WO2019025975A1

WO2019025975A1 - Drying and aeration of grain

Info

Publication number: WO2019025975A1
Application number: PCT/IB2018/055735
Authority: WO
Inventors: Casparus BRESLER
Original assignee: Bresler Casparus
Priority date: 2017-07-31
Filing date: 2018-07-31
Publication date: 2019-02-07

Abstract

A method of drying a body of grain (14) stored within a silo (10), comprising: allowing first and second drying fronts (50, 52) to propagate within the body of grain (14) from first and second inlets (22, 24) towards an outlet (26), so that a dried first layer (54) of grain (14) is formed between the first inlet (22) and the outlet (26), while a wet second layer (56) of grain (14) is located between the first layer (54) and the outlet (26), and so that a dried third layer (58) of grain (14) is formed between the second inlet (24) and the outlet (26), while a wet fourth layer (60) of grain (14) is located between the third layer (58) of grain (14) and the outlet (26). The first and second drying fronts (50, 52) are allowed to continue propagating towards the outlet (26) until an average moisture content of the body of grain (14) reaches a predetermined average moisture content.

Description

DRYING AND AERATION OF GRAIN

INTRODUCTION AND BACKGROUND

This invention relates to grain silos and more particularly to a method of aerating and/or drying a body of grain stored within a silo, and to a silo for storing a body of grain, which silo is adapted to aerate and/or dry a body of grain stored therein.

It will be appreciated that references to "grain" include any granular crop which may benefit from aeration and/or drying out, and the moisture content of which may be reduced by exposure to sufficient rates of air flow at a predetermined relative humidity.

"Grain aeration" generally refers to the providing of a flow of air through a harvested and stored body of grain and is mainly used for temporally preserving grain prior to drying, or, environmental conditions permitting, physically drying the grain. Aeration and drying of grain are therefore neither necessarily synonymous nor mutually exclusive. During aeration without drying, a "cooling front" or "heating front" propagates from an air inlet towards an outlet for air from the body, whereas during drying, a "drying front" propagates from the air inlet towards the outlet for air from the body. For the purpose of this disclosure, an "air front" will collectively be used to refer to either a cooling front or a drying front. Successful grain aeration and drying requires a certain minimum air flowrate.

Amongst others, the average particle size, particle orientation and moisture content of the specific body of grain influences the resistance to airflow through the grain. The air pressure within the body is therefore a function of the resistance to air flow, which directly impacts on the hardware requirements for providing sufficient level of aeration. For a specific type of grain, the path distance and air flow rate of the air through the body of grain therefore has a direct impact on the resistance, the pressure and thus the hardware requirements (such as the size of air pumps and power consumption) of the aeration system. It will be appreciated that a maximum airflow rate exists beyond which aeration and/or drying would no longer be viable, since the size of the pumping equipment (and therefore the speed and velocity of the air) is limited by practical considerations (energy consumption, capital cost etc.).

A drying front occurs when the relative humidity of the air forced through the body of grain is such that moisture from the grain is absorbed by the passing air. When the air becomes saturated, no more absorbing of moisture takes place while the air continues to moves through the grain. The drying front propagates through the grain relatively slowly, compared to the flow velocity of the air moving through the grain. The moisture content of grain downstream and upstream of the drying front remains relatively constant as the air moves through the grain, while the moisture content within the drying front varies relatively linearly. The portion of grain upstream of the drying front is therefore "dry", whereas the portion of grain downstream of the drying front remains "wet".

The moisture content of the "dry" portions of grain may be influenced by factors such as the temperature, the relative humidity and the flow rate of the air. The "dry" portions may become "over-dried" (according to industry standards) if too much moisture is absorbed from the grain by the air.

The relative humidity of the air is generally lowered by heating the air before entering the grain. "Over-drying" of grain is generally avoided, too much weight in the form of moisture may be lost, while too much energy may be expended during the drying cycle.

On the other hand, "under-dried" grain may spoil if stored for too long.

Conventionally, during drying, the aim is to maximise the amount of air flowing through the grain, while minimising the amount of heat added to the air, to thereby prevent over-drying of the grain. The air forced through the grain is typically conditioned such that such that it has a relative humidity of between 60% and 65%, to prevent "rewetting" of the grain. The minimum flow rate of air is then determined by the safe storage time of the grain, given its moisture content. The drying front has to travel through the whole body of grain, before any portion of the body of grains starts spoiling. For this reason, smaller diameter silos (which are therefore taller, and for which the flow path of air through the grain is longer) make drying of air within the silo impractical. Since the rate of drying in such a smaller diameter silo is often too slow, these silos are not filled to its full capacity before commencing with a drying cycle. Grain piled into a silo from the top forms a conical pile having an "angle of repose" (the angle of the pile relative to a horizontal plane, at which the pile is stored without slumping).

When grains are stored in this way, aeration and drying will be most efficient if the contour line or profile of the cooling or drying front matches the profile of the grain.

Vertical silos provide an efficient means of storing grain. However, the smaller the diameter of the silo, the longer it becomes (for a specific weight carrying capacity) and the more difficult aeration and drying becomes (because of the increased path length of air through the grain). Consequently, grain is often dried in a separate process, after which the dried grain is stored in the silos. This process is laborious. Larger diameter silos on the other hand take up more space and are difficult to unload.

Since blowers are usually utilised to provide the flow of air to the grain, most aeration systems either require the silo to be completely filled with grain before aeration can commence, or alternatively require various inlets or outlets located at different levels to be opened or closed depending on the level of grain within the silo. This is laborious and adds cost and complexity to the silo.

