Juice is extracted from sugar cane principally by
Answer: A
A tandem of roller mills with imbibition water recovers the great majority of the sugar. Diffusion is used for beet and occasionally for cane, but milling remains the dominant cane practice. Imbibition water raises the extraction further.
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Assertion (A): Imbibition water is added between the mills of a cane tandem.
Reason (R): Diluting the residual juice in the bagasse lets the following mill extract more of the sugar.
Answer: B
Both are true and the reason gives the purpose: the water flows counter-current to the cane, so the cleanest water meets the most exhausted bagasse and the extraction approaches its limit. The last mill sees the cleanest water of all.
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The fibrous residue left after cane juice extraction is called
Answer: C
It is burned in the mill boilers and often makes the factory self-sufficient in energy. Molasses is the final syrup from which no more sugar can economically be crystallised. The two are constantly confused in reading a flowsheet.
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Match each material in a sugar mill with what it is.
List I
A. Bagasse
B. Massecuite
C. Molasses
D. Filter cake
List II
1. the final syrup no longer worth crystallising
2. the fibrous residue burned as fuel
3. the mud removed after clarification
4. the mixture of crystals and mother liquor
Answer: D
Correct answer: A-2, B-4, C-1, D-3
Four materials from four points in the mill. Bagasse is the fibrous residue left after the juice is crushed out, and burning it usually supplies all the steam and power the factory needs. Massecuite is the boiled mixture of crystals and mother liquor leaving the pan. Molasses is the syrup from which no more sugar can economically be crystallised. Filter cake is the mud settled out during clarification.
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Clarification of cane juice is usually carried out by
Answer: A
Correct answer: liming and heating to settle impurities
Milk of lime is added to raise the pH and the juice is heated, which precipitates calcium phosphate and coagulates the colloidal and suspended matter into a floc that settles or is filtered off. It is the simplest step in the factory and among the most important, since impurities carried forward interfere with crystallisation and colour the sugar.
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State whether the following is true or false.
Sugar juice is concentrated in a single evaporator body.
Answer: B
Multiple effect evaporation is used, with the vapour from one body heating the next, because a single body would consume several times as much steam. Four or five effects are usual in a cane factory. Vapour bleeding supplies heat elsewhere in the plant.
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Assertion (A): Multiple effect evaporation is universal in sugar manufacture.
Reason (R): The vapour from each body serves as the heating medium for the next, so one kilogram of steam evaporates several of water.
Answer: C
Both are true and the reason gives the economy: with five effects roughly five kilograms of water leave per kilogram of live steam, which transforms the energy balance of the factory. Boiling point rise limits how many effects are worth having.
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A quadruple effect evaporator is fed 1 tonne of steam per hour. Roughly how much water can it evaporate?
Answer: D
Each effect reuses the vapour of the one before, so the steam economy is roughly the number of effects. Losses and boiling point rise make the real figure a little lower than the ideal one. Steam economy is the figure a mill actually quotes.
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Crystallisation of sugar is carried out in a vacuum pan in order to
Answer: A
Sugar darkens and inverts if held hot, so reducing the pressure lets the syrup boil near seventy degrees. The same reasoning applies to many heat sensitive products in the food industry. Colour and inversion are both temperature driven.
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Arrange the stages of cane sugar manufacture in order.
1. evaporation to a thick syrup
2. milling of the cane to extract juice
3. crystallisation and centrifuging
4. clarification of the juice
Answer: B
Correct answer: 2 - 4 - 1 - 3
The order is fixed by what each step needs. The cane is milled to extract the juice, the juice is clarified before it is concentrated so that the impurities do not become more troublesome, the clear juice is evaporated to a thick syrup, and the syrup is boiled to crystals which are then separated by centrifuge. Evaporating before clarifying would concentrate the impurities along with the sugar.
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