Background Art For handling, such as discharging, of bulk goods, and above all pulverulent bulk goods, a device comprising an intermediate storage container is frequently used. The bulk goods are fed into the intermediate storage con- tainer during a filling phase by means of a suitable de- vice, such as a feeding hopper, a screw, belt or chain unit or a pneumatic unit for drawing in the bulk goods into the container. During a subsequent emptying phase, the container is pressurised. All connections to the con- tainer are closed, after which gas is introduced into the container. When a requisite pressure above atmospheric has been obtained in the container, an outlet valve is opened, whereby the bulk goods are pressed out of the container via the outlet valve to a conveyor pipe for further transport to, for example, a storage silo. Gas is continuously introduced into the container for maintain- ing a requisite pressure above atmospheric in the same.

When the intermediate storage container is being pressurised during the emptying phase, the bulk goods in

the container are compressed. As a result, the viscosity of the bulk goods increases, which makes the discharge of the bulk goods via the outlet difficult. For this reason, a number of nozzles are normally arranged in connection with the outlet, through which nozzles gas is introduced into the container. The container can be designed in such manner that all the gas, or only part thereof, which is introduced into the container for pressurising the same, is introduced via the nozzles. The gas introduced into the container via the nozzles counteracts the compression caused by the pressure above atmospheric by the viscosity of the bulk goods being lowered. Consequently, the dis- charge of the bulk goods from the container is facili- tated.

When the container is empty, the outlet valve is closed and the container is prepared for a new filling phase. In many cases, devices of the type described above comprise at least two such containers, which operate al- ternately, i. e. one is being filled as the other is being emptied and vice versa.

Devices of the type described above, however, suffer from a number of drawbacks.

It has been found difficult to fully counteract the compression of the bulk goods caused by the pressure above atmospheric. In consequence, the emptying phase takes a long time, which reduces the capacity of the device.

When changing between said filling phase and said emptying phase, a stop period arises during which the container is pressurised. During this stop period, nei- ther emptying nor filling of the container occurs. As a result, the total capacity is of course lowered, with which the device can handle a load of bulk goods.

With a view to minimising this stop period, the con- tainer should be pressurised as quickly as possible. This requires that a fairly large gas flow be introduced into the container through the nozzles to counteract said com-

pression of the bulk goods. The high gas flow, however, means that the gas speed through the nozzles becomes high, which in itself causes compression of the bulk goods. Owing to the compression of the bulk goods, the subsequent emptying phase will take a longer time. Conse- quently, a shortened pressurising phase results in an ex- tended emptying phase.

The above problems have to some extent been solved by means of a discharging device according to DE 38110191.

This discharging device differs from the type described above in that it comprises a breaking-up bottom in the area of the discharge means of the respective containers.

The bulk goods located straight above the breaking-up bottom are fluidised through the same, thereby preventing compression in connection with pressurising. Further, in each container nozzles are arranged, which act to break up the non-fluidised bulk goods, so that they fall into the fluidised area. The device also comprises pressure control devices, which sense the pressure in each container and, in response to measuring of predetermined pressures, send signals to actuators for opening of outlet valves.

This discharging device is well suited for dis- charging a load of a bulk vehicle to, for example, a silo. However, the device is not suited for continuous discharging of a shipload where a quick change between filling phase and emptying phase, as well as quick emptying, is required. The reason for this is that quick pressurisation of a container inevitably causes compres- sion of the non-fluidised bulk goods, and that the device operates against predetermined pressure levels for ini- tiating emptying, which pressure levels necessarily are not optimal.

There is thus a need for a device of the type described above, the container of which allows a quick change between filling phase and emptying phase as well as quick emptying of bulk goods positioned therein.

Summary of the Invention In view of that stated above, an object of the present invention is to provide an improved device for handling bulk goods.

A specific object is to provide a device comprising a container which allows a quick change between filling phase and emptying phase as well as quick emptying of bulk goods positioned therein.

Another specific object is to provide a method which allows a quicker change between filling and emptying as well as quicker emptying of bulk goods from a container of a device of the type described above.

Additional objects of the present invention will be evident from the following description and the appended claims.

According to the present invention, the objects are achieved by a device for handling bulk goods, having the features stated in claim 1, a container for bulk goods having the features stated in claim 9, and a method for handling bulk goods having the features stated in claim 11. Preferred embodiments of the inventive device are evident from claims 2-8. A preferred embodiment of the inventive container is defined in claim 11, and a prefer- red embodiment of the inventive method is defined in claim 12.

