Solvent extractors designs

Initial Extraction Technique Continuous extraction apparatus was employed, including an extractor designed to contain the starting plant materials, a distillation flask to hold the solvent mixture, the flask being equipped with a reflux condenser, a drip device to facilitate the removal of the volatilized mixture from the condenser and to percolate it through the continuous extractor, and a Soxhiet type return. Means for heating the continuous extraction system were provided. 

A small-scale chain conveyor type of extractor was developed in the 1940s at Iowa State University with the intent of using trichloroethylene solvent to extract soybeans. Crown Iron Works of Minneapolis, Minnesota, licensed the technology and extractor design, and supplied several continuous solvent extraction plants in 1951 using the new extractor and trichloroethylene solvent (6). The meal from these plants proved detrimental to animals, so the plants were either closed or converted to petroleum-based solvents (7). The chain-type extractor apparatus continued on and is the basis of the modern Crown Iron Works Model III extractor used today. 

Vmin implies that the feed and the leaving extract phase are in phase equilibrium. This is only possible with an infinite number of separating stages or with an infinite transfer time. Therefore, the actual solvent ratio v has to be chosen such that it is larger than Vn in. The value of v for extractor design and operation should result from cost estimates according to Fig. 6-16. 

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... 

Early extractor designs based on solvent percolation were basket-type extractors in which flaked seeds were placed in baskets with perforated bottoms. These systems looked like an enclosed bucket elevator. The baskets were supported by endless chains in a sealed housing and continuously raised and lowered at a slow rate (1 revolution/h). Each basket was filled with flaked seeds by an automatic feed hopper at the top. As the basket started descending solvent is sprayed over the baskets. The spent flakes in baskets ascended to the top of the housing on the opposite side of the feed hopper. At the top baskets were automatically inverted and spent seeds were discharged into a hopper, from which they were transferred to a meal desolventizer on a conveyor belt. Basket type extractors were bulky and hard to maintain. The newer extractor designs are horizontal and rotary type. The design principle for horizontal extractors is similar to the basket-type extractors but the baskets rotate in a... 

Immersion-type extractors have been made continuous through the inclusion of screw conveyors to transport the soHds. The Hildebrandt immersion extractor (18) employs a sequence of separate screw conveyors to move soHds through three parts of a U-shaped extraction vessel. The helix surface is perforated so that solvent can pass through the unit in the direction countercurrent to the flow of soHds. The screw conveyors rotate at different speeds so that the soHds are compacted as they travel toward the discharge end of the unit. Alternative designs using fewer screws are also available. 

The Hildebrandt total-immersion extractor is shown schematically in Fig. 18-80. The hehx surface is perforated so that solvent can pass through countercurrently. The screws are so designed to compact... 

If the desired product is fairly water soluble, simple extraction into organic solvents may not be an efficient means of recovery. In that case, continuous extraction of the aqueous solution with an organic solvent may be necessary to effect the recovery. Either of two types of apparatus are normally employed, and the correct design depends on the density of the organic solvent. For solvents less dense than water, the apparatus should be set up as in Fig. A3.11a. The barrel of the extractor is charged with the... 

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