Device for removing the pith from plant stem parts

Abstract

Device for removing pith from plant stem parts which have a hard, substantially dimensionally stable bark and a compressible pith, with a straw mill which has a cutting chamber in which rotatable knives are arranged in a vertical plane, and a feed pipe which extends laterally from an inlet opening to an outlet opening, wherein the outlet opening is connected to the cutting chamber and the feed pipe has a channel-shaped loading element at the outlet opening which extends from the outlet opening into the feed pipe at a distance of at least the bottom of the feed pipe.

Description

[0001] The invention relates to a device for removing pith from plant stem parts which have a hard, substantially dimensionally stable bark and a compressible pith, as well as stem parts from which the pith has been removed by means of the device.

[0002] Plant material is increasingly being used as a filler in concrete components. Such components typically use a concrete composition based on binder, sand, gravel, water, and an elongated plant aggregate, such as stem pieces of grasses, hemp, Jerusalem artichoke, flax, and the like. Such stem pieces have a hard, essentially dimensionally stable bark and a compressible pith. Compressible pith refers to the inner stem material enclosed by the essentially rigid bark, which is compressed under the action of a certain compressive force and returns to its essentially original shape when the compressive force is removed or significantly reduced. The compressible pith is therefore spongy in nature.

[0003] The concrete compositions described above for the production of building elements are well known in the professional world. "Concrete composition" refers to a composition that contains all the components necessary to harden the composition into a concrete-like material. Those skilled in the art are familiar with such compositions and also know that different concrete compositions can be produced depending on the intended use. In addition to the most common so-called 1-2-3 concrete, in which the weight ratio of cement:sand:gravel / granulate is 1:2:3 and the water content is 0.5 times that of the cement, there are also drier and wetter forms of concrete, which are defined by the degree of settlement according to the NEN standard EN12350-4. For example, earth-moist concrete, which is well known in the professional world, is classified as C1 with a compaction ratio of 1.45 to 1.26. The much wetter shotcrete has a compaction ratio of 1.10 or less.Plant-based aggregates are commonly used in concrete compositions as fillers and to achieve a lower specific gravity. The addition of plant-based materials also results in a favorable carbon footprint, as the organic matter contained in the sheet material is not converted into CO2.

[0004] However, the inclusion of plant material as a filler in concrete compositions is not without problems. It has been shown that the adhesion of the plant material to the concrete composition is inadequate. To reduce this lack of adhesion, the plant material is treated with a mineralizer before being added to a concrete composition. EP1307411, for example, describes the addition of finely ground rock flour as a mineralizer to a concrete composition containing plant aggregate. EP2069255 describes a process for producing a concrete composition, wherein the composition contains alkali such as calcium hydroxide. From EP2069255, cut stem parts of grasses, hemp, Jerusalem artichoke, flax, or palm fronds, and mixtures thereof, are known as plant aggregate.

[0005] In addition to adhesion problems, the plant material swells under the influence of the water contained in the concrete composition, resulting in a weakened product. NL2021223 describes a process in which plant filler is added to a concrete composition without a mineralizer, after which the concrete is allowed to cure and then processed into granules. These granules are then used as a component of a subsequent concrete composition. This would reduce both the adhesion problem and the swelling problem. However, this process is less attractive because the production of a concrete composition actually requires a duplicate production of the composition.

[0006] It has been found that the problem of adhesion and swelling can be significantly reduced or eliminated by removing a significant portion of the pith from the aforementioned stem material before incorporating the stem material into the concrete composition as an aggregate. This eliminates the undesirable dynamic character of the stem material and produces an aggregate with the desired static character.

[0007] It has been shown that most of the pith can be removed from the stalk material using a specially adapted straw mill, also called a shredder. Straw mills are well known in practice, e.g. from the company Himel or Agerskov. Such straw mills have a cutting chamber with blades rotating in a vertical plane and a feed pipe extending laterally from an inlet opening to an outlet opening, with the outlet opening being connected to the cutting chamber. By applying an air flow moving essentially transversely to the direction of rotation of the rotating blades, the material to be shredded is led from the feed opening through the feed pipe into the cutting chamber. The air flow is usually generated by a fan located on the side of the cutting chamber opposite the side to which the feed pipe is connected.The blower sucks the material to be shredded into the cutting chamber and then blows it out through an outlet.

