SE541550C2 - System for feeding non-wood biomass - Google Patents

Abstract

The invention relates to a system (1) for feeding non- wood biomass comprising a feeding device (2) comprising a channel (3), a channel inlet (8), an outlet section (S2) comprising a channel outlet (9), and a feed screw (4). The system further comprises a charger (5) comprising a chamber (6), a chamber inlet (11), and a chamber outlet (12) adapted to be connected to the outlet section. The chamber comprises an expansion zone (7) for said non-wood biomass, which expansion zone extends between a first plane and a second plane, which first and second planes are located on opposite sides of the chamber inlet (11). The shortest diameter (D) of the expansion zone is equal to or above 2.7 times the shortest diameter (D) of the channel. The longest diameter (D) of the expansion zone is equal to or below 3.5 times the shortest diameter (D) of the channel.

Description

SYSTEM FOR FEEDING NON- WOOD BIOMASS TECHNICAL FIELD The present invention relates to a system for feeding non-wood biomass. The system comprises a feeding device that comprises a channel, a channel inlet for receiving said non-wood biomass, an outlet section comprising a channel outlet for discharging said nonwood biomass, and a feed screw arranged at least partly within said channel for compressing and feeding said non-wood biomass from said channel inlet to said channel outlet. The feeding system further comprises a charger comprising a chamber, a chamber inlet for receiving said non- wood biomass, and a chamber outlet for discharging said nonwood biomass. The outlet section and the chamber inlet are adapted to be connected to one another so that said non-wood biomass may be delivered through the channel outlet and into the chamber.

BACKGROUND It is known to use a feeding device to feed biomass into a charger. The charger may in turn be adapted to deliver said biomass to a reactor, wherein chemical and/or biological reactions are carried out. The reactor may be pressurized, in which case the biomass may be compressed within the feeding device to form a gas impermeable plug that prevents pressurized gas from the reactor to flow through the feeding device against the biomass transport direction, so called blow back. One example of a suitable plug forming feeding device is a plug screw feeder. It is also known to arrange a blow back damper at a plug screw feeder outlet, which blow back damper is adapted to apply a counter pressure on the biomass within the feeding device to further increase the density of the plug. The blow back damper may also be used to break up the plug of biomass when the plug is discharged from the feeding device into the charger, and to seal the outlet when there is a risk of blow back.

The charger is usually vertically arranged, so that biomass discharged from the feeding device into the charger falls towards an outlet at the bottom of the charger. As mentioned above, the biomass is compressed within the feeding device, sometimes up to twelve times its initial density. Thus, the biomass undergoes rapid volume expansion when it enters the charger and more or less returns to its initial density. The expanding biomass may cause plugging of the charger, i.e. the biomass forms a bridge between opposite sides of the charger and thus prevents biomass from falling downwards towards the outlet. Plugging, or bridging, of the charger brings the entire process to a stop and leads to increased manufacturing costs.

WO 2015/049060 relates to a system for feeding ligno-cellulosic feedstock to a pressurized vessel. The feedstock is fed through a plug forming chamber and through a feedstock inlet into said vessel. A sealing head is movable between a sealing position located at the feedstock inlet and a rest position located at a distance from said feedstock inlet. WO 2015/049060 addresses the problem of feedstock forming a bridge with the sealing head that prevents break-up of the feedstock. The solution is to move the sealing head towards the rest position at a velocity which is higher than the velocity of the feedstock plug entering the vessel. The rest position is sufficiently far away from the feedstock inlet to ensure that there is no bridging with the sealing head. However, this document does not address the problem of bridging between opposite sides of a charger.

OBJECT OF THE INVENTION The object of the invention is to reduce the risk of plugging in a feeding system for nonwood biomass as initially described in a cost efficient manner.

DEFINITIONS For the purpose of this disclosure, the term non-wood biomass is used for all kinds of plant/plant part containing material not being defined as wood. The invention is particularly suitable for bulky non-wood material with a density of 35-90 kg/m<3>. Examples of suitable non-wood biomass materials are wheat straw, bagasse, sugar cane straw, different grass species, com, com stover and agrowaste.

For the purpose of this disclosure, a diameter of a geometric shape, e.g. a circle or an ellipse, is any straight line segment that passes through the center of said geometric shape and whose endpoints lie on outer boundaries of said geometric shape.

