EP1601523A1

EP1601523A1 - A compaction unit for a pelletizing machine, a machine for pelletizing and a method for making fuel pellets

Info

Publication number: EP1601523A1
Application number: EP03792927A
Authority: EP
Inventors: Jan Anjou
Original assignee: MINIPELL AB
Current assignee: MINIPELL AKTIEBOLAG
Priority date: 2002-08-21
Filing date: 2003-08-21
Publication date: 2005-12-07
Also published as: SE523347C2; WO2004018189A1; SE0202490L; SE0202490D0; AU2003253541A1

Abstract

The invention relates to a compaction unit (1) for a pelletizing machine (2). The compaction unit (1) comprises a tube (3) with a through passage (5). Raw material can be supplied into a feeding chamber (9), via an opening (8) in the wall of tube (3). The through passage of the tube has a section (10) having a converging cross-section. A piston (12) is lodged to slide in the tube (3) and arranged to be guided through the through passage of the tube (3) in order to compact shavings to fuel pellets. The piston (12) has two parts that are held together by a flexible coupling. The invention also relates to a machine that utilizes the inventive compaction unit and a method for making fuel pellets.

Description

A COMPACTION UNIT FOR A PELLETIZING MACHINE, A MACHINE FOR PELLETIZING AND A METHOD FOR MAKING FUEL PELLETS.

TECHNICAL FIELD

The present invention relates to a compaction unit for the compaction of comminuted raw material into pellets that can be used as a fuel. The raw material can be wood shavings - sawdust e.g. - but it is also possible to use other materials, such as e.g. straw or linseed. The invention also relates to a machine for making fuel pellets and a method for making fuel pellets.

BACKGROUND OF THE INVENTION

Wood shavings, e.g. sawdust and chips, result as a surplus material in e.g. saw mills. Such material can be used as biofuel. Chips and shavings however have a tendency to sinter in an incinerator. It is therefore necessary to convert the raw material into biopellets that should have a hard and smooth surface and that flow freely when fed into an incinerator. In order to convert the raw material into pellets, the material should be exposed to high pressure and high heat. It is known that when lignin-containing wood material is compacted at high pressure, lignin will be released and act as a natural binding agent to give the pellets a hard surface. It should however be understood that the invention also can be applied on non-ligmn-containing raw materials. It is previously known to produce pellets in a machine that has an annular matrix and a tool rotating in the matrix. In such a device, the pressure in each hole will however be hard to determine beforehand. It is known in this case to supply hot steam to the shavings material, in order to avoid clogging problems. This will however make the process more expensive. It is therefore an object to provide a method for making fuel pellets from wood shavings, in which the pressure of the process can be precisely controlled and in which the need to supply hot steam to the shavings material is reduced or completely avoided. It is furthermore an object to provide a method for making fuel pellets, that enables an economically rational production.

ACCOUNT OF THE INVENTION

The invention relates to a compaction unit for a pelletizing machine. The compaction unit comprises a tube having a through passage and an outlet end of the passage. On the tube, there is a section including an opening in the wall of the tube, by which opening raw material can be supplied into the tube, to a feeding chamber. On the tube, there is also at least one section in which the through passage of the tube has a cross-section converging in a direction towards the outlet end of the passage so that raw material that passes through the tube is compacted.

A piston is lodged to slide in the tube and arranged to be guided through the through passage of the tube from a retracted position in which the feeding chamber of the tube is exposed and from there through the feeding chamber and further on in direction towards the outlet end of the through passage of the tube. The piston comprises an inner piston part and an outer piston part. The outer piston part can move along with the inner piston part. On the outer piston part, there is a first stop and on the tube, there is a second stop arranged to interact with the first stop. Thereby, the movement of the outer piston part in direction towards the outlet end can be arrested as the first stop meets the second stop. The inner and outer piston parts are held together by a flexible coupling between the inner and the outer piston parts, which flexible coupling however allows the inner piston part to continue to move towards the outlet end even after the movement of the outer piston part has been arrested.