[0008] In order to separate the pith from the bark of the stem parts, it has now been discovered that the stem parts should be fed into the cutting chamber in free flow. This means that the stem parts are no longer in contact with the feed tube before entering the cutting chamber, so that the stem parts move through the air stream essentially parallel to the direction of the air flow. It has been found that in this orientation, i.e. essentially perpendicular to the rotating knives, the stem parts are hit so hard by the knives that a significant portion of the pith is detached from the bark. In order to achieve such a free air flow, contact between the stem parts in the feed tube should be prevented, at least near the feed opening in the cutting chamber, so that the stem parts can align themselves parallel to the direction of the air flow.

[0009] To achieve the desired alignment of the stem parts, the straw mill comprises an elongated loading element that extends from outside the feed tube through the feed opening at a distance of at least the bottom of the feed tube into the feed tube. The loading element can be plate-shaped, with the plate extending into the feed tube at least as far as the bottom of the feed tube. This loading element thus divides the inlet opening into at least a first air inlet opening, which is bounded by the top side of the loading element and the top side of the feed tube, and a second air inlet opening, which is bounded by the bottom side of the loading element and the bottom side of the feed tube. At the location of the inlet opening, the air flow is thereby divided into a first air flow located above the loading element and a second air flow located below the loading element.The part of the loading element located outside the feed tube serves to load the stem parts to be processed for subsequent movement through the feed tube into the cutting chamber. The loading element does not extend the entire length of the feed tube, i.e., up to the outlet opening, but only a portion of it. Preferably, the loading element extends a maximum of half the feed tube, preferably a quarter or less.

[0010] By inserting the stem parts into the feed tube via the loading element, the stem parts are moved into the cutting chamber by the first air stream, while the second air stream enters the feed tube from the feed opening below the loading element. While the spindle parts are moved towards the cutting chamber in the feed tube by the first air stream, the second air stream below prevents the stem parts from coming into contact with the underside of the feed tube. It is also possible for the second air stream to be present on one or both sides of the feed tube or around the first air stream. For this purpose, the loading element can, for example, be designed in a groove shape with a smaller width than the feed tube, so that the second air inlet opening is also formed on one or both sides next to the loading element.Alternatively, the charging element can be tubular at the location of the supply line's inlet opening and have a smaller dimension than the supply line at the location of the inlet opening. In this way, a second airflow opening can be formed surrounding the first airflow opening, so that the stem parts moved through the supply tube by the first airflow are surrounded by the second airflow, which promotes the alignment of the stem parts parallel to the direction of the airflow.

[0011] By applying the air flow and inserting the stem parts into the feed tube via the loading element, the stem parts are moved in the intended orientation parallel to the direction of the air flow through the feed tube and enter the cutting chamber in this orientation, where the stem parts are struck by the blades, splitting the stem lengthwise and removing a significant portion of the stem's pith.

[0012] The applied airflow moves the extracted pith and the pithless bark out of the cutting chamber, and the pith can then be separated from the bark. Since the pith is usually heavily pulverized by the treatment in the cutting chamber, while the bark material is essentially only cut into narrower pieces by the splitting process, it can easily be separated, for example, based on size differences or specific gravity, by sieving or with the aid of a conventional downdraft cleaning process. The powder can be collected for use as filler in a variety of applications, for which, for example, wood sawdust is also used. In an attractive embodiment, the thus cored stem pieces are sieved on a shaker with sieve openings of 2-4 mm, whereby the powdery pith and undersized stem fragments are removed.

