Improvements in Sugar-refining.
Year: 1896

page_text: Date of Application, 17th Feb., 1896-Accepted, 21st Mar., 1896
COMPLETE SPECIFICATION.
Improvements in Sugar-refining.
I, MAX ZAHN, of Artern, Thuringia, Germany, Sugar-factory Manager, do
hereby declare the nature of this invention and in what manner the same is to
be performed to be particularly described and ascertained in and by the following
statement :-
In the process heretofore employed for refining sugar in the centrifugal machine,
the whitening has been effected by means of steam (sometimes in a perfectly dry
state) or steam mist (a mixture of steam and air). But this method entails certain
drawbacks. The steam condenses and the water of condensation dissolves the
syrup adhering to the layers of sugar, this action commencing at the centre and
proceeding outwards. But as the steam is compelled to pass always through the
more central layers in order to reach the outer layers, and becomes continually
condensed during the said passage, the crystals of the more central layers become
partly dissolved, and considerable loss of sugar results therefrom. This loss is
such that the yield of white sugar amounts scarcely to 86 per cent. at the best.
The use of steam, even when dry, as heretofore carried out involves the disadvantage
that too much steam is condensed to water before the sugar is sufficiently heated.
Now according to this invention, in order to reduce such loss to a minimum,
superheated steam, or a mixture of superheated steam and air is employed instead
of saturated or dry steam as heretofore.
The temperature of the superheated steam should be such as to allow of
condensation taking place to an extent sufficient for detaching the syrup that
adheres to the sugar crystals. The heat which the superheated steam can give up
before condensation takes place, is imparted to the sugar-crystals, which therefore
acquire from the said superheated steam gradually, from the interior outwards, a
temperature which is almost or quite high enough to prevent any more steam from
condensing on the sugar crystals, so that no more water of condensation will be
produced to continually dissolve the sugar, as heretofore. By this means
considerably better yield (about 93 per cent.) of white sugar is obtained.
a
The sugar itself does not actually become heated to the temperature of the
superheated steam, because, as the sugar becomes heated, the temperature of the
superheated steam falls. Therefore when superheated steam of about 180° C. is
used, the sugar is heated to at most 96° C. It has been found that there is not
the slightest decomposition of or damage to the sugar produced by using super-
heated steam having a pressure of about 0-3 atmosphere and a temperature of
180° C.
The condensation of the superheated steam which at first takes place when
whitening is effected with such steam, first causes the syrup adhering to the crystals
to become sufficiently liquid to flow out of the centrifugal machine.
But owing to
the use of superheated steam, the condensation of the steam very soon ceases, and
the superheated steam can give up a large amount of heat, so that the sugar which
is brought into contact therewith is soon rendered so hot that very little more
steam will condense thereon.
This improved method of whitening sugar can also be advantageously combined
with a process for blueing the sugar.
As is well known, sugar must in many cases be blued in the course of manufacture
in order to suit the prevailing taste of the public. This blueing is effected at the
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page_text: present time either by adding blue to the material under treatment in the vacuum-
apparatus, or in processes in which the sugar is whitened with water in the
centrifugal machine, by mixing the blue with such water.
Both methods have considerable disadvantages, the most important being that
the blue is for the greater part contained in the waste water and is lost therewith.
If the blue is put into the vacuum-apparatus, it becomes only partly deposited
in and upon the sugar crystals, the greater part thereof floating in the syrup
present between the crystals. But it is not advantageous to put the blue upon the
surfaces of the crystals before they are perfectly clean, because although the blue
does certainly increase the whiteness of the crystals, just as the whitening of lime
is rendered more intense by an addition of blue, yet the blue forins with the
brownish syrup that adheres to the crystals, only a dirty green color.
Drawbacks of this kind take place only when the sugar is whitened by means of
blued water that is (water mixed with blue) because (1) the greater part of the
blue passes through the layer of crystals; and (2) the blue which remains on the
layer of crystals, becomes fixed before the crystals are perfectly clean.
If it were attempted first to cleanse the crystals with unblued water and then to
blue them with water mixed with blue, there would be such a loss of sugar as
might render the process unprofitable.
The disadvantages mentioned are completely obviated by the following method.
After the sugar has been suitably whitened with superheated steam (or, say,
during the last minute or half minute of the whitening, at the commencement of
which the most central layers of sugar will have already been completely whitened),
there is placed in communication with the piping that conducts the superheated
steam to the centrifugal machine, a nozzle pipe, which dips into a vessel which
contains the blue triturated into or mixed with a few cubic centimetres of water or
syrup. The steam flowing through the piping carries the blue, in an extremely
finely divided state, along with it and projects it against the layer of sugar. In
this case the blue may without detriment, be principally directed toward the most
central layers of sugar and remains attached to these in contradistinction to the
application of blue water-for as the sugar is only slightly moist and it will be
necessary further to moisten it in order that it may be forced out of the drum the
contents of the centrifugal machine can very easily be mixed in such a manner that
they assume a uniformly blue tone that is to say the water contained on the moist
sugar, distributes the blue amongst the contents of the drum. The blue is thus
distributed in an extremely fine and uniform way over all the layers of sugar.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. In the method of whitening sugar in a centrifugal machine, the superheated
steam, or a mixture of superheated steam and air, substantially as hereinbefore
described for the purpose specified.
2. The herein described method of blueing the whitened or nearly whitened
sugar in a centrifugal machine by introducing the blue mixed or triturated in
water or syrup into superheated steam that is on its way to the centrifugal machine
so that the steam carries the blue along with it in an extremely finely divided state
and conducts it to the sugar in the said machine, substantially as hereinbefore
described.
Data: 151
2000
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.