WO1999028578A1

WO1999028578A1 - Grain storage silo

Info

Publication number: WO1999028578A1
Application number: PCT/IL1998/000551
Authority: WO
Inventors: Shlomo Navarro; Ezra Donahaye; Miriam Rindner; Avihu Azrieli
Original assignee: State Of Israel - Ministry Of Agriculture
Priority date: 1997-12-04
Filing date: 1998-11-11
Publication date: 1999-06-10
Also published as: IL122456A; IL122456A0

Abstract

A grain storage silo (10) including a sealable flexible liner (14) adapted for storing therein grain, a rigid sheath (26) peripherally placed around the liner (14), a sealable loading sleeve (16) extending from a top surface of the liner (14), the loading sleeve (16) being in fluid communication with the liner (14), and a sealable unloading sleeve (22) extending from a bottom surface of the liner (14), the unloading sleeve (22) being in fluid communication with the liner (14). The loading sleeve (16) is preferably generally conical and collapsible, and preferably includes a strap (18) which can be secured against the loading sleeve (16) when the loading sleeve (16) is collapsed to substantially seal the loading sleeve (16).

Description

GRAIN STORAGE SILO

FIELD OF THE INVENTION

The present invention relates generally to a sealed silo and a storage method for conserving small quantities of grain without the use of toxic chemicals. BACKGROUND OF THE INVENTION

Throughout the developing world, the on-farm storage of harvested grain by small-scale farmers is critically important in providing food security for rural communities. In the past, traditional storage structures provided some protection against storage losses, particularly by insects and rodents, though annual losses at the village level which are estimated to run at between 5 and 10% were usually considered as inevitable. Attempts to reduce these losses through the introduction of modern storage technologies have consistently failed being either socio-economically unacceptable, or inappropriate to local climatic conditions and agrotechnical practices.

Hermetic grain silos are known. Applicant/assignee's Israel Patent 87301 discloses a reusable, portable container for storing sacks of dry grain comprising a frameless, foldable container formed of a flexible material (such as PVC) which is resistant to ultraviolet radiation and which is substantially impermeable to gas. The container has an airtight seal that comprises a closed loop of interlocking plastic profiles. The liner of the container is extremely durable under a large range of weather conditions and is resistant to solar radiation. Although the hermetic principle of grain storage is widely known and has been applied in larger structures, such as in the abovementioned Israel Patent 87301, past experience has shown that it is extremely difficult to apply this principle to the storage of small quantities of grain. This is because the smaller the structure, the larger the ratio of surface area to volume, and consequently the greater the danger of air infiltrating into the structure due to partial permeability of the structure, leaks, and incomplete sealing.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved grain silo which is particularly useful as a sealed structure for grain storage by small-scale farmers.

The storage structure of the present invention has the following characteristics which are essential pre-conditions to acceptance by farmers throughout the developing world: a) Design basically similar to those of many traditional storage structures (cylindrical container raised above ground on a platform, having an upper loading port and a lower spout to remove the grain). b) Storage capacity is appropriate to harvest volumes of small-scale and subsistence farmers. c) Certain elements of the structure (that do not form part of the basic invention) are usually freely obtainable locally (raised platform, straw roof) and contribute to the acceptability of the structure by farming societies. d) Minimal and affordable price with an anticipated life-time of several years. e) The method of grain preservation is environmentally sound, user friendly, and does not require application of chemical pesticides.

A novel and inventive feature of the structure is that the grain is contained within a sealed flexible plastic liner, while rigidity is obtained using a rigid, preferably polypropylene (PP), sheath. The structure contains unique features to enable the grain to be loaded and unloaded, with the possibility of periodic removal of limited quantities, after which the openings are sealed. It is thus possible to maintain the storability of the grain, without affecting significantly the principle of gas-tightness needed for control of insect pests. This obviates the need for employing residual insecticides and fumigants with the accompanying hazards they pose to users and the environment.