Grain entrapment or engulfment is a phenomenon where a person becomes submerged within a body of grain, often leading to suffocation. Ideally, entry into a container such as a silo filled with grain should be avoided at all cost.

Throughout this disclosure, the word "propagate' with reference to an air front, cooling front, heating front or drying front is to be taken to relate to the spreading, transmitting, translation or continuation of the particular front through the body of grain in a particular direction.

OBJECT OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method of aerating and/or drying a body of grain stored within a silo and a silo for storing a body of grain, which silo is adapted to aerate and/or dry a body of grain stored therein, with which the applicant believes the aforementioned disadvantages may at least be alleviated or which will provide useful alternatives for known methods and silos.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of drying a body of grain from an initial moisture content to a predetermined average moisture content, the method comprising the steps of:

- storing the body of grain in a silo;

- providing a first inlet to facilitate flow of a first stream of air into the silo and towards an outlet from the silo;

- providing a second inlet to facilitate flow of a second stream of air into the silo and towards the outlet from the silo;

- allowing a first drying front to start propagating in the vicinity of the first inlet, so that a first layer of grain having a first average moisture content, which is below the initial moisture content, is formed between the first inlet and the outlet, and so that a second layer of grain having a second average moisture content which is higher than the first average moisture content is located between the first layer of grain and the outlet, and allowing a second drying front to start propagating in the vicinity of the second inlet so that a third layer of grain having a third average moisture content, which is below the initial moisture content, is formed between the second inlet and the outlet, and so that a fourth layer of grain having a fourth average moisture content which is higher than the third average moisture content is located between the third layer of grain and the outlet; and

- allowing the first and second drying fronts to continue to propagate towards the outlet until an average moisture content of the body of grain reaches the predetermined average moisture content.

A pressure within the silo may be maintained below an atmospheric pressure outside of the silo to facilitate flow of the first and second streams of air into the first and second inlets respectively. A pump may be utilized to suck air from the outlet to thereby maintain the pressure within the silo below the atmospheric pressure. Further according to the first aspect of the invention, the method may comprise the further step of conditioning the first and second streams of air to a first and second condition respectively, to facilitate propagation of the first and second drying fronts towards the outlet. Yet further according to the first aspect of the invention, the method may further comprise, after the predetermined average moisture content is obtained, aerating the body of grain, to average out the first to fourth moisture contents of the first to fourth layers towards the predetermined average moisture content.

The first and second streams of air may be conditioned to a third and fourth condition respectively, to thereby cause the grain to be aerated by the first and second streams of air.

At least a portion of the body of grain may be unloaded from a bottom of the container, such that at least some of the first and second layers of grain may become mixed. The portion of the body of grain that has been unloaded from the silo may have a relatively uniformly distributed average moisture content which may be in the region of the predetermined average moisture content. The first and second streams of air may be conditioned to the first and second conditions respectively, by decreasing the relative humidity of the first and second streams of air before being provided into the silo.

The relative humidity of the first and second streams of air may be decreased by increasing the temperature of the first and second streams of air from an ambient temperature to a predetermined higher temperature. A first and second heat exchanger may be provided and used to increase the temperature of the first and second streams of air to the predetermined higher temperature. The first and second heat exchangers may be supplied with heat by first and second burners, first and second heating elements, or first and second solar heaters.

The first stream of air may be conditioned to the third condition, by increasing the relative humidity of the first stream to a relative humidity which is above the relative humidity of the first stream of air when conditioned in the first condition. The second stream of air may be conditioned to the fourth condition, by increasing the relative humidity of the second stream to a relative humidity which is above the relative humidity of the second stream when conditioned in the second condition. According to a second aspect of the invention there is provided a silo for a body of grain, the silo comprising:

- a container for receiving the body of grain, the container comprising a bottom end and a top end a substantially rigid wall;

- a first inlet for operatively providing a first flow of air into the container; - a second inlet for operatively providing a second flow of air into the container; and

- an outlet for the first and second flows of air from the container, wherein the first inlet is arranged closer to the outlet than the second inlet, the first and second inlets being configured such that the second flow of air at least partially converges with the first flow of air before exiting the container through the outlet.

The first inlet may be provided at a first vertical distance from the outlet. The second inlet may be provided at a second vertical distance from the outlet. The second distance may exceed the first distance. Each of the first and second inlets may be in the form of a perforated portion of the wall of the container. Alternatively, each of the first and second inlets may comprise a duct extending from the substantially rigid wall at least partially into the container. The duct may comprise perforations arranged to operatively allow air within the duct to enter into the container.

Each of the first and second inlets may extend substantially horizontally at and least partially along a periphery of the container. Preferably, each of the first and second inlets may extend all the way along the periphery of the container. A bottom portion of the container may converge towards the bottom end thereof. The container may be substantially cylindrical so that the bottom portion may be substantially conical. The outlet may be in the form of a perforated floor. Alternatively, the outlet may comprise a perforated duct extending substantially vertically proximate the bottom end of the container in a direction towards the top end thereof. Alternatively, the outlet duct may be arranged substantially horizontally within the container.

The outlet may be provided in fluid flow communication with a pump for operatively providing suction to the outlet.

The substantially rigid wall may be formed from metallic plates. The container may further be provided with vertical support structures for lending rigidity to the wall.

