CENTRIFUGAL EXTRACTOR(LIQUID-LIQUID EXTRACTION)

Group no. 1211BCH056-60

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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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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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• Mix and separation.• Separation by direct feed.• Multi-stage processing.

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CONFIGURATION OF CENTRIFUGE

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MIX AND SEPERATION

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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

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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.

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MULTISTAGE PROCESSING

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• 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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