Ash Per Cent Impurity in Raw Sugar

8/17/2019 Ash Per Cent Impurity in Raw Sugar

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FORTIETH CONFERENCE

SH PER CENT IMPURITY IN R W SUG R

By L. J FING ER and G E. MITCHELL,

Fairymead

Mill

undaberg Sugar Company Limited Bundaberg

bstract

The relationship between

;

p01 and ash

/:,

impurity of raw sugar

is illustrated by regression analyses on production for five years at Fairy-

mead. The process of reducing the level of ash

%

impurity in shipment

sugar by add ing centrifuged B molasses is discussed. Analysis has

indicated however, that the ash % impurity of a centrifuged B

molasses is in fact higher than that predicted by the regression analysis

for a wash-syrup removed from the crystal. Wide variation in ash %

impurity is known to exist and, therefore, the analysis would only apply

to the particular mill area.

Relationship between sh % Impurity and Polarization

A relationship was noted by Chen (1967). H e pointed o ut that , while

washing a sugar to a higher polarization did reduce the ash level in the

sugar, the ash impurity level increased. This phenom enon may be

due t o the com position of included syrup which Pow ers (1970) considers

to differ significantly from the mother syrup . The analysis of Fairym ead

high p01 ration sugar held for this purpose and raw sugar washed in

the laboratory centrifugal indicated a rise of ash

%

impurity with polari-

zation. Such a rise would reduce any benefit gained by spraying

B

molasses on a washed raw sugar of high polarization.

To obtain a reliable quantitative measure of this rise, a regression

analysis was made of analyses of Fairymead raw sugar for the years

1968 to 1972. The correlation of polarization and ash impurity was

highly significant in all years. The equations for each year from the

regression analysis are listed in Table I and shown on Figure 1.

The variations in the equations for each year are probably depend-

ent on seasonal conditions. In particular, the Reducing SugariAsh

ratio was very low for 1969 at 0.48 and high, by local standards, at

1.00 in 1970. The slope of the regression line appears greatest for low

Reducing Sugar/Ash ratio sugars.

TABLE

I Regression equations

Regression equation Deterrninations

Y

24.23X 355.95

1971970

Y

30.00X6.08X6.87X 925.5552.49632.94

.S50404

1972

Y

24.52X 386.52 .566


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F O R T I E T H C O N F E R E N C E

98.50

38 60

38.70

93 80 98.90

99.00 99 10 99.20 39.30 39.40

9950.

D R Y POL

Fig. I-Relationship bet we en pol dry basis) and ash im pu rit y in raw sugar for

seasons 196 1972.

Centrifuged

B

Molasses

One possibility for reducing the level of ash impurity is to add a

centrifuged molasses to high p01 washed sugar. The sludge removed

from molasses is rich in insoluble ash and the ash impurity of the

mother syrup is reduced. The normal syrup film on raw sugar could be

replaced by this treated material. Samples of B molasses at various

per cent Brix were centrifuged, or allowed to settle for 24 hours. The

treated samples were then analysed and ash impurity con tent com-

pared with the control samples. The results are recorded in Table 11.

These results show that the removal of sludge has only a m arginal effect

on the ash impurity level of the

B

molasses. The effect may be due to

the high aconitic acid content of Fairymead molasses Simpson & Deicke,

1961). This organic constituen t forms a significant portion of the sludge

and reduces sludge ash impurity.

Effects of Addition of Centrifuged Molasses

The level of ash impurity in the added molasses must be lower

than that of the syrup removed from the crystal if any benefit is to be

gained.

The polarization of a shipment sugar is normally about

99.0

dry

basis). For the purposes of the discussion it is assumed that this material

could be economically washed to 99.5 polarization dry basis). If a further

assumption regarding the purity of the wash syrup is made, the ash

impurity of this material may be calculated by a solids balance. The ash

impurity of the washed sugar is predicted from the regression analysis.

A solids balance calculation assuming a wash syrup purity of 90

is shown in Appendix I for

1968

season sugar. The expected ash


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u

A

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S

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A

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r

y

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S

A

Y

B

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8


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2 14 FORT IETH CON FER ENC E

TABLE

Ill-Calculated Ash lmp uri ty in Wash Syrup

impurity of wash syrup for each of the five years tabulated is shown in

Table 111.

This relationship is very similar to that existing in centrifuged

B

molasses. It would appear therefore that no reduction in levels of

ash impurity in raw sugar will be achieved by this metho d.

The purity assumed for wash syrup has only a marginal effect

on the predicted ash impurity of this material. The pur ity, however,

would have a substantial effect on the quantity of material to be recycled.

Season

99.0 Pol

dry basis)

Conclusions

Ash Impurity

The increase in ash

;,

impurity in raw sugar with polarization has

been demonstrated by statistical analysis. This factor limits improve-

ment in ash impurity which could be expected by the add ition of

centrifuged molasses to a washed raw sugar.

1968

-

54.9 3 1.7

I969 59.5 3 .O

99.5 Pol

dry basis)

Acknowledgements

The authors wish to thank the management of Fairymead Sugar

Company Limited for permission to publish this paper.

Syrup

wash)

REFERENCES

Chen J. C. P.

(1967). Sulphated ash and total non sugars in Peruvian raw sugars, Sug. J

30,

6,

9.

Powers

H. E.

C.

(1970). Sucrose crystals: Inclusions a nd structu re. Sug. Technol. Reviews.

1 L ILL.

Simpson C. and Deicke R. (1961). The Rem oval of insoluble impu rities from B Molasses.

Proc. Qd. Soc. Sug. Cane Technol. Twenty-eighth Conf. 307.

Appendix I

Calculations of Ash 9 Impurity in Wash Syrup

Assume 100 tons of Fairymead sugar at normal analysis of (dry

basis)

:

Pol

. .

99.000

Ash . . . .428

Other Imp

.

. . . .572

Ash Imp . . . . 42.8

If this sugar is then washed to a polarization (dry) of 99.50, the

expected analysis will be

Pol . . . . 99.500

Ash . . . .275

Other 1Ap .

.

.225

Ash Imp

.

. .

54.9 (from regression

analysis)


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973 FORTIETH CONFERENCE 2 5

Assuming that the wash is removed at

90

purity a total of

5.263

tons of dry solids will be removed per

100

tons

99.50 9.00 94.737

9.50

Hence the tonnage per

100

tons of each component can be found in

the wash syrup and ash impurity derived.

Tons per Original 100 tons

Original W ashed W ash

sugar sugar syrup

Polarization

. . . .

99.000 94.263 4.737

Ash

. . . . .428 261 .l 67

Other Imp

. . . .572 .213 .359

Total . . 100.000 94.737 5.263

The predicted level of ash impurity in the wash will be

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Ash Per Cent Impurity in Raw Sugar