GB1559920A

GB1559920A - Process and device for the production of frozen granulates

Info

Publication number: GB1559920A
Application number: GB53984/77A
Authority: GB
Original assignee: Boehringer Mannheim GmbH
Current assignee: Roche Diagnostics GmbH
Priority date: 1976-12-30
Filing date: 1977-12-28
Publication date: 1980-01-30
Also published as: IE46022L; SE7714822L; AT356498B; AU3192277A; FR2375901A1; AR214108A1; ZA777184B; FI773941A7; ATA940677A; NL7714401A; IL53695A0; IE46022B1; AU506746B2; BE862370A; DE2659546A1; CA1106686A; CH625332A5; JPS53114783A; DD133295A5; IT1089419B

Abstract

The device has a cooling column (1) with supply devices for coolant flows (2) and product liquid flows (3) in the centre of the upper part of the cooling column (1) and a removal opening (4) for the granulate at the lower end of the cooling column as well as discharges for gaseous coolant (7). The device serves in particular for manufacturing frozen granulates of foods and pharmaceuticals. <IMAGE>

Description

(54) PROCESS AND DEVICE FOR THE PRODUCTION OF FROZEN GRANULATES (71) We, BOEHRINGER MANNHEINI G.m.b.H., of Mannheim-Waldhof, Federal Republic of Germany, a Body Corporate organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is concerned with a process and device for the production of frozen 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 preparations, 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 is 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 cooled conveyor belt from which after solidification, it is again removed means of appropriate scrapers or scratchers.

In the case of one variant of these apparatus, heat is removed not by cooling the substrate but by spraying on readily evaporating cooling agents, for example, carbon dioxide, nitrous oxide and, especially, liquid nitrogen. A disadvantage common to all of these processes is that, due to the comminution or removal of the frozen product, particles are obtained of greatly varying size and shape, together with a considerable amount of fines, which makes difficut the further working up by the freeze drying (see Schormuller, Handbuch der Lebensmittelchemie, pp. 262-266, pub. 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 our British Patent Specifications Nos. 1,381,588 and 1,502,580.

It is known from British Patent Specification No. 1,376,972 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", as cooling agent.

("Freon" is a Registered Trade Mark). 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 continuous process 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.

According to the present invention, there is provided a process for the production of frozen granulates, wherein a liquid product solution is introduced into a moving stream of a readily evaporable liquid cooling agent and the frozen granulates of the product remaining after evaporation of the cooling agent are separated off.

The process of the present invention results in the liquid product solution being suddenly frozen to give small, spheroidal particles. These spheroids can then easily be separated after evaporation of the gaseous cooling agent, freeze dried by known pro cesses and further worked up. The freezedried granulates produced in this manner are, surprisingly, very uniform, dissolve readily and can be readily worked up due to their spheroidal shape, whereas, in point of fact, non-uniformly-formed granules or snowflake-like products of greatly varying size distribution were to have been expected.

Especially good results are achieved when the streams of liquid product solution and liquid cooing agent run in the direction of the gravitational force since an especially long-lasting heat exchange is thereby 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 liquid cooling agent at different speeds and thus a classification or grading is achieved insofar as there are again formed granules of greatly differing size.

As liquid cooling agent, there can be used all liquid materials which evaporate at atmospheric pressure below the freezing point of the liquid product solution and which do not react with the product. By way of example, there can be mentioned nitrous oxide, alkylene oxides, ammonia, carbon dioxide, low boiling point hydrocarbons, such as butane and propane, and fluorinated hydrocarbons, such as "Freon".

Liquid nitrogen has proved to be especially advantageous since it is inexpensive to obtain, does not react with any of the liquid product solutions, does not cause contamination of the environment due to escaping gases and, because of its low boiling point, cools the product very quickly to a low temperature. In the case of products which are not sensitive to oxygen, liquid air can also be used in the same manner.

The present invention also provides a device for the continuous production of frozen granulates, comprising a cooling column, supply means for streams of liquid cooling agent and streams of liquid product solution in the centre of the upper part of the column, a removal opening for the frozen granulates of the product at the lower end of the cooling column and removal means for evaporated cooling agent.

