FIELD OF THE INVENTION

The present invention relates to silos suitable for storing bulk material, such as PET flakes obtained by diminution of PET bottles, e.g. by shredding PET bottles, and a method to store and extract such bulk material from such silos.

BACKGROUND

PET flakes generated by shredding recycled PET bottles are known. A disadvantage of such flakes is the possible inconsistency in or absence of uniformity of its quality, e.g. varying dimensions, crystallinity, and specific weight.

From e.g. EP2748358B1, such flakes are known as raw material for BCF filament yams, fit for making broadloom carpets. An important aspect in the production of BCF filament yarns is ensuring the consistency of quality of the raw material used to feed the extrusion and spinning process.

Also, in various other storage silos fit for storing bulk material, inconsistency of the composition of the discharged bulk material may occur. This typically occurs when the bulk material comprises particles with varying properties, like varying dimensions, varying specific weight, and/or other varying physical properties. A kind of demixing can occur in such silos.

SUMMARY

In the production of BCF from PET flakes, the quality of the end product is often affected by the quality of the PET flakes fed into the extruder that is used to melt the flakes into molten recycled PET. The inventors found out that one of the key issues in variation of the PET flakes fed, originates from the silos that the PET flakes were stored in and extracted from in order to feed the extruders. In one particular example, although the PET flakes were supplied to the silos as a substantially uniform stream of flakes, e.g., a mixture of flakes with varying individual properties but substantially uniform properties as a mixed stream, the extracted PET flake stream did not have such substantially uniform properties as a mixed stream. Thus, in this example, a kind of demixing was observed.

The inventors found that the silo, and the related methods of running the silo according to various embodiments of the invention, remedied this demixing effect, i.e., of PET flakes stored in a silo, to a large extent. According to a first aspect, a silo for storing bulk material is provided, the silo comprising: o a container defining an inner space,

o at least one supply opening for receiving bulk material being provided near or at the upper side of the container,

o an insert located in said inner space, the insert having the shape of a capped cone with a top side having a top rim and a bottom side having a bottom rim, wherein:

^■ the top side of the insert is oriented towards the upper side of the

container,

^■ the bottom rim of the insert is mechanically coupled to the inner surface of the container thereby defining within the container an upper inner space above the insert and a lower inner space below the insert,

^■ the insert has one or more openings, such as slits, along its bottom rim for allowing bulk material to pass from the upper inner space to the lower inner space;

o a first group of discharge openings comprising at least one discharge opening, said openings of said first group of discharge openings being provided near or at the lower side of the container in the surface of the container for discharging bulk material from the lower inner space, wherein the top rim is coupled to a second group of discharge openings comprising at least one discharge opening for discharging bulk material from the upper inner space,

o a recirculation system coupled to the discharge openings of one of the first and second group of discharge openings, for transporting bulk material from said discharge openings to said supply opening, and

o an extraction system coupled to the discharge openings of the other of the first and second group of discharge openings for extracting bulk material towards the exterior of the silo.

According to some embodiments, the recirculation system may be coupled to the discharge openings of the first group of discharge openings, the extraction system being coupled to the discharge openings of the second group of discharge openings.

According to some embodiments, the recirculation system may be coupled to the discharge openings of the second group of discharge openings, the extraction system being coupled to the discharge openings of the first group of discharge openings.

According to some embodiments, the silo is a silo for storing PET flakes. For PET flakes, the recirculation system is preferably coupled to the discharge openings of the first group of discharge openings, the extraction system being coupled to the discharge openings of the second group of discharge openings.

PET as used herein refers to polyethylene terephthalate. The PET flakes refer to flakes mainly comprising polyethylene terephthalate, optionally further comprising other polymers or copolymers.

In particular embodiments, the container is open at its top side or is closed at its top side by means of a closing lid or cover.

According to various embodiments, the container may define the inner space by having an upper cylindrical part and a lower conical part.

The silo may have a hopper-like shape. The lower conical part is oriented such that the top of the conical shape is directed downwards.

