Carousel extractors

Carousel extractors suitable for extracting phytochemicals from plant materials have also been adopted from equipment used extensively in the oilseed extraction industry. The carousel extractor consists of a sectioned cylinder, as shown in Figure 11.14. Raw material is slurried with extract and loaded into the initial cell. Solvent is added to each cell countercurrently, collecting at the bottom of each cell, and is then pumped to the next cell. Either flooded (deep bed) or trickle (shallow bed) operation is possible depending on the solvent flow rate to each cell and equipment design. After draining the solvent in the last cell, the marc is discharged from the cell and conveyed to external solvent removal equipment. Concentrated extract is collected from the raw material feed cell. 

Throughputs available for carousel extractors range from 450 to 270,000 kg/hr (1-300 tons/hr). Retention times range between 45-180 minutes, again requiring proper raw material grinding to achieve percolation while having sufficiently rapid extraction. These extractors also require low labor to operate. 

Apart from different capacities of pumps, columns and vessels there are other equipment parameters which have to be chosen in respect to the product or the product group to be treated e.g. the number and type of separators, the number and arrangement of extractors (parallel, in series or in carousel mode), reflux systems or ex-proof design. A very important tool is the possibility to generate extract fractions using several separators in series. However, depending on the product requirements the separator types have to be chosen carefully because of their different characteristics. The following separators are available as a standard ... 

Employing a carousel, this extractor can operate with up to 24 extraction vessels. The speediness is a remarkable advantage over Soxhlet extraction. 

Hardly any batch-type oilseed extractors remain, and modern solvent extractors mainly are of two basic designs. In shallow bed-type extractors, a 0.5- to 1-meter-thick layer of collets or flakes is pulled across a linear screen (Fig. 8.6), or conveyed on a woven belt, and repeatedly percolated with solvent. Deep bed extractors mainly are constructed as carousels with pie-shaped cells (baskets), that are alternately filled (2-3 meters deep), extracted, and unloaded. In some designs, the baskets rotate between the loading, extraction, drainage, and unloading stations (Fig. 8.7) in others, the baskets are stationary with the various stations revolving (Fig. 8.8). Solvent flow always is countercurrent to the direction of... 

Fig. 8.7. Cutaway drawing of Rotocell Solvent Extractor. A carousel with deep-bed baskets rotates by a series of collet/flake loading, solvent extraction, drainage, and unloading stations. (By permission of Davy-Dravo, Inc., Pittsburgh, PA.)...

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