Percolation extractors

A more recently developed continuous extractor is the horizontal perforated belt extractor, probably the simplest percolation extractor from a mechanical view point. Here... 

The American company, French Oil Mill Machinery Company of Piqua, Ohio, developed continuous solvent extraction plants starting in 1939, using a multistage BoUman-type percolation extractor (3). Soon thereafter, the Belgian Company, Extraction De Smet, started manufacturing continuous multistage belt-type extractors in 1945. V.D. Anderson of Cleveland, Ohio, joined the solvent extraction equipment supply market in 1948 with continuous HUdebrandt-type immersion extractors (5). 

Batch extractors mix a charge of solids and solvent and then let it drain. Immersion extractors cause the solids to pass through a pool of solvent. Percolation extractors carry the solids through a vapor-light chamber where solvent rains down through the solids, dissolving out the oil, similar to the way a coffee percolator works. There are hve major types of percolation extractors basket, rotary, perforated belt, slid-ing-bed, and rectangular loop (151). 

Perforated Belt Extractors. Another type of percolation extractor uses a moving, perforated belt underneath an extended bed of material. The belt is flexible and moves, with material riding on top, through the extraction chamber. 

Fresh hexane enters on the lower bed, makes several passes, or stages, on the lower bed, then continues on the upper bed in true countercurrent fashion, similar to other percolation extractors. Krupp s sliding-bed extractor accepts flaked materials. 

Crown also offers a ModellV extractor specifically designed for continuous extraction of powdery materials that cannot be extracted in percolation extractors (Figure 28). 

Percolation extractors provide for washing the solid material with solvent and for allowing the solvent and dissolved oil to separate from the solids through internal screens. Trying to do this with powdery materials would require screens with such fine mesh that the powder would blind the screen and prevent adequate solvent flow. 

Extraction equipment can be classified by the method used to contact the solid with the solvent. Two general extraction methods are used for extracting plant raw materials dispersed-solids extraction and percolation extraction. During dispersed-solids extraction, enough solvent is used to suspend the solids within the liquid. A stirred tank is the simplest example of a dispersed-solids extraction. In a percolation extractor, solvent flows through a fixed bed of ground raw material. 

Two principle types of extractors have been employed—immersion extractors and percolation extractors (Fig. 11.11). An immersion extractor immerses and soaks the material to be extracted in solvent (a laboratory example is the Soxhlet extractor). Immersion extractors require more solvent usage and have material conveyance problems therefore, percolation extractors almost exclusively predominate in the industry today. Early soybean extractors were immersion extractors, but the industry quickly moved to percolation extractors. In a percolation extractor, the solvent percolates by... 

The extraction principles employed by most percolation extractors are the same, but the method by which each achieves countercurrent flow of solvent to flakes is different. The shallow-bed, chain extractor (Fig. 11.12), which resenibles a full-loop conveyor, is one of today s widely used extractors. Crown Iron Works (Minneapolis, MN) manufactures this type of extractor. In early versions that still exist in the industry, flakes are fed into an inlet hopper and are conveyed down the first leg of the loop where they are washed with moderately dilute miscella to extract surface oil and penetrate the cells. As the flake bed moves into the bottom horizontal section, full miscella is recycled through the bed for filtering, and then to a liquid cyclone for final... 

Wingard and Philhps developed a madiematical model to describe the effect of temperature on extraction rate using a percolation extractor as follows ... 

Arnold and Choudhury reported results derived from a lab scale extraction of soybean and cottonseed flakes in a tubular percolation extractor at 135-140T with pure, high purity and commercial hexane, and reagent grade benzene. They claimed that pure hexane extracted soybean slower than high purity and commercial hexane. During the first 60 minutes of extraction, benzene extracted more oil than the hexanes. However, at the end of 80 minutes, benzene extracted only slightly more than pure hexane but definitely less than the commercial hexanes. Similar results were obtained for the four solvents when cottonseed flakes were extracted. 

Figure 14.10.3. Schematic of bench-scale dynamic percolation extractor.

In a BoUmann extractor solids are continuously passed through, percolation extractor, gas-proof shell with endless chain and buckets for solids transport, cocurrent flow of solids and sprayed solvent on the left side, countercurrent flow on the right side of the bucket elevator, self-filtration effect. 

Percolation extractor with solids transport by a belt conveyor from chamber to chamber countercurrently to the solvent. Solvent is sprayed on the solids by means of feed pumps, increase of extraction yield possible by increasing solvent supply and if the solvent is circulated before it is passed to the next stage. 

Revolving extractor, countercurrent gravity percolation extractor, solvent-proof body with slowly rotating vanes (rotating individual extraction sections). The rotary-vane passes the continuously fed conditioned solids from the feed shaft over a fixed sieve tray in one rotation to the solids discharge shaft. Sieve tray slots are concentric and expanded at the bottom. At the same time solvent is trickled over the solids. Solvent percolates through the solids and the sieve tray and collected in underneath extract chambers. Countercurrent flow of solids and solvent. 

Combination of immersion and percolation extractors has also been used for oil extraction from oilseed. This process involves partial extraction of the oil in a percolation extractor (until there is 10-15% residual oil in the seeds) followed by wet flaking of the partially defatted seed as it comes out of the percolation extractor. This operation is carried out in a special solvent-tight flaker operating in a solvent vapor-saturated atmosphere. Finally, flaked seeds are extracted in an immersion-type extractor. The advantage of this process is that seeds are extracted at a low temperature (maximum 50 °C) and the subsequent meal desolventizing is carried out lower than 105 °C, producing a meal suitable for protein concentrates and isolates manufacturing (Bemardini, 1976). 

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