NZ299472A - Pre-gassing powder method and apparatus for replacing oxygen present in perishable powders with an inert gas comprises a pre-gassing vessel with powder inlet, replacement gas inlet and gas outlet - Google Patents

Description

1 ' Patents Form # 5 099472 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION AFTER PROVISIONAL#: 299472 DATED : 27 September 1996 TITLE : Continuous Pre-gassing Method and Apparatus We, Equipment Technology Limited Address: 9 Newton Place, Hamilton, New Zealand Nationality: New Zealand 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: , . „ Intellectual Property . 1. Office of NZ 11 DEC 1997 PF05.JWP FEE CODE 1050 Received ( I t 1 29 9 472 CONTINUOUS PRE-GASSING METHOD AND APPARATUS This invention relates to a method and apparatus for pre-gassing perishable powders with an inert gas.

By replacing oxygen in a powder mass with an inert gas such as nitrogen, the life of 5 perishable powders can be extended. A method of pre-gassing a perishable powder as disclosed in NZ patent No. 235798 involves subjecting a powder in a vessel to a vacuum to remove the air (oxygen) from the powder, and then introducing nitrogen from within the powder to replace the removed air (oxygen). Another known method involves delivering a pre-set amount of powder to a pre-gassing vessel, and then introducing low 10 pressure nitrogen to the bottom of the vessel so that the nitrogen percolates up through the powder until a desired low oxygen level is reached. A powder dump valve at the bottom of the vessel is then opened and the powder removed, after which the sequence is repeated.

With these pre-gassing methods, the process is carried out in batches. This results in 15 intermittent flow of powder through the system which affects flow rates and hence processing output.

It is therefore an object of the present invention to address the foregoing problems, or to at least provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the 20 ensuing description which is given by way of example only.

According to one aspect of the present invention there is provided a method of pre-gassing powder comprising the steps of: introducing powder into a pre-gassing vessel through a powder inlet; introducing a replacement gas such as nitrogen into the pre-gassing vessel though a replacement gas inlet; removing gas from the pre-gassing vessel 25 via a gas outlet; and continuously removing powder from the pre-gassing vessel.

D295vcs.997 # 299472 According to another aspect of the present invention there is provided an apparatus for pre-gassing powder comprising: a pre-gassing vessel having powder introducing means for introducing powder into the pre-gassing vessel; a replacement gas inlet whereby a replacement gas is introduced into the pre-gassing vessel; a gas outlet whereby gas is 5 removed from the pre-gassing vessel; and powder removal means for continuously removing powder from the pre-gassing vessel, With such a method and apparatus, the powder may be removed continuously from the pre-gassing vessel while being subjected to an atmosphere of a replacement gas such as nitrogen to replace the air (oxygen) in the powder. Since the powder is removed 10 continuously from the pre-gassing vessel, problems inherent with batch flow systems such as slow treatment rates and poor flow due to intermittent operation can be avoided.

The powder removal means may comprise any suitable means whereby powder can be removed from the pre-gassing vessel. For example this may comprise a device such as a rotary valve or an auger, whereby the removal rate of powder can be controlled by 15 varying the rotation speed of the rotor.

The replacement gas inlet and the gas outlet may be disposed at any suitable location in the vessel, the main requirement being that the powder is subjected to an environment of replacement gas as it passes through the pre-gassing vessel. Preferably the replacement gas inlet and the gas outlet are disposed such that the powder accumulated in the pre-20 gassing vessel lies therebetween, and the gas is removed from the pre-gassing vessel by creating a pressure differential through the powder between the replacement gas inlet and the gas outlet. This pressure differential may be created by using pressurised replacement gas, and or an extraction fan connected to the gas outlet.

In a preferred configuration the replacement gas inlet is disposed below the gas outlet, for 25 example close to the powder outlet, so that the replacement gas flows through the powder in the opposite direction to the flow of the powder through the pre-gassing vessel.

Alternatively however, the replacement gas inlet may be disposed above the gas outlet so that the replacement gas flows downward though the powder. This arrangement may D295vcs.997 liave an advantage in that a higher flow rate of replacement gas through the powder can be used (compared to when the replacement gas inlet is disposed below the gas outlet), without creating vertical channels through the powder, which can result in poor distribution of nitrogen through the powder.

