Separator's Digest 2009/1 min. - GEA Westfalia Separator Group

Irrespective of the filter type, the solids content can be reduced to less than
approx. 0.5 percent (by volume) with a centrifuge upstream of filtration. If conditions
are adjusted or if appropriate products are used, the solids content can be reduced
to trace levels. This considerably increases the service lives of filters, and interruptions
for cleaning or diafiltration are reduced. The solids from the centrifuge can be
disposed of together with the pomace, and accordingly do not constitute separate
waste. However, retentate is still produced in the filter, although in much lower
quantities.
Centrifugal separation technology in bypass to filtration
In the processes which process retentate, there is a further variation of processing
possibilities with various advantages and disadvantages which have to be considered
individually for each specific application.
A separator can be subsequently integrated in any production line. However, a
machine is then required for the entire product flow, which may involve a relatively
large investment. If a centrifuge or a decanter is operated in a bypass arrangement,
a smaller machine will also be sufficient. By using a bypass arrangement for a
centrifuge for clarifying part of the overall product flow, the speed of the normal
process of concentrating the solids in the cross-flow filter cycle can be reduced.
A decanter can also be used as an alternative to a separator at the
same place. A decanter is more tolerant with regard to abrasive
media, e.g. bentonite, than a separator, and is also suitable
for higher trub contents in juice. In addition, the clarification
performance of centrifugal separation can be significantly
improved by raising the retentate temperature. The service life of the
filter is increased, depending on various factors, to 3 to 5 working days.
Processing the retentate with a decanter
A further possibility for processing retentate is to collect the retentate at the end of
filtration in a separate tank and to clarify it parallel to normal day-to-day operation.
The retentate is diluted with water, and is then clarified in the decanter. The clarified
juice downstream of the decanter has a residual solids content of approx. 0.5 percent
(by volume), and can be recycled back into ongoing production. These relatively dry
solids can also be disposed of with the pomace. The dry matter of the solids is within
a range of up to 3 percent dry matter. Because this process runs parallel to normal
juicing operations, the hourly capacity of this line can be relatively small, resulting in
limited investment costs.
Attractive cost-effectiveness
Rising prices for juice and concentrate in conjunction with disposal costs for waste
substances mean that retentate processing is becoming more and more attractive
from the point of view of cost-effectiveness. For this purpose, centrifugal
separation technology offers individual solutions, which are characterised
by high product quality and high cost-effectiveness.
GEA Westfalia Separator Process 25
Separator’s Digest 1 | 2009