Note: Descriptions are shown in the official language in which they were submitted.
The present invention is concerned with a process and
apparatus for the production of ~rozen granulates
It is known to preserve foodstuffs, for example, fish,
meat and vegetables, by freezing. Drinks, for example, fruit
juices, coffee, tea and soups, can be converted, by freezing
and drying in a frozen state, into readily soluble granulates,
i.e. into so called instant powders. Pharmaceutical pre-
parations, too, which are administered in the form of a
solution but which are not stable in the solvent to be used,
have, for many years, been stored in the form of lyophilisates
In order to avoid the destruction of the structure
of the solid foodstuffs or the demixing of the solutions, it
i~ necessary to freeze these products as suddenly as possible.
In the past, a large number of techniques have been developed,
particularly for freezing solutions.
Thus, it is known to freeze out the solvents in
cooled containers in block form and to comminute the blocks
by cold grinding. According to another process, the liquid
~ is sprayed on to a cooled, rotating cylinder or on to a
20 cooled conveyor belt from which, after solidification, it is
again removed by means of appropxiate scrapers or scratchers.
In the case of one variant of these apparatus, heat is removed
not by cooling the ~ubstrate but by spraying on readily evapo-
rating cooling agents, for example, carbon dioxide, nitrous
o~ide and, especially, liquid nitrogen~ A disadvantage common
to all of the3e processes is that, due to the comminution or
removal of ~he frozen product, particles are obtained of greatly
varying size and shape, together with a considerable amount of
fine~, which makes difficult the further working up by the
freeze drying ~see Schormuller, Handbuch der Lebensmittelchemie,
pp. 262-266, pubo Springer-Verlag, 1974). Furthermore, frozen
granulates which are readily flowable, i.e~ are substantially
spheroidal, are also desired for the production of porous
tablets according to the process described in German
Offenlegungsschriften No. 2,246,013 Heinemann et al, filed
20~9,72, published 28.3.74 and ~o. 2,S56,561, Knitsch et al
filed 16.12.75, published 30.6.77
It is known from German Offenlegungsschrift No.
2,140,747 Briggs et al, filed 13.8.71, published 17.2.72,
that granulates of substantially uniform shape and size can be
obtained when the solution to be frozen is sprayed through
appropriate nozzles into a moving bath of a boiling fluorinated
hydrocarbon, such as Freon (trademark), as cooling agent. The
resultant granulate is normally removed discontinuously since
a continuous removal requires the use of expensive apparatus.
Products frozen on to parts of the apparatus, especially on to
the stirrer, make it difficult to change quickly from one
product to another, this only being possible after complete
emptying, warming and thorough cleaning of the plant
Therefore, the problem exists of providing a con-
tinuous proces~ for the production of uniform, frozen
granulates for freeze drying which, with the lowest possible
expense for apparatus, permits a rapid change from one product
to another.
The present invention overcom~3s this problem in
that, in suEficiently cooled surroundings, a stream of a readily
evaporatable liquid cooling agent is brought into contact with
a stream of liquid product, for exa~ple, a solution, the liquid
cooling agent evaporates and the heat energy for the evaporation
i~ taken from the product liquid which is thereby suddenly
frozen. The frozen granulate being found to be in the form of
small, spheroida~ particles, These sph~roids can then easily
b~ separated from the gaseous cooling agent, freeze dried in a
conventional manner and further worked up.
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,
The freeze-dried granulates produced in this manner
are, surprisingl~, very uniform, dissolve readily and can be
readily worked up due to their spheroidal shape, whereas,
non-uniformly-formed granules or snowflake-like products of
greatly varying size distribution were to have been expected.
According to the invention there is provided a
process for the production of a frozen granulate from a
product liquid comprising, contacting the product liquid
with a moving stream of readily evaporatable liquid cooling
agent, allo~ing the liquid cooling agent to evaporate and
frozen granulate to form from said product liquid, and
recovering said frozen granulate; said cooling agent being
inert to said product liquid.
Especially good results are achieved when the product
liquid and the cooling agent streams run in the direction
of gravitational force since an especially long-lasting heat
exchange is thex~by achieved. On the other hand, by an oblique
guiding of the streams from below upwardly the result is
achieved that the granules formed, on the basis of their size,
drop down from the stream of cooling agent at diffexent
speeds and thus a classification or grading is achieved insofar
as there are again formed granules of greatly differing size.