The apparatus may also comprise oxygen level sensing means for sensing a level of oxygen in the gas being removed from the pre-gassing vessel, and control means for controlling the flow rate of replacement gas into the pre-gassing vessel and or controlling the flow rate of powder removal from the pre-gassing vessel, to maintain a predetermined oxygen level. In this way optimum processing of the powder can be achieved.

The abovementioned powder introducing means for introducing powder into the pre-gassing vessel may involve any suitable apparatus, whereby powder can be supplied to the pre-gassing vessel. This may simply involve a dump valve through which powder is dumped into the pre-gassing vessel from a hopper, at commencement of the pre-gassing operation, and which may also be opened intermittently during the pre-gassing operation 15 to allow powder to fall therethrough under gravity. The powder introducing means may also involve a vacuum transport system incorporating: a vacuum vessel having a powder inlet; a powder feed device connected between the vacuum vessel and the pre-gassing vessel for feeding powder from the vacuum vessel to the pre-gassing vessel, and a vacuum pump connected to the vacuum vessel for creating a vacuum in the vacuum 20 vessel to draw powder into the vacuum vessel via the powder inlet.

The powder feed device may for example involve a positive feed device such as a rotary valve or auger whereby powder can be positively fed into the pre-gassing vessel, irrespective of the pressure therein.

The invention may also broadly be said to consist in the parts, elements and features 25 referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents these are deemed to be incorporated herein as if individually set forth.

D295vcs.997 299472 Further aspects of the present invention will become apparent from the following description given in conjunction with the appended drawings in which: FIG. 1 is a schematic diagram of a pre-gassing apparatus according to one embodiment of the present invention, with replacement gas introduced from within a powder being de-5 gassed, and FIG. 2 is a schematic diagram of a pre-gassing apparatus according to another embodiment of the present invention, with replacement gas introduced from above a powder being de-gassed, and fitted with a vacuum transport system.

As shown in FIG. 1, a powder pre-gassing apparatus according to the present invention 10 generally indicated by arrow 1 comprises a pre-gassing vessel 2 having a powder introducing device in the form of a powder inlet 3 and inlet valve 4 whereby a powder is selectively introduced into the pre-gassing vessel 2, and a nitrogen inlet 5 whereby nitrogen serving as a replacement gas, is introduced into the pre-gassing vessel 2, located towards the bottom of the pre-gassing vessel 2. The pre-gassing vessel 2 is also provided 15 with a gas outlet 6 and filter 7 through which gas is removed from the pre-gassing vessel 2. The gas outlet 6 is located at the top of the pre-gassing vessel 2 above a maximum powder fill level shown by dotted lines. Respective upper and lower level sensors 9 and 10 are provided for detecting upper and lower powder levels. Gas is removed from the pre-gassing vessel 2 by creating a pressure differential through the powder between the 20 nitrogen inlet 5 and the gas outlet 6. This pressure differential is created by using compressed nitrogen stored in a container (not shown) connected to the nitrogen inlet 5 via a pressure regulating valve 11.

The pre-gassing vessel 2 is also provided with a powder outlet 12 fitted with a rotary valve 13 serving as a powder removal means for continuously removing powder from the 25 pre-gassing vessel 2, and a standard oxygen sensor 14. The rotary valve 13 is a standard type rotary valve for use with powder or granular materials, the removal rate of the powder being controlled by varying the rotation speed of the rotor. Instead of the rotary valve 13, an auger device may be used. The powder outlet 12 feeds into a bulk bin 15 D295vcs.997 299472 which incorporates suitable sealing means to keep the powder isolated from the atmosphere.

The pre-gassing vessel 2 is also provided with a vibrator in the form of a conical vibration element 16 which is powered by compressed air introduced via an inlet pipe 17 and a 5 control valve 18. The vibration element 16 is vibrated as desired by supplying compressed air thereto, to facilitate compacting and feeding of the powder.

