Screw press, rotatable screw conveyor, method for the preparation of a solid material and a pressed solid material

Abstract

The invention relates to a screw press (1), in particular a vertical or horizontal screw-feeder press, for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, comprising: - an enclosure (3) comprising: - at least one inlet opening (5), - at least one outlet opening (7), - at least one rotatable screw conveyor (9) enclosed by the enclosure (3) for pressing the liquid-containing solid material and for advancing the liquid-containing solid material from the inlet opening (5) towards the outlet opening (7), the screw conveyor (9) comprising: - a shaft (11) with a rotation axis (R), and - a helicoid structure (13) wound circumferentially around the shaft (11) longitudinally extending at least from the at least one inlet opening (5) towards the at least one outlet opening (7); the screw conveyor (9) and the enclosure (3) defining a path (27) for the forced material advancement from the inlet opening (5) to the outlet opening (7), characterized in that the at least one screw conveyor (9) comprises - a material flow limiting plate (33) comprising a plate body (69) bounded by a forward surface (71), a rearward surface (73) and preferably a circumferential surface (75), which material flow limiting plate (33) is located at an outlet opening (7) facing end (39) of the helicoid structure (13) such that the path (27) is limited in an axial direction and wherein the material flow limiting plate (33) is fixed to the shaft of the screw press (1), wherein the rearward surface (73) is extending in an angle, preferably perpendicular to the rotation axis (R).

Description

[0001] The present invention relates to a screw press for pressing a liquid-containing material, in particular liquid-containing solid material, a rotatable screw conveyor for pressing a liquid-containing material, a method for the preparation of a pressed material and a pressed, preferably solid material, prepared according to such a method.

[0002] Screw presses, screw conveyors, corresponding methods and pressed material of the aforementioned type are generally known state of the art. These are used for reducing the content of water of raw materials and / or intermediate product in a food production process. Particularly in the sugar sector it is an important process step to extract the liquid from beet pulp and / or other parts of plants for further production of sugar products and corresponding by-products. Thus, the pressed solid material may be of interest as an end product, for example as feed for animals.

[0003] Such known screw presses usually comprise a helicoid structure for advancing the relevant material from an input opening towards an output opening. The helicoid structure is wound around a rotating shaft such that the material is advanced towards the outlet opening when the rotating shaft rotates. The rotating shaft is dimensioned such that towards the end of the path for advancing the material, said path being essentially defined by the helicoid structure and the rotation thereof, and thus towards the outlet opening, the pressure on the advanced material increases. This can be achieved by an enclosure surrounding the rotating shaft, wherein the rotating shaft itself comprises a diameter which increases towards the outlet, such that the remaining space between the rotating shaft and the surrounding enclosure decreases the closer the material gets to the outlet opening. This usually requires the radial extension of the helicoid blades to decrease at the same rate as the diameter of the rotating shaft increases. The yield of such known screw presses is, however, not optimal. Particularly, there is too much liquid remaining in the pressed material.

[0004] Particularly when a subsequent drying process is desired or even required to increase preservability and / or to reduce transport costs, the drying process needs a lot of time and energy when there is too much liquid left in the pressed material, which particularly leads to higher production and / or transportation costs.

[0005] The object of the present invention is to provide a screw press, a rotatable screw conveyor, a method for the preparation of a solid material and a pressed solid material, wherein the above-mentioned problems are solved or at least reduced. In particular, it is an object of the present invention to increase the water reduction of a raw material running through the screw press wherein keeping costs of the production and of the process itself low. Further, it is an object of the present invention to provide said screw press, said method and said rotatable screw conveyor which can be easily integrated in existing industrial processes of water reduction in the food production, particularly sugar sector without the need for significant constructional or methodical changes to existing workflows.

[0006] The object is solved by a screw press, rotatable screw conveyor, method for the preparation of a solid material and a pressed solid material as described below and particularly by providing the screw press, rotatable screw conveyor, method for the preparation of a solid material and a pressed solid material according to the embodiments described hereinafter and particularly by the objects of the claims.

[0007] The object of the invention is preferably solved by providing a screw press, in particular a vertical or horizontal screw-feeder press, for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, particularly sugar beet pulp, comprising an enclosure with at least one inlet opening and at least one outlet opening, wherein the screw press further comprises at least one rotatable screw conveyor enclosed by the enclosure for pressing the liquid-containing solid material and for advancing the liquid-containing solid material from the inlet opening towards the outlet opening, wherein the screw conveyor comprises a shaft with a rotation axis, and a helicoid structure wound circumferentially around the shaft longitudinally, the helicoid structure extending at least from the at least one inlet opening towards the at least one outlet opening, wherein the screw conveyor and the enclosure define a path for the forced material advancement from the inlet opening to the outlet opening. The screw press is characterized in that the at least one screw conveyor comprises a material flow limiting plate comprising a plate body bounded by a forward surface, a rearward surface and preferably a circumferential surface, wherein the material flow limiting plate is located at an outlet opening facing end of the helicoid structure such that the path is limited in an axial direction and wherein the material flow limiting plate is fixed - particularly in an axial direction of the rotating shaft - to the screw press, preferably wherein the material flow limiting plate is fixed to the shaft of the screw press, wherein the rearward surface is extending in an angle, preferably perpendicular, to the rotation axis. Thereby, the remaining liquid in the pressed material is very low and further drying processes can be shortened. Also, such subsequent drying requires less energy. Further, the preservability of the pressed material is increased. The presence of the material flow limiting plate according to the present invention allows to build up a favorable particularly high pressure over the length of the screw press, in particular up to 10 to 12 bar close to the material flow limiting plate. At the location where the present material flow limiting plate is operating there is a complete closure of the material flow path.

[0008] Advantageously, the present screw press does not need pre-concentration elements or a dewatering compartment and thus provides means for a method for the preparation of a pressed material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, without the need to preconcentrate the material to be pressed. In the present method and screw press, dewatering and pressing is conducted in one single step and compartment, namely the press, without the need to provide two or more method steps or compartments.

