Twin screw extruder, pellet production equipment, and how to use a twin screw extruder

Abstract

To provide a twin-screw extruder or the like capable of suppressing degradation of processing efficiency caused by volatile components coming from raw material and reducing clogging of a vent caused by raw material entry, when the raw material of high moisture content is supplied to the twin-screw extruder.SOLUTION: There is proposed a twin-screw extruder equipped with a cylinder having a raw material supply port and a biaxial screw installed in the cylinder. A vent hole communicating the cylinder inside with the cylinder outside is formed downstream from the supply port in the cylinder. The twin-screw extruder is equipped with a stuffer device fitted into the vent hole, the stuffer device having a piston member that is arranged in the vent hole and can reciprocate along the communication direction of the vent hole.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present application relates to a twin-screw extruder, a pellet production device, and a method for using the twin-screw extruder, and more particularly to a twin-screw extruder, a pellet production device, and a method for using the twin-screw extruder, which includes a cylinder having a raw material supply port and two screws disposed within the cylinder, and which is used to compression mold or heat-compression mold plant-derived raw materials, for example. [Background technology]

[0002] In recent years, wood fuel pellets have been attracting attention as a biomass material made from carbon-neutral resources. Torrefaction (heat treatment) technology is known as a method for manufacturing wood fuel pellets. Torrefaction technology is defined as "heat treatment carried out at 200-300°C in an oxygen-free atmosphere," and in Japan it is sometimes translated as "low-temperature carbonization" or "semi-carbonization." Torrefaction technology is a manufacturing method that can improve upon the shortcomings of conventional wood pellets, such as poor water resistance and low calorific value, and provide high-performance wood fuel pellets.

[0003] Furthermore, a conventional extruder having two screws is known as a wood fuel pellet manufacturing device (see Patent Document 1). This extruder is configured so that raw materials are fed into a cylinder through an inlet, and the raw materials are heated and kneaded by the screws inside the cylinder to produce pellets. The cylinder is also provided with a vent for discharging gas components generated from the raw materials into the atmosphere. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-83876 Summary of the Invention [Problem to be solved by the invention]

[0005] When the torrefaction technology described above is applied to a screw extruder, if the feedstock has a high moisture content (moisture content), volatile components from the feedstock remain in the cylinder, resulting in reduced processing efficiency. Furthermore, providing a vent hole for volatilization of volatile components can easily cause a "vent-up" phenomenon, in which woody biomass feedstock enters the vent. If the feedstock enters and clogs the vent, the pelletization yield decreases. Furthermore, because vent maintenance work delays the entire manufacturing process and the gases generated by the feedstock contain components that are harmful to the body, there is a desire to avoid or reduce maintenance work due to vent blockage. Possible approaches to suppressing this vent-up phenomenon include providing a vent on the side of the cylinder, adjusting the screw shape, and providing a dedicated fitting to prevent the feedstock from entering the vent. However, the occurrence of vent-up varies depending on the operating conditions of the extruder and the state of the feedstock, and the above-mentioned countermeasures have sometimes been unable to sufficiently prevent the feedstock from entering the vent.

[0006] In view of the above circumstances, one of the objects of the present application is to provide a twin-screw extruder, a pellet production apparatus, and a method for using a twin-screw extruder that can suppress a decrease in processing efficiency due to volatile components from the raw material when a raw material with a high moisture content is supplied to the twin-screw extruder, and can reduce clogging of the vent due to the intrusion of the raw material. [Means for solving the problem]

[0007] According to one embodiment, a twin-screw extruder is proposed, which includes a cylinder having a raw material supply port and twin screws disposed within the cylinder. The cylinder has a vent hole formed downstream of the supply port that connects the inside of the cylinder to the outside of the cylinder. The twin-screw extruder also includes a stuffer device attached to the vent hole, the stuffer device having a piston member disposed within the vent hole and configured to be reciprocally movable along the direction of communication with the vent hole. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a pellet manufacturing apparatus according to this embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the pellet manufacturing apparatus as seen from the direction AA in FIG. [Figure 3] FIG. 3 is a diagram corresponding to FIG. 2 showing a modified pellet manufacturing apparatus. [Figure 4] FIG. 4 is a diagram schematically illustrating a piston member according to a modified example. [Figure 5] FIG. 5 is a diagram schematically showing a piston member according to a modified example. [Figure 6] FIG. 6 is a diagram schematically showing a piston member according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings described below, the same or corresponding components are designated by the same reference numerals, and redundant description will be omitted.