According to various embodiments, the bottom rim may be mechanically coupled to the inner surface of the container at the transition between the upper cylindrical part and the lower conical part. As an alternative, the bottom rim may be mechanically coupled to the inner surface of the container at a position along the upper cylindrical part. In various embodiments, the distance between the transition between conical and cylindrical part and the mechanical coupling is between 0 and 1 meter.

According to various embodiments, the bottom rim may be mechanically coupled to the inner surface of the container at a position along the conical part.

Preferably, the mechanical coupling is positioned at a height along the axis of the conical part, which height is of between 10% and 75% of the total height of the conical shape of the conical part, such as between 25% and 60% (e.g. between 45% and 55%) wherein a height“being zero” along the axis of the conical part is the position at the transition between conical and cylindrical part.

In alternative embodiments, the bottom rim may be mechanically coupled to the inner surface of the conical part of the container, e.g., at a height along the axis of the conical part, which height is in the range of 25% to 75%, such as about 50% of the total height of the conical shape of the conical part.

According to various embodiments, the extraction system may comprise an extraction duct. Preferably, this duct is coupled to the at least one discharge openings of the first or second group of discharge openings, as the case may be. In particular embodiments, the extraction duct is coupled to the upper, top rim, i.e., the upper or top rim of the insert. This upper or top rim is in that case provided with one or more discharge openings of the second group of discharge openings. The upper rim may circumscribe the one discharge opening. The perimeter of this one discharge opening may coincide with the top or upper rim.

In various embodiments, the extraction duct intersects with the lower conical part of the container at the top of the conical shape of the conical lower part. The capped conical shape of the insert, the cylindrical and conical part of the silo, and the extraction duct may be coaxially mounted.

Alternatively, the extraction duct system comprises an extraction duct that passes through the surface of the conical part of the container at a position that is different from the top of the conical shape of the conical lower part.

In embodiments where the container defines the inner space by having an upper cylindrical part and a lower conical part, according to some embodiments, the cylindrical part may have a diameter in the range of 6 to 12 feet. More preferred, in various embodiments, the cylindrical part has a diameter in the range of 7 to 10 feet, such as 8 feet.

According to some embodiments, the silo may comprise a supply duct for supplying fresh bulk material, such as fresh PET flakes.

According to some embodiments, one discharge opening of the first group of discharge openings is provided at the top of the conical part of the container. In such embodiments, the conical part may have the shape of a capped cone, with the discharge opening being the rim at the top of this capped conical shape.

According to some embodiments, 2 or more (e.g., at least 3) discharge openings of the first group of discharge openings are provided, substantially equally spread along the circumference of the container. Most preferably these openings may be provided in the wall of the conical part of the container.

More preferred, in particular embodiments, the silo has 4 or more discharge openings in its first group of discharge openings, such as 4, 5, 6, 7, 9 or even 10 discharge openings. Preferably, each of these discharge openings is coupled to the recirculation system, e.g., by its own discharge duct.

Preferably, the supply opening for supplying the fresh bulk material, such as PET flakes, is situated at the top of the silo. Most preferably, this supply opening is provided in the lid or cover of the container, if the container has a lid or cover. The supply opening may be coaxial with the vertical axis of the container and/or coaxial with the axis of the capped cone shape of the insert.

In the alternative, the container is open at its upper side. The supply opening in such

embodiments may be defined by the upper rim of the container According to some embodiments, the silo may comprise at least a first supply opening coupled to the supply duct and one or more further supply openings being coupled to the one or more discharge openings.

Optionally, each discharge opening of the group of discharge openings coupled to the recirculation system is coupled to its own supply opening such that the bulk material, such as PET flakes, from this discharge opening is transported to this one supply opening, thereby recirculating the bulk material, such as PET flakes.

According to some embodiments, the discharge openings of the group of discharge openings coupled to the recirculation system may be coupled to said at least one supply opening by means of a bucket conveyor system.

According to some embodiments, the volume of the inner space above the insert may be more than 10 times the volume of the inner space below the insert.

