Chemistry Reference
In-Depth Information
can be increased to 130 g lactose/100 g water (62% TS for whey
permeates), the potential yield would be increased to 85.3%.
2. Cool the crystallisation batch to a lower temperature. If it could be
cooled to 58C, the concentration in the mother liquor at equilibrium
would be 12.6 g lactose/100 g water, resulting in a theoretical max-
imum yield of 88.6% with an evaporator concentration of 110 g
lactose/100 g water and yield of 90.3% if the evaporator concentra-
tion is 130 g lactose/100 g water.
3. By allowing crystallisation to occur in the evaporator, even higher
concentrations could conceivably be achieved and this enables even
higher yields to be obtained. If the concentration can reach 200 g
lactose/100 g water (71% TS for whey permeates) and that the batch
is cooled to 58C, the yield would be 93.7%.
These examples have not taken into account other practical limitations
that might occur, such as calcium deposits in the evaporators or crystalline
concentrates too viscous to pump. The actual limits that can be achieved will
vary between factories depending on whey purity, plant cleanliness and the
specifics of the plant design.
The precipitation of calcium phosphate on the evaporator tubes limits
the run time of the evaporators. Steps can be taken to minimise this problem,
such as the addition of agents to sequester calcium ions or the use of ion
exchange or ion chromatography to remove the calcium phosphate from the
whey before it reaches the evaporator.
Actual plant data are commercially sensitive and hence the figures given
here are indicative to show how plant yield can be influenced by changing
plant conditions.
Actual plant yields are usually considerably below the theoretically
possible yields due to inefficiencies in the harvesting and washing stages in
the plants. According to APV (2007), a 65% yield is typical. Plants have
reported yields as low as 50%, which is completely unacceptable. It should
be possible to improve the yield to the mid-60% range by altering the plant
operating conditions. Many of the problems can often be traced to the
generation of fines within the system which end up passing out in the mother
liquor or causing an increased load on the evaporators through recycling
which leads to more water going through the process and hence to larger
losses. Control of nucleation within the plant is the only way to tackle this
problem as it is nucleation that determines the number of crystals in the
concentrate and hence the final particle size distribution.
Incorrect cooling procedures can also lead to local nucleation events
occurring at the walls within the crystallisers or even to induce a second major
