Joint International Conference on Long-term Experiments ...

Circulation speed of
the concentrated
syrup
Table 5. Total coefficients of thermal transfer, in W/(m 2 .grade)
at thick juice preheaters (concentrated syrup)
Thermal transfer
coefficients for content of
dry substance in °BRIX,
DE
m/s 60 65
0,3 404 299
0,5 676 466
0,7 752 543
0,9 927 676
Observations
In the case of calculation of
newly assembled preheaters we
will use values of juice or syrup
speed:for juices 1,5 m/s
- for syrups 0,7 m/s
RESULTS AND DISCUSSIONS
Results obtained in the principles of using the thin juice concentration installation
In the thin juice tank, placed in front of the concentration installation, there must be a
permanent stock of juice that ensures the feeding of the concentration installation for
10-15 min . If this stock of thin juice is lacking we have to introduce in the tank
condensate from the third level of the concentration station with multiple effect.
The functioning of the concentration station is based on the circulation of the juice
and of the forward flow steam, with the gradual reduction of pressure and temperature.
From every body of the concentration station, secondary steams are taken over and
directed for heating in various technological points of the plant, at various equipments
and installations. Generally, the last concentration effect of a concentration installation
works under vacuum, the equipment that represent this effect being connected to its
own barometric condenser.
The quantity of vaporized and removed water from the juice in the concentration station
depends on the following factors:
• content of sugar of the processed cane and the sutirage made at the sugar extraction
installation
• dilution grade of juice during the calco-carbonic purification process
• final concentration of thick juice that is evacuated from the last level of the
concentration installation.
The physical and chemical phenomena that occur during the thin juice concentration are
the following:
• saccharose decomposition under the influence of high temperature
• formation of coloring substances that determine the increase of the dyeing with 5
units ICUMSA/min – 100 g saccharose. Generally, during the concentration of the
juice, the dyeing increases with 50-100%
• decomposition of groups of non-saccharates, for example, amides and inverted
sugar existing in the juice, firstly of those quantities that have not been destroyed
in the specific phases of calco-carbonic purification. As an effect of amides
decomposition ammonia is given off;
• precipitation of insoluble salts, firstly carbonate, sulphite, oxalate and aluminiumcalcium
silicates. The phenomenon is due to the increase of the juice concentration,
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