewatering ratio 0.5 will be suitable to
achieve the 23 %w/w moisture.
Solids Throughput
The final step to filter sizing is the specific solids through-
put which is plotted in a Figure 4.
Figure 4 shows the benefit of modern vacuum disc fil-
ters with high slurry level and a dewatering ratio of 1 versus
the standard vacuum disc filters with low slurry level and a
dewatering ratio of 2. The standard design reaches a specific
solids throughput of 60 kg/m2/h while the modern design
is getting up to 110 kg/m2/h. However, for a total of 170
t/h this would result in a requirement of filtration area of
1545 m2. This would be 9 modern vacuum disc filters with
176 m2 each. However, the moisture would be 17.5 %w/w.
This leads directly into the optimization of the sizing which
can be done by increasing the feed solids (no option as the
thickener is fix) or addition of flocculant which normally
has a negative impact on moisture.
Figure 5 shows the cake moisture with increasing
amount of flocculant added. And the results show that with
increasing amount of flocculant, the moisture increases.
The maximum permitted moisture is 23 %w/w which will
be reached at a flocculant dosage of about 90 g/t (based
Figure 2. Moisture of filter cake plotted versus filtration
pressure difference
Figure 3. Moisture content vs dewatering ratio (cake drying
time /cake formation time)
Figure 4. Specific solids throughput versus dewatering ratio
Figure 5. Moisture content of filter cake vs flocculant dosage
Subsequently, 60 kPa was chosen as the pressure differ-
ence (–60 kPa vacuum) for further laboratory testing.
Different types of vacuum filters and different suppliers
use different filter settings. In order to be able to compare
these settings, Figure 3 shows the cake moisture plotted ver-
sus the dewatering ratio which is defined as the quotient of
the cake drying time divided by the cake formation time.
Modern vacuum disc filters are designed for maximum
solids throughput and run with slurry levels of up to 50 %.
This means that half of the filtration area is used for cake
formation and the other half for cake drying. This results
in a dewatering ratio of 1. Standard vacuum disc filters are
designed to minimize manufacturing cost and run with
slurry levels of up to 35 %.This means that a quarter of the
filtration area is used for cake formation and about half for
cake drying. This results in a dewatering ratio of 2. Figure 3
shows that any dewatering ratio 0.5 will be suitable to
achieve the 23 %w/w moisture.
Solids Throughput
The final step to filter sizing is the specific solids through-
put which is plotted in a Figure 4.
Figure 4 shows the benefit of modern vacuum disc fil-
ters with high slurry level and a dewatering ratio of 1 versus
the standard vacuum disc filters with low slurry level and a
dewatering ratio of 2. The standard design reaches a specific
solids throughput of 60 kg/m2/h while the modern design
is getting up to 110 kg/m2/h. However, for a total of 170
t/h this would result in a requirement of filtration area of
1545 m2. This would be 9 modern vacuum disc filters with
176 m2 each. However, the moisture would be 17.5 %w/w.
This leads directly into the optimization of the sizing which
can be done by increasing the feed solids (no option as the
thickener is fix) or addition of flocculant which normally
has a negative impact on moisture.
Figure 5 shows the cake moisture with increasing
amount of flocculant added. And the results show that with
increasing amount of flocculant, the moisture increases.
The maximum permitted moisture is 23 %w/w which will
be reached at a flocculant dosage of about 90 g/t (based
Figure 2. Moisture of filter cake plotted versus filtration
pressure difference
Figure 3. Moisture content vs dewatering ratio (cake drying
time /cake formation time)
Figure 4. Specific solids throughput versus dewatering ratio
Figure 5. Moisture content of filter cake vs flocculant dosage