For the purpose of this application, a charger is a device adapted to receive non-wood biomass from a feeding device and deliver it to a reactor. The charger is suitably arranged on top of the reactor. The non- wood biomass may be subjected to further treatment within the charger. A charger may also be referred to as a t-pipe.

SUMMARY OF THE INVENTION The object of the invention is achieved with a feeding system as initially described, wherein the chamber comprises an expansion zone for said non-wood biomass, which expansion zone extends between a first plane, which extends orthogonally to a first longitudinal axis of said chamber inlet, and a second plane, which extends orthogonally to the first longitudinal axis and is located a distance from the first plane in a direction towards the chamber outlet, wherein the first and second planes are located on opposite sides of the chamber inlet. The shortest diameter of the expansion zone is equal to or above 2.7 times the shortest diameter of the channel between the channel inlet and the channel outlet, and the longest diameter of the expansion zone is equal to or below 3.5 times the shortest diameter of the channel between the channel inlet and the channel outlet.

The channel extends through a feeding device housing that defines the outer boundaries of the channel. The non-wood biomass is compressed during transport through the channel and then discharged into the chamber within the charger. The charger is usually vertically arranged, i.e. the first longitudinal axis extends vertically, so that gravity causes the nonwood biomass to fall downwards through the chamber towards a chamber outlet located at the bottom of the chamber. The external pressure acting on the non- wood biomass is significantly reduced when the non-wood biomass enters the chamber and, as a consequence thereof, the non-wood biomass undergoes rapid expansion as it falls towards the chamber outlet. The section of the chamber wherein most of this expansion occurs, and wherein the risk of bridging is highest, is herein referred to as the expansion zone. The expansion zone extends longitudinally between the first and second planes and laterally between insides of a charger housing that defines the outer boundary of this section of the chamber. Tests have shown that the risk of the expanding non- wood biomass forming a bridge between opposite sides of the charger housing is significantly reduced if the length of the shortest diameter of the expansion zone is at least 2.7 times the length of the shortest diameter of the channel between the channel inlet and the channel outlet.

However, an increase of the charger dimensions also results in an increase in material costs. Tests have shown that increasing the diameter of the expansion zone to a length of 3.5 times the shortest diameter of the channel between the channel inlet and the channel outlet is sufficient to essentially eliminate the risk of plugging of the charger, and consequently there is no need to increase the diameter of the chamber beyond this limit. Thus, the diameter of the expansion zone is advantageously equal to or below 3.5 times the shortest diameter of the channel between the channel inlet and the channel outlet in order to keep material costs down.

The feeding device may be connected to the charger in many different ways. For example, the outlet section may be adapted to be received in the chamber inlet, so that the channel inlet and channel outlet are located on opposite sides of the chamber inlet. Alternatively, the channel outlet and chamber inlet may be arranged aligned and adjacent to one another to form a continuous channel from the channel inlet and into the chamber.

The diameter of the channel is measured within a plane extending orthogonally to the longitudinal axis of the channel, hereinafter referred to as the second longitudinal axis, and between opposite sides of an inner channel surface that defines the outer boundary of the channel within said plane, which inner channel surface is part of the feeding device housing.

The diameter of the chamber is measured within a plane extending orthogonally to the first longitudinal axis and between opposite sides of an inner chamber surface that defines the outer boundary of the chamber within said plane, which inner chamber surface is a part of the charger housing.

The first plane of the expansion zone is located in level with or above an uppermost part of said chamber inlet. The extension of the expansion zone, measured along the first longitudinal axis, is, suitably, between 20 cm and 1 m but at least the diameter of the chamber inlet.

Some of the non-wood biomass that enters the chamber may, initially, be hurled upwards and away from the chamber outlet before gravity causes it to fall downwards towards the bottom of the chamber. Thus, in some embodiments, the expansion zone may extend a distance upwards beyond the chamber inlet.

An increase of the diameter of the expansion zone further reduces the risk of plugging of the chamber. Thus, in some embodiments, the shortest diameter of the expansion zone may be equal to or above 2.77, more advantageously 2.9 and even more advantageously 3.0 times the shortest diameter of the channel between the channel inlet and the channel outlet.

Advantageously, the largest diameter of the expansion zone is equal to or below 3.16 times the shortest diameter of the channel between the channel inlet and the channel outlet. This will further reduce the material and manufacturing costs for the charger.

