WO2015005780A1

WO2015005780A1 - Blender for particulate materials

Info

Publication number: WO2015005780A1
Application number: PCT/NL2014/050462
Authority: WO
Inventors: Gerrit Jan Fons
Original assignee: J&D Beheer B.V.
Priority date: 2013-07-09
Filing date: 2014-07-08
Publication date: 2015-01-15
Also published as: NL2011126C2; EP3019270A1

Abstract

A gravity blender 1 for receiving particulate material comprises a silo 2 having a cylindrical upper portion 4 and a hollow interior 3 and a mixing chamber 8. A plurality of blending conduits 10 is provided externally of the cylindrical upper portion and extend downwards from the upper portion of the silo to communicate with the mixing chamber. A plurality of passageways 20 each extend from a respective upper outlet 22 from the hollow interior into a respective blending conduit such that the particulate material can flow from the hollow interior to the mixing chamber via the blending conduits. The blending conduits also extend upwards, beyond the respective upper outlet to a respective access location allowing access to the blending conduit for cleaning purposes.

Description

BLENDER FOR PARTICULATE MATERIALS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a gravity blender of the type used for the storage and subsequent delivery of particulate materials.

2. Description of the Related Art

Particulate materials, such as polymer granules, can be stored in bulk in a silo. Silos are large storage facilities in which many tonnes of particulate material may be stored. During production of polymer material, the material properties, such as physical and mechanical properties, are desired to be constant. This is important for subsequent processing of the polymer material.

Before polymers were used at a large scale in applications such as continuous film or filament production, the need for precision blending of bulk solids products were met with mechanical tumbler, ribbon or screw blenders. Capacities of these units ranged from less than one cubic meter to over 100 cubic meters.

As the demand for polymers has grown, much larger blender volumes have become necessary to allow continuous production lines in polymers producing plants to operate without frequent shutdowns caused either by variations in material properties or by contamination inherent in the production process. This has led to a demand for tumble blenders in the range of 700 cubic meter capacity.

The high cost of large tumble blender installations induced industry-wide efforts to develop a blending capability in storage silos to comply with the product uniformity requirements of the polymer industry. This was the start of the development of, amongst others, gravity blenders with capacities of up to 3000 cubic meter.

Gravity blenders generally use internal tubes having openings to allow solids in the silo to flow to a separate mixing chamber below the silo. The tube openings in the main body of the silo are located so that material drained into the mixing chamber represents a typical composition of the material in the main silo body.

Such a gravity blender is described in European patent EP0538445. The described gravity blender comprises a bin to receive and store particulate material, the bin having an upper portion and a downwardly converging lower portion. Blending conduits are provided within the bin, the blending conduits extending along an inside of the bin downward from the top of the bin and terminating in apertures in a baffle provided between the upper portion and lower portion of the bin. The blending conduits have a number of apertures through which particulate material can enter the blending conduits and be conveyed by the blending conduits to the lower portion of the bin. The principle of operation is well-know and often referred to as the moving top-hole principle.

Use of such gravity blenders results in more constant material properties of the produced polymer material by blending of material from several levels in the silo before processing of the polymer material.

However, a disadvantage of these gravity blenders is that residual particulate material can remain in the blending conduits and/or the silo. If a change of product is required, complete removal of all traces of the previous material may be required. For a number of applications, such as for very thin polymer foil, it is highly desired to have material properties within a very narrow range to facilitate further processing of the polymer material.

It would be desirable to provide a gravity blender that would result in a decrease in residual material in the silo and blending conduits to improve the resulting material properties of the produced polymer material.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a gravity blender operable to receive and store a mass of particulate material, the gravity blender comprising: a silo having a cylindrical upper portion and a hollow interior; a mixing chamber; a plurality of blending conduits provided externally of the cylindrical upper portion and extending downward from the upper portion of the silo to communicate with the mixing chamber; and a plurality of passageways each extending from a respective upper outlet from the hollow interior into a respective blending conduit, such that the particulate material can flow from the hollow interior to the mixing chamber via the blending conduits, wherein the blending conduits extend upwards beyond the respective upper outlet to a respective access location.

