WO1989007568A1

WO1989007568A1 - A method in the storage of particulate material

Info

Publication number: WO1989007568A1
Application number: PCT/SE1989/000043
Authority: WO
Inventors: Timothy J. Thexton; Olaf Essmann
Original assignee: AGA AB
Current assignee: Linde Sverige AB
Priority date: 1988-02-17
Filing date: 1989-02-06
Publication date: 1989-08-24
Anticipated expiration: 1990-08-17

Abstract

The disclosure relates to a method, in the storage of a solid material which may be negatively influenced by air and/or its humidity, in the form of particles, powder or granulate in a storage silo, filling being effected from a container in that the material is transported pneumatically with ambient air through a conduit from the container into the upper region of the silo, and emptying is effected in that the material is caused, by its own weight and/or assisted by compressed ambient air, to depart from the silo through an outlet opening in its bottom. The ambient air employed for the pneumatic transport is replaced at least partially by a dry, preferably also inert gas, in particular an oxygen-free gas, for example nitrogen or carbon dioxide.

Description

1989 -0 - 0

TITLE OF INVENTION: A METHOD IN THE STORAGE OF

PARTICULATE MATERIAL

TECHNICAL FIELD

The present invention relates to a method in the storage of a solid material which may be negatively influenced by air and/or its moisture and is in the form of particles, powder, dust or 5 granules in a storage tower, filling being effected from a container in that the material is conveyed pneumatically with ambient air through a conduit from the container into the upper region of the tower, and emptying is effected in that the material is caused, by its own weight and/or assisted by compressed ambient 0 air, to depart from the tower through an outlet opening in its bottom.

In particular, the present invention relates to a method of preventing the negative action of moisture on transport and silage, i.e. storage in a silo, of granulated, pulverulent and/or 5 particulate material, hereinafter generally designated pulverulent material, for example flour, sugar, salt, pulverized ore and carbon powder and - in special cases - for preventing the survival and, especially, the propagation of insects and the like in biological materials, for example, flour, sugar, cocoa and milk 0 powder, while under storage in silo and cells. BACKGROUND ART

As a rule, hygroscopic and other pulverulent materials are conveyed, after production to the consumer, in bulk vehicles (road tankers) and are there conveyed, with the aid of ambient air 5 aspirated by stationary or portable fans, to existent storage towers or silos by the intermediary of a conduit from the container of the vehicle to the upper region of the silo.

SUBSTITUTESHEET Depending upon the prevailing RH in the ambient air, greater or lesser quantities of moisture will be entrained by the compressed air generated by the fans into the pulverulent material. The hygroscopic properties of the individual materials are decisive for the amount of moisture this material will absorb and the amount of moisture which enters therewith into the silo cell.

Many materials, such as for instance flour, show a marked tendency to lump together at a sufficiently high moisture content. Other materials, for example cement, show a capacity to bound the water of the air and form a solidifying mass.

No matter the form of the material on its production, dust will be formed by abrasion which, because of the presence of moisture, will adhere to the walls of the silo and there form a material layer which, with time, grows in thickness. The greatest problem inherent in this material layer is that, after a certain time, it will have become so thick that it must be removed manually, with a considerable labour input.

Such depositions may also occur in conduits and shut-off devices, for example valves. A further critical point is depositions on filters for the air which departs from the silo or tower on filling and which enters into the silo on its emptying. Moreover, there is also the probability that large pieces may come loose from an uneven layer, normally during emptying of the silo cell, and subsequently find their way into a production line.

Such an event may lead to considerable processing and quality problems.

Furthermore, moist material shows a ready propensity to form lumps and thereby material bridges in a silo cell. This lump formation obstructs or impedes complete emptying of the silo cell, in particular if this emptying is effected in a valve or conduit from the silo cell .

Biological pulverulent materials often house larvae and similar vermin, for example moths (Pyralis farinalis) in flour. Once these have gained access to a storage silo, they rapidly

SUBSTITUTE SHΣΞET multiply and often build up so-called nests in the upper region of the storage silo. These nests may often be of large size.

Consequently, it is necessary to implement regular complete emptying of these storage silos, manual cleaning of the silos, destruction of the nests and then extermination of the remaining vermin by gas. Moreover, there is the risk that parts of these nests may come loose and fall down into the pulverulent material and, on withdrawal of material, become entrained in a production line and, hence, into the final products, for example baker products. The facts as outlined above lead to considerable operational disruption, costs and, possibly, also to a failure to meet inspection standards by health authorities. Since prussic acid is commonly used in the extermination process, there are considerable environmental risks and hazards to personnel. OBJECT OF THE PRESENT INVENTION

The object of the present invention is to obviate the problems described in the foregoing in the handling of hygroscopic and/or biological pulverulent material.

This object will be attained according to the present invention by way of the method disclosed by way of introduction which is characterized in that the ambient air employed for the pneumatic transport is wholly or partly replaced by a dry gas, in particular a dry, inert gas.