More specifically, according to the present inven- tion a device is provided for handling bulk goods, com- prising a container with an inlet means and an outlet means arranged in a bottom region thereof, said container defining a volume communicating with said inlet means and outlet means, and a gas unit for introducing gas into the volume for applying a pressure above atmospheric, which prevails therein and which acts to discharge bulk goods in the volume via the outlet means, a bottom surface being arranged at said bottom region of the container, said bottom surface having a gas-permeable portion, and the gas unit acting, in connection with application of a

pressure above atmospheric in the volume, to introduce at least part of the gas into the volume via said portion in order to counteract compression, caused by the pressure above atmospheric, of bulk goods in the volume, said device being characterised in that said gas-permeable portion covers essentially the entire bottom surface, and that the outlet means comprises a non-return valve which is movable between an open and a closed position, the non-return valve being arranged to take its open position if the pressure prevailing in the volume exceeds the pressure prevailing in a discharge conduit connected to the outlet means.

This results in a device which allows a quick change between the filling phase and the emptying phase as well as quick emptying of bulk goods from the volume during the actual emptying phase. This is achieved by means of the gas-permeable portion of the bottom surface, through which portion a large gas flow can be introduced into the volume at a very low speed. The low speed is due to the fact that the gas-permeable portion provides a large surface through which the gas can be introduced into the volume. The low gas speed efficiently counteracts com- pression and ensures good fluidisation, i. e. provision of a sufficiently low viscosity of the bulk goods, of the bulk goods in the volume. This enables emptying of the volume as soon as the gas starts to be introduced into the volume, which results in a quick change between the filling phase and the emptying phase. Moreover, the good fluidisation also enables quick emptying of bulk goods from the volume.

Further the gas-permeable portion covers essentially the entire bottom surface. This results in a large sur- face through which the gas can be introduced into the volume, which of course results in the gas speed being advantageously low, thereby allowing introduction of a large gas flow without any risk of compression of the bulk goods in the volume. Moreover fluidisation of all

the bulk goods in the container is allowed, which accel- erates the subsequent emptying.

The non-return valve, which is arranged to take its open position if the pressure prevailing in the volume exceeds the pressure prevailing in a discharge conduit connected to the outlet means, ensures that the emptying phase in connection with pressurisation of the volume is always initiated in the most optimal pressure condition, which enables a maximum emptying capacity.

According to a preferred embodiment, the inventive device further comprises a first pressure transducer for measuring the pressure prevailing in the volume, a second pressure transducer for measuring the pressure prevailing in the discharge conduit, downstream of the non-return valve, and a valve means, which, if the pressure indi- cated by the first pressure transducer is equal to the pressure indicated by the second pressure transducer, is adapted to interrupt the supply of gas to the volume and to introduce gas into the discharge conduit in a position downstream of the non-return valve. This results in a de- vice which allows a quick change between emptying phase and filling phase. When the measured pressures are equal, this is an indication that the container is empty, or in any case essentially empty. The supply of gas to the con- tainer is interrupted while gas starts to be supplied to the discharge conduit. This, in turn, results in the non- return valve closing since the pressure in the discharge conduit will exceed the pressure in the container. After that the container can be prepared for filling.

To ensure good emptying of the volume, the bottom surface is advantageously angled to guide bulk goods in the volume towards the outlet means in connection with discharge of the bulk goods from the volume. The volume is suitably cylindrical and the bottom surface suitably has the form of a truncated cone, where the narrow end faces away from the volume, to which narrow end the out- let means is connected. The angle of the bottom surface

relative to a plane which is perpendicular to a longitu- dinal axis of the container is preferably in the range 6°-70° and most preferably in the range 30°-55°. If the angle is in the latter range, experiments have demon- strated that an optimal emptying capacity is obtained in the inventive device.

According to a preferred embodiment of the device, the gas-permeable portion is formed of one or more plates made of sintered plastic beads.

The gas-permeable portion is advantageously made of a material which is dimensionally stable when subjected to load. This ensures, on every occasion, sufficient guiding of the bulk goods towards the outlet means.

