Title: OIL AND FAT TECHNOLOGY LECTURES III Crude Oil Production
1OIL AND FAT TECHNOLOGY LECTURES III (Crude
Oil Production)
- Prof.Dr.Aytaç SAYGIN GÜMÜSKESEN
- Yrd.Doç.Dr.Fahri YEMISÇIOGLU
2Extraction of Vegetable Oils
- Basic approaches
- Mechanical Oil Extraction
- - cold pressing means no heat applied
- - hot pressing - external heat is applied
- Solvent Extraction
- - organic solvent (hexane, isopropyl alchool)
- - supercritical solvent (carbondioxide)
3Mechanical oil extraction
- Mechanical oil extraction (expression) is a
solid-liquid phase seperation method which is
applied to cooked seed flakes. - It can be executed by batch, mainly
hydraulically, and by continous, mainly
mechanically, working presses.
4- Screw presses
- In oil industry, screw presses (expellers) are
mostly utilized for expression. The main parts of
continous-screw press are - Seed feeder,
- Cone-shaped cage
- Adjustable cone for press-cake outlet
- Worm (pressure and feed)
5Cooked seed flakes
Adjustable cone for press-cake outlet
knife
Cone shaped pressure cage
Main worm shaft
cake
Crude oil
6- The seeds enter the barrel and falls on the
helical pressure worm.During movement in the
barell, between worm and cage is gradually
reduced and the seed flakes are subjected to
increasing pressure.The cage is made of a number
of special stell bars which let liquids pass
through. The oil passes between the bars an flows
out of the cage. The cone moves along the shaft
of the expeller and the space between the worm
and cone can be regulated.This permits easy
control of the thichnesses of cakes and of the
degree of pressure to which the cooked flakes are
subjected.
7Screw Press
8Shaft Arrangement-- Screw Press
9Cage ArrangementFrench Press
10- Advantages and disadvantages of the expeller
process - Expellers can be used with almost any kind of
oilseeds and nuts. The process is relatively
simple and not capital-intensive. While the
smallest solvent extraction plant would have a
processing capacity of 100-200 tons per day,
expellers are available for much smaller
capacities, from a few tons per day and up. - The main disadvantage of the screw-press process
is its relatively low yield of oil recovery. Even
the most powerful presses cannot reduce the level
of residual oil in the press-cake below 3 to 5.
In the case of oil-rich seeds such as sesame or
peanuts this may still be acceptable.
Furthermore, most of the oil left in the cake can
be recovered by a stage of solvent extraction.
Such two stage processes (pre-press/solvent
extraction) are now widely applied . In the case
of soybeans, however, a 5 residual oil level in
the cake represents an oil loss of about 25.
Solvent extraction of the cake would not be
economical, because of the bulk of material which
must be processed.
11- The quality of the meal is therefore a factor of
particular importance in the selection of a
processing method for soybeans. In this respect,
the expeller process has several disadvantages.
The first is the poor storage stability of the
press-cake, due to its high oil content.
Furthermore,the extreme temperatures prevailing
in the expeller may impair the nutritive value of
the meal protein, mainly by reducing the
biological availability of the amino acid lysine.
At any rate, expeller press-cake is not suitable
for applications requiring a meal with high
protein solubility.
12Crude oil production (mechanical expression)
- Cooked flakes
- Screw press
- Crude oil seed particles
Cake -
(4-6oil) - Crude oil seed particles
13Crude oil production (pre-pressing extraction
solvent extraction)
- Cooked flakes
- Screw press
- Crude oil
Oily cake -
(10-16 oil) -
- Cake (0.5 oil)
Solvent extraction -
-
Crude oil
14Solvent extraction(solid-liquid
extraction-leaching)
- The lowest levels of residual oil after pressing
are 3-8 exhaustive removal of the oil present
in the cake by mechanical means alone is
imposible. The residual oil in cake , therefore,
only be removed by a different approach, this
being solvent aided extraction.
15 miscella V1
Solvents V0
Seed flakes solvents
Cake L1
flakes L0
L0 V0 L1
V1
16 A B C
A C
B C
B
A inert solid B solvent C oil
17- Basic principles of solvent extraction The
extraction of oil from oilseeds by means of
non-polar solvents is, basically, a process of
solid-liquid extraction. The transfer of oil from
the solid to the surrounding oil-solvent solution
( miscella ) may be divided into three steps - diffusion of the solvent into the solid
dissolution of the oil droplets in the - solvent diffusion of the oil from the
solid particle - to the surrounding liquid
18- Due to the very high solubility of the oil in the
commonly used solvents, the step of dissolution
is not a rate limiting factor. The driving force
in the diffusional processes is, obviously, the
gradient of oil concentration in the direction of
diffusion. Due to the relative inertness of the
non-oil constituents of the oilseed, equilibrium
is reached when the concentration of oil in the
miscella within the pores of the solid is equal
to the concentration of oil in the free miscella,
outside the solid. These considerations lead to a
number of practical conclusions -
19- Since the rate-limiting process is diffusion,
much can be gained by reducing the size of the
solid particle. Yet, the raw material cannot be
ground to a fine powder, because this would
impair the flow of solvent around the particles
and would make the separation of the miscella
from the spent solid extremely difficult. The
oilseeds are rolled into thin flakes, thus
reducing one dimension to facilitate diffusion,
without impairing too much the flow of solvent
through the solid bed or contaminating the
miscella with an excessive quantity of fine solid
particles.