Preferably, the volume of the inner space above the insert is more than 25 times, more than 50 times, or even more than 100 times the volume of the inner space below the insert.

According to some embodiments, the openings along the bottom rim of the insert may have a total surface of between 4 and 15 feet ² .

Preferably, the openings along the bottom rim of the insert have a total surface of between 4 and 10 feet ²

According to some embodiments, the discharge opening of the second group of discharge openings may be between 5 and 20% of the surface of the cross section of the inner space defined by the plane with which the opening defined by the top rim is coplanar.

Preferably, the area of the discharge opening of the second group of discharge openings is between 2.6 and 10% of the surface area of the cross section of the inner space defined by the plane with which the opening defined by the top rim is coplanar.

According to some embodiments, the surface area of the discharge opening of the second group of discharge openings may be between 25 and 75% of the surface area of the total surface area of openings along the bottom rim of the insert.

Preferably, the surface area of the discharge opening of the second group of discharge openings is between 30 and 55% of the surface area of the total surface area of openings along the bottom rim of the insert. According to some embodiments, the capped cone may have an inclination angle b between its surface and its axis of between 30 and 60°. Preferably, the capped cone has an inclination angle b between its surface and its axis of between 35 and 50°, such as 45°.

A silo comprising a container of which the inner space is defined by an upper cylindrical part and a lower conical part preferably has a conical part having the inclination angle a of its surface with its axis is in the range of between 35° and 70°, such as in a range of between 40° and 60°.

Preferably, the inclination angle a of the capped cone shape and the inclination angle of the conical part of the container are substantially equal.

It should be understood that the inclination angle is the smallest angle between the axis and the surface.

According to some embodiments, the height of the container above the mechanical coupling of the insert to the inner surface of the container may be between 30 and 60 feet. Preferably, the height of the container above the mechanical coupling of the insert to the inner surface of the container is between 40 and 55 feet.

According to some embodiments, the height of the container below the mechanical coupling of the insert to the inner surface of the container may be between 1 and 5 feet. Preferably, the height of the container below the mechanical coupling of the insert to the inner surface of the container is between 1.5 and 4 feet.

The silos according to the various disclosed embodiments have the advantage that the demixing tendency that occurs when the silo is in use for storing bulk material, such as PET flakes, is to a large extent avoided.

This is especially the case when the silo is used to store PET flakes with the recirculation system being coupled to the discharge openings of the first group of discharge openings and the extraction system being coupled to the discharge openings of the second group of discharge openings. The flakes discharged from the discharge openings under the insert are recycled and added to the fresh PET flake stream. This stream is believed to be comprise to a larger extent coarse and heavy flakes, which tend to move to the side of the container, while less heavy and/or smaller particles are believed to stay in the middle of the silo. By increasing the heavy and/or coarse portion of the flakes, the percentage of coarse and/or heavy flakes in the stream taken out of the silo in the middle of the silo through the opening defined by the upper rim of the insert will increase and come to a stable throughput of all flakes, smaller and larger, heavier and lighter, will be generated. According to a second aspect, a method to extract PET flakes from a silo is provided, the method comprising the steps of

o providing a silo according to the first aspect of the invention;

o feeding fresh bulk material to said silo via a supply opening;

o simultaneously discharging bulk material via the discharge openings of the first and second group of discharge openings; and

o recirculating the bulk material discharged via recirculation system to the silo via a supply opening.

According to some embodiments, the volume per hour of bulk material extracted via the extraction system substantially equals the volume per hour of the fresh bulk material fed to said silo via a supply opening.

According to some embodiments, the disclosed methods may use a silo wherein the recirculation system is coupled to the discharge openings of the first group of discharge openings and the extraction system is coupled to the discharge openings of the second group of discharge openings, wherein the volume per hour ratio of the volume of bulk material extracted via the extraction system to the volume of bulk material recirculated via the recirculation system is in the range of between 1/1 and 1/25.

