EP0613955B1 - Loading device comprising a flow-control member - Google Patents

Description

The present invention relates to a device for loading fitted with a flow adjustment device, for supply an enclosure with a predetermined flow rate of one solid matter.

It relates more particularly to a device for charging to supply an enclosure with a flow predetermined solid material comprising: a hopper with material provided with a funnel-shaped lower part, which defines a central flow axis substantially vertical; a supply pipe to the enclosure, which is located axially below said part lower of the material hopper; and a retainer and adjusting the material flow.

Such devices are used for example on baking ovens, more especially on baking ovens tank which are equipped with a distribution chute oscillating and / or rotary. The hopper then constitutes a loading material vertical lock container and further comprises a lower sealing member, which isolates the hopper from the oven under pressure.

Such a device, which is designed to equip a tank fitted with a rotary distribution chute or oscillating, is known from patent specification EP-62,770. In this document is proposed a retainer and adjustment of the combined material flow, which includes two registers in the form of spherical caps. Movement relative of these two caps allows to vary the section of symmetrical passage around the central flow axis of the material. These registers are arranged in a room waterproof, located directly below the hopper. This sealed chamber is provided at its lower end with the lower sealing member. This includes a valve which can be swiveled between a lateral position, in which it is sheltered from the discharged material hopper, and a closed position, in which it is transverse to the axis of flow of the material. In this shutter position the valve is applicable, for an axial translational movement, on a seat. This seat peripherally surrounds the discharge opening of the hopper and has a sealing surface facing bottom, i.e. in the direction of flow of the matter.

A device of the kind described in the booklet of Patent EP-62,770, knows how to give complete satisfaction of the point characteristic view of flow and point adjustment sealing view, even for an enclosure in which high working pressures prevail. Its only disadvantage is its high mounting height, which results the fact that the combined retaining and adjusting member of the material flow and the sealing member are superimposed below the hopper. In order to remedy, if necessary, to this disadvantage, one could for example think of replace the flow control device located below the hopper, by a flow control member which is directly integrated into the hopper.

From patent specification EP-88 253, there is known a device for loading a shaft furnace, of the type described in the preamble, which is provided with a combined organ of retaining and adjusting the material flow comprising a bell which is integrated in the material hopper. This bell, which has the shape of a cone of revolution flaring in direction of its lower edge, is movable vertically along the axis of the hopper. In position descended, it cooperates with a first seat in the level of the hopper discharge opening to close off this one. In the raised position, it defines an opening annular flow between the funnel-shaped wall hopper and its lower edge. The passage section of this annular opening is a function of the stroke vertical of the bell. However, it is well known that with a bell like that, you can't necessarily have satisfaction with the characteristic of material flow adjustment. To overcome this drawback, the patent specification EP-88 253 proposes to provide the bell, on the side of its lower edge, with a body oblong and pointed which is coaxial with the central axis of the discharge opening and which extends axially across this in the direction of the supply manifold of the chute. The profile of this body should then theoretically to determine the adjustment characteristic, ie the "material flow / vertical stroke" function of the retaining and adjusting member ". The result obtained is disappointing, however.

Patent specification EP-88 253 also provides a lower sealing member which is integrated into the hopper. This includes a shutter disc, which is arranged below the bell and provided with a seal of peripheral sealing on the side of its lower face. When the bell is resting on its seat, the disc can be applied axially on a second seat. This last, which is located below said first seat, has a smaller passage section than this and is provided a sealing surface facing the interior of the hopper. This waterproof member does not, however, satisfaction. Indeed, said second seat, which is exposed to wear by materials flowing through the discharge opening, is rapidly deteriorated and does not can no longer ensure a gas-tight shutter under pressure.

Now, if we want to replace in the loading of the patent specification EP-88 253, the organ lower seal, which is integrated into the hopper, by a pivotable sealing valve, of the type of that known of patent specification EP-62,770, we lose all advantage of point of view mounting height. When the bell is resting on its seat, said oblong body and pointed is necessarily located below the opening from the hopper. Like the sealing valve swivel cannot pass through said oblong body, it is necessary therefore provide, below the material hopper, a sealed chamber in which said oblong body can penetrate its entire length. The sealing valve will be then integrated into the lower end of this chamber waterproof, the height of which is certainly not less at the height of the sealed chamber containing said registers in the form of spherical caps known from the patent specification EP-62,770.