According to a third aspect of the invention, there is provided a silo for a body of grain, the silo comprising:

- a container for receiving the body of grain, the container comprising a bottom end and a top end separated by a substantially rigid wall;

- a first inlet for air into the container, arranged so that in use, a portion of the first inlet is in contact with grain; - a second inlet for air into the container, arranged so that in use, a portion of the second inlet is in contact with grain;

- an outlet for air from the container; and

- a suction apparatus provided in fluid flow communication with the outlet, for operatively creating a pressure below atmospheric pressure within the body of grain, thereby causing first and second streams of air to enter the silo through the first and second inlets.

The first inlet for air may project into the container so that in use, a portion of the first inlet inside the container may be surrounded by grain. Similarly, the second inlet for air may project into the container, so that in use, a portion of the second inlet inside the container may be surrounded by grain. The first and second inlets may comprise first and second inlet ducts extending substantially horizontally from the substantially rigid wall into the container. The first inlet duct may be arranged a first distance from the outlet. The second inlet duct may be arranged a second distance from the outlet, in a direction of the first inlet duct, the second distance exceeding the first.

Each of the first and second inlet ducts may extend from one portion of the wall to an opposing portion of wall and through a centre of the container. The first inlet may comprise at least two perforated inlet ducts located at the first distance from the outlet. The two perforated inlet ducts may project partially across the container, and towards each other. The second inlet may comprise at least two perforated inlet ducts located at the second distance from the outlet. The two perforated inlet ducts may project partially across the container and towards each other.

The two perforated inlet ducts projecting into the container may extend from a first wall portion of the container at least 10%, alternatively 20%, alternatively 30%, alternatively 40%, alternatively 50%, towards a centre of the silo.

Alternatively, the second inlet duct may be arranged at an acute angle relative to the side wall of the container, the angle being commensurate with an angle of repose of the grain in use stored in the container. The first perforated inlet duct may be arranged parallel to the second perforated inlet duct. Alternatively, the first perforated inlet duct may be arranged at an acute angle smaller than the angle of repose of the grain. The first and second inlets may extend substantially vertically within the container between the top end and the bottom end of the container. The first and second inlets may comprise perforated portions in the substantially rigid wall of the container, that extend substantially vertically at least partially along the container. Alternatively, the first and second inlets may comprise first and second perforated ducts that extend substantially vertically within the container at least partially along the container.

The first and second inlet ducts may be fixed to the substantially rigid wall.

Alternatively, the first and second inlet ducts may be spaced a first and second radial distance from a vertical centre line of the container. The configuration may be such the first and second radial distances may be equal. Alternatively, the configuration may be such that the second radial distance may exceed the first radial distance.

According to a fourth aspect of the invention, there is provided a method for storing and aerating a body of grain, the method comprising:

- storing the body of grain in a silo comprising a bottom end and a top end separated by a rigid wall, and an outlet for air from the silo;

- providing a first stream of air at a first mass flow rate through a first inlet projecting into the body of grain, so that the body of grain surrounds at least a portion of the first inlet, thereby propagating a first air front within the body of grain towards the outlet, the first inlet duct being spaced a first distance from the outlet; and

- providing a second stream of air at a second mass flow rate through a second inlet into the body of grain so that the body of grain surrounds at least a portion of the second inlet, thereby propagating a second air front within the grain towards the outlet, the second inlet being spaced a second distance from the outlet. The container may have a vertical extent and a horizontal extent.

Preferably, the vertical extent may exceed the horizontal extent. Alternatively, the horizontal extent may exceed the vertical extent. Further alternatively, the vertical and horizontal extents may be similar. Preferably, a means for providing a flow of air in the container may be arranged in fluid flow communication with the outlet and may maintain a pressure below atmospheric pressure within the grain. Alternatively, the means for providing a flow of air in the container may be arranged in fluid flow communication with the first and second inlets and may maintain a pressure above atmospheric pressure within the grain within the container.

The rigid wall of the container may be perforated to serve as an additional inlet for air into the container. The container may be substantially cylindrical. Each inlet duct may project through the wall of the container, and may comprise an open outer end, in fluid flow communication with an atmosphere outside of the container. Each inlet duct may comprise a substantially rigid pipe, with perforations in the form of elongate slits through a wall of the pipe. The slits may be located along the length of the pipe to facilitate a predetermined flow rate at specific positions along the length of the pipe.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein:

figure 1 is a diagrammatic side view of a silo according to a first example embodiment of the invention, wherein inlet ducts extend horizontally;

figure 2 is a sectioned perspective view of an alternative example embodiment of the silo of figure 1 ;

figure 3 is a sectioned side view of a silo of figure 1 showing first and second drying fronts propagating through a body of grain stored within the silo;

figure 4 is a diagrammatic side view of a silo according to a further example embodiment of the invention, wherein inlets for air are arranged substantially vertically;

figure 5 is a top view of the silo of figure 4;

figure 6 is a sectioned perspective view of an alternative example embodiment of the silo of figure 4; figure 7 is a diagrammatic top view of the silo of figure 6, showing drying fronts propagating through a body of grain stored within the silo; and

figure 8 is a diagrammatic plan view of a silo according to a further example embodiment of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A silo for a body of grain is generally indicated by reference numeral 10 in the figures. The silo is used for storing the body of grain, while aerating and/or drying the body of grain stored therein.

The silo comprises a container 12 for in use receiving the body of grain 14. The container 12 comprises a bottom end 16 and a top end 18, and a substantially rigid wall 20.

The silo 10 further comprises a first inlet 22 for operatively facilitating a first flow of air into the container 12, and a second inlet 24 for operatively facilitating a second flow of air into the container 12. The silo 10 further comprises an outlet 26 for air from the container 12. In one embodiment of the invention (as particularly illustrated in figure 2), the first and second inlets (22, 24) comprise first and second perforated inlet ducts that project at least partially into the container. The arrangement of the first and second inlet ducts (22, 24) is such that in use, when the container 12 is filled with grain, at least a portion of the first and second inlet ducts are surrounded by grain. Alternatively (not shown), the first and second inlets may be in the form of perforated portions formed in the substantially rigid wall 20.

