In processing plants for the Food & Dairy industry for
powder production, there will often be an evaporator. The evaporator is used to
remove water from the product before further processing - typically spray
drying or for transport purpose to another plant site.
All flowsheet animations are available in the
GEA Niro download
area.
The evaporation process
The evaporation of water from a product is typically done
in falling film multi-effect evaporators with either thermal (TVR) or
mechanical (MVR) recompression of the vapours to a higher energy level for
re-using it to save energy. As a general rule, as much water as possible is
removed in the evaporator, as it is ten-fold cheaper here compared
to spray drying.
The maximum solids content in the concentrate from the
evaporator is given by the product composition which is responsible for the
viscosity in the concentrate. Besides the evaporation of the milk, the
preheating/pasteurizing is very important to be able to produce powders with
exact specifications and low content of thermophile and mesophile bacteria.
Evaporators for infant milk formula Evaporators for
infant milk formula are typically high concentrators
as they operate in the range from 30 % TS to 56 % TS. High-heat treatment of
the concentrate, either before or after the evaporation, is today a requirement
from the industry to ensure a product with minimal bacteria content. To comply
with this requirement, we have developed the SaniHeat technology which,
depending on solids content and composition of the concentrate, will bring the
temperature up to 140° C for a split second before the product is flashed down
to 80° C and then spray dried.
Evaporation of fruit juices Evaporation of
fruit juices is an integrated part of the process to make
fruit juice concentrate, be it citrus or apple juices, which are concentrated
up to 50 % Brix or more. The design and engineering of this falling film
evaporator is done by
GEA Wiegand GmbH.
Evaporation of coffee
extracts Evaporation of coffee extracts is
likewise done in a falling film evaporator. When the coffee extract leaves the
extractor, it
is passed t hrough an aroma recovery flash unit to separate the coffee aroma,
as that will otherwise disappear during the subsequent evaporation. This aroma
fraction is mixed with the concentrate.
The evaporation is typically done in a 2-3 effect falling film
evaporator, where the coffee extract is
evaporated from 6-7 % solids to 43-47 %
solids, if the concentrate is to be
freeze dried. If the concentrate is to be spray dried,
then the concentrate is further evaporated in a high concentrator to 55 %
solids, before the aroma fractions is mixed back again. The high solids content
(sugar) will encapsulate the aroma and only a small portion is lost during the
spray drying.
Freeze concentration
Freeze concentration is applied where fo cus is on aroma
reten tion and high quality products. It is specially suited for heat sensitive
products. Freeze concentration is used for
coffee extracts,
juices and beer
and wine. Freeze concentration has been practiced for centuries. In its
earliest form it was as simple as leaving a barrel of liquid outside in the
cold winter night.
Water would
crystallize and grow as a thick layer of ice along the inside walls of the
barrel. The next day they would simply cut a hole through the ice shell and
drain the now concentrated product. The water (now ice) was simply discarded.
Modern freeze concentration processes
consist of a crystallization section, where part of the water is converted into
solid ice crystals using a refrigeration system. The ice crystals are then
separated by filters, centrifuges or using the GEA Niro PT technology - wash
columns. This patented technology is a specific form of suspension melt
crystallization and has made freeze concentration economically feasible for a
wide range of applications.