28.3 Technical Questions

1. What is special about the sugar production process from sugarcane ?

Ans: Sugarcane is a biological resource for sugar.  If sugar is used for the production of alcohols which can be in turn used as fuels in modern cars, then the original source for obtaining these fuels is the agricultural industry.  In other words, a biological source for fuels is an interesting technological concept for energy requirements of the modern society.  On the other hand, over consumption of sugars for fuel requirements could enhance sugar demand for food usage and could spiral up the prices of the sugarcane.  Therefore, a careful policy needs to be adopted for the utilization of sugar towards various process routes and technologies.

2. Why last effect evaporator is maintained at 63cm vacuum ?

Ans:

• • To allow the flow of juice from first effect to other due to pressure drop.

• To increase temperature gradient for better heat transfer.

3. What is the technical difference between sulfitation and carbonation clarification process ?

Ans: Sulfitation process is based on large quantities of sulfurous acid with proportional quantity of lime. Calcium sulfite formed prevents oxidation and darkening of juice. It also precipitates gums and albuminous matter thereby it helps in filtration.
In this process at about 65°C, SO₂ gas is bubbled to juice to slightly increase acidity. The juice is then heated to boiling point for 2 hours. After sulfitation process, PH becomes 7 and concentration becomes 12 to 13 Brix.
In carbonation process, 1 to 1.5% of lime by weight at 50 to 55°C is added to the juice. CO₂ gas is bubbled to remove alkalinity. The temperature is raised to the boiling point to remove excess carbonic acid.

4. What are the byproducts of sugar industries ?

Ans: Bagasse, filtercake and molasses.

5. Discuss energy economy in the sugar manufacturing process ?

Ans:

• • Bagasse can be used to generate steam. Steam can be used for electricity generation which can be used to run machinery in the plant. Additional power can be exported to household usage and thus save consumption of fuel.

• Bagasse is also used as raw material for paper industries as fertilizer and cattle feed.

• The final mother liquor; molasses is sent for the production of ethyl alcohol by fermentation process.

• Press mud is used as phosphatic fertilizer in farms.

6. What is the problem in storage of sugarcane ?

Ans: There should be no delay in transporting freshly cut sugarcane to sugarmill because after 24 hours of cutting causes loss of sucrose by inversion to glucose and fructose (monosaccaharides).
      C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ + C₆H₁₂O₆
            Sugar            glucose     fructose
The extent of inversion is measured by polarimeter. The non inverted sugar has +97° polarization and completely inverted sugar has -20° polarization.
This inversion of sucrose is maintained by quick delivery of freshly cut sugarcane to sugar mills.

7. Why vacuum pan crystallizer is used ?

Ans: With the use of vacuum pan crystallizer, the pressure is reduced so as to super saturate the sugar solution. After supersaturation the formation of crystals starts. When the volume of massecuite (sugar solution + crystals) exceeds certain limit, then it is transferred to centrifuge for separation.

8. What are the environmental problems faced by sugar industries ?

Ans:

• • Flue gas(fly ash) produced by combustion of bagasse.

• The untreated effluent from sugar mills have BOD of 1.7 to 6.6 g/lit, COD of 2.3  to 8g/lit, TSS up to 5g/lit and high ammonium content.

• Mill generates  lot of dust and odor.

•  Sometimes pesticides are also present in sugar cane juice.