[0013] In a typical application of a straw mill, the feed pipe is usually arranged diagonally upwards from the hall floor on which the straw mill stands, whereby the material to be cut is sucked from the hall floor through the feed pipe into the cutting chamber against gravity. In the process, a significant portion of the material to be cut comes into contact with the underside of the conveyor pipe. To carry out the method according to the invention, in which the stem parts are to be introduced into the cutting chamber in free flow, it is advantageous if the feed pipe of the continuous mill is arranged diagonally downwards from the inlet opening to the outlet opening and the stem parts are moved into the cutting chamber partly by gravity in step d. With this arrangement, the stem material is moved into the cutting chamber in a downward movement by both the air flow and gravity.It was found that in this arrangement, the stem material does not or hardly comes into contact with the underside of the feed tube due to the presence of the underlying second air stream, while the flow velocity of the stem material is correspondingly higher than if the feed tube extends from the ground to the cutting chamber.

[0014] In a further advantageous embodiment, the supply tube is rectangular at the location of the supply opening, and the charging element is designed as a rectangular channel, with the width of the channel corresponding to the width of the supply opening. Thus, a second airflow opening is formed beneath the charging element across the entire width of the supply tube, so that the second airflow is located beneath the first airflow across the entire width of the supply tube.

[0015] Preferably, the loading element is tiltable relative to the feed tube near the feed opening. By tilting, the angle of the loading element relative to the feed tube can be changed so that the stem material loaded on the loading element enters the feed tube at the desired angle. If the loading element has a flat base plate that protrudes beyond the feed opening in the feed tube, the height of the second air stream can also be adjusted by tilting. When tilted downwards, the flat base plate reaches closer to the bottom of the feed tube, resulting in a narrower passage for the second air stream. If, on the other hand, the loading element is tilted upwards, the passage increases. This embodiment is particularly advantageous if the loading element has a flat base plate whose width preferably corresponds to the width of the feed tube, which in this case is preferably rectangular.In this embodiment, too, the loading element is preferably designed as a tipping chute.

[0016] In a further advantageous embodiment, the plane in which the blades rotate in the straw mill has a diameter of 0.8 - 1.2 m, and the rotation speed is preferably 1200 - 1800 revolutions per minute (rpm).

[0017] The invention also relates to an assembly comprising a feed tube and a loading element as described above.

[0018] The invention also relates to plant stem parts with a length of 10 - 80 mm, which naturally contain a hard, substantially dimensionally stable bark and a compressible pith, wherein the natural volume of the pith is greater than the natural volume of the bark from which the pith has been removed, which stem parts are obtainable by a. introducing an air flow directed from the inlet opening to the cutting chamber into the inlet pipe of the straw mill described above, wherein at the inlet opening a first air flow is formed by the channel-shaped loading element and a second air flow is formed which is located below the channel-shaped loading element and the first air flow; b. introducing the stem parts into the feed tube via the loading element, wherein the stem parts are moved into the cutting chamber by the first air stream and the second air stream prevents contact of the stem parts with at least the underside of the feed tube; c. the stem parts are exposed to the rotating knives in the cutting chamber, the stem parts are split and the pith is removed from the bark; and d. emptying the cutting chamber and separating the split, pith-free stem parts and the emptied pith.

[0019] Stem pieces of the desired length can be obtained by harvesting suitable crops, i.e. crops whose stem has a substantially dimensionally stable bark surrounding a compressible pith, and cutting the stalks to the desired length. This can be done mechanically, e.g. with a maize harvester, which can automatically provide stalk pieces of the desired length. The length of the stalk pieces can usually be adjusted in the harvester. The stem length is preferably 10 - 80 mm, more preferably 10 - 40 mm. This stem length can be achieved by setting the stem length in the harvester to 20 mm. After harvesting, the stalk pieces still contain all of the pith, which by volume makes up significantly more than half of the total stem material, the remainder being made up of the bark. In Miscanthus, the bark proportion is about 70% of the volume.