According to some embodiments, the method uses a silo wherein the recirculation system is coupled to the discharge openings of the first group of discharge openings, the extraction system is coupled to the discharge openings of the second group of discharge openings, and the silo is used to store PET flakes, wherein the volume per hour ratio of the volume of PET flakes extracted via the second group of discharge openings to the volume of PET flakes extracted via the first group of discharge openings may be in the range of 1/25 to 1/1, preferably in the range of between 1/20 and 1/1.25.

According to some embodiments, the PET flakes are flakes obtained by diminution of PET bottles. This diminution may be the shredding of PET bottles, thereby providing“recycled PET” flakes.

The PET flakes typically have dimensions from about 4 cm ² to about 0.25 cm ² . The density of the flakes may vary widely, for example, depending on the part of the bottle from which the flake originates. The bulk density of the flakes may vary from between about 10 pound per cubic feet to about 25 pound per cubic feet.

The independent and dependent claims set out particular and preferred features of the disclosed embodiments. Features from the dependent claims may be combined with features of the independent or other dependent claims, and/or with features set out in the description above and/or hereinafter as appropriate.

The above and other characteristics, features, and advantages of the disclosed embodiments will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

This description is given for the sake of example only, without limiting the scope of the disclosed embodiments. The reference figures quoted below refer to the attached drawings.

Various embodiments are also described in the following listing of concepts:

1. A silo for storing bulk material comprising:

a container defining an inner space;

at least one supply opening for receiving bulk material, the at least one supply opening being disposed near or at an upper side of the container;

an insert disposed within the inner space, the insert having a shape of a capped cone with a top side having a top rim and a bottom side having a bottom rim, wherein:

the top side of the insert is oriented towards the upper side of the container, the bottom rim of the insert is mechanically coupled to an inner surface of the container thereby defining, within the container, an upper inner space above the insert and a lower inner space below the insert, and

the insert defines one or more openings, such as one or more slits, along its bottom rim for allowing bulk material to pass from the upper inner space to the lower inner space;

a first group of discharge openings comprising at least one discharge opening, the openings of the first group of discharge openings being provided near or at the lower side of the container in the surface of the container for discharging bulk material from the lower inner space below the insert, wherein the top rim is provided with a second group of discharge openings comprising at least one discharge opening for discharging bulk material from the upper inner space above the insert;

a recirculation system coupled to the discharge openings of one of the first and second group of discharge openings, for transporting bulk material from said discharge openings to said supply opening; and an extraction system being coupled to the discharge openings of the other of the first and second group of discharge openings for extracting bulk material towards the exterior of the silo.

2. A silo according to concept 1, wherein, the container defines the inner space by having an upper cylindrical portion and a lower conical portion that define the inner space.

3. A silo according to concept 2, wherein the bottom rim is mechanically coupled to the inner surface of the container at the transition between the upper cylindrical portion and the lower conical portion.

4. A silo according to concept 2, wherein the bottom rim is mechanically coupled to the inner surface of the container at a position along the conical portion.

5. A silo according to any one of concepts 2 to 4, wherein the extraction system comprises an extraction duct coupled to the upper rim.

6. A silo according to any one of concepts 2 to 5 wherein the upper cylindrical portion has a diameter in the range of 6 feet to 12 feet.

7. A silo according to any one of the preceding concepts, wherein the silo comprises a supply duct for supplying fresh bulk material.

8. A silo according to any one of the preceding concepts, wherein the volume of the upper inner space above the insert is more than 10 times the volume of the lower inner space below the insert.

9. A silo according to any one of the preceding concepts, wherein the openings along the bottom rim of the insert have a total surface area of 4 to 15 feet ² .

10. A silo according to any one of the preceding concepts, wherein the opening defined by the top rim is 5 to 20 % of the surface of the cross section of the inner space defined by the plane with which the opening defined by the top rim is coplanar with.

