Continuous centrifugal extractors

A new countercurrent continuous centrifugal extractor developed in the former USSR (214) has the feature that mechanical seals are replaced by Hquid seals with the result that operation and maintenance are simplified the mechanical seals are an operating weak point in most centrifugal extractors. The operating units range between 400 and 1200 mm in diameter, and a capacity of 70 m /h has been reported in service. The extractors have been appHed in coke-oven refining (see Coal conversion processes), erythromycin production, lube oil refining, etc. 

Countercurrent contactors, design of, 10 757 Countercurrent continuous centrifugal extractor, 10 781... 

After the neutralisation of the alkaline catalyst with an acid, the polyether is diluted with n-hexane. The polyether solution is contacted with water in counter flow using continuous centrifugal extractors. As a consequence of the extraction, two layers appear the upper layer contains a solution of polyether in hexane and the lower layer contains water and the potassium salt. The upper layer is separated and the pure polyether is obtained by solvent vacuum distillation. The disadvantages of this process are a large volume of wastewater and the necessity of solvent recovery and recycling. 

Wiped film stills in place of continuous still pots —Centrifugal extractors in place of extraction columns —Flash dryers in place of tray dryers —Continuous reactors in place of batch —Plug flow reactors in place of CFSTRs —Continuous in-line mixers in place of mixing vessels... 

Morita, Y., Kubota, M., Glatz, J.P. et al. 1996. Actinide partitioning from HLW in a continuous DIDPA extraction process by means of centrifugal extractors. Solvent Extr. Ion Exch. 14 (3) 385-400. 

Continuous glycerin washing of soap produced by saponification has been demonstrated in a countercurrent centrifugal extractor (38). The device achieves phase separation with as little as 0.02 specific gravity difference and accomplishes up to 10 theoretical stages of extraction. Some of the advantages over prior operations reportedly include flexibility in feed, low holdup, less waste due to more efficient separation, simple operation, rapid startup, and small space requirements. 

The continuous centrifuge is fed with salt slurry from the evaporators. Figure 5 shows the main components and operating principles for this type of unit. The salt slurry from the evaporators is continuously fed from the top inlet where it falls between the helicoidal blades of the extractor and the conical basket. The basket... 

The Podbielniak and Alfa Laval centrifugal extractors are essentially continuous differential contactors. The Westfalia and Robatel centrifugal extractors contain discrete mechanical stages, and flow from one to another is effected by spill over discs and skimmers according to usual centrifugal clarifier practice. As the number of discrete stages is increased, the allowable flow rates are proportionately decreased. 

Centrifugal extractor product of the density difference with the interfacial tension (Mg/m, mN/m) <1 and number of theoretical stages needed <6. Cannot handle dirty systems or high phase ratios. For continuous differential type machines (density differences >0.05 kg/L drop diameter >200 pm) six to eight stages per machine. For discrete, disc type machines (density differences >0.02 kg/L and handle drops <200 pm) 2 to 3 stages per machine. 

Alternative The washing can be done in a Podbielniak centrifugal extractor, which is continuous countercurrent extraction. Alternately, the same can be done in a cascade of annular centrifugal extractors configured in the countercurrent mode. It is known that the amount of cold water required and the loss of the API would be far less compared with values for the crosscurrent process [18]. 

When a continuous-flow centrifuge or pressure filter apparatus is used, the determination of the soluble binder content is conducted by the weight difference method, as in the case of the extraction method with a centrifugal extractor (see Section 9.6.1.1). 

With the development in the fermentation broth of concentrations of the order of 500 O.U./cu. cm. total penicillin (80 per cent penicillin-G), the concentration procedures have not required adsorption on activated carbon (158). A presently recommended flowsheet (89) involves continuous, countercurrent, multistage extraction of the filtered and acidified (pH 2 to 2.15) broth with a one-fifth volume of amyl acetate in the centrifugal extractor at room temperature similar extraction into a volume of cold buffer solution (pH 6.8 to 7.0) acidification to pH 2 and reextraction into a K... 

Apart from the extraction equipment itself, columns, mixer-settlers, or centrifugal extractors, the remainder of the plant is usually fairly conventional. It is usually necessary to provide vessels for conditioning the feed solution to the correct acidity or for correcting the concentrations of the principal solute or other salts. This may be carried out continuously or in special batch conditioning vessels. In the latter case, batch feed vessels will also no doubt be required. 

H Hemfort. (Westfalia) Continuously operating solid-jacket counterflow centrifugal extractor. US Patent 4147293, 3 April 1979 W Ostkamp. K H Brunner, F Wibbelt. (Westfalia) Continuously, completely jacketed, countercurrent centrifugal extractor. US Patent 4451247, 29 May 1984 A H Shapiro. (Bird Machine) Conveyorless clarifier. US Patent 5067939, 26 November 1991... 

Laboratory Extractors. Pilot-Scale Testing, and Scale-Up. Several laboratory units arc useful in analysis, process control, and process studies. The AKUFVE contactor incorporates a separate mixer and centrifugal separator. It is an efficient instrument for rapid and accurate measurement of partition coefficients, as well as for obtaining reaction kinetic data. Miniature mixer-settler assemblies set up as continuous, bench-scale, multistage, countercurrent, liquid-liquid contactors are particularly useful Tor the preliminary laboratory work associated with flow-sheet development and optimization because these give a known number of theoretical stages. 

Details of Centrifugal Separators and Use.—No continuously operating separator of the extractor type has been successful. The stumbling block to attaining this end has been the continuous removal of the solids formed but a choice of machine best suited to the work will often increase capacity. If there be not much liquid to be extracted the batch to be placed in the machine may be worked in a removable basket. 

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