GB2262878A

GB2262878A - Straw processing

Info

Publication number: GB2262878A
Application number: GB9224999A
Authority: GB
Inventors: Peter George Fredrick Grant; Nigel David Sampson
Original assignee: SAMGRAN STRAW Ltd
Current assignee: SAMGRAN STRAW Ltd
Priority date: 1991-11-28
Filing date: 1992-11-30
Publication date: 1993-07-07
Also published as: GB9224999D0

Abstract

A method for processing harvested straw, comprises the steps of (a) chopping harvested straw to produce a mixture comprising chopped straw pieces; and (b) separating chopped straw pieces, suitable for use as animal bedding, and material suitable for use in animal feed from said mixture. Apparatus for performing the method includes a shredder (6), hammer mills (7, 15), a pneumatic screen separator (8), a cyclone separator (12) and a bagging machine (20). <IMAGE>

Description

STRAW PROCESSING DESCRIPTION The present invention relates to the production of material suitable for use as animal bedding and material suitable for use in animal feed.

As a by-product of the production of cereals large quantities of straw are produced. The straw is widely used as animal bedding but, nevertheless, suffers from a number of shortcomings. During harvesting, straw is conventionally bound into large bales which are inconvenient and not well suited to the needs of small scale users of straw. Furthermore, conventionally baled straw tends to be longer than is optimum for animal bedding and also contains additional material such as cereal grains and dust, which serve no useful function in animal bedding and, where dust is present, can cause respiratory problems in sensitive animals. It is in the nature of most known methods of harvesting straw that the harvested straw contains such additional material.Indeed, when straw is cut during harvesting (or any subsequent chopping procedure) straw particles can break away from the severed ends of individual pieces of straw and contribute to the quantity of dust in a final straw product.

Attempts have been made in the past to develop apparatus and methods for processing harvested straw to produce a product which is better adapted for use as animal bedding and which may be handled more conveniently. However, known systems have all suffered from defects which have limited their commercialisation. For instance, one known method employs a cyclone to separate chopped straw from other matter but the cyclone is unable to discriminate effectively between chopped straw and cereal grains.

It is an aim of the present invention to overcome the aforementioned defects.

According to a first aspect of the present invention there is provided a method for processing harvested straw, comprising the steps of: a) chopping harvested straw to produce a mixture comprising chopped straw pieces, and; b) separating chopped straw pieces, suitable for use as animal bedding, and a material suitable for use in animal feed from said mixture.

Preferably, the harvested straw is in the form of a straw bale or bales derived from a conventional harvesting process.

Preferably, the material suitable for use as aminal feed is ground to produce meal. The meal can then be pelleted.

In an embodiment the mixture comprising chopped straw pieces, formed in step (a), includes non-straw matter and straw particles of insufficient size for use as animal bedding. Generally such particles have a maximum dimension of 19mm, although the dividing line between chopped straw pieces, suitable for animal bedding, and straw particles of insufficient size for such use, depends upon the animals being provided for.

Thus, the chopped straw pieces for animal bedding, preferably, includes pieces having a length of at least 10mm to 30mm, with smaller pieces being treated as straw particles of insufficient size for use as animal bedding. Preferably, these straw particles are included in the material suitable for use in animal feed.

Advantageously, a conditioning substance, such as a mould and spore inhibitor, may be added to the material suitable for animal bedding.

Preferably, the straw is chopped to a length less than a predetermined length. In an embodiment, the straw pieces in the material suitable for animal bedding are less than 90mm in length and, thus, are suitable as horse bedding. However, a 50mm maximum length may be chosen for the production of pig and poultry bedding.

According to a second aspect of the present invention, there is provided a separator comprising conveyor means, including a tubular structure and screw means located coaxially within the tubular structure, wherein a section of the tubular structure comprises a screen for selectively passing material propelled by the screw means.