As cooling agent, there can be used all liquid
materials which evaporate at atmospheric pressure ~elow the
freezing point of the product liquid and which do not react
with the productn By way of example, there can be mentioned
nitrous oxide, alkylene oxides, ammonia, carbon dioxide, low
boiling point hydrocarbons, for example, butane and propane,
and fluorinated hydrocarbons, for example, Freon (trademark).
Liquid nitrogen ~as proved to be especially advantageous since
it is inexpansive to obtain, does not react with any of the
product liquids, does not cause contamination of the environment
2~i
due to escaping gases and, because of its low bsiling point,
- cools the product very quickly to a low temperature. In the
case of prcducts which are not sensitive to oxygen, liquid
air can also be used in the same manner.
In a further aspect of the invention there is pro-
vided a frozen granulate pr ~luced by the process of the
invention and characterized by a spheroidal shape and sub-
stantially uniform dimensions.
The present i~vention also provides an apparatus for
the continuous productivn of granulates, comprising a cooling
column, supply means for streams of cooling agent and streams
of product liquid in an upper part of the column, a removal
opening for the granulate at the lower end of the cooling
column and removal means for the gaseous cooling agent.
' The supply means for the streams suitably comprise
injection nozzles disposed so as to introduce said streams into
the centre of the upper part of the column.
It will be understood that the column is appropriately
dimensioned to permit granulate formation. In particular the
height of the column, or more particularly of the contact
zone for product liquid and cooling agent, should be sufficient
to permit evaporation of the liquid cooling agent in contact
~ith the product liquid to form a frozen granulate of said
product liquid.
The invention can be employed with any product liquid
which can be frozen, the invention is especially suitable for
producing a frozen granulate from a solution. In particular
the invention is suitable for forming a frozen granulate from
agueous product liguids~ It will be understood, however, that
other liquid media might be employed although water will be the
most common medium. Of course, the liquid m~dium should be one
which will provide a product liquid having a freezing point
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such that it can be readily frozen by the cooling effect of the
evaporation of the liquid cooling agent. The suitability of
potential liquld media in conjunction with particular liquid
cooling agents can be readily determined by simple experiment
and/or a determination of the freezing point of a particular
product liquid employing a particular liquid medium~
The invention is illustrated in a particularly
preferred embodlment by reference to the accompanying drawings
in which:
FIGURE 1 shows a,~ apparatus according to the
invention, and
FIGURE 2 shows a detail of the injection noæzles
in the apparatus of Figure 1.
With further reference to Figure 1 an apparatus A for
the continuous production of granulates comprises a cooling
column 1, a storage container 12 of cooling agent, a storage
container 13 of product solution, a freeze drying plant 18 and
a confectioning or storage station 19.
The column 1 is vertically up-standing, having an
upper cylindrical portion and a lower conically-shaped portion
which narrows in the downward direction; the upper part of
the colurnn 1 has a centrally positioned inlet nozzle 2 for a
cooling agent, as well as one or more nozzles 3 for a product
liquid an outlet 4 is located in a lower end of the column 1
for the remov~l of frozen granulate and for the e.scape of evapo-
rating cooling agent.
The column 1 is suitably provided with an insulating
outer mantel 5 and an inner lining 6, between which the
evaporating cooling agent can flow off, as cooling and insulating
material, via a va~ve 7.
For the upply of cooling agent and of product solution,
, there are provided regulatable valves 8 and 9 in pipe lines 11
;3$
and 15 respectively.
The amount of gaseous cooling agent flowing off via
valve 7, which serves for the cooling o~ the outer mantel 5,
can ~e regulated by an additional overpressure valve 10 in
pipe line 14. The inlet nozzle 2 communicates via pipe line
11 with the storage container 12, the pressure in container 12
~ringing about the conveyencing o~ the cooling agent. The
nozzle(s) 3 communicate via pipe line 15 with the storage
container 13, which is preferably also constructed with double
walls and can be cooled by cooling agent removed vla valves 7
and 10 through the pipe line 14. A pump 16 is disposed in
pipe line 15 and forces product solution into the product
nozzle 3 vla valve 9. The product nozzle 3 is preferably
heatable in order to prevent freezing up~
The frozen granulate falls out through the outlet
4 due to the gravitational force and can be collected in a
collection container and passed discontinuously to a freeze
drying plant.