The container has a vertical extent or dimension a and a horizontal extent or dimension b (shown in fig 1 ). Generally, the silo is elongate with the vertical extent a exceeding the horizontal extent b (to constitute a vertical silo). However, the use of silos of which the vertical extent a and horizontal extent b are similar, or wherein the horizontal extent b exceeds the vertical extent a is possible. Examples provided herein will be provided in terms of a vertical silo.

In a first example (shown in figures 1 to 3) the first and second inlets (22, 24) are in the form of perforated ducts or conduits that are fixed to an inner surface of the substantially rigid wall, so that the first and second inlets (22, 24) extend substantially horizontally within the container 12. The inlet ducts may extend at least partially along the periphery, but preferably all the way along, the periphery of the container 12 (as shown best in figure 2). When the container 12 is cylindrical, the inlet ducts are therefore ring- shaped (as shown).

The first inlet 22 is arranged a first distance 28 from the outlet 26, whereas the second inlet 24 is arranged a second distance 30 from the outlet 26.

The second distance 30 exceeds the first distance 28, so that the second inlet 24 is spaced relatively further away from the outlet 26 than the first inlet 22. As shown in figures 1 , and 4 the outlet 26 of the container may comprise a perforated floor 32 at the bottom end 16 of the container 12, allowing air to pass from the body of grain. Alternatively, the outlet may comprise a perforated outlet duct 34 extending into the container 12. In figures 2, 3 and 6 the perforated outlet duct 34 extends substantially vertically into the container 12, and is in use, at least partially surrounded by grain. The perforated outlet duct 34 may alternatively be arranged horizontally (not shown) at the bottom end 16 of the container 12.

Means for providing a flow of air in the container 12, and between the first and second inlets (22, 24) and the outlet 26, is provided in the form of an air pump (not shown) that causes a pressure differential between the first and second inlet ducts (22, 24) and the outlet 26. Preferably the air pump is a suction pump (not shown). The suction pump is connected in fluid flow communication with the outlet 26 via a suction pipe (not shown). In use, the portion of the outlet within the container is completely covered by grain. The suction pump therefore causes a pressure within the body of grain 14 which is below an atmospheric pressure 36 outside of the silo 10, so that air will naturally tend to flow from the inlets (22, 24) towards the outlet 26. Alternatively, or additional to the suction pump, one or more blowers may be arranged in fluid flow communication with the inlet ducts, causing a pressure above that of the atmosphere 36 within the inlets, so that air naturally flows from the first and second inlets (22, 24), through the body of grain 14, to the outlet 26.

The wall 20 of the container may also be perforated, for air to enter the body of grain 14 when a suction pump is used. Typically, a major portion of the container 12 is cylindrical, as can be seen in figure 2. In use, the first and second inlets (22, 24) project into the grain within the container 12 and comprise an open outer end 38 (shown in figure 1 ), in fluid flow communication with the outside atmosphere 36. Each inlet comprises a substantially rigid pipe or conduit, such as a metal

(for example steel) or polymeric (such as PVC or other plastics) pipe. Preferably the pipe or conduit has perforations in the form of elongate slits through an outer wall of the pipe. The slits may be located along the length of the pipe to facilitate a predetermined flow rate at specific positions along the length of the pipe, and therefore are not necessarily uniform in size or spacing. Alternatively, the perforations may comprise holes of a circular or other shape.

It will be understood that since the first inlet 22 is closer to the outlet 26 than the second inlet 24, the configuration is such that the second flow of air at least partially converges with the first flow of air before exiting the container 12 through the outlet 26.

In one example embodiment, which is best illustrated in figure 2, a bottom portion 40 of the container 12 converges towards the bottom end 16 (to constitute a so-called "hopper bottom silo"). When the container 12 is substantially cylindrical, the bottom portion 40 is therefore substantially conical.

An outlet 41 for grain is provided at the bottom end 16. This outlet 41 for grain comprises a door (not shown) that is closed when grain is stored within the silo and opened to allow grain to be unloaded from the silo.

The use and operation of the silo 10 in a method to dry a body of grain 14 will now be described with reference to figures 1 , 2 and 3. The body of grain 14 has an initial moisture content. The object of the below method is therefore to reduce the moisture content of the body of grain from the initial moisture content to a predetermined average moisture content which is below the initial moisture content. The predetermined average moisture content is, amongst others, determined by industry requirements and storage requirements of the type of grain.

In use, the body of grain 14 is stored in the container 12, typically by piling the grain through an inlet for grain 43 located at the top end 18 into the container 12. The inlet for grain 43 comprises a door that can be closed once a desired amount of grain has been piled into the container 12. An upper surface of the body of grain describes a profile 42.

The air pump is utilised to cause first and second streams of air to flow from the atmosphere 36 surrounding the silo 10 into the silo 10, through the first and second inlets (22, 24) respectively. Because of the pressure differential, air is provided at a first mass flow rate through the first inlet 22 and at a second mass flow rate through the second inlet 24. The first stream of air forms a first air front 44 that starts propagating in the vicinity of the first inlet 22 through the body of grain 14 towards the outlet 26, while the second stream of air forms a second air front 46 that starts propagating in the vicinity of the second inlet 24 through the body of grain 14 towards the outlet 26.