The objective of the present invention is to provide a loading device, of the kind described in the preamble, in which the retaining and adjusting member of the material flow is integrated in the hopper, but which not all the disadvantages mentioned above for the device of patent specification EP-88 253.

This goal is achieved by a loading device for supply an enclosure with a predetermined flow rate of one solid material, comprising a material hopper provided with a funnel-shaped lower part which defines an axis substantially vertical flow central, a tubing supply to the enclosure, which is located axially below of said lower part of the hopper, an organ retaining and adjusting the material flow which encompasses a bell movable in the hopper between a position lower shutter of a discharge opening in said lower part of the hopper and a position upper lift, and a central oblong metering body and significantly more slender than the bell, coaxial with said axis central flow of the material and movable along the latter so as to penetrate more or less through said discharge opening towards the tubing supply, characterized in that the bell and the body dosing units are relatively movable one by relative to each other, so that the vertical distance that separates the two is freely adjustable. It is specified that the term "bell" also encompasses a retaining body which does not necessarily have the shape of a bell.

In the proposed device, the central metering body is no longer a component of the bell, but a independent element, whose position in relation to the discharge opening can be adjusted independently relative to the position of the bell in the hopper matter. This feature allows the bell to be placed a distance from the discharge opening, in which it almost no longer influences the flow rate flowing through this one. This flow can therefore be essentially regulated by moving the central dosing body. It follows that the setting characteristic, i.e. the function Q = f (C), where Q is the flow of material flowing at through the discharge opening and C is the stroke of the body dosing center, may be determined by the choice of longitudinal profile of the oblong and slender body, which fills now with satisfaction its role as the central body of dosage. It is thus for example possible to obtain a linear characteristic Q = k. C, where k is a constant depending on the nature and the grain size of the material loading.

It will be noted that if we wanted to obtain with the device of patent specification EP-88 253 of the results analogs should be given to the central dosing body excessive length. For a hopper whose part in funnel shape has an angle at the top of 80 ° this length will for example be greater than twice the diameter of the discharge opening.

Another advantage of the proposed device lies in the fact that the position of the bell in the hopper can be varied freely upstream of the position in which it almost no longer influences the flow rate flowing through the discharge opening. This possibility of power vary the location of the bell in the hopper, without as much act on the flow, allows to choose for the bell a location in the hopper in which it influences optimally homogeneity of the flow of matter inside the hopper. This will reduce the following solid particle segregation phenomenon their particle size. This well-known phenomenon finds its origin in the fact that the finer particles have tendency to flow through the center of the hopper, while the larger particles rather flow along the walls. By an optimal location of the bell in the material, which is chosen and adjusted according to the nature and the grain size of the loading material, as well as the filling height of the hopper, we know cause a more uniform emptying of the material hopper. Adjusting the location of the bell according to the loading height can for example be done so continues based on a device output signal weighing of the hopper.

In a preferred embodiment the central body of dosage includes a lower trunk, which first flares out of the bottom up and ending in one end upper which tapers towards a rod ordered. The lower trunk acts as an element of setting. The upper end, on the other hand, is designed so as to influence as little as possible the flow of material, i.e. the setting characteristic.

Preferably the bell is provided with a hollow or a cavity in which the central metering body is fully removable, for example when the bell is in its lower position closing the opening of flow. It follows that there is, in position shutter of the discharge opening, no more elements which penetrates through it.

Equipped with a lower sealing member, the device can be installed on an enclosure under pressure, for example a shaft furnace. The hopper is then used from a solid lock container to load into the pressure vessel.

In a first embodiment, such a body lower seal includes a valve which can be swiveled between a lateral position, in which it protected from the material discharged from the hopper, and a closed position, in which it is transverse to the axis of flow of the material and in which it can be applied axially on a seat. The latter surrounds peripherally the hopper discharge opening and has a downward facing sealing surface. It will be noted that this sealing member is not exposed the wear of materials flowing from the opening of discharge from the material hopper. When the central body can be fully removed from the bell, the sealing valve can also be directly mounted downstream of the discharge opening; which allows achieve a significant gain in mounting height by relative to the known device of the patent specification EP-62,770.