Preferably, however, the granulate falling out is
passed continuously on a conveyor belt 17 through the continuous
freeze drying plant 18 and thereafter passes into the confection-
ing or ~torage station 19.
For protection against ambient temperature and
moisture, the conveyor belt 17 is, up to the point of entry
into the freeze drying plant 18, also surrounded by a mantel
20, the inner space of which can also be cooled by the
evaporating cooling agent. If liquid nitrogen or liquid air
i5 not u~ed a~ the cooling agent, then it is also necessary
to provide a device for the collection or reliquifaction of the
evaporated cooling agent.
With furthex reference to Figure 2 there i~ shown 6
product nozzles 3 communicating with supply pipe 15 and the cool-
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ing agent nozzle 2 o~ the apparatus A of Figure 1.
It has proved to be advantageous to supply the pro-
duct liquid to the nozzles 3 with a temperature just a little
above the freezing point of the product liquid since, in this
way, the cooling agent is best utilised. By variation of the
size of the nozzles 2 and 3 and of the pressure with which the
cooling agent and the product liquid is fed in, the size of
the granules can be varied within wide limits. For economic
reasons, the amount of liquid cooling agent ~ed in is adjusted
in such a manner that it just su~fices to freeze the product
liquid and to cover the heat losses to the surroundings.
Depending upon the concentration of the product liquid, in
the case of the preferred use of liquid nitrogen, the con-
sumption of cooling agent is 2 - 3 kg. per kg. of product
liquid.
In operation product solution is pumped from
- container 13 by pump 16, via pipe line 15 and valve 9 and is
injected through nozzles 3 into a stream of cooling agent
injected into column 1 through inlet nozzle 2, The cooling
agent evaporates thereby cooling the product solution and
freezing it to form small, spheroidal particles which fall
through outlet 4 onto conveyor belt 17. The spheroidal
particles are conveyed through freeze drying plant 18, where
~; they are freeze dried, on conveyor belt 17 and are collected
; in the confectioning or storage station 19.
Of course, numerous variations of the above-described
apparatus are conceivable with which the process according to
the present invention can also be carried out. Thus, for
example, the column 1 can, of course, also be cylindrical
30 or double-conical, instead of a simple cooling agent and
product feed in, several such nozzles can also be provided and
the products can, instead of being continuously passed to a
reeze drying plant, also be collected in a storage tank and
then used at some later time.
~ or the construction of the apparatus, it is
possible to use practically all materials which still have,
at the temperature of the liquid cooling agent, a sufficient
stability and strength, stainless steel, copper, polyethylene
and the like being mentioned by way of example.
By a simultaneous spraying in, vla two different
nozzles, it is possible to spray components which are
incompatible with one another and thus to obtain a
statistically mixed granulate. By means of a different nozzle
size or of a different spray pressure, if desired there can
also be obtained a differing particle size for a particular
granulate.
The following Example is given for the purpose of
illustrating the present invention:-
1. Formation of the frozen granulate.
Use was made of a cocliny column 1 according to
~ Figure 1 of the accompanying drawings which had a height of200 cm., a diameter of 80 cm. and an ou~let 4 with a width of
20 cm. The upper cylindrical part of the column had a
length of 60 cm. and the conically-shaped part had an angle
of 30 from the vertical. Pipes, valves and storage vessels
were according ~o Figure 1 but instead of the illustrated
continuously operating freeze drying plant, th re was employed
a c~oled storage vessel below the outlet 4.
1 kg. Saccharose was dissolved in 10 litres distilled
water to give a l~/o solution which was placed in a thermo-
statically contr~olled storage vessel 13 and kept there at atemperature of about ~1C., the freezing point of this solution
being about -0.5C
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. - ,
. , ~ : , . . . . .
æ~
From a second storage container 12, liquid nitrogen
(LN2) was supplied via an insulated copper pipe 11 and a
regulating valve 8 to the LN2 nozzle, this nozzle having an
inner diameter of 8 mm. The column 1 was pre-cooled until,
at the outlet 4, a temperature of about -50C. was achieved
in the outflowing stream of nitrogen.
