EP0033996A1

EP0033996A1 - Silo outlet

Info

Publication number: EP0033996A1
Application number: EP81200150A
Authority: EP
Inventors: Hendrik Magchiel Willem Croese
Original assignee: Ir Hmw Croese Raadgevend Ingenieursbureau Bv
Current assignee: Ir Hmw Croese Raadgevend Ingenieursbureau Bv
Priority date: 1980-02-08
Filing date: 1981-02-05
Publication date: 1981-08-19
Also published as: NL8002484A

Abstract

A silo having a cylindrical storage section terminating at the bottom in a discharge section accommodating a roof-top-shaped core (14) having guide surfaces (12) sloping in the direction of outlet openings (25). The discharge section is defined above each outlet opening (25) by upright sidewalls (8) to form a laterally outwardly off-set bay (4) comprising an expansion compartment located above the level of the ridge (15) of the roof-top-shaped core (14) and accessible from the outside.

Description

This invention relates to a silo, and in particular to the outlet thereof.
It is known to use deep silos for the storage of bulk materials. These have advantages over and above storage on the ground, in sheds and the like, such as better utilization of the available surface area of the ground, withdrawal without aids, such as scrapers, and no trouble from dusting.
A condition for the use of silos, however, is that the silo is capable of being emptied in a controlled manner, that is to say, that so-called arching or bridging is avoided. Arching means that the bulk material keeps hanging at a given level in the silo, while the subjacent material flows away. Not only does arching cause difficulties in discharge, but it is also dangerous, because as soon as the arch breaks the silo is loaded to such an extent that it may collapse.
Under normal conditions, at any level of the silo the superjacent column of material is supported by both the subjacent part of the column and by the friction of the superjacent-part-of-the column on the silo wall. It is clear that, in a given silo, friction plays a more important role according as the superjacent column is longer, which means that according as the level under consideration is lower, the role of friction increases and the supporting function of the subjacent part of the column decreases. It is, however, this very supporting function of the subjacent part of the column that is important for proper throughflow of material in the silo. For it is only if the subjacent part of the column actually supports the superjacent part of the column, at least in part, that the withdrawal of material from the subjacent part of the column, whereby this support is removed, will cause the superjacent part of the column to sink. If, at a given level in the silo, the mere friction on the wall should be sufficient to support the column of material upwards of that level, uniform downward movement of the entire column of material during withdrawal from the bottom of the silo is no longer ensured. In order to minimize the risk of arching, silos are designed taking into account that arching is more likely to occur according as the silo diameter is smaller, the silo taller, and wall friction higher.
The above considerations apply to the major part of the silo, which extends between the top and the bottom outlet, and in which no variations in diameter occur. At the outlet, however, there must be a decrease in diameter to provide a transition from the full silo diameter to the outlet proper. It is in this, often conical transitional -zone that, unless the contents of the silo consist of a materal having very good flow characteristics, bridging is virtually certain to occur because, whereas in the cylindrical portion high wall friction and a high pressure of the product against the wall are conditions for the formation of an arch, this is no longer necessary in an outlet cone, because the product will just stand on the sloping conical wall. The abrupt transition from cylinder to cone and the pronounced reduction in cross-sectional area in the cone also promote the formation of bridges.
In Dutch patent No. 96,974, there is described a silo having a storage section having a cylindrical configuration or a polygonal configuration which approaches the cylindrical form, and at the bottom thereof a discharge section, in which discharge section there are provided guide surfaces sloping in the direction of the outlet openings to form a core having a roof configuration, and in which the outlet section comprises at least above each of the rectangular outlet openings an outlet chamber defined by upright sidewalls and off-set laterally outwardly relatively to the storage section.