The top end 18 of the container 12 may furthermore be in fluid flow communication with the atmosphere 36 so that a third air front 48 propagates from the upper surface of the body of grain 14 towards the outlet 26.

At least a portion of the first and second air fronts converge before exiting through the outlet 26.

The first stream of air is conditioned to a first condition before entering the silo through the first inlet 22, so that a first drying front 50 starts propagating in the vicinity of the first inlet 22 towards the outlet 26. Similarly, the second stream of air is conditioned to a second condition before entering the silo through the second inlet 24, so that a second drying front 52 starts propagating in the vicinity of the second inlet 24 towards the outlet 26. The first drying front 50 is allowed to continue to propagate at least partially towards the outlet 26, so that a first layer 54 of grain, having a first average moisture content, which is below the initial moisture content, is formed between the first inlet 22 and the outlet 26. This is best illustrated in figure 3.

The first layer 54 is followed by a second layer 56 of grain, which is located between the first layer 54 and the outlet 26, which second layer 56 has a second average moisture content which is higher than the first average moisture content of the first layer 54.

Similarly, the second drying front 52 is allowed to continue to propagate at least partially towards the outlet 26, so that a third layer 58 of grain, having a third average moisture content, which is below the initial moisture content, is formed between the second inlet 24 and the outlet 26. The third layer 58 is followed by a fourth layer 60 of grain, which is located between the third layer 58 and the outlet 26, which fourth layer 60 has a fourth average moisture content which is higher than the third average moisture content of the third layer 58.

In practical terms, the first and third layers (54 and 58) are layers of grain through which the first and second drying fronts (50 and 52) have respectively passed. These layers are therefore layers of "dry" grain. On the other hand, the second and fourth layers (56, 60) are portions of the body of grain through which the first and second drying fronts (50 and 52) have yet to pass completely. These layers are therefore layers of "wet" grain.

The first and second conditions of the first and second streams are conditioned such that the moisture contents of the layers of "dry" grain (54 and 58) are below the predetermined moisture content (these layers are therefore "over-dried" according to industry standards).

The first and second drying fronts (50 and 52) are allowed to continue propagating towards the outlet 26 until the predetermined average moisture content of the body of grain 14 is reached (this is illustrated in figure 3).

Therefore, by the time the average moisture content of the body of grain 14 reaches the predetermined moisture content, the body of grain contains portions of "over-dried" grain (the first and third layer (54 and 58)) as well as portions of "wet" or "under-dried" grain (the second and fourth layers (56 and 60)). The average moisture content of the body of grain 14 is measured by measuring the moisture content of the air exiting the container through the outlet 26. Alternative known methods may also be applied. The first and second air streams are conditioned to the first and second conditions respectively, by decreasing the relative humidity of the first and second air streams before entering the body of grain 14. The relative humidity of the first and second streams is decreased by known methods, typically by increasing the temperature of the first and second streams of air, from an ambient temperature to a predetermined higher temperature. For this purpose, first and second burners, solar heaters or electrical elements (not shown) may be utilized to supply heat to first and second heat exchangers respectively.

Once the average moisture content of the body of grain 14 reaches the predetermined moisture content, at least a portion of the body of grain may be unloaded from the bottom of the silo 10. During the unloading of this portion of the grain, the first and second layers (54 and 56) becomes blended or mixed, so that the unloaded grain has a relatively uniformly distributed moisture content which is very close to the predetermined moisture content. Therefore, during the mixing as aforementioned, grain particles of the first layer 54 and grain particles of the second layer 56 become mixed so as to form a mixture of particles, the average moisture content of which falls within a range close to the predetermined moisture content. The mixing of the first and second layers (54, 56) occurs automatically during the unloading, and is enhanced by the conical shape of the bottom portion 40. Alternative to directly unloading the grain to thereby blend the first and second layers (54 and 56), the first and second streams of air may be conditioned to a third and fourth condition respectively, that would result in the aeration of the body of grain 14. The relative humidity of the first and second streams of air conditioned in the third and fourth conditions respectively, is higher than the relative humidity of the first and second streams of air conditioned in the first and second conditions respectively. During this aeration step, the moisture contents of the different layers of grain within the container are averaged out (in other words, the moisture contents of the "dry" layers increase while the moisture contents of the "wet" layers decrease). If this aeration step is allowed to endure long enough, the moisture content of the whole body of grain 14 will be relatively uniformly distributed and will be around the predetermined moisture content. At any time during the aeration step can grain be unloaded through the outlet for grain 41 , and the mixing as aforementioned will take place.

The first and second air streams are conditioned to the third and fourth conditions respectively, by increasing the relative humidity of the first and second air streams above the relative humidity of the first and second conditions. This is typically achieved by decreasing the amount of heat added to the first and second streams of air or allowing the first and second streams of air to remain at ambient temperature before entering the grain (in other words, by adding no additional heat to the air before entering the body of grain).

As was stated above, the energy related to the aeration of the grain is a function of the path length that the air has to travel along and the mass flow rate of the air travelling through the grain. Furthermore, the efficiency of the aeration or drying of the grain is influenced by the relative humidity (which is a measure of the level of saturation) of the air flowing through the body of grain 14.

There are therefore functional limits to the amount of air that can be provided through a body of grain 14 stored in a silo 10.

By providing more than one air front propagating through the body of grain towards the outlet, the average path length of the air through the body of grain is shortened and the average mass flow rate of the air through the grain is reduced, resulting in lower energy input requirements.