[0009] The present invention in particular relates to a screw press, in particular a vertical or horizontal screw-feeder press, for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, comprising: an enclosure comprising: at least one inlet opening, at least one outlet opening, at least one rotatable screw conveyor enclosed by the enclosure for pressing the liquid-containing solid material and for advancing the liquid-containing solid material from the inlet opening towards the outlet opening, the screw conveyor comprising: a shaft with a rotation axis, and a helicoid structure wound circumferentially around the shaft longitudinally extending at least from the at least one inlet opening towards the at least one outlet opening; the screw conveyor and the enclosure defining a path for the forced material advancement from the inlet opening to the outlet opening, characterized in that the at least one screw conveyor comprises a material flow limiting plate comprising a plate body bounded by a forward surface, a rearward surface and preferably a circumferential surface, which material flow limiting plate is located at an outlet opening facing end of the helicoid structure such that the path is limited in an axial direction and wherein the material flow limiting plate is fixed to the screw press, in particular the shaft of the screw press, wherein the rearward surface is extending in an angle, preferably perpendicular to the rotation axis (R) and wherein the material flow limiting plate of the rotatable screw conveyor extends from a starting position of the rotatable screw conveyor in circumferential direction - preferably in counterclockwise or clockwise direction - over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein the starting position of the rotatable screw conveyor in circumferential direction is located where the last turn of the helicoid structure ends in axial direction, preferably in counterclockwise or clockwise direction.

[0010] In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0011] Preferably, the screw press is a horizontal screw press, meaning the screw press is horizontally positioned.

[0012] Preferably, the material flow limiting plate is fixed to the end of the shaft that is configured to be closer to the outlet opening when installed in a screw press, in particular the outlet opening facing end of the shaft.

[0013] Preferably, the material flow limiting plate does not contain openings or holes.

[0014] The rearward surface faces the end of the helicoid structure, and particularly the end of the path of the advanced material and is thus oriented from the limiting plate towards the inlet opening. In operating mode of the screw press, the material is pressed against this rearward surface whereby the extraction rate of liquid is increased.

[0015] The forward surface is preferably on the backside of the rearward surface. It is particularly preferred that the forward surface is arranged parallel to the rearward surface. Further, it is preferred that the circumferential surface connects the forward surface with the rearward surface at the radially outer end of the plate body. Alternatively, the forward surface connects directly to the rearward surface with the circumferential surface. In that latter case, the forward and rearward surfaces may run towards each other in an acute angle. Further, it is preferred that the forward surface connects with the rearward surface at the radially inner end of the plate body via an inner circumferential surface.

[0016] The angle between the rearward surface and the rotation axis is preferably between 1° and 179°, preferably between 70° and 110°, preferably between 80° and 100°.

[0017] In a preferred embodiment, the material flow limiting plate is directly fixed to the rotating shaft itself, particularly such that the material flow limiting plate is locked axially and rotationally to the rotating shaft. Thereby the advanced material is pressed in axial direction of the rotating shaft against the material flow limiting plate, which further reduces the amount of liquid in the material. Thereby, abrasion, particularly abrasion of the material flow limiting plate, is reduced.

[0018] When fixed to the screw press, the material flow limiting plate outreaches the radial dimension of the rotating shaft in at least one radial direction. This means that at least in one radial direction, particularly the first radial direction, the material flow limiting plate comprises a first distance from its radial outer end to the rotational center, which is the rotation axis, wherein said first distance is larger than a corresponding distance of the shaft, wherein the corresponding distance is measured in the same radial direction, which is the first radial direction. Preferably, the material flow limiting plate outreaches the shaft in every radial direction of its circumferential extension.

[0019] Preferably, the at least one shaft of the screw conveyer has a circular cross-section in a plane perpendicular to its rotational axis.

[0020] In particular, the material flow limiting plate can be formed integrally with another base structure, it is mounted upon, wherein said base structure comprises a lower radial extension, such that it does neither limit nor interfere with the path of the advancing material. In that case, the material flow limiting plate as mentioned above is preferably defined as the part of the said base structure which outreaches the radial extension of the shaft.

[0021] The radial outer end of the material flow limiting plate is preferably located in a radial distance to the rotation axis that equals the distance between the rotation axis and the outer end of the helicoid structure, particularly the helicoids, at least at the end - in axial direction - of the helicoid that faces the material flow limiting plate. This increases pressure on the material and decreases the residual liquid remaining in the material after pressing.

[0022] The enclosure preferably provides the bearing for the rotational movement of the rotating shaft. It further comprises a cavity, in which the rotating rotatable screw conveyor is enclosed, wherein the screw conveyor is particularly enclosed such that the radially outer border of the helicoid structure abuts a particularly cylindrically wall of the cavity. Said cavity is preferably formed cylindrically. Thereby, the path for advancing the material is defined and / or limited by, radially inwards, the rotating shaft, in preferably both axial directions by the helicoid structure, particularly its blades, and, radially outwards, by the wall of the cavity.

[0023] Further, the enclosure preferably comprises a maintenance opening for accessing the cavity, particularly for removing the rotatable screw conveyor. During operation of the screw press, i.e. when advancing and pressing the material, the maintenance opening is preferably closed, however, for maintenance purposes the opening can be opened.

[0024] The helicoid structure preferably comprises a preferably blade-shaped helicoid, which may be called blade, extending from the rotating shaft radially outwards, preferably in an angle between 45° and 135°, in particular perpendicularly, to the rotation axis. The helicoid structure comprises a single helicoid or multiple, particularly two helicoids, wherein at least one of the helicoids is wound circumferentially around the shaft. Preferably, all helicoids are wound circumferentially around the shaft, particularly in the same direction and, more in particular, with the same helix angle.

[0025] When multiple helicoids are provided, in axial direction the individual blades comprise the same or different lengths, wherein there is preferably an axial section in which axial extensions of the blades overlap.

