Reading. Read the text and explain why it is sometimes necessary to extract oil but not to press. Processes.

Cakes obtained by pressing operations still retain 3 to 15 percent of residual oil. When the value of the oil is considerably greater as oil than as a part of the meal, it is desirable to obtain more complete extraction with solvents. Modern commercial methods of solvent extraction use volatile purified hydrocarbons, especially the various grades of petroleum benzin. In large-scale operations, solvent extraction is a more economical means of recovering oil than is mechanical pressing. In the United States and increasingly in Europe, there are many instances of simple petroleum benzin extraction of seeds, mainly soybeans. For seeds or nuts containing a higher oil content than soybeans it became customary to press the material in screw presses to remove a large proportion of the oil before extraction.

A typical extraction system consists of:

1) cleaning to remove tramp iron, dirt, foreign weed seeds, and stones, 2) removing hulls in cracking, aspirating, or screening operations,

3) cracking or rough grinding the prepressed cake, 4) steaming (tempering or cooking) of the meats,

5) flaking the small pieces between smooth flaking rolls, 6) extracting the oil with solvent,

7) separating the meal, or marc, from the oil-solvent solution, and

8) removing the solvent from the marc. The marc may be toasted or pelletized, or both, for use in animal feeds.

Most extracted meals contain less than 1 percent of residual oil. The amount varies depending on the amount of prepressing, the type of material being extracted, and the efficiency of the extracting system.

Extractors.

Solvent extraction was first practiced in Europe, using batch extractors for the recovery of additional oil from the residues obtained from mechanical pressing. The greater efficiency of solvent extraction encouraged direct application to oilseeds, and the batch extractor gradually gave way to continuous units in which fresh flakes are added continuously and subjected to a counterflow of solvent. One of the earliest continuous extractors, and a type still considered to be one of the best, was the Bollman or Hansa-Mühle unit from Germany, in which solvent percolates through oilseed flakes contained in perforated baskets moving on an endless chain. After the extraction cycle is complete, the baskets of extracted flakes are dumped automatically and then refilled with fresh flakes to initiate another cycle. Many extractor designs have been proposed, but only a few have found wide acceptance. In the DeSmet extractor, popular in Europe and in a number of developing countries, a bed of flakes on an endless horizontal travelling belt is extracted by solvent percolation. The Blaw-Knox Rotocell has become the most popular extractor in the 139

huge American soybean industry. The flakes are conveyed into wedge-shaped segments of a large cylindrical vessel. Solvent percolating through the cells falls into the bottom of the extractor housing, where it is picked up by a series of pumps and recirculated countercurrent to the flakes.

Exercise 2. Translate the following word-combinations.

The bottom of the extractor housing, wedge-shaped segments, the efficiency of the extracting system, screening operations, the prepressed cake, purified solvents, marc pelletizing, in large-scale operations, between smooth flaking rolls, a large cylindrical vessel, on an endless horizontal travelling belt, a series of pumps.

Exercise 3. Answer the questions.

1. Why is it sometimes necessary to do extraction?

2. What are the most widespread solvents used in oil extraction? 3. What are the essential stages of an extraction system?

4. What factors does the residual oil amount depends on? 5. What are the most popular extractors?

Exercise 4. Give a title for the logical words group. 1) iron, dirt, foreign weed seeds, stones;

2) cracking, aspirating, screening;

3) wedge-shaped segments, cylindrical vessel, extractor housing, pumps.

Exercise 5. Complete each sentence with a word or phrase from the box.

commercial methods Blaw-Knox Rotocell screw presses cakes continuous solvent extractors

1. In ___ fresh flakes are added continuously and subjected to a counterflow of solvent. 2. ___ is the most popular extractor in the American soybean industry.

3. Modern ___ of solvent extraction use different organic solvents. 4. The seeds and nuts are pressed in ___ before extraction.

5. ___ containing up to 15% of residual oil are being processed to obtain more oil.

Exercise 6. Rewrite the following sentences replacing the words underlined with the expressions from the text which have similar meanings.

1. Baskets of extracted flakes are emptied automatically.

2. After the extraction cycle is finished, the baskets are refilled with fresh flakes to initiate another cycle. 3. Only some extractor designs have found wide application.

4. After dumping the baskets refilled to begin another cycle.

5. Solvent filtering through the cells falls into the bottom of the extractor housing.

Exercise 7. Complete the following sentences and rearrange them to get the summary of the text. 1. A typical extraction system consists of ….

2. First extractors were of the … type, but … extractors became more popular …. 3. The most popular extractor in Europe is ….

4. There are many …, but only a few ….

5. The solvent extraction is practised when …. 6. In the Blaw-Knox Rotocell ….

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Exercise 8. Translate in the written form.

LM Extractor

In the LM extractor the prepared material is transported on a perforated belt through the horizontal body of the extractor. Fresh solvent is introduced at the discharge end of the extractor and circulates against the flow of material, via a series of pumps, to become rich miscella (oil-solvent mixture) at the inlet of the extractor.

Thus, the extractor yields crude oil and meal, both laden with solvent, which is removed in the next sections.

The generally recognised advantages of the LM extractor are:

- the extractor comprises only one moving part: the belt conveyor,

- the layer of material going through the extractor is its own filter, which allows operation without miscella filters, the best possible design for very large plants,

- readily adjustable height of material and speed of the belt make it easy to process materials with different percolation parameters,

- the belt has a 3 percent upward slope, to accommodate materials of poor permeability.

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