Steps involved in industrial sugar crystallization

The installation is supplied with thick juice of 92% purity.

A crystallizer’s magma is called massecuite. By centrifugal dewatering, this provides crystallized sugar and a filtrate.

Crystallization occurs as a cascade in three steps that give three qualities of sugar: A, B and C.

Magma M.S.

Filtrate purity

Magma purity

Crystal fraction

Crystal purity

A

89-92

80

90-95

25

> 99

B

93-94

70

88

94-98

C

95-96

60

76

55

81-93

Table 3.7. Qualities of types of sugar

Beetroot is only affected by sugars A and C.

The filtrate of massecuite C is known as molasses.

In reality, numerous processes exist with various means of recycling sugar or filtrate. Details can be found in the works of Bartens [BAR 98].

Step C works with a greater supersaturation than for A as the liquid-phase viscosity is greater, which reduces the diffusivity of sugar together with its transfer to the solid phase. This must be compensated by the concentration gradient, both across the diffusion film and the phase of integration to the solid.

NOTE.- A series of at least six theoretical crystallizers is required (for example, 10 real compartments in order to approach vat operation for crystals that are uniform in size).

The crystals have a mean size in the order of 0.8 mm for quality (A). This size decreases in the ratio of 2 for quality (B) and in the ratio of 3 for quality (C).

 
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