With such an outlet system, the risk of arching is much less than with a downwardly tapering conical outlet. Not only is the constriction in the downward flow path for the material less abrupt with a roof-shaped core than in the well-known conical outlet, but the provision of a laterally outwardly off-set chamber opposite each inclined guide surface makes arching more difficult. Now, in the silo disclosed in Dutch patent 96,974, each outlet opening is only so off-set outwardly, and the associated outlet chamber is so disposed that the line of the natural slope of the bulk material, starting from the lower end of the cylindrical storage section of the silo terminates approximately in the outlet opening. This means that, especially with poorly flowing material, having a steep natural slope, the outlet is rather close to the projection of the inner wall of the silo cylinder, and with a silo thus designed, if a material having better flow characteristics is stored, the outlet will no,longer have an optimum location. Making the outlet openings larger in order to overcome this drawback is unfavourable in practice, because the size of the outlet openings is determined by the transportation used.
This prior'construction has still other drawbacks, however. In the first place, the chamber has a roof immediately adjoining the lower edge of the cylindrical silo section, and practice has shown that the space under the roof can hardly provide the pressure relief contemplated, because during the filling of an empty silo, and also when material flows shock-wise from the storage section into the outlet chamber, the latter will be filled virtually completely. Indeed, it is found that in silos constructed in conformity with the Dutch patent arching occurs regularly above the outlet opening. In order to disrupt such an arch, it is necessary for an attendant to strike against it from the bottom through the outlet opening, which is a hazardous operation.
Furthermore, in the prior arrangement the outlet section has the form of a block, with the cylindrical storage section resting on the foundation through the walls of the outlet section. It is clear that, under these conditions, access to the outlet openings, and hence the choice of the means of transportation for carrying off the material are limited. As far as no roof-shaped guide core is used, it is proposed in Dutch patent No. 96,974 to provide a plate on the flat silo bottom, which plate can be moved up and down by means of a jack, and which is contemplated to disrupt a residual pyramid. For disturbing an arch, such a plate is indeed unsuitable, because, in raising the plate, the pressure of the column of material resting on it must be overcome.
It is an object of the present invention to overcome all of these disadvantages and drawbacks, and to provide a silo in which, for all current bulk materials, the risk of arching, and generally the risk of failures during discharging, is minimized, and in which the outlet openings may have dimensions adapted to conventional means of transportation for discharge of the material, and the silo may be discharged using a great variety of means of transportation.
For this purpose, according to the invention, the storage section, which is at least substantially cylindrical, is supported through an annular beam on the outlet section, the apex of the roof-shaped core is disposed no higher than the level of the bottom of the annular beam, and an expansion compartment is provided above each outet chamber next to said annular beam and on the radial outside thereof, which expansion compartment can be made freely accessible from the outside.
As the annular beam extends as a skirt down into the outlet chamber of each outlet opening, the expansion compartment located above the level of the lower edge of the skirt can never be filled, and the zone over the outlet opening is ensured to be free of pressure under all circumstances.
In order to protect the outlet chamber from weather influences, the expansion compartment may be closed with a removable hood, for example of metal, which may be provided with a manhole. For example, in case the material has stood still in the silo for a long period of time, owing to which it has become consolidated, and no longer flows, the material can be loosened in the outlet chamber, either through the manhole or, after removal of the hood, via the open expansion compartment.