There is thus provided in accordance with a preferred embodiment of the present invention a grain storage silo including a sealable flexible liner adapted for storing therein grain, a rigid sheath peripherally placed around the liner, a sealable loading sleeve extending from a top surface of the liner, the loading sleeve being in fluid communication with the liner, and a sealable unloading sleeve extending from a bottom surface of the liner, the unloading sleeve being in fluid communication with the liner. The loading sleeve is preferably generally conical and collapsible, and preferably includes a strap which can be secured against the loading sleeve when the loading sleeve is collapsed to substantially seal the loading sleeve. In accordance with a preferred embodiment of the present invention a sealing cap is provided which seals the unloading sleeve. The sealing cap is preferably constructed of polyvinyl chloride (PVC). The rigid sheath is preferably constructed of white polypropylene (PP), and the liner is preferably constructed from a material based on a PVC formulation.

Further in accordance with a preferred embodiment of the present invention a plurality of support struts are spaced around and attached to the sheath.

Additionally in accordance with a preferred embodiment of the present invention there is provided apparatus for maintaining tautness of the flexible liner during unloading thereof. Still further in accordance with a preferred embodiment of the present invention a floor is placed beneath the liner, formed with a hole through which protrudes the unloading sleeve.

Additionally in accordance with a preferred embodiment of the present invention an upper cover is placed upon the loading sleeve when the loading sleeve is collapsed. The floor and/or the upper cover are preferably constructed of PP. A layer of insulating material may be placed upon the silo.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

Figs. 1A and IB are simplified side and top view illustrations, respectively, of a grain storage silo constructed and operative in accordance with a preferred embodiment of the present invention;

Fig. 2 is a graphical illustration of carbon dioxide and oxygen concentrations in the silo of Figs. 1A and IB infested with three stored-product insect species;

Figs. 3 A and 3B are simplified illustrations of apparatus for maintaining tautness of a bag of the silo of Figs. 1A and IB, in accordance with a preferred embodiment of the present invention, respectively when the bag is full and partially emptied; and

Fig. 4 is a simplified pictorial illustration of a grain storage silo constructed and operative in accordance with another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Reference is now made to Figs. 1A and IB which illustrate a grain storage silo 10 constructed and operative in accordance with a preferred embodiment of the present invention. Grain storage silo 10 preferably includes a bag 12 of typically 500 kg nominal capacity, for example, and is fabricated in a form intended to hold the harvested grain. Bag 12 preferably comprises a cylindrical liner 14 equipped with an upper, generally conical, collapsible loading sleeve 16 extending therefrom for loading. Liner 14 is preferably constructed from a material based on a PVC formulation, typically, but not necessarily, 1.1 m high and 0.9 m in diameter, thereby having a volume of approximately 700 liters.

A preferred PVC formulation is as described in applicant/assignee's Israel Patent

87301, namely, a food grade PVC which has physical properties as listed in the non-limiting example set forth below: • Permitted water vapor permeation of about 8 g/m² per 24 hours at 38°C and relative humidity of 90%.

• Permitted O₂ gas permeation of about 407 ml/m² per 24 hours.

• Permitted CO gas permeation of about 2355 ml/m² per 24 hours. • Minimum tensile strength according to ASTM (American Standard Test Methods) D-882, lengthwise: 200 kg/cm , crosswise: 185 kg/cm².

• Elongation at break according to ASTM D-882, length 290%, transverse 305%.

• Tear propagation according to ASTM D-1004, angle tear test, length: 75 kg/cm, transverse: 71.6 kg/cm. • Shrinkage at 0°C compared to 35°C is 0.9%.

• Dimensional changes at 100 °C according to ASTM D-1204 in 15 minutes, length: -1.19%, transverse: +0.50%.

• Coefficient of linear expansion between 0.007 and 0.025% per °C.

• Weight per unit area according to ASTM D-374, 1 140 g/m² . • Impact cold crack according to BS 3424 is at -25°C.

• Cold bend temperature test according to BS 2782 Method 104A, passed at -50°C.

