Tools for improving the separation in batch and continuous centrifugals

By Tim Diringer and Bjarne Christian Nielsen, Neltec Denmark A/S

British Society of Sugar Technologists ATM 11th October 2018 OXNEY VINEYARD, BECKLEY, RYE, EAST SUSSEX

„Nowhere in processing can so much sugar

be lost so quickly and with so little notice

as in centrifugation“

Payne (1992)

16% 1%

69%

14%

Sugar losses in cane sugar factories

Bagasse Filter Cake Molasses Unknown

For batch centrifugals

A new approach to: 1. Reduce the risk of vibrations 2. Optimise the product quality 3. While reducing spray water 4. Get more uniform moisture 5. Improve run-off separation

Signals given by the Neltec ColourQ 1700 BC

Colour

Filling

RPM

Purging

What do the signals bring? The colour tells, when liquid is visible on the inside of the wall of crystals.

Stop acceleration at higher RPM until it is safe to proceed. The filling level tells, how well the capacity is utilised.

Increase filling at low static pressure, and when safe. The filling rate tells, how fast massecuite is feeding.

Get a warning at liquid massecuite. The purging rate tells, when it is time to start spraying in order to avoid

drying the film of mother liquor on the crystals. Avoid the need to increase spraying in order to clean dry crystals.

The purging rate tells for how long the spinning should continue. Avoid too dry or too wet crystals.

When do we need to start spraying?

0

200

400

600

800

1000

1200

0 50 100 150 200

Filling

Acceleration

Washing

Spinning

Deceleration

Discharge

Screen wash

0

200

400

600

800

1000

1200

0 50 100 150 200

Filling

Acceleration

Washing

Spinning

Deceleration

Discharge

Screen wash

Mother liquor

Wash syrup

Wash water

Early wash

Late wash

Old wisdom - Eichhorn, 1967

When to start spraying

Using the purging signal

Purging signal at washing time

50 %

1. The first spray (19:29:10 to 19:29:24) is a little early. A colour ring is seen.

2. The second spray (19:29:39 to 19:29:47) is too late. The purging rate has decreased to 50%. There is no trace of liquid on the inside of the crystal wall.

25 %

When the purging is almost finished at start of spraying, the spray water rushes through the open structure of the already dry crystals in the sugar wall. Notice the immediate increase in purging. Massecuite properties are not taken into consideration by timers.

Purging signal at washing time

Purging signal for run-off separation

25 %

The purging signal tells: 1. When the low purity run-off starts purging during basket filling. 2. When the syrup wash run-off starts purging. 3. When the high purity run-off from the water wash starts purging.

When should decelaration start?

Purging signal at start of decelaration

15 %

20 %

Purging signal at start of decelaration

Summary

The Neltec ColourQ 1700 BC can:

Prevent any significant amount of liquid on the sugar wall.

Pause or stop acceleration if a massecuite is not purging.

Start the water spray always at the same purging rate of the syrup leaving the centrifugal, thereby ensuring the most efficient use of spray water and getting the lowest ash.

Start the deceleration always at the same purging rate of the syrup leaving the centrifugal, thereby keeping the sugar moisture more uniform.

Help improving run-off separation.

Continuous centrifugals

Factors influencing the work in continuous centrifugals

Viscosity

Crystal size

Crystal size distribution

Crystal content

Water addition

Steam addition

Massecuite temperature Feed rate

„Due to the various influencing parameters, the molasses losses cannot be controlled. Optimization can only be approached by trial and error.“ „Continuous centrifugals need continuous attention by the operator.“

Payne (1992)

Centrifugal control for continuous centrifugals

by using the Neltec ColourQ 1700

Information given by the Neltec ColourQ 1700

Sugar colour

TESTS

Set-up test 1

20 l/min

15 l/min

10 l/min

5 l/min

Colour increase while reducing the combined water flow in test 1

Set-up test 2

20 l/min

15 l/min

10 l/min

5 l/min

0 l/min

Colour increase while reducing the combined water flow in test 2

Set-up test 3

Colour variation if water flow on lower valve is completely stopped (Timely high resolution signal)

Set-up test 4

Colour variation if water flow on lower valve is set to 2l/min (Timely high resolution signal)

Comparison standard colour control vs.

colour control with ColourQ 1700CC

Standard colour control Colour control with Neltec ColourQ 1700

R² = 0.1555

0

5000

10000

15000

20000

25000

30000

35000

40000

15 20 25 30 35

Co

lou

r

water flow (l/min)

R² = 0.7939

0

5000

10000

15000

20000

25000

30000

35000

15 20 25 30 35

Co

lou

r water flow (l/min)

Standard colour control Colour control with Neltec ColourQ 1700CC

Relation between C-sugar colour and molasses purity

Date Time Sugar Molasses

Bx Pol Purity Colour Bx Pol Purity

20.03.2017

14:30 97.08 89.72 92.42 7864 83.36 33.68 40.40

18:00 96.4 84.4 87.55 13466 85.72 33.08 38.59

22:17 96.52 84.68 87.73 16473 86.62 32.47 37.49

09:00 96.92 89.88 92.74 5691 82.96 32.88 39.63

11:00 96.4 84.28 87.43 21453 85.76 32.6 38.01

14:00 95.68 81.24 84.91 21482 86.08 32.52 37.78

18:00 96.68 89.12 92.18 16525 84.2 31.72 37.67

23:46 97.48 88.16 90.44 12452 83.32 31.28 37.54

22.03.2017

08:00 96.8 87.2 90.08 19842 84.56 31.36 37.09

11:00 97.48 89.64 91.96 10942 84.12 31.76 37.76

14:15 97.2 91.88 94.53 7184 83.82 32.4 38.65

23:37 96.8 89.28 92.23 10589 84.56 32.16 38.03

23.03.2017

02:26 97.08 89.88 92.58 11508 85.52 32.65 38.18

08:00 96.28 82.16 85.33 20636 87.54 33.6 38.38

36.50

37.00

37.50

38.00

38.50

39.00

39.50

40.00

40.50

41.00

5000 7000 9000 11000 13000 15000 17000 19000 21000 23000

pu

reza

mie

l fin

al

color semilla

Relation between molasses purity and sugar colour

84.00

86.00

88.00

90.00

92.00

94.00

96.00

5000 7000 9000 11000 13000 15000 17000 19000 21000 23000

Pu

reza

se

mill

a

Color Semilla

Relation between sugar purity and sugar colour

Process improvements

Colour variations in March

Colour variations in April

Colour variations in automatic mode

Tests published by factories/mills

ESST 2017 Amalgamated Sugar, Nampa factory. Published in Sugar Industry.

SIT 2018 American Sugar Refining, Chalmette refinery.

SIT 2018 British Sugar, Bury St. Edmunds factory.

ASSCT 2018 US Sugar, Clewiston.

More are under preparation.

Thank you for your attention!