[0020] Plant stem material is preferably selected from cut stems of grasses, hemp, Jerusalem artichoke, flax, or palm fronds, and mixtures thereof, especially grasses from the Miscanthus family, especially Miscanthus gigantheus, also known as elephant grass. Elephant grass stem material has proven to be an excellent aggregate for concrete components, especially when most of the pith has been removed. Elephant grass also absorbs a large amount of carbon dioxide, allowing a large amount of carbon dioxide to be stored in the concrete.

[0021] The plant parts introduced into the device according to the invention preferably have a bulk density of 100 - 140 kg / m 3 The bulk density is determined by scattering the dried material from a height of 2 - 5 cm into a 1-liter measuring cup with a diameter of 12 cm without compaction and weighing the 1-liter volume.

[0022] The plant stem parts are preferably washed with a flow velocity of 10 - 20 m 3 / h into the cutting chamber. This flow rate can be easily adjusted by a professional, depending on the angle of the feed tube relative to the working surface, the airflow extension, the position of the loading element, the loading speed of the stem material, and the choice of stem material.

[0023] After conventional harvesting and cutting to the desired length of 10-80 mm, plant stem parts typically contain 60-80% pith and correspondingly 20-40% bark by volume. Using the process described here, it is possible to remove up to 90% of the pith from the stem material. This means that with an original pith:bark volume ratio of 70:30, after treatment according to the process described here, the ratio can be 7:30, resulting in a pith volume that is more than four times smaller than the bark volume.Accordingly, the invention also relates to stem parts with a length of 10 - 80 mm, which naturally have a hard, essentially dimensionally stable bark and a compressible pith, wherein the natural volume of the pith is greater than the natural volume of the bark from which the pith was removed, wherein the volume of the pith after removal is smaller than the volume of the bark, preferably by twice, more preferably by three times, and even more preferably by four times the volume of the bark. Preferably, the bulk density increases by at least 20%, more preferably by 20 - 40%, as a result of the removal of the pith. The bulk density of the plant stem parts after removal of the pith is preferably 20 - 40% higher than the bulk density before removal of the pith.

[0024] The natural volume of the pith and bark can be easily determined from the bulk density by weighing and measuring the volume of the starting material, consisting of stem parts with rigid bark and compressible pith, on the one hand, and the stem parts with the pith removed, on the other. To do this, the material is scattered from a height of 2-5 cm into a 1-liter measuring cup with a diameter of 12 cm, without compaction, and then the 1-liter volume is weighed.

[0025] The plant stem parts according to the invention are preferably selected from cut stem parts of grasses, hemp, Jerusalem artichoke, flax or palm fronds and mixtures thereof, in particular from grasses, especially from the Miscanthus family, in particular Miscanthus gigantheus, also called elephant grass.

[0026] Plant stem pieces, especially elephant grass, preferably have an average diameter of 5–7 mm before pith removal and an average diameter of 2–3 mm after removal. This diameter was determined by separately measuring 200 individual stem pieces. It was found that the variation in diameter and mean value did not change significantly when more than 200 stem pieces were measured.

[0027] The plant stem parts preferably have an average length of 20–30 mm before pith removal and an average length of 10–20 mm after removal, with the length after removal being 50–75% of the length before removal. The length was also determined by separately measuring 200 individual stem parts. When determining the length, it was also found that the variation in diameter and mean value did not change significantly when more than 200 stem parts were measured.

[0028] The invention is explained in more detail with reference to the following figures and examples. Figure 1 is a view of a device according to the invention, and Figure 2 is a cross section of the device from Fig. through line L. Figure 3 is a photograph of harvested and dried elephant grass stem material with an average length of 25 mm, with most stem pieces ranging between 10 and 80 mm in length. The average diameter of the stem pieces is 6 mm. Figure 4 is a photograph of the stem material from Fig. which was treated according to the method according to the invention, the average length being reduced to 16 mm and the average diameter of the stem parts being reduced to 2.5 mm. Reference numbers: 1 straw mill 2 cutting chambers 3 knives 4 supply line with upper part 4A, lower part 4B and sides 4C 5 Filling opening 6 Exit opening 7 Charging element 8 fans 9 Procedure 10 Hinge 11 first vent opening 12 second vent S1 first air flow S2 second air flow

