GB2159689A - Apparatus for and method of compressing straw or other cellulosic material - Google Patents

Abstract

A mobile apparatus for collecting and compressing straw comprises a mobile frame and a pick-up mechanism 14 for picking up cut straw. Feed rollers 15 and 16 feed the straw to a chopping mechanism 17 which chops the straw into a predetermined size range, and blows the chopped straw to a holding tank 20 having an upwardly inclined auger 21. Additives are sprayed (from 24) onto the straw leaving the chopping means 17, and mixed by the auger 21. A force-feeding auger 26 feeds the chopped and mixed straw under pressure to a radial extrusion press 27 which extrudes compressed pellets of straw. The pellets are conveyed to a holding tank 33 where they are cooled by a blower 34. The chopped straw from the chopper 17 has a low meal content giving a higher content of chopped straw in the final compressed product, the compression being achieved by the combination of the force-feeding auger 26 and the radial extrusion press 27. <IMAGE>

Description

SPECIFICATION Apparatus for and method of compressing straw or other material The present invention relates to apparatus for and a method of compressing straw or other cellulosecontaining material of vegetable origin, and relates in particular, but not exclusively, to a mobile harvesting machine for harvesting strawfrom the ground and compressing the straw by the mobile apparatus.

Avast quantity of straw is burned after harvest each yearforwant of a better way of disposing of it.

Increasing quantities are however being utilised for cattle feed, due, in part, to the enhancement ofthe nutritional value ofthe material by chemical treatment, for example by caustic soda application or ammonia injection. These treatments are economically useful only on farms reasonably close to, or actually producing straw, the costs oftransporting straw rendering the habitual movement of the commodity over anything but short distances unattractive. This deficiency is partially overcome, at present, by taking straw to strategically sited industrial premises where the said straw is treated, milled and cubed. The end product is dense enough to produce a more worthwhile payload, and nutritionally useful enough to compete in the market place with other options.

However, the compressing process, as at present practised, demands considerable power inputs to achievethe milling and pulverising of the straw which is deemed necessaryto be ableto "cube" the end product, that is to say to compress the straw into a compressed unit in which the straw adheres together.

Furthermore, the fibre structure of the end product is not best suited to optimising digestion in the rumen of cattle, through which, by virtue of its very short length, it tends to pass too quickly.

It is one object ofthe present invention to overcome or reduce the problem of transport of straw, by providing apparatus for compressing straw which is mobile and may be utilised in the harvest field. It is another object to provide a compressed straw product which has an improved composition, both from the point of view of density and convenience of handling of compressed straw units, and from the point of view of improved nutritional quality to cattle or other ruminants. Howeverthe invention also provides advantage in static apparatus forcompressing straw, and in apparatus for compressing straw for use as fuel ratherthan for animal feed.

It is also known to provide a mobile apparatus for compressing forage material, namely a machine produced by John Deere and others and known as a hay cuber. In this machine, cut hay was picked up, moistened, and chopped by a cylinder cutter head which chopped and mixed the hay and water. Two spiral knives sliced the crop to an average length of 35mm. A radial extrusion press forced the hay through a plurality of 30mm dies and formed compressed cubes of average length in the range 50 to 75mm. The apparatus was limited to use with hay; utilised a relatively low density ratio of the compressed to uncompressed hay; and formed a relatively large final compressed unit.

Another apparatus which can be used in the field to compress straw, is known as the Ecobriquet, in which straw is ground by a knife drum, and is then compressed by a single throw of a piston compresser, which provides cylindrical, pressed straw, units of approximate size 50 to 75mm. Although this machine may be used in the field, the straw is carried to the machine and loaded into the machine, which then operates in a stationary manner. Afurtherform of such a machine is known as the Promill mobile granulation unit.

It is a further object of the present invention to provide an apparatus and method for compressing straw, to provide compressed straw units, which have a high density relative to the unpressed straw; in which the straw adheres togetherwellto provide a stable unit; and which provides a size of compressed unit allowing convenient mechanical handling.

Itisto be appreciatedthatthe apparatus and method of the present invention are not limited to straw but are applicable to other forms of cellulosecontaining material of vegetable origin. Examples are dried green crop; dried beet pulp; sunflower, rice or coffee husks; and wood-based material such as wood shavings, wood chips and the like. Such material is sometimes known as biomass. Where reference is made to straw in describing examples of use of the invention, itshould be understood that this includes other material where applicable.

