by chandresh

1. By-Praveen Tiwari

2. Definition-
 Mechanical-
 operated by a machine or machinery.
 Separation-
 it is a method to achieve any phenomenon that converts a
mixture of chemical substance into two or more distinct
product mixtures, which may be referred to as mixture, at
least one of which is enriched in one or more of the
mixture's constituents.
 In some cases, a separation may fully divide the mixture into
its pure constituents.

3. Introduction-
 Mechanical separation in food processing include two
main operations i.e. removal of substances or material
and their classification.
 Mechanical separation equipment is used extensively
in food manufacturing, preservation or preparatory
operation.
 Mechanical separation are based on differences of
density and size/shape of the food particles/pieces.

4. Separation table

5. Process involved
Mechanical separations can be divided into four
groups –
 sedimentation,
 centrifugal separation,
 filtration and
 sieving.

6. 1. sedimentation
 It is settling of matter to
the bottom of a fluid so as
to separate suspended
solids from fluids.
 Sedimentation is very often
used in the food industry
for separating dirt and
debris from incoming raw
material, and dust or
product particles from air
streams.

7. 1.1 Sedimentation of Particles in a Gas
 An important application, in the food
industry, of sedimentation of solid particles
occurs in spray dryers.
 In a spray dryer, the material to be dried is
broken up into small droplets of about 100
micro m diameter and these fall through
heated air, drying as they do so.
 The necessary area so that the particles will
settle can be calculated in the same way as
for sedimentation.

8. 2. Centrifugal separation
 Centrifugal separation or centrifugation is a process in
which two heterogeneous mixtures of phases are separated
from each other by the application of centrifugal force.
 The phases may be solid, liquid or gas. The basic principle
governing is the density difference.

9. 2.1 Solid-liquid separation
 The fruit fibres are suspended in juice. Sugar is
crystallized from the solution and separated thereafter.
 The solid matter either floats or settles in the tank in
due course of time because of the density difference
between the two phases.
 To achieve quick settling centrifugal force is used, and
the process is called centrifugal settling.

10. Centrifugal filtration
 allowing the slurry through a porous medium.
 The rate of separation depends on the particle size of
the slurry, the pore size of the filter medium and the
pressure differential at both side of the filter medium.
 the filters are attached concentrically to the cylindrical
bowl and the flow of liquid is horizontal unlike
normal filtration process.
 can be batch or continuous types.

11. 2.2 Liquid-liquid separation
 Because of density differences, the lighter liquid
separates from the heavier liquid, if allowed to stand
for some time.
 Milk is a good example of emulsion where fat is in the
finely dispersed state where as the skim milk is in
continuous phase.

12. 2.3 Solid-gas separation
 Solid particulates separation from a gas stream is very
common phenomenon in food processing operations.
 The separation of milk powder from the drying air
stream coming from the drying chamber of a spray
dryer after drying is a good example of solid-gas
separation.
 The peripheral attachment required for this operation
to accomplish is called cyclone separator.

13. 3. Filtration
 Filtration is a unit operation where
separation of insoluble solids from a
solid-liquid suspension is done with the
application of mechanical or gravity force
through a porous membrane.
 The solids are retained in the porous
medium and form a layer, called filter
cake.
 The driving force for the separation of
the two phases may be gravity force or
mechanical force.

14. 3.1 principle of operation
 The driving force for filtration is most often the
pressure difference.
 In the beginning of the filtration process, filtrate flows
easily through the medium with least resistance.
 The rate of filtration which is the ratio of filtrate
volume and time of filtration is high in the beginning.
 But, as the filtration progresses, the layer of cake
deposition upstream gradually increases.

15. 4. Sieving
 During sieving the sample is
subjected to horizontal or vertical
movement in accordance with the
chosen method.
 This causes a relative movement
between the particles and the sieve;
depending on their size the
individual particles either pass
through the sieve mesh or are
retained on the sieve surface.
 Sieve shakers are used for
mechanical sieving.

16. Why to use mechanical separation?
 To save time,
 Cost efficient method,
 Increases efficiency,
 Can used for wide range of application, etc.