Meal desolventizing

All necessary storage tanks and receiving tanks The slurry tank complete with agitator Batch filter and meal desolventizer Decanter still Water still... 

In 1855, Deiss of Marseilles, France, was first to employ solvent extraction (1). He used carbon disulfide to dissolve olive oil retained in spent olive cakes. This technology used batch solvent extraction, where the material was held in a common kettle for both the extraction process as well as the subsequent meal desolventizing process. Deiss obtained a patent for batch solvent extraction of olive oil in 1856 (1). Small batch solvent extraction plants were installed in France and Italy, and by 1870, small batch solvent extraction facilities had spread across Europe. Larger scale solvent extraction plants were supplied by Rose, Downs, and Thompson (2) of Hull, England, starting in 1898. 

In the first continuous solvent extraction plants in Germany, the meal was desolventized in Schnecken s desolventizers. The Schnecken s desolventizer design consisted of a series of steam-jacketed conveyors, stacked one above the other, which used indirect heat to desolventize the meal. This was the prevalent meal desolventizer design used by all equipment suppliers through the 1940s. 

Because of special safety considerations, the solvent extraction process is constructed in a separate facility from the seed preparation process. The solvent extraction process consists of five closely interrelated unit processes solvent extraction, meal desolventizing, meal drying and cooling, miscella distillation, and solvent recovery. 

The solvent retention of the drained material is a bit of a misnomer, and it would be more accurately defined as the weak miscella retention. The weak mis-cella retained in the drained material contains approximately 1 % oil. In the meal desolventizer, the solvent is evaporated leaving behind the traces of oil, often referred to as the residual oil. In order to minimize the residual oil left in meal, it is important to minimize the amount of weak miscella carried forward to the meal desolventizer. 

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. 

The solvent extraction process consists of the unit operations of solvent extraction, meal desolventizing, meal drying and cooling, miscella distillation, and solvent recovery. These unit operations are highly interrelated, primarily because of various heat recovery methods that link the operations together. A process upset in any one of the unit operations will typically cause abnormal operation in the others. The key to efficient solvent extraction operation is process consistency. Consistency of seed preparation, consistency of rate, and consistency of solvent extraction operating parameters are all important factors in operating a safe, environmentally friendly, and cost-effective solvent extraction process for oil extraction. 

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. 

Table 10.3 shows the results regarding product quality. It is compared with PDI and contents of secondary plant substances of different materials a commercial press cake from an oil mill, a commercial meal made from this press cake in the same oil mill, two at 75°C and 95°C fluidized-bed desolventized meals, produced by extraction of the commercial press cake in our own small pilot-scale extraction facility as well as an air desolventized meal. The meals desolventized in the fluidized-bed desolventizer have the highest PDI. On the other hand, there is no effect of the fluidized bed desolventizing on secondary plant substances. 

Becker, K. W. 1983. Current trends in meal desolventizing. JAOCS, 2, 216-219. 

In the 1800 s small batch type oil extraction systems were common in Europe. The same vessel was used for both extraction and meal desolventizing. Today, only extraction of specialty and high value oils and recovery of oil from spent bleaching clay are carried out in batch extractors. A rotating drum and a vertical cylindrical kettle equipped with a vapor tight cover and a low-speed agitator are two popular batch type extractor designs. 

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... 

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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