In a structurally favourable embodiment of the silo, each chamber, with the expansion compartment at the top, and the outlet opening at the bottom thereof, is formed as a bay projecting laterally and radially from the storage section and the silo base, the bay having sidewalls extending from a substantially vertical end wall diagonally, and substantially tangentially to the silo cylinder, a guide surface of the core extending into the bay up to the outlet opening, and in which, above the rectangular outlet opening, the diagonal sidewalls connect with the end wall by way of transition surfaces oriented at right angles to said end wall to form a second expansve compartment directly above the outlet opening, which prevents bridging.
The bay has a cantilever portion under which means of transportation may be provided, or under which motor- lorries may pass, etc. Furthermore, according to the invention, the annular beam may have an interior, downwardly diverging profile, whereby a third, so-called pre-expansion compartment is formed. Accordingly, the material moving downwards in the storage section of the silo is given an opportunity, before reaching the apex of the core, to expand laterally into the pre-expansion compartment. The material forced to flow laterally by the guide surfaces of the core can expand in an outlet chamber, and finally material can again expand just before flowing out of the outlet opening.
To provide for the case that, for example with a material having very poor flow characteristics, such as tapioca, the material still gets stuck in the outlet chamber somehow, and in practice this turns out to be possible even without there being any bridge formation, namely, owing to the material remaining on a guide surface of the core as a thick, overhanging layer, according to a further feature of the present invention, loosening means may be provided in the guide surfaces for disturbing material resting in full or in part on the guide surfaces.
Utilizing the cantilever construction of the base, in a further elaboration of the invention, the loosening means may be accessible from the outside, while the guide surfaces of the core extending within the cylinder zone of the storage section and within the base zone can also be made accessible from the outside, namely, from below the guide surfaces, by making the base hollow.
Preferably, the loosening means take the form of plates having an active upper surface extending at least substantially flush with the guide surface concerned, and which plates are movable downwardly and upwardly again according to the slope of the guide surface by means of an operating device provided at the underside thereof. The advantage of this arrangement over and above loosening elements in the form of plates movable at right angles to their own plane, as described'in Dutch patent No. 96,974, is that the plates do not have to overcome any material pressure. In fact they only have to cooperate with gravity for example to move down a leg of an arch, as a result of which an arch will immediately be disrupted, and the relief of the pressure on the plate as the material from the arch flows downwardly can be utilized for moving the plate upwardly back into its starting position with a low consumption of power.
According to the invention, an indicator for the absence of material may be provided in the sidewalls of the outlet chambers, for example, in the form of an infrared transmitter and receiver, with the loosening means being actuated in response to signals from such indicator.
On structural grounds, the part of the outlet chamber and the guide surface linking up with the outlet opening may be made of metal, so that this can be mounted on the concrete structure as one or more pre-fabricated elements.
In order to ensure that the outlet openings are free from the silo pressure, each rectangular outlet opening is preferably spaced such a distance from the axis of the silo that the boundary edge of the outlet opening proximal to the silo axis is spaced from the imaginary, downward prolongation of the cylindrical storage section a distance at least equal to the width of the outlet opening.
In a construction having two diametrically opposed outlet openings, the silo base supporting the core maybe provided with passages for a means of transportation capable of serving both outlet openings at the same time.
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings. In said drawings,

