SUGAR INDUSTRY :
Cane Sugar or table sugar is chemically kinown as sucrose. Which is used
all over the world as a sweetening agent, being the important sugar
economically.
In India Cane Sugar or Sucrose is obtained from sugar cane.
MANUFACTURE OF CANE SUGAR :
Sucrose or Cane Sugar is Manufactured by following steps.
1)
Extraction of juice.
2)
Purification of juice.
3)
Concentration or evaporation of juice.
4)
Crystallisation of Sugar.
5)
Separation of crystals.
1)
EXTRACTION OF JUICE :
The cane is first washed to remove mud and dirt. Then the sugar cane are
cut into small pieces by sharp revolving knives. The cane chips (piece) are then
passed to a two rolled crusher and four (4) three rolled mills arranged in series
to extract juice.
As the cane pieces passes through the crusher 50% of the juice is extract,
then the bagasse passes to the first rolling mill containing three rollers. As the
bagasses pass from crusher to first rolling mill a juice from 2nd rolling mill is
spread to extract maximum cane sugar (Sucrose) from it. The juice is collected
in the pan kept below chrusher and first rolling mill, which is directly send to
boiling house.
Bagasse still contains some juice which is then successively passed to
second, third and fourth rolling mill. As the bagasse moves from first mill to
second mill the juice from 3rd rolling mill is spread on bagasse, then when the
bagasse moves from 2 nd mill to 3rd mill the judice collected at bottom pan of the
4th rolling mill is spread. While moving the bagasse from 3rd to 4th rolling mill
not water spread on bagasse. Thus totally 96% of the sucrose is extract from
sugar cane.
2)
PURIFICATION OF JUICE :
The juice is brownish green opaque liquid containing 10-20% sugar and
water soluble and insoluble impurities like pectic substances, organic matter,
colouring matter, reducing sugars, gums, mineral salts, fine particles of bagasse,
vegetable protein. All these impurities hampers crystallization of sucrose. The
juice is acidic having a pH from 5.1 to 5.7, the acidic pH of juice helps to
convert sucrose into glucose and fructose which are non crystallisable. So
immediate after extraction the pH of juice is adjusted to 7 to 7.3 and filter to
remove the impurities the process is called defection.
DEFINITION :
Defection is a process in which solid and suspended impurities are
removed from juice by filtration.
After removal of solid impurities the judice is taken to defection tanks.
The syrup is heated and then treated with milk of lime with required quantity
and pH of the juice is maintained at 7 to 7.3. Due to this treatment pectice
substances, vegetable protein, gums, colloidal matter, pitch, fibre, clay etc are
precipitated. Here phosphate is also ppt as tricalcium phosphate.
Then the hot juice is taken into settling tank where it separates into three
layers. The upper layer is a thick scum of ppt. matter, middle layer is a clear
juice and bottom layer is heavy precipitates like mud particles etc.
The middle layer consisting of juice is taken out, filtered, concentrated
and crystallized into raw sugar. Thus raw sugar is obtained. Which is slightly
coloured.
To obtain the white sugar sulphitation and carbonation process are
followed.
The juice from the setting tank after defection is taken into contact
bottomed tank & sulphur dioxide gas is passed through the heated juice at 103o
C. Thus the suspended impurities get settled down. This process is called as
sulphitation process. Many times this process is repeated from second time so it
is called as double sulphitation.
In some industries the white sugar is prepared by carbonation process.
After defection process the juice is filtered off. Then excess of lime juice is
added and high alkaline condonation is maide due to which the non-sugar and
coloured impurities are ppt in the folm of non soluble precibitates. The process
of carbonation is repeated for second time which is called as double
carbonation.
The juice is then filtered and sent to concentration in multiple effect
evaporators. During filtration mud and scum are filtered under pressure to
produce cakes. Cakes contain some sucrose and phosphate salts so it is used as
manure.
(3)
CONCENTRATION OF JUICE :
(Concn of Juice to Syrup)
The clarified juice or purified judice contains about 85% water. It is
concentrated into thnk syrup under reduced pressure in multiple effect
evaporators. Usually triple effect evaporators are used in which heating is done
by stem.
An evaporator is a tall cylindrical iron vessel with a bottle necked top and
spheroidal bottom. It is fitted with two steel plates thus dividing the vessel into
three parts the top and bottom chambers are called juice chambers and the
middle chamber is steam chamber for heating. The top and bottom juice
chambers all connected by several narrow and few wide pipes, the juice moves
up through narrow tubes and comes down through under tubes, thus gets heated
by circulation.
Three such evaporators P1, P2 and P3 all connected to each other having
an heating col. C1, C2 and C3, the last is connected to vaccum pump. Heating
of juice in evaporator P1 is carried by passing steam through heating coil C1. At
this time pressure in first evaporator i.e. P1 is maximum and vacuum is
minimum. Thus the water in juice is converted in Vapour i.e. steam and this
steam is passed to evaporator II where the juice is heated, thus in evaporator II
the pressure is less than P1 and vacuum II more than P1. Due to this low
pressure and high vacuum in P2 the low temp. Steam coming from P1 keeps the
juice boiling and these the juice becomes more concentrate. Then the juice is
passed from top of P2 evaporator to bottom of P3 similarly it is healed by steam
from P2 and the juice is concentrated into a thick syrupy liquid. Thus the syrup
is a conc. juice, which is then passed to crystallization.
4)
CRYSTALLISATION :
The thick syrup obtained from multiple effect evaporator still contains
about 9% water. The syrup is again conc. in a single effect evaporator or
vacuum pan. Which is smilar to evaporator used in conc. of juice or multiple
effect evaporator, it is fitted with heating coil, vacuum gauge, candenser, a
thermometer sampling stick. Here the juice is concentrated upto crystallization
point.
