Chemical Engineering August 2022 - 26

Cover Story
Scrolling or Pushing?
Choosing the Right Type
of Filtration Centrifuge
Understanding the working principles of scrolling and pushing centrifuges can help
when deciding which type to use. Feed properties and other factors also play a role
Malte Junker
and Peter
Schmidt
Andritz Separation
GmbH
W
IN BRIEF
TECHNOLOGY AND
OPERATING PRINCIPLES
FEEDING CONDITIONS
CAKES, MOISTURE AND
WASHING
FILTRATE QUALITY
MAINTENANCE AND
OPERATION
CONCLUDING REMARKS
hen looking for a proven solution
for mechanical dewatering,
you will most likely come
across centrifuges. In particular,
filtration centrifuges, such as pusher
or screen-scroll centrifuges, have made a
name for themselves due to their continuous
operating mode and their versatile field
of application. In this article, we discuss
the main differences between these popular
centrifuges to help answer the question:
" Scrolling or pushing - which filtration
centrifuge fits my process? " To find the
answer, we introduce the two most common
continuous-filtration centrifuges -
the pusher centrifuge and the screen-scroll
centrifuge - and explain their advantages
and disadvantages in order to derive practical
decision criteria for using them.
The question of which combination of
technologies makes sense, or even which
technologies make sense for a particular
process step, cannot be answered reliably in
a general way. This is because there are, of
course, different ways of conducting solidliquid
separation. Many of these ways are
not mutually exclusive, but there is a selection
of technologies whose reasonable sequencing
combines to create a system that
works efficiently.
However, some statements can be made
that are at least frequently true. In many
cases, for energy and budget reasons, it
makes sense to provide at least two-stage
solid-liquid separation, which is divided into a
thermal and a mechanical separation stage.
The decision in favor of specific technologies
is considerably more complex, because, on
the one hand, the material parameters of the
system (density, viscosity, particle size and
so on) must be observed, and on the other
hand, the objective of the separation step,
the value of the end product and the local
conditions must also be considered.
For non-compressible or moderately
compressible solids with average particle
diameters larger than 80 µm, continuous
filtration centrifuges have proven to be an
efficient solution, as they allow very good
dewatering on the one hand, and a high
throughput in
relation
to the investment
costs on the other hand [1].
Technology and operating principles
As shown in Figure 1, there are no significant
differences between a pusher centrifuge
and a screen-scroll centrifuge at first glance
when viewed from the outside.
Both machines are filled via a feed pipe,
and the solids are ejected at the front, with
Andritz
Andritz
FIGURE 1. A direct comparison of a pusher centrifuge (left) and a screen-roll centrifuge (right) does not reveal significant differences
from the outside
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