In a preferred embodiment, the screen is arranged for allowing straw particles and other matter, of insufficient size for use as animal bedding, to pass therethrough. Thus the screen can be arranged to allow material having a maximum dimension of between 10 and 30 mm, preferably 19mm, to pass therethrough and to retain larger matter.

Preferably, the tubular structure has a circular cross-section and the screw means can be an archimedes screw.

Preferably, the separator includes a housing for constraining material which has passed through the screen and means for drawing such material from the housing can also be provided. The housing can include an outlet and said means can comprise a fan, arranged to draw said material through the outlet from within the housing.

Preferably, the screen is cylindrical and coaxial with the screw.

Preferably, the screen comprises curved sheet material provided with a plurality of holes. The holes may be circular and, preferably, have a diameter of 10 to 30mm and most preferably of about 19mm.

According to a third aspect of the present invention, there is provided a method of producing material suitable for animal bedding comprising passing chopped, harvested straw through a separator according to the second aspect of the present invention.

Preferably, material suitable for use in animal feed is retrieved from the chopped straw in the separator.

According to a fourth aspect of the present invention, there is provided an apparatus for processing harvested straw to produce a product suitable for animal bedding and a product suitable for use in an animal feed, including cutting means for converting harvested straw into a mixture, comprising straw pieces of a length less than a predetermined length and non-straw matter, and separating means for processing said mixture so as to produce material suitable for use as animal bedding, comprising substantially only straw pieces, and a material suitable for use in animal feed substantially free of straw pieces over a predetermined size.

Preferably, the separating means includes a separator according to the second aspect of the present invention.

Preferably the cutting means includes a hammer mill.

Suitable screen sizes for the hammer mill are 25mm, 50mm and 90mm.

Preferably, the apparatus further comprises bagging means for compressing and bagging the material suitable for use as animal bedding.

Preferably, the apparatus includes a further hammer mill for grinding at least a portion of the material suitable for use in animal feed to form meal. More preferably, the further hammer mill is provided with a 5mm screen.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of an apparatus according to the third aspect of the present invention; and Figure 2 shows a separator according to the second aspect of the present invention.

Referring to Figure 1, a conveyor 1, in the form of a bale track such as produced by JIK Industries, leads to a combing station 2. The combing station 2 comprises a pair of vertically spaced rotatable shafts 3,4. A plurality of blades 5 extend radially from each of the shafts 3,4. The shafts 3,4 are driven in contrarotation by a motor (not shown) so as to draw material from the end of the conveyor 1 through the space between them.

A shredder 6 is arranged to receive material passing from the combing station 2. The shredder 6 comprises a horizontal rotating disc 6a housed within an annular housing 6b. A plurality of blades 6c (only four of which are shown) extend radially outwardly from the circumference of the disc 6a. The blades 6c are dimensioned such that they end just short of the housing 6b. First and second outlets 6d,6e extend tangentially from the housing 6b at locations spaced from each other by about 1800 about the housing 6b.

An inlet (not shown) is provided above the disc 6a through which material to be shredded may be fed.

In operation, material to be shredded is fed through the inlet onto the upper surface of the rotating disc 6a. The rotation of the disc 6a causes the material thereon to move towards its circumference. As the material begins to fall from the circumferential edge of the disc 6a, it is cut by the blades 6c.

A first hammer mill 7 is coupled to the first outlet 6d of the shredder 6 to receive shredded material therefrom. A suitable hammer mill is a JIK Industries 40HP model with a 50mm screen. Further ducting couples the first hammber mill 7 to a separator 8. The separator 8 will be described in more detail hereinafter. The separator has a first outlet 9 and a second outlet 10.

A compressor 11, such as are produced by CAS Products Ltd., has its input coupled to the first outlet 9 of the separator 8.

The second outlet 6e of the shredder 6 is fed to a second hammer mill and a second shredder which form a parallel path indicated in Figure 1 by a broken line.

Ducting leading from the outlet of the compressor 11 merges with ducting from another compressor included in the parallel path and continues to the inlet of a cyclone 12. The cyclone 12 is of a conventional type having a first outlet 13 for air and ultra-fine particles and a second outlet 14 for larger particles.

