GB2085392A - A method of packaging powdered or granular material in an atmosphere having a low oxygen content - Google Patents

Abstract

During transport of powdered or granular material to a packaging facility, the material is contacted by a gas having a low oxygen content, e.g. a predominantly nitrogen or carbon dioxide atmosphere, so as to purge the material of oxygen. The material is subsequently packaged in an atmosphere of the same composition as the purging gas. In one embodiment a stream of the gas serves to convey the material towards the packaging facility and in another embodiment the material gravitates slowly through a fluidizer to which said gas is supplied. The purging gas may be heated and circulated.

Description

SPECIFICATION A method of bringing powdered or granular substances into a gas atmosphere and keeping them therein This invention relates to a method of bringing powdered or granular substances into a gas atmosphere and keeping them therein.

For many powdered or granular substances, for example food products, it is desirable that they are packaged and stored in a packet that is as free of oxygen as possible; this in order to enhance the keeping characteristics of these products. This applies in particular to food products sensitive to oxidation, such as milk powder, coffee, and the like.

For packaging and storing substances in a medium poor in oxygen, a method is known in which these subtances are introduced into a final package, whereafter the same is degassed and the air present in the powdered substances, or the air "appendant" from these substances is replaced by a different gas, poor in oxygen, for example nitrogen.

In such a method, for example, the powder is transported from a production facility or storage facility to the place where eventual packaging is effected by means of pneumatictransportation, in which air is used as the transporting medium.

At the packaging location, the powder is introduced into the ultimate package, for example consisting of tin, whereafter the package is placed in a vacuum bell. Subsequently, commonly by means of a repeated treatment, the air is evacuated from the bell jar, and then replaced by a gas poor in oxygen.

Thereafter the package is closed.

This method has several disadvantages. In the first place it is complicated, because the degassing process must be effected batchwise. Furthermore, the performance of this method requires a relatively high consumption of energy, because each time the entire quantity of air present in the bell jar and the powder must be removed and replaced by a different gas. Finally, it is very difficult, if not impossible in this method to control the temperature of the replacing gas, because it is difficult to maintain the temperature in the vacuum bell art a different value from the ambient temperature.

It is an object of the present invention to eliminate these disadvantages, and to provide a method, using which the gas atmosphere of packaged powdered or granular substances can be controlled at random, both as regards composition and initial temperature of the gas, and this in combination with a low consumption of energy and gas.

According to the invention, during transportation from a production or storage facilityto a packaging facility, the substances are contacted with a gas poor in oxygen, maintaining such a difference in velocities between the substances and the gas that the substances are transported by said gas, whereafter the substances are packaged in an atmosphere of the same gas.

In carrying out the method according to the invention, use can be made of a pneumatic transport method known per se, in which both subatmospheric pressure (suction method) and superatmospheric pressure (pressure method) can be used.

In one embodiment of the method according to the invention, the powdered or granular substance, for example, milk powder, is introduced into a container or the like provided with a perforated plate. In the case of milk powder this contains approximately its own volume of entrapped air. A gas poor in oxygen or a gas mixture having the desired temperature and composition is blown or sucked into the container. By means of this transport medium, the powdered substance is transported to the packaging facility. In the packaging facility the powder is separated from the gas poor in oxygen, e.g., using a known per se cyclone and/or by means of filtration. Subsequently, the powder is packaged in the atmosphere of this same gas, so that the composition of the gas within the package is equal to that of the gas used as the transporting medium, which is poor in oxygen.The transporting gas is recycled to the container containing the powder, via a filter device.

Hereinafter, the expressions "gas poor in oxygen" and "transporting gas" are used synonymously.

In order that the packaged powdered or granular substance is surrounded with a well-preserving gas atmosphere, the oxygen content in the transporting gas must not exceed a predetermined value. This means that the gas originally present in the powdered or granular substance, or the gas "appendant" from it, in particular air, must be effectively diluted with the transporting gas. Forthis purpose fresh gas poor in oxygen is regularly added to the transporting gas, while transporting gas enriched in oxygen is regularly allowed to escape.

