Mechanical Extraction and Sieving

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Mechanical Extraction

Robi Andoyo, STP., M.Sc


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Basic Principles

Mechanical force involved : pressing

Product : extract liquid suspension (oil, juices)

Driving force : pressure diff. And maximum pressureapplied

Resistance : structure or physical characteristics ofmaterials being extracted, size, viscosity of liquid phase(extract)

Separate components from cell (fruit juices)

flowtoResistance

)difference(pressureforceDrivingextractionofRate !


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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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Factors Influence Extraction

Pressure

Time of maximum pressure applied

Size and shape of material being extracted Physical characteristic of solid component

(hard, soft, semi elastic)

Viscosity of liquid component (internalresistance)


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Maximum Extraction Rate

High pressure (gradual), longer time of pressing

Heating : less viscous, easy to flow, remove

moisture, release oil from intact cells

Add solvent : easy realese, less viscous

Size reduction : > surface area, cell wall

destructed 2 step

ex : coconut oil extractionstep 1 : > surface area

step 2 : cake size reduction


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Juices Extraction

Goal: maximum quantity of juice

No substantial quantities of solids,

No phenolic compounds (skins) :bitternessand browning

Achieved by :

Lower pressures and

Fewer pressings

Increase the pressure slowly (dense cake)


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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 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.


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Screw Press


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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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Tank Press

Equipment for

expressing juice or oils

Increase in pressure

during pressing process

High yields of good-

quality juice are obtained

Capacities ranging from3600 kg to 25 000 kg


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Hydrolic Press


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Sieving

Robi Andoyo, STP., M.Sc


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SIEVING

Solid-solid separation

To give a series of particles classified into size

ranges

The material is shaken or agitated above a

mesh or cloth screen;

Particles of smaller size than the mesh openings

can pass through under the force of gravity. The mesh was originally the number of

apertures per inch


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Rates of throughput of sieves

Nature and the shape of the particles

Frequency and the amplitude of theshaking

Methods used to prevent sticking orbridging of particles in the apertures ofthe sieve

Tension and physical nature of the sievematerial.


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Tyler Sieve

A convenient factor of 20.5and this has

been chosen for the standard series of

sieves in use in the United States, the

Tyler sieve series


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Fineness Modulus (FM)

An empirical factor obtained by

adding the total percentages of a

sample of the aggregate retained oneach of a specified series of sieves,

and dividing the sum by 100.

In general a small value indicated a fine material

while a large value indicates a coarse material


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Standard sieve size

US Mesh Sieve Hole Size (mm) Total Percent

Retained

3/8 0,371 0

4 0,185 4

8 0,093 21

14 0,046 46

28 0,0232 74

48 0,116 89

100 0,0058 957 329

FM = 329/100 = 3,29


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Average Diameter (Davg)

D = 0.0082 (2)F

M

Smallest sieve size diameter x 20.5 x ratioFM


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Industrial Sieves

Mechanical Extraction and Sieving

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