This invention relates to grain storage apparatus, e.g. silos of the type which are used to store cereal grain such as wheat grain. In general, however, the invention relates to apparatus for storing any type of particulate material which can form, unrestricted at rest, a stable mass having an upper surface at a positive angle to the horizontal.

In general, cereal grain is stored in cylindrical silos mounted axially vertically. With an outlet near the bottom of such a cylindrical silo, it can often ^* prove difficult to discharge grain from the silo since clogging occurs and the discharge rate can vary enormously while aggregates of grain form or, having formed, break up. In a cold climate, grain may be satisfactorily stored in a silo for a period of one year or more.

Conversely, a maximum storage period of one month or even as little as one week may be the rule in a humid climate. The storage conditions are therefore often carefully controlled, so that the water content is less than 15% and the ambient temperature less than 5°C.

Alternatively, or in addition, partial vacuum may be_ used; this gives several advantages, allowing removal of humidity at low temperatures, reducing the* influence of insects and bacteria, and economising on energy consumption. However, these advantages have hitherto been offset by the cost of equipment and of the silo material.

Grain at the bottom of a high cylindrical silo supports the weight of the grain above it. Although it is known to control the atmospheric conditions of grain

storage, with particular reference to temperature, humidity and the concentrations of oxygen and carbon oxides, the lower levels of grain often have less ambie oxygen and "breathe" at a lower ^' rate than grain in the higher levels. It is known to store grain under nitrogen, but even under these conditions, intramolecul breathing can lead to decay.

It is desirable to prevent the aggregation of gr during storage and to ^' ensure that the individual grains are stored under substantially uniform conditions. It is therefore conventional to cause movement of the gra relative to the storage atmosphere, e.g. by stirring o circulating the grain and/or by providing natural or artificial air-conditioning. The necessary movement c be achieved by forcing dry cool air into the grain or discharging grain from the bottom of a silo ^' and trans¬ ferring the discharged grain to the top of the same or an adjacent silo. The necessary air-conditioning, circulation and/or control equipment is expensive. In general, it may be stated that, while short- term storage of grain is not very useful, long-termsto is expensive and/or unsatisfactory.

According to the present invention, in storage apparatus for grain which, unrestricted at rest, has a stable sloping surface, an inner surface of the apparatus is substantially parallel to the sloping surface. For convenience, apparatus of the invention will be referred to herein as a "silo".

In the invention, the shape of the silo, at leas on its inner surface, is determined by the natural configuration, which in all cases slopes from the highest point ^" to the base at a characteristic

angle, • which the grain adopts. For example, if grain is discharged from a single stationary outlet it naturally assumes a right conical configuration. A silo of the invention may therefore be a right cone. Alternatively, if the grain is discharged from an outlet moving along a straight line, the grain assumes a configuration whose horizontal cross-section is oval (also known as "race track-shaped"). A silo of the invention may have a corresponding shape. In general, as will be appreciated, a silo of the invention has an inner surface of a configuration which grain may adopt, unrestricted at rest. A silo of the invention will usually be provided with a grain inlet and the shape of the silo will be determined in consid- eration of the configuration which the grain adopts when discharged through the inlet or, ^" if desired, inlets.. Each inlet may- be stationary or movable.

A silo of the invention may also be provided with an outlet through which the grain can be removed, e.g. under gravity or under vacuum, suitably in conventional manner. Preferably, the silo is provided with a grain outlet corresponding to each grain inlet in a manner which allows grain removal to be a substantially exact mirror of the grain filling process. This may be achieved by providing a grain outlet in a manner such that it removes grain from around the base of a mass deposited from a corresponding grain inlet. As a portion of the grain is removed from around the base of the mass, the natural tendency of the grain is to form a mass of the same shape as before removal, but progressively

smaller. This is a mirror of the natural tendency of th grain mass to form a particular configuration determined by the path, if any, of the inlet and then to retain tha configuration while increasing in size as more grain is added to the mass from the inlet.

The inner surface of the silo which is substantial parallel to the sloping surface of the gran may extend throughout the height of the storage space. It will usually extend through at least 30%, preferably at least 50% and usually at least 75% of the height of the space, any remainder usually being vertical. Thus, for the particular example of a right conical mass of grain, the silo may have a conical top portion and a right cylindrical base, a conical top and conical base portion and a cylindrical intermediate portion. Alternatively, ^• it may be a truncated cone or, preferably, a full cone. A silo of ^* .the Invention will usually have an internal capacity of at least 30, and often at least 1 10000,,m ⁵ . It may have a capacity similar to conventional silos.

A silo of the invention can be partially or wholly filled with grain. In either case, the only pressure borne by the grain can be independent of any restriction of the shape of the silo. Grain of the type which can be stored in apparatus of the invention may form a slope, with respect to the horizontal, of more than 20, 25 or 30 ^Q , but -seldom more than 45 or, more usually, 35°. The desired angle of the inner surface of the silo can of course be determined in advance for the particular grain which is to be stored. If the silo is to be used for the storage of various types of grain with different angles of slope the shape of the inner surface of the silo will usually be determined in consideration of the grain with the

steepest slope. By "substantially parallel", I mean that the respective slopes of the grain and the inner surface of the silo are within 10°, more preferably within 5°, and most preferably within 2°. The inner wall of the silo may therefore be at an angle of from 10 to 55° to its base, for the grain described above.

