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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    T

     

    B

    L

     

    A

    l

    e

    s

    n

    B

    m

    o

    a

    a

    v

    o

    B

    x

     

    C

    o

    o

    S

    e

    C

    e

    r

    u

      A

    D

     

    S

    b

    A

    D

    ry

    S

    b

     

    D

    r

    y

     

    A

    S

    A

     

    Y

    B

    r

    x

    s

    a

    P

    A

    I

    m

    p

    s

    a

    P

    A

     

    m

    p

    s

    a

    P

    A

     

    m

    p

    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