11. A silo according to any one of the preceding concepts, wherein a height of the container above a mechanical coupling of the insert to the inner surface of the container is between 30 and 60 feet. 12. A silo according to any one of the preceding concepts, wherein a height of the container below a mechanical coupling of the insert to the inner surface of the container is between 1 and 5 feet. 13. A silo according to any one of the preceding concepts, wherein the recirculation system is coupled to the discharge openings of the first group of discharge openings, and the extraction system is coupled to the discharge openings of the second group of discharge openings.

14. A silo according to any one of the concepts 1 to 12, wherein the recirculation system coupled to the discharge openings of the second group of discharge openings, the extraction system being coupled to the discharge openings of the first group of discharge openings.

15. A method to extract bulk material from a silo, the method comprising the steps of

o providing a silo according to any one of the concepts 1 to 14;

o feeding fresh bulk material to said silo via a supply opening;

o simultaneously discharging bulk material via the discharge openings of the first and second group of discharge openings;

o recirculating the bulk material discharged via recirculation system to the silo via a supply opening.

16. A method according to concept 15, wherein a volume per hour of bulk material extracted via the extraction system substantially equals the volume per hour of the fresh bulk material fed to the silo via the supply opening. 17. A method according to any one of the concepts 15 to 16, wherein a silo according to concept

13 is provided, and a volume per hour ratio of a volume of bulk material extracted via the extraction system to a volume of bulk material recirculated via the recirculation system is in the range of 1/1 to 1/25. 18. A method according to any one of the concepts 15 to 17, wherein the bulk material are PET flakes.

BRIEF DESCRIPTION OF THE DRAWINGS

Having described various embodiments in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIGS. 1 - 3 are schematic diagrams of silos according to the first aspect of the invention. The same reference signs refer to the same, similar or analogous elements in the different figures.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various embodiments will now be described in greater detail. It should be noted that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps, or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the claimed embodiment, the only required components of the device are A and B.

Throughout this specification, references to "one embodiment" or "an embodiment" are made. Such references indicate that a particular feature described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, though they could.

Furthermore, the particular features or characteristics described may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

A silo 100 for storing bulk material, in this case PET flakes 900, is shown in FIG. 1. The silo 100 comprises a container 110 defining an inner space. The container 110 is closed at its top side by means of a closing lid 112 .

The container defines the inner space 114 by having an upper cylindrical part 116 and a lower conical part 118 . The lower conical part 118 is oriented with its top of the conical shape downwards. The silo 100 has a hopper-like shape. As an example, the cylindrical part has a diameter of 8 feet. In an example, the height of the cylindrical part may be, for example, 56 feet. The height of the conical part may be 7 feet and the inclination angle a is 30°.

The container 100 has at least one supply opening 120 for receiving PET flake being provided at the upper side of the container and is centrally positioned. As such the supply opening is coaxial with the axis of the cylindrical and conical part of the container. The silo comprises a supply duct 121 for supplying fresh PET flakes. The supply duct for supplying the fresh and recirculated PET flakes is situated at the top of the silo 100, in this embodiment in the lid 112 of the container.

A first group of four discharge openings 122 are provided on the lower side of the container 110 in the surface of the container, in this embodiment in the conical part 118 of the container 110. The four openings are equally distributed at the conical part 118 of the container 110. Via a recirculation ducting system 124, the discharge openings 122 are coupled to the supply opening 120. In particular embodiments, this system is provided with means (not shown) to transport the flakes using air current. Each discharge opening 122 is coupled to its own discharge duct 126. In particular embodiments, all discharge openings 122 and the supply duct 121 are coupled to one supply opening 120. The discharge openings 122 may have a circular shape with diameter of, e.g., 12 inches and the ducts 126 coupled to these openings may have the same diameter.

The silo 100 further comprises an insert 130 located in the inner space 114, which insert 130 has the shape of a capped cone with a top side 132 having a top rim 134 and a bottom side 136 having a bottom rim 138. The top side 132 of the insert 130 is oriented towards the upper side of the container 110. The capped cone has an inclination angle b between its surface and its axis of about 55°. The top rim circumscribes the one discharge opening 133 of the second group of discharge openings.

