Colour, Solids and Purity Balance of Refinery Sugar Massecuite Boiling

This article is given a general idea about color, Solid and purity balance and intermediate product colors in Refined Sugar Massecuite Boiling.

Intermediate Products Color, Solids and Purity of Crystallization in Sugar Refinery Process

Pan Boiling/Crystallization Scheme of refined sugar

a) This fine liquor obtained from second decolurization process is evaporate in falling film evaporator upto 70-75^o brix is called as concentrated fine liquor.

b) The concentrated liquor from melt concentration is pumped to the pan supply tanks for feed to pans. The liquor is boiled in vacuum pan for crystallization.

c) For refined massecuite boiling, vacuum pan should be of low head with fast natural circulation, rapid boiling calendria.

d) First boiling uses concentrated fine (decolorized) liquor as feed and syrup separated from this massecuite is used as feed for second boiling, syrup from second boiling is feed for third, and so on.

e) Refined massecuite (R1, R2 & R3 grades) are discharged from vacuum pans to enclosed receiver and then to refined sugar centrifugal distributor. According to requirement of final blended sugar quality R4 grade sugar also divert to bagging.

f) For Producing of M sugar use R2 and R3 sugar taken as footing material of R1 massecuite boiling and Dry seed taken as footing material of R2 and R3 massecuite boiling.

g) R3 or R4 massecuite runoff and surplus raw washing are processed in three massecuite boiling system (Rec1/A , Rec2/B & Rec3/C grades) to produce final molasses.

h) Runoff from R3/R4 grade massecuite is feed of Rec1 or A massecuite boiling. Rec1 runoff is used for boiling Rec2. Similarly, Rec2 syrup is used for Rec3 boiling.

i) Rec 1 sugar is melted and sent to clarification along with raw melt. Rec2 and Rec3 sugar is melted and recycled to Rec1 boiling. Some quantity of final molasses is also recycled to Rec3 massecuite boiling according to purity of Rec3 runoff (final molasses).

Color transfer to the crystal, or alternatively the fraction of color included in the crystal, is different in raw sugar mills compared to refineries, because of the different spectrum of colorants in the liquor from which the sugar is crystallized.

In refinery, color formation from feed liquor to dropping massecuite was found to be directly related to boiling time, temperature of the boiling massecuite and aeration of liquor. Generally, color formation was found to double with an increase in temperature of 10^oC. Faster boiling with mechanical circulators will minimize color formation.

Some guidelines for refined sugar massecuite colour balance.

a) Mass balance of massecuite to dry sugar is vary from 55% to 65% depends on final dropping brix and purity of pan discharged massecuite.

b) The crystal content is limited to 55 to 60% by the need to have enough mother liquor to fill the gaps between the crystals, plus a small excess to provide fluidity.

c) After centrifuging the massecuite, overall yield from massecuite to dry solids will be 50 to 55% in refined massecuite.

d) Color increase during boiling of massecuite from feed liquor will be around 5% to 10%. The incorporation of color from feed liquor into the sugar in three ways.

i) Co-crystallization with sucrose

ii) Adsorption on the crystal surface

iii) By being trapped in a liquid inclusion in the crystal.

e) Color Transfer: This term is used to describe the incorporation of color into the sucrose crystal during crystallization. It can be defined as the ratio of color of the affinated crystal to the color of pan feed.

f) The color transfer to the crystal is different in the raw sugar massecuite boiling compared to refined massecuite boiling.

g) Colour transfer from refined massecuite to sugar will be in the range of 4% to 10%. The rate of colour transfer will depends as follows.

i) Process chosen for raw melt first and second decolourization process

ii) Grade of massecuite ( i.e R1, R2, R3 & R4 ).

iii) Non sugar percentage in massecuite ( i.e massecuite purity).

Take an example of refined sugar four massecuite boiling ( R1, R2, R3 & R4 )

Assumptions:

Concentrated fine liquor colour 180 IU & Purity 99.4%
Take four massecuite boiling R1, R2, R3 and R4
Crystal Yield for R1 & R2 – 55% , R3 & R4 – 52%
Colour ratio from massecuite to sugar for R1 – 10% , & R2 – 8% , R3 – 6% & R4 – 5%
Colour gain from pan feed liquor to massecuite – 105%

Refined Sugar Purity – 99.9

Now calculate colour Balance and colour of intermediate products in Refinery Sugar massecuite boiling

Strike – 1: R1 massecuite

Melt Solids – 100

R1 massecuite colour – 180 x 105% = 189 IU

R1 Sugar solids – 100 x 55% = 55

R1 Sugar Colour – 189 x 10% = 18.9 IU

Purity of R1 runoff (P1) = (100 x 99.4 = 55 x 99.9 + 45 x P1 )

P1 = 98.8

Colour of R1 runoff (C1) – (100 x 189 = 55 x 18.9 + 45 x C1 )

C1 = 397

Strike – 2: R2 massecuite