GB2088343A - Silos - Google Patents

Abstract

A silo for grain or the like has a circular wall 3, composed of curved corrugated sheets whose corrugations extend horizontally (in the circumferential direction of the wall), and a discharge outlet 8 located at or adjacent the base of the wall. The corrugations provided have a larger than usual ratio (greater than 5:1, and preferably 10:1 or 12:1) of pitch (crest-to-crest) to depth (crest-to- trough) and the friction forces on the wall are thereby much reduced. The stated location of the discharge outlet permits incorporation of an air jet emptying and floor-clearing system e.g. as disclosed in G.B. Patent No. 1,115,224. <IMAGE>

Description

SPECIFICATION Grain-storage silos This invention relates to silos for the storage of grain and the like.

Such silos are often made with a substantially circular-cylindrical vertical external wall, which extends upwardly from the perimeter of a substantially circular floor, and the floor is often formed with a controlled discharge outlet, located either at the centre of the floor or at or adjacent the base of the wall. Central location of the discharge outlet has the disadvantage that, unless sufficient height is available below the discharge outlet for it to open into a discharge chute inclined at a substantial angle, a power-driven feed screw or auger has to be provided to move the discharged material radially outwardly from below the outlet to a point beyond the edge of the floor; and the whole of the discharge operation must be effected by use of the auger.For that reason the preferred location for a discharge outlet is at or adjacent the base of the wall, since in that case the discharged material is immediately accessible for removal and does not clog up the discharge aperture, and the discharge can proceed without power assistance, under the influence of gravity alone, until the stored material (at a stage during the discharging operation which will depend on its angle of repose) no longer flows into the discharge outlet. Further emptying of the silo then requires some means of moving the remaining stored material towards the discharge outlet, and one very suitable means of doing this is disclosed and claimed in our Patent No. 1,115,224.

As disclosed in our said patent, the silo floor is formed with air-entry apertures supplied with air from sub-floor ducts and directed so as to provide a substantially horizontal movement of air across the floor such as to move grain or the like stored material across the floor to the discharge outlet.

The stored material then leaves the silo via the discharge outlet, whereas the air is deflected upwardly to escape from the top of the silo. This "airsweep" technique is, effectively, limited to silos with their discharge outlets located at or near the base of the external wall: with a centrally located discharge outlet it would be necessary to arrange an approximately radially inward flow of air across the floor towards the centre from all directions, which has proved virtually impossibie to achieve without an intolerable degree of air turbulence within the silo. The constitutes another reason why it is preferred to locate the discharge outlet at or near the base of the external wall rather than at the centre of the floor.

However, one common form of circular silo which it has not hitherto seemed practical to provide with a discharge outlet located at or near the base of the external wall is that in which the wall is to be self-supporting and is made from curved sheets or panels secured together and, for increased strength, formed with corrugations which, in the assembled wall, extend horizontally in the circumferential direction of the wall.It has been known that in such silos, if a discharge outlet is located at or near the base of the wall, discharge of stored material through the outlet is accompanied by a downward movement of that part of the stored material which is above the outlet and against the adjacent part of the wall, and this downward movement results in frictional forces which act on the wall in the downward direction and which are not only highly asymmetrical (in that they are concentrated on the part of the wall adjacent and above the discharge outlet) but also of very considerable magnitude because the horizontally extending corrugations greatly increase the frictional effect as compared with a smooth vertical surface.In fact the force so generated during discharge could have led to the collapse of such silos, and for that reason it has not been considered practical to locate the discharge outlet of a silo at or adjacent the base of its external wall when that wall was composed of the corrugated sheets commonly used in silo construction.

It has now been found, and the present invention is based on the fact, that by using a modified form of corrugated sheet the frictional forces generated during discharge can be much reduced, to the point where it becomes permissible to locate the discharge outlet of a corrugated-wall silo at or adjacent the base of the wall. One of the advantages thereby gained is that it becomes practical to incorporate in such silos the "airsweep" floor-clearing technique to which the above-mentioned patent relates. In the corrugated sheets commonly used in silo construction hitherto, typical dimensions would be a corrugation pitch (crest-to-crest) of three inches (7.6 cm) and a corrugation depth (crest-to-trough) of three-quarters of an inch (1.9 cm), giving a pitch-to-depth ratio of 4 :1.It is found that, for the purposes of the present invention, use should be made of corrugated sheets in which (the sheets being otherwise similar to those hitherto employed) the pitch-to-depth ratio of the corrugations is not less than 5 :1. A ratio greater than 6 :1 is preferred.

The substantial increase in pitch-to-depth ratio which is provided in accordance with the invention leads to a marked decrease in the vertically acting friction forces generated during discharge without, however, reducing to an unacceptable extent the lateral rigidity of the corrugated sheets and the capacity of the wall which they form to bear the static loads imposed by the stored material (including unbalanced lateral thrusts due to asymmetrical distribution of the material in the silo).

