Sugar Industry: Manufacture of Crystalline sugar: Extraction of the Juice, Clarification of the Juice – Two step and One step
process – Classification of Juice by Double carbonation process - Evaporation of Clarified juice to make syrup - Crystallization of Syrup – Use of Seed Crystals for Crystallization – Curing of
Sugar – Double Centrifuging – Treatment of Molasses –
Composition of Back strap – Refining of Raw sugar – Recovery of Bone char – Utilization of Bagasse – filter cakes used as
manure – Testing and Estimation of Sugar – Industrial Spirit –
Absolute Alcohol – Cane sugar industries in Tamil Nadu and in
India.
Nature has provided foods from ample stores from vegetable kingdom to supply the sweetness that human requires for their diet. Sucrose (C
12H
22O
11)
Cane sugar Beet
Maple friut
Sweet Sorghum Palm tree
Pineapple Apricot Ripe banana
13 % of the energy required for existence is supplied by the sugar.
About 2500 years ago cane sugar was used as a source of sweetness in crude and refined form in India. Our Country is the one of the chief sugar producing nation in the world.
Later on it was cultivated in Cuba and many other Countries.
In Europe honey was used as the source of sweetness in 327 B.C
Beet sugar was discovered in 1747.
Sucrose occurs in nature as Cane sugar and sugar Beet.
Its concentration in lower part of cane sugar is greater than that in the upper part.
Maximum source of sugar is from Sugar cane and beet.
Beet contains 6% sucrose and it is increased to 28% by research.
In India sucrose is obtained from sugar cane only.
Sugar Cane Contains
Water - 70-75%
Crystalline sugar – 10-15%
Reducing sugar –0.5- 1.5%
Fibre - 10-18%
Ash - 1%
Organic acids - 1%
1. Extraction of Juice 2.Purification of juice
3.Concentration or Evaporation.
4.Crystallisation.
5.Separation of crystals.
6.Refining of crystals.
7. Recovery of Sucrose from molasses.
Manufacture of alcohol from Molasses by fermentation is done in India.
The cane is first washed to remove mud and trash.
It is then cut into small lengths by means of sharp moving knives ( 500- 600r.p.m) fitted on a horizontal shaft and then dropped over the moving belt
The moving belt is also known as the cane carrier. It is then sent to the extractor consisting of one two rolled toothed crusher and four three rolled grooved mills.
The crusher fitted with a set of revolving knifes make diagonal cuts, converting the canes into chips through a series of milk, each of which consists of three grooved rolls that exert a pressure of about 3 to 6 tons per sq.inch.
When the chips are fed into the crusher , they pass through the rollers
to extract about 50% of the juice. .
The bagasse containing 50% of juice is then introduced into the first mill.
Before passing the bagasse to the first mill the juice from the second mill is sprayed on the bagasse for efficient pressing. .
Juice extracted from the first mill is collected in the strainer below from where the juice is transferred to the raw juice tank.
The juice from the third mill is sprayed on the bagasse between first and second mill and
juice from the fourth mill is sprayed on the bagasse, as it passes from second to third mill.
The bagasse from third mill to the fourth mill is sprayed with hot water to extract last traces of juice.
About 90 to 96% of juice is extracted from cane.
Finally the spent cane bagasse is collected in the storage, which is either burned for fuel or used in the manufacture of paper, hardboard or insulating materials.
By this method majority of juice is extracted.
The juice is brownish green opaque liquid.
It contains
Sugar-10-20%;pectic substances,water,organic matter, coloring matter, reducing sugar ,gums, mineral salts, fine particles of bagasse in suspension and small quantities of vegetable proteins.
These impurities hinder the crystallization of sugar.
pH of cane juice is 5.1 to 5.7.Thus the acidic nature helps in conversion of sucrose to reducing non-crystalline sugars.
The juice after extraction is made alkaline, because pectic substances present
In it will undergo fermentation into pectic acids, which catalyze the change of cane sugar into non-crystalline sugars.
This process is known as deflection.