According to the present invention there is provided apparatus for compressing straw or other cellulosecontaining material ofvegetable origin comprising chopping meansforcutting material to lengths lying substantially in a selected range,thechopping means including size limiting means arranged to pass chopped lengths of material of an average length less than a predetermined maximum, and to return other material to the chopping means, means for adding to the chopped material additives for changing the consistency and/or chemical composition of the material, means for mixing the cut material and additives, the mixing means being arranged to retain the material and additives during mixing for a selected period of time, and means str compressing the cut material and extruding the compressed material to form units of compressed material in which the material adheres together, the compressing means comprising a rotary extrusion press comprising a die member having a plurality of extrusion apertures, and a roller memberforforcing the chopped material out through the extrusion apertures, the die member and the roller member being arranged to rotate relative to each other, and there being provided force-feeding means for urging the chopped material into the extrusion press byapplication offorcetothe material.

Preferably the said maximum set by the size limiting means lies in the range 6mm to 25mm, more preferably 8mm to 1 6mm and most preferably approximately 1 2mm. Such a size limiting means may The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy.

conveniently comprise an apertured screen, for exam ple extending around a rotary cutting mechanism, the rotary cutting mechanism effecting transport ofthe chopped material through the apertured screen by a fan effect of rotating blades of the chopping mechanism. The effect of a size limiting means such as has been set out, may be arranged to provide chopped material having an average length in the range 6to 25mm,preferably5to 16mm,and most preferably approximately 8mm.

Byway ofexample, where for example a 1 2mm screen is used, the average length of chopped straw will be in the rangeSto 8mm.

It is a particularly significantfeature of preferred forms ofthe present invention that the chopping means is of a kind such thatthe chopped material, especially chopped straw, has a low meal content, for examplethe proportion of material in the cut straw which comprises meal of particle size less than 0.5m m, being less than 20% by weight ofthetotal chopped straw leaving the chopping means, most preferably being less than 8% by weight.

With reference to the said extrusion die, preferably the aperture size of each extrusion die lies in the range 8mm to 20mm. most preferably 1 Omm to 16mm.

A particularly preferred form of chopping means comprises a cutting rotor having its blades extending transverse to the direction of movement of the material into the chopping means, and operating to chop the material by co-operation of the rotating blades with a static blade also transverseto the direction of material moving into the chopping means. Such a chopping means may be ofthe kind used on a precision chop forage harvester. Other forms of chopping means which may be used include a fly-wheel forage harvester chopper.

Convenientlythe said chopping means is of a kind having rotating blades such as to effect transport of the chopped material from the chopping means to the mixing means by a fan effect ofthe blades, (for example as found in a precision chop forage harvester), and the said means for adding additives to the chopped material includes or consists of means for spraying additives onto the chopped material while it is being blown from the chopping means to the mixing means.

Convenientlythe said mixing means comprises an inclined, upwardly directed auger arranged in such a mannerthatthe chopped material is lifted up the auger but partially falls back down the auger so that material is delayed in the auger during transport throughtheauger,and is mixed byatumbling action.

Preferably the said force-feeding means comprises an augerforfeeding the cut material tothe compressor means under pressure, or similar means.

Therewill normally be provided in accordance with the invention meansforstoring thecompressed units, known as pellets or cubes, upon leaving the compressing means, forexample a hopper, and means for effecting cooling ofthe compressed units in the said container, for example by means of a fan for blowing airthrough the compressed units.

In addition, there may be provided means for adding additives to the material while it is being mixed in the said mixing means.

Although the invention has application when used in the static mode, the invention finds particular advantagewherethe apparatus comprises a mobile apparatus including a mobile frame for movement overthe ground, and a pick-up mechanism for picking up material from the ground.

In its broadest form in this aspect, there is provided in accordance with the present invention apparatus for compressing straw or other cellulose-containing material ofvegetable origin comprising a mobile framefor movement overthe ground,a pick-up mechanism for picking up material from the ground, chopping means for cutting the material to lengths lying substantially in a selected range, means for adding te the chopped material additives for changing the consistency and/or chemical composition ofthe material, means for mixing the cut material and additives, the mixing means being arranged to retain the material and additivesfora selected period oftime during mixing, and means for compressing the cut material and extruding the compressed material to form units of compressed material in which the material adheres together.