Advantageously, the chamber and the expansion zone has a circular cross-section as this increases the structural strength of the charger. That is, the section of the chamber that constitutes the expansion zone has a circular cross-section along its entire length. However, the chamber and the expansion zone may have any suitable shape, e.g. a somewhat elliptic cross-section.

The expansion zone may have a constant cross-section (as seen orthogonal to the first longitudinal axis) along the first longitudinal axis, that is, the expansion zone has the shape of a cylinder. Alternatively, the expansion zone may have a widening cross-section (as seen orthogonal to the first longitudinal axis) in a direction towards the chamber outlet. For example, the expansion zone may have the shape of a truncated cone.

The channel has an essentially circular cross-section, although the diameter of the crosssection may vary along the second longitudinal axis.

The optimal relationship between the shortest diameter of the expansion zone and the shortest diameter of the channel depends on a plurality of factors, most importantly the compression rate of the non-wood biomass that is fed through the channel. The compression rate of the non-wood biomass depends on a plurality of parameters, for example the cross-sectional area(s) of the channel, the material properties of the biomass, the rate at which the biomass is fed in the transport direction, the amount of friction between the biomass and the feeding device housing, and additional treatment of the biomass within the feeding device (dewatering etc.). The compression rate of the nonwood biomass may also be increased by means of a back blow damper arranged at the channel outlet to exert a pressure on the biomass within the outlet section. It is also possible to pre-compress the biomass before it enters the feeding device, for example by means of a force feed screw. A high compression rate is advantageous in that it reduces the risk of blow back, i.e. gases flowing against the biomass transport direction through the feeding device. Typically, the non-wood biomass is compressed to a density of about 3-12 times its initial density, and advantageously 6-12 times its initial density. The initial density of the non-wood biomass is usually about 55-90 kg/m<3>and the density of compressed non- wood biomass is usually about 500-700 kg/m<3>.

The feeding system according to the invention is particularly suitable when the density of the non-wood biomass is significantly increased during transport through the feeding device. This makes the invention particularly suitable for a feeding system wherein the feeding device is a plug screw feeder.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further explained hereinafter by means of non-limiting examples and with reference to the appended drawing, wherein: Fig. 1 is a schematic illustration of a cross-section through a feeding system according to a first embodiment of the invention; Fig. 2 is a cross-section through a charger according to said first embodiment of the invention; Fig. 3 is a cross-section through a charger according to a second embodiment of the invention; and Fig. 4 is a schematic illustration of a cross-section through a feeding system according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In the drawings, similar or corresponding elements are denoted by the same reference numbers. Some elements have been removed from the figures for the sake of clarity.

Figure 1 illustrates a feeding system 1 comprising a feeding device 2 in the form of a plug screw feeder and a charger 5. The feeding device 2 comprises a feeding device housing 2a that defines an internal channel 3 that extends along a longitudinal axis of the channel 3, hereinafter referred to as the second longitudinal axis X. The channel 3 connects a channel inlet 8 and a channel outlet 9 located at opposite ends of the channel 3. The channel inlet 8 and the channel outlet 9 are through-holes that extend through the feeding device housing 2a and connects the channel 3 to the outside of the feeding device 2. The channel inlet 8 is adapted to be connected to another feeding device (not shown) comprising a force feed screw for feeding the biomass through the channel inlet 8. The channel outlet 9 is adapted to discharge said non- wood biomass into a chamber 6 within the charger 5. The channel 3 comprises three sections: an inlet section S1, an intermediate section S2 and an outlet section S3. The inlet section S1 is arranged to receive the biomass from the channel inlet 8 and deliver it to the intermediate section S2. The intermediate section S2 is conical with a narrowing cross-section in a biomass transport direction, whereas the inlet and outlet sections S1 and S3 both have essentially constant cross-sections in the transport direction. The biomass is compressed during transport through the channel 3. Note that the sections may have different shapes in other embodiments. For example, the outlet section S3 may have an expanding cross-section in the transport direction. The inlet, intermediate and outlet sections S1, S2, S3 all have circular cross-sections.