[0029] The Fig. show a drum 1 with a circular cutting chamber 2, in which the knives 3 rotate around the axis A during operation. A feed tube 4 extends slightly upwards from the side of the cutting chamber 2. The feed tube 4 has a rectangular feed opening 5 and tapers to a circular outlet opening 6, which is connected to the cutting chamber 2 and whose center is the axis A. The feed opening 5 is limited in height by the top 4A and the bottom 4B of the feed tube 4 and in width by its sides 4C. The feed channel 4 can also be circular from the feed opening 5 onwards, regardless of whether it tapers towards the outlet opening 6 or not.

[0030] An elongated loading element 7 extends from outside the feed tube 4 through the feed opening 5 at a distance of at least the underside 4B of the feed tube 4 into the feed tube 4. In the region of the inlet opening 5, the loading element 7 divides the inlet opening 5 into an upper first air inlet opening 11 and a second lower air inlet opening 12. In the case shown, the loading element is channel-shaped with a substantially flat base plate 7A and side walls 7B. The loading element extends with the base plate 7A into the supply channel 4. In the case shown, the width of the loading element 7 corresponds to the width of the feed opening 5, which is defined by the two side walls 4C of the feed tube 4.

[0031] At point 12, the loading element can be tilted perpendicular to the feed tube 4.

[0032] The loading element can also extend into the loading tube 4 as a closed cylindrical tube at the filling opening 5, which is particularly true if the filling opening 5 of the loading tube 4 is circular. The loading element then has a smaller diameter than the filling opening and therefore preferably extends concentrically. In such an arrangement, a concentric second air inlet opening is formed around a first air inlet opening. A flexible hose, e.g., with a suction nozzle, can then be connected to the loading element, through which the stem parts can be fed into the drums.

[0033] Behind the cutting chamber, i.e. on the side opposite the inlet hose attachment, a fan is arranged which can generate an air flow which flows through the inlet opening 5 through the inlet hose 4 through the cutting chamber and is blown out of the cutting chamber 2 through a tangentially arranged exhaust air duct 9.

[0034] Due to the presence of the charging element 7 in the inlet opening 5 of the supply pipe 4, the air flow is divided into a first air flow S1 and a second air flow S2, which, in the illustrated case, flow through the first air inlet opening 11 and the second air inlet opening 12, respectively. The air inlet opening 11 is bounded by the top side 4A and the sides 4C of the supply pipe 4, as well as by the base plate 7A of the charging element 7. The air inlet opening 12 located below is bounded by the bottom side 4B and the sides 4C of the supply pipe 4, as well as by the base plate 7A of the charging element 7.

[0035] After the air flow has been applied, the stem parts are placed on the part of the loading element 7 located outside the feed tube 4, whereupon the stem parts are sucked into the cutting chamber 2 by the first air flow S1. The second air flow S2 located underneath prevents the stem parts from colliding with the underside 4A of the feed tube 4 and thereby losing speed and no longer being able to be guided parallel in the air flow, which is necessary for the longitudinal splitting of the stem parts and the removal of the pith from the bark. The height of the second air flow can be varied by tilting the loading element at the tilting point 12 relative to the feed tube 4.When tilted upward, the inlet angle for the stem material becomes sharper and the flow rate increases, while the second air stream is narrowed because the end of the charging element 7 located in the inlet pipe 4 is moved toward its bottom 4A, reducing the distance d between them. The second air stream thus becomes narrower but also faster.

[0036] Because the stem parts are aligned parallel to the airflow in the first air stream, they are split lengthwise by the rotating blades in the cutting chamber, and most of the pith is separated from the bark. The split bark and pith are then blown out of the cutting chamber through outlet 9, where they can be separated from each other.

[0037] Fig.shows stem material of elephant grass before the longitudinal splitting described above, whereby the stem parts are either still intact all around or already split, but the pith is still connected to the bark.