In an advantageous embodiment, the opening of the tube has a rear edge and a front edge, which front edge forms the second stop. The first stop may be constituted by a pin that projects from the outer piston part, which pin sets the bounds for the movement of the outer piston part, in interaction with the rear and front edges of the opening.

The coupling between the outer and inner piston parts may be a friction coupling. Alternatively, the coupling between the outer and inner piston parts may comprise at least one elastic member that acts on the piston parts in order to bring them back to an equilibrium position as soon as the piston parts start to move in relation to each other. In another conceivable embodiment, the flexible coupling comprises a hydraulic or pneumatic element that counteracts a relative movement of the outer and inner piston parts. It is also conceivable that the flexible coupling comprises a thread.

A final section of the through passage, immediately before the outlet end, may suitably have a diverging cross-section.

In an advantageous embodiment, the outer and inner piston parts are essentially circular cylindrical and at least a part of the through passage has a circular cylindrical cross- section. The invention also relates to a pelletizing machine for conversion of raw material - such as wood shavings - to fuel pellets. The inventive machine comprises at least one compaction unit. The compaction unit has a tube with an opening through which wood shavings can be supplied into a feeding chamber. The tube has a through passage, the cross-section of which converges in direction towards an outlet end of the passage and a piston that is lodged to slide in the tube in order to compact the raw material placed in the feeding chamber. The machine has at least one container in which the compaction unit is placed, and at least one power device is arranged to act on an end of the piston in order to force the piston through the through passage and thereby to compact raw material such as wood shavings that has been supplied to the feeding chamber of the compaction unit.

Preferably, a number of compaction units are placed in the container, but embodiments are also conceivable in which only one compaction unit is used.

The power device of the machine is preferably a power device that is arranged to operate in two directions. The power device may e.g. be constituted by or comprise a double-acting hydraulic cylinder that is fixedly connected to the piston of one or more compaction units in order to move the piston forwards as well as backwards, by the double-acting hydraulic cylinder. Then, the machine suitably comprises two containers having compaction units placed on either side of the power device in order to allow the power device to make in both directions alternating operational strokes. In an advantageous embodiment, the machine also has a hood to cover the containers provided with compaction units. The hood has openings to let in wood shavings via the hood and on to the containers provided with compaction units. Preferably, a rotary mounted stirring member is arranged in connection with at least one of the openings in the hood. Embodiments without a stirring member are however also conceivable.

The invention further relates to a method for making fuel pellets from raw material such as wood shavings. The method comprises the providing of a tube with a through passage that mouths in an outlet end of the tube. In the tube, there is a feeding chamber that opens out to allow wood shavings to be supplied into the feeding chamber, and the through passage of the tube has at least one section with a converging cross-section. In connection with the feeding chamber, an elongated piston is arranged, which piston comprises an inner piston part and an outer piston part that are connected to each other but movable in relation to each other in the longitudinal direction of the tube. An amount of raw material is filled into the feeding chamber and the piston is moved through the feeding chamber, from a retracted position, to force wood shavings present in the feeding chamber into the through passage of the tube, while at the same time compacting it in a first compaction stage. The movement of the outer piston part is arrested and the inner piston part continues to move through at least a portion of the through passage section having a converging cross-section, so that the shavings material is compacted by the inner piston part, in a second compaction stage.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the inventive compaction unit, as seen in perspective. Fig. 2 shows the inventive compaction unit, as seen in cross-section.

Fig. 3 shows an initial phase of the compaction.

Fig. 4 shows an later phase of the compaction.

Fig. 5 shows a final phase of the compaction.

Fig. 6 shows the inventive pelletizing machine, as seen in perspective. Fig. 7 shows the inventive pelletizing machine, as seen from above.

Fig. 8 shows an alternative embodiment of the inventive compaction unit.

