Meal desolventizer toaster

After the prepared material has had its oil extracted in the solvent extractor, it is conveyed to the meal desolventizer toaster, commonly referred to as the DT. The material entering the DT is typically at the extractor temperature of 60°C, and it contains 25-35 %(w/w) of solvent. The primary purpose of the DT is to remove the solvent from the meal fraction so that the solvent can be recovered. 

Condensed solvent and water from the meal desolventizer/toaster and the oil stripper must be separated in gravity water separators before recycling solvent to the extractor. The water phase is then heated to remove residual hexane. Hexane losses must be minimized, and much engineering has gone into reducing hexane loss, which is now typically - I L/metric ton of soybeans processed. 

Mechanically Extracted Meals. Solvent extracted oilseed meals typically contain less than 1.5% residual fat unless the gums (hydrated phosphatides) or soapstock have been added back to the meal before the desolventizer-toaster or meal dryer. Mechanically extracted (expeller or screw-pressed) meals can contain 4—9% oil, which can be a significant calorie source in animal feeds. Fat contents of extracted meals are not part of the definition, although typical analyses are shown below. 

High nitrogen solubihty index (NSI), soy protein for manufacture of meat analogs is prepared in flash desolventizers. Some soybean extraction plants send part of their marc through a flash desolventizer to serve the high NSI soy flour market and the balance of their marc through desolventizer/toasters to serve the animal feed soy meal market. The first flash desolventizer was commissioned by EMI Corporation (Em. Corp., Des Plaines, Illinois) in 1960 (214). 

The meal goes through a desolventizer/toaster and is cooled and stored. High heat in the de-solventizer/toaster is an important step for the complete removal of solvent and for the deactivation of tripsin inhibitor which is critical for feeding ruminants. 

The residual solvent in the meal as it leaves the extractor is usually about 25%-35% by weight. The desolventizer-toaster heats the meal and solvent and vaporizes and steam strips the solvent from the meal at atmospheric pressure. 

Pressing followed by hexane extraction leads to the highest oil yield. The meal contains only about 1% residual oil. After solvent extraction, the used hexane has to be removed from the meal which is done in desolventizer toaster (DT) systems. During this process step, the proteins within the meal are partially damaged leading to losses of functionality (Becker, 1983 Natsch, 2006 Krause, 2007). 

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