It is however also possible to equip the device proposed a lower sealing member comprising: a obturation element arranged directly below the bell and axially movable relative to it, said closure element being provided with a surface lateral device in which a seal is integrated inflatable seal and a central opening of passage for the central metering body; means for move the obturator axially between a protected position below the bell and a position operational outside the bell, when this the latter is in said lower shutter position; and a seat mounted axially below the opening of discharge, said seat being provided with a first surface seal that faces down and surrounds said inflatable seal when the closure element is located in said operational position. This organ lower seal reduces the height of mounting the loading device even more. In effect, it is no longer necessary to provide, between the opening of hopper discharge and supply line the pressure vessel, a chamber containing a valve waterproof. Compared to the known device of the booklet of Patent EP-62,770, this preferential execution of the proposed device allows, beyond the advantages obtained from characteristic setting point of view, to avoid wear seal seat too fast. It is therefore of a preferential execution which is characterized by excellent qualities from the characteristic point of view of adjustment and wear resistance of the sealing member lower, as well as by a minimum mounting height.

In a first variant of execution, the bell is fitted with an upper sleeve which is extended upwards outside the hopper. This sleeve allows to introduce and extract the central metering body through this sleeve and at the same time constitutes an axial guide of the central body dosing. At least one first cylinder located outside of the material hopper is connected between the latter and the muff. This or these first cylinders are sized for provide the necessary effort to raise the bell to through matter. The central dosing body is provided a coaxial rod which is guided axially inside sleeve, and at least one second cylinder is connected axially between the sleeve and this rod. This second cylinder is slaved to the first cylinder (s), so that a stroke (c) of the bell in a first direction simultaneously causes a stroke (c) of the central body of dosing in the opposite direction.

In a second variant, the hopper is provided with a fixed guide sleeve which extends axially from top to bottom inside the material hopper. The bell is provided with an upper sleeve which is can be engaged on this fixed sleeve. The central dosing body is fitted with a coaxial rod which is guided axially to inside the fixed sleeve. At least one first cylinder is connected between the hopper and said upper sleeve, and at minus a second cylinder is connected between the hopper and the rod inside the fixed sleeve.

• la Figure 1 montre schématiquement, dans une coupe verticale, un dispositif de chargement d'un four à cuve ;
• la Figure 2 montre une première variante d'exécution du dispositif de la Figure 1 ;
• les Figures 3 à 5 montrent schématiquement le fonctionnement du dispositif selon la Figure 1 ou 2 ;
• la Figure 6 montre une deuxième variante d'exécution du dispositif selon la Figure 1 ;
• la Figure 7 montre un détail de l'exécution de l'organe d'étanchéité de la Figure 6.

Other advantages and characteristics of the proposed device will emerge from the detailed description of preferred embodiments, presented below, by way of illustration only, with reference to the appended drawings in which:

• Figure 1 shows schematically, in a vertical section, a device for loading a shaft furnace;
• Figure 2 shows a first alternative embodiment of the device of Figure 1;
• Figures 3 to 5 schematically show the operation of the device according to Figure 1 or 2;
• Figure 6 shows a second alternative embodiment of the device according to Figure 1;
• Figure 7 shows a detail of the execution of the sealing member of Figure 6.

Figure 1 shows an embodiment of a charging device according to the present invention, designed to equip a shaft oven. The reference 10 marks a housing of a drive mechanism of a chute rotary or oscillating distribution (not shown). The reference 12 marks the vertical axis of the shaft furnace. A supply pipe 14 axially passes through the casing 10 to feed the distribution chute with a material loading, for example coke, chipboard, pellets etc. This supply pipe 14 is coaxial to the vertical axis 12 of the shaft furnace.