DETAILED DESCRIPTION OF THE INVENTION

It is now referred to Fig. 1. and Fig. 2. The invention relates to a compaction unit 1 for a pelletizing machine 2. The inventive compaction unit 1 comprises a tube 3 having a through passage 5 and an outlet end 6 of the passage 5. On the tube 3, there is a section 7 with an opening 8 in the wall 4 of the tube 3. Raw material - such as sawdust - can be supplied into the tube 3, via the opening 8 and into a feeding chamber 9. On the tube 3, there is also at least one section 10, 11, in which the through passage 5 of the tube 3 has a cross-section that converges in direction towards the outlet end 6 of the passage 5. Therefore, raw material such as sawdust or shavings will be compacted as it passes through the tube 3. A piston 12 is lodged to slide in the tube 3 and arranged to be guided through the through passage 5 of the tube 3 from a retracted position in which the feeding chamber 9 of the tube 3 is exposed and from there through the feeding chamber 9 and further on in direction towards the outlet end 6 of the through passage 5 of the tube 3. The piston 12 comprises an inner piston part 13 and an outer piston part 14, which outer piston part 14 can move along with the inner piston part 13. A first stop 15 is arranged in the outer piston part 14 and a second stop 16 is arranged on the tube 3. The second stop 16 is arranged to interact with the first stop 15, to bring the movement of the outer piston part 14 in direction towards the outlet end 6 to a standstill as the first stop 15 meets the second stop 16. The inner and outer piston parts are held together by a flexible coupling 18 between the inner 13 and the outer 14 piston parts, which flexible coupling however allows the inner piston part 13 to continue to move towards the outlet end 6 even after the movement of the outer piston part 14 has been arrested.

The opening 8 of the tube 3 has a rear edge 17 and a front edge 16, which front edge 16 can form the second stop 16; and the first stop 15 can consist of a pin 15 that projects from the outer piston part 14 and that in interaction with the rear and front edges of the opening 8 sets the bounds for the movement of the outer piston part 14.

In one embodiment of the invention, the coupling 18 between the outer and the inner piston parts 13, 14 is a friction coupling 19. The friction between the inner piston part 13 and the outer piston part 14 can be set by a nut, which presses a collar material against the inner piston part 13. Thereby, the dullness and the force that the outer piston part presses with, is adjustable. Embodiments in which the coupling is composed of something else are however also conceivable. The coupling may for example comprise at least one elastic member 20 that acts on the piston parts 13, 14 in order to bring them back to an equilibrium position as soon as the piston parts 13, 14 start to move on relation to each other. In Fig. 8, there is shown how the piston parts 13, 14 are connected by a tense spring 20 that is stretched as the piston parts 13, 14 slide in relation to each other. The tense spring 20 can rest against e.g. a collar 50 on the inner piston part 13. Embodiments are also conceivable in which the coupling comprises a hydraulic or pneumatic element that counteracts a relative movement of the outer and inner piston part.

In yet another conceivable embodiment, the coupling could comprise a thread.

In one embodiment of the invention, which is most clear from Fig. 3 to Fig. 5, a final portion of the through passage 5 is arranged such that the passage 5 has a diverging cross-section 21 immediately before the outlet end 6. This portion of the passage 5 is a decompression section. Thereby, the advantage is obtained that the pellets do not easily crack.