In operation of the pre-gassing apparatus 1, a pre-set amount of powder is introduced into the pre-gassing vessel 2 via the powder inlet 3 and inlet valve 4. Once the powder has been filled to a predetermined level detected by the level sensor 9, the powder inlet valve 10 4 is closed and the regulating valve 11 opened, thus creating a pressure differential between the nitrogen inlet 5 and the gas outlet 6 causing the nitrogen to flow up through the powder and be discharged through the gas outlet 6 and filter 7. After a predetermined interval (to give a required drop in oxygen content), the rotary valve 13 is started, leaving the regulating valve 11 open. When the powder level falls below the level sensed by the 15 level sensor 10, the powder inlet valve 4 is again opened allowing more powder to flow into the pre-gassing vessel 2 under gravity.

In the above operation, the infeed and outfeed rates are matched by increasing or decreasing the speed of the rotary valve 13 and appropriate operation of the inlet valve 4 to keep a practically constant level of powder in the pre-gassing vessel 2, thus giving a 20 continuous flow situation. Moreover, the replacement gas flow rate is adjusted by the pressure regulator 11 to maintain the desired lew oxygen level at the outlet 12.

The above procedure is preferably carried out by means of a controller (not shown) comprising a microcomputer which takes inputs from the level sensors 9 and 10, and the oxygen sensor 14, and outputs control signals to the respective valves to thereby achieve 25 the above sequence of operations.

A powder supply apparatus for delivering powder to the pre-gassing vessel 2 may involve for example a conveying belt, or a vacuum transport system delivering into a hopper.

D295vcs.997 299472 Feed from the hopper may then be by gravity feed, or by a positive feed device such as rotary valve or auger to the powder inlet 3.

A second embodiment of the present invention will now be described with reference to FIG. 2. The second embodiment of FIG. 2 differs from the first embodiment.of FIG. 1 in 5 that the nitrogen is introduced from above the powder. Moreover details of a possible vacuum transport system (which may also be applicable to the embodiment of FIG. 1) are also shown.

As shown in FIG. 2, a powder pre-gassing apparatus according to the second embodiment generally indicated by arrow 20, comprises a pre-gassing vessel 21 having a powder inlet 10 22, with a powder feed device in the form of an inlet rotary valve 23, whereby a powder is fed to the pre-gassing vessel 21 from a vacuum transport system generally indicated by arrow 40 (to be described hereunder), and a nitrogen inlet 26 whereby nitrogen serving as a replacement gas, is introduced into the vessel 21. The nitrogen inlet 26 is located in the pre-gassing vesse1 21 at a level above a maximum powder fill level shown by a dotted 15 line. Respective upper and lower level sensors 27 and 28 are provided for detecting the upper and lower powder levels. The pre-gassing vessel 21 is also provided with a gas outlet 29 through which gas is discharged from the pre-gassing vessel 21. The gas outlet 29 is located close to the bottom of the pre-gassing vessel 21. A pressure differential is created between the nitrogen inlet 26 and the gas outlet 29 by using compressed nitrogen 20 stored in a container 30 connected to the nitrogen inlet 26 via a pressure regulating valve 31. The gas outlet 29 is fitted with a filter 32, a flow control valve 33, and a standard oxygen sensor 34. The filter 32 is a standard powder filter for removing powder from the outlet gases. The flow control valve 33 may be a standard on/off valve, and may be manually or automatically controlled to regulate the pressure differential between the 25 nitrogen inlet 26 and the gas outlet 29. The pre-gassing vessel 21 is also provided with a powder outlet 35 fitted with a rotary valve 36 for continuous discharge of the powder from the pre-gassing vessel 21.

The vacuum transport system 40 comprises a filter can 41 (vacuum vessel) mounted on top of the pre-gassing vessel 21, with the inlet rotary valve 23 therebetween, a powder D295vcs.997 299472 suction inlet 42 fitted with a valve 43, and a vacuum pump 44 connected to an outlet 45 from the filter can 41 via a vacuum outlet valve 46.

In operation of the pre-gassing apparatus 20, powder is transported from a storage hopper (not shown) into the filter can 41 via the powder suction inlet 42 and the valve 43 using 5 the vacuum transport system 40. This process involves removing the air from the filter can 41 via the vacuum outlet 45 by means of the vacuum pump 44, to create a negative pressure to thereby draw powder into the filter can 41. The inlet rotary valve 23 is then operated to feed powder into the vessel 21. Once the powder has been filled to a predetermined level detected by the level sensor 27, the inlet rotary valve 23 is stopped, 10 and both the regulating valve 31 and the flow control valve 33 are opened, thus creating a pressure differential between the nitrogen inlet 26 and the gas outlet 29 causing the nitrogen to flow down through the powder and be discharged through the gas outlet 29, via the filter 32, the flow control valve 33 and past the oxygen sensor 34. At this time, the pressure differential is adjusted by the regulating valve 31 to a predetermined value 15 which gives an optimum flow rate for removal of the oxygen from the powder.