Reference 18 globally identifies a hopper with material, which constitutes a lock container for the loading material of the shaft furnace. This matter of loading is marked inside the hopper 18 by the reference 20. The material hopper 18 comprises a part upper 22, in the form of a cylinder coaxial with the axis vertical 12. In this upper part 22 are arranged two loading openings 24 and 26, through which the hopper can be filled. The filling is done by example, in a manner known per se, through two skip carriers 28 and 30.

Each of these loading openings 24 and 26 is equipped with an upper sealing valve 32 and 34. These upper sealing valves guarantee, in position closed, the tightness of the hopper with respect to the outside atmosphere. In Figure 1 they are shown, in dashed lines, in the open position. We notes that they are, in this position, each located in a lateral tube 36, 38 of the hopper, well at protected from the material discharged by the skips 28, 30 to through the loading openings 24 and 26. Each of these pipes 36, 38 is provided with a flange shutter 40, 42 removable, which allows access to respective valve for maintenance work.

The upper part 22 of the material hopper 18 is extends into a lower part 44, which has the shape of a funnel or trunk of coaxial cone of revolution to the axis 12. The angle at the top of the cone of revolution is by example between and 60 ° and 80 °, which corresponds to a slope of an internal wall 46 of the order of 50 ° to 60 °.

A lower opening 48, coaxial with axis 12, is provided with a sealing member 50. The latter ensures, in closed position, tightness of the hopper 18 relative to in the oven.

In the execution shown in Figures 1 to 5, the sealing member 50 comprises a valve sealing 52, pivotable from a lateral position (shown in broken lines in Figures 1 and 2), in which it is sheltered from matter flowing from the opening 48, in a position shutter, in which it is transverse to the axis 12. In this closed position the valve 52 can be applied, in a manner known per se, axially on a seat 54, peripherally surrounding the opening 48 and provided a sealing surface 56 which is oriented downwards. The space required to pivot the valve 52 below of the hopper 18 is obtained by connecting the latter to using a sealed chamber 58 to the tubing supply 14. A side tube 60, provided with a removable flange 62, allows access to inside the sealed chamber 58, to replace the valve 52 or seat 54.

Reference 64 globally identifies the retaining member and material adjustment. The latter includes a bell 66 and a central metering body 68, displaceable one relative to the other along axis 12.

The bell 66 has the shape of a hollow truncated cone, which is coaxial with axis 12 and which flares towards a lower horizontal edge 70. In Figures 1 and 2 the bell is shown in a closed position. She is supported with its lower edge 70 on the wall interior 46 of the hopper 18, so as to seal a passage section 72 in the conical part of the hopper 18, upstream of the sealing member 50. In in other words, this passage section constitutes a discharge opening 72 of the hopper 18, which can be closed by the bell 66 and which can be released in removing the bell 66 upwards.

The central metering body 68 has an oblong shape, significantly more slender than the bell 66. It is by example of a body of revolution composed of two trunks of cone 74, 76 superimposed, which widen from the bottom to the top and which define the actual adjustment profile. AT its upper end 78, this body of revolution gradually thins towards a stem support 80, which is coaxial with axis 12. The choice of profile of the central metering body 68 is determined, ie experimentally, either by calculations. What matters is that the central metering body 68 is oblong and above all significantly more slender than the bell 66. With the profile shown in the Figures, good linearity was obtained of the setting characteristic Q = f (C) for conventional loading materials for a shaft furnace. We note that the angle at the top of the truncated cone 76 is slightly less than the angle at the top of the hopper; than the angle at the top of the truncated cone 74 is substantially equal at the angle at the top of the hopper; and that the cumulative height of the two truncated cones 74, 76 is substantially identical to the diameter of said lower opening 48.

The axial positioning of the central metering body 68 in the lower opening 48 of the hopper 18 delimits therein an annular passage opening. The section of this annular passage opening is determined by the cross section of the central body of dosage 68 at this lower opening 48. When moving the central metering body 68, shown in Figure 1, from bottom to top across said lower opening 48, the passage section in this last increases from a minimum value to a value maximum, which corresponds to the cross section fully released by the central dosing body.

The devices shown in Figures 1 and 2 are distinguish only by drive mechanisms different for bell 66 and the central body of dosage 68.