In a particular preferred form of the invention in this aspect, there is provided apparatus for compressing straw comprising a mobile frame for movement over the ground, a pick up mechanism for picking up straw from the ground, chopping meansforcutting straw to lengths lying substantially in a selected range, the chopping means including size limiting means arranged to pass chopped lengths of straw of average length lessthana predetermined maximum,andto return other straw to the chopping means, the said predetermined maximum lying in the range 6mm to 25morn, the chopping means being a rotary chopping mechanism of a kind such that the chopped straw has a iowmealcontent, meansforadding to the chopped straw additives for changing the consistency and/or chemical composition ofthe straw, means for mixing the cut straw and additives, the mixing means being arranged to retain the straw and additives during mixing for a selected period of time, means for compressing the cut straw and extruding the compressed straw to form units of compressed straw in which the straw adheres together, the compressing means comprising a radial extrusion press comprising an outer annular die member having a plurality of extrusion apertures, and an inner press memberfor forcing the chopped straw out through the extrusion apertures,the outer die member and the inner press member being arranged to rotate relative to each other, each aperture diameter lying in the range 8mm to 1 6mm, a force-feeding augerfor urging the chopped straw in to the compressing means by application offorce, and cooling means for cooling the compressed straw units.

There is also provided in accordancewiththe present invention a method of compressing straw or other cellulose-containing material or vegetable origin comprising the steps of chopping the material to lengths lying in a selected range such that the average crop length lies in the range 6to 25mm, and the proportion of meal of particle size lessthan 0.5mm in the chopped material is less than 20% by weight, and compressing the cut material and extruding the compressed material to form units of compressed material in which the compressed material adheres together.

In accordance with the preferred form of thins aspect ofthe invention,there is provided a method of compressing straw comprising the steps of chopping straw to lengths lying in a selected range such that the average crop length lies in the range 6 to 25mm, and the proportion of meal of particle size less than 0.5mm in the chopped straw is lessthan 20% byweight, adding to the chopped straw additives for changing the consistency and/or chemical composition ofthe straw, mixing the cut straw and additives in mixing means, including retaining the cutstrawand additives in the mixing means during mixing for a selected period oftime, compressing the cut straw and extruding the compressed straw to form units of compressed straw in which the compressed straw adheres together, the compressing and extruding steps including compressing the chopped straw by a rotary extrusion press comprising a die member having a plurality of extrusion apertures, and a roller memberforforcing the chopped straw out through the extrusion dies, the die member and the inner press member being arranged to rotate relativetteach other, and extruding the compressed strawthrough dies having an aperture diameter lying in the range 8mm to 1 6mm, the method also including the step of force-feeding the chopped straw into the radial extrusion press under pressure, and cooling the extruded units of compressed straw.

In general, features and aspects of the invention which have been set out hereinbefore with regard to apparatus, are also provided in accordance with the method aspects ofthe invention.

Itwill be appreciated that the present invention, at least in preferred forms, provides a convenient, compact, mobile apparatus in which a number of features combine to allow effective compression of straw in a mobile apparatus. The use of a chopping means for cutting the straw, in place of the conventional grinding apparatus used for grinding straw in static applications, provides a lighter and more mobile cutting means. The provision of a size limiting means for providing cut straw with lengths lying in a selected range, allows the straw length to be selected for a convenient length for subsequent compression, and also a convenient length for use as animal feed. The use of a chopping mechanism giving a low meal content is of particular importance in providing a much higher proportion of cut straw in a product for animal feed as compared with cubes formed from ground straw.It has previously been supposed that ground straw having a low meal content would give rise to insuperable difficulties in straw compression, and as a result a high meal content has been provided in straw to be compressed. However, such a high meal content is unsatisfactory for providing an animal feed product, where the absorption ofthe product by the animal depends upon the length of time that the product remains in the rumen of the animal.This timing in turn requires a high proportion of chopped straw, rather than ground meal which passes easily through the eigestive system ofthe animal without absorption.Thus it has beenfound particularly advantageous that the use of a chopping mechanism in place of a grinding mechanism provides a lighter, more mobile apparatus, with lower powerconsump- tion, and also provides an improved product for animal feed purposes.In accordance with the inven tin, the more difficulttask of compressing the material in the absence of a high meal content, is obviated by the combination of a force-feeding mechanism such as an augerforfeeding the chopped straw to the compressing unit, and the use of a radial extrusion press in place of the previously used reciprocating piston extrusion press which has been used in previous mobile straw compressors.

