60
Z. Xiao et al.
There are several types of extractors today. The deep-bed extractor and the
shallow-bed extractor are popular. The deep-bed extractor operates largely in a semicontinuous fashion with some individual baskets. The baskets are initially filled with
the flakes about depths of 2–3 m. The flakes are supported on a drainage screen,
which allows the miscella to pass but retaining the solid-phase material. As the
rotary extractor is constantly moving at a slow speed, the extract time in the extractor
is about 30–45 min. Shallow-bed extractors, whose bed depths are generally less
than 1 m, provide similar drainage screens in the form of slotted bars. The oilseeds
pretreated are continuously conveyed through zones where the countercurrent washing of the miscella occurs. After extracting, all the solid-phase material is dropped
into a hopper and is conveyed to the desolventizing system.
Temperature control is extremely important during the extraction process. As
extractability is enhanced with high temperatures, the operator generally desires
to keep temperatures as high as possible. However, phospholipase enzyme activity
affects the oil quality at these elevated temperature conditions, partially causing an
increase in non-hydratable phosphatides. While this trade-off is generally not a problem, when processing field-damaged seed it may be necessary to reduce extraction
temperature, sacrificing residual fats somewhat, in order to produce oil that can be
acceptably processed without undue refining losses. As mentioned earlier, several
processes have been developed to help inactive enzyme activity prior to extraction.
The extracted meal is drained in the extractor for some minutes, but, after discharge, it is still wet with residual solvent around 25–35%. The wet meal is conveyed from the extractor to the Desolventizer Toaster (DT). In the traditional system,
steam is used to counter-currently flash the volatile solvent from the solid phase. The
vapor phase then passes through the distillation system on its way to condensing and
collection.
The solvent from the DT is condensed, but it is usual to utilize the heat in the
solvent vapors to assist in distilling the solvent from the miscella. The air and vapors
from the solvent condensers and other parts of the extraction plant are finally freed
from the solvent before being discharged into the atmosphere.
2.5 Oil Refining
Preparing with crushing or extracting, without refined oils, is known as raw oil. Raw
oil’s main ingredient is triglyceride oil, commonly known as neutral oil. In addition,
the oil also exists in the other ingredients that are collectively referred to as impurities.
So vegetable oil products need raw oil to be refined. The general process is as shown
in Fig. 2.2.
Z. Xiao et al.
There are several types of extractors today. The deep-bed extractor and the
shallow-bed extractor are popular. The deep-bed extractor operates largely in a semicontinuous fashion with some individual baskets. The baskets are initially filled with
the flakes about depths of 2–3 m. The flakes are supported on a drainage screen,
which allows the miscella to pass but retaining the solid-phase material. As the
rotary extractor is constantly moving at a slow speed, the extract time in the extractor
is about 30–45 min. Shallow-bed extractors, whose bed depths are generally less
than 1 m, provide similar drainage screens in the form of slotted bars. The oilseeds
pretreated are continuously conveyed through zones where the countercurrent washing of the miscella occurs. After extracting, all the solid-phase material is dropped
into a hopper and is conveyed to the desolventizing system.
Temperature control is extremely important during the extraction process. As
extractability is enhanced with high temperatures, the operator generally desires
to keep temperatures as high as possible. However, phospholipase enzyme activity
affects the oil quality at these elevated temperature conditions, partially causing an
increase in non-hydratable phosphatides. While this trade-off is generally not a problem, when processing field-damaged seed it may be necessary to reduce extraction
temperature, sacrificing residual fats somewhat, in order to produce oil that can be
acceptably processed without undue refining losses. As mentioned earlier, several
processes have been developed to help inactive enzyme activity prior to extraction.
The extracted meal is drained in the extractor for some minutes, but, after discharge, it is still wet with residual solvent around 25–35%. The wet meal is conveyed from the extractor to the Desolventizer Toaster (DT). In the traditional system,
steam is used to counter-currently flash the volatile solvent from the solid phase. The
vapor phase then passes through the distillation system on its way to condensing and
collection.
The solvent from the DT is condensed, but it is usual to utilize the heat in the
solvent vapors to assist in distilling the solvent from the miscella. The air and vapors
from the solvent condensers and other parts of the extraction plant are finally freed
from the solvent before being discharged into the atmosphere.
2.5 Oil Refining
Preparing with crushing or extracting, without refined oils, is known as raw oil. Raw
oil’s main ingredient is triglyceride oil, commonly known as neutral oil. In addition,
the oil also exists in the other ingredients that are collectively referred to as impurities.
So vegetable oil products need raw oil to be refined. The general process is as shown
in Fig. 2.2.