In Figure 1, the bell 66 is provided at its end upper of a sleeve 82, which is extended axially upwards outside the material hopper 18. A axial sealing device 84, for example a device of the type of a cable gland, provides axial guidance and the sealing of the sleeve 82 through an upper wall of the hopper 18. Two cylinders 86 and 88 are connected between arms 90 and 92, integral with the upper end of the sleeve 82, and the hopper 18. These jacks 86 and 88 must be sized to provide the necessary effort allowing the bell 66 to be raised through the material 20. A third cylinder 94 is tightly mounted on the upper end of the sleeve 82. Its rod 96 penetrates axially in the sleeve 82, where it is connected to the upper end of the rod 80 of the central body of metering 68. This rod 80 is guided inside the sleeve 82 during its vertical displacement relative to the hopper 18. A regulator 100 ensures that a displacement of stroke (c) of cylinders 86 and 88 in one direction, causes a synchronous displacement movement (c) of the cylinder 94 in the opposite. The regulator 100 therefore makes it possible to keep the central metering body 68 stationary by compared to the hopper 18, when the bell 66 is raised or lowered by cylinders 86 and 88.

In Figure 2 the bell 66 is provided at its end upper part of a sleeve 102, which is axially engaged on a fixed sleeve 104. The latter is coaxial with the axis 12 and is attached to an upper wall of the hopper 18. Two cylinders 106 and 108 are mounted on this upper wall, and their respective cylinder rod 110, 112 enters the material hopper 18, where it is connected to the end upper part of sleeve 102. Cylinders 106 and 108 must be sized to provide the necessary effort allowing the bell 66 to be raised through the material 20. A third cylinder 114 is mounted on the upper wall of the hopper 18, so as to penetrate with its jack rod 116 axially in the fixed sleeve 104, where it is connected to the rod 80 of the central metering body 68. This rod 80 is guided axially inside the fixed sleeve 104, during its vertical displacement relative to the hopper at material 18. A cylindrical cage 118 surrounds the rods of cylinders 110 and 112, to protect them against contamination and wear by the loading material.

The hopper discharge operation, fitted with the organ retaining and adjusting the material and the organ lower seal described above, will be studied at using Figures 3, 4, and 5.

In Figure 3 the lower sealing member 50 is closed, i.e. the valve 52 is applied so waterproof on its seat 54. The bell 66 is entirely lowered into its closed position, in which it closes the discharge opening 72 and retains the material of loading upstream of the sealing member 50. The body metering unit 68 is reassembled inside the bell 66 and is in a maximum raised position.

In Figure 4 the lower sealing member 50 is open, i.e. the valve 52 is pivoted in its side protected position. Bell 66 is still fully lowered into its closed position and retains the loading material 20 in the hopper 18. The central dosing body 68 is lowered into a position which corresponds to the desired flow. In other words, the stroke C of the central metering body, i.e. the distance from its maximum position, is chosen taking into account the characteristic Q = f (C) valid for the loading material 20 contained in the hopper 18. The device is now prepared for loading material discharge 20.

In Figure 5, the bell 66 is in its position raised in which it releases the opening of discharge 72. Its position in matter 20 will be chosen from so as to have a minimal influence on the flow of material flowing through the discharge opening 72 and maximum influence on the homogeneity of the emptying of the material hopper 18. The bell travel will be, for therefore, determined according to the particle size and the nature of the loading material. It could be adjusted according to the level of loading in the hopper 18, which naturally lowers during emptying of it. This adjustment will be done, for example, automatically based on an output signal from a hopper continuous weighing device 18.

Figure 6 shows a variant of the device of Figures 1 and 2. Replacing an organ seal 50, which was provided with a pivotable valve 52 installed below the material hopper 18, the Figure 6 device includes a sealing member lower 200, which is fully integrated into the hopper to matter 18. This member 200 comprises a seat 202, which is tightly mounted on the hopper 18 at the lower opening 48, and a closure element 204, having the shape of a crown.