The non-wood biomass is usually fed into the inlet 8 by means of a force feed screw (not shown), adapted to achieve a precompressed biomass in inlet 8. A valve (not shown) may also be arranged at the channel inlet 8. The flow of biomass may be controlled by a user by means of said force feed screw or said valve or by a dosing system located before the said force feed screw or the said valve. A feed screw 4 is at least partly accommodated within said channel 3. The feed screw 4 comprises a central shaft 4a, which at one end located opposite the channel outlet 9 is connected to and adapted to be rotated by a motor Ml. A conveying element 4b (schematically shown) in the form of a screw helix extends around a central portion of the central shaft 4a with a suitable pitch. The outermost portions of said central shaft 4a are without conveying elements. The conveying element 4b is adapted to feed the non-wood biomass through the channel 3 from the channel inlet 8 towards and through the channel outlet 9.

The feeding device 2 may comprise additional means (not shown) for treatment of the biomass as it is fed through the channel 3. The biomass may, for example, be subjected to dewatering during transport through the channel 3. Such means are well known to the skilled person and need not be explained in detail herein.

The charger 5 comprises a hollow charger housing 10. The charger housing 10 comprises a a vertical wall section 10a and a top section 10b that together define the boundaries of the chamber 6 within said charger 5. The chamber 6 has a circular cross-section and extends vertically along a longitudinal axis of the chamber 6, hereinafter referred to as the first longitudinal axis Y. The chamber 6 connects a chamber inlet 11, which extends through the wall section 10a, and a chamber outlet 12, which is defined by the vertical wall section 10a and located opposite the top section 10b. The outlet 12 may be connected to another device, e.g. a pressurized reactor (not shown). The chamber inlet 11 is adapted to receive the feeding device housing 2a of the feeding device 2 so that the outlet section S3 of the channel 3 extends through the chamber inlet 11. Thus is formed a continuous conduit for the biomass from the channel inlet 8 to the chamber outlet 12.

A blow back damper 14 is arranged within the chamber 6. The blow back damper 14 comprises a reciprocally movable rod 14a, which at one end is provided with a conical damper head 14b and at the opposite end is connected to a hydraulic or pneumatic system (not shown) arranged to apply a pressure on the rod 14a to move the damper head 14b, axially towards and away from the channel outlet 9. The damper head 14b can be moved by means of said hydraulic or pneumatic system from a retracted position, wherein the damper head 14b does not interact with the biomass discharged through the channel outlet 9, to an intermediate position, wherein the damper head 14b exerts a counter-pressure on the biomass discharged through the channel outlet 9, and to a forward position wherein the damper head 14b is brought into contact with the outlet section S3 to seal the channel outlet 6 (e.g. when a blow back is detected). The intermediate position may vary depending on the force to be applied to the biomass and the density of the biomass plug. The conical damper head 14b is attached to the rod in such a way that the tip of the damper head 14b points towards the channel outlet 6. This arrangement allows the damper head 14b to shred the plug of biomass leaving the channel outlet 9. The base of the damper head 14b, which faces away from the channel outlet 9, has a radial extension such that it can be used to seal the channel outlet 6 when the damper head 14b is brought to the forward position, wherein it is in physical contact with the feeder device 2.

As mentioned above, the biomass is fed through the channel inlet 8 and into the inlet section S1 of the channel 3. The first motor Mi is activated and rotates the central shaft 4a of the feed screw 4, so that the conveying element 4b on the feed screw 4 pushes the biomass in the transport direction through the inlet and intermediate sections S1 and S2 and into the outlet section S3. The biomass is subjected to compression (often to between 6-12 times its original density) during transport through the channel 3, which results in the formation of an essentially gas impervious plug within the channel 3 that prevents gas from the reactor to move against the transport direction. Simultaneously, excess fluids are pressed out of the biomass and transported away from the channel 3 by means of one or more pipes (not shown) connected to the channel 3. Once the plug is formed the blow back damper 14 moves back or is pushed back by the plug from its forward position, wherein it closes the channel opening 9, to an intermediate position, wherein it engages the plug of biomass that is fed out of the channel outlet 9. The blow back damper 14 thus contributes to the compression of the biomass within the channel 3 and shreds the biomass as it is pushed out of the channel outlet 9 and into the chamber 6. Biomass is continuously fed into the channel 3 via the channel inlet 8 and added to the plug of biomass.