Fig. 1 is a diagrammatic perspective view of a first embodiment of the silo according to the present invention;
Fig. 2 is a cross-sectional view, taken on the line II-II of Fig. 1;
Fig. 3 is a cross-sectional view, taken on the line III-III of Fig. 2;
Fig. 4 is a diagrammatic perspective view of the discharge section, in axial cross-section;
Fig. 5 is a view taken on the line IV-IV of Fig. 4;
Fig. 6 is a part-sectional view, taken on the line VI-VI of Fig. 5;
Fig.7 is a view according to the arrow VII of Fig. 4;
Fig. 8 is a perspective view of a loosening plate; and
Fig. 9 is a cross-sectional view, taken on the line IX-IX of Fig. 8.

Referring to the drawings, in particular Fig. 1, the silo according to the invention comprises a cylindrical superstructure 1, approximately 35 meters high and having a diameter of, for example, 16 meters, a base 2 and an intermediate outlet zone 3, which includes bays 4 projecting laterally from the silo cylinder. Each bay 4 is bounded at the top by a flat wall 5 and has a bottom opening 6 fitted with an outlet 7, preferably formed as a steel funnel. Each bay 4 further has sidewalls 8 tangentially merging with the local cylinder wall 9 of the silo. The cylindrical silo section will not be desribed in more detail herein, as its construction does not form part of the present invention. Suffice it to say that the silo cylinder 1 is equipped at the top with a cover 9' having a filling opening 10 therein.
Sidewalls 8 and the end wall 11 of each bay 4 together with a sloping guide surface 12 refine a taparing supply channel for bulk material from silo 1 to the outlet funnel 7. In this supply channel, bridging cannot occur, because the surface of the material in the top end of bay 4, in cross-section, has approximately the configuration indicated at 13, in other words, although each sloping guide surface 12 could form a supporting surface for an arch, there is no supporting surface opposite guide surfaces 12 for supporting the other "leg" of such arch.
Guide surfaces 12 form part of a core 14 having a roof top configuration, the ridge 15 of which is at the level of the upper end of bays 4. Guide surfaces 12 intersect the cylinder wall 9 in the manner shown in Fig. 1 according to curved lines 16 sloping downwards to outlet 7, so that nowhere in the supply passage to outlets 7 are there any horizontal parts that could prevent the flow of the material. If, in the case of material having very poor flow characteristics, such as flour, fodder and the like, any clogging should occur in bays 4, work can be done in the bay through a hole 17 formed in the top wall 5 thereof.
In base 2, ports 18 may be formed for allowing the passage of a means of transportation capable of serving both outlets 7.
In the embodiment shown in Figs. 4-9, the storage section 1 of the silo is supported on side base 2 through an annular beam 20, the bottom side 21 of which is not lower than ridge 15 of the roof-top-shaped core. The inner surface 22 of annular beam 20 diverges downwardly, so that material sinking from the storage section 1 can expand laterally already before it reaches ridge 15 of the core within beam 20. Accordingly, the annular beam defines a pre-expansion zone.
In this embodiment, silo base 2 is formed by core 14 and by vertical walls 23, which either connect to vertical walls 24 or, as indicated by dot-dash lines in Fig. 5, intersect each other radially outwards of beam 20. The upright walls 23 are connected to the end walls 11 of bays 4 by cantilever wall portions 8, which at least in part form the upright sidewalls of base 3.
In this manner the storage section is supported on its foundation in a reliable manner through annular beam 20 and walls 23( and possibly 24).
Provided at the bottom end of each bay 4 is a rectangular outlet opening 25, and the superjacent part of the outlet chamber A present in bay 4 is defined by a prolongation 12' of guide surface 12 of the core, and further by an extension 8' of bay sidewall 8, an extension 11'of end wall 11, and a transition surface 26 between surface 8' and surface 11'. Transition surface 26 provides for connection of the sloping surfaces 8' to the rectangular outlet opening 25, and owing to the presence of transition surfaces 26 the extended end surface 11' diverges downwardly. The result is an expansion compartment just above each outlet opening 25.
Outlet chamber A is in principle open at the top, where in the embodiment of Figs. 1-3 the flat roof wall is provided, so that the interior of chamber A is freely accessible from the outside. As indicated in Fig. 4, use can be made of a detachable hood 27 having a manhole 28 therein for protecting the contents of chamber A from weather influences. The space under hood 27 forms an expansion chamber located next to, and on the radial outside of, annular beam 20, so that it cannot be filled with the material stored in the silo under any circumstance. The material located over each outlet opening 25 is accordingly absolutely ensured to be free from the column pressure in the storage section 1 of the silo.
One or more loosening elements 29 may be provided on guide surfaces 12 and 12', which will be described hereinafter with reference to Figs. 8 and 9.
In the embodiment shown in Figs. 8 and 9 (diagrammatically in Fig. 8 and in more detail in Fig. 9), each loosening element 29 takes the form of a plate 30 which, with its upper surface substantially flush with the adjacent surface of guide surface 12 or 12' is supported by means of strips 31 on freely rotating rollers 32 journalled on cross-beams 33. Plate 30 is accessible from the bottom between cross-beams 33. Mounted on plate 30 is a piston-and-cylinder assembly 34, with which plate 30 can be moved downwardly and upwardly again. In Fig. 8, the plate is shown in its lowermost position. In the inoperative position, the plate is located with its upper edge 35 in a cavity 36 of a superjacent portion of guide surface 12, 12', which cavity it can enter by way of a stepped portion 37 in guide surface 12, 12'.
The upward and downward movement of plates 30 can be controlled in response to signals from sensors 38 in the sidewalls 8' of the outlet chambers A so that, as soon as the sensors register that no material is present just above outlet openings 25, which implies that the material has become stuck at a higher level, loosening plates 30 are put into operation for disrupting a bridge and/or a stationary layer of material on guide surfaces 12, 12'.
In the apparatus according to the invention, there are no constrictions in which the material is under the column pressure anywhere in the path of travel of the material, either in the storage section or in the outlet section. In fact, everywhere where such an undesirable situation could occur, i.e. in the bottom end of the storage section, in the tapering part of the outlet chambers, and just above the outlet openings, adequate expansion facilities are provided.