[0026] Between the inlet opening and the outlet opening, the rotating shaft comprises an increasing diameter, such that the diameter is larger at a section closer to the outlet opening than at a section closer to the inlet opening. The wall of the cavity and / or the outer ends of the helicoid structure are preferably located at a constant distance to the central axis of the rotating shaft, but at least the increase of the distance to said central axis is smaller than the increase of the diameter of the rotating shaft. Thereby, the space between a surface of the rotating shaft and the wall of the cavity is smaller at the section closer to the outlet opening compared to the section closer to the inlet opening. Preferably, the radial extension of the helicoid structure, particularly its helicoids, i.e. its distance from the radial outer edge to the surface of the rotating shaft, decreases, particularly at the same rate as the diameter of the rotating shaft increases, such that the sum of diameter of the rotating shaft and radial extension of the helicoid blades stays constant in axial direction. This increases the pressure on the material on its way along the path from the inlet opening towards the outlet opening and, thus, the reduction of liquid in the material is increased.

[0027] According to a preferred embodiment, at least one helicoid of the helicoid structure ends axially distanced from the material flow limiting plate. Thereby, the pressure forces are at a good level, wherein a large amount of liquid can be pressed out of the material while also keeping the wear and the requirements for the construction material of the screw press low.

[0028] According to another preferred embodiment, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, in particular with their rotational axes parallel to each other. This increases the amount of processable material at a time. Beyond that, further increases the amount of liquid which can be pressed out of the material. Thus, the pressed material comprises a lower residual liquid.

[0029] Alternatively, to the parallel alignment of the two axes it is also preferred the two axes enclose a small angle between 0,1° and 10°, preferably between 1° and 5°, such that the meshing between two screw conveyors is constant when the screw conveyors taper towards the inlet opening. Therefore, the angle between the two axes equals preferably the combined tapering angle of the screw conveyors.

[0030] While the first rotatable screw conveyor comprises a first shaft with at a helicoid structure, comprising at least one first helicoid, and a first material flow limiting plate, the second rotatable screw conveyor comprises a second shaft with a second helicoid, comprising at least one second helicoid, and a second material flow limiting plate.

[0031] The screw press is preferably configured to rotate the first and the second rotatable screw conveyor at the same rotational speed.

[0032] According to another preferred embodiment, the material flow limiting plate of a first rotatable screw conveyor extends from a starting position of the first rotatable screw conveyor in circumferential direction - preferably in counterclockwise direction - over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170 °, wherein the starting position of the first rotatable screw conveyor is located - in circumferential direction - where the last turn of the helicoid structure of the first rotatable screw conveyor ends in axial direction. Said angle is also called first angle of extension. Thereby, the residual liquid in the pressed material is low. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0033] In a preferred alternative, the material flow limiting plate of a first rotatable screw conveyor extends from the starting position of the first rotatable screw conveyor in circumferential direction - in clockwise direction - over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein the starting position of the first rotatable screw conveyor is located - in circumferential direction - where the last turn of the helicoid structure of the first rotatable screw conveyor ends in axial direction. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0034] Unless stated otherwise, in this document, clockwise respectively counterclockwise directions are interpreted as such in an axial direction from the outlet to the inlet. This corresponds to a view from the limiting plates at the end of the rotating shaft in a direction to the rotating shaft.

[0035] The starting position of the first rotatable screw conveyor preferably marks one of the two ends of the material flow limiting plates of said first rotatable screw conveyor, or is at most 90°, preferably at most 30°, preferably at most 15°, preferably at most 5° offset relative to one of the two ends of that material flow limiting plate. This results in very good pressure and low residual liquid in the pressed material.

[0036] It is also preferred, that there is a contact between the helicoid of the first rotatable screw conveyor and the material flow limiting plate at the starting position of the first rotatable screw conveyor.

[0037] According to another preferred embodiment, the material flow limiting plate of a second rotatable screw conveyor extends from a starting position of the second rotatable screw conveyor in circumferential direction - preferably in clockwise direction - over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein, preferably, the starting position of the second rotatable screw conveyor in circumferential direction is located where the last turn of the helicoid structure ends in axial direction. Said angle is also called second angle of extension. Thereby, the residual liquid in the pressed material is low. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0038] In a preferred alternative, the material flow limiting plate of a second rotatable screw conveyor extends from a starting position of the second rotatable screw conveyor in circumferential direction - in counterclockwise direction - over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein, preferably, the starting position of the second rotatable screw conveyor in circumferential direction is located where the last turn of the helicoid structure ends in axial direction. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0039] The starting position of the second rotatable screw conveyor preferably marks one of the two ends of the material flow limiting plates of said second rotatable screw conveyor, or is at most 90°, preferably at most 30°, preferably at most 15°, preferably at most 5° offset relative to one of the two ends of that material flow limiting plate. This results in very good pressure and low residual liquid in the pressed material.

[0040] It is also preferred, that there is a contact between the helicoid of the second rotatable screw conveyor and the material flow limiting plate at the starting position of the second rotatable screw conveyor.

[0041] The limiting plate of the first rotatable screw conveyor is also referred to as the first limiting plate, wherein the limiting plate of the second rotatable screw conveyor is also referred to as the second limiting plate. Similarly, the starting position of the first rotatable screw conveyor is also referred to as the first starting position, wherein the starting position of the second rotatable screw conveyor is also referred to as the second starting position.

[0042] In a particularly preferred embodiment, one of the material flow limiting plates of a screw press comprising a first and a second screw conveyor is installed in clockwise direction and the other limiting plate is installed in counterclockwise direction.

[0043] It another particularly preferred embodiment, the material flow limiting plate of the second rotatable screw conveyor extends in counterclockwise direction over the second angle of extension when the material flow limiting plate of the first rotatable screw conveyor extends in clockwise direction over the first angle of extension. Alternatively, the material flow limiting plate of the second rotatable screw conveyor extends in clockwise direction over the second angle of extension when the material flow limiting plate of the first rotatable screw conveyor extends in counterclockwise direction over the first angle of extension. This means, that it is preferred the two limiting plates of the two rotatable screw conveyors extend circumferentially in opposite directions with respect to clockwise / counterclockwise direction. This leads to very good pressure rates and low residual liquid in the pressed material. It also provides a similar load on the individual screw conveyors, resulting the wear of both conveyors to be similar.