Preferred dry inert gases according to the invention are carbon dioxide and nitrogen. The carbon dioxide may be liquid carbon dioxide which is gasified before being employed for the contemplated purpose. A suitable source of nitrogen is liquid nitrogen which is vapourized before being employed to convey a pulverulent material from, for instance, a road tanker to a storage silo.

In certain cases, ambient air may be employed, in which a dry gas has been admixed for lowering the RH of the gas. The quantity of admixed dry gas which is required depends greatly upon the material which is to be transported and stored. Preferably, use is made exclusively of the dry gas instead of ambient air.

SUBSTITUTE SHEET In the employment of nitrogen and, in particular, carbon dioxide, it is advantageous to collect the gas which is forced out in the silo when the pulverulent material is supplied pneumatically. This gas is supplied to the fan or other means of compression which compresses the gas to such pressure that it may be used for the pneumatic transport. In such a manner, the dry gas will be reused and this will keep consumption at the lowest possible level .

In particular for extremely hygroscopic pulverulent materials and other materials which show a ready tendency to lump together and, possibly, to harden into continuous layers, it is necessary to maintain a dry atmosphere over the material.

This also applies to biological material, in which event the gas must also be oxygen-free, i.e. neither contain nor emit oxygen. This will prevent any possibly present vermin from multiplying or surviving any length of time. In the employment of nitrogen, it is, granted, possible to prevent present vermin from multiplying, but this will nevertheless be able to survive at least for a brief period if it subsequently comes into contact with a life-supporting gas, especially oxygen.

The present invention will be described in greater detail hereinbelow by means of one Example which is not limitative of the scope of the present invention, and with reference to the Drawing figure which schematically illustrates a storage silo and a portable container from which flour for intermediate storage is transferred, with the aid of a dry inert gas, to the storage silo. EXAMPLE

Referring to the Drawing, a storage silo 1 of, for example, substantially cylindrical configuration and with a conical bottom 7 tapering to a point is intended to constitute a buffer store for flour. In the tip of the conical bottom, there is provided an outlet opening for the flour, i.e. the pulverulent material, to which opening a conduit 2 provided with a valve 3 is connected. The conduit 2 is intended for transport of the material to its point of consumption.

SUBSTITUTE SHEET An intake opening 8 is provided in the upper region of the storage silo 1 for the supply of the flour. A conduit 9 with a valve 10 is connected to this opening 8. Furthermore, there is an opening 4 in the upper region of the tower 1 in which a filter (not shown) is disposed. A conduit 5 with a valve 6 is connected to the opening 4. The Figure further shows a container 11 which may be disposed on a truck or railway wagon. The container 11 has a downwardly tapering bottom 12 in whose centre or tip an outlet opening 13 is provided. A conduit 14 with a valve 15 is connected in the opening 13. A conduit 16 connectable to the conduits 9 and 14 places the container 11 in communication with the silo 1. In the upper region of the container 11, there is provided an intake opening 17 through which pulverulent material is introduced into the container 11 and gas is aspirated for the pneumatic emptying of the container 11. A conduit 18 is connected to the opening 17, the conduit 17 being provided with a valve. A conduit 21 connected with a stationary or mobile fan 20 is removably connected to the conduit 18.

In the filling of the silo 1 from the container 11 and subsequent emptying of the silo 1 according to state-of-the-art methods, the take-off conduit 14 of the container 11 is connected to the intake conduit 9 of the silo 1 by the conduit 16 and the fan 20 is connected by the intermediary of the conduit 21 to the container 11. Thereafter, the valve 15 and the valve 19 are opened, as well as the valve 10 and the valve 6 if these are not already in their opened positions. The fan 20 is then started which, in its upstream end, aspirates air and compresses it so much that it transports the pulverulent material, i.e. in the present case flour, from the container 11 to the silo 1. The filter in the opening 4 of the storage silo 1 prevents the particulate material from departing from the silo 1, for which reason only the gas entering into the silo 1 with the material may depart hence. After filling of the silo 1, the valve 10 is closed.

Filling of the storage silo 1 is thereby completed.

SUBSTITUTE SHEET In the later emptying of, or withdrawal of material from the silo 1, the valve 3 is opened, on which occurrence the material may depart, by its own weight, from the silo 1 and the removed material is replaced by a corresponding volume of air which is sucked into the silo by the partial vacuum thus forming through the filter in the opening 4, the valve 6 being, naturally, opened. In that case when material cannot depart from the silo solely by its own weight, a fan is connected to the conduit 9 which forces the material through the conduit 2. In this latter case, the valve 6 is closed.

According to the present invention, it is the intention to prevent moisture, i.e. water, and in certain cases oxygen, from coming into contact with the material. In the present case, when the material is flour, neither moisture nor oxygen should come into contact with this material, since moisture would entail that flour lumps together and oxygen would entail that any possibly present flour beetle larvae or other vermin may multiply.