The external pressure acting on the biomass within the chamber 6 is much lower than the pressure acting on the biomass within the channel 3, and as a consequence thereof, the biomass rapidly expands as it is pulled by gravity towards the bottom of the chamber 6. Usually, the biomass more or less returns to its original density and volume.

An expansion zone 7 is defined as the section of the chamber 6 wherein most of the biomass expansion occurs. The expansion zone 7 in figure 1 extends a distance H from a first plane that extends orthogonally to the first longitudinal axis Y at the uppermost part of the chamber inlet 11 to a second plane located below the chamber inlet 11. Depending on several factors, such as the flow rate of the biomass, the compression rate of the biomass and the shape of the head 14b of the blow back damper 14, some of the biomass may initially be flung upwards towards the top section 10b of the chamber 6. In these embodiments, the first plane of the expansion zone 7 may be located closer to the top section 10b, above the chamber inlet 11.

The non-wood biomass may be subjected to further treatment within the chamber 6. For example, chemicals and steam could be added in chamber 6. Such features are known to the skilled person and will not be further described herein. Suffice to say that for this purpose additional channels or pipes may be connected to the chamber 6.

The cross-section of the expansion zone 7 in figure 1 and 2 is circular with a constant cross-sectional area along the entire length of the expansion zone 7. The circular crosssection of the wall section 10a is advantageous in that it increases the strength of the wall section 10a and in that material costs are kept at a minimum. Of course, in alternative embodiments, the cross-section of the expansion zone 7 may have any suitable shape, including non-circular shapes such as oval or elliptic, and the cross-sectional area of the expansion zone may vary along the first axis as long as the shortest diameter of the expansion zone is maintained equal to or above 2.7 times the diameter of the narrowest part of the channel 3 between the channel inlet 8 and the channel outlet 9.

It is essential to prevent the expanding non-wood biomass from forming a bridge between opposite sides of the wall section 10a that surrounds the chamber 6. As mentioned above, a plurality of factors affect the expansion rate of the biomass within the chamber 6, most importantly the compression rate of the biomass within the channel 3 of the feeding device 2 as well as the characteristics of the biomass. Tests have shown that the risk of bridging is significantly reduced if the shortest diameter DESof the expansion zone 7, measured orthogonally to the first longitudinal axis Y, is equal to or above 2.7 times the shortest diameter DCSof the narrowest part of the channel 3 between the channel inlet 8 and the channel outlet 9. The risk of bridging is further reduced if the shortest diameter of the expansion zone is 2.77, or even more preferable 3.0, times the diameter of the narrowest part of the channel 3 between the channel inlet 8 and the channel outlet 9. An expansion zone 7 with a shortest diameter DEShaving a length 3.0 times the length of the shortest diameter DCSof the channel 3 is usually sufficient to essentially eliminate the risk of bridging within the chamber 6. Because an increase in the cross-sectional area of the expansion zone 7 results in increased material costs for the charger 5, it is also advantageous to ensure that the longest diameter DEMof the expansion zone 7, measured orthogonally to the first longitudinal axis Y, is equal to or below 3.5 times the shortest diameter DCSof the channel 3 between the channel inlet 8 and the channel outlet 9. Even more advantageously, the diameter is equal to or below 3.16 times the shortest diameter of the channel 3.

Thus, the non-wood biomass enters the chamber 6 within the charger 5 through the chamber inlet 11 and the channel outlet 9, and then falls towards the chamber outlet 12. The biomass is then transferred through the chamber outlet 12 to, for example, a reactor for further treatment of said non-wood biomass.

In the embodiment shown in figures 1 and 2, the length of the shortest diameter DESof the expansion zone 7 is equal to the length of the longest diameter DEMof the expansion zone 7, because of the circular cross-section of the expansion zone and the fact that the expansion zone has a constant cross-section along the first longitudinal axis Y.

Figure 3 shows a second embodiment wherein the expansion zone 7, and thus the chamber 6, has a somewhat elliptic cross-section, so that the longest diameter DEMof the expansion zone 7 is longer than the shortest diameter DESof the expansion zone 7.

Figure 4 shows a third embodiment of the system according to the invention, wherein the expansion zone 7 has a circular cross-section and an increasing cross-sectional area along the first longitudinal axis Y towards the chamber outlet 12. Thus, the longest diameter DEMof the expansion zone 7 is measured within a different plane than the shortest diameter DESof the expansion zone 7.