The first outlet 13 of the cyclone 12 is coupled to the inlet of a reverse jet bag filter 16. The second output 14 of the cyclone 12 is coupled to the inlet of a third hammer mill 15, such as a JIK Industries Limited 25HP model with a 5mm screen. The outlet of the third hammer mill 15 is also coupled to the inlet of the reverse jet bag filter 16. The outlet of the reverse jet bag filter 16 leads to a feed auger, not shown, which leads to a storage area or to means for further processing.

The second outlet 10 of the separator 8 is connected to a gravity feed 19 of a bagging machine station 20, including at least one bagging machine, e.g. an LMS Challenger. The bagging machine station is also coupled to the second outlet of the separator in the parallel path.

Referring to Figure 2, the separator 8 comprises a steel tube 21 both ends 21a,21b of which are closed. A feed screw 22 is mounted coaxially within the tube 21.

An inlet 23 comprises a short tube extending radially from one end 21a margin of the tube 21. The inlet 23 is arranged to be coupled to ducting 24.

The second outlet 10 of the separator 8 is displaced by approximately 180 about the tube 21 from the inlet 23 and comprises a short rectangular cross section conduit 25 which blends with the contours of the tube 21 and extends radially from the tube 21 adjacent the other end 21b thereof. A drive motor 26 is mounted on a side of the conduit 25 with its shaft extending towards the second end 21b of the tube 21. A gearbox 27, also supported on the same side of the conduit 25, receives the shaft of the motor 26 and drives a pulley wheel which in turn drives the screw 22 by means of a toothed belt. The pulley wheel and the tooth belt are enclosed within a guard 28. The ends of the shaft carrying the screw 22 extend through the ends 21a,21b of the tube 21 where they are supported by bearings.

A medial portion of the tube 21 takes the form of a screen 29. The screen 29 is of the same diameter as the tube 21 and is provided with a plurality of regularly spaced apertures each of about 19mm diameter.

A housing 30 comprises a cylindrical portion 31 mounted coaxially about the screen 29. In Figure 2, parts of the cylindrical portion 31 and the screen 29 have been cut away in order to show the screw 22. The first outlet 9 is circular in cross-section and forms one axial extremity of a tube-like portion 32 which gradually blends into the cylindrical portion 31 of the housing 30 over its axial extent.

In operation, the separator 8 would be mounted in an inclined manner such that the end 21b having the second outlet 10 is raised above the end 21a having the inlet 23. Material to be separated, for instance a mixture of chopped straw, grain and dust particles is fed to the inlet 23 along the conduit 24. Rotation of the screw 22 under the influence of the motor 26 propels the mixture towards the second outlet 10. As the mixture passes the screen 29, smaller particles such as grain or dust pass through the holes therein and are extracted through the first outlet 9. The extraction of the smaller particles is assisted by a fan (not shown) drawing a stream of air out through the outlet 9 from within the screen 29.Larger particles of the mixture, primarily chopped straw, are retained within the tube by the screen 29 and are ultimately propelled to the second outlet 10 where they are discharged.

A process according to the present invention will now be described with reference to Figure 1.

A straw bale 33 including incidental other matter, e.g.

grains, is placed on the conveyor 1 whereupon its bindings are cut. The conveyor 1 transports the now loose straw 34 towards the combing station 2. The rotation of the upper shaft 3 and the lower shaft 4 of the combing station is such that the loose straw 34 is drawn between them where it is coarsely chopped by the blades 5.

The coarsely chopped straw is then funnelled into the shredder 6 where the straw is cut into shorter lengths.

The first hammer mill 7 and the second hammer mill draw the cut straw and other matter from the first shredder mill 6 along lengths of ducting and cuts the straw more finely to form straw pieces. The straw pieces are propelled, by the action of the first 7 and second hammer mills, towards the first separator 8 and the second separator along further lengths of ducting. The first separator 8 and the second separator operate as described hereinbefore and output substantially only straw pieces over a predetermined size from their second outlets 10, the remaining material being output from their first outlets 9.