[0010] FIG. 1 is a diagram showing the overall configuration of a pellet manufacturing apparatus according to this embodiment. The pellet manufacturing apparatus according to this embodiment is equipped with a twin-screw extruder and is used to manufacture pellets from wood raw materials, for example, by semi-carbonizing the raw materials. The raw materials may be plant-derived, such as various types of wood, and may contain additives such as binders. The pellet manufacturing apparatus (twin-screw extruder) according to this embodiment is suitable for use with materials having a high moisture content (e.g., materials with a moisture content of 10% by weight or more), but can also be used with raw materials that are not plant-derived.

[0011] 1, the pellet manufacturing apparatus 10 includes a cylinder 20 having a raw material supply port 22, twin screws 30 (one of the screws is not shown) housed inside the cylinder 20, and a compression molding module (molding module) 40 connected to the cylinder 20. Here, the cylinder 20 and the twin screws 30 constitute a "twin-screw extruder."

[0012] The cylinder 20 is hollow and defines a guide path therein for feeding the raw material. A screw 30 is disposed inside the cylinder 20. In the present embodiment, as an example, the longitudinal directions of the guide path and the screw 30 are horizontally disposed. A supply port 22 for supplying the raw material is provided near one end (the right end in FIG. 1 ) of the cylinder 20. In the present embodiment, as an example, the supply port 22 is provided so as to open upwardly of the cylinder 20. Furthermore, the cylinder 20 is provided with a vent hole 24 downstream of the supply port 22 (left side in FIG. 1 ) for discharging volatile components separated from the raw material from the cylinder 20. Furthermore, the cylinder 20 is provided with a liquid addition port 26 for humidity control downstream of the vent hole 24. The liquid addition port 26 does not necessarily have to be provided in the cylinder 20. Furthermore, a compression molding module 40 for molding and producing pellets is connected to the end of the cylinder 20 (the left end in FIG. 1 ), which is downstream of the liquid addition port 26 and opposite the supply port 22. The compression molding module 40 is equipped with a motor for rotating the screw 30 and a mill (not shown) for cutting the pellets to a desired size. A ring die type or flat die type granulator may be used as the compression molding module 40.

[0013] As shown in Fig. 1, the cylinder 20 may be formed by connecting multiple pieces in the longitudinal direction. As an example, the cylinder 20 is formed by connecting a first piece 20A having a supply port 22, multiple second pieces 20B accommodating the screws 30, and a third piece 20C having a vent hole 24. The cylinder 20 may further include a fourth piece 20D having a liquid addition port 26 for humidity control. With this configuration, it is easy to configure a cylinder 20 of a desired length, particularly by changing the number of second pieces 20B.

[0014] The interior of the cylinder 20 can be functionally divided into multiple regions from upstream to downstream. That is, downstream of the supply port 22, there are a torrefaction zone 82 where the raw material is heated and torrefied, a pressure adjustment and devolatilization zone 84 where vent holes 24 are formed and the pressure of the raw material is adjusted and devolatilized, and a humidity control and cooling zone 86 where liquid addition ports 26 are formed and the humidity of the raw material is adjusted and cooled, all of which are connected to the compression molding module 40. For example, in the torrefaction zone 82, the raw material is heated to 60°C to 400°C. For example, in the pressure adjustment and devolatilization zone 84, the pressure inside the cylinder 20 is 0.1 to 0.2 MPa.

[0015] The screw 30 is configured by two parallel screws with the same spiral direction, which are configured to rotate to extrude and knead the raw materials from upstream to downstream (from right to left in FIG. 1).

[0016] The liquid addition port 26 is provided with a liquid addition nozzle 28. The liquid addition nozzle 28 is configured to supply the humidity control liquid to the raw material in the cylinder 20 via, for example, a pump 28a. The liquid supplied from the liquid addition port 26 is not limited to, but may be, for example, wood vinegar made from the volatile components discharged from the vent hole 24.

[0017] A stuffer device is provided in the vent hole 24 as a devolatilization pressure adjustment module 50 for adjusting the pressure inside the cylinder and devolatilizing the volatile components inside the cylinder. The term "vent hole" refers to a vent hole formed in the cylinder 20. However, if a metal fitting or a base is attached to the hole, the vent hole formed in the metal fitting or base may also be included in the "vent hole." In this embodiment, a vent fitting 25 is attached to the cylinder 20, and the vent hole formed in the vent fitting 25 corresponds to the "vent hole." The volatile components discharged to the outside from the vent hole may be resupplied into the cylinder 20 through the liquid addition port 26, as described above.