The crown-shaped closure element 204 is tightly attached to the lower end of a sleeve 206, in which a central metering member 208, equivalent to the metering member 68 of FIG. 1 or 2, can be removed. At its upper end the sleeve 206 is extended by a tube 210, which is engaged so waterproof, for example using a cable gland 212, on a fixed sleeve 214. This is fixed to the hopper 18 of so as to be coaxial with axis 12. The interior of the sleeve 206, tube 210 and fixed sleeve 214 are from when located from the pressure point of view, on the tank furnace side.

A bell 216, which corresponds to bell 66 of the Figure 1 or 2, constitutes a material retaining member upstream of the sealing member 200. It will be noted that the tube 210 can slide in a sheath 218, coaxial with axis 12 and attached to the upper end of the bell 216.

Two cylinders 220 and 222 are connected between the tube 210 and the hopper 18. A control rod 224 extends axially the central metering member 208 through the tube 210 in the fixed sleeve 214, where it is connected to a piston rod 226 of a cylinder 228, which is mounted axially on the material hopper 18. These are the cylinders 220 and 222 which make it possible to raise the bell 216 to through the material 20. In fact, when the tube 210 is lifted by cylinders 220 and 222, the bell 216 remains first stationary, and the shutter member 204 is removed inside the bell 216. By the time the end upper of the sleeve 206 bears on the bell 216, it is lifted from its seat to be raised by the tube 210, together with the closure element 204.

Figure 7 shows execution details of the seat 202 and the shutter element 204. Seat 202 has the shape of a sleeve 273, which is coaxial with the axis 12. From inner side, this sleeve 273 is provided with a first sealing surface 276 and a second surface sealing 278. The first sealing surface 276 describes a truncated cone of revolution, which is coaxial with the vertical axis 12 of the device and which flares slightly in the direction of flow of the material. The second sealing surface 278, which is located upstream of the first sealing surface 276, describes a truncated cone of revolution, which is coaxial with the vertical axis 12 of the device and which flares inwards from the hopper to matter 18. At their intersection the two surfaces determine a bottleneck 279. The two surfaces sealing 276, 278 are preferably coated with a 280 anti-abrasive and anti-corrosion coating. On the side outside the sleeve 273 is provided with an annular channel 282, which surrounds the two sealing surfaces 276 and 278. This channel 282 is equipped with go connection pipes and back for a liquid. These lines are schematically represented by arrows 284 and 286 on Figure 2. Reference 288 schematically represents a liquid packaging unit, which ensures that the temperature of the liquid circulating in the channel annular 282 is such that the surface temperature of the sealing surfaces 276 and 278 is never lower at dew point, to avoid condensation, and never higher than an upper limit temperature, determined for example by the working temperature limit a seal applied against one of the two surfaces 276 and 278.

In Figure 7, we see the shutter element 204 in an operational position. The element shutter 204 is applied in this position with a upper peripheral edge 292, which is provided with a seal elastomer 294, against said second sealed surface 278 of the seat 202. The peripheral edge 292 could however also be applied directly against said second watertight surface 278, ensuring a metal seal against metal. In this case it will preferably have the form of a spherical crown. Starting from this peripheral edge upper 292, the closure element 204, which is delimited laterally by a lower peripheral surface 296, decreases in cross section to be able to penetrate axially, through the throat 279, in the space surrounded by said first surface seal 276.

An inflatable elastomeric seal 298 is housed in a annular cavity 300, which is arranged in the surface lower device 296. In said position operational, this inflatable seal 298 faces said first sealing surface 276. When it is deflated, seal 298 is set back from the surface lower device 296 (see Figure 2). When he is swollen, i.e. pressurized by a fluid, the seal 298 is however firmly applied to said first sealing surface 276 and thus ensures the seal between the closure element 204 and the seat 202. An annular channel 302, which is arranged in the sealing element 204 supplies the inflatable seal 298 with pressurizing fluid. This channel supply 302 is preferably provided with supply lines outward and return connections, shown schematically by arrows 304 and 306. In this way we can organize a circulation of a liquid cooling through the inflatable seal 298. This liquid can also be identical to the liquid circulated at through the annular channel 282 of the seat.