Moreover, according the present invention, a con- tainer for bulk goods is provided, which internally de- fines a volume, comprising an inlet means communicating with said volume and intended for bulk goods, an outlet means which also communicates with said volume and is arranged in a bottom region of the container and which is intended for bulk goods, a gas inlet means, via which gas is introducible into the volume for applying a pressure above atmospheric therein, and a bottom surface arranged in said bottom region and having a gas-permeable portion which forms part of said gas inlet means and via which at least part of the gas is introducible into the volume, said container being characterised in that said gas- permeable portion covers essentially the entire bottom surface, and that the outlet means comprises a non-return valve which is movable between an open and a closed posi- tion, the non-return valve being arranged to take its open position if the pressure prevailing in the volume exceeds a pressure prevailing in a discharge conduit which is connectable to the outlet means.

Finally, according to the present invention a method is provided for discharging bulk goods from a volume de- fined by a container, via an outlet means arranged in a bottom region of the container, comprising the step of

introducing gas into the volume for applying a pressure above atmospheric therein, whereby the bulk goods are discharged from the volume via the outlet means, said method being characterised by the steps of introducing at least part of the gas into the volume via a bottom sur- face, covered by a gas-permeable portion and arranged in said bottom region, of the container, in order to coun- teract compression, caused by the pressure above atmos- pheric, of bulk goods in the volume, and discharging the bulk goods via a non-return valve arranged in the outlet means by opening the non-return valve, which is arranged for opening if the pressure in the volume is higher than or equal to the pressure prevailing in a discharge con- duit connected to the outlet means.

According to a preferred embodiment of the method, the pressure prevailing in the volume and the pressure prevailing in the discharge conduit in a position down- stream of the non-return valve are measured and, if the pressures are equal, the supply of gas to the volume is interrupted and gas is introduced into the discharge con- duit in a position downstream of the non-return valve.

The fact that the pressures are equal means in fact that the volume is emptied, and by interrupting the supply of gas to the volume and introducing gas into the discharge conduit in a position downstream of the non-return valve, the pressure prevailing in the discharge conduit becomes higher than the pressure prevailing in the volume, which makes the non-return valve take its closed position. Sub- sequently the pressure above atmospheric prevailing in the volume can be evacuated, after which the filling phase can be initiated.

The invention will now be described by way of example with reference to the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a schematic, partly sectional side view of a device according to the present invention.

Fig. 2 is a partly sectional perspective view of a container of the device in Fig. 1.

Fig. 3 is a schematic illustration of an inventive device, whose outlet means comprises a non-return valve.

Description of Embodiments A device for handling bulk goods according to a pre- ferred embodiment of the present invention is illustrated in Figs 1 and 2, to which reference is made.

The device comprises a container 1 and a gas unit 2 schematically shown in Fig. 1.

The container 1 is formed as a cylindrical vessel closed at both ends. An inlet means 3 for bulk goods is arranged in a top region 4 of the container 1 and an out- let means 5 for bulk goods is in the radial direction centrally arranged in a bottom region 6 of the container 1. In said bottom region, also a gas inlet means 13 is arranged. The outlet means further comprises a non-return valve 15, which will be described below with reference to Fig. 3.

The gas inlet means 13 comprises a bottom surface 7 arranged in the container 1 at said bottom region 6. The bottom surface 7 has a gas-permeable portion 8, which allows gas to pass but which prevents particles, i. e. the bulk goods, from passing through. In the shown embodi- ment, the portion 8 is formed of a plurality of plates 9, which together form a structure which essentially has the form of a truncated cone, where the wide end faces away from the outlet means 5 and connects to the cylindrical inner wall 10 of the container 1 and where the end facing the outlet means 5 connects to the outlet means 5. The plates 9 are made of a gas-permeable material, such as a porous, relatively hard sheet, which is made of sintered plastic beads. The bottom surface 7 internally divides the container 1 into a first Vl and a second V2 defined

volume. The gas-permeable plates 9 cover essentially the entire bottom surface 7. The bottom surface 7 is arranged so as to be inclined relative to a plane which is perpen- dicular to a longitudinal axis 11 of the container 1.

Each plate 8 can be inclined at an angle (p relative to said longitudinal axis 11 which is in the range 6°-70°.

Preferably the angle (p is in the range 30°-55°.

A gas pipe 12 extends from the schematically illustrated gas unit 2 to the second volume V2, which is comprised by the gas inlet means 13. The gas unit 2 comprises a compressor and is adapted to introduce com- pressed gas into the second volume V2.

In connection with filling of the container 1, bulk goods are supplied to the first volume Vl of the con- tainer 1 through the inlet means 3. The bottom surface 7 is dimensioned so that it carries the bulk goods supplied to the first volume Vl and maintains its shape. It is also important for the bottom surface 7 not to have any apertures through which the bulk goods can pass to the second volume V2.