[0018] FIG. 2 is a diagram illustrating an example of a pellet manufacturing apparatus as viewed from the AA direction in FIG. 1 . As shown in FIG. 2 , in this embodiment, the vent hole 24 is formed to open upward in the cylinder 20. However, this is not limited to this example, and the vent hole 24 may be formed to open to the side or downward in the cylinder 20. In this embodiment, the vent hole 24 is specifically formed above the twin screws 30 but at a position offset from the center of the twin screws 30. The vent hole 24 is preferably provided vertically above the midpoint Csm between the axial centers Cs1 and Cs2 of the twin screws 30 and the axial center Cs1 of one of the screws 30. This arrangement prevents raw materials or coagulated materials from dropping through the vent hole 24 and falling directly between the twin screws 30, causing jamming. Furthermore, by providing the vent hole 24 above a region close to the center of the cylinder 20, volatile components can be suitably guided to the vent hole 24.

[0019] In this embodiment, the devolatilization pressure adjustment module 50 (stuffer device) includes a piston member 60 that is provided within the vent hole 24 and is configured to be reciprocally movable along the communication direction of the vent hole 24. Here, the communication direction of the vent hole 24 refers to the direction in which the inside of the cylinder 20 is connected to the outside of the cylinder 20 by the vent hole 24, and refers to the vertical direction in FIGS. 1 and 2. In this embodiment, at least a portion of the vent hole 24 has a circular cross section (a cross section viewed from the vertical direction in FIGS. 1 and 2), and the piston member 60 is a cylindrical member that corresponds to the outer diameter of the vent hole 24. The piston member 60 is preferably shaped to have a gap of, for example, 1 mm or several mm from the inner wall of the vent hole 24.

[0020] It is preferable that at least the end of the piston member 60 on the cylinder interior side (the lower end in Figures 1 and 2) is made of a material softer than the screw 30. In other words, it is preferable that the screw 30 is made of a material harder than the piston member 60. As an example, the screw 30 may be made of iron or steel, and the piston member 60 may be made of a soft metal such as aluminum. In this way, even if the piston member 60 and the screw 30 come into contact, damage to the screw 30 can be suppressed. As for "hardness," for example, the measurement results from a Rockwell hardness test or a Shore hardness test can be used as a standard.

[0021] In this embodiment, a spring 62 that expands and contracts along the communication direction of the vent hole 24 is attached to the piston member 60. One end of the spring 62 is attached to the piston member 60, and the other end is fixed to the cylinder 20 or the housing of the devolatilization pressure adjustment module 50, or the like. As an example, a coil spring or a leaf spring can be used as the spring 62. Note that the piston member 60 does not necessarily have to be equipped with a spring. Also, in this embodiment, a gripping portion 64 that can be gripped by a user or maintenance worker of the pellet manufacturing apparatus 10 is attached to the piston member 60. With this configuration, a user or the like can grip the gripping portion 64 to move the piston member 60 within the vent hole 24.

[0022] It is preferable that the piston member 60 has a movable range defined so as not to come into contact with the screw 30. As an example, the piston member 60 is configured to be able to approach the screw 30 within a distance of several millimeters to several tens of millimeters, for example, 10 mm. The piston member 60 may also be equipped with an adjustment mechanism for adjusting the movable range. As an example, the adjustment mechanism can adjust the movable range of the piston member 60 by adjusting the position of the fixed end of the spring 62 in the vertical direction. Furthermore, as an example, the piston member 60 of this embodiment is equipped with a stopper member 66 that comes into contact with the cylinder 20 or the housing of the devolatilization pressure adjustment module 50 to limit the movement of the piston member 60 toward the lower end.

[0023] As described above, the pellet manufacturing apparatus 10 of this embodiment is equipped with the piston member 60 that can reciprocate within the vent hole 24. By moving the piston member 60 within the vent hole 24, it is possible to prevent raw material from entering or accumulating within the vent hole 24. The piston member 60 may be operated by a user or the like while the pellet manufacturing apparatus 10 is in operation, or at a predetermined maintenance timing. In this embodiment, a spring 62 is attached to the piston member 60, which facilitates the reciprocating motion of the piston member 60. As described above, the pellet manufacturing apparatus 10 of this embodiment can prevent the vent hole 24 from being clogged, thereby improving the efficiency of pellet manufacturing.