The material emerging from the second outlets 10 of the first separator 8 and the second separator is fed via the gravity feed 19 to respective bagging machines at the bagging machine station 20. The bagging machines compress predetermined volumes of straw pieces and seals them in polythene bags. In order to achieve a higher packing density several compression strokes may be carried out before each bagging operation.

The material from the first outlet 9 of the separator is drawn by the compressor 11 and propelled to the cyclone 12.

The cyclone 12 operates in a conventional manner and discharges air and ultra-fine particles through its first outlet 13 and larger particles through its second outlet 14. The material emerging from the first outlet 13 of the cyclone 12 proceeds to the inlet of the reverse jet bag filter 16.

Before passing to the second outlet 14 of the cyclone 12, the larger particles pass through a rotary valve 12a which acts as an air lock to maintain the air pressure within the cyclone 12 as the larger particles are removed. The material from the second outlet 14 of the cyclone 12 is drawn to the third hammer mill 15.

In order for the third hammer mill 15 to work correctly on this material, additional air is introduced into the ducting between the cyclone 12 and the second hammer mill 15 by means of a simple hole therein. The second hammer mill 15 grinds the material from the cyclone 12 and propels the grounds to the inlet of the reverse jet bag filter 16.

The reverse jet bag filter 16 removes the ultra-fine particles and the grounds from the second hammer mill 15 from the air stream entering it and outputs clean air through a first port and meal 35, suitable for use in animal feed, through a second port. The meal 35 includes the grounds from the third hammer mill 16 and the ultrafine particles from the cyclone 12.

Prior to bagging, the output from the second outlet 10 of the separator 8 may be sprayed with a conditioning agent such as a mould or spore inhibitor.

In the aforegoing description an apparatus with a parallel path has been described. However, a single path may be employed or each stage duplicated as desired.

The first hammer mill 6 has been described with a 50mm screen and produces straw pieces suitable for use as poultry or pig bedding. If a 100mm screen is used straw pieces suitable for use as horse bedding are produced. Poultry bedding may be produced from new waxy straw using a 25mm screen.

Optionally, the entire apparatus can be operated under a negative internal pressure, in the sense that material can be caused to move therein by appropriately located suction means. For example, suction means, such as a fan or pump, can be used to draw air from the reverse jet bag filter 16 and, thus, draw air and material from the first outlet 9 and through the cyclone 12 and the third hammer mill 15. In this example, the compressor 11 may be dispersed with.

Also, the second part of the reverse jet bag filter can be connected to a conventional meal pelleting machine, where the meal 35 can be pelleted into a final product.

Claims

1. A method for proccessing harvested straw, comprising the steps of: (a) chopping harvested straw to produce a mixture comprising chopped straw pieces; and (b) separating chopped straw pieces, suitable for use as animal bedding, and a material suitable for use in animal feed from said mixture.

2. A method as claimed in claim 1, wherein the mixture comprising chopped straw pieces, formed in step (a), includes non-straw matter and straw particles of insufficient size for use as animal bedding.

3. A method as claimed in claim 2, wherein in step (b), the chopped straw pieces, suitable for use as an animal bedding, are separated from the mixture in a form substantially free of non-straw matter and straw particles of insufficient size for use as animal bedding.

4. A method as claimed in any of claims 1-3, wherein the chopped straw pieces, suitable for use as animal bedding, are at least lOmm to 30mm long.

5. A method as claimed in claim 4, wherein the chopped straw pieces, suitable for use as animal bedding, are at least 19mm long.

6. A method as claimed in any of claims 2-5, wherein the straw particles of insufficient size for use as animal bedding have a maximum dimension of between lOmm and 30mm and, preferably, of about 19mm.

7. A method as claimed in any of claims 2-6, wherein the straw particles of insufficient size, for use as animal bedding, are included in the material suitable for use in animal feed.