When the oxygen level detected by the oxygen sensor 34 reaches a desired level, the rotary valve 36 is started, leaving the regulating valve 31 and the outlet valve 33 open. When the powder level falls below the level sensed by the level sensor 28, the inlet rotary valve 23 is again started feeding more powder into the vessel 21.

In the above operation, the infeed and outfeed rates are matched by increasing or decreasing the speed of the rotary valve 36 and appropriate operation of the inlet rotary valve 23 to keep a practically constant level of powder in the pre-gassing vessel 21, thus giving a continuous flow situation. Moreover, the nitrogen flow rate is adjusted by the pressure regulator 31 to maintain the desired oxygen level at the outlet 35 (sensed by the 25 oxygen sensor 34).

With this embodiment also, the above procedure is preferably carried out by means of a controller (not shown) comprising a microcomputer which takes inputs from the level sensors 27 and 28, the oxygen sensor 34, and a pressure sensor 47 for detecting the D295vcs.997 299472 -9 pressure in the vessel 21, and outputs control signals to the respective valves to thereby achieve the above sequence of operations.

Due to the above arrangement wherein the nitrogen flows through the powder from the top, a relatively high flow rate can be used without the problems of channelling inherent 5 with methods wherein nitrogen is introduced from the bottom of the powder.

Moreover by appropriate dimensioning of the pre-gassing vessel 21, and providing suitable flow rates (pressure differential through the powder), a plug flow of the nitrogen down through the powder replacing the air (oxygen), can be achieved, minimising mixing of the nitrogen with the air. With the present embodiment, the vessel cross-sectional area 10 tapers from a circular cross-section of approximately 700mm at the top to a circular cross-section of approximately 300mm at the bottom over a height of approximately 1500mm, giving a maximum inclined wall angle of approximately 20 degrees. Moreover, the pressure differential is limited to a maximum of 30psi, since higher pressures require that the pre-gassing vessel design conforms to pressure vessel codes. However, the invention 15 is not limited to these pressures and dimensions and other suitable shapes and pressures may be used which achieve a desirable effect.

With the above embodiments, the pressure differential across the powder is achieved due to the pressure of the inlet nitrogen. It is also possible however to provide a suction fan on the outlet to achieve the pressure differential. If a fan is provided, then an additional 20 pressure gauge may be required at the outlet to determine the pressure and maintain a pressure differential through the powder.

Moreover the embodiments have been respectively described using a gravity feed system and a vacuum transport system 40 to transport powder to the pre-gassing vessels 2 and 21. However the invention is not limited to these arrangement, and powder may be introduced 25 to the pre-gassing vessel by any suitable means.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the invention as defined in the appended claims.

D295vcs.997

Claims (23)

299472 - 10- What we claim is:

1. A method of pre-gassing powder comprising the steps of: introducing powder into a pre-gassing vessel through a powder inlet; introducing a replacement gas into said pre-gassing vessel through a replacement gas 5 inlet; removing gas from said pre-gassing vessel via a gas outlet; and continuously removing powder from said pre-gassing vessel.

2. A method of pre-gassing powder according to claim 1, wherein said step of continuously removing powder from said pre-gassing vessel, involves powder removal 10 means.

3. A method of pre-gassing powder according to claim 2, wherein said powder removal means comprises a rotary valve.

4. A method of pre-gassing powder according to claim 2, wherein said powder removal means comprises an auger. 15

5. A method of pre-gassing powder according to any one of claims 1 through 4, wherein said replacement gas inlet and said gas outlet are disposed in said pre-gassing vessel such that powder accumulated in said pre-gassing vessel lies therebetween, and said gas is removed from said pre-gassing vessel by creating a pressure differential through said powder between said replacement gas inlet and said gas outlet. 20

6. A method of pre-gassing powder according to any one of claims 1 through 5, wherein said replacement gas inlet is disposed below said gas outlet, so that replacement gas flows through said powder in the opposite direction to the flow of said powder through said pre-gassing vessel.