According to a first embodiment of the method according to the present invention, a conduit 22 is connected to the conduit 21 on the upstream side of the fan 20. The conduit 22 is connected to a vapourizer 24 in series with a tank 25 for liquid nitrogen. In the same way as described in the foregoing, flour is now transferred from the container 11 to the silo 1. But instead of air from the ambient atmosphere, which has a more or less high RH, the fan 20 aspirates absolutely dry nitrogen gas, which is compressed and transfers flour to the storage silo 1. The nitrogen gas which enters into the silo 1 departs thence through the opening 4 by the intermediary of the filter (not shown) and the conduit 5, and is dissipated into the ambient atmosphere. By such means, it will be ensured that there is excess pressure in the silo 1. After completed filling, the valve 6 and valve 10 are closed, so that excess pressure is maintained in the storage s lo 1.

There are now two possibilities available on emptying of the silo 1 or withdrawal of material from the silo. The silo may be

SUBSTITUTESHEET emptied with or without the aid of a fan, for example the fan 20, which is connected to the conduit 9. In this event, the fan is supplied with dry, inert gas from the vapourizer 24 which is connected to the tank 25. In the former case, the product of the gas volume over the material in the silo and its pressure must be at least equal to the product of the volume of the silo 1 and the ambient pressure. In the latter case dry nitrogen is supplied, which replaces the volume of the material withdrawn.

By establishing a dry, oxygen-free atmosphere in the silo 1 above the material, no vermin can multiply, even if it may possibly survive.

According a particularly preferred embodiment, the conduit 5 is connected to the conduit 22 by the intermediary of a conduit 23. In this instance, the conduit 22 is connected at its ends to the conduit 21 with the fan 20 and the vapourizer 24, respectively. By such means, the dry gas entering into the storage silo 1 and departing through the filter in the opening 4 and conduit 5 will be recycled to the fan 20. The advantage inherent in this recycling of gas from the silo 1 is that the consumption of gas from the tank 25 will be reduced, with the result that the costs of the dry, inert gas will be considerably lower.

According to yet a further embodiment of the method according to the present invention, a conduit (not shown), preferably provided with a valve, is connected to the conduit 22. The conduit 22 is connected, at its ends, to the conduit 21 with the fan 20 and the vapourizer 24, and the conduit 5 from the silo 1 discharges into the ambient atmosphere. In such instance, the ambient air, as well as nitrogen from the tank 25, will be aspirated by the fan 20. The quantity of air which is permitted to enter into the fan is governed by means of the valve in the conduit (not shown). Hence, a portion of the ambient air is replaced by a dry, inert gas. The gas which, in this case, enters into the silo 1 is normally led out into the atmosphere. Naturally, it is also possible to combine this embodiment with the particularly preferred employment of the circulation of nitrogen.

SUBSTITUTE SHEET The tank 25 with liquid nitrogen and the vapourizer 24 may be replaced by another source of gaseous nitrogen.

The present invention should not be considered as restricted to the employment of nitrogen or carbon dioxide. Nor is it necessary, in certain cases, to employ an oxygen-free gas. For certain physical applications, in which oxygen-free gas is not necessary, dry air may, for example, also be used. The advantage inherent in the employment of liquid nitrogen or liquid carbon dioxide which is vapourized is, int. al. that an absolutely dry gas may reliably be obtained.

SUBSTITUTESHEET

Claims

WHAT WE CLAIM AND DESIRE TO SECURE BY LETTERS PATENT IS:

1. A method in the storage of a solid material which may be negatively influenced by air and/or its moisture, and is in the form of particles, powder, dust or granulate in a storage silo, in which filling is effected from a container in that the material is transported pneumatically with ambient air through a conduit from the container into the upper region of the silo, and emptying is effected in that the material is caused, by its own weight and/or assisted by compressed ambient air, to depart from the tower through a withdrawal opening in the bottom thereof, characterized in that the ambient air employed for the pneumatic transport is at least partially replaced by a dry gas.

2. The method as claimed in Claim 1, characterized in that the ambient air supplied for emptying of the silo is at least partially replaced by a dry gas.

3. The method as claimed in Claim 1, characterized in that on emptying of the silo, in particular on emptying of the silo with the sole assistance of the natural weight of the material, the withdrawn material is replaced by a thereto corresponding volume of dry gas at atmospheric pressure or slightly higher pressure.

4. The method as claimed in Claim 1 or 2, characterized in that the gas is an inert gas.

5. The method as claimed in any one or more of Claims 1-3, characterized in that the dry gas is carbon dioxide, preferably vapourized liquid carbon dioxide.

6. The method as claimed in any one or more of Claims 1-3, characterized in that the dry gas is nitrogen, preferably vapourized liquid nitrogen.

7. The method as claimed in any one or more of Claims 1-5, characterized in that the employed dry gas wholly replaces the employed ambient air.

8. The method as claimed in any one or more of Claims 1-6, characterized in that a minor excess pressure of the dry gas is established over the material in the silo.

SUBSTITUTE SHEET

9. The method as claimed in any one or more of Claims 1-8, characterized in that the gas forcibly expended on filling of the silo with the material is employed for the pneumatic transport of the material from the container to the silo.

SUBSTITUTE SHEET