The juice is then taken to crystallisaton tank. Crystalisation is carried by
two ways.
(1)
Graining :- As the syrup is again concentrated in single evaporator or
vacuum pan the sucrose percentage is increased to 85%. At this conc. and temp
even sucrose doesn’t crystallizes, it can be crystallized by
1)
Waiting method.
The Syrup is gradually cools down to break super saturation and thus
sucrose crystallizes out.
2)
Shock treatment.
In this treatment the syrup is suddenly cooled down by mixing large
quantity of cooled syrup or by increasing vacuum. The symp is tested on watch
glass and if shining small crystal all observed it is a breakdown point.
2)
Growth of Crystals :
After small crystals all seen in the syrup i.e. graining point, some sucrose
crystals all added as a seedings and then large quantity of syrup is added again
and sucrose is forced to come out of syrup.
A semisolid mass of syrup is called as massecuite. A massecuite is then
taken crystallizer which is a hollow rotating tank with acuum in it. The
massecuite is cooled slowly. Then the sucrose crystallizes out. The sucrose from
masseuite. A is called a grade sugar. While from B and C are College B Sugar
and C Sugar resp. the molasses from massecuite A, B C all molasses A, B, C.
In molasses B & C the syrup is added again and massecuite having
similar sucrose percentage as massecule A is prepare.
5)
SEPARATION OF CRYSTALS :
(CENTRIFUGATION)
The massecuite is then taken to the centrifuge machine to separate the
sugar crystals from the mother liquor. The centrifuge machine is a perforated
cylindrical basket. Mounted on a vertical shaft, which rotates the basket,
through the poses of basket only liquid can pass but not the sugar crystals.
The hot massecuote is taken into centrifuge machine and the basket is
rotated at an 2000 rpm. Due to this the syrup flows through the holes
(perforations) and the sugar crystals remain in basket. The sugar crystals are
grayish brown in colour due to fine film coating of molasses, which are washed
by a spray of water.
Then the sugar crystals are dried, separated according to the size.
* REFINING OF RAW SUGAR :
A raw light brown sugar which is converted to pure white sugar by
processes is called refining of raw sugar, which is done by following operations.
1)
Affination :
The raw brown sugar is mixed with a sugar syrup containing 60-80%
sucrose. Due to this upper thin coloured film of molasses get dissolved into the
syrup. Thus the impurities around the sugar crystals are removed. The sugar
crystals are all shed with water and dissolved in water and a syrup of sucrose
having 50-60% sucrose is made. Which is then sent for purification.
2)
Purification :
During the manufacture of raw sugar some insoluble impurities like clay,
gum, pectins, some coloured comps. Which escapsed through the purification
process all removed hereby defection.
To adjust the pH and remove these impurities liming, sulphitation and
carbonation processes are used. Due to these the impurities are converted into
insoluble precipitates. Some heavy ppt settles down and other remain floating
on surface. Both these are removed by filtration.
3)
DECOLOURISATION :
The filtered liquid is clear, dark brown in colour, having still some
dissolved impurities. Then this liquid is passed through the bone charcoal. As
the liquid passes through the bone charcoal the coloured and dissolved
impurities get adsorbed on charcoal and a clear, colourless pure Syrup is
obtained.
Other methods used for decolusisation are.
(a)
Activated cabon process.
A fine powder of activated carbon is used for decolmrisation. It is more
effective than bone charcoal. It is added to the defected juice in purification step
and then it is removed by filtration. Thus the judice is made colourless to obtain
while sugar.
(b)
ION exchange region.
To remove the coloured and dissolved impuntes, the juice is passed
through cation exchange column and then through anium exchange column, it is
a modern technique, but more costly and the advantage of this method is that the
resin can be used for several times.
(c)
Sulphitation Process :
To the clear juice SOA2 Sulphur dioxide gas is passed to precipitate the
coloured soluble impurities and the juice is filtered off. As the SO2 gas is
passed for second time the process is double sulphitation.
(d)
Carbonation Process :
Here excess of lime is again added to precipitate the gum, pectims and
other soluble impurities.
4)
Crystallisation :
The Sugar juice due to defection process is dilute it is concentrated by
evaporator in vacuum and under reduced pressure. The thick syrup is then sent
to crystallizes. Where due to centrifugal force the liquid is removed and the
sucrose crystals are separated by centrifugation in vacuum pan or crystallizes
pan. The sucrose is washed and dried by passing hot air.
Manufacture of white Sugar.
Same as manufacture of Sugar.
BY PRODUCTS OF SUGAR INDUSTRY :
Use of byproducts of Sugar industry reduces the price of Sugar (Sucrose)
manufacturing, it also gives additional employment and reduces the waste.
The two important by products of Sugar Industry all (1) Molasses (2)
Bagasse.
(A)
Bagasse :
It is a cane residue obtained from the last roller mill after complete extra
of juice. It contains about 50-55% sold and rest is water the solid mainly is
cellulose fiore and pith.
The vasions uses of bagasse are
1)
It is used as a fuel to raise steam.
2)
Used to mancifacutre hard board or particle board called celotax. As it is
bad conductor of heat it is used as insulator.
3)
It is used in manufacture of paper.
4)
It is used as a fectilizers.
5)
After removing gum or stick substances it is used to manufacture
valuable wax and gums.
6)
Pith is separated from the fibre then on acid treatment it is converted to
furfural. A imp. industrial chemical used in preparation of hylon intermediates.
(B)
MOLASSES :
A dark black coloured syrup, a Mother liquor left behind after
crystallization of sugar is called as molasses.
It contains about 30 to 40% sucrose, 30% water, 70% solid impurities.
10-20% org. matter roughly.