In operating a radial extrusion press with a low meal content chopped straw material, particular care is needed in the selection of die. Parameters to be considered include the diameter of the aperture of the die, the length or wall thickness of the die, the texture of the material being compressed, and the shape of the die, for example the lead-in to the die aperture. It has been found that a wall thickness less than that normally used forthe die member may be advantageous, for example the wall thickness may be reduced from a conventional lOOmm thickness to a thickness of 95mm. It is found that operating conditions in the field may affect the type of die used.

Particular care must be taken to provide adequate cooling for the compressed units or pellets to prevent these catching fire when stored, for example in a hopper. Conveniently cooling can be provided by a blower blowing air intothe containerforthe com- pressed straw units.

The delay provided forthe straw being conveyed and tumbled up the auger may conveniently be three to four minutes.

The additives which may be applied will chiefly be liquid additives sprayed as mentioned above onto the chopped straw when passing between the chopping means and the mixing means, but in addition dry additives may be added to the material during the mixing process. The purpose of the additives will be chieflyto changethe constituency of the straw to give added food value, and/orfor binding together the strawduringthe compressing process, and/orto enhance the feed value of the material for example by adding minerals, and/orforthe lubrication ofthedie.

However, where the end product isto be used for fuel, additives may be added for the purpose of binding the material during the compression, and/or in orderto add to the calorific value ofthe compressed units.

Considering again the use ofthe chopped and compressed straw as a cattle feed, an overall objective of the chopping and compressing process is to provide in the finished compressed pellet a fibre length in the range 5mm to 1 Omm. The chopped length of straw before compression required to achieve this depends upon the degree offurther reduction of fibre length imposed by the compression process. Fibres in the range 5mm to 1 Omm are retained in the rumen ofthe animal and hence are subjected to the full effect ofthe digestive system, as ompared with meal of smaller dimensions which is flushed through the rumen without being properly prepared forthefurther digestive tracts.

Embodiments of the invention will now be de scribed by way of example with reference to the accompanying drawings in which: Figure lisa diagrammatic side view of apparatus for compressing straw embodying the invention; and Figure 2 is a diagrammatic, exploded, view of the main components ofthe apparatus shown in Figure 1.

Referring to the Figures, a mobile frame 11 for movementovertheground has landwheels 12 and a tow hitch 13.A pick-up rotor 140f conventional kind lifts the strawfrom the field and loads it into two pairs offeed rolls 15 and 16, of a forage chopper 17. The chopping mechanism 17 may be of any of a number of conventional forage chopping mechanisms,forexamplea rotary drum chopper or a fly-wheel chopper, but the preferred form shown comprises a cutting rotor 18 (Figure 3) having its blades 19 extending transverse to the direction of movement of straw into the chopping means, and operating to chop straw by co-operation ofthe rotating blades 19 with a static blade (not shown) which is also transverse to the direction of straw moving into the chopping means.

The chopped straw is blown by fan effect of the blades 1 9to a mixing means 20 formed by an inclined upwardly directed auger 21 arranged in such a mannerthatthe chopped straw is lifted up the auger but partially falls back down the auger so thatthe material is delayed in the auger during transport through the auger, and is mixed by a tumbling action.

The auger 21 hasacontinuousflightformed as a ribbon held in relation to its axial drive shaft 22 by radial extensions 23 thereof,the extensions forming paddles connecting the ribbon flighttothe axial drive shaft 22. The driven auger 21 acts as a mixerwhilst impelling a proportion of the chopped straw out of the mixing means 20, which acts in effect as a holding tank.

Between the chopping means 17 and the mixing means 20, are liquid injectors 24 for spraying additives onto the chopped strawwhilst it is being blown from the chopper 17to the mixing means 20. The additives are provided forchanging theconsistency and/or chemical composition ofthe straw. In some circumst- ancesforcertain straw, the machine maybe operated without the use of additives.

The auger 21 is driven, in a preferred embodiment, byan hydraulic motor 25 whose speed may be regulated in accordance with throughput of crop, and the auger 21 discharges the mixed material, by gravity, to a force-feed auger 26 which feeds the chopped and mixed material under pressure to compressing means for compressing the chopped straw.