The filling of the first volume V1 can be carried out in one of several different ways. The bulk goods can, for example, be conveyed to the inlet means 3 by means of a belt conveyor or by means of a screw. It is also pos- sible to arrange a feeding hopper above the container 1, from which the bulk goods are fed to the first volume V1 under the action of gravity. In the shown embodiment, an outlet means 14 for gas is arranged in the top region 4 of the container 1. By evacuating gas from the con- tainer 1 through said outlet means 14, a sub-atmospheric pressure can be generated in the container 1, whereby suction arises in a suction conduit (not shown) connected to the inlet means 3. This makes it possible to draw in the bulk goods to the first volume V1 through said suc- tion conduit.

In connection with emptying of the bulk goods in the first volume V1, the gas unit 2 is activated for intro-

ducing compressed gas into the second volume V2 of the container 1 via the gas pipe 12. The gas supplied to the second volume V2 will penetrate through the gas-permeable plates 9 of the bottom surface 7 and be introduced into the first volume V1. The pressure will now increase in the entire container 1, whereby the bulk goods are pressed out through the outlet means 5. The generated pressure above atmospheric will act to compress the bulk goods in the first volume V1, thereby increasing the viscosity thereof, which renders the emptying of the bulk goods difficult. This compression is counteracted by the gas which is introduced into the first volume V1 via the bottom surface 7, which gas acts to fluidise the bulk goods. This ensures satisfactory emptying of the bulk goods from the first volume Vl.

To accelerate the change between filling phase and emptying phase, it is desirable to build up, as quickly as possible, a requisite pressure above atmospheric in the first volume V1. This is carried out by introduction of a large gas flow into the volume V1. In conventional containers for bulk goods, introduction of a large gas flow causes the bulk goods in the container to be com- pressed, which makes the subsequent emptying phase diffi- cult. In the inventive container 1, however, compression of the bulk goods caused by a high gas speed is prevented in spite of introduction of a large gas flow. Owing to the fact that the gas is introduced into the first volume Vl via the gas-permeable portion 8, i. e. the plates 9, of the bottom surface 7, introduction of a large gas flow into said volume V1 is in fact allowed, while the speed of the gas flow is low. The reason for this is that the gas-permeable plates 9 provide a relatively large flow area for the gas flow, which means that the speed of the gas flow can be kept at an advantageously low level.

Practical experiments have shown that the emptying phase can be begun as soon as the gas penetrates into the first volume Vl. The reason for this is that the gas

introduced into the first volume VI causes an extremely good fluidisation of the bulk goods in the first volume Vl. It is thus not necessary to delay the beginning of the emptying phase until a requisite pressure above atmospheric has been built up in the container 1. As a result, the change between filling phase and emptying phase occurs very quickly, which of course improves the capacity of the device.

For satisfactory emptying of conventional containers for handling bulk goods, it is necessary that they have a bottom which is inclined towards an outlet means at an angle which is normally in the range 55°-60°. The reason for this relatively great inclination is that the angle of repose of the bulk goods must be overcome. Thanks to the efficient fluidisation of the bulk goods in the container 1 of the inventive device, the inclination of the bottom surface 7 can have such a small angle (p as about 6° while still ensuring satisfactory emptying of the first volume V1. This means that the container 1 with its height retained can define a considerably larger volume than the corresponding volume of conventional containers, which is advantageous from the viewpoint of capacity.

It will be appreciated that it is also possible to design the bottom surface 7 of the container 1 so as to be parallel with the plane perpendicular to the longi- tudinal axis 11 of the container 1. In this case, how- ever, complete emptying of the bulk goods in the first volume V1 is not guaranteed.

However, the bottom surface 7 is advantageously inclined at an angle (p which is in the range 30°-55°.

Experiments that have been carried out in fact demon- strate that the emptying occurs considerably quicker if the bottom surface is inclined at an angle (p in this range. Consequently, an optimal emptying capacity is obtained in this range of angle. Compared with a con- ventional container it is possible to increase the

emptying capacity of the inventive container by 200-300% if the bottom surface 7 is inclined at an angle ç in the range 30°-55°.

The inventive device consequently allows a very quick change between filling phase and emptying phase.