[0044] Alternatively, it is preferred, that the material flow limiting plate of the first and second rotatable screw conveyors extend both in clockwise or both in counterclockwise direction over the first respectively second angle of extension. This means that both limiting plates circumferentially extend in the same direction with respect to clockwise / counterclockwise direction.

[0045] In a particularly preferred embodiment, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, wherein the sum of the angle of extension of the first limiting plate and the angle of extension of the second limiting plate, in particular the sum of the first angle of extension and the second angle of extension, is at most 360°, preferably at most 355°, preferably at most 350°, preferably at most 345°, preferably at most 340°, preferably at most 335°, preferably at most 330°.

[0046] Preferably, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, wherein the sum of the angle of extension of the first limiting plate and the angle of extension of the second limiting plate, in particular the sum of the first angle of extension and the second angle of extension, is at least 90°, preferably at least 120°, preferably at least 150°, preferably at least 180°, preferably at least 210°, preferably at least 240°, preferably at least 270°, preferably at least 300°.

[0047] Particularly preferred, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, wherein the sum of the angle of extension of the first limiting plate and the angle of extension of the second limiting plate, in particular the sum of the first angle of extension and the second angle of extension, is 90 to 360°, preferably 180 to 355°, preferably 270 to 350°, preferably 300 to 345°, preferably 320 to 340°.

[0048] In a further preferred embodiment, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, wherein the angle of extension of the first limiting plate and the angle of extension of the second limiting plate, in particular the first angle of extension and the second angle of extension, differ for one another by at most 90°, preferably at most 60°, preferably at most 45°, preferably at most 30°, preferably by at most 15°, preferably by at most 10°.

[0049] Particularly preferred, the screw press comprises at least two rotatable screw conveyors, in particular two rotatable screw conveyors, wherein the angle of extension of the first limiting plate and the angle of extension of the second limiting plate, in particular the first angle of extension and the second angle of extension, are identical.

[0050] According to another preferred embodiment, the limiting plates of the rotatable screw conveyors, in particular of the at least two rotatable screw conveyors, in particular of the two rotatable screw conveyors, are arranged to each other so that the rotatable screw conveyors are freely rotatable.A-mounting setup:

[0051] According to a particularly preferred embodiment, the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said first screw conveyor. Respectively, the limiting plate of the second screw conveyor preferably extends over the second angle - starting from the respective starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said second screw conveyor. This is called the A-mounting setup. Thereby, the liquid in the pressed material is effectively reduced by the screw press.

[0052] Thus, in such an embodiment, the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said first screw conveyor and the limiting plate of the second screw conveyor extends over the second angle - starting from the respective starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said second screw conveyor. Thus, limiting plates extend in a direction opposite to the rotational directions of the screw conveyors.

[0053] The presence of the material flow limiting plate according to the present invention in the configuration of the A-mounting setup allows to build up a favorable high pressure over the length of the screw press, in particular up to 10 bar close to the material flow limiting plate.

[0054] The above-mentioned A-mounting setup preferably corresponds to the following embodiment, which is also preferred for reducing liquid from the material. Accordingly, following a particularly non-rotating helicoid from the inlet to the outlet and, thus, in the direction of the limiting plate, the first and / or second limiting plates - in circumferentially direction - extend from their respective first resp. second starting position over their respective first resp. second angle in a direction that corresponds to the winding direction of the helicoid. As such, considering the winding path of the helicoid, the limiting plate forms an extension of the helicoid in a circumferential direction over the first respectively second angle.

[0055] Thus, in a particularly preferred embodiment, the first and second limiting plates - in circumferentially direction - extend from their respective first respective second starting position over their respective first respective second angle in a direction that corresponds to the winding direction of the helicoid.

[0056] Thus, in a preferred embodiment, the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said first screw conveyor and the limiting plate of the second screw conveyor extends over the second angle - starting from the respective starting position - in a direction that corresponds to the opposite of the rotational direction of the shaft of said second screw conveyor and the first and second limiting plates - in circumferentially direction - extend from their respective first respective second starting position over their respective first respective second angle in a direction that corresponds to the winding direction of the helicoid.

[0057] In a preferred embodiment, the limiting plates of the first and second conveyor are positioned in the opposite rotation direction of the screw conveyor starting from the starting point.B-mounting setup:

[0058] Alternatively to and even preferred over the abovementioned A-mounting setup, it is particularly preferred that the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the rotational direction of the shaft of said first screw conveyor. Respectively, the limiting plate of the second screw conveyor preferably extends over the second angle - starting from the respective starting position - in a direction that corresponds to the rotational direction of the shaft of said second screw conveyor. This is also referred to as the B-mounting setup. Thereby, the liquid in the pressed material is effectively reduced by the screw press.

[0059] Thus, in a particularly preferred embodiment, the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the rotational direction of the shaft of said first screw conveyor and the limiting plate of the second screw conveyor extends over the second angle - starting from the respective starting position - in a direction that corresponds to the rotational direction of the shaft of said second screw conveyor. Thus, limiting plates extend in the same direction as the rotational directions of the screw conveyors.

[0060] The presence of the material flow limiting plate according to the present invention in the configuration of the B-mounting setup allows to build up a favorable particularly high pressure over the length of the screw press, in particular up to 11 to 12 bar close to the material flow limiting plate.

[0061] The above-mentioned B-mounting setup preferably corresponds to the following embodiment, which is also preferred for reducing liquid from the material. Accordingly, following a particularly non-rotating helicoid from the inlet to the outlet and, thus, in the direction of the limiting plate, the first and / or second limiting plates - in circumferentially direction - extend from their respective first respective second starting position over their respective first respective second angle in a direction opposite to the winding direction of the helicoid.

[0062] Thus, in a particularly preferred embodiment, the first and second limiting plates - in circumferentially direction - extend from their respective first respective second starting position over their respective first respective second angle in a direction opposite to the winding direction of the helicoid.