[0024] <Modification> FIG. 3 is a diagram corresponding to FIG. 2 and illustrates a modified pellet manufacturing apparatus. Details of the modified pellet manufacturing apparatus that overlap with those of the pellet manufacturing apparatus 10 of the above-described embodiment will not be described. The modified pellet manufacturing apparatus 10A includes a power source 68 for reciprocating the piston member 60 within the vent hole 24. The power source 68 can be various mechanisms, such as a pneumatic cylinder, a solenoid, or a motor. In the example shown in FIG. 3, a DC motor is used as the power source 68. As a specific example, in the example shown in FIG. 3, a link member 68a is provided that is eccentrically attached to the rotation axis Am of the DC motor. The link member 68a may be configured to adjust the eccentric distance from the rotation axis Am, thereby adjusting the range of movement of the piston member 60. The power source 68 may be configured to reciprocate the piston member 60 while the pellet manufacturing apparatus 10 is in operation. Alternatively, the piston member 60 may be reciprocated by a maintenance worker or the like at a predetermined maintenance timing. According to the modified pellet manufacturing device, the power from the power source 68 can be used to automatically prevent the vent hole 24 from being blocked.

[0025] 4 to 6 are schematic diagrams showing modified piston members. The piston member 60 may have a groove 60a formed on its side surface. In the example shown in FIG. 4, the groove 60a is formed on the side surface of the piston member 60 along the movement direction of the piston member 60 (the vertical direction in FIG. 4). In the example shown in FIG. 5, the groove 60a is formed on the side surface of the piston member 60 perpendicular to the movement direction of the piston member 60. Furthermore, in the example shown in FIG. 6, the spiral groove 60a is formed on the side surface of the piston member 60. In the examples shown in FIGS. 4 and 6, the groove 60a is preferably formed so as to continue from the lower end to the upper end of the piston member 60. As an example, the cross section of the groove 60a may be U-shaped or V-shaped. It is believed that forming the groove 60a on the side surface of the piston member 60 in this way can further prevent the vent hole from being blocked.

[0026] The present invention can also be described in the following aspects. [Form 1] According to Form 1, a pellet manufacturing apparatus is proposed, which is a twin-screw extruder including a cylinder having a raw material supply port and twin screws arranged within the cylinder, wherein a vent hole that connects the inside of the cylinder with the outside of the cylinder is formed in the cylinder downstream of the supply port, and a stuffer device attached to the vent hole, the stuffer device having a piston member that is arranged within the vent hole and configured to be able to move back and forth along the communication direction of the vent hole. According to the first aspect, when processing a raw material with a high moisture content, volatile components can be removed through the vent hole, and the piston member can prevent the vent hole from being blocked.

[0027] [Mode 2] According to Mode 2, in Mode 1, a spring is further provided attached to the piston member. According to the second aspect, the piston member can be reciprocated appropriately by the spring.

[0028] [Mode 3] According to Mode 3, in Mode 1 or 2, the device further comprises a power source for reciprocating the piston member within the vent hole. According to the third aspect, the piston member can be reciprocated by the power source.

[0029] [Configuration 4] According to Configuration 4, in Configurations 1 to 3, the vent hole opens vertically upward from the inside of the cylinder toward the outside of the cylinder. According to the fourth embodiment, gases and moisture generated from the raw materials can be suitably removed.

[0030] [Mode 5] According to Mode 5, in Mode 4, the vent hole is provided vertically above the midpoint between the axial centers of the two screws and the axial center of one of the screws. According to the fifth aspect, gases and moisture generated from the raw materials can be suitably removed.

[0031] [Mode 6] According to Mode 6, in Modes 1 to 5, the piston member has a cylindrical shape corresponding to the outer shape of the vent hole.

[0032] [Feature 7] According to feature 7, at least the end of the piston member on the cylinder interior side is made of a material softer than the screw. According to the seventh aspect, it is possible to prevent the screw from being damaged by the piston member.

[0033] [Mode 8] According to Mode 8, in Modes 1 to 7, a groove is formed on the side surface of the piston member along the direction of movement of the piston member or a groove perpendicular to the direction of movement of the piston member. According to the eighth aspect, clogging of the vent hole can be further suppressed.

[0034] [Feature 9] According to feature 9, in features 1 to 8, a spiral groove is formed on the side surface of the piston member. According to the ninth aspect, clogging of the vent hole can be further suppressed.

[0035] [Mode 10] According to Mode 10, in any of Modes 1 to 9, a heating unit is further provided for heating the raw material supplied into the cylinder to 60°C or higher and 400°C or lower. According to the tenth aspect, the raw material can be torrefied.

[0036] [Form 11] According to Form 11, there is provided a pellet production apparatus for compression molding or heat compression molding of plant-derived raw materials, the pellet production apparatus comprising a twin-screw extruder according to any one of Forms 1 to 10 and a molding module for molding pellets. According to the eleventh aspect, the same effects as those of the twin-screw extruder described above can be achieved.