Let it be supposed that, for example, it is desired to package and store a quantity of milk with a starting volume of 2 dm3/kg in a gas atmosphere having an oxygen content of no more than 3%. Using such a transport gas, the transportation of 104 kg/hour powder, in a conventional apparatus, requires approximately 600 m3 gas. 104 Kg powder contains approximately 10 m3 air, which contains 2 m3 oxygen. The 600 m3 gas may contain no more than 3% oxygen, or 18 m3 oxygen. The amount of 600 m3 gas may accordingly be recycled nine times, i.e. per hour, approximately 11% or 66 m3 gas must be replaced. Because the powder continues to retain 10 m3 gas, approximately 56 m3gas must be removed per hour. This means a saving of approximately 10 m3 gas/hour relative to the conventional gassing method.

In the practice of the method according to the invention, an oxygen detection system known per se is provided, for example, in the recycling circuit of the transporting gas. The signal thereof is used for proportionally controlling a valve (if the method is carried out in a system employing superatmospheric pressure), or a displacement pump (if the method according to the invention is carried out using sub-atmospheric pressure), so that gas enriched in oxygen is released. A similar oxygen detection system can be used for controlling the supply of fresh transporting gas poor in oxygen.

Using the method according to the invention, in which the rate of gassing the powder is determined by the difference in velocities between powder and gas, the gassing rate is considerably higher than that obtained in the known method. The optimum of the difference in velocities referred to depends on the particle size of the powder, the ratio of volumes of gas and powder, and on pressure gas velocity. This means that the period needed for gassing depends on the powder used, the type of gas and the transporting velocity.

A suitable velocity of the transporting gas ranges between 1 and 25 m/sec. It has been found that in the case of whole milk powder in a pipe system at a transporting velocity of 10 m/sec. and a transporting gas velocity of 25 m/sec., the powder was surrounded by the ultimately required gas atmosphere after a period as short as 3 sec. A suitable transporting gas is nitrogen, but it is clear that, depending on the purpose contemplated, other gases, for example carbon dioxide, or mixtures of gases may be used.

The method according to the invention has the important advantage that the transporting gas can be brought to any desired temperature. This makes it possible to effect a change in pressure in the ultimate package, caused by the changed temperature of the transporting gas.

The invention will be elucidated with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows an apparatus suitable for use in carrying out the method according to the present invention, both for subatmospheric and superatmospheric pressure; and Figure 2 illustrates the gassing of granulated substances.

Referring to Figure 1, there is shown an apparatus which can be used in carrying out the method according to the present invention, both with superatmospheric and subatmospheric pressure. The powder with "appendant" or entrapped gases, mostly air, falls from a container, or is supplied by way of a vibrating bottom or the like into a so-called dispatch box 1. This dispatch box is a closed box, commonly made of stainless steel, and equipped with a perforated plate which collects the powder.

Via return duct 10 inert gas (poor in oxygen) is blown into the dispatch box 1 at the bottom of the plate. By means of a correct pressure distribution, the powder is fluidized, whereafter transportation (horizontal, vertical or a combination thereof) begins. Via conduit 2, the powder is transported to powder separator 3, where the powder is separated from the transporting gas in a manner known per se, for example, by means of tangential cycloning and filtration. Through opening 9, the powder leaves the powder separator, whereafter it is mixed and/or packaged in an atmosphere of the transporting gas.

The transporting gas is returned by means of suction/compression blower 6, through filter 4 and heat exchanger 7, through return conduit 10 to dispatch box 1. In return conduit 10, an oxygen detection system 5 is provided, whose signal is used to control a system of valves and pumps, by means of which transporting gas enriched in oxygen is removed from the circuit, and fresh transporting gas is supplied to the circuit at 8.

