Direct solvent extraction extractor design

For oleaginous materials having a low oil content (18-20%), such as soybean and rice bran, solvent extraction is often applied for oil recovery. Hexane is widely accepted as the most effective solvent used today. Most of the extractors currently used are designed as countercurrent flow devices. The solid material flows in an opposite direction of solvent-oil miscella with an increasing oil concentration. The miscella containing around 25-30% oil after extraction is subjected to solvent distillation to recover the oil. The extracted solid material, commonly known as white flakes, is also conveyed to the desolventizing process. 

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. 

A true continuous extraction requires that fresh solvent continuously flow through the sample and that fresh sample be continuously flowing in the opposite direction. If the system is designed properly, the compound of interest will be completely extracted from the sample just as the sample reaches the end of the apparatus, and the extracting solvent will be saturated with the extracted compound when it reaches the end of the apparatus. Several such continuous countercurrent extractors are shown in Figure 10-2. 

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... 

---