According to the invention, therefore, there is provided a storage silo for grain or the like having a discharge outlet and a substantially circularcylindrical vertical external wall which is selfsupporting and is composed of curved corrugated sheets of which the corrugations extend horizontally, in the circumferential direction of the wall, wherein the pitch-to-depth ratio of the corrugations is greater than 5:1 and the discharge outlet is located at or adjacent the base of the wall.

Preferably the pitch-to-depth ratio is greater than 6 :1. In one very suitable galvanised-steel corrugated sheet material, the corrugation pitch is about four inches (10.2 cm) and the corrugation depth is about 8 mm, giving a pitch-to-depth ratio of about 12.7:1. In another, the pitch is 10 cm and the depth is 10 mm, giving a ratio of 10:1.

In a preferred embodiment, a silo according to the invention has a floor formed with air-entry apertures communicating with air supply ducts below the floor and directed to provide, when supplied with air from such ducts, a substantially horizontal movement of air across the floor for moving grain thereacross to the discharge outlet.

In one such preferred embodiment the floor (being substantially circular) has the discharge outlet disposed at one end of a diameter and is divided, by two chords equally inclined to the said diameter on opposite sides thereof and intersecting one another at or near the said one end thereof, into two segmental regions (each bounded by a respective one of the chords) and a main region (extending between the two chords and bisected by the said diameter), and air-entry apertures in the main region of the floor being directed generally parallel to the said diameter, in the direction towards the discharge outlet, and the air-entry apertures in each segmental region of the floor being directed generally parallel to the respective chord and in the direction towards the discharge aperture.

The angle between the said two chords may be about 800, each making an angle of about 40 with the said diameter.

In another preferred embodiment, the floor, being substantially circular, has the discharge outlet disposed at one end of a diameter and is divided, by two chords parallel with that diameter and equidistant therefrom on opposite sides thereof, into two segmental regions and a diametral region between them, the air-entry apertures in the diametral region of the floor being directed generally parallel to the said diameter, in the direction towards the discharge outlet, and the air-entry apertures in each segmental region being directed generally transverse of the said diameter, in the direction towards the diametral region.

In this latter preferred embodiment, preferably, the air-flow direction from the segmental regions is perpendicular to the said diameter, and an upwardly projecting baffle extends along the diameter to arrest the transverse movement of material blow to the diametral region from the segmental regions.

The invention will be more fully understood from the following description of two such preferred embodiments, with reference to the accompanying drawings, in which: Figure 1 is a vertical sectional view taken on the central axis of a first circular-cylindrical silo which embodies the invention; Figure 2 is a diagrammatic floor plan of the silo shown in Figure 1 (which is taken on the line I-I of Figures 2); Figure 3 is a fragmentary sectional view, on a larger scale, of a corrugated vertical external wall of the silo shown in Figures 1 and 2; Figure 4 is a fragmentary sectional view, also on a larger scale, of a perforated floor of the silo shown in Figures 1 and 2; and Figure 5 is a diagrammatic floor plan, corresponding to Figure 2, of a second silo embodying the invention.

The silo illustrated in Figures 1 to 4 has a circular floor 1 supported on a base 1, and a circular-cylindrical external vertical wall 3 which extends upwardly from the perimeter of the floor.

A roof 4 is supported at the upper edge of the wall 3 by roof support means 5 in such a way as to leave ventilation slots 6 between the roof and the edge of the wall 3. The roof has a central charging aperture 7, closable by means of a removable cover (not shown), through which the silo may be filled with grain or the like.

The base 2 is formed with a discharge outlet in the form of a short inclined chute 8, located closed to the base of the wall 3 at one end of that diameter of the floor 1 on which the section 1-1 is taken, as shown in Figure 2. The circular floor 3 is divided by two chords 9a and 9b into two segmental regions 1 a and 1 b (each bounded by a respective one of the chords) and a main region (extending between the two chords and bisected by the diameter along the line I-I) which is subdivided into sub-regions 1 c, 1 d, 1 e, 1 f and 1 g.

The two chords 9a and 9b, which intersect one another at the discharge-outlet end of the diameter along the line I-I, make an angle of about 800 with one another and are equally inclined to that diameter, each at an angle of about 400, on opposite sides thereof. Below the floor 1, the base 2 is formed with walls 2a and 2b extending along the lines of chords 9a and 9b away from the edge of the discharge chute 8, and with walls 2c, 2d, 2e and 2f extending from the walls 2a and 2b, parallel to one another and to the aforesaid diameter; and these, together with a peripheral wall 2h of the base 2, which serves also as a footing for the wall 3, serve to provide in the base 2 a plurality of air supply ducts each below and corresponding to a respective one of the floor regions 1a and 1 b and sub-regions 1 c, 1 d, le, 1f and ig, and each provided with air entry means not otherwise shown but such as an entry port 10 shown in Figure 1 for the sub-region between walls 2d and 2e.

