yoil and fat technology lectures iii crude oil production

8/10/2019 Yoil and Fat Technology Lectures III Crude Oil Production

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Extraction 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)


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Mechanical 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.


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Screw presses;

In oil industry, screw presses (expellers) aremostly 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)


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Screw pressCooked seed flakes

Crude oil

Main worm shaft

knife

cake

Adjustable cone for press-

cake outlet

Cone shaped pressure

cage


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The seeds enter the barrel and falls on the helical

pressure worm.During movement in the barell,

between worm and cage is gradually reduced andthe 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.


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Screw Press


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Shaft Arrangement--

Screw Press


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Cage Arrangement

French Press


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Advantages and disadvantages of theexpeller process;

Expellers can be used with almost any kind of oilseeds and nuts. Theprocess is relatively simple and not capital-intensive. While thesmallest solvent extraction plant would have a processing capacityof 100-200 tons per day, expellers are available for much smallercapacities, from a few tons per day and up.

The main disadvantage of the screw-press process is its relatively lowyield of oil recovery. Even the most powerful presses cannot reducethe level of residual oil in the press-cake below 3 to 5%. In the caseof oil-rich seeds such as sesame or peanuts this may still beacceptable. Furthermore, most of the oil left in the cake can berecovered by a stage of solvent extraction. Such two stage

processes (pre-press/solvent extraction) are now widely applied . Inthe case of soybeans, however, a 5% residual oil level in the cakerepresents an oil loss of about 25%. Solvent extraction of the cakewould not be economical, because of the bulk of material which mustbe processed.


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The quality of the meal is therefore a factor of

particular importance in the selection of aprocessing method for soybeans. In thisrespect, the expeller process has severaldisadvantages. The first is the poor storage

stability of the press-cake, due to its high oilcontent. Furthermore,the extremetemperatures prevailing in the expeller mayimpair the nutritive value of the meal protein,mainly by reducing the biological availability ofthe amino acid lysine. At any rate, expellerpress-cake is not suitable for applicationsrequiring a meal with high protein solubility.


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Crude oil production

mechanical expression)

Cooked flakes

Screw press

Crude oil + seed particles Cake

(4-6%oil)

Crude oil seed particles


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Crude 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


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Solvent 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 mechanicalmeans alone is imposible. The residual oil

in cake , therefore, only be removed by a

different approach, this being solvent aided

extraction.


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Single stage leaching

Seed flakes +

solvents

flakes L0

Solvents V0

Cake L1

miscella V1

L0 + V0 = L1 + V1


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Ideal equilibrium

A + C

B B + C

A ; B + C

A : inert solid

B : solvent

C : oil


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Basic principles of solvent extraction:The

extraction of oil from oilseeds by means of

non-polar solvents is, basically, a processof solid-liquid extraction. The transfer of oil

from the solid to the surrounding oil-

solvent solution ( miscella ) may be dividedinto three steps:

*diffusion of the solvent into the solid

*dissolution of the oil droplets in thesolvent

*diffusion of the oil from the solid particle

to the surrounding liquid


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Due to the very high solubility of the oil in

the commonly used solvents, the step ofdissolution is not a rate limiting factor. Thedriving force in the diffusional processesis, obviously, the gradient of oilconcentration in the direction of diffusion.Due to the relative inertness of the non-oilconstituents of the oilseed, equilibrium isreached when the concentration of oil inthe miscella within the pores of the solid isequal to the concentration of oil in the freemiscella, outside the solid. Theseconsiderations lead to a number ofpractical conclusions:


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* 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 thespent 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 throughthe solid bed or contaminating the miscella with

an excessive quantity of fine solid particles.


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The effect of flake thickness on the efficiency of

solvent extraction

Diffussion extraction

Solution extraction


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*The rate of extraction can be increased

considerably by increasing the

temperature in the extractor. Highertemperature 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 havebeen proposed for increasing the porosity

of oilseeds before solvent extraction.


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*Although most of the resistance to

mass transfer lies within the solid, therate of extraction can be increased

somewhat by providing agitation and

free flow in the liquid phase aroundthe solid particles. Too much agitation

is to be avoided, in order to prevent

extensive disintegration of the flakes.


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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 othercomponents 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.


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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 untilthe residual oil content in the batch of

flakes is reduced to the desired level.


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Batch extractor

solvent

cake

miscella

Seed flakes


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In continuous extraction, both the

oilseeds and the solvent are fed intothe 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.