• Volatile loss at 100 °C according to ASTM D-1023, Method A 1.93%, Method B 1.56%.

Loading sleeve 16 typically, but not necessarily, has an upper diameter of 300 mm and a lower diameter of 200 mm at the point of entry into liner 14. Loading sleeve 16 is preferably provided with a welded strap 18 and a corrosion-resistant buckle 20 (shown for the sake of clarity only in Fig. 1A) to enable loading sleeve 16 to be rolled up when not in use and firmly sealed by applying pressure by tightening strap 18.

The bottom of bag 12 is equipped with a generally cylindrical, flexible, unloading sleeve 22, typically, but not necessarily, 50 mm in diameter, for unloading grain. Unloading sleeve 22 is preferably plugged by a cap 24, such as a durable PVC screw-on cap. Bag 12 is preferably supported inside a rigid sheath 26, preferably constructed of white polypropylene (PP). Sheath 26 is typically, but not necessarily, constructed of a board 1.15 m high, 5.6 m long and 1 mm thick, which is curved into a cylinder, thereby forming the sheath surrounding the vertical sides of flexible bag 12. To provide stability to the structure, a plurality of wooden struts 28 are equidistantly spaced around the outside of sheath 26. As particularly seen in Fig. IB, four struts 28 may be provided, each of which may be typically, but not necessarily, 1.15 m long, 50 mm wide and 50 mm thick. Struts 28 are preferably connected together and held in place by means of steel cables 30. Cables 30, typically three in number, may be positioned at heights of

300 mm, 550 mm and 800 mm, for example, above the base of bag 12. Each cable 30 is preferably passed or threaded through holes in struts 28 and then joined to itself by means of an adjustable steel clamp to form a continuous band.

A platform 32 is preferably provided (shown for the sake of clarity only in Fig.

1A) at least 1 m above the ground to protect silo 10 from rodent attack. Bag 12 may thus be unloaded from beneath platform 32. Platform 32 may be constructed from locally available material or may be provided with bag 12, but is not essential to the present invention. Platform legs 34 should be provided with rodent barriers (not shown) about 45 cm above the ground to prevent rodents from climbing on to the platform. Platform 32 is preferably at least 1 meter square, and a 100 mm diameter hole is preferably formed at its center through which unloading sleeve 22 is inserted from above.

Before grain is loaded into bag 12, two semi-circular plates 36 of rigid PP are placed on platform 32 beneath bag 12 to form a floor of silo 10. Plates 36 are typically, but not necessarily, 900 mm in diameter with a 100 mm diameter central cut-out to allow for passage of unloading sleeve 22. Bag 12 is then placed on the floor of plates 36, unloading sleeve 22 is passed through the hole in platform 32 and cap 24 is fastened to sleeve 22.

Grain may be easily introduced through loading sleeve 16 until bag 12 is filled to a height of about 20 cm. Sheath 26 is placed in position, as described above, and loading is then resumed. Tension of cables 30 may be adjusted, if required, to obtain a stable structure.

Bag 12 need not be filled completely, but when the desired amount of grain has

- been loaded, the upper surface of the grain should be flattened and loading sleeve 16 should be rolled up and securely sealed with strap 18 and buckle 20. Loading sleeve 16 is then placed flat over the top of bag 12, and the upper surface of bag 12 is then preferably covered with an additional two semi-circular plates of rigid PP.

To reduce the effect of solar radiation on the grain, the top of bag 12 may be covered with a layer of insulating material such as straw. This is best done by placing a conical shaped straw roof over the top of bag 12, which may be held in place with an appropriate attachment to sheath 26. Other roofing methods used in traditional storage structures may also be used.

Grain may be unloaded in small quantities at intervals or all of bag 12 may be unloaded in one operation. Unloading is carried out simply by opening cap 24 and permitting the grain to flow into a container held beneath platform 32. To arrest the flow of grain, unloading sleeve 22 should be constricted by hand pressure above cap 24 (typically about 10 cm), leaving a portion of sleeve 22 below the constriction empty so that cap 24 can be tightened into position. Because loading sleeve 16 remains sealed and bag 12 decreases in volume during emptying, there is consequently no tendency for ingress of air when grain is removed and the modified atmosphere remains stable.