The tops of the walls 2h and 2a to 2f serve to support the edges of floor panels of the floor 1 which, as shown in Figure 4 and as described in our earlier patent No. 1,11 5,224, are slit and pressed out to form louvres which constitute directed air-entry apertures 11 so that air supplied under pressure to the under-floor ducts issues through the apertures 11 to produce a substantially horizontal movement of air across the floor for moving grain or the like across the floor.The floor panels of the sub-regions 1 c, 1 d, 1 e, 1 f and 1 g all have their apertures 11 oriented to produce air movement towards the left (in Figures 2), i.e. parallel to the diameter on the line I-I, as indicated by arrows in Figure 2, so as to sweep grain or the like either directly into the discharge outlet 8 or into the segmental regions 1 a and 1 b; and the floor panels of these latter regions 1 a and 1 b have their apertures aligned to produce air movement parallel to the chords 9a and 9b respectively as indicated by corresponding arrows and thus to sweep grain or the like into the discharge outlet.

The discharge outlet is provided with closure means (not shown) which enables discharge to be controlled and which, when closed, enables the silo to be filled. With the closure means opened, the silo will discharge under gravity until, with an angle of repose as represented by the chain line 12 in Figure 1, the upper surface of the grain or the like meets the wall 3 in a curve represented approximately by the broken line 1 3. The silo must be strong enough to accept the stresses which this asymmetrical distribution of the stored material imposes on it, and to assist in conferring on the wall 3 the necessary strength and rigidity it is composed, in known manner, of sheets of corrugated galvanised steel curved to conform with the curvature of the wall and with their corrugations extending, horizontally, in the circumferential direction of the wall 3.As explained above, it would not normally be permissible with a wall 3 of this kind to locate the discharge outlet close to the base of the wall; but, as shown in Figure 3, the corrugations of the sheets used in the illustrated silo, in accordance with the invention, have a ratio of crest-to-crest pitch P to crest-to-trough depth d which is unusually high. In a preferred embodiment of the invention, the pitch p may be about 4 inches (10.2 cm) and the depth d about 8 mm, giving a pitch-to-depth ratio of about 12.7:1 as is illustrated in Figure 3, or a pitch p of 10 cm may be provided in combination with a depth d of 10 mm, giving a ratio of 10:1.

Continued emptying of the silo after it has reached the condition represented by the lines 1 2 and 13 is achieved by supplying air under pressure, by means not shown, to the ducts under floor 1 and under the control, if desired, of valves (not shown) which enable the air to be supplied to the ducts selectively. This air acts first to blow into the discharge outlet 8 the grain or the like immediately round the edge of the outlet, where the grain depth is least; and the material thus removed is replaced by material which slides down from higher up and is blown, in its turn, into the outlet 8.Material originally near the floor in the sub-regions 1 c, 1 d, 1 f and 1 g will be blown not directly to the discharge outlet but initially into the regions 1 a and 1 b, whence it is subsequently blown into the discharge outlet.

The air blown up through, and across, the floor 1 all travels in the same general direction (i.e. to the left in Figure 2) and reaches the vicinity of the discharge outlet 8, and is there deflected upwardly, without the production of excessive turbulence. The air then escapes via the ventilation slots 6 between the wall 3 and roof 4.

The silo embodying the invention whose floor plan is represented diagrammatically by Figure 5 is closely similar to that already described with reference to Figures 1 to 4, apart from some details of its floor and of the supporting base therefor. In particular, the silo to which Figure 5 relates has a circular, cylindrical external vertical wall (not shown) corresponding to the wall 3 in Figures 1 to 3 and composed of curved corrugated sheets with a pitch-to-depth ratio of about 10:1 or 12 :1. As shown in Figure 5, this silo has a circular floor 1 supported on a base 2 which is formed with a discharge outlet chute 8 which the floor 1 does not cover.The chute 8 of this silo, like that previously described, is provided with closure means (not shown) by means of which discharge from the silo can be controlled and prevented, and the base 2 is formed with under-floor ducts defined between walls formed in the base. In this embodiment, the discharge outlet 8 being at one end of a diameter of the floor 1 and base 2, the base is formed with two walls 2k which extend parallel to that diameter on opposite sides thereof and define between them a diametral main duct.

Each of the two remaining segments of the base 2 is divided by transverse walls 2m into a plurality of transverse or lateral ducts which extend perpendicular to the diametral main duct.