The outer 14 and the inner piston parts 13 are preferably designed to be essentially circular cylindrical and at least a portion of the through passage 5 is suitably designed with a circular cylindrical cross-section. A suitable diameter for the inner piston part 13 can be 8 mm and a suitable diameter for the outer piston part 14 can be 16 mm. The function of the inventive compaction unit 1 is best understood from Fig. 3 to Fig. 5. In an initial compaction phase, the piston 12 operates as a low pressure piston to compact wood shavings in the converging section 10. Then, the movement of the outer piston part 14 is arrested as the pin 15 meets the edge 16 of the opening 8 in the tube. The coupling 18 will however allow the inner piston part 13 to move in relation to the outer piston part 14. The friction coupling 19 will yield as the power that acts on the coupling exceeds a given value. Now, the inner piston part 13 acts as a high pressure piston and presses the shavings material in a second compaction stage in the converging section 10. Suitably, the process is arranged not to force the finally compacted shavings material completely out from the compaction unit in the second compaction stage. Instead, the material can rest for about 1 second to "harden", before it is driven out by the material that is compacted in the next operating stroke. By performing the compaction with a piston that operates in a tube, the advantage is attained that the pressure in each hole can be controlled very precisely. The pressure is located where desired. Thereby, the need to supply hot steam to the shavings material decreases or is eliminated. By performing the compaction in two steps, the advantage is attained inter alia that more material can be used in each operating stroke. Another advantage is that a completely solid piston would build up to large a resistance. The passage 5 would have to be longer if a completely solid piston 12 was used. It should be understood that when the piston 12 moves backwards after a finished operating stroke, the pin 15 will meet the rear edge 17 of the opening 8 in the tube. Then, the movement of the outer piston part 14 will again be arrested, while the inner piston part 13 continues to move. The piston parts will then resume their original position in relation to each other.

It should also be realised that embodiments are conceivable in which the forward movement of the outer piston part 14 is not delimited by the pin 15, but in which the forward movement of the outer piston part 14 is delimited e.g. by the setting of a nut in the coupling 18 and the gradual building up of pressure in the passage 5.

It is now referred to Fig. 6. and Fig. 7. The invention also relates to a pelletizing machine 2 for conversion of raw material, such as wood shavings, to fuel pellets. The pelletizing machine comprises at least one compaction unit 1 with a tube 3 with an opening 8 through which wood shavings can be supplied into a feeding chamber 9. The tube 3 has a through passage 5, the cross-section of which converges in direction towards an outlet end 6 of the passage. Furthermore, the tube 3 has a piston 12 that is lodged to slide in the tube 3 to compact wood shavings or some other material placed in the feeding chamber 9. Furthermore, the machine comprises at least one frame or container 23, 24, in which the compaction unit 1 is placed. At the same time, the container 23, 24 acts as a receiver for wood shavings supplied from the outside. At least one power device 25 is arranged to act on an end of the piston 12 to force the piston 12 through the through passage 5 and thereby to compact wood shavings or some other material that has been supplied to the feeding chamber 9 of the compaction unit 1. The power device 25 of the machine is preferably arranged to operate in two directions; e.g. the power device 25 can be a double-acting hydraulic cylinder 25. The machine 2 may then comprise two containers 23, 24 having compaction units 1, which containers have been placed on either side of the power device 25 to enable the power device 25 to make alternating operational strokes in both directions. Suitably, the power device 25 is fixedly connected to the piston 12 to enable the power device to move the piston 12 forwards as well as backwards. When the hydraulic cylinder 25 returns from a container 24, after an operating stroke, the machine may at the same time perform an operating stroke towards the second container 23, as is shown in Fig. 7.

In an advantageous embodiment of the invention, a number of compaction units 1 are placed in a container.

As is shown in Fig. 6, the machine may suitably comprise a hood 26 to cover the containers provided with compaction units 1. In Fig. 6 it is indicated that the hood is pivotable to be opened to an open position, e.g. in connection with maintenance and/or reparations. The hood 26 has openings 27, 28 in order to let in wood shavings via the hood 26 and on to the containers 23, 24 provided with compaction units 1. A rotary- mounted stirring member 29 is arranged in connection with at least one of the openings 27, 28 of the hood 26, to stir shavings or some other material about to pass through the opening or openings 27, 28 of the hood. Thereby, the advantage is attained inter alia that the risk of clogging of the openings 27, 28 decreases. The machine is suitably provided with such compaction units 1 that are described more elaborately with reference to Fig. 1 to Fig. 5, even if it is conceivable to let the machine 2 use compaction units 1 of some other design. The machine can be used in direct connection with a saw mill or wood processing industry e.g.

