Chemistry Reference
In-Depth Information
Steam
Air
Wash water
Cyclone
Fines
Whey storage
Washer
settler
Crystalliser
Evaporator
Fluidized Bed
Drier
Screen
Centrifuge
Centrifuge
Cooling
water
Mother liquor
Flash Drier
Hot air
Cold Air
Pump
Pump
Pump
Fines recycle
Baggers
Figure 4.2.
Process flow diagram of a plant for the manufacture of edible-grade
-lactose
monohydrate.
The process for making edible-grade lactose is relatively straightfor-
ward in that the basic procedure is to concentrate whey, and then allow it to
cool, so that the lactose crystallises out of the mother liquor. The crystals are
then separated from the mother liquor, washed, dried and packed. A descrip-
tion of this process was given by Weisberg (1954). Figure 4.2 is a process flow
diagram showing a typical lactose production plant. Most manufactures
follow this method, with some variations, depending on the site. Some
producers like to include various steps either before or after concentration
and different concentration techniques can be used, including reverse osmosis
before a final concentration by evaporation. All the processes known to the
author include a final evaporation step to achieve the desired solids level.
The critical steps in the process are as follows:
1. Removing
as
much
water
as
possible
in
the
final
stages
of
evaporation.
2. Transfer of the high-solids concentrate from the evaporator to the
crystalliser without uncontrolled nucleation. Where a process uses
higher concentrations than it was originally designed for, it may
require an appropriate increase in temperature before transfer to the
crystalliser to limit supersaturation. The key here is to maintain the
same absolute level of
-lactose supersaturation as it enters the crys-
talliser, thus maintaining similar conditions to those that occurred in
the original process at the time of nucleation. This is because the rate
of nucleation is a strong function of the absolute level of
-lactose
supersaturation as well as the fluid dynamics of the crystalliser.