Figure 2 diagrammatically shows the gassing of granulated, granular substances. This embodiment is particularly suitable for the gassing of substances which can be subjected to small mechanical forces only. In this embodiment the transporting force is provided by gravity. When this vertical system is used, granulate velocity is relatively low, while a large difference in velocity is maintained between granulate and transporting gas. Through filling opening 11, the material, for example, coming from container 1 or via a supply conduit not shown, from a silo, reaches a top sieve plate 13 of fluidizer 12. Via a second sieve plate 13 and opening 9 the substance reaches a mixer or packaging machine (not shown).

The gas poor in oxygen is passed through conduit 10, in which heat exchanger 7 and oxygen detection system 5 is provided, to fluidizer 12. Gas enriched in oxygen is removed from the system through valves and/or pumps, not shown, controlled by signals from oxygen detection system 5, and fresh oxygenpoor gas is supplied at 8.

The advantages that can be obtained using the method according to the invention are numerous.

Thus a simple apparatus, requiring minimum attendance can be used, which, in particular if the signal from the oxygen detection device automatically operates a system of valves and pumps, operates substantially automatically and continuously. It is the very fact that the discontinuous gassing plant is no longer necessary, and gassing is effected continuously, by virtue of which a considerable increase in production of packaged powder is possible. A further advantage over and above the prior method is that the product is gassed more fully, i.e., an initially low oxygen content in the package is not increased upon storage. Also, the apparatus suitable for carrying out the method according to the invention requires a relatively low investment, and the apparatus itself occupies little space. Finally, both gas and power consumption are considerably lower than in the known method.

Example I By means of suction transport, using nitrogen as the transporting gas, 10 ton/hour of pressuresprayed whole-milk powder was passed through a stainless steel tube having an internal diameter of 100 mm and a length of 30 m, and subsequently canned in the atmosphere of the transporting gas.

Gas velocity was 21.2 m/sec. and powder velocity 0.7 m/sec. The bulk volume of the powder was 20 m3/ton. The residual oxygen content of the powder in the package was 1%. Per hour, 198 m3 transporting gas enriched in oxygen was released and 198 m3 fresh transporting gas was supplied.

Example Il Example I was repeated, but now 66 m3/hour fresh transporting gas was supplied, and 66 m3/hourwas released. The oxygen content in the packaged powder was now 3%.

Claims (9)

1. A method of bringing air-bearing powdered or granular substances into a gas atmosphere and keeping them therein, wherein during transportation from a production or storage facility to a packaging facility, such substances are contacted with a gas poor in oxygen, maintaining such a difference in velocities between the substances and the gas that the substances are transported by said gas, whereaf teethe substances are packaged in an atmosphere of the same gas.

2. A method as claimed in claim 1,wherein powdered substances are transported to the packaging facility in a pipe system, using a transporting gas poor in oxygen, whereafter packaging is effected in an atmosphere of the same transporting gas.

3. A method as claimed in claim 1 or claim 2, wherein the oxygen content in the gas poor in oxygen is maintained within the range of 0.5 to 5% by volume.

4. A method as claimed in claim 3, wherein the oxygen content in the gas poor in oxygen is controlled by releasing gas enriched in oxygen and supplying fresh gas in relation to the quantity of oxygen contained by the powder or granular substances.

5. A method as claimed in any one of claims 1 to 4, wherein nitrogen is used as the gas poor in oxygen.

6. A method as claimed in any one of claims 1 to 5, wherein the velocity of the gas is 1 to 25 m/sec.

7. A method as claimed in any one of claims 1 to 6, wherein the difference in temperature between the transporting gas and the environs is selected in relation to the desired subatmospheric or superatmospheric pressure in the final package.

8. A method as claimed in claim 1 and substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

9. A method as claimed in claim 1 and substan tiaily as hereinbefore described with reference to Example I or Example II.