It is the preparation of raw liquor for filtration and clarification by removing solid impurities.
After removal of suspended impurities the juice is immediately transferred into the defection tanks which is a circular tank with conical bottoms and fitted with steam and air connections.
The syrup is neutralized by addition of milk of lime (pH7-7.3).
The treated precipitates, pectic substances as insoluble calcium precipitates coagulates the vegetable proteins,gums,etc.,and converts sucrose into calcium sucrosate. Along with this fibre and clay are also deposited.
Lime converts soluble phosphates into insoluble tricalcium phosphates that is precipitated.
The hot lime juice is then pumped into the settling tank, where it separates into three layers.
The precipitated matter, which forms a thick scum at the surface forms the upper layer and lies above the middle layer of clear juice.
The muddy precipitate forms the bottom layer.
The top and bottom layer are removed by filter press.
The clear juice containing calcium sucrosate and calcium hydroxide is drained off.
During filtration process, the cakes are washed with water and dried.
The wash water is sent to the clarifier and filter cakes containing sucrose and phosphates are used as manure after rotting for a year.
The defection process by making use of lime does not eliminate all the
impurities completely.
The crystallization of the concentrated juice is termed as syrup.
The raw sugar is obtained is converted into white crystalline sugar by refining .
This is done by carbonation and sulphitation.
The syrup is clarified by passing sulphur dioxide through lime juice
The sulphur dioxide passed along the concentrated syrup helps in bleaching the syrup and checks the formation of brown mass by oxidation.
The solution should be kept neutral during sulphitation.
This process is known as double sulphitation process.
In this process sulphur dioxide is passed till neutral pH (6.9-7.1), heated steam and lime juice is sprayed in the reaction vessel.
This process is known as first sulphitation process.
The juice is then transferred into the second juice heater and heated to about 103deg.C.
The juice is then sent to the settling tank or clarifier, the liquid separates into clear liquid and muddy juice.
The clear juice is sent to the boiling house for evaporation to concentrated juice called syrup.
In this process sulphur dioxide is passed till pH 5.5 to get white sugar.
This process is known as double sulphitation process.
In some cases flocculants are added for effective clarification.
Clarification is also done using carbon dioxide is added to lime juice to precipitate the excess of lime as calcium carbonate.
C
12H
22O
11.3CaO+3CO
2→ C
12H
22O
11+3CaCO
3Ca(OH)
2+CO
2→CaCO
3+H
2O
The cane sugar is heated to about 50-55deg.C and milk of lime is added to it .The lime juice is kept at this temperature in the tank and carbon dioxide is passed until the solutions alkalinity is represented by 0.05percent of lime.
The juice containing suspended precipitate is filtered and heated to boiling. It is then saturated with carbon dioxide and boiled to
decompose the bicarbonate formed.
The juice containing suspended precipitate is filtered and heated to boiling. It is then saturated with carbon dioxide and boiled to
decompose the bicarbonate formed.
The juice is then again filtered and sent to the boiling house for
evaporation to syrup.
The clarified juice obtained is concentrated into thick syrup under reduced pressure in multi-effect evaporators.
Concentration of sugar solution by evaporators
An evaporator is a tall cylindrical vessel made of mild steel plates or cast iron. Its top is bottle necked and bottom is spheroidal.
They are arranged vertically in a series of three or four.
The three evaporators P
1,P
2and P
3are fitted with three sets of heating coils C
1, C
2and C
3are connected with exhaust pump.
The evaporators are filled with the juice to be concentrated upto the same level.
Pressure in the evaporator is so maintained that it is lowest in evaporator P
3and higher in P
1.
The evaporators are filled with the juice to be concentrated upto the same level.
The steam produced in P
1is then led to heater C
2of the evaporator P
2, which keeps the liquid in P
2boiling on account of still lower pressure.
The low temperature steam from the evaporator P
1helps rapid evaporation of the liquid in P
2because of high vacuum maintained in P
2and so on…
Finally the pale yellow thick syrup is led into the syrup tank, sent to the sulphitation tank . The syrup is introduced from top and sulphur dioxide is introduced from the
bottom. It bleaches the sugar syrup.