One embodiment of the device according to the present invention is illustrated in Fig.

1 of the accompanying drawings. This device comprises a vertically standing, conicallyshaped cooling column (1) which narrows in the downward direction, the upper part of the column having a centrally positioned inlet nozzle (2) for a liquid cooling agent, as well as one or more nozzles (3) for a liquid product solution and on the lower end of the column having an opening (4) for the removal of frozen granulates of the product and for the escape of evaporating cooling agent. The column (1) is preferably provided with an insulating outer mantel (5j, as well as with an inner lining (6), between which evaporated cooling agent flows off, as cooling and insulating material, via a valve (7). Furthermore, for the supply of liquid cooling agent and of liquid product solution, there are provided regulatable valves (8) and (9). The amount of gaseous cooling agent flowing off via valve (7), which serves for the cooling of the outer mantel, can be regulated by an additional overpressure valve (10) provided in an outlet at the top of the column (1). The liquid cooling agent is fed in via a pipe (11) from a storage container (12), the pressure in this storage vessel bringing about the conveyencing of the liquid cooling agent. The storage container (12) is preferably constructed with double walls and can be cooled by cooling agent removed via valves (7) and (10), through a pipe (14). The liquid product solution is taken from a storage container (13), which is preferably also constructed with double walls and can also be cooled by cooling agent removed via valves (7) and (10), through pipe (14), through a pipe (15) and forced by means of a pump (16) and through valve (9) into the product nozzle (3). The product nozzle is preferably heatable in order to prevent freezing up. The frozen granulate falling out through the opening (4) due to the gravitational force 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 a continuous freeze drying apparatus (18) and thereafter passes into a confectioning or storage 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, 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 is not used as the cooling agent, then it is also necessary to provide a device for the collection or reliquifaction of the evaporated cooling agent.

Fig. 2 of the accompanying drawings schematically shows a cross-sectional view of an arrangement according to the present invention of 6 liquid product solution nozzles (3) with supply pipe (15) and liquid cooling agent nozzle (2).

It has proved to be advantageous to supply the liquid product solution to the nozzles with a temperature just a little above the freezing point of the solution since, in this way, the liquid cooling agent is best utilised. By variation of the diameter of the nozzles (2) and (3) and of the pressure with which the liquid cooling agent and the liquid product solution is sprayed in, the size and solids content of the granules can be varied within wide limits. The size and solids content of the granules can also be varied by the concentration and viscosity of the liquid product solution. For economic reasons, the amount of liquid cooling agent fed in is adjusted in such a manner that it just suffices to freeze the liquid product solution and to cover the heat losses to the surroundings.

Depending upon the concentration of the liquid product solution, in the case of the preferred use of liquid nitrogen, the consumption of cooling agent is 2-3 kg. per kg. of liquid product solution.

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 columns can, of course, also be cylindrical or double-conical, instead of a simple liquid cooling agent and liquid product solution feed in, several such nozzles can also be provided and the products can, instead of being continuously passed to a freeze drying plant, also be collected in a storage tank and then used at some later time.

For the construction of the device, 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, via 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: Example.

1. Formation of the frozen granulate.

Use was made of a cooling column (1) according to Fig. 1 of the accompanying drawings which had a height of 200 cm., a diameter of 80 cm. and an outlet opening (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 to Fig. 1 but instead of the illustrated continuously operating freeze drying plant, there was employed a cooled storage vessel below the exit opening (4).

1 kg. Saccharose was dissolved in 10 litres distilled water to give a 10% solution which was placed in a thermostatically controlled storage vessel (13) and kept there at a temperature of about +1 0C., the freezing point of this solution being about --0.5"C.

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 reaction chamber (1) was pre-cooled until, at the outlet opening (4), a temperature of about -500C. was achieved in the outflowing stream of nitrogen.

