2 Industrial Plant Oil Extraction
57
operations refer to receiving, sampling, drying, storage, and cleaning. Although there
are some variants, for example, some processors may clean the oilseed both before
and after the drying operations, the basic operations are designed to accomplish the
same task, which is to provide a safe haven for the oilseed and deliver it at the proper
time and condition at the processing facility.
As the fresh oilseeds are from the field, they will contain some contaminants,
consisting of sticks and pods, metal and rock accumulated during handling, and
contamination from weed seeds and other seeds. People will sample the oilseeds
and make adjustments in the price paid based on the moisture, heat damage, and
other factors. Typically the oilseeds receipts are segregated based on these quality
factors, with the moisture content being one of the prime factors for separation. For
proper storage and subsequent processing, the contaminants must be removed and
the oilseeds must be dried prior to storage. As oilseeds freshly harvested may have a
moisture content of up to 40%, they must generally be dried to around 13% moisture
for safe extended storage. High moisture damage typically results in reduced oil
content, decreased protein, and increased color, and refining loss of the extracted oil.
A precursor to this damage is often indicated by a rising oilseed temperature, and
many storage facilities are equipped with a series of temperature cables embedded
in the oilseeds with indicating and recording equipment located in the manager’s
office. If left unchecked, the oilseeds will spontaneously heat and become damaged
and under extreme conditions, a fire may develop. It is routine practice to monitor the
temperature of the oilseeds daily and, if heating is occurring, immediately process
the oilseeds. If this is not possible, or the degree of heating is not severe, the manager
may simply move the oilseeds from one place to another.
The oilseed is usually scaled when arriving at the preparation facility. After weighing the seed, it then undergoes a thorough cleaning process to remove sand, stalks,
plant debris, and any other foreign matter. Cleaning is by rotary or table sieves, usually with air aspiration by fans, and cyclones for dust removal from the air. After
cleaning, some seeds with hull should be decorticated by impacting the seed, breaking and separating the hulls. The traditional process continues with the cracking
rolls, which are a set of two or three high corrugated rolls turning at relatively high
speeds that break the oilseeds into several pieces. After decortication, the oilseeds
are delivered to the conditioner where heat is gently applied to make the cracks soft
and pliable for the subsequent flaking operation. Conditioning is carried out in a
cooker equipped to heat the seeds by indirect steam, adding water and direct steam
as required. Flaking of the seed particles is done in roller mills with smooth roller
surfaces. The flake thickness in a typical case is between 0.2 and 0.3 mm. To achieve
this reduction in thickness, the rollers of the mill are pressed together, usually by
hydraulic pressure, and rupture of the seed cells occurs, which makes oil recovery
possible.
57
operations refer to receiving, sampling, drying, storage, and cleaning. Although there
are some variants, for example, some processors may clean the oilseed both before
and after the drying operations, the basic operations are designed to accomplish the
same task, which is to provide a safe haven for the oilseed and deliver it at the proper
time and condition at the processing facility.
As the fresh oilseeds are from the field, they will contain some contaminants,
consisting of sticks and pods, metal and rock accumulated during handling, and
contamination from weed seeds and other seeds. People will sample the oilseeds
and make adjustments in the price paid based on the moisture, heat damage, and
other factors. Typically the oilseeds receipts are segregated based on these quality
factors, with the moisture content being one of the prime factors for separation. For
proper storage and subsequent processing, the contaminants must be removed and
the oilseeds must be dried prior to storage. As oilseeds freshly harvested may have a
moisture content of up to 40%, they must generally be dried to around 13% moisture
for safe extended storage. High moisture damage typically results in reduced oil
content, decreased protein, and increased color, and refining loss of the extracted oil.
A precursor to this damage is often indicated by a rising oilseed temperature, and
many storage facilities are equipped with a series of temperature cables embedded
in the oilseeds with indicating and recording equipment located in the manager’s
office. If left unchecked, the oilseeds will spontaneously heat and become damaged
and under extreme conditions, a fire may develop. It is routine practice to monitor the
temperature of the oilseeds daily and, if heating is occurring, immediately process
the oilseeds. If this is not possible, or the degree of heating is not severe, the manager
may simply move the oilseeds from one place to another.
The oilseed is usually scaled when arriving at the preparation facility. After weighing the seed, it then undergoes a thorough cleaning process to remove sand, stalks,
plant debris, and any other foreign matter. Cleaning is by rotary or table sieves, usually with air aspiration by fans, and cyclones for dust removal from the air. After
cleaning, some seeds with hull should be decorticated by impacting the seed, breaking and separating the hulls. The traditional process continues with the cracking
rolls, which are a set of two or three high corrugated rolls turning at relatively high
speeds that break the oilseeds into several pieces. After decortication, the oilseeds
are delivered to the conditioner where heat is gently applied to make the cracks soft
and pliable for the subsequent flaking operation. Conditioning is carried out in a
cooker equipped to heat the seeds by indirect steam, adding water and direct steam
as required. Flaking of the seed particles is done in roller mills with smooth roller
surfaces. The flake thickness in a typical case is between 0.2 and 0.3 mm. To achieve
this reduction in thickness, the rollers of the mill are pressed together, usually by
hydraulic pressure, and rupture of the seed cells occurs, which makes oil recovery
possible.