The syrupy liquid is further concentrated by removing most of the water by heating in a single effect evaporator, called vacuum pan.
It is further connected with steam coils, vacuum guage,condensor and a thermometer, a sample tube is carried out to the crystallization point.
The concentrated syrup is then led to crystallizing tanks and cooled slowly , when crystals of sugar separate out.
The crystallization is done by introducing externally the sugar crystals in the syrup to induce crystallization and to save fuel.
Crystals of sugar are then separated from the molasses by whirling in centrifugal machine (1200-1400r.p.m), which is composed of a perforated basket suspended on the lower end of a vertical shaft , the upper end of which is held on a roller bearing.
These machines are usually driven by water under pressure.
Due to the high revolving motion, the crystals are easily separated and liquid portion is drained out. Remaining traces of crystals are removed by spraying cold water while swirling in the centrifugal machine.
Double centrifugation is done to obtain white sugar.
Centrifugation
The crystals of raw sugar obtained are dried by dropping them in a long pipe through which hot air or super heated steam is passed and finally bagged.
The sugar syrup obtained on third boiling gives a dark, viscous black strap Molasses C ,it has a robust flavor.
In this stage, the sucrose has been crystallized and removed.
The black strap Molasses has small sugar content, hence small calorific value.
Composition
Vitamin B6, Minerals – Calcium,Magnesium,Iron , Manganese and Potassium.
It has been sold as a dietary fibre
Blackstrap molasses is bitter in taste.
It finds uses in baking or the production of ethanol as an ingredient in
cattle feed and also as a fertilizer.
The sugar crystals obtained are dissolved in hot water and then boiled with animal charcoal or norit for decolorisation of the solution and then filtered.
It is further concentrated under pressure in multi-effect evaporators. India follows double carbonation process for manufacture of cane sugar.
It is governed by National Sugar Institute (NSI) every year.
Sugar standards are supplied to sugar factories for visual comparison and sieve analysis for every grade.
Medium 30 and large 29 signify for the grain size, the measurement of visual whiteness.
The molasses obtained as mother liquor after the separation of sucrose crystals still contains a considerable amount of sucrose.
The mother liquor is first boiled, then cooled slowly when some fresh crystals of sucrose separate out and the remaining is removed by chemical methods.
The liquid obtained after separation of crystals is diluted with water and then treated with strontium hydroxide in a tank. The distrontium sucrosate separates out, which is filtered through a filter press.
The precipitate is then suspended in water and then decomposed into sucrose and strontium carbonate by the strong use of carbon di oxide.
The precipitate of strontium carbonate is removed by filtration.
The filter is then decolorized by animal charcoal and vaporized under reduced pressure in multieffect evaporators to concentrate the solution.
In the syrupy liquid,CO2 is again passed to decompose any distrontium sucrosate and then crystallized.
C12H22O11.2SrO+ 2CO2→ C12H22O11+2SrCO3
• Bone char is primarily made from cattle and pig bones. The bones are heated in a sealed vessel at up to 700 °C, under low oxygen.
• Heating bones in an oxygen-rich atmosphere gives bone ash, which is chemically quite different.
• Used bone char can be regenerated by washing with hot water to remove impurities, followed by heating to 500 °C (932 °F) in a kiln with a
controlled amount of air.
Sugars in white color (refined ), while the, brown indicates unrefined sugar.
Bone char was often used in sugar refining process.
It removes color and ash from cane sugar.
Bone char will be effective only in higher concentration.
It removes impurities like sulphates of Mg and Ca, thereby reducing scaling.
Activated Carbon and Ion exchange resins has been used as suitable alternate to
bone char.
About 70% of the bagasse produced after recovery of cane juice is used as a fuel for generating steam for power heat to run the mill.
Remaining 30% is used for making insulating and building board like Celotex or for paper manufacture after digesting it with chemicals such as NaOH etc.,
Coal or coke is used as an alternative for bagasse.
The bagasse is made available for making hard board known as Celotex.
