Equipment Podbielniak extractor

During recent years pilot scale equipment, smaller than the prototype pilot plants described and capable of operating with exceedingly high efficiency, has been designed. Such equipment as the York-Scheibel solvent extraction tower and the Podbielniak countercurrent centrifugal mixer and extractor are typical. Data from this equipment may be correlated with commercial performance. 

Residence time can be as short as 10 sec. One 750 gpm unit is said to have a total liquid holdup of 200 gal. From 3-10 stages per unit have been reported, although Table 14.8 shows a range of 1.8-7.7. A 65 in. dia casing can accommodate throughputs up to 25,000 gal/hr. An economic comparison of a Podbielniak with other extractors is made in Table 14.5(b). Although its basic cost is high, it requires few auxiliaries so that the overall cost of an extraction plant is not drastically out of line in every instance. Nevertheless, this equipment is used primarily when short residence time and other characteristic features are indispensable. 

Extraction is a process that utilizes the difference in solubility of the product of interest between two immiscible phases. Liquid-liquid extraction is commonly used in classical biotechnological downstream processing for production of antibiotics and other small molecules. The second liquid phase is usually a water immiscible organic solvent. Reciprocating plate, Podbielniak centrifugal extractors, Delaval contactors, and Westfalia extraction-decanters are examples of some of the equipment available for carrying out extraction. 

Proprietary Extractors. Manufacturers or proprietary design extraction equipment (such as the Podbielniak Centrifugal Extractor or the RTL (raining bucket) Contactor) provide catalogs listing the relative capacities of the various sizes of equipment which are offered. Pilot equipment is usually available for determining extraction performance, and the manufacturer utilizes both the pilot data and experience with similar systems to provide assured commercial designs. 

Most large-scale equipment for liquid-liquid extraction is available for two-phase extraction and usually multistage systems have to be used for obtaining high yields. Ktihni type columns, Podbielniak centrifugal extractors and disk and bowl centrifuges have been used (Kula et al. 1981 Veide et al. 1983 Cunha and Aires-Barros 2002). 

Figure 5.6 Podbielniak centrifugal extractor. Source With permission from B P Process Equipment and Systems LLC.

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