Furthermore also the emptying of the bulk goods from the container 1 can be carried out quickly. More spe- cifically, this is achieved by means of a bottom surface 7 which is arranged in the container 1 and which has a gas-permeable portion 8, for instance in the form of plates 9, which covers the entire bottom surface 7 and via which gas is conducted to a first volume Vl of the container 1 while applying a pressure above atmospheric in the container 1. Bulk goods in said volume V1 will then be fluidised, thereby counteracting compression thereof caused by the pressure above atmospheric. Thanks to the inclination of the bottom surface 7 to the outlet means 5, the bulk goods are quickly discharged from the first volume Vl. The discharge can be initiated imme- diately in connection with the fluidisation of the bulk goods, which means that the change between filling phase and emptying phase can occur quickly. Furthermore, experiments have shown that the emptying, if the bottom surface 7 is inclined at an angle (p in the range 30°-55°, is extremely quick. In this case it has been found that the quickness is independent of the degree of filling of the volume V1 and of the pressure above atmospheric prevailing in the container 1. On the other hand, it is assumed that the coefficient of friction of the bottom surface 7 has an effect on said quickness, and therefore as low a coefficient of friction as possible is strived for.

The inventive device thus has an improved emptying capacity compared with conventional devices for handling of bulk goods. This makes it possible to provide, by means of a reduced effect of the compressor of the gas unit, an emptying capacity which is similar to that of

conventional devices with considerably larger compres- sors.

As mentioned above, it is possible to initiate the emptying phase even in connection with the pressurisation of the container 1. However, it is not always advanta- geous to initiate the emptying immediately in connection with the pressurisation of the container 1. This may be due to the fact that the pressure prevailing in a dis- charge conduit 16 connected to the container 1 does not allow such immediate emptying. This is conventionally solved by letting a predetermined pressure above atmos- pheric be built up in the container before the emptying is initiated. It goes without saying that this makes the time of changing unfavourably long. This problem has been solved according to the invention by means of the non- return valve 15 shown in Fig. 3.

The outlet means 5 of the container 1 for the bulk goods thus comprises the non-return valve 15 connected to the discharge conduit 16. Moreover, advantageously a first pressure transducer 17 is arranged to measure the pressure prevailing in the container 1 and a second pres- sure transducer 18 is arranged downstream of the non- return valve 15 to measure the pressure prevailing in the discharge conduit 16. Finally, a valve means 19 is advan- tageously arranged in the gas pipe 12, which extends between the compressor of the gas unit 2 and the second volume V2 of the container 1. This valve 19 allows guiding of the gas flow supplied from the compressor to the second volume V2 of the container 1 and/or to the discharge conduit 16 in a position of the same downstream of the non-return valve 15 via a pipe 21.

To empty a filled container 1, the compressor is activated for pressurising the container 1. When the pressure in the container 1 slightly exceeds the pressure prevailing in the discharge conduit 16, the non-return valve 15 will take its open position, thereby enabling discharge of the bulk goods in the container 1. When the

emptying phase is completed, i. e. when the container 1 is empty, or in any case essentially empty, of bulk goods, the two pressure transducers 17,18 will indicate the same pressure. Now the valve means 19 is operated so that all gas is supplied to the discharge conduit 16, which makes the non-return valve 15 take its closed position since the pressure prevailing downstream of the non- return valve 15 will exceed the pressure prevailing upstream of the non-return valve 15. After that, a ventilation valve 20, which is shown in more detail in Fig. 2, can be opened to evacuate the pressure above atmospheric in the container 1. Subsequently the con- tainer can be once more filled with bulk goods.

As the bulk goods are being discharged from the discharge conduit 16, the pressure in the same will fall.

It is ensured, however, that the filling phase proceeds quicker than the time it takes to empty the conduit 16, which is also usually the case since the discharge con- duit normally has a considerable extent, in the normal case 200-300 m. Thanks to the filling phase being quicker than the time it takes to empty the discharge conduit, a pressure above atmospheric is ensured in the discharge conduit 16 after completion of the filling phase, whereby it is ensured that the non-return valve 15 remains closed during the entire filling phase. Subsequently the con- tainer 1 is pressurised, and the non-return valve 15 again takes its open position when the pressure pre- vailing in the container 1 slightly exceeds the pressure prevailing in the discharge conduit 16. Thus it is en- sured that the non-return valve 15 of the outlet means 5 always opens in the most optimal pressure condition, whereby an optimal emptying capacity of the inventive device is achieved.

It will be appreciated that the present invention is not limited to the shown embodiments. Several modifica- tions and variations are feasible and the invention is thus defined exclusively by the appended claims.