The compressing means 27 comprises a radial extrusion press comprising an outer annular die member 28 having a plurality of extrusion apertures (not shown), and an inner press member 29 forforcing the chopped strawoutthroughthe extrusion apertures,the outer die member 28 and the inner press member 29 being arranged to rotate relative to each other.

The compressing means 27 discharges the compressed straw units (variously referred to in the art as "cubes" or "pellets") into a trough 30 having an auger 31 which transfers the pelletsto an elevator32. The elevator 32 conveys the pellets to a holding tank 33 in which the pellets are cooled by a blower 34 driving air along a conduit 35 to the base of the holding tank 33.

Within the tank 33, the material is distributed by an auger 36, and atthe base of the tank 33 is a further auger 37 which is operated intermittantlyto drive material to an elevating auger 38 used for discharging material from the holding tank 33 to a separate bulk trailer39.

The apparatus may be tractor-drawn and driven, tractor-drawn and driven by a separate prime mover, or a combination of the two, or may be self propelled.

Furthermore, in some arrangements, the apparatus may be operated in a static mode.

Various sensing and controlling means may be applied at appropriate points throughouttheflow path through the apparatus,to monitor and controlthe various functions of the apparatus. A sensor may warn the operator of an excessive build-up of material and so to avoid a time consuming blockage. Similarly purposed sensors may be located in the holding and mixing tank 20 and in the finished pellettank33, the warning means being located adjacenttothe operator, who in the case of a tractor-drawn machine, will be remote from the main apparatus. The control of the apparatus and maximisation of output may require the automatic control of a numberoffacets of operation. Crops are, regretably uneven, and the intake of straw to the apparatus is therefore similarly uneven, and the addition of additives requires regulation according to the volume of material being chopped.

Additives may be injected for: the improvement of the nutritive value of the finished product, having nutritional value in their own right; for lubricating the compressing process to reduce power inputs and cut-down wear on the compressor; to act as binding agents forthe improved stability ofthe end product under storage, and handling in the process of delivery to the end user; and forthe improvement of the nutritional value ofthe raw material by chemical reaction therewith, as for example occurs in the use of caustic soda.

Claims (21)

1. Apparatusforcompressing straworother cellulose-containing material of vegetable origin comprising chopping means for cutting material to lengths lying substantially in a selected range, the chopping means including size limiting means arranged to pass chopped lengths of material of an average length less than a predetermined maximum, and to return other material to the chopping means, means for adding to the chopped material additives for changing the consistency and/or chemical composition ofthe material, means for mixing the cut material and additives,the mixing means being arranged to retain the material and additives during mixing for a selected period of time, and means for compressing the cut material and extruding the compressed material to form units of compressed material in which the material adheres together, the compressing means comprising a rotary extrusion press comprising a die member having a plurality of extrusion apertures, and a roller member for forcing the chopped material out through the extrusion apertures, the die member and the roller member being arranged to rotate relative to each other, and there being provided force-feeding means for urging the chopped material into the extrusion press by application of force to the material.

2. Apparatus according to claim 1 in which the said maximum set by the size limiting means lies in the range 6mm to 25mm.

3. Apparatus according to claim 1 in which the said maximum set by the size limiting means lies in the range 8mm to 16mm.

4. Apparatus according to any preceding claim in which the chopping means is of a kind such that the chopped material has a low meal content, the proportion of material in the cut material which comprises meal of particle size less than 0.5mm, being less than 20% byweightofthetotal chopped material leaving the chopping means.

5. Apparatus according to any preceding claim in which the aperture size of each extrusion die lies in the range8mmto 16mm.

6. Apparatus according to any preceding claim in which the wall thickness of each extrusion die lies in the range 50mm to 11 Omm.

7. Apparatus according to any preceding claim in which the chopping means comprises a cutting rotor having its blades extending transverse to the direction of movementofthe material into the chopping means, and operating to chop the material by co-operation of the rotating blades with a static blade also transverse to the direction of material moving into the chopping means.

8. Apparatus according to any preceding claim in which the size limiting means comprises a screen, having apertures, extending around a rotary cutting mechanism, the rotary cutting mechanism effecting transport of the chopped material through the apertured screen by a fan effect ofthe rotating blades ofthe chopping mechanism.

9. Apparatus according to any preceding claim in which the said chopping means is of a kind having rotating blades such asto effect transport of the chopped crop from the chopping means to the mixing means by a fan effect of the blades, the said means for adding additives to the chopped material including or consisting ofmeansforspraying additives onto the chopped material while it is being blown from the chopping means to the mixing means.