8. A method as claimed in any of the preceding claims, wherein the straw pieces, suitable for use as animal bedding, have a maximum length of about 90mm, or less.

9. A method as claimed in claim 8, wherein the straw pieces, suitable for use as animal bedding, have a maximum length of 50mm or less, or 25mm or less.

10. A separator comprising conveyor means, including a tubular structure and screw means located co-axially within the tubular structure, wherein a section of the tubular structure comprises a screen for selectively passing material propelled by the screw means.

11. A separator, as claimed in claim 10, wherein the screen is arranged for allowing straw particles and other matter, of insufficient size for use as animal bedding, to pass therethrough.

12. A separator, as claimed in claim 11, wherein the screen is arranged for allowing material having a maximum dimension of between 10 and 30mm, preferably of about 19mm, to pass therethrough and to retain larger matter.

13. A separator, as claimed in any of claims 10-12, wherein the tubular structure has a substantially circular cross-section and the screw means is an archimedies screw.

14. A separator, as claimed in any of claims 10-13, including a housing for constraining material which has passed through the screen and means for drawing such material from the housing.

15. A separator, as claimed in claim 14, wherein the housing includes an outlet and the means for drawing material from the housing comprises a fan.

16. A separator, as claimed in any of claims 10-15, wherein the screen is cylindrical and co-axial with the screw.

17. A separator, as claimed in any of claims 10-16, wherein the screen comprises curved sheet material, provided with a plurality of holes.

18, A method of producing material suitable for animal bedding, comprising passing chopped, harvested straw through a separator as claimed in any of claims 10-17.

19. A method as claimed in claim 18, wherein material suitable for use in animal feed is retrieved from the chopped straw in the separator.

20. Apparatus for carrying out a method for processing harvested straw, as claimed in claim 1, including cutting means for converting harvested straw into a mixture comprising chopped straw pieces and separating means for separating said mixture into a material comprising straw pieces, suitable for use as animal bedding, and a material suitable for use in animal feed.

21. Apparatus, as claimed in claim 20, wherien the separating means includes a separator, as claimed in any of claims 10-18.

22. Apparatus, as claimed in claim 20 or claim 21, wherein the cutting means includes a hammer mill.

23. Apparatus, as claimed in claim 22, wherein the hammer mill includes a 25mm, 50mm, or 90mm screen.

24. Apparatus, as claimed in any of claim 20-23, further comprising means for compressing and bagging the material suitable for use as animal bedding.

25. Apparatus, as claimed in any of claim 20-24, comprising further hammer mill means for grinding at least a portion of the material suitable for use in animal feed, to form meal.

26. Apparatus as claimed in claim 25, wherein said further hammer mill means is provided with a 5mm screen.

27. Apparatus as claimed in any of claims 20-26 arranged to carry out a method as claimed in any of claims 2-9.

28. Animal bedding, comprising straw pieces having a length within a predetermined range and substantially free of non-straw matter, other than an optional conditioning substance, and straw particles of less than said predetermined length.

29. Animal bedding whenever produced by a method as claimed in any of claims 1-9, 33 and 34, by employing a separator as claimed in any of claims 10-18, or by a method as claimed in any of claims 19-27.

30. Animal feed comprising straw particles of insufficient size for use as animal bedding.

31. Animal feed, as claimed in claim 30, whenever produced by a method as claimed in any of claims 1-9, using a separator as claimed in any of claims 10-17, or by apparatus as claimed in any of claims 18-27.

32. Animal feed as claimed in claim 30 or claim 31, whenever extracted from harvested straw.

33. A method as claimed in any of claims 1-9, wherein the material suitable for use in animal feed formed in step (b) is ground into a meal and, optionally, formed into pellets.

34. A method as claimed in any of claims 1-9 and 33, wherein the strawpieces, suitable for use as animal bedding, are treated with a conditioning substance.

35. A method, a separator, or apparatus, substantially as hereinbefore described with reference to the accompanying drawings.