A centrifugal extractor uses the rotation of an internal rotor to mix two immiscible liquids and separate them using centrifugal force. As the liquids enter the rotor, they are accelerated toward the wall and separation begins based on density differences. Weirs allow each separated phase to exit individually and flow by gravity to downstream stages without pumps. Configurations include mixing and separating the phases, separating pre-mixed liquids via direct feed, and multi-stage processing for continuous solvent extraction.

1. CENTRIFUGAL EXTRACTOR
(LIQUID-LIQUID EXTRACTION)
Group no. 12
11BCH056-60

2. INTRODUCTION
A centrifugal extractor—also known as a centrifugal
contactor or annular centrifugal contactor—uses the
rotation of the rotor inside a centrifuge to mix
two immiscible liquids outside the rotor and to separate
the liquids in the field of gravity inside the rotor. This way,
a centrifugal extractor generates a
continuous extraction from one liquid phase (fermentation
broth) into another liquid phase (organic solvent).
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3. WORKING OF CENTRIFUGE
Two immiscible liquids of different densities are fed to the separate
inlets and are rapidly mixed in the annular space between the
spinning rotor and stationary housing. The mixed phases are directed
toward the center of the rotor by radial vanes in the housing base. As
the liquids enter the central opening of the rotor, they are accelerated
toward the wall. The mixed phases are rapidly accelerated to rotor
speed and separation begins as the liquids are displaced upward. A
system of weirs at the top of the rotor allow each phase to exit the
rotor where it lands in a collector ring and exits the stage. Flow from
between stages is by gravity with no need for inter-stage pumps. The
centrifugal contactors thus acts as a mixer, centrifuge and pump.
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4. • Mix and separation.
• Separation by direct feed.
• Multi-stage processing.
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CONFIGURATION OF
CENTRIFUGE
CENTRIFUGE

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MIX AND
SEPERATION
CENTRIFUGE

6. The mix & separation configuration is the standard
operation for centrifugal contactors used for liquid-
liquid extraction processes. The two liquids (typically
an aqueous phase (heavy) and an organic phase (light))
enter the annular mixing zone where a liquid-liquid
dispersion is formed and extraction occurs as solutes
(e.g. dissolved metal ions) are transferred from one
phase into the other. Inside the rotor, the liquids will be
separated into a heavy (blue) and a light (yellow) phase
by their respective densities. This proportion of each
phase (phase ratio), total flow rate, rotor speed, and
weir sizes are varied to optimize separation efficiency.
The separated liquids are discharged without pressure
and flow by gravity to exit the stage
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SEPERATION BY DIRECT FEED
CENTRIFUGE

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For applications requiring only separation of a
pre-mixed dispersion (e.g. oil/water
separation in environmental cleanup), the
direct feed offers the option to feed the mixed
liquid stream at a low sheer force directly into
the rotor. Inside the rotor, the liquids will be
separated into a heavy (blue) and a light
(yellow) phase. This principle is used to
optimize the separation efficiency. The
separated liquids will be discharged without
pressure.
CENTRIFUGE

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MULTISTAGE PROCESSING
CENTRIFUGE

10. • Typically for solvent extraction processes in stage-
wise equipment such as the centrifugal contactor,
we would have multiple contactors in series for
extraction, scrubbing, and stripping (and perhaps
others). The number of stages needed in each
section of the process would depend on process
design requirements (necessary extraction
factor). In this case, four interconnected stages
provide a continuous process in which the first
stage is a decanting stage. The next two stages
show a counter current extraction. The last stage
is a neutralization as a cross stream
interconnection.
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