10. Apparatus according to any preceding claim in which the said mixing means comprises an inclined upwardly directed auger arranged in such a manner thatthe chopped material is lifted up the auger but partially falls back down the auger so that material is delayed in the auger during transportthrough the auger, and is mixed by a tumbling action.

11. Apparatus according to any preceding claim in which the said force-feeding means comprises an augerforfeeding the cut material into the radial extrusion press under pressure.

12. Apparatus according to any preceding claim including means for storing the compressed units leaving the compressing means, and means for effecting cooling ofthe compressed units in the said container.

13. Apparatus according to claim 12 in which the said cooling means comprises a fan for blowing air through the compressed units.

14. Apparatus according to any preceding claim in which the means for adding additives includes means for adding dry additives to the material while being mixed in the said mixing means.

15. Apparatus according to any preceding claim comprising a mobile apparatus including a mobile frame for movement over the ground, and a pick-up mechanism for picking up material from the ground.

16. Apparatus fOr compressing straw or other cellulose-containing material of vegetable origin comprising a mobile frame for movement over the ground, a pick-up mechanism for picking up material from the ground, chopping means for cutting the material to lengths lying substantially in a selected range, Means for adding to the chopped material additives for changing the consistency and/or chemical composition ofthe material, means for mixing the cut material and additives, the mixing means being arranged to retain the material and additives for a selected period oftime during mixing, and means for compressing the cut material and extruding the compressed material to form units of compressed material in which the material adheres together.

17. Apparatusforcompressing straw comprising a mobile frame for movementoverthe ground, a pick up mechanism for picking up straw from the ground, chopping meansforcutting strawto lengths lying substantially in a selected range, the chopping means including size limiting means arranged to pass chopped lengths of straw of average length less than a predetermined maximum, and to return other straw to the chopping means, the said predetermined maximum lying in the range 6mm to 25mm, the chopping means being a rotary chopping mechanism of a kind such that the chopped straw has a low meal content, means for adding to the chopped straw additives for changing the consistency and/or chemical composition of the straw, means for mixing the cut straw and additives, the mixing means being arranged to retain the straw and additives during mixing for a selected period of time, means for compressing the cut straw and extruding the compressed straw to form units of compressed straw in which the straw adheres together. the compressing means comprising a radial extrusion press comprising an outer annular die member having a plurality of extrusion apertures, and an inner press memberforforcing the chopped straw out through the extrusion apertures, the outer die member and the inner press member being arranged to rotate relative to each other, each aperture diameter lying in the range 8mm to 16mm, a force-feeding augerfor urging the chopped straw in to the compressing means by application of force, and cooling means for cooling the compressed straw units.

18. Amethodofcompressing straworother cellulose-containing material ofvegetable origin comprising the steps of chopping the material to lengths lying in a selected range such thatthe average crop length lies in the range 6to 25mm, and the proportion of meal of particle size less than 0.5mm in the chopped material is iess than 20% by weight, and compressing the cut material and extruding the compressed material to form units of compressed material in which the compressed material adheres together.

19. Amethodofcompressing strawcomprising the steps of chopping strawto lengths lying in a selected range such that the average crop length lies in the range 6 to 25mm, and the proportion of meal of particle size less than 0.5mm in the chopped straw is less than 20% by weight, adding to the chopped straw additives for changing the consistency and/or chemical composition ofthe straw, mixing the cut straw and additives in mixing means, including retaining the cut straw and additives in the mixing means during mixing fora selected period of time, compressing the cut straw and extruding the compressed straw to form units of compressed straw in which the compressed straw adheres together, the compressing and extruding steps including compressing the chopped straw by a rotary extrusion press comprising a die member having a plurality of extrusion apertures, and a roller memberforforcing the chopped strawoutthrough the extrusion dies, the die memberandthe inner press member being arranged to rotate relative to each other, and extruding the compressed straw through dies having an aperture diameter lying in the range 8mm to 16mm, the method also including the step of force-feeding the chopped straw into the radial extrusion press under pressure, and cooling the extruded units of compressed straw.

20. Apparatus for compressing straw substantially as hereinbefore described with reference to Figures 1 and 2 ofthe accompanying drawings.

21. A method of compressing straw substantially as hereinbefore described with reference to Figures and 2 ofthe accompanying drawings.