20- The effect of flake thickness on the efficiency
of solvent extraction
Solution extraction
Diffussion extraction
21- The rate of extraction can be increased
considerably by increasing the temperature in the
extractor. Higher temperature means higher
solubility of the oil, higher diffusion
coefficients and lower miscella viscosity. - An open, porous structure of the solid
material is preferable, because such a structure
facilitates diffusion as well as percolation. A
number of processes have been proposed for
increasing the porosity of oilseeds before
solvent extraction.
22- Although most of the resistance to mass
transfer lies within the solid, the rate of
extraction can be increased somewhat by providing
agitation and free flow in the liquid phase
around the solid particles. Too much agitation is
to be avoided, in order to prevent extensive
disintegration of the flakes.
23- Choice of solvents
- An ideal solvent for the extraction of oil from
oil seeds should possess the following
properties - Good solubility of the oil. Poor
solubility of non-oil components. High
volatility (i.e. low boiling point), so that
complete removal of - the solvent from the miscella and the
meal by evaporation is - feasible and easy. Yet, the boiling
point should not be too low, so that extraction
can - be carried out at a somewhat high
temperature to facilitate mass - transfer. Low viscosity. Low latent
heat of evaporation, so that less energy is
needed for - solvent recovery. Low specific heat, so
that less energy is needed for keeping the - solvent and the miscella warm. The
solvent should be chemically inert to oil and
other - components of the seed flakes. Absolute
absence of toxicity and carcinogenicity, for the
solvent - and its residues. Non-inflammable,
non-explosive. Non-corrosive Commercial
availability in large quantities and low cost.
24- A typical commercial solvent for oil extraction
would have a boiling point range (distillation
range) of 65 to 70oC and would consist mainly of
six-carbon alkanes, hence the name "hexane by
which these solvents are commonly used in oil
extraction. - The quality parameters which make up the
specifications usually include boiling
(distillation) range, maximum non-volatile
residue, flash point, maximum sulphur, maximum
cyclic hydrocarbons, colour and specific gravity.
25- Types of Extractors
- Solvent extractors are of two types
- batch
- continuous
- In batch processes, a certain quantity of flakes
is contacted with a certain volume of fresh
solvent. The miscella is drained off, distilled
and the solvent is recirculated through the
extractor until the residual oil content in the
batch of flakes is reduced to the desired level.
26 Seed flakes
solvent
cake
miscella
27- In continuous extraction, both the oilseeds and
the solvent are fed into the extractor
continuously. The different available types are
characterized by their geometrical configuration
and the method by which solids and solvents are
moved one in relation to the other, in
counter-current fashion.
28- Two different methods can be used to bring the
solvent to intimate contact with the oilseed
material - percolation
- immersion
29- In the percolation method, the solvent trickles
through a thick bed of flakes without filling the
void space completely. A film of solvent flows
rather rapidly over the surface of the solid
particles and efficiently removes the oil which
has diffused from the inside to the surface. This
mode of contact is preferable whenever the
resistance to diffusion inside the flake is
relatively low (thin flakes with large surface
area, open tissue structure).
30- In the immersion mode, the solid particles are
totally immersed in a slowly moving, continuous
phase of solvent. Immersion works better with
materials offering a greater internal resistance
to oil transfer (thick particles, dense tissue
structure).
31Percolation type extractor
- Belt extractors_(DE SMET extractor) The
extractor consists of a horizontal, sealed vessel
in which a slowly moving screen belt is
installed. Flaked oil seeds are fed on the belt
by means of a feeding hopper. A damper attached
to the hopper outlet acts as a feed regulating
valve and maintains the solids bed on the belt at
constant height. This height can be adjusted
according to the expected rate of percolation of
the miscella through the bed. Difficult
percolation is compensated for by lowering bed
height. The throughput rate of the extractor is
adjusted by changing the belt speed. There are no
dividing baffles on the belt and the solid bed is
one continuous mass. Yet the extractor is divided
to distinct extraction stages by the way in which
the miscella stream is advanced.
32- The solvent is introduced at the spent flake
discharge end. It is sprayed on the flakes,
percolates through the bed, giving the spent
flakes a last wash and removing some oil. The
resulting dilute micella is collected in a
sectional hopper underneath the belt, from which
it is pumped and sprayed again on the flakes at
the next section in the direction opposite to
belt movement. This process of miscella
collection, pumping and spraying at the next
section is repeated until the miscella leaves the
hopper at the head-end of the extractor, carrying
the highest concentration of oil (heavy
miscella).