Then, by means of pump 16, at a spraying in pres-
sure of 1.5 bar., the saccharose solution was sprayed, via
a polyethylene pipe 15, a regulating valve 9 and six product
nozzles 3, into the stream of liquid nitrogen. The six
nozzles 3, which were arranged in the form of a circle at a
conical angle of 60 around the LN2 stream, each had an inner
diameter of about 0.15 mm. The distance between the exit
point of the LN2 from the LN2 nozzle 2 and the point of mixing
with the solution was 125 mm. and the distance from the
product nozzle 3 to the mixing point was 30 mm. Upon contact
with the LN stream, the saccharose solution froze suddenly
to give small spheroids, whereas the greater part of the L~2
evaporated~ This gaseous, cold nitrogen was further used for
cooling the column 1 and the storage container 13~ - -
The frozen spheroids fell down~ardly in the reaction
chamber 1 and were removed through the outlet 4 and collected
in a deep-cooled Dewar vessel. The diameter size of these
pheroids was between 0.16 and 1.0 mm,, the Gaussian dis-
;~ tribution having it~ maximum at 0.63 mm. with 85% by weight
of the particles. Over 9~! of the granulate had a spheroidal
3hape. The granulate flowed readily and did not stick together.
In a cooled container, the granulate can be stored practically
without time limit,
The consumption of LN2 was 2,5 kg~/kg. of solution
(including pxe-cooling of the reaction chamber and losses).
2. Freeze dryinq of the frozen granulate.
The f~ozen spheroids collected in the De~ar vessel
were shaken on to a pre-cooled metal sheet (-50C.) of a
lyophilisation plant and discontinuously freeze-dried under
the following conditions:
a) 13 hours at 0.2 mbar and 25C.
b) 5 hours at 1.333 10 3 mbar and 25C.
After lyophilisation, the particle size distribution
and the spheroidal form of the granulate had not changed from
that of the frozen state. Its density was calculated to be
about 116 kgO/m3. The residual water content was 1.6~
by weight. The product had a homogeneous, white colour Upon
shaking up and sieving, the granulate retained its shape.
It could easily be rubbed between the fingers. The electro-
static charginy was low. The spheroids scarcely stuck together
and did not stick at all to the walls of bottles in which it
was ~tored. The flowability was very good, the flow
behaviour of the granulate resembling that of a liqu-d. In
order again to produce the initlal concentration of the 1~/9
saccharose solution, 100 g. of granulate were added to 1 litre
of distilled water. Without mechanical movement of the liquid,
the dis301ving time was 32 seconds.
It will be understood~that the dimensions of the drop-
lets of product liquid in the stream of product liquid, and ~-
hence the dimension of the granulate will depend on a number
of factors. In particular the dimensions will depend on the
diameter of the orifices of the nozzles 3, the pressure under
which the product liquid is delivered into column 1, and the
vi3cosity of the product liquid. It will be apparent that
these three parameters can be varied within wide boundarie~ and
that appropriate parameters for any desired granulate can be
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'
readily determined by experiment. Similarly the diam~ter of
the orifice of inlet nozzle 2 is subject to wide variation.
In a general manner, however, and having regard to
economic realities it is convenient to employ nozzles 3 having
orifices with a diameter of 0.005 to 2 mm, with the product
liquid being delivered under a pressure of 1.1 - 10 bar. The
orifice(s) of the inlet nozzle 2 for liquid cooling agent may
conveniently have a diameter of 1 - 20 mm. There is, o~ course,
no limit to the number of nozzles 3 which might be employed,
nevertheless it i9 found convenient to employ from 3 to 8
nozzles bearing in mind the limitations of plant size and
spatial disposition.
I~ will be understood that the inlet nozzle 2 and
the nozzle or nozzles 3 may be single orifice or multi-orifice
nozzle~ for injection of liquid into column 1.
Generally speaking the pressure of delivery of the
product liquid through product nozzle 3 is sufficient t~ pre-
vent product liquid from freeziny and solidifying on the
orifice~. Furthermore, as described previously, product
nozzle 3 may suitably include means for heating it to prevent
build-up of frozen product liquid in the nozzle line.
The invention h s been described in general by
reference to an embodiment in which the product liquid is a
solution. As indicated previously the inventlon can be
employed with liquids other than solutions, for example,
dispersions, suspensions and emulsions.
- ~ The invention finds special application in the manu-
facture of particular diagnostic materials, however, it has wide
application and can be employed in the particular industries
described in the ~ ove description of the prior artJ