Also, the outlet section S3 of the feeding device 2 now abuts against the outside of the vertical wall section 10a of the chamber 6, so that the channel outlet 9 is aligned with the chamber inlet 11.

Several tests have been conducted to verify that the problem of bridging can be solved with the solution presented herein.

For example, one test showed that no bridging occurred when a system similar to the ones described with reference to figures 1-4 had a ratio of 2.77 between the shortest diameter of the expansion zone and the shortest diameter of the channel between the channel inlet and the channel outlet. This system was designed for operation at 1-3 ton/day Another test showed that no bridging occurred when a system similar to the ones described with reference to figures 1-4 had a ratio of 3.16 between the shortest diameter of the expansion zone and the shortest diameter of the channel between the channel inlet and the channel outlet. This system was designed for operation at 50-100 ton/day.

Other tests showed that systems with a ratio of 2 and 2.5 experienced bridging, which led to production stops.

The scope of protection provided by the claims is not limited to the above described embodiments, and the skilled person realizes that the embodiments described herein can be combined in many different ways without departing from the scope of protection. For example, the charger 5 in figure 1 may have an expanding cross-section towards the bottom of the charger 5 and the chargers 5 in figures 1 and 4 may have both circular and elliptic cross-sections. Also, the feeding devices 2 in figures 1 and 4 be any suitable type of feeding devices and not necessarily plug screw feeders.

Claims (9)

1. System (1) for feeding non- wood biomass, which feeding system (1) comprises: - a feeding device (2) comprising a channel (3), a channel inlet (8) for receiving said non-wood biomass, an outlet section (S2) comprising a channel outlet (9) for discharging said non-wood biomass, and a feed screw (4) arranged at least partly within said channel (3) for compressing and feeding said non-wood biomass from said channel inlet (8) to said channel outlet (9); and - a charger (5) comprising a chamber (6), a chamber inlet (11) for receiving said non- wood biomass, and a chamber outlet (12) for discharging said non- wood biomass; wherein the outlet section (S2) and the chamber inlet (11) are adapted to be connected to one another so that said non-wood biomass may be delivered through the channel outlet (9) and into the chamber (6); characterized in that: - said chamber (6) comprises an expansion zone (7) for said non-wood biomass, which expansion zone (7) extends between a first plane, which extends orthogonally to a first longitudinal axis (Y) of said chamber (6), and a second plane, which extends orthogonally to the first longitudinal axis (Y) and is located a distance (H) from the first plane in a direction towards the chamber outlet (12), which first and second planes are located on opposite sides of the chamber inlet (11); and wherein - the shortest diameter (DES) of the expansion zone (7) is equal to or above 2.7 times the shortest diameter (DCS) of the channel (3) between the channel inlet (8) and the channel outlet (9); and - the longest diameter (DEM) of the expansion zone (7) is equal to or below 3.5 times the shortest diameter (DCS) of the channel (3) between the channel inlet (8) and the channel outlet (9).

2. System (1) according to claim 1, wherein the shortest diameter (DES) of the expansion zone (7) is equal to or above 2.77 times the shortest diameter (DCS) of the channel (3) between the channel inlet (8) and the channel outlet (9).

3. System (1) according to claim 2, wherein the shortest diameter (DES) of the expansion zone (7) is equal to or above 3.0 times the shortest diameter (DCS) of the channel (3) between the channel inlet (8) and the channel outlet (9).

4. System (1) according to any of the preceding claims, wherein the longest diameter (DEM) of the expansion zone (7) is equal to or below 3.16 times the shortest diameter (DCS) of the channel (3) between the channel inlet (8) and the channel outlet (9).

5. System (1) according to any of the preceding claims, wherein the expansion zone (7) has a constant cross-section along the first longitudinal axis (Y).

6. System (1) according to any of claims 1-4, wherein the expansion zone (7) has a widening cross-section in a direction towards the chamber outlet (12).

7. System (1) according to any of the preceding claims, which system is (1) adapted to compress the non- wood biomass to a density about 6-12 times its initial density before said non- wood biomass enters the expansion zone (7).

8. System (1) according to any of the preceding claims, wherein the feeding device (3) is a plug screw feeder.

9. System (1) according to any of the preceding claims, wherein a force feed screw is used to feed said non-wood biomass into the channel (3).