The uses of bagasse are fuel, manure and cattle feed.
The bagasse is introduced into rotary digesters by means of endless belt and it is cooked under pressure.
This is done to loosen the sticking material in the fibres.
The resulting pulp is washed to remove dust and impurities.
It is then agitated with resin and alum to remove irregularities by a process known as sizing.
The fibres are refined in 2% suspension and fed to the head box of the board machine from stock chests.
The solution is diluted to 0.5 %and fed to forming screens and then drying felts and finally to press rolls.
The sheets are felted together to give the required thickness.
It is then dried in a continuous sheet at about 300-450deg.F.in800-1000 ft long driers, heated with superheated steam or gas. .
The product leaves the drier it is at once sprayed with water in order to bring it up to its normal water content (8%).
The board is finally cut and fabricated.
Beet contains18-2 8 %sucrose
The sucrose is recovered in a diffusion battery of diffusers .
It follows a counter current as well as diffusion principle.
Principle: Dialysis –the cell wall acts as a membrane permitting sugar and
other crystalloids to diffuse out of the cell walls retaining the colloidal matter like albumin inside the cell wall.
The beets are washed, weighed and sliced into chips. It is known as cossettes.
The cossettes are dropped into a designed counter current diffuser or 12V battery connected in series.
The sugar is extracted along with hot water.
The diffuser has two doors, one for entry of cossettes and other for used cossettes.
Juice from Previous diffuser
To next diffuser
Charging door for beets
Discharge door for spent beets -- ---
--- --- --- --- --- --- --- - ---
In the diffuser the hot water enter at the bottom and leaves at the top and the cossettes remain in the diffuser.
In the diffuser 1 the hot water first enters and maximum extraction of sugar is done in comparison with diffuser 2 etc., upto diffuser 10, where fresh cossettes is added.
The fresh water dissolves as much sugar it can and forms a concentrated solution, known as diffusion.
1 1
2 3
4
5 6
7 9 8
10 11
12 Fresh water
Diffuser juice
Diffuser
The diffuser No.12 was diffuser No.1previously and then the same is repeated from diffuser 11 to diffuser 2, which becomes first while diffuser 11 is last.
The operation is continuous and each diffuser receives fresh water at one end of the battery and cossettes at the other.
The resulting raw juice is a blue black 10-12% solution with a small amount of inverted sugar and ash : 2-3% ash.
The pulp containing 0.1-0.3% water is dewatered in filter press and dried and is sold as cattle feed.
The remaining procedure is the same as sugar extraction from cane sugar.
Sugar may contain non-sugar or invert sugar (glucose and fructose) as impurity.
To 5ml of sample add 1ml of Fehling's solution and boil. An yellow or red precipitate indicates the formation of invert sugar or reducing hexose.
Fehling's solution is not reduced by Sucrose and non-sugars.
When there is no precipitate formation ,sample +0.5ml of Conc.HCl, boil for few minutes ,cool it and neutralize it with 10% NaOH solution.
An yellow or red precipitate is formed by boiling the solution with 1ml of Fehling's solution.
This indicates the presence of sucrose or any polyose which gets hydrolyzed with dilute HCl to invert sugar
Estimation of sugar is done by Polarimeter in which optical rotation is indicated.
The rotatary power of a substance is expressed in terms of specific rotation
Alpha is observed rotation of polarized beam at t deg.C
Lamda is the wavelength of light used.
L is the length of the liquid column in decimeters.
Where is the concentration of the solution in gms/c.c..
Since Sodium light is generally used
In the case of a solution
d is the density of the liquid used.
Specific rotation is defined as the angle of rotation produced by a liquid which in a volume of 1ml contains 1 gm of active substance when the length of the column through which the light passes is 1 decimeter.
Specific rotation of
Sucrose = 66.6˚ Glucose = 52.8 ˚ Fructose = -92.8 ˚
Hence specific rotation of invert sugar is
If the sample is pure sucrose the specific rotation will be - 20 deg.C. When the value is less, it indicates the presence of non-sugar.