The invention also relates to a method of converting material such as wood shavings, to fuel pellets. The inventive method comprises the following steps. Providing a tube 3 with a through passage. The through passage 5 of the tube 3 mouths at an outlet end 6 of the tube 3, and a feeding chamber 9 arranged in the tube 3 is outwards open to allow wood shavings to be supplied into the feeding chamber 9. The passage has at least one section 10, 11 with a converging cross-section. Furthermore, an elongated piston 12 is provided, which piston 12 comprises an inner piston part 13 and an outer piston part 14 that are connected to each other but can move in relation to each other in the longitudinal direction of the tube 3, and which piston 12 is arranged inside the tube 3 in connection with the feeding chamber 9. An amount of material, such as wood shavings, is charged to the feeding chamber 9. When the feeding chamber 9 has been filled, the piston 12 is moved from a retracted position and forwards through the feeding chamber 9, to force wood shavings present in the feeding chamber 9 into the through passage 5 of the tube 3, while at the same time compacting it in a first compaction stage. Thereafter, the movement of the outer piston part 14 is arrested. The movement of the inner piston part is however allowed to continue through at least a part of the through passage 5 section having a converging cross-section, so that the inner piston part 13 compacts the shavings material in a second compaction stage. It should be understood that the inventive compaction unit is used in the inventive method and that the method also comprises such steps that follow naturally from the use of the inventive compaction unit, independent of if such steps have been expressively given or not.

The end pellets product suitably obtains a diameter of about 8 mm and a length of about 20 mm.

The compaction unit is suitably designed to convert shavings having a density of about 200 kg/m³ to pellets having a density of about 600 kg/m³.

Friction heat also results from the high pressure that is obtained in the process, which friction heat contributes to the bonding of the material.

Claims

1) A compaction unit (1) for a pelletizing machine (2), which compaction unit (1) comprises: a) a tube (3) with a through passage (5) and an outlet end (6) of the passage (5), b) on the tube (3), a section (7) with an opening (8) in the wall (4) of the tube (3), via which opening (8) raw material can be supplied into the tube (3), to a feeding chamber (9), c) on the tube (3), at least one section (10) in which the through passage (5) of the tube (3) has a cross-section converging in a direction towards the outlet end (6) of the passage (5) so that raw material that passes through the tube (3) is compacted, d) in the tube (3), a piston (12) lodged to slide in the tube (3) and arranged to be guided through the through passage of the tube (3) from a retracted position in which the feeding chamber (9) of the tube (3) is exposed and from there through the feeding chamber (9) and further on in direction towards the outlet end (6) of the through passage (5) of the tube (3), which piston (12) comprises an inner piston part (13) and an outer piston part (14), which outer piston part (14) can move along with the inner piston part (13), e) on the outer piston part ( 14), a first stop (15), f) on the tube (3), a second stop (16) arranged to interact with the first stop (15), to bring the movement of the outer piston part (14) in direction towards the outlet end (6) to a standstill as the first stop (15) meets the second stop (16), g) a flexible coupling (18) between the inner (13) and the outer (14) piston parts, which flexible coupling (18) holds together the inner (13) and the outer (14) piston parts but allows the inner piston part (13) to continue to move towards the outlet end even after the movement of the outer piston part (14) has been arrested.

2) A compaction unit (1 ) according to claim 1, characteri s ed in that the opening (8) of the tube (3) has a rear edge (17) and a front edge (16), which front edge (16) forms the second stop (16), and in that the first stop (15) consists of a pin (15) that projects from the outer piston part (14) and that in interaction with the rear and front edges of the opening (8) sets the bounds for the movement of the outer piston part (14). 3) A compaction unit (1 ) according to claim l or 2, characteris ed in that the coupling (18) between the outer and the inner piston parts (14, 13) is a friction coupling (19).