Furthermore, by allowing more than one drying front to propagate through the body of grain 14 and allowing certain layers of the grain to become

"over-dried" (according to industry standards) whilst others remain "wet" (or "under-dried", according to industry standards), the predetermined average moisture content of the body of grain 14 is reached much earlier than when a single drying front is allowed to propagate through the complete body of grain, that is utilised to dry the whole body of grain to the predetermined moisture content. Also, by either unloading and thereby mixing the different layers of "dry" and "wet" grain, or alternatively or additionally aerating the body of grain after the average moisture content of the body of grain reaches the predetermined moisture content, the moisture content of the body of grain 14 becomes relatively evenly and consistently distributed throughout the whole body of grain 14. Since the first and second inlets (22, 24) are located at different vertical levels in the container 12 (owing to the second distance 30 exceeding the first 28), the efficiency of the system is not influenced by the level to which the container 12 is filled with grain. Until the body of grain is removed from the container, a portion of the body of grain separates the inlets from the outlet (when a perforated floor is utilised). The inlets and outlet are therefore not in direct flow communication, and the mass flow rate from the inlets first need to pass through a portion of the body of grain before exiting through the outlet. In cases where the container 12 has a perforated wall 20, a further air front propagates from the wall 20 towards the outlet 26. The substantially rigid wall may be manufactured from metal such as steel plates. Vertical support structures (not shown) may be used to impart rigidity to the silo 10. In an alternative example embodiment, as shown in figures 4 to 7, the silo

10 is again provided with a first and second inlet (22, 24). The first and second inlets are arranged so that at least a portion of the inlets are in contact with grain, when the container 12 is filled with grain. A suction apparatus (not shown) is arranged in fluid flow communication with the outlet 26, to create a pressure within the grain that is below the atmospheric pressure. The outlet 26 is similar as disclosed above. Since air is sucked towards the outlet 26, aeration and/or drying of grain can commence as soon as the outlet is covered with grain, and therefore before the silo is filled with grain.

In one example, the first and second inlets (22, 24) may extend substantially horizontally across the container, and may therefore comprise first and second perforated inlet ducts that project into the body of grain 14 contained within the silo, so that at least a portion of the inlet ducts may be surrounded by the body of grain 14.

In this example, the first and second perforated inlet ducts (22, 24) extend from a first portion of the wall 20 towards an opposing portion of the wall 20. It will be understood that the first and second inlet ducts (22,24) may extend all the way across the container, or alternatively project into the container for a predetermined distance. However, generally all the inlet ducts are arranged to be symmetrical about a longitudinal plane 62 running through the centre of the silo 10. It is therefore possible that the first inlet duct 22 is constituted of two opposing first inlet ducts (not shown) extending less than 50% towards the opposing portion of the wall 20, the two first inlet ducts being arranged symmetrically about the plane 62. The horizontally extending ducts are particularly useful where the profile

42 of the body of grain stored within the silo is flat.

Also, it should be noted that the pressure within each inlet duct is relatively constant along the length of the inlet duct, which means that the streams of air throughout the width of the container are relatively constant. This advantageously enables aerating grain located towards the middle of the container.

By varying the size of the perforations along the length of the inlet duct, the profile of the air fronts (44, 46) can be altered to better accord with the profile 42 of the grain or with a profile of the bottom end of the container. In a further example (as is shown in figures 4 to 7) the first and second inlet ducts (22, 24) are arranged substantially vertically within the container and therefore extend between the bottom end 16 and the top end 18 of the container 12.

The substantially vertically extending inlet ducts are arranged radially about a vertical centre line 68 which coincides with the longitudinal plane 62. The first inlet duct 22 is arranged a first radial distance 70 from the centre line 68, while the second inlet duct 24 is arranged a second radial distance 72 from the centre line 68. The first and second radial distances

(70, 72) are equal. Alternatively, the second radial distance 72 may exceed the first radial distance 70.

Figures 4 and 5 furthermore shows a plurality of further vertical inlet ducts 74 all or any of which may be included or excluded in the silo 10, depending on the need therefore.

As shown in figure 4, the vertical inlet ducts have openings 76 that, in use, extends out of the body of grain 14, so that each inlet duct is arranged in fluid flow communication with an outside atmosphere 36.

As is shown in figures 6 and 7, the vertically extending inlets may be fixed to the substantially rigid wall 20. The inlets fixed to the substantially rigid wall have openings through the wall 20 to the atmosphere 36. Alternatively (not shown), the first and second inlets may comprise vertically extending perforated portions formed in the substantially rigid wall 20. The silo 10 shown in figures 6 and 7 is used to dry the body of grain 14 stored therein. The first and second streams of air are again conditioned to the first and second conditions for the purpose of drying. Figure 7 shows a first and second drying front (80, 82) propagating towards the outlet 26. The first and second drying fronts propagate from along the length of the first and second inlets, substantially radially inwardly and in a direction towards the outlet. Again an "over-dried" layer 86 followed by an "under- dried layer" 88 is formed between the first inlet 22 and the outlet 26, while an "over-dried" layer 90 followed by an "under-dried layer" 92 is also formed between the second inlet 24 and the outlet 26. Again, the drying fronts are allowed to propagate towards the outlet until the average moisture content of the body of grain 14 reaches the predetermined moisture content, at which point, at least a portion of the grain may be unloaded to blend the "over-dried" and "under-dried" layers of grain as stated above, or the first and second streams of air may be conditioned to the third and fourth conditions to aerate the grain, to thereby average out the moisture content of the different layers, as stated above. The further inlets 74 are associated with further drying fronts 94, further layers of "over-dried" grain 96 and further layers of "under-dried" grain 98 as the first and second inlets (22, 24).