The bottom rim 138 of the insert 130 is mechanically coupled to the inner surface of the container 100 by means of a limited number of studs, e.g. 4 studs. As such an upper inner space 142 above the insert 130 and a lower inner space 144 below the insert 130 is defined. The bottom rim 138 is mechanically coupled to the inner surface of the container 100 at the transition between the upper cylindrical part 116 and the lower conical part 118.

In particular embodiments, the whole container and the ducting systems are made of steel. The mechanical coupling may be a welding.

In particular embodiments, the volume of the inner space 142 above the insert 130 is about 14 times of the volume of the inner space 144 below the insert 130.

The insert 130 has a plurality of openings 150 along its bottom rim 138 for allowing PET flakes to pass from the upper inner space 142 to the lower inner space 144.

The discharge opening 133 at the top rim 134 is coupled to the duct of an extraction system 160 for extracting PET flakes from the upper inner space 142 towards the exterior of the silo. The extraction system 160 comprises an extraction duct 162 coupled to the upper rim 134 of the insert 130 while the extraction duct 162 intersects with the lower conical part 118 of the container 110 at the top of the conical shape of the conical lower part 118.

In particular embodiments, the discharge opening 133 defined by the top rim 134 has a diameter of 12 inches and the duct 162 coupled to this opening 133 has the same diameter. The capped conical shape of the insert 130, the cylindrical 116 and conical part 118 of the silo, the supply opening 120, and the extraction duct of the extraction ducting system 160 may be coaxially mounted.

As an alternative, the bottom rim may be mechanically coupled to the inner surface of the container at a position along the upper cylindrical part, such that the distance between the transition between conical and cylindrical part and the mechanical coupling is between 0 and 3 feet.

In various embodiments, the bottom rim 138 of the insert 130 is coupled to the container with four studs positioned radially equidistant one from the other. The openings 150 along the bottom rim 138 of the insert 130 have a slit shape with width of about 6 inches. The total surface area of these openings is about 12 feet ² .

In steady state operation, the container may be filled with PET fakes. Fresh PET flakes, e.g. flakes of PET obtained by recycling PET bottles, are provided to the container 100 via opening 120 and duct 121. At the bottom of the container, PET flakes are extracted via opening 134 and duct 162, preferably at the same volume rate per hour as is applicable for the fresh PET flake feed.

PET flakes may be recirculated by extraction through the discharge openings 122 and recirculated to the supply opening 120.

In particular embodiments, the volume per hour ratio of the volume of PET flakes extracted via the top rim opening 133 to the volume of PET flakes extracted via the one or more discharge openings 122 is in the range of between 1/25 and 1/1, preferably in the range of between 1/20 and 1/1.25. For example, the volume per hour ratio of the volume of PET flakes extracted via the top rim opening 133 is about 40000 pound per hour, whereas the volume of PET flakes extracted via the discharge openings 122 is 8000 pounds per hour.

Another silo 1000 for storing PET flakes 900 is shown in FIG. 2. The silo 1000 comprises a container 1010 defining an inner space 1014. The container 1010 is open at its top side.

The container defines the inner space 1014 by having an upper cylindrical part 1016 and a lower conical part 1018. The lower conical part 1018 is oriented with its top of the conical shape directed downwards. The silo 1000 has a hopper-like shape. In particular embodiments, the cylindrical part has a diameter of 8 feet. The height of the cylindrical part may, e.g., be 46 feet. The height of the conical part may, e.g., be 4 feet and the inclination angle a may, e.g., be 45°.

In various embodiments, the open top of the container 1000 provides one supply opening 1020 for receiving PET flake being provided at the upper side of the container. The silo comprises a supply duct 1021 for supplying fresh PET flakes. The supply duct for supplying the fresh and recirculated PET flakes is situated at the top of the silo 1000.

One discharge opening 1022 is provided at the lower side of the container 1010, in this embodiment at the top of the conical part 1018 of the container 1010. Via a recirculation system 1024 comprising a bucket conveyor system 1026, the discharge opening 1022 is coupled to the supply opening 1020, being the open top of the cylindrical part 1016. In particular embodiments, the discharge opening has a circular shape with diameter of 12 inches.