In a lower peripheral edge of the element obturation 204, an annular channel 308 is arranged, which is connected by a passage 310 to a compressed air circuit or a pressurized gas. This annular channel 308 feeds a annular orifice 312, which is directed obliquely towards the low. When lowering the shutter element 204 in its seat 202, the air blown through this orifice ring finger 312 cleans the second, then the first surface sealing from top to bottom.

It will be noted that the inner wall of the hopper 18 consists of a wear coating 314, a slope from about 50 ° to 60 °. The latter is interrupted by a vertical cylindrical surface 316, directly above said second sealing surface 278, which reduces wear of this surface.

Note that in the device of Figure 6, the material retaining member 216, the adjusting member of the material flow 208 and the sealing member lower 200 are integrated all three in the hopper to material 18. This characteristic makes it possible to connect the lower outlet opening 48 of the hopper to material 18, directly to the loading nozzle 14, without passing an intermediate sealed chamber, of the type of chamber 58 in Figure 1. This results in a gain appreciable in mounting height.

Claims (8)

1. Charging device for feeding an enclosure with a predetermined flow rate of a solid material, comprising

   a hopper (18) including a funnel-shaped lower part (44) which defines a substantially vertical central outflow axis (12),

   a pipe (14) for feeding the enclosure, which is situated axially below the said lower part (44) of the hopper (18), and

   a member (64) for retaining and for regulating the flow rate of material, which includes a bell (66), which is movable inside the hopper (18) between a lower position for closing off a discharge opening (72) in said lower part (44) of the hopper (18) and an upper raised position, and a central metering body (68), which is oblong and distinctly more slender than the bell (66), coaxial with said central outflow axis (12) and movable along the latter so as to penetrate to a greater or lesser degree through the said discharge opening (72) in the direction of the feed pipe (14),

      wherein the bell (66) and the said central metering body (68) are axially movable relative to one another, so that the distance which separates the two of them can be freely adjusted.
2. Charging device according to Claim 1, wherein the central metering body (68) comprises a frustum (74, 76) which flares out firstly upwards and which terminates in an upper end (78) which tapers in the direction of a control rod (80) to which the central metering body is attached.
3. Charging device according to Claim 1 or 2, wherein the bell (66) includes a cavity entirely receiving the central metering body (68).
4. Charging device according to any one of Claims 1 to 3, comprising a lower sealing member (50) including a pivotable shutter (52) and a seat (54), said seat (54) being mounted below the hopper (18) and provided with a sealing surface (56) which points downwards.
5. Charging device according to any one of Claims 1 to 4, wherein the bell (66) includes a sleeve (82) which is extended upwards axially through the hopper (18), and wherein the central metering body includes a control rod (80) guided axially in the sleeve (82).
6. Charging device according to Claim 5, wherein at least one first hydraulic cylinder (86, 88) is connected between the sleeve (82) and the hopper (18), and at least a second hydraulic cylinder (94) is connected between the sleeve (82) and the control rod (80).
7. Charging device according to any one of Claims 1 to 4, wherein the hopper (18) includes a fixed guide sleeve (104) which extends axially downwards inside the hopper (18),

   the bell (66) includes a sleeve (102) which can be engaged on the fixed sleeve (104),

   the central metering body (68) includes a control rod (80) which is guided axially inside the fixed sleeve (104),

   at least a first hydraulic cylinder (106, 108) is connected between the hopper (18) and the sleeve (102), and

   at least a second hydraulic cylinder (114) is connected between the hopper (18) and the control rod (80).
8. Charging device according to any one of Claims 1 to 3, comprising a lower sealing member (200) including

   a closing off element (204) set out directly below the bell (216) and axially movable with respect to the latter, said closing off element (204) including a lateral peripheral surface (296) in which is incorporated an inflatable seal (298) and a central passage opening (205) for the central metering body (208),

   means (228) for moving the closing off element axially between a protected position below the bell (216) and an operational position outside the bell (216), when the latter is in the said lower closing off position, and

   a seat (202) mounted axially below the discharge opening (72), the said seat (202) including a first sealing surface (276) which points downwards and which surrounds said inflatable seal (298) when the closing off element (204) is situated in said operational position.

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