By providing the blending conduits at the exterior of the silo, interior structures within the silo are avoided. Interior structures can cause collection or hang-up of particulate material, which can contaminate subsequent material to be stored in the silo. In the event that a different material is to be filled into the silo, it is essential that all of the previous material is removed. Although existing designs may attempt to minimize such internal structures, even the minutest of flanges or welds can collect residue. In the present design, the blending conduits may be provided exclusively and only at the exterior of the silo, at least in the upper portion of the silo where the particulate material is received. In other words, it may be excluded that the blending conduits pass through a portion of the silo where particulate material is stored.

According to an important aspect of the invention, by extending the blending conduits upwards beyond the respective upper outlet to a respective access location, improved access to the blending conduits can be provided for the purpose of cleaning and inspection. In this manner, the interior of the blending conduits is accessible and may be cleaned out to remove residue. To further reduce or prevent contamination of the produced polymer material, the blending conduits should be free of residual particulate material before storing a next load of material in the silo. In this context, access to the interior of the respective blending conduit is intended to refer to the fact that an opening can be provided directly into the blending conduit. Furthermore, in this context the upper outlet denotes the uppermost outlet into a respective blending conduit from the hollow interior.

According to a preferred embodiment of the invention, the access locations for each blending conduit are located at the same height with respect to the silo. This allows construction of a gantry at a single location e.g. above the level of the upper portion whereby access by personnel may be provided to the access locations. It will nevertheless be understood that a gantry around the upper portion could also provide access to the access locations.

In a still further preferred embodiment, there may be provided a silo cleaning system for cleaning the hollow interior of the silo. The silo cleaning system may be provided at the top of the upper portion of the silo, in particular at a central location. The silo cleaning system may be otherwise conventional and provides a water film for flushing down the internal walls of the silo. As a result of the absence of blending conduits within the hollow interior, the silo cleaning system may better perform its function and may be able to reach all parts of the circumferential wall. According to a still further aspect of the invention, the gravity blender may further comprise a conduit cleaning system communicating with the access locations for cleaning the interior of the blending conduits. The conduit cleaning system may comprise multiple supplies in star formation or a single ring-main connected to the blending conduits at or adjacent to the access locations. The conduit cleaning system may comprise individual spray heads for each access location, each of which may be otherwise conventional. Flushing of the blending conduits is thus facilitated.

According to the invention it will be understood that the hollow interior is completely free of blending conduits i.e. there may be no blending conduit passing through or extending into the hollow interior. According to a still further aspect of the invention, the hollow interior may be free of all internal structures on which retention of particulate material could occur. As it will be understood, defining the absence of internal structures may be considered a matter of scale, nevertheless, in the context of the particulate material to be stored, the hollow interior should be free of structures on which particles of this size could be retained. The interior may therefore be free of welds, flanges, bolts, pipes, horizontal surfaces and the like and otherwise smooth within the order of magnitude of the particles to be stored.

Most preferably, the hollow interior of the upper portion of the silo will be free of all obstructions having a horizontal extent of more than 5 mm. Most preferably it will not have obstructions having a horizontal extent of more than 2 mm and still more preferably, any obstruction or surface should have a horizontal extent of less than 1 mm. Preferably, the same will apply to the interior of the blending conduits.

Furthermore, according to the invention, the blending conduits and passageways may each have a barrier-free inner surface such that retention of particulate material is prevented. Usually the blending conduit is made up of several parts that are connected together. By providing the blending conduits external to the hollow interior of the silo, external flanges and welds may be used in their construction. As a result, the blending conduits may have perfectly smooth inner surfaces having a similar smoothness to that discussed above in the context of the hollow interior.

In order to further enhance the ability to clean and inspect the interior of the blending conduits, these preferably extend downwardly parallel to the outside of the silo and are straight from the access location over at least the length of the upper portion. In this manner, visual inspection may be achieved from the access location and any intervention may take place in a line of sight.