It is preferable to keep bag 12 taut during unloading to ensure proper emptying of bag 12. Reference is now made additionally to Figs. 3 A and 3B which illustrate a preferred apparatus for maintaining tautness of bag 12 in accordance with a preferred embodiment of the present invention. Loading sleeve 16 is preferably rolled around a pipe 37 and securely tightened with strap 18 and buckle 20. Pipe 37 may be typically, but not necessarily, 40 cm in length and 5 cm in diameter. A horizontal cross strut 38 is preferably slipped through pipe 37 and is positioned across the top of silo 10. Cross strut 38 is supported by and/or fastened to one or more of struts 28. As grain is removed from below and the grain level drops, the top of bag 12 remains suspended beneath cross strut 38, but collapses inwards from the sides so that the volume at the top of bag 12 remains minimal, as seen in Fig. 3B. Bag 12 takes on the general shape of an inverted cone, which has the advantage, inter alia, of preventing accumulation of rain-water on the top of the bag.

Grain within bag 12 is preserved and protected from damage and losses from insect infestations due to the fact that the gas tightness of liner 14 is enhanced by both the low permeability of the specially formulated PVC and the high density PP that forms a laminate to the walls, floor and top of bag 12. Under these conditions any respiratory metabolism by insects in the stored product, causes a reduction in concentration of oxygen in the intergranular air-spaces and an increase in the concentration of carbon dioxide, until an oxygen depleted and carbon dioxide enhanced atmosphere is reached that is lethal to the insects.

The unique features of the present invention enable a level of sealing to be provided that fill the requirements for hermetic storage and provide a method for storing grain that is affordable to the small scale farmer in the developing world.

Experimental Evidence A series of non-public experimental trials were carried out in Israel, to verify whether the presence of a stored-product insect infestation in the grain does indeed generate an atmosphere sufficiently lethal to kill the insects, and whether the grain can be safely stored without intervention with insecticides as disclosed above. The findings in the first trial are given below:

Methodology

Silo 10 was set up and filled with maize. The maize was stored over the summer of 1997 for a period of two months, as described hereinabove. Infestation:

To obtain an in initial infestation, 1,000 adults of the rice weevil Si tophi lus oryzae, 1,000 adults of the lesser grain borer Rhyzopertha dominica and 1,000 adults of the flour beetle Tribolium castaneum were taken from laboratory cultures and added to the grain from the top, thereby introducing an infestation level of 6 insects per kg. Temperature, humidity and atmospheric composition in the silo:

A temperature and humidity logger was inserted into the grain to enable hourly readings of temperature and relative humidity to be recorded at the bottom of the bulk and the top (above the grain surface layer). A polyethylene tube was inserted through the upper sleeve opening into the grain to enable daily readings of gas composition to be taken. Ambient conditions during the trial were recorded using a weather monitor. Results Gas composition within the silo:

Daily readings of carbon dioxide (CO₂) and oxygen (O₂) concentrations are given in Fig. 2. It can be seen that there was a rapid drop in O₂ concentration down to 0.2% within 13 days coupled with an increase in CO₂ concentration to 12%. For the following 54 days both O₂ and CO₂ concentrations remained stable at these levels. Upon removal of the grain at the end of this period, sampling revealed that all insects were dead. On 4 August 97, when the bag was opened, the moisture content of the grain at the top of the bulk was found to be 14.7%. This indicated that there had been slight moisture migration towards the surface and that the low O₂ contents maintained over the past two months had been due to initial insect respiration followed by limited respiration of microorganisms in the grain. The fact that CO₂ concentrations did not rise above 12% is indicative that mold development was limited to the surface layer, and possibly only at the point of contact between the grain and the side walls. Grain moisture content To verify whether gas exchange within bag 12 was being produced by respiration of insects or microorganisms, three grain samples were removed on 14 August 97. Moisture content (MC) analysis of these was as follows: MC (%) ERH (Equilibrium relative humidity)

Top center 12.9 67.8

Middle center 12.6 66.3 bottom center 12.6 60.9 This clearly indicates that the grain had remained at safe moisture contents that would not permit respiration by microorganisms and that if moisture migration had occurred it was not in the central region of the bag. Temperature and humidity changes

The temperature in the silo ranged between 25 and 34 C, which falls within the optimum range of temperatures for development of all three insect species.