[0037] [Mode 12] According to Mode 12, there is proposed a method of using a twin-screw extruder, which includes a cylinder having a supply port for raw materials and twin screws arranged within the cylinder, the cylinder having a vent hole formed in the cylinder downstream of the supply port that connects the inside of the cylinder to the outside of the cylinder, the method including the steps of: supplying raw materials from the supply port; moving the raw materials supplied from the supply port within the cylinder by rotating the twin screws; and, in a stuffer device attached to the vent hole, moving a piston member arranged within the vent hole back and forth along the communication direction of the vent hole. According to the eleventh aspect, when a raw material with a high moisture content is treated, volatile components can be removed through the vent hole, and the piston member can prevent the vent hole from being clogged.

[0038] Although the embodiments of the present invention have been described above, the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes equivalents thereof. Furthermore, any combination of the embodiments and modifications is possible within the scope of solving at least part of the above-described problems or achieving at least part of the effects, and any combination or omission of the components described in the claims and specification is possible. [Explanation of symbols]

[0039] 10, 10A... Pellet manufacturing equipment 20...Cylinder 22...Supply port 24...Vent hole 26...Liquid addition port 28...Liquid addition nozzle 30...Screw 40...Compression molding module (molding module) 50... Devolatilization pressure adjustment module (stuffer device) 60...Piston member 60a...groove 62...Spring 64...Gripping part 68...Power source 82…Trefoil region 84…Pressure regulation / devolatilization area 86...Humidity control and cooling area 10A...Pellet manufacturing equipment

Claims

1. A twin-screw extruder including a cylinder having a raw material supply port and twin screws disposed in the cylinder, a vent hole communicating the inside of the cylinder with the outside of the cylinder is formed in the cylinder downstream of the supply port, a stuffer device attached to the vent hole, the stuffer device having a piston member arranged in the vent hole and configured to be reciprocally movable along the communication direction of the vent hole; The vent hole opens vertically upward from the inside of the cylinder toward the outside of the cylinder, and is provided vertically above the midpoint between the axial centers of the two screws and the axial center of one of the screws. Twin screw extruder.

2. 10. The twin screw extruder of claim 1, further comprising a spring attached to the piston member.

3. 3. The twin-screw extruder according to claim 1, further comprising a power source for reciprocating the piston member within the vent hole.

4. The twin-screw extruder according to claim 1 , wherein the piston member has a cylindrical shape corresponding to an outer shape of the vent hole.

5. 5. The twin-screw extruder according to claim 1, wherein at least an end of the piston member on an inner side of the cylinder is formed of a material softer than that of the screw.

6. 6. The twin-screw extruder according to claim 1, wherein a groove is formed on a side surface of the piston member along a moving direction of the piston member or perpendicular to the moving direction of the piston member.

7. The twin-screw extruder according to claim 1 , wherein a spiral groove is formed on a side surface of the piston member.

8. The twin-screw extruder according to claim 1 , further comprising a heating section for heating the raw material supplied into the cylinder to a temperature of 60° C. or higher and 400° C. or lower.

9. A twin-screw extruder comprising a cylinder having a raw material supply port and twin screws disposed within the cylinder, a vent hole communicating the inside of the cylinder with the outside of the cylinder is formed in the cylinder downstream of the supply port, a stuffer device attached to the vent hole, the stuffer device having a piston member arranged in the vent hole and configured to be reciprocally movable along the communication direction of the vent hole; A groove perpendicular to the direction of movement of the piston member is formed on the side surface of the piston member. Twin screw extruder.

10. A twin-screw extruder comprising a cylinder having a raw material supply port and two screws disposed within the cylinder, a vent hole communicating the inside of the cylinder with the outside of the cylinder is formed in the cylinder downstream of the supply port, a stuffer device attached to the vent hole, the stuffer device having a piston member arranged in the vent hole and configured to be reciprocally movable along the communication direction of the vent hole; A spiral groove is formed on the side surface of the piston member. Twin screw extruder.

11. A pellet manufacturing apparatus for compression molding or heat compression molding of plant-derived raw materials, The twin-screw extruder according to any one of claims 1 to 10, a molding module for molding the pellets; A pellet manufacturing apparatus comprising:

12. A method using a twin-screw extruder including a cylinder having a raw material supply port and twin screws disposed in the cylinder, the cylinder having a vent hole formed downstream of the supply port that communicates between the inside and outside of the cylinder, supplying a raw material from the supply port; a step of moving the raw material supplied from the supply port within the cylinder by rotating the twin screws; a step of reciprocating a piston member disposed in the vent hole in a stuffer device attached to the vent hole along a communication direction of the vent hole; Including, a vent hole that opens vertically upward from inside the cylinder toward the outside of the cylinder and is provided vertically above the midpoint between the axial centers of the twin screws and the axial center of one of the screws.

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