By arranging the inlets vertically, a resultant air front (not shown) flowing towards the outlet 26 increases in mass flow rate along the length of the container 12. This means that the resultant air front is consistently supplemented with unsaturated air. The arrangement also ensures that the average flow path length of air, and the air flow rate within the body of grain is lower than what it would have been, had the silo only comprised a single inlet.

The relative size and spacing of perforations of the various inlet ducts (22, 24, 74) may be varied along the length of said inlet ducts to vary the flow rate of the streams of air entering the body of grain 14 along the length of said ducts. In this way, the propagation of the resultant air front may be managed according to predetermined drying or aerating schemes.

A further example of a silo for storing a body of grain is generally designated by reference numeral 100 in figure 8. The silo 100 comprises at least one substantially rigid wall 102, a first end 104 and an opposing second end 106. The silo also comprises a first outlet 108 for air from the body of grain, a first inlet 1 10 for air into the silo 100 and a second inlet 1 12 for air into the silo 100. The first inlet 1 10 is spaced a first distance 1 14 from the outlet 108, in the direction of the first end 104, while the second inlet 1 12 is spaced a second distance 1 16 from the first inlet 1 10 in the direction of the first end 104. The first outlet 108 is the closest outlet to the both the first and second inlets (1 10, 1 12).

A means of providing a flow of air between the first and second inlets (1 10, 1 12) and the outlet 108 is provided, preferably in the form of a suction pump connected to the outlet 108. In use, the air pressure within the first and second inlets (1 10, 1 12) is maintained within a predetermined threshold. The threshold is maintained by either arranging the first and second inlets (1 10, 1 12) such that the second distance 1 16 exceeds the first distance 1 14 or by providing flow regulating means (in the form of valves or orifices (not shown)) in the inlets. A third and fourth inlet (1 18, 120) are furthermore provided between the outlet 108 and the first end 104. The third inlet 1 18 is spaced a third distance 122 from the second inlet 1 12 and the fourth inlet 120 is spaced a fourth distance 124 from the third inlet 1 18. The pressure within the third and fourth inlets (1 18, 120) are maintained within the predetermined threshold in similar fashion as the first and second inlets (1 10, 1 12). The first to fourth inlets (1 10, 1 12, 1 18 and 120) constitute a first set of inlets 126. The silo 100 further comprises a second set of inlets 128, arranged symmetrically about the outlet 108. Each inlet and outlet comprise a perforated duct projecting into the body of grain in use. Furthermore, each inlet and outlet may comprise a set of two spaced apart perforated ducts.

The outlet 108, first set of inlets 126 and second set of inlets 128 constitutes a first arrangement 130. The silo 100 may be provided with further arrangements, similar to the first arrangement 130, should the need therefore arise. By in use maintaining the pressure within each inlet within a predetermined threshold, the drying of the body of grain can be better controlled.

The silo may be a conventional silo with substantially rigid side walls, such as concrete or steel side walls, or may alternatively be a bunker wherein the grain is covered with a flexible sheet. The inlets and outlets may project into the body of grain through any of a side wall, a top or a bottom of the silo.

It will be appreciated by those skilled in the art that the invention is not limited to the precise details as described herein and that many variations are possible without departing from the scope and spirit of the claimed invention.

It is foreseen that the risk of grain entrapment may be mitigated when using the silo 10, since entry into the silo to close valves will not be required.

Although only certain embodiments of the invention have been described herein, it will be appreciated by those skilled in the art that other modifications, variations, and possibilities of the invention are possible without departing from the spirit and scope of the claimed invention. Such modifications, variations and possibilities are therefore to be considered as falling within the spirit and scope of the invention and hence forming part of the invention as herein described and/or exemplified.

For instance, further inlets that extend vertically along the periphery of the container may be provided, to facilitate further drying fronts to propagate towards the outlet. Generally, the more inlets are provided, the quicker the average moisture content of the body of grain will be reached, and the better the blending of the grain will be when unloading the grain from the silo. Furthermore, the outlet of any of the embodiments provided and exemplified herein may be located towards the top end 1 8.

Also, the ends of all of the inlets (such as ends 38) may all be provided in fluid flow communication via an inlet manifold (not shown). A single heat source and heat exchanger may therefore be provided in fluid flow communication with the inlet manifold, for conditioning the air before entering the container through any or all of the inlets. A pressure above atmospheric pressure may be maintained within the inlet manifold, by external means (not shown).

The description above is presented in the cause of providing what is believed to be the most useful and readily understandable description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The words used should therefore be interpreted as words of description rather than words of limitation.

Claims

1 . A method of drying a body of grain from an initial moisture content to a predetermined average moisture content, the method comprising the steps of:

- storing the body of grain in a silo;

A method of drying a body of grain according to claim 1 , wherein a pressure within the silo is maintained below an atmospheric pressure outside of the silo to facilitate flow of the first and second streams of air into the first and second inlets respectively, wherein a pump is utilized to suck air from the outlet to thereby maintain the pressure within the silo below the atmospheric pressure.

A method of drying a body of grain according to any one of claims 1 and 2, further comprising conditioning the first and second streams of air to a first and second condition respectively, to facilitate propagation of the first and second drying fronts towards the outlet.

A method of drying a body of grain according to any one of the preceding claims, further comprising, after the predetermined average moisture content is obtained, aerating the body of grain, to average out the first to fourth moisture contents of the first to fourth layers towards the predetermined average moisture content.

A method of drying a body of grain according to claim 4, comprising conditioning the first and second streams of air to a third and fourth condition respectively, to thereby cause the grain to be aerated by the first and second streams of air.