7. A method of pre-gassing powder according to any one of claims 1 through 5, 25 wherein said replacement gas inlet is disposed above said gas outlet, so that replacement gas flows downward through said powder. D295vcs.997 2.9 9 4 7 ^ 20

8. A method of pre-gassing powder according to any one of claims 1 through 7, further involving the steps of: sensing a level of oxygen in said gas being removed from said vessel, and controlling the flow rate of replacement gas into said vessel and or controlling the flow rate of powder removal from said vessel, to maintain a predetermined oxygen level.

9. A method of pre-gassing powder according to any one of claims 1 through 8, wherein said step of introducing powder involves; removing air from a suction vessel connected to said pre-gassing vessel, via a vacuum outlet to create a negative pressure to thereby draw powder into said suction vessel via a powder inlet; and introducing powder into said pre-gassing vessel using a powder supply device.

10. A continuous pre-gassing apparatus for continuous pre-gassing of powder according to the method of claim 1 comprising: a pre-gassing vessel having powder introducing means for introducing powder into said pre-gassing vessel; a replacement is nlet whereby a replacement gas is introduced into said pre-gassing vessel; a gas outlet whereby gas is removed from said pre-gassing vessel; and powder removal means which enables the continuous removal of power from said pre-gassing vessel while powder therein is being pre-gassed.

11. A continuous pre-gassing apparatus according to claim 10, wherein said powder removal means comprises a rotary valve.

12. A continuous pre-gassing apparatus according to claim 10, wherein said powder removal means comprises an auger.

13. A continuous pre-gassing apparatus according to any one of claims 10 through 12, wherein said replacement gas inlet and said gas outlet are disposed in said pre-gassing INTELLECTUAL PROPERTY OFFICE OF N.Z. D295voal.998 28 SEP 1998 RECEIVED -12- 299472 vessel such that powder accumulated in said pre-gassing vessel lies therebetween, and said gas is removed from said pre-gassing vessel by creating a pressure differential through said powder between said replacement gas inlet and said gas outlet.

14. A continuous pre-gassing apparatus according to claim 13, wherein said pressure 5 differential is created by using pressurised replacement gas.

15. A continuous pre-gassing apparatus according to any one of claims 10 through 14, wherein said replacement gas inlet is disposed below said gas outlet, so that replacement gas flows through said powder in the opposite direction to the flow of said powder through said pre-gassing vessel. 10

16. A continuous pre-gassing apparatus according to any one of claims 10 through 14, wherein said replacement gas inlet is disposed above said gas outlet, so that replacement gas flows downward through said powder.

17. A continuous pre-gassing apparatus according to claim 16, wherein said pre-gassing vessel has a tapered portion with a cross-sectional area reducing from a top 15 portion to a bottom portion.

18. A continuous pre-gassing apparatus according to claim 17, wherein said tapered portion is approximately 1500mm in height.

19. A continuous pre-gassing apparatus according to either one of claims 17 and 18, wherein said tapered portion has a maximum inclined wall angle of approximately 20 20 degrees.

20. A continuous pre-gassing apparatus according to any one of claims 10 through 19, further comprising; oxygen level sensing means for sensing a level of oxygen in said gas being removed from said vessel, and 25 control means for controlling the flow rate of replacement gas into said vessel and or controll'.ig the flow rate of powder removal from said vessel, to maintain a predetermined oxygen level. D295voal.998 -13- ?99A7&

21. A continuous pre-gassing apparatus according to any one of claims 10 through 20, wherein said powder introducing means for introducing powder into said vessel comprises: a vacuum vessel having a powder inlet; 5 a powder feed device connected between said vacuum vessel and said pre-gassing vessel for feeding powder from said vacuum vessel to said pre-gassing vessel, and a vacuum pump connected to said vacuum vessel for creating a vacuum in said vacuum vessel to draw powder into said vacuum vessel via said powder inlet.

22. A method of pre-gassing powder substantially as described herein with reference 10 to the drawings.

23. A continuous pre-gassing apparatus substantially as described herein with reference to the drawings. James W Piper ?., Co Attorneys For: Equipment Technology Limited