4) A compaction unit (1) according to claim 1 or 2, characteris e d in that the coupling between the outer and inner piston parts (14, 13) comprises at least one elastic member (20) that acts on the piston parts (14, 13) in order to bring them back to an equilibrium position as soon as the piston parts (14, 13) start to move in relation to each other.

5) A compaction unit (1) according to claim 1 or 3, characteris e d in that the coupling comprises a hydraulic or pneumatic element that counteracts a relative movement of the outer and inner piston parts.

6) A compaction unit (1) according to claim 1 or 2, characteris ed in that the coupling comprises a thread.

7) A compaction unit (1) according to any one of the preceding claims, characteri s ed in that a final portion (21) ofthe through passage (5) has a diverging cross-section immediately before the outlet end (6).

8) A compaction unit ( 1 ) according to claim 1, characterised in that the outer (14) and the inner (13) piston parts are essentially circular cylindrical and in that at least one portion ofthe through passage (5) has a circular cylindrical cross-section. ^•

9) A pelletizing machine (2) for conversion of raw material, such as wood shavings, to fuel pellets, which pelletizing machine comprises: a) at least one compaction unit (1) that comprises a tube (3) with an opening (8) by which raw material can be supplied into a feeding chamber (9), a through passage (5), the cross-section of which converging in direction towards an outlet end (6) ofthe passage (5) and a piston (12) that is lodged to slide in the tube (3) in order to compact raw material placed in the feeding chamber (9), b) at least one container (23, 24) in which the compaction unit (1) is placed, c) at least one power device (25) arranged to act on an end ofthe piston (12) to force the piston (12) through the through passage (5) and thereby to compact raw material that has been supplied to the feeding chamber (9) ofthe compaction unit (1). 10) A pelletizing machine (2) according to claim 9, characteri s ed in that a number of compaction units (1) are placed in the container.

11 ) A pelletizing machine (2) according to claim 9 or l0, characteris e d in that the power device ofthe machine is a power device that is arranged to operate in two directions, such as a double-acting hydraulic cylinder (25), and in that the machine (2) comprises two containers (23, 24) with compaction units (1), which have been placed on either side ofthe power device to enable the power device (25) to make alternating operating strokes in both directions.

12) A pelletizing machine (2) according to any one of claims 10 to 12, characteri sed in that the machine (2) further comprises a hood (26) to cover the containers provided with compaction units (1) and which hood has openings (27, 28) to let in raw material, such as wood shavings, via the hood (26) and on to the containers (23, 24) provided with compaction units (1) and wherein a rotary mounted stirring member (29) is arranged in connection with at least one ofthe openings (27, 28) in the hood (26).

13) A method for making fuel pellets from comminuted raw material such as e.g. sawdust, which method comprises the following steps: a) providing a tube (3) with a through passage (5) that mouths in an outlet end (6) ofthe tube (3) and a feeding chamber arranged in the tube (3), which feeding chamber opens out to allow raw material to be supplied into the feeding chamber (9), and which through passage (5) has at least one section (10) with a converging cross-section, b) providing an elongated piston (12), which piston (12) comprises an inner piston part (13) and an outer piston part (14) that are connected to each other but can move in relation to each other in the longitudinal direction ofthe tube (3), and which piston (12) is arranged inside the tube (3) in connection with the feeding chamber (9), c) filling an amount of raw material into the feeding chamber (9), d) moving the piston (12) from a retracted position, through the feeding chamber (9), to force raw material present in the feeding chamber (9) into the through passage (5) ofthe tube (3), while at the same time compacting it in a first compaction stage, e) bringing the outer piston part (14) to a standstill, and continuing to move the inner piston part (13) through at least a part ofthe through passage (5) section (10) having a converging cross-section, so that the inner piston part (13) compacts the shavings material in a second compaction stage.