Each blending conduit may connect to a single outlet from the hollow interior. Nevertheless, in a preferred embodiment, each blending conduit has a plurality of further passageways extending from further outlets located at different heights with respect to the silo. This allows each conduit to operate according to the moving top- hole principle, which is otherwise well-known from the above-mentioned reference. More preferably, the respective upper outlets are located at different heights with respect to the silo. Furthermore, the blending conduits are preferably evenly distributed around the exterior of the silo. It will of course be understood that the passageways and further passageways slope downwards from the respective outlets.

The further outlets may be provided both in the upper portion and the mid- portion. The outlets may be restricted to the upper portion only, although this is generally less preferred.

According to another preferred embodiment, the silo comprises a downwardly- directed, conically-shaped baffle serving as a divider between an interior of the mid- portion of the silo and the mixing chamber. The baffle preferably has a central passage at its lowest point, communicating with the mixing chamber and allowing for emptying of the silo into or through the mixing chamber. The central passage may be provided with an appropriate valve arrangement, if required.

The mixing chamber will generally be provided directly connected to the mid- portion although it is not excluded that it could be separate therefrom. Preferably, the mixing chamber comprises a first portion connected to the mid-portion of the silo and a second portion moveably connected to the first portion to allow opening of the mixing chamber. This further facilitates cleaning of the gravity blender and can allow better access to the lower ends of the blending conduits.

According to a further embodiment, the blending conduits extend downwardly parallel to the outside of the silo, converging towards the mixing chamber along an outside of the converging mid-portion of the silo. Each blending conduit may have a single bend or angle at the transition between the mid-portion and the upper portion. The blending conduit may thus be fully accessible partly from the top, via the access location and from the bottom via the mixing chamber. According to another embodiment, the upper portion is provided with a skirt, which may support the silo in use. The skirt may extend downwardly over at least part of the mid-portion along at least part of a circumference of the outside of the silo.

Due to the external blending conduits, a skirt allows support of the silo in use. Preferably, the skirt is arranged around the blending conduits to allow passage of the blending conduits. For instance the skirt can be provided with a recess extending from a free end of the skirt towards the silo at the position of a blending conduit. Alternatively, the blending conduits can extend through the skirt at openings positioned at a section of the skirt and the blending conduits.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:

Figure 1 shows a partially sectioned side view of a gravity blender according an embodiment of the invention;

Figure 2 shows a lower portion of the gravity blender of Fig. 1 in more detail;

Figure 3 shows a perspective view from the top of the gravity blender of Fig. 1;

Figure 4 shows an enlarged view of detail IV of Fig. 1;

Figure 5a shows an enlarged view of a joint according to detail VI of Fig. 1; and Figure 5b shows an alternative embodiment of the joint of Fig. 5a.

DESCRIPTION OF ILLUSTRATIVE EMBODFMENTS

Figure 1 shows a gravity blender 1 according to a preferred embodiment of the invention in partially sectioned side view. The gravity blender 1 comprises an upright silo body 2 having a hollow interior 3. The silo 2 has a generally cylindrical upper portion 4 and a funnel shaped mid-portion 6 extending to a mixing chamber 8 at the base 16 of the silo 2. The mixing chamber has a delivery port 9 at its lower extremity.

Around the exterior of the silo 2 are located blending conduits 10. The blending conduits 10 each extend from the mixing chamber 8 to an access location 12 at the top 14 of the silo 2. A gantry platform 18 is provided over the top 14 of the silo 2 allowing access to the access locations 12.

Each blending conduit 10 connects via an upper passageway 20 to an upper outlet

22 from the silo 2. A number of further passageways 24 are provided at lower levels connecting from further outlets 26 from the silo 2 to the blending conduits 10. Also visible in Figure 1 is a silo cleaning system 28 and a conduit cleaning system 30 located on the gantry platform 18.

The silo 2 is constructed in a conventional manner using flanged panels 32, which are welded or bolted together to ensure a smooth internal surface 34. The skilled person will recognise that alternative constructions including butt welding could also be employed. At the base 16 of the silo 2, a conically-shaped baffle 36 is provided, separating the mid-portion 6 from the mixing chamber 8. The baffle 36 is provided with a central passageway 38 communicating with the mixing chamber 8. This may be provided with appropriate valving means (not shown) as required. The mixing chamber 8 is also formed in two parts with a first portion 40 connected to the mid-portion 6 and a second portion 42 connected to the first portion by a hinge 44 to allow opening of the mixing chamber 8.