Then, by means of pump (16), at a spraying in pressure 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, which were arranged in the form of a circle at a conical angle of 60 around the LN2 stream, had an inner diameter of about 0.15 mm. The distance between the exit point of the LN2 from the LN2 nozzle and the point of mixing with the solution was 125 mm. and the distance from the product nozzle to the mixing point was 30 mm. Upon contact with the LN2 stream, the saccharose solution froze suddenly to give small spheroids, whereas the greater part of the LN2 evaporated. This gaseous, cold nitrogen was further used for cooling the reaction chamber (1) and the storage container (13).

The frozen spheroids fell downwardly in the reaction chamber (1) and were removed through the opening (4) and collected in a deep-cooled Dewar vessel. Their diameter size of these spheroids was between 0.16 and 1.0 mm., the Gaussian distribution having its maximum at 0.63 mm. with 85% by weight of the particles. Over 99% of the granulate had a spheroidal shape. It flowed readily and did not stick together. In a cooled container, it can be stored practically without time limit.

The consumption of LN2 was 2.5 kg/kg.

of solution (including pre-cooling of the reaction chamber and losses).

2. Freeze drying of the frozen granulate.

The frozen spheroids collected in the Dewar vessel were shaken on to a pre-cooled metal sheet (--50"C.) of a lyophilisation plant and discontinuously freeze-dried under the following conditions: (a) 13 hours at 0.2 mbar and 25 C.

(b) 5 hours at 1.333 10-3 mbar and 25"C.

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 kg./m3. The residual water content was 1.6% by weight. The product had a homogeneous, white colour. Upon shaking up and sieving, the granulate air tained its shape. It could easily be rubbed between the fingers. The electrostatic change ing was low. The spheroids scarcely stuck together and did not stick at all to the walls of bottles in which it was stored. The flowability was very good, the flow behaviour of the granulate resembling that of a liquid. In order again to produce the initial concentration of the 10% saccharose solution, 100 g. of granulate were added to 1 litre of distilled water. Without mechanical movement of the liquid, the dissolving time was 32 seconds.

WHAT WE CLAIM IS: - 1. A device for the continuous production of frozen granulates, comprising a cooling column, supply means for streams of liquid cooling agent and streams of liquid product solution in the centre of the upper part of the column, a removal opening for the frozen granulates of the product at the lower end of the cooling column and removal means for evaporated cooling agent.

2. A device according to claim 1, wherein the product removal opening is connected via a conveyor belt with a continuously operating freeze drying plant.

3. A device according to claim 1 for the continuous production of frozen granulates.

substantially as hereinbefore described and exemplified.

4. A process for the production of frozen granulates, wherein a liquid product solution is introduced into a moving stream of a readily evaporatable liquid cooling agent and the frozen granulates of the product remaining after evaporation of the cooling agent are separated off.

5. A process according to claim 4, wbere- in the stream of liquid cooling agent moves downwardly in the direction of the gravita tonal force.

6. A process according to claim 4 or 5, wherein the size and solids content of the granules is varied by the concentration, viscosity and spray in pressure of the liquid product solution, as well as by the nozzle diameter.

7. A process according to any of claims 4 to 6, wherein the liquid cooling agent used is liquid nitrogen.

8. A process according to claim 4 for the production of frozen granulates, substantially as hereinbefore described and exemplified.

9. Frozen granulates, whenever produced with the device according to any of claims 1 to 3.

10. Frozen granulates, whenever produced by the process according to any of claims 4 to 8.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ing was low. The spheroids scarcely stuck together and did not stick at all to the walls of bottles in which it was stored. The flowability was very good, the flow behaviour of the granulate resembling that of a liquid. In order again to produce the initial concentration of the 10% saccharose solution, 100 g. of granulate were added to 1 litre of distilled water. Without mechanical movement of the liquid, the dissolving time was 32 seconds. WHAT WE CLAIM IS: -

1. A device for the continuous production of frozen granulates, comprising a cooling column, supply means for streams of liquid cooling agent and streams of liquid product solution in the centre of the upper part of the column, a removal opening for the frozen granulates of the product at the lower end of the cooling column and removal means for evaporated cooling agent.

substantially as hereinbefore described and exemplified.