[0063] In a particularly preferred embodiment, the limiting plate of the first screw conveyor extends over the first angle - starting from the starting position - in a direction that corresponds to the rotational direction of the shaft of said first screw conveyor and the limiting plate of the second screw conveyor extends over the second angle - starting from the respective starting position - in a direction that corresponds to the rotational direction of the shaft of said second screw conveyor and the first and second limiting plates - in circumferentially direction - extend from their respective first respective second starting position over their respective first respective second angle in a direction opposite to the winding direction of the helicoid.

[0064] In a particularly preferred embodiment, the limiting plates of the first and second conveyor are positioned in the same rotation direction of the screw conveyor starting from the starting position.

[0065] The rotational direction of a shaft is particularly that direction in which the shaft is configured to rotate for advancing the material forward in the direction of the outlet. The rotational direction is indeed the direction needed for forwarding the material to the outlet. A rotation in the opposite rotational direction would result in an advancing into the opposite direction to the inlet.

[0066] If two screw conveyors are provided, the two screw conveyors are preferably configured to rotate in opposite directions with respect to clockwise / counterclockwise directions. Therein, if the rotational direction of one of the two screw conveyors corresponds to a clockwise direction, the rotational direction of the other of the two screw conveyors corresponds to a counterclockwise direction.

[0067] Thus, in a preferred embodiment, in a screw press comprising a first and a second screw conveyor one of the screw conveyors is configured to rotate in clockwise direction and the other screw conveyor is configured to rotate in counterclockwise direction. Thus, in a preferred embodiment, the screw conveyors are configured to rotate in opposite directions to each other.

[0068] In a preferred embodiment, in a screw press comprising a first and a second screw conveyor, wherein one of the screw conveyors is configured to rotate in clockwise direction and the other screw conveyor is configured to rotate in counterclockwise direction the screw conveyors are configured to rotate convergent to each other, thus rotating towards the inside of the screw press.

[0069] In a preferred embodiment, in a screw press comprising a first and a second screw conveyor, wherein one of the screw conveyors is configured to rotate in clockwise direction and the other screw conveyor is configured to rotate in counterclockwise direction the screw conveyors are configured to rotate divergent to each other, thus rotating towards the outside of the screw press.

[0070] According to another preferred embodiment, there is a relative rotational position of the at least two rotatable screw conveyors to each other, in which the starting position of the first rotatable screw conveyor has a minimum distance to the second rotatable screw conveyor, wherein - in this relative rotational position - the starting position of the first rotatable screw conveyor is opposed to a minimum distance position of the second rotatable screw conveyor, wherein the minimum distance position corresponds to the starting position of the second rotatable screw conveyor or wherein the starting position of the second rotatable screw conveyor is offset from the minimum distance position by 1 to 179°, in particular 5 to 30°, in particular 15°. These values correspond to very good positioning of the two material flow limiting plates relative to each other. Thereby, the residual liquid in the pressed material is particularly low.

[0071] This minimum distance position relates to an auxiliary position for describing the arrangement. The minimum distance position does not necessarily refer to an actual, physical structure. It can correspond to the second starting position. However, the second starting position may also be offset as mentioned above.

[0072] The rotational position defining the minimum distance position is the rotational position of the first screw conveyor wherein the distance between the second screw conveyor and the first starting position is minimal. That is the rotational position where the first starting position is closest to the second screw conveyor.

[0073] Herein, it is preferably assumed, that both screw conveyors are configured to rotate at the same rate, such that if the first screw conveyor is rotated by a specific rotation angle, the second screw conveyor is rotated by the same specific rotation angle.

[0074] According to another preferred embodiment, the helicoid structures of the rotatable screw conveyors are arranged to each other so that the rotatable screw conveyors mesh and are freely rotatable. This allows undisturbed operation of the screw press, wherein the residual liquid in the pressed material is very low.

[0075] It is noted that the limiting plate has a synergetic effect when combined with two or more screw conveyors because, particularly in the meshing region between the two conveyors, the pressure increase is particularly large very and leads to very high extraction rates of liquid when combined with one or more limiting plates.

[0076] To avoid the meshing of the two rotatable screw conveyors, the two rotatable screw conveyors are preferably configured to rotate in opposite directions. Further, preferably, the helix angle of the helicoid structure of the first rotatable screw conveyor equals the helix angle of the helicoid structure of the second rotatable screw conveyor, in absolute values.

[0077] Preferably, the first rotatable screw conveyor is configured to rotate in counterclockwise direction, while the second rotatably screw conveyor is configured to rotate in clockwise direction, resulting in low residual liquid in the pressed material.

[0078] According to another preferred embodiment, the material flow limiting plate comprises reinforcement ribs, in particular between the forward surface (71) and an adjacent supporting surface 85. Thereby, the lifetime of the screw press is increased. This also leads to a better stability of the limiting plates allowing increased pressure on the material and, thus, better liquid extraction rates and lower residual liquid in the pressed material.

[0079] According to another preferred embodiment the shaft comprises at least one at least partially hollow tubular body section which has along its circumferential surface a plurality of holes and / or wherein the enclosure comprises at least one section with a plurality of holes. Thereby, collecting liquid is facilitated as the liquid may intrude via the plurality of holes into the hollow tubular body section.

[0080] Preferably, the shaft of the first and / or second rotational screw conveyor comprises at its end facing the material flow limiting plate a plurality of first mounting structures, particularly threaded holes, for mounting the material flow limiting plate to the shaft. The material flow limiting plate comprises a plurality of corresponding second mounting structures, particularly holes, which can be threaded holes or threadless holes, for mounting the material flow limiting plate to the shaft. In the case, that the first mounting structure is a threaded and the second mounting structure is a hole, the screw press comprises a screw for passing through the hole of the material flow limiting plate to engage into the threaded hole of the shaft, thereby fixating the material flow limiting plate onto the shaft.

