Nueva Tecnologia En Centrifugas
Páginas: 15 (3605 palabras)
Publicado: 3 de febrero de 2013
Paper Number: 72G
Title:
CONTINUOUS LIQUID-LIQUID EXTRACTION VIA AN IMPROVED CENTRIFUGAL CONTACTOR
by:
David Meikrantz, Director of Technology Scott B. Meikrantz, Applications Chemist Mitch St. George, Regional Manager CIT
Prepared for presentation at the AIChE Spring National Meeting, March 8-12, 1998 Symposium on Extraction in Practice
Copyright © 1998 CIT January 15, 1998AIChE shall not be responsible for statements or opinion contained in papers or printed in its publication.
SUMMARY An improved annular centrifugal contactor design is being commercially employed in numerous liquid-liquid extraction applications. It is mechanically driven by a directly coupled motor at relatively low rotor speeds. The combination of interchangeable heavy phase weirs and variablerotor drive makes this centrifuge applicable to a wide range of processes. Single stage efficiencies of 90% or higher are typical for chemical systems with rapid kinetics. Mixing and disengaging times range from 10 to 30 seconds each, dependent on the feed rate to the unit and the unit size. Efficient two phase mixing is achieved in the annulus between the spinning rotor and fixed housing. Forversatility, a low mix sleeve can also be used to process shear sensitive liquids, often encountered in washing applications. Annular centrifugal contactors with rotor diameters of 5 to 51 centimeters which range in throughput from 2 to 750 liters per minute are now readily available. The criteria used to select the proper size and operating parameters needed will be discussed. In addition,convenient methods of using this technology to convert batch to continuous processing will be given. Advantages in yield improvement and waste minimization will be discussed, and process equipment footprint will be given. Finally, some field examples which describe the versatility of this liquid-liquid centrifugal contactor will be presented. INTRODUCTION
General Centrifuge
Clarification of processstreams has been one of the niches in the process arena carved by liquid-liquid centrifuges, especially whenever emulsions or liquids close in density have been involved (Davies et. al., 1972). Difficulties that often arise in separation of immiscible liquids include: poor or slow phase separation, emulsion or rag layer formation, and poor process control in batch systems. Centrifuges accelerateseparation processes by enhancing the specific gravity differences. Liquid-liquid dispersions requiring hours to separate at 1G will proceed much faster at 100 to 1000 G, with greatly improved efficiency and outflow quality. The efficiency of the physical separation of two phases can be several percent higher using centrifuges versus decanting from tanks.
Contactors as Extractors and WashersLiquid-liquid centrifuges are valuable separation devices because of their small size and the rapid, yet efficient operation. However, they become even more valuable when employed as liquid-liquid contactors. The ability of a centrifuge to thoroughly mix two phases in the annular zone prior to separation in the rotor broadens its scope. Good mixing is very important to ensure optimal mass transfer andto minimize solvent
Page 2
or water usage. Chemical processes requiring extraction and washing (or neutralization) as well as separation can be performed in one step utilizing liquid-liquid centrifugal contactors. Better process control, low retained fluid volume during processing, and reduced plant space usage are realized when using these devices in place of traditional tanks, mixersettlers, and extraction columns. ANNULAR CENTRIFUGAL CONTACTORS
History
Annular centrifugal contactor design and development has been pursued by various Department of Energy labs for more than 30 years. It has been employed in solvent extraction processes for metals valuable to the nuclear industry. Commercialization of this technology began in 1990 when a patent was granted for continuous...
Title:
CONTINUOUS LIQUID-LIQUID EXTRACTION VIA AN IMPROVED CENTRIFUGAL CONTACTOR
by:
David Meikrantz, Director of Technology Scott B. Meikrantz, Applications Chemist Mitch St. George, Regional Manager CIT
Prepared for presentation at the AIChE Spring National Meeting, March 8-12, 1998 Symposium on Extraction in Practice
Copyright © 1998 CIT January 15, 1998AIChE shall not be responsible for statements or opinion contained in papers or printed in its publication.
SUMMARY An improved annular centrifugal contactor design is being commercially employed in numerous liquid-liquid extraction applications. It is mechanically driven by a directly coupled motor at relatively low rotor speeds. The combination of interchangeable heavy phase weirs and variablerotor drive makes this centrifuge applicable to a wide range of processes. Single stage efficiencies of 90% or higher are typical for chemical systems with rapid kinetics. Mixing and disengaging times range from 10 to 30 seconds each, dependent on the feed rate to the unit and the unit size. Efficient two phase mixing is achieved in the annulus between the spinning rotor and fixed housing. Forversatility, a low mix sleeve can also be used to process shear sensitive liquids, often encountered in washing applications. Annular centrifugal contactors with rotor diameters of 5 to 51 centimeters which range in throughput from 2 to 750 liters per minute are now readily available. The criteria used to select the proper size and operating parameters needed will be discussed. In addition,convenient methods of using this technology to convert batch to continuous processing will be given. Advantages in yield improvement and waste minimization will be discussed, and process equipment footprint will be given. Finally, some field examples which describe the versatility of this liquid-liquid centrifugal contactor will be presented. INTRODUCTION
General Centrifuge
Clarification of processstreams has been one of the niches in the process arena carved by liquid-liquid centrifuges, especially whenever emulsions or liquids close in density have been involved (Davies et. al., 1972). Difficulties that often arise in separation of immiscible liquids include: poor or slow phase separation, emulsion or rag layer formation, and poor process control in batch systems. Centrifuges accelerateseparation processes by enhancing the specific gravity differences. Liquid-liquid dispersions requiring hours to separate at 1G will proceed much faster at 100 to 1000 G, with greatly improved efficiency and outflow quality. The efficiency of the physical separation of two phases can be several percent higher using centrifuges versus decanting from tanks.
Contactors as Extractors and WashersLiquid-liquid centrifuges are valuable separation devices because of their small size and the rapid, yet efficient operation. However, they become even more valuable when employed as liquid-liquid contactors. The ability of a centrifuge to thoroughly mix two phases in the annular zone prior to separation in the rotor broadens its scope. Good mixing is very important to ensure optimal mass transfer andto minimize solvent
Page 2
or water usage. Chemical processes requiring extraction and washing (or neutralization) as well as separation can be performed in one step utilizing liquid-liquid centrifugal contactors. Better process control, low retained fluid volume during processing, and reduced plant space usage are realized when using these devices in place of traditional tanks, mixersettlers, and extraction columns. ANNULAR CENTRIFUGAL CONTACTORS
History
Annular centrifugal contactor design and development has been pursued by various Department of Energy labs for more than 30 years. It has been employed in solvent extraction processes for metals valuable to the nuclear industry. Commercialization of this technology began in 1990 when a patent was granted for continuous...
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