The upper portion 4 of the silo 2 terminates at its lower side in a downwardly extending skirt 46 which partially surrounds the mid-portion 6. The skirt 46 is provided with openings 48 by which the blending conduits 10 can traverse the skirt 46. The skilled person will understand that further elements may be present in the construction of the gravity blender 1 that have here been omitted for clarity. In particular, the skirt 46 provides a support by which the silo 2 can be supported.

Figure 2 shows an enlarged view of the lower part of the gravity blender 1 of

Figure 1, with the mixing chamber 8 opened. In this view, it can be more clearly seen how the blending conduits 10 traverse the skirt 46 via the openings 48. It may also be noted that at this location, the blending conduits 10 have a single bend or angle 11. The blending conduits 10 are otherwise straight over their upper sections from the angle 11 to the access locations 12 and over their lower sections, from the mixing chamber 8 to the angle 11.

Figure 3 shows a perspective view from above the gravity blender 1 of Fig. 1, in which the gantry platform 18 is better visible. Also visible is the conduit cleaning system 30 and the silo cleaning system 28. The conduit cleaning system 30 comprises a number of spray heads 56 each connected by a connection piece 58 to a ring main 60. The connection for the silo cleaning system 28 is not shown, but it will be understood that this can also be connected to the ring main 60 or otherwise. Figure 4 shows a detailed cross-section of view IV in Figure 1 showing the conduit cleaning system 30 in greater detail. As can be seen, the blending conduit 10 extends upwards through the gantry platform 18 to the access location 12. Each access location 12 is provided with a closure 54 which can be selectively opened as required to provide access into the interior of the blending conduit 10. The spray heads 56 extend through the closure 54 and are connected by the connection piece 58 to the ring main 60. The silo cleaning system 28 is substantially similar to the conduit cleaning system 30 and is not further described.

Figure 5a shows an enlarged view of detail V of Figure 1 illustrating a welded joint construction used in manufacture of the blending conduits 10. The blending conduits 10 are formed from individual tube segments 10a, 10b, joined at a weld 62. The weld 62 is formed from the outside surface of the blending conduit and each tube segment 10a, 10b has a chamfered end 64 to ensure that the inner surface of the blending conduit 10 at the weld 62 is smooth and free of obstructions.

Figure 5b shows an alternative embodiment of a flanged joint to be used in the blending conduit. In this embodiment, blending conduit 110 is formed from individual tube segments 110a, 110b, joined by flanges 162. Because the blending conduit 110 is located outside of the silo 2, the flanges 162 can be formed extending from the outside surface of the blending conduit 110 without risk that they will serve as a location for hang-up of particulate material. The flanges 162 are held together by bolts 164 as is otherwise conventional, leaving the inner surface of the blending conduit smooth and free of obstructions.

Use of the gravity blender 1 of the present invention will briefly be described with reference to Figures 1 to 4. In use, the silo 2 is filled with particulate material from the top 14 via an appropriate port (not shown). The particulate material filled in to the silo 2 may vary slightly in composition and particle size throughout the hollow interior 3. It is therefore important that on withdrawing material from the silo 2, this takes place from a number of locations simultaneously in order to provide a relatively constant aggregate flow to the mixing chamber and from the delivery port 9. The location of the upper outlets 22 and further outlets 26 ensure that material is withdrawn simultaneously from different levels. As the level of the material within the silo 2 drops, additional further outlets become active according to the moving top-hole principle. If it is desired to proceed with a different batch of material e.g. of a different composition, the silo 2 is emptied completely and subsequently cleaned using the silo cleaning system 28 and the blending conduits are cleaned using the conduit cleaning system 30. To this end, water or other appropriate cleaning liquid is sprayed from the silo cleaning system 28 into the interior of the silo 2 and forms a liquid film running down the internal surface of the silo 2. This flushes out residual material and also serves to remove static charge from the surface. Owing to the complete absence of obstructions within the silo 2, the liquid film can form evenly around the full periphery of the hollow interior 3. Furthermore, because there are no locations where material can collect, an enhanced degree of cleaning is achievable. The conduit cleaning system 30 is also operated in a similar way, with all the spray heads 56 being supplied with cleaning liquid from the ring main 60 via the connection pieces 58. The cleaning liquid is flushed through the length of the blending conduits 10 to the mixing chamber 8. On completion of the cleaning process, the closures 54 may be opened and a visual inspection of the blending conduits can be performed. Because of the manner in which the blending conduits 10 are manufactured using welds 62, the interior is smooth and the presence of any residual material can be readily perceived.