[0038] Fig. shows the stem material after longitudinal splitting, where it is clearly visible that most of the pith has disappeared. Example 1Removal of the marrow

[0039] Miscanthus grass, harvested with a harvester (New Holland, USA) with a stem length setting of 20 mm, was dried to a bulk density of 120 kg / m 3 The bulk density was determined by scattering the dried material from a height of 2-5 cm without compaction into a 1-liter measuring cup with a diameter of 12 cm and weighing the 1-liter volume. The stem pieces had an average length of 25 mm and an average diameter of 6 mm and are Fig.This material was fed into a straw mill (Himel, Germany) with the feed pipe facing upwards towards the hall floor. A funnel-shaped trough measuring 40 x 10 cm and 100 cm long was inserted into the rectangular feed opening, with 10 cm of the trough extending into the feed pipe. The part of the trough outside the feed pipe tapered from a width of 80 cm to 40 cm. The section inside the feed pipe was 40 cm wide. The trough was angled at 15° to the feed pipe.

[0040] The flow mill was operated at 1800 rpm and the flow rate of elephant grass was 15 m 3 / h.

[0041] The material was collected at the straw mill outlet and sieved on a vibrating screen with a mesh size of 3 mm. The obtained material had an average length of 16 mm and an average diameter of 2.5 mm and is Fig. It is clearly visible that the material has lost most of its pulp. The bulk density of the collected material was 150 kg / m 3 , which corresponds to an increase of 25% compared to the starting material.

[0042] The average length and diameter were determined by measuring 200 individual stem segments separately. It was found that the variations in length and diameter and the respective average values did not change significantly when more than 200 stem segments were measured.

[0043] Table 1 shows the relative amounts of pith and bark before and after treatment. Table 1: Relative proportions of medulla and cortex Miscanthus mark bark Vol.% Für 70 30 After 9 81 Example 2Production of concrete componentsProduction of the concrete composition

[0044] The following ingredients were mixed together: 775 kg fine river sand 0 - 2 mm (Morssinkhof Group, Malden, Netherlands) 380 kg Gravel 4 - 16 mm (Morssinkhof Group, Malden, Netherlands) 185 kg Gap 2 - 5 mm (Morssinkhof Group, Malden, Netherlands) 690 kg Concrete rubble granulate 2 - 16 mm (Morssinkhof Group, Malden, the Netherlands) 308 kg Blast furnace cement ENCI CEM III (Morssinkhof Group, Malden, the Netherlands) 24 kg Miscanthus split, or split and crushed, 10 - 25 mm (Biobound, Cruquius, Netherlands) 90 kg Water

[0045] Fine river sand (0-2 mm) and miscanthus were mixed, then gravel was added. Cement was added during mixing, and after these ingredients were thoroughly blended, water was added and mixed until a homogeneous mixture of earth-moist concrete was formed. This material is processed into the desired building element in the usual way. Example 3: Production of paving slabs (30 x 30 x 6 cm)

[0046] A coating mortar was poured into the brick molds to a height of 6–8 mm. The coating mortar was prepared by dry mixing, by weight, 1 part fine sand (0–2 mm), 1 part medium sand (1–3 mm, Morssinkhof Group, Malden, Netherlands), and 1 part cement, with the addition of 200 l of water per m². 3 Mortar made.

[0047] The mold was then filled with the concrete composition of Example 1 to a filling height of 6 cm and the molds were pressed in a concrete press (Henke, Germany). Example 4Comparative tests

[0048] Paving slabs according to Example 3 were produced in the manner described above, in which the concrete composition contained miscanthus which had only been dried in longitudinal cuts after the harvesting described above, without and with the addition of mineraliser (products M0 and M0 +). In the case of the mineralizer, in a composition prepared according to Example 1, 9 kg per m 3 Calcium carbonate (Bassermann Minerals, Germany) was added prior to the cement addition. Both products were compared with a product made from Miscanthus material that was split after drying according to Example 1 (Product M1). The products were tested for ultimate load and flexural strength according to EN 1339.