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Two different methods can be used to

bring the solvent to intimate contact with

the oilseed material:

percolation

immersion


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In the percolation method, the solventtrickles through a thick bed of flakes

without filling the void space completely.A film of solvent flows rather rapidlyover the surface of the solid particlesand efficiently removes the oil which has

diffused from the inside to the surface.This mode of contact is preferablewhenever the resistance to diffusion

inside the flake is relatively low (thinflakes with large surface area, opentissue structure).


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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).


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Percolation type extractor

Belt extractors_(DE SMET extractor);The extractorconsists of a horizontal, sealed vessel in which a

slowly moving screen belt is installed. Flaked oilseeds are fed on the belt by means of a feedinghopper. A damper attached to the hopper outletacts as a feed regulating valve and maintains thesolids bed on the belt at constant height. This

height can be adjusted according to the expectedrate of percolation of the miscella through the bed.Difficult percolation is compensated for bylowering bed height. The throughput rate of theextractor is adjusted by changing the belt speed.There are no dividing baffles on the belt andthe solid bed is one continuous mass. Yetthe extractor is divided to distinct extractionstages by the way in which the miscellastream is advanced.


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The solvent is introduced at the spent flakedischarge end. It is sprayed on the flakes,percolates through the bed, giving the spentflakes a last wash and removing some oil.The resulting dilute micella is collected in asectional hopper underneath the belt, from

which it is pumped and sprayed again onthe flakes at the next section in the directionopposite to belt movement. This process ofmiscella collection, pumping and spraying

at the next section is repeated until themiscella leaves the hopper at the head-endof the extractor, carrying the highestconcentration of oil (heavy miscella).


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Belt Extractor DeSmet)

Seed flakesPure solvent

Miscella

Cake (0.5% oil)Full miscella 25% oil

high oil

seed

flakes


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Continuous horizontal extractor


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Basket 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 fordraining. 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.


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Sliding cell extractor (Lurgi)


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Roto-cell extractor

Reflex extractor-DeSmet)


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Hildebrandt extractor

immersion type)

The solid material is extracted according to

the immersion method. Screw conveyors

are installed in the extractor fortransporting the solid material. Again the

solvent flows countercurrent to the solid

materials through the extractor.



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Extraction unit (DeSmet)


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Post-extraction operations

Two streams leave the solvent extraction stage ;

an oil-rich fluid extract(full miscella)

cakemeal(spent flakes)The next operations have the objective ofremoving and recovering the solvent from each

one the two streams.


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a.Miscella distillation:Full miscella contains typically30% oil. Thus, for every ton of crude oil some 2.5 tons ofsolvent must be removed by distillation. Most

manufacturers of solvent extractors also offer miscelladistillation systems.

The characteristics of a good miscella distillationsystem are:

good energy economy,

minimal heat damage to the crude oil and itscomponents,

minimal solvent losses ,

efficient removal of the last traces of solvent from

the oil good operation safety.

The modes of solvent vaporization include flashevaporation, vacuum distillationand steam stripping.


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Miscella filtration ;Because of the quality criteria

for crude oils, but also to ensure the least

possible fluid transport defects (clogging inpumps, 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 longtubetype evaporators with a vapor head.


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b. Meal desolventizing:The spent flakescarry 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.


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The most common type of desolventizer-

toaster consists of a vertical cylindrical

stack of compartments or "pans". Eachcompartment is fitted with stirrers or racks

attached to a central vertical shaft. Spent

flakes are fed at the top of thedesolventizer-toaster. The pan floors are

equipped with adjustable-speed rotating

valve, to permit downward movement ofthe material , through the pans, at the

desirable rate.


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Direct steam is used for three reasons:

*The transfer of heat from the heated surface of the panfloor to the oilseed material is slow and difficult,

especially after a considerable proportion of the solventhas been removed and no fluid medium is available forheat transfer. In this case, direct contact between thesolid material and condensing steam is a more efficientmethod 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 toastingeffect 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.


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Desolventizer
http://www.fao.org/inpho/content/compend/img/ch19/ph02600.htm


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Soybean oil production
http://www.fao.org/inpho/content/compend/img/ch19/ph02600.htm


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Sunflower oil production

Sunflower seed

Cleaning foreign matter

Dehulling hulls

Flaking

Cooking

Pressing crude oil

Oily cake

Solvent extraction cake l + solvent

Miscella Toaster solvent

Distllation solvent Cake

Crude oil


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Cottonseed oil production

Cottoseed


Delinting lints

Dehulling hulls

Flaking

Cooking

Pressing crude oil

Oily cake




Crude oil


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Rapeseed oil production

Rape seed


Flaking

Cooking

Pressing crude oil

Oily cake




Crude oil

yoil and fat technology lectures iii crude oil production

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