The invention has thus been described by reference to certain embodiments as discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, it will be understood that other methods of use and cleaning of the gravity blender may be applicable. Other modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention as defined by the claims.

Claims

1. Gravity blender (1) operable to receive and store a mass of particulate material, the gravity blender comprising:

a silo (2) having a cylindrical upper portion (4) and a hollow interior (3);

a mixing chamber (8);

a plurality of blending conduits (10) provided at an exterior of the cylindrical upper portion and extending downward from the upper portion of the silo to communicate with the mixing chamber; and

a plurality of passageways (20) each extending from a respective upper outlet

(22) from the hollow interior (3) into a respective blending conduit, such that the particulate material can flow from the hollow interior to the mixing chamber via the blending conduits, wherein the blending conduits extend upwards beyond the respective upper outlet to a respective access location (12).

2. Gravity blender according to claim 1, wherein the access locations comprise closures providing selective access to an interior of the respective blending conduit.

3. Gravity blender according to claim 1 or claim 2, wherein the access locations for each blending conduit are located at the same height with respect to the silo.

4. Gravity blender according to any of the preceding claims, further comprising a silo cleaning system (28) for cleaning the hollow interior of the silo, the silo cleaning system being provided at the top of the upper portion of the silo.

5. Gravity blender according to any of the preceding claims, further comprising a conduit cleaning system (30) communicating with the access locations for cleaning the interior of the blending conduits.

6. Gravity blender according to any of the preceding claims, wherein the hollow interior is free of internal structures, such that retention of particulate material is prevented.

7. Gravity blender according to any of the preceding claims, wherein the blending conduits and passageways each have a barrier-free inner surface such that retention of particulate material is prevented.

8. Gravity blender according to any of the preceding claims, wherein the blending conduits extend downwardly parallel to the outside of the silo and are straight from the access location over the length of the upper portion.

9. Gravity blender according to any of the preceding claims, wherein each blending conduit has a plurality of further passageways extending from further outlets located at different heights with respect to the silo.

10. Gravity blender according to any of the preceding claims, wherein the respective upper outlets are located at different heights with respect to the silo.

11. Gravity blender according to any of the preceding claims, wherein the blending conduits are evenly distributed around the exterior of the silo.

12. Gravity blender according to any preceding claim, wherein the silo comprises a funnel-shaped mid-portion extending from the upper portion to the mixing chamber.

13. Gravity blender according to claim 12, wherein the further outlets are provided in both the upper portion and the mid-portion of the silo.

14. Gravity blender according to claim 12 or claim 13, further comprising a downwardly-directed, conically- shaped baffle (36) serving as a divider between an interior of the mid-portion of the silo and the mixing chamber.

15. Gravity blender according to claim 14, wherein the baffle has a central passage at its lowest point, communicating with the mixing chamber.

16. Gravity blender according to any of claims 13 to 15, wherein the mixing chamber comprises a first portion (40) connected to the mid-portion of the silo and a second portion (42) moveably connected to the first portion to allow opening of the mixing chamber.

17. Gravity blender according to any of claims 13 to 16, wherein the blending conduits converge towards the mixing chamber along an outside of the mid-portion of the silo.

18. Gravity blender according to any claims 13 to 17, further comprising a skirt (46), the skirt extending downwardly over at least part of the mid-portion along at least part of a circumference of the outside of the silo.

19. Gravity blender according to claim 18, wherein the blending conduits traverse the skirt.