(i) Quiz on Centrifugation (Raw sugar 2)

 

Selection one answer for each question.

1.

The separation performance of a batch centrifugal can ne improved by:

     

    a) Increase the coefficient of variation (CV) of the massecuite.

     

    b) Increasing the size of the sugar crystals (MA) in the massecuite.

     

    c) Reducing the temperature of the massecuite.

     

    d) Increasing the amount of massecuite fed into the centrifugal basket.

2.

The separation performance of a batch centrifugal can be improved by:

     

    a) cing the size of the sugar crystals (MA) in the massecuite.

     

    b) Reducinng thRedue temperature of the feed massecuite.

     

    c) Increasing the time at maximum spin speed (spin time) of the centrifugal.

     

    d) Increasing the time taken to remove the sugar from the centrifugal basket. CV.

3.

The separation performance of a centrifugal:

 

    a) Is best when the CV equals 100.

 

    b) Is reduced by boiling sugar with a lower CV (Coefficient of Variation).

 

    c) Is improved by boiling sugar with a lower CV.

 

    d) Is not altered by changes to the sugar.

4.

The normal hole size or slot width in a batch centrifugal screen is:

 

    a) About the same as the average size of the sugar crystals in the massecuite.

 

    b) Less than 1/5 (0.2) of the average size of sugar crystals in the massecuite.

 

    c) More than 5 times bigger than the average size of the sugar crystals in the massecuite.

 

    d) The hole or slot size is not important.

5.

In a batch centrifugal a non uniform layer of massecuite after feeding can be caused by:

 

    a) A basket speed during feeding that is too high.

 

    b) A basket speed during feeding that is too low.

 

    c) A basket speed during feeding that is too high or too low.

 

    d) A faulty basket discharge valve.

6.

What is the approximate amount of sugar that can be dissolved in 1Lb(0.45 kg) of water at 140F (60C):

 

    a) 2.5 Lb. (1.1 kg).

 

    b) 1Lb. (0.45kg).

 

    c) 0.5 Lb. (0.23 kg).

 

    d) 0.2 Lb. (0.09kg).

7.

For good washing in a batch centrifugal it is important to:

 

    a) Wash only when the basket is spinning at a constant speed.

 

    b) Use wash water that is much cooler than the massecuite temperature.

 

    c) Adjust the wash jets to give an even spray over the sugar layer in the centrifugal basket.

 

    d) Adjust the wash jets to spray on to the top half of the basket.

8.

When washing the sugar in a batch centrifugal cake it is best to:

 

    a) Use a large amount of wash water to ensure the sugar is always well washed.

 

    b) Se the smallest amount of wash water necessary to get the correct sugar quality.

 

    c) Wash the cake at least twice during each centrifuge cycle.

 

    d) Apply enough wash water to dissolve at least 10% of sugar crystals.

9.

A sugar cake that is difficult to wash and turns a dark brown or black color when wash water is sprayed onto the cake indicate:

 

    a) High level of dextran (or other polysaccharides) in the massecuite.

 

    b) Wash water that is too hot.

 

    c) A crystal size that is too large.

 

    d) Low levels of ash in the massecuite.

10.

A sugar layer left in the basket of a batch centrifugal after discharge (plowing) is:

 

    a) Bad, because it reduces the sugar yield from the massecuite and wastes energy.

 

    b) Bad, because it wears out the centrifugal careen.

 

    c) Good, because it reduces crystal breakage.

 

    d) Good, because it increases the sugar yield from the massecuite and saves energy.

11.

The benefits of using an electronic variable speed drive on a batch centrifugal are:

 

    a) A less complex drive system.

 

    b) Lower energy consumption and a variable spin speed that can be altered to suit process conditions.

 

    c) More efficient washing of the sugar.

 

    d) A lower cost to purchase the centrifugal and smaller control panels.

12.

Batch centrifugals are used to process ‘A’ massecuites. Low grade continuous centrifugals are not used because:

 

    a) Batch centrifugala use less electrical power and have a higher thruput per hour.

 

    b) Batch centrifugals give dryer sugar, better washing and do not break the crystals.

 

    c) Batch centrifugals are more reliable.

 

    d) Batch centrifugals use less wash water and the screens do no wear.

13.

Heating the massecuite into a continuous centrifugal is important because:

 

    a) It increases the life of the centrifugal screens.

 

    b) It increases the amount of sugar crystals in massecuite.

 

    c) It reduces the power consumption of the continuous centrifugal.

 

    d) T reduces the viscosity of the massecuite and improves the separation performance of the centrifugal.

14.

If the amount of massecuite fed to a continuous centrifugal is increased then the color line in the basket:

 

    a) Moves toward the bottom of the basket (i.e. nearer tk where the massecuite is fed on to the basket).

 

    b) Moves towards the top of the basket (i.e. nearer to where the sugar is discharged from the basket).

 

    c) Cannot ne seen as it is covered by the massecuite.

 

    d) Does not change its position.

15.

A large molasses purity rise across a continuous centrifugal is:

 

    a) Good, because the purity if the sugar is higher and the sugar is dryer.

 

    b) Good, because the purity of the molasses is increased.

 

    c) Bad, because there is more sugar in the molasses and less discharged as crystals.

 

    d) Bad, because less sugar has been dissolved.

16.

The correct hole size or slot width in a continuous centrifugal screen is:

 

    a) Less than 1/5 (0.2) of the averge size of the sugar crystals in the massecuite.

 

    b) About equal to the average size of the sugar crystals in the massecuite.

 

    c) About 5 times the average size of the sugar crytals in the massecuite.

 

    d) The hole or slot size is not important.

17.

Continuous centrifugal screens should be checked:

 

    a) Regularly to check for damage, slot wear and deposits at the back of the screen.

 

    b) Once per crop.

 

    c) Two times per year.

 

    d) When the centrifuge motor current increases.

18.

When comparing the performance of a Batch Centrifugal and a high Grade Continuous Centrifugal (HGCC) on the same massecuite – The sugar discharged from the Batch Centrifugal is:

 

    a) Wetter with less crystal damage.

 

    b) Wetter with more crystal damage.

 

    c) Dryer with more crystal breakage.

 

    d) Dryer with less crystal breakage.

19.

The best way to check a centrifugal basket for cracks is to:

 

    a) Undertake a visual inspection.

 

    b) Put the basket in a tank of water andlook for bubbles.

 

    c) Weigh the basket; a reduction in weight indicates a problem.

 

    d) Use crack detection methods such as dye penetrant, magnetic particle inspection or ultrasonics.

20.

Centrifuge baskets should be checked for cracks and corrosion:

 

    a) Only when the vibration level on the centrifugal increases significantly.

 

    b) Every 10 years.

 

    c) Every 5 years.

 

    d) Every year.

   
   
   
 

last updated 10/30/2017