A method of drying a body of grain according to any one of the preceding claims, further comprising unloading at least a portion of the body of grain from a bottom of the container, such that at least some of the first and second layers of grain become mixed, so that the portion of the body of grain that has been unloaded from the silo has a relatively uniformly distributed average moisture content which is in the region of the predetermined average moisture content.

7. A method of drying a body of grain according to claim 3, wherein the first and second streams of air are conditioned to the first and second conditions respectively, by decreasing the relative humidity of the first and second streams of air before being provided into the silo.

A method of drying a body of grain according to claim 7, wherein the relative humidity of the first and second streams of air is decreased by increasing the temperature of the first and second streams of air from an ambient temperature to a predetermined higher temperature.

9. A method of drying a body of grain according to claim 8, wherein a first and second heat exchanger is used to increase the temperature of the first and second streams of air to the predetermined higher temperature, and wherein one of a) first and second burners; b) first and second heating elements; and c) first and second solar heaters, are utilized to provide heat to the first and second heat exchangers.

10. A method of drying a body of grain according to claim 5, wherein the first stream of air is conditioned to the third condition, by increasing the relative humidity of the first stream to a relative humidity which is above the relative humidity of the first stream of air when conditioned in the first condition, and wherein the second stream of air is conditioned to the fourth condition, by increasing the relative humidity of the second stream to a relative humidity which is above the relative humidity of the second stream when conditioned in the second condition.

1 1 . A silo for a body of grain, the silo comprising:

12. A silo according to claim 1 1 , wherein the first inlet is provided at a first vertical distance from the outlet, and the second inlet is provided at a second vertical distance from the outlet, wherein the second distance exceeds the first distance.

13. A silo according to claim any one of claims 1 1 and 12, wherein each of the first and second inlets is in the form of a perforated portion of the wall of the container.

14. A silo according to claim any one of claims 1 1 and 12, wherein each of the first and second inlets comprise a duct extending from the substantially rigid wall at least partially into the container, the duct comprising perforations arranged to operatively allow air within the duct to enter into the container.

15. A silo according to claim any one claims 1 1 to 14, wherein each of the first and second inlets extend substantially horizontally at least partially along a periphery of the container.

16. A silo according to any one of claims 1 1 to 15, wherein each of the first and second inlets extend all the way along the periphery of the container.

17. A silo according to any one of claims 1 1 to 16, wherein a bottom portion of the container converges towards the bottom end thereof.

18. A silo according to any one of claims 17, wherein the container is substantially cylindrical and wherein the bottom portion of the container is substantially conical.

19. A silo according to any one of claims 1 1 to 18, wherein the outlet is in the form of a perforated floor.

20. A silo according to any one of claims 1 1 to 18, wherein the outlet comprises a perforated duct extending substantially vertically proximate the bottom end of the container in a direction towards the top end thereof.

21 . A silo according to any one of claims 1 1 to 20, wherein the outlet is provided in fluid flow communication with a pump for operatively providing suction to the outlet.

22. A silo according to any one of claims 1 1 to 21 , wherein the substantially rigid wall is formed from metallic plates, and wherein vertical support structures are provided for lending rigidity to the wall.

23. A silo for a body of grain, the silo comprising:

- a first inlet for air into the container, arranged so that in use, a portion of the first inlet is in contact with grain;

- a second inlet for air into the container, arranged so that in use, a portion of the second inlet is in contact with grain;

- an outlet for air from the container; and

24. A silo according to claim 23, wherein the first inlet for air projects into the container so that in use, a portion of the first inlet inside the container is surrounded by grain, and wherein the second inlet for air projects into the container, so that in use, a portion of the second inlet inside the container is surrounded by grain.

25. A silo according to claim 24, wherein the first and second inlets comprise first and second inlet ducts extending substantially horizontally from the substantially rigid wall into the container.

26. A silo according to claim 25, wherein the first inlet duct is arranged a first distance from the outlet and wherein second inlet duct is arranged a second distance from the outlet, in a direction of the first inlet duct, the second distance exceeding the first.

27. A silo according to any one of claims 25 and 26, wherein each of the first and second inlet ducts extend from one portion of the wall to an opposing portion of wall and through a centre of the container.

28. A silo according to any one of claims 25 and 26, wherein the first inlet comprises at least two perforated inlet ducts located at the first distance from the outlet and projecting partially across the container, and wherein the second inlet comprises at least two perforated inlet ducts located at the second distance from the outlet and projecting partially across the container.

29. A silo according to claim 23, wherein the first and second inlets extend substantially vertically within the container between the top end and the bottom end of the container.

30. A silo according to claim 29, wherein the first and second inlets comprise perforated portions in the substantially rigid wall of the container, that extend substantially vertically at least partially along the container.

31 . A silo according to claim 29, wherein the first and second inlets comprise first and second perforated ducts that extend substantially vertically within the container at least partially along the container.

32. A silo according to claim 31 , wherein the first and second inlet ducts are fixed to the substantially rigid wall.

33. A silo according to claim 31 , wherein the first and second inlet ducts are spaced a first and second radial distance from a vertical centre line of the container, and wherein the configuration is one of: a) such that the first and second radial distances are equal; and b) such that the second radial distance exceeds the first radial distance. A method for storing and aerating a body of grain, the method comprising:

- providing a second stream of air at a second mass flow rate through a second inlet into the body of grain so that the body of grain surrounds at least a portion of the second inlet, thereby propagating a second air front within the grain towards the outlet, the second inlet being spaced a second distance from the outlet.