The silo 1000 further comprises an insert 1030 located in the inner space 1014, which insert 1030 has the shape of a capped cone with a top side 1032 having a top rim 1034 and a bottom side 1036 having a bottom rim 1038. The top side 1032 of the insert 1030 is oriented towards the upper side of the container 1010. In particular embodiments, the capped cone has an inclination angle b between its surface and its axis of 45°.

In various embodiments, the bottom rim 1038 of the insert 1030 is mechanically coupled to the inner surface of the container 1000 with four studs radially equally distant one from the other. As such, an upper inner space 1042 above the insert 1230 and a lower inner space 1044 below the insert 1030 is defined. The bottom rim 1038 is mechanically coupled to the inner surface of the conical part 1018 of the container 1000 at a height along the axis of the conical part. In particular embodiments, such a height is about 50% of the total height of the conical shape of the conical part 1018.

In particular embodiments, the whole container and the ducting systems are made of steel. The mechanical coupling may be a welding.

The insert 1030 has 4 slit-shaped openings 1050 along its bottom rim 1038 for allowing PET flakes to pass from the upper inner space 1042 to the lower inner space 1044.

The one discharge opening 1033 of the second group of discharge openings is circumscribed by the top rim 1034, which may be coupled (e.g., on its turn) to an extraction duct system 1060 for extracting PET flakes from the upper inner space 1042 towards the exterior of the silo. The extraction duct system 1060 comprises an extraction duct 1062 coupled to the upper rim discharge opening 1033 of the insert 1030, where the extraction duct 1062 intersects with the lower conical part 1018 of the container 1010 along the side of the conical part 1018.

In particular embodiments, the opening 1033 defined by the top rim 1034 has a diameter of 12 inches and the duct 1062 coupled to this opening 1038 initially has the same diameter, broadening to 24 inches further downstream. In particular embodiments, the capped conical shape of the insert 1030, the cylindrical 1016 and conical part 1018 of the silo, the supply opening 1020, the discharge opening 1022 of the recirculation ducting system 1024, and the extraction duct 1062 of the extraction ducting system 1060 are coaxially mounted.

In particular embodiments, the openings 1050 along the bottom rim 1038 of the insert 1030 have a slit-like shape with width of about 6 inches.

In steady state operation, the container is filled with PET fakes. Fresh PET flakes, e.g., flakes of PET obtained by recycling PET bottles, may be provided to the container 1000 via the opening 1020 at the top of the container and duct 1021. At the bottom of the container, PET flakes may be extracted via opening 1033 and duct 1062, preferably at the same volume rate per hour as is applicable for the fresh PET flake feed.

In various embodiments, via discharge openings 1022, PET flakes are recirculated by extraction through these openings and recycled to the supply opening 1020.

The volume per hour ratio of the volume of PET flakes extracted via the top rim opening 1033 to the volume of PET flakes extracted via the discharge openings 1022 may be in the range of between 1/25 and 1/1, for example, in the range of between 1/20 and 1/1.25. In particular embodiments, the volume per hour ratio of the volume of PET flakes extracted via the top rim opening 1033 is about 40000 pound per hour, whereas the volume of PET flakes extracted via the discharge openings 1022 is 8000 pounds per hour.

It should be understood that these silos 100 and 1000 may be used for bulk material other than PET flakes.

A further silo 2000 for storing bulk material 2900, is shown in FIG. 3. The silo 2000 comprises a container 2110 defining an inner space. The container 2110 is closed at its top side by means of a closing lid 2112.

The container defines the inner space 2114 by having an upper cylindrical part 2116 and a lower conical part 2118. The lower conical part 2118 is oriented with its top of the conical shape downwards. The silo 2000 has a hopper-like shape. In particular embodiments, the cylindrical part has a diameter of 8 feet. The height of the cylindrical part may be, e.g., 56 feet. The height of the conical part may be, e.g., 7 feet and the inclination angle a may be, e.g., 30°.