[0081] It is particularly preferred that the shaft and / or the material flow limiting plate comprise a large number of such first and second mounting structures. It has been found that fixating the material flow limiting plate to the shaft with at least one mounting structure combination, consisting of first and second mounting structure, per 30°, preferably per 20°, preferably per 10°, results in a very good tradeoff between stability and maintenance effort.

[0082] According to another preferred embodiment, in helicoid pitch direction between the starting position of the first or second rotatable screw conveyor and the middle of the last turn of the helicoid structure a fraction 1 / x of the helicoid pitch of the last turn of the helicoid structure, in particular a distance in a range from 100 to 300 mm, in particular 170 to 240 mm, in particular 176 mm or 237 mm, is provided, wherein x is a natural number of 1 to 100, in particular 2.

[0083] In a preferred embodiment, the distance between the last helicoid turn and the limiting disc at its circumferential end opposing its end at the starting position is in a range from 100 to 300 mm, preferably 160 to 250 mm, in particular 176 mm or 237 mm.

[0084] In a preferred embodiment, the helicoid pitch of the last helicoid turn proximal to the limiting plate is in a range from 350 to 480 mm, preferably 365 mm or 466 mm.

[0085] Preferably, the helicoid pitch describes the axial displacement of the helicoid after one turn. Thus, the helicoid pitch is correlated with the helix angle, and with the radius, resp. diameter of the shaft. It is preferred that the two helicoids have the same pitch. In any case, it must be ensured that the helicoids can still mesh with each other, which means that their blades can overlap in a radial direction, while still allowing rotation of the shafts around the rotation axes.

[0086] The object of the invention is preferably also solved by providing a rotatable screw conveyor for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, in particular for use in a screw press according to one of the precedingly described embodiments of the screw press, comprising a shaft with a rotation axis and a helicoid structure wound circumferentially around the shaft in axial direction of the shaft defining a material advancement direction, wherein the rotatable screw conveyor comprises a material flow limiting plate comprising a plate body bounded by a forward surface, a rearward surface and preferably a circumferential surface, which material flow limiting plate is located at a material advancement direction end of the shaft, and wherein the material flow limiting plate is fixed to the shaft, wherein the rearward surface is extending in an angle, preferably perpendicular to the rotation axis. Such a rotatable screw conveyor allows high extraction rates of liquids when pressing a material in the screw press, which on the other hand leads a low residual liquid in the pressed material. Thereby, subsequent drying processes require less energy and less time.

[0087] According to another preferred embodiment, the material flow limiting plate of the rotatable screw conveyor extends from a starting position of the rotatable screw conveyor in circumferential direction over an angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein the starting position of the rotatable screw conveyor in circumferential direction is located where the last turn of the helicoid structure ends in axial direction. Thereby, the residual liquid of the pressed material is low. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0088] It is alternatively preferred that the limiting plate covers the whole 360° angle which also increases the extraction of liquid from a pressed material.

[0089] The object of the invention is preferably also solved by providing a method for the preparation of a pressed, preferably solid, material, preferably pressed chicory root pulp or pressed sugar beet pulp, in particular pressed sugar beet pulp, comprising the following steps: a) providing a material, preferably plant material, in particular pulp, in particular root or beet pulp, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, in particular sugar beet cossettes, to be pressed, b) pressing the material provided in step a) with a screw press according to the present invention, and c) obtaining a pressed material, in particular pressed pulp, preferably pressed chicory root pulp or pressed sugar beet pulp, in particular pressed sugar beet pulp.

[0090] In a most preferred embodiment, the pressed pulp is pressed sugar beet pulp.

[0091] The method is preferably carried out using a screw press and / or a rotatable screw conveyor according to one of the present embodiments. This particularly leads to the same advantages and effects as described above in the context of the screw press and / or the rotatable screw conveyor.

[0092] According to another preferred embodiment of the method, the pressed, preferably solid, material obtained in step c) has an average dry substance content of more than 31,1 % at 1300 rpm of a rotatable screw conveyor with two screws.

[0093] Preferably, the invention, in particular the present method, enables an additional increase of dry matter of at least 1 wt.-% points, preferably 1 to 2 wt.-% points, more preferably an additional increase of 1.5 or 2.0 wt.- % points compared to comparative pressing methods with a conventional screw press having the identical construction but without limiting discs.

[0094] The object of the invention is preferably also solved by providing a pressed material prepared according to a method according to one of the embodiments of the present invention. Such a pressed material has a very low amount of residual liquid.

[0095] In the context of the present invention, the starting position of the rotatable screw conveyor in circumferential direction is located where the last turn of the helicoid structure ends in axial direction, in particular at the end of the shaft of the screw conveyor oriented towards the outlet opening, if the last turn ends at the shaft end and, if the last turn of the helicoid structure terminates at an axial distance from said shaft end, the starting position is given by the axial prolongation of the end of the last turn up to the shaft end.

[0096] In the context of the present invention, the term "limiting plate extends from a starting position of the rotatable screw conveyor in circumferential direction over an angle of 1 to 359°, in particular 40 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165°" means that the limiting plate extends in circumferential direction, relative to the starting point, from the starting point to an circumferential end of the limiting plate located at an angular value with the given range, or if referred to a particular angular value, located at said particular angular value. Thus, the limiting plate extends over a circular sector of the screw conveyor from a starting position to its circumferential end which is defined by an angular value of the given value or an angular value within the given numerical range of angular value. Preferably, the material flow limiting plate is in form of an annular sector.

[0097] The invention is further described in the following example and accompanying figures, which are not limiting the scope of the present invention.

