K-Patents SeedMaster 2 - Manual (Page 9)

2 SUGAR CRYSTALLIZATION IN BRIEF 9
9
NOTE:
The use of slurry (or crystal footing) alone is no guarantee for correct full seeding. Besides the right amount
of slurry or footing (with the right number of crystals in it) supersaturation must not exceed its limit value.
2.4 Crystal content
Good control of the process of crystallization requires some information on the crystal content of the
massecuite, too. The amount of sugar needed to feed the growth of crystals increases as the surface area of
the crystal mass increases. Feed syrup is supplied to fill the need.
The control of crystallization in a vacuum pan, for example, should be a co-ordinated process. Control
parameters, like vacuum, heating steam (vapour) pressure, feed syrup input are connected in a complex
way to the massecuite parameters. The actual value of supersaturation depends on quite a few parameters
(see Eq. 1.) From these, concentration depends on the rate of evaporation and syrup feed, while
temperature is basically determined by the absolute pressure above the massecuite.
In batch crystallization some indirect measure of crystal content is being used to signal the end of the strike.
2.5 Product quality and supersaturation
The importance of supersaturation in product quality can not be overstated. Its role in seeding has already
been discussed, while Fig. 2.4 (scale: 1 by 1 mm) proves its effect all over the strike. In this figure a fairly
wide crystal size (from 1 mm to perhaps 0,05 mm) distribution can be observed. Most probably there were
much smaller size crystals, too, but they had escaped through the screen of the centrifuge only to increase
the amount of recirculated crystallized sugar in the green syrup (Fig. 2.6). It is evident that the smaller
crystals (the “young generation”) are due to spontaneous nucleation in the later phases of the strike. These
crystals therefore did not have time enough to grow to a larger size till the end of the strike (it is assumed
that the size of the seed crystals (the “old ones”) was fairly equal).
Fig. 2.4
In Fig. 2.5 (scale: 1 by 1 mm) among well developed crystals quite a few conglomerates (a cluster of
mutually intergrown crystals) of different sizes can be observed.
Fig. 2.5
conglomerates