The container 2000 has at least one supply opening 2120 for receiving bulk material being provided at the upper side of the container and is centrally positioned. As such, the supply opening may be coaxial with the axis of the cylindrical and conical part of the container. The silo comprises a supply duct 2121 for supplying fresh bulk material. The supply duct for supplying the fresh and recirculated bulk material may be situated at the top of the silo 2000, in this embodiment in the lid 2112 of the container.

In various embodiments, a first group of four discharge openings 2122 are provided on the lower side of the container 2110 in the surface of the container, in this embodiment in the conical part 2118 of the container 2110. The four openings are equally distributed at the conical part 2118 of the container 2110.

The discharge opening 2122 are coupled to the duct of an extraction system 2160 for extracting bulk material from the lower inner space 2144 towards the exterior of the silo. The extraction system 2160 comprises extraction ducts 2162 coupled to the discharge openings 2122.

The silo 2000 further comprises an insert 2130 located in the inner space 2114, which insert 2130 has the shape of a capped cone with a top side 2132 having a top rim 2134 and a bottom side 2136 having a bottom rim 2138. The top side 2132 of the insert 2130 is oriented towards the upper side of the container 2110. The capped cone has an inclination angle b between its surface and its axis of about 55°. The top rim circumscribes one or more discharge openings 2133 of the second group of discharge openings.

Via a recirculation ducting system 2124, the discharge opening 2133 is coupled to the supply opening 2120. This system is provided with means (not shown) to transport the flakes using air current. The discharge opening 2133 is coupled to a discharge duct 2126. In particular embodiments, the discharge openings 2133 have a circular shape with diameter of 12 inches and the ducts 2126 coupled to these openings having the same diameter.

In various embodiments, the bottom rim 2138 of the insert 2130 is mechanically coupled to the inner surface of the container 2000 by means of one or more studs, e.g., 4 studs. In this way, an upper inner space 2142 above the insert 2130 and a lower inner space 2144 below the insert 2130 may be defined. The bottom rim 2138 may be mechanically coupled to the inner surface of the container 2000 at the transition between the upper cylindrical part 2116 and the lower conical part 2118.

In particular embodiments, the whole container and the ducting systems are made of steel. The mechanical coupling may be a welding.

In particular embodiments, the volume of the inner space 2142 above the insert 2130 is about 14 times of the volume of the inner space 2144 below the insert 2130.

The insert 2130 may have a plurality of openings 2150 along its bottom rim 2138 for allowing bulk material to pass from the upper inner space 2142 to the lower inner space 2144. In particular embodiments, the discharge opening 2133 defined by the top rim 2134 has a diameter of 12 inches and the duct 2126 coupled to this opening 2133 has the same diameter.

In particular embodiments, the capped conical shape of the insert 2130, the cylindrical 2116 and conical part 2118 of the silo, the supply opening 2120, and the part of the duct 2014 where it is coupled to the opening 2133 are coaxially mounted.

In various embodiments, the bottom rim may be mechanically coupled to the inner surface of the container at a position along the upper cylindrical part, such that the distance between the transition between conical and cylindrical part and the mechanical coupling is, for example, between 0 and 3 feet.

In particular embodiments, the bottom rim 2138 of the insert 2130 is coupled to the container with four studs positioned radially equidistant one from the other. The openings 2150 along the bottom rim 2138 of the insert 2130 have a slit shape with width of about 6 inches. The total surface area of these openings is about 12 feet ² .

In steady state operation, the container may be filled with bulk material. Fresh bulk material is provided to the container 2000 via opening 2120 and duct 2121. At the bottom of the container, bulk material is extracted via openings 2122 and duct 2160, preferably at the same volume rate per hour as is applicable for the fresh PET flake feed.

In various embodiments, , bulk material is recirculated by extraction through discharge openings 2133 and recirculated to the supply opening 2120.

It is to be understood that although specific embodiments and/or materials have been described herein, various modifications or changes may be made without departing from the scope and spirit of this invention.