Claims

1. A silo comprising a storage section having a cyling drical configuration or a polygonal configuration whicn approaches the cylindrical form and at the bottom thereof a discharge section, in which discharge section there are provided guide surfaces sloping in the direction of the outlet openings to form a core having a roof-top configuration, and in which the outlet section comprises at least above each of the rectangular outlet openings an outlet chamber defined by upright sidewalls and off-set laterally outwardly relatively to the storage section, characterized in that the storage section, which is at least substantially cylindrical is supported through an annular beam on the outlet section, that the apex of the roof-top-shaped core is disposed no higher than the level of the bottom of the annular beam, an¿ an expansion compartment is provided above each outlet chamber next to said annular beam and on the radial outside thereof, which expansion compartment can be made freely accessible from the outside.

2. A silo as claimed in claim 1, characterized in that in order to protect the outlet chamber from weather influerces the expansion compartment is closed with a removable hood, preferably of metal, which is optimally provided with a manhole.

3. A silo as claimed in claim 1 or 2, characterized in that in a structurally favourable embodiment of the silo, each outlet chamber, with the expansion compartment at the top, and the outlet opening at the bottom thereof, is formed as a bay projecting laterally and radially from the storage section and the silo base, the ba^y having sidewalls extending from a substantially vertical end wall diagonally, and substantially tangentially to the silo cylinder, a guide surface of the core extending into the bay up to the outlet opening, and in which, above the rectangular outlet opening, the diagonal sidewalls connect with the end wall by way of transition surfaces oriented at right angles to said end wall to form a second expansion compartment directly above the outlet opening.

4. A silo as claimed in any one of the preceding claims, characterized in that the annular beam has an interior, downwardly diverging profile, whereby a third, so-called pre-expansion compartment is formed.

5. A silo as claimed in any one of the preceding claims, characterized in that loosening means are provided in the guide surfaces for disturbing material resting in full or in part on the guide surfaces.

6. A silo as claimed in claim 5, characterized in that the loosening means are accessible from the outside.

7. A silo as claimed in claim 5 or 6, characterized in that the loosening means have the form of plates having an active upper surface extending at least substantially flush with the guide surface concerned, and which plates are movable downardly and upwardly again according to the slope of the guide surface by means of an operating device provided at the underside thereof.

8. A silo as claimed in any one of claims 5-7, characterized in that an indicator for the absence of material is provided in the sidewalls of the outlet chambers, said loosening means being adapted to be actuated in response to signals from such indicator.

9. A silo as claimed in any one of the preceding claims, characterized in that the part of the outlet chamber and the guide surface linking up with the outlet opening are made of metal, so that this can be mounted on the concrete structure as one or more pre-fabricated elements.

10. A silo as claimed in any one of the preceding claims, characterized in that each rectangular outlet opening is spaced such a distance from the axis of the silo that the boundary edge of the outlet opening proximal to the silo axis is spaced from the imaginary, downward prolongation of the cylindrical storage section a distance at least equal to the width of the outlet opening

11. A silo as claimed in any one of the preceding claims having two diametrically opposed outlet openings, characterized in that the silo base supporting the core is provided with passages for a means of transportation capable of serving both outlet openings at the same time.