During storage, relative humidities of the interstitial air were stable in the bottom section of the bag. In contrast, at the top of the bag, they rose to about 85% towards the end of the trial. This was attributed to strong diurnal temperature fluctuations at the walls of the bag due to the fact that in the first prototype, the rigid wall was constructed of black polyethylene. To overcome this problem, the following prototypes were constructed of white polypropylene. Thus the first initial trial clearly revealed the capability of silo 10 to retain- the modified atmosphere necessary to control insect infestations, and thereby enable safe storage of grain for a prolonged period.

Reference is now made to Fig. 4 which illustrates a grain storage silo 40 constructed and operative in accordance with a preferred embodiment of the present invention. Silo 40 is particularly useful for the transport and storage of small quantities of grain in food aid operations. Silo 40 preferably includes a plastic bag 42 of 1 m³ capacity forming a cube with each side 1 m long. Bag 42 includes a top loading sleeve 44 and a bottom unloading sleeve 46. Sleeves 44 and 46 may be constructed substantially similar to sleeves 16 and 22 described hereinabove. Straps 48 are provided for lifting and loading bag 42, such as by means of a fork lift or crane, on to trucks or freight cars at a point of dispatch and for offloading onto platforms at a point of delivery and usage. The structure of silo 40 is durable and convenient for short scale storage under emergency situations.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes combinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.

Claims

C L A I M SWhat is claimed is:

1. A grain storage silo (10) comprising: a sealable flexible liner (14) adapted for storing therein grain; a rigid sheath (26) peripherally placed around said liner (14); a sealable loading sleeve (16) extending from a top surface of said liner (14), said loading sleeve (16) being in fluid communication with said liner (14); and a sealable unloading sleeve (22) extending from a bottom surface of said liner

(14), said unloading sleeve (22) being in fluid communication with said liner (14).

2. A silo (10) according to claim 1, wherein said loading sleeve (16) is collapsible.

3. A silo (10) according to claim 2, wherein said loading sleeve (16) comprises a strap (18) which can be secured against said loading sleeve (16) when said loading sleeve (16) is collapsed to substantially seal said loading sleeve (16).

4. A silo (10) according to claim 1, wherein said loading sleeve (16) is generally conical.

5. A silo (10) according to claim 1 further comprising a sealing cap (24) which seals said unloading sleeve (22).

6. A silo (10) according to claim 5 wherein said sealing cap (24) is constructed of polyvinyl chloride (PVC).

7. A silo (10) according to claim 1, wherein said rigid sheath (26) is constructed of white polypropylene (PP).

8. A silo (10) according to claim 1, wherein said liner (14) is constructed from a -material based on a PVC formulation.

9. A silo (10) according to claim 1 further comprising a plurality of support struts (28) spaced around and attached to said sheath (26).

10. A silo (10) according to claim 1 further comprising a floor beneath said liner (14) formed with a hole through which protrudes said unloading sleeve (22).

11. A silo (10) according to claim 2 further comprising an upper cover placed upon said loading sleeve (16) when said loading sleeve (16) is collapsed.

12. A silo (10) according to claim 10, wherein at least one of said floor and said upper cover is constructed of PP.

13. A silo (10) according to claim 1 further comprising a layer of insulating material placed upon said silo (10).

14. A silo (10) according to claim 1 further comprising apparatus (37, 38) for maintaining tautness of said flexible liner (14) during unloading thereof.

15. A silo (10) according to claim 1 further comprising lifting straps (48).