[0098] The figures show: figure 1shows a cross section along the rotational axis of a rotatable screw conveyor of a screw press according to a first embodiment, figure 2shows two rotatable screw conveyors of a screw press according to the embodiment shown in figure 1, figure 3shows an outlet opening section of a screw press according to a second embodiment in a profile view, figure 4shows the outlet opening section in a top view, figure 5shows a detail of the profile view of figure 3, figure 6shows a cross sectional view through the rotational axes of two rotatable screw conveyors according to the second embodiment, figure 7shows perspective view of the two rotatable screw conveyors according to the second embodiment, figure 8shows a side view of one rotatable screw conveyors according to the second embodiment, figure 9shows another perspective view of the two rotatable screw conveyors according to the second embodiment, figure 10shows two rotatable screw conveyors of a screw press according to a third embodiment, figure 11shows a perspective view of two rotatable screw conveyors of a screw press according to a fourth embodiment, figure 12shows another perspective view of the two rotatable screw conveyors shown in figure 11, figure 13shows a perspective view of two rotatable screw conveyors according to the fifth embodiment, figure 14shows a segment of a material flow limiting plate and figure 15provides a schematic presentation of the course of pressure in a screw press without limiting plate (control) and comprising the A- and B-mounting setups of the present invention.

[0099] Fig. 1 shows a screw press 1 according to a first embodiment for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, particularly sugar beet pulp. The screw press 1 comprises an enclosure 3 with at least one inlet opening 5 and at least one outlet opening 7, wherein the screw press 1 further comprises at least one rotatable screw conveyor 9 enclosed by the enclosure 3 for pressing the liquid-containing solid material and for advancing the liquid-containing solid material from the inlet opening 5 towards the outlet opening 7.

[0100] The screw conveyor 9 comprises a shaft 11 with a rotation axis R, wherein the screw conveyor 9 in the screw press 1 is configured to rotate around the rotation axis R. The shaft comprises a cylindrical form, wherein on the surface of said shaft a helicoid structure 13 with at least one helicoid is formed. Thus, the screw conveyor 9 further comprises the helicoid structure 13 which is wound circumferentially around the shaft 11. Longitudinally, the helicoid structure 13 extends at least from the inlet opening 5 towards the outlet opening 7. In figure 1 it is indicated where the helicoid structure 13 is located. However, details of the helicoid structure 13 are apparent in subsequent figures.

[0101] The axial direction in which the pressed material is to be advanced is indicated by a straight arrow A, which points from the right to the left in figure 1, which is the direction towards the outlet opening 7. However, the axial direction is not the only relevant direction for advancing the material. Due to the nature of a rotating screw press, the material is also advanced circumferentially around the shaft 11.

[0102] For mounting the shaft 11, there are two bearings, particularly a first bearing 15 at the side of inlet opening 5 and a second bearing 17 at the side of the outlet opening 7.

[0103] The outlet opening 7 is preferably for discharging the pressed material. Preferably, there is a separate space, particularly a chamber 19 for collecting the liquid, which is pressed out of the material on its path from the inlet opening 5 to the outlet opening 7. The chamber 19 is located under the screw conveyor 9 and may comprise a further discharge opening 20 for discharging the liquid. Such a discharge opening 20 is for example shown in figure 3.

[0104] The enclosure 3 encloses a cavity 21 for housing the screw conveyor 9 and its shaft 11. In the present embodiment the chamber 19 is a part of the cavity 21. However, the chamber 19 can also be formed separately to the cavity 21 of the enclosure.

[0105] Fig. 2 shows two rotatable screw conveyors 9, preferably according to the embodiment of the screw press 1 as shown in figure 1. A first screw conveyor 23 of the two rotatable screw conveyors 9 is shown in figure 2 left of a second screw conveyor 25 of the two rotatable screw conveyors 9. The first screw conveyor 23 is configured to rotate around a first rotation axis R1, while the second screw conveyor is configured to rotate around a second rotations axis R2.

[0106] Rotational direction of the screw conveyors 9 is indicated by dashed arrows, wherein a first arrow T1 indicates the direction of the first screw conveyor 23 and wherein a second arrow T2 indicates the direction of the second screw conveyor 25. So, it is preferred that the directions of rotation of the two screw conveyors 9 is respectively opposite to one another. For example, in figure 2 the first screw conveyor 23 is configured to rotate in counterclockwise direction, wherein the second screw conveyor 25 is configured to rotate in clockwise direction.

[0107] Each of the rotatable screw conveyors 9, particularly the first screw conveyor 23 and the second screw conveyor 25, define a path 27 which is - in both axial directions - limited by the helicoid structure 13 and - in a radial inward direction - by the shaft 11. Additionally, in the radial outwards direction, the enclosure 3 limits the path 27. Particularly, in a first section 29 close to the outlet opening 7, the helicoid structure 13 can be immediately adjacent to a wall of the cavity 21 of the enclosure 3, such that the defined path 27 is a radially outwards confined in a closing manner. In a second section 31 closer to the inlet opening, however, the path 27 may be formed as an open path 27, comprising gaps in an axial direction between the wall of the cavity 21 of the enclosure 3 and the helicoid structure 13. Thereby, the pressure on the advancing material can be increased along its way from the inlet opening 5 to the outlet opening 7.

[0108] Those gaps are particularly formed by a tapering of the shaft 11 and respectively the helicoid structure 13 towards the inlet opening 5, which can be clearly seen in figure 1. Thereby, the radius of the shaft 11 and the distance between the radial outer ends of the helicoid structure 13 and the rotation axis R increases towards the outlet opening 7, while the cavity 21 of the enclosure 3 is - at least over the greater part of the axial dimension, which is in figure 1 the whole cavity 21 with the exception of the inlet opening region at the very right of the cavity 21 - formed cylindrically.

[0109] The shaft 11 may be formed at least partially hollow, such that it comprises an interior chamber 32, wherein on its surface the shaft 11 comprises a filter region permeable for liquid, particularly formed by holes like a sieve. Thereby, the separation of pressed material and liquid is facilitated. Such a filter region is preferably formed at the end of the shaft 11 which is facing the outlet opening 7 as the pressure in this region is very high.

[0110] Each of the screw conveyors 9 of the screw press 1 further comprises a material flow limiting plate 33. As there are two screw conveyors 9 in figure 2, there are also two material flow limiting plates 33, namely a first limiting plate 35 and a second limiting plate 37. These limiting plates increase the pressure on the material when it advances towards the outlet opening 7.