[0049] The results are shown in Table 2 below Table 2 M0 M0+ M1 Breaking load (kN) 14,9 15,1 15,3 Flexural tensile strength (N / mm2) 5,0 5,1 5,3

[0050] It is clear that the product M1 performs better than M0 and M0 . + QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 1307411

[0004] EP 2069255

[0004] NL 2021223

[0005]

Claims

[1] Device for removing pith from plant stem parts which have a hard, substantially dimensionally stable bark and a compressible pith, with a straw mill which has a cutting chamber in which rotatable knives are arranged in a vertical plane, and a feed pipe which extends laterally from an inlet opening to an outlet opening, wherein the outlet opening is connected to the cutting chamber and the feed pipe has a channel-shaped loading element at the outlet opening which extends from the outlet opening into the feed pipe at a distance of at least the bottom of the feed pipe. [2] Arrangement according to claim 1, wherein the feed pipe of the straw mill is arranged obliquely downwards from the inlet opening to the outlet opening. [3] Arrangement according to claim 1 or 2, wherein the feed tube is rectangular in the region of the feed opening and the loading element is designed as a rectangular groove, wherein the width of the groove corresponds to the width of the feed opening, which groove is preferably tiltable in the region of the feed opening relative to the feed tube. [4] An assembly comprising a feed tube and a loading element for use in a straw mill having a cutting chamber containing rotating blades in a vertical plane, for carrying out the method according to any one of the claims, wherein one end of the feed tube has an inlet opening and the other end has an outlet opening, the outlet opening being intended to be connected to the cutting chamber of the straw mill, and a channel-shaped loading element is provided in the feed tube at the location of the inlet opening, the channel-shaped loading element extending into the feed tube from the inlet opening at a distance of at least the bottom of the feed tube. [5] Assembly according to claim 4, wherein the feed tube is rectangular in the region of the inlet opening and the loading element is designed as a rectangular groove, the width of the groove corresponding to the width of the inlet opening, which groove is preferably tiltable relative to the feed tube in the vicinity of the inlet opening. [6] Vegetable stem parts with a length of 10 - 80 mm, which naturally have a hard, essentially dimensionally stable bark and a compressible pith, the natural volume of the pith being greater than the natural volume of the bark from which the pith has been removed, the stem parts being obtainable by a. introducing an air flow directed from the feed opening to the cutting chamber into the feed pipe of the straw mill according to one of claims 1 to 3, wherein at the feed opening a first air flow is formed by the channeled loading element and a second air flow is formed which is located below the channeled loading element and the first air flow; b. introducing the stem parts into the feed tube via the loading element, wherein the stem parts are moved into the cutting chamber by the first air stream and the second air stream prevents contact of the stem parts with at least the underside of the feed tube; c. the stem parts are exposed to the rotating knives in the cutting chamber, the stem parts are split and the pith is removed from the bark; and d. Emptying the cutting chamber and separating the split, pith-free stem parts from the extruded pith. [7] Plant stem parts according to claim 6, wherein the volume of the pith after removal is smaller than the volume of the bark, preferably by two times, more preferably by three times and even more preferably by four times the volume of the bark. [8] Plant stem parts according to claim 6 or 7, wherein the bulk density after removal of the pith is 20 - 40% higher than the bulk density before removal of the pith. [9] Plant stem parts according to one of claims 6 to 8, wherein the plant stem parts are selected from cut stem parts of grasses, hemp, Jerusalem artichoke, flax or palm fronds and mixtures thereof, in particular of grasses, especially from the Miscanthus family, in particular Miscanthus gigantheus. [10] Plant stem parts according to any one of claims 6 to 9, wherein the plant stem parts have an average diameter of 5 to 7 mm before removal of the pith and an average diameter of 2 to 3 mm after removal. [11] Vegetable stem parts according to any one of claims 6 to 10, wherein the vegetable stem parts have an average length of 20 to 30 mm before removal of the pith and an average length of 10 to 20 mm after removal, the length after removal being 50 to 75% of the length before removal.

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