The top of the walls 2k and 2m, and of the peripheral wall 2h of the base 2 which also serves as a footing for the cylindrical external wall of the silo, support panels of the floor 1 which are as described above with reference to Figure 4. These panels, in a diametral main region 1 k of the floor where they cover the diametral main duct, have their apertures 11 oriented as indicated by arrows to produce air movement over the floor towards the outlet 8. Over the remaining segments of the floor they constitute respective lateral regions 1 m each covering a respective one of the transverse or lateral under-floor ducts; and in these lateral regions the floor panels have their aperture 11 directed to produce air movement over the floor towards the diametral region 1 k, as is also indicated by arrows.Air supply to the under-floor ducts is provided by a blower unit 14 connected to the diametral duct at its end remote from the outlet aperture 8. The walls 2k are formed with openings 1 5 each giving access from the diametral duct to a respective one of thtt lateral ducts and each closable by a door 16, there being provided means (not shown) accessible from outside the silo for opening and closing each of the doors 1 6 individually so as to control the supply of air via the diametral duct to the lateral ducts. A baffle 1 7 projects vertically up from the diametral region 1 k of the floor, and extends along the whole length of the region 1 k from the discharge outlet 8 to the opposite end of the diameter.

After emptying of the silo to which Figure 5 relates has proceeded to that point where the angle of repose has been reached, air from the blower 14 may be fed first only to the floor region 1 k so as to clear it progressively from its end adjacent the discharge outlet 8. After the floor region 1 k has thus been partially or entirely cleared, the door 1 6 to one or each of the two floor regions 1 m immediately adjacent the discharge outlet 8 may be opened, so that one or each of them is also cleared. Then one or both of the next pair of doors 1 6 may be opened, to clear the next region 1 m on one or both sides of the region 1 k. Preferably, the floor regions 1 m on only one side of the region 1 k are cleared first, clearing of the regions 1 m on the other side being carried out afterwards.The baffle 17, which need only project upwardly a few inches from the floor region 1 k, is effective to prevent grain from being blown completely across the floor region 1 kfrom a region 1 m on one side to the opposite region 1 m on the other side. Thus grain from a region 1 m is blown first on to the region 1 k and then along the region 1 k to the discharge outlet 8.

Effective movement of grain across the silo floor by the "airsweep" technique may call for an air supply rate of the order of 100 cu ft per minute per square foot of floor (30 m3 per minute per m2 of floor) and, particularly in larger silos, of greater than, say, 6 m diameter, it is desirable to have the floor area divided into regions to which the air can be supplied selectively, as described, thus enabling the floor to be cleared by a blower 1 4 whose capacity would be inadequate to supply effectively the whole floor area simultaneously.

Claims (8)

1. A storage silo for grain or the like having a discharge outlet and a substantially circular cylindrical vertical external wall which is self supporting and is composed of curved corrugated sheets of which the corrugations extend horizontally, in the circumferential direction of the wall, wherein the pitch-to-depth ratio of the corrugations is greater than 5 :1 and the discharge outlet is located at or adjacent the base of the wall.

2. A silo as claimed in Claim 1, having a floor formed with air-entry apertures communicating with air supply ducts below the floor and directed to provide, when supplied with air from such ducts, a substantially horizontal movement of air across the floor for moving grain thereacross to the discharge outlet.

3. A silo as claimed in Claim 2, wherein the floor, being substantially circular, has the discharge outlet disposed at one end of a diameter and is divided, by two chords equally inclined to the said diameter on opposite sides thereof and intersecting one another at or near the said one end thereof, into two segmental regions (each bounded by a respective one of the chords) and a main region (extending between the two chords and bisected by the said diameter), the air-entry apertures in the main region of the floor being directed generally parallel to the said diameter, in the direction towards the discharge outlet, and the air-entry apertures in each segmental region of the floor being directed generally parallel to the respective chord and in the direction towards the discharge aperture.

4. A silo as claimed in Claim 3, wherein the said chords each make an angle of about 400 with the said diameter and 800 with one another.

5. A silo as claimed in Claim 2, wherein the floor, being substantially circular, has the discharge outlet disposed at one end of a diameter and is divided, by two chords parallel with that diameter and equidistant therefrom on opposite sides thereof, into two segmental regions and a diametral region between the, the air-entry apertures in the diametral region of the floor being directed generally parallel to the said diameter, in the direction towards the discharge outlet, and the air-entry apertures in each segmental region being directed generally transverse of the said diameter, in the direction towards the diametral region.

6. A silo as claimed in Claim 5, and having provided on its floor an upwardly extending baffle disposed substantially along the said diameter and serving to arrest the transverse movement of material blown to the diametral region from the segmental regions.

7. A silo as claimed in Claim 5 or Claim 6, wherein the air-entry apertures in the segmental regions are directed-generally perpendicular to the said diameter.

8. A storage silo for grain or the like substantially as described herein with reference to Figures 1 to 4, or Figure 5, of the accompanying drawings.