33- The screen is washed with heavy miscella at the
head-end, just before the entrance of fresh
flakes, and then again with fresh solvent, right
after the discharge of spent flakes.Washing of
the screen is essential to prevent clogging.
Washing with full miscella at the feed-end
provides surface lubrication and prevents
adhesion of the flakes to the surface of the
screen. The entire extractor vessel is maintained
at a slight negative pressure so as to prevent
leakage of solvent vapours to the atmosphere.
34Belt Extractor (DeSmet)
Seed flakes
high oil seed flakes
Pure solvent
Miscella
Cake (0.5 oil)
Full miscella 25 oil
35Continuous horizontal extractor
36Bollmann extractor
37Basket type- Sliding cell extractor (Lurgi)
In this class of extractors, the flakes do not
constitute a continuous mass but are filled into
separate, delimited elements (baskets) with
perforated bottoms for draining. The baskets can
be moved vertically (bucket elevator extractors),
horizontally ( frame belt and sliding cell
extractors), or can be rotated around a vertical
axis (roto-cell extractors). Vertical
bucket-chain extractors are among the first
industrial solvent extractors constructed for
continuous operation. Many are still in operation
but they are less frequently found in more recent
installations.
38Sliding cell extractor (Lurgi)
39Roto-cell extractor (Reflex extractor-DeSmet)
40Rotocell extractor
41Hildebrandt extractor(immersion type)
- The solid material is extracted according to the
immersion method. Screw conveyors are installed
in the extractor for transporting the solid
material. Again the solvent flows countercurrent
to the solid materials through the extractor.
42Hildebrandt extractor
43 44- Post-extraction operations
-
- Two streams leave the solvent extraction stage
- an oil-rich fluid extract (full miscella)
- cake meal (spent flakes)
- The next operations have the objective of
removing and recovering the solvent from each one
the two streams.
45- a.Miscella distillation Full miscella contains
typically 30 oil. Thus, for every ton of crude
oil some 2.5 tons of solvent must be removed by
distillation. Most manufacturers of solvent
extractors also offer miscella distillation
systems. - The characteristics of a good miscella
distillation system are - good energy economy,
- minimal heat damage to the crude oil and its
components, - minimal solvent losses ,
- efficient removal of the last traces of solvent
from the oil - good operation safety.
- The modes of solvent vaporization include flash
evaporation, vacuum distillation and steam
stripping.
46- Miscella filtration Because of the quality
criteria for crude oils, but also to ensure the
least possible fluid transport defects (clogging
in pumps, pipes etc.) and heat transfer
resistances, the miscella must be freed of solide
meal particles with special closed filter presses
before proceeding to distillation. - Miscella distillation Distillation is the most
energy consuming part of the total extraction
process.In general the evaporation is carried out
in two or three stages, mostly in longtube type
evaporators with a vapor head.
47- b. Meal desolventizing The spent flakes carry
with them about 35 solvent. The removal and
recovery of this portion of the solvent is also
one of the most critical operations in oil mill
practice, since it determines, to a large extent,
the quality of the meal and its derivatives.
48- The most common type of desolventizer-toaster
consists of a vertical cylindrical stack of
compartments or "pans". Each compartment is
fitted with stirrers or racks attached to a
central vertical shaft. Spent flakes are fed at
the top of the desolventizer-toaster. The pan
floors are equipped with adjustable-speed
rotating valve, to permit downward movement of
the material , through the pans, at the desirable
rate.
49- Two methods of heating are used
- direct steam heating
- indirect steam heating
- For heating with indirect steam, the pans are
equipped with double bottoms acting as steam
jackets. For direct steam heating, hot live steam
is injected into the mass through spargers. The
rotating stirrers spread the material and provide
the necessary mixing action.
50- Direct steam is used for three reasons
- The transfer of heat from the heated surface of
the pan floor to the oilseed material is slow and
difficult, especially after a considerable
proportion of the solvent has been removed and no
fluid medium is available for heat transfer. In
this case, direct contact between the solid
material and condensing steam is a more efficient
method of heating. Condensation of the steam adds
moisture to the flakes. - The added moisture facilitates the protein
denaturation reactions leading to the
inactivation of trypsin inhibitor (for soybean
cake). It is also believed that the toasting
effect accomplished by the combined action of
heat and moisture enhances the palatability of
the meal to animals. - The steam distillation effect is necessary in
order to remove last traces of solvent from the
meal.
51 52Soybean oil production
53Sunflower oil production
- Sunflower seed
- Cleaning
foreign matter -
- Dehulling hulls
- Flaking
- Cooking
- Pressing
crude oil
54Cottonseed oil production
- Cottoseed
- Cleaning
foreign matter - Delinting lints
- Dehulling hulls
- Flaking
- Cooking
- Pressing
crude oil
55Rapeseed oil production
- Rape seed
- Cleaning
foreign matter -
- Flaking
- Cooking
- Pressing
crude oil - Oily cake