Since the inner surface of the silo conforms to the natural shape of the grain, unrestricted at rest, the surface of the silo-is statically non-stressed by the grain. This is in distinction to a conventional silo ahd allows the novel silos to be constructed from cheaper materials. Even when a partial vacuum is applied, the lesser Internal and external stresses allow relatively cheap construction with respect to known silos, particularly when the novel silo is a right cone. It is a particular advantage of the present invention that the material of the cone, can be non-self- supporting, i.e. the inner surface of the silo can rest on the mas of grain and continue to conform to the con- figuration of the latter as grain is introduced into, or removed from, the silo. For example, a silo of the invention may comprise a cone or other suitable config¬ uration of a flexible material such as rubber. Alterna¬ tively, a rigid sloping silo roof may be contained within fixed walls between which the roof can move vertically.

For example, during grain removal, a flexible or "floating" roof will move downwards and this can assist even discharge.

A silo of the invention may be formed of flexible wallswhich are fixed at least at the base and also, if desired, at the apex, e.g. by a pillar. When grain is stored in such a silo, under partial vacuum,' without filling it, the walls may bow inwards. In this case, it will be convenient to consider the angle at which the the walls are set in the unbowed state. In general, -of ^'

course, a pillar may be used to support the apex of a silo of the invention, e.g. a central pillar for a conic silo, whether or not the material of the walls is flexible. It is a particular advantage of silos of the prese inventionthat they can be simply adapted to allow circul ation of the grain therewithin, without the need for means for transferring grain from the bottom thereof to the top of the same, or another, silo. Accordingly, storage apparatus -of the invention comprises therewithin means which can move along a path within the silo and can transfer grain fro one point to another along its path. In order to allow satisfactory working of the transfer means, it is desiiεble that the grain inlet should of itself allow, or should be controlled such that it allows, at least pa of the base area of the silo to remain uncovered by grai

This aspect of the invention will now be illustrat by way of example .with reference to the accompanying drawings, in which:-

Figures 1 to 3 are vertical cross-sections through ϋree different embodiments of silos of the invention ^* containing . grain; and

Figures 4 to 6 are plan views of the embodiments shown in Figures 1 to 3, respectively.

Figures 1 and 3 show circular silos of triangular cross-section and Figure 2 a conical silo, each having walls 1. Each silo is shown containing grain 2 which

stands unrestr..cted at rest but does not fill the silo. The silo shown in Figure 2 includes a central pillar 3-

The degree to which the grain fills the silos shown in Figure. 1 is illustrated in the plan view of Figure 4. The grain covers one-half of the floor of the silo plus the area under two semi-conical faces bounded by the lines 4 and 5. The dot-dash line 6 represents the path of travel of means (not shown) which can transfer grain from the bottom of the ^' face 4 to the face 5. When a given amount of grain is removed from the face 4, the remaining grain naturally assumes the same configuration as before, but terminating at the line 3'. When the same amount of grain is transferred to the face 5, the grain at that face naturally -assumes the same configuration as before but terminating.at line 4 ¹ . By continuous transfer using the transfer means passing along the path 6, the faces of the grain precess around the silo and the grain is thoroughly- circulated entirely from within. A similar arrangement is illustrated in Figure 5, a plan view of the partially filled silo shown in Figure 2. The proximity of the faces 5 and 6 shown in Figure 5 is determined by the degree to which- he silo is filled with grain and the relative diameters of the pillar 3 and the silo. For a decreasingly wide pillar 3, the configuration shown in Figure 5 tends to that, shown in Figure 2, for a given degree of grain filling.

The effective grain storage volume of the silo shown in Figure 2 is the same as for that shown in Figure 3. However, for an increasingly thick pillar 3

or -an increase in the central area of a silo as shown in Figure 3, it may be desirable to hold less grain within the silo, in order to avoid contact of the faces 4 and 5. In the limit case, the grain mass may be a right cone whose base is shown in Figure 6, a plan view of the silo shown in Figure 3-

By using transfer means of the type described, apparatus of the invention can provide continuous and, if desired, full automated aeration and circulation, without exposing the ambient atmosphere to dust or the storage space to, say, bacteria. While this aspect of the invention has been illustrated with reference to a circular precession, it is also applicable to other configurations of silos of the invention, e.g. in which two separate masses of grain are held. Particularly for circular precession of the type illustrated, it is preferred that the transfer means should move in a path substantially parallel to the inner surface of the silo. Ground space for the situation of silos is often at a premium in, for example, dockyards. It will be appreciated that, for a given storage volume, a silo of the invention may take up more ground space than a cylindrical silo. However, this is not necessarily a disadvantage in certain places, where there may be much unused ground space. Without taking into account the ground area, however, the surface:volume ratio for a conical silo is smaller than for a cylindrical silo. This again has the advantage .of saving the material from which the silo is constructed.

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