[0111] Although the details of the limiting plates 33 are not visible in figure 1, it is indicated in figure 1 that the limiting plates 33 are located at an end 39 of the screw conveyor 9 that is closer to the outlet opening 7, which corresponds to the mounting location in figure 2. The limiting plates 33 are both located at the end 39 of the rotatable screw conveyor 9 that is configured to be closer to the outlet opening 7 when installed in a screw press 1. In figure 2 the end 39 is facing forwardly towards the viewer. Said end 39 can also comprise a mounting protrusion 41 for mounting the rotatable screw conveyor 9 using the second bearing 17.

[0112] The mounting protrusion 41 comprises a mounting part 43, which can for example be a hole in which a corresponding protrusion of the second bearing 17 engages. Alternatively, the mountain part 43 can be formed as another protrusion, which is supported by the second bearing 17 when installed in the screw press 1. The mounting protrusion 41 further comprises a first segment 45, extending between the shaft and the mounting part 43, which preferably serves as a distance holding element 47.

[0113] As both mounting protrusions 41 of the first and the second screw conveyor 9 are essentially formed identically, herein the same reference numbers are used to describe the respective parts of the mounting protrusions of the first and second screw conveyor 9.

[0114] The limiting plate 33 has a synergetic effect when combined with two or more screw conveyors 9 because particularly in the meshing region between the two conveyors, the pressure increase is very advantageous and leads to high extraction rates of liquid when combined with one or more limiting plates 33.

[0115] Figure 2 also shows that the limiting plates 33 are fixed to an end face 49 of the shaft (11) at the end 39 facing the outlet opening 7 when installed in the screw press 1. The end face 49 comprises a plurality of holes 51, which are particularly equidistantly formed on said end face 49 and which are arranged circumferentially around the whole end face 49. These holes 51 are used to fixate the limiting plates 33 onto the shaft 11, particularly onto the end face 49. In the presently shown embodiment, fixation elements 53, particularly screws or bolts, are used for fixation. It is preferred to provide a plurality of fixation elements 53 and to spread them such that axial forces on the limiting plate 33 can be absorbed rather homogenously. As the pressure in axial direction on the limiting plate 33 can be very high, this leads to a very strong fixation of the limiting plate 33 to the shaft 11.

[0116] Fig. 3 shows a section of the screw press 1 according to a second embodiment in a profile view. The not-shown parts of the screw press 1 according to this second embodiment preferably correspond to the corresponding parts of the previously in figure 1 and figure 2 shown screw press 1.

[0117] As can be seen in this figure, the limiting plate 33 is located and fixed at the side of the shaft 11 that is closest to the outlet opening 7.

[0118] In this side view in figure 3, the fixation elements 53 can also be seen. Further, it is shown that the mounting protrusion 41 protrudes in axial direction towards the second bearing 17. Thereby, the rotatable screw conveyor 9 is mounted in the screw press.

[0119] In figure 3 there are particularly two rotatable screw conveyors 9 visible. The rotatable screw conveyor 9 in the background, however, only slightly rises above the screw conveyor 9 in the foreground, such that its helicoid structure 13 is visible between the helicoid structure 13 of the screw conveyor 9 in the foreground. It is noted in this context, that the two screw conveyors mesh with each other without interfering. As a consequence, in this side view, the visible part of the helicoid structure 13 of the screw conveyor 9 in the background is located right in between the windings of the screw conveyor 9 in the foreground.

[0120] Figure 3 further shows a power and control system 55 for driving the rotatable screw conveyor 9.

[0121] In the view of the screw press 1 shown in figure 3 the upper part of the enclosure 3 is not shown in the section closer to the limiting plate 33, to allow unhindered view on the screw conveyors 9 and their helicoid structure 13. In an alternative embodiment, this might also facilitate access to the screw conveyors 9, even in operation. However, it is preferred, that the upper part of the enclosure 3 covers the screw conveyor 9 throughout the axial extension of the screw conveyor 9, thus, protecting the screw conveyor 9 from external impacts, as well as protecting the environment from the rotating screw conveyors 9 in operation mode.

[0122] Similarly, in fig. 4 the covering of the enclosure is not shown to allow the viewer to take a look into the interior cavity 21 of the enclosure from a top view. Thereby, the first rotatable screw conveyor 23 and the second rotatable screw conveyor 25 are both clearly visible. As in figure 2 the visible helix angle as seen from the top is such that it is slanted inwardly when looking from above, which means, that in figure 4 - where the helix angle of the helicoids is just the opposite of the one seen in figure 2 - the first screw conveyor 23 is the one in the lower half of the figure, wherein the second screw conveyor 25 is shown in the upper half of the figure. In other words, screw conveyors shown in figure 4 are shown from approximately the opposite direction than in figure 2.

[0123] It is pointed out, that both screw conveyors mesh in a meshing region 57 between them. This means that a first helicoid 59 of the first screw conveyor 23 overlaps in radial direction of the two rotation axes R1, R2 with a second helicoid 61 of the second screw conveyor 25. This allows high pressure rates resulting in low residual liquid in the pressed material after discharging said material through the outlet opening 7. It is noted that there can be more than one helicoid per screw conveyor 9, however, in the shown embodiment of figure 4 there is only helicoid on each of the screw conveyors 9.

[0124] Furthermore, in figure 4 it is shown that the helicoid structure adjoins a side wall 63 of the cavity 21 at least to the outer sides of the screw press 1. This is achieved in that the side wall is not exactly parallel to the rotation axes R1 respectively R2, but instead it follows the same tapering angle as the first respectively second screw conveyor. Thereby, the defined path 27 is radially outwards closed without allowing any gaps between the helicoid structure and the side wall 63 of the cavity, resulting in improved pressure rates on the material when advancing to the outlet opening 7.

[0125] When looking at figure 4 and figure 2 in combination, one also recognizes that the limiting plates of both screw conveyors 9 are arranged such that limiting plates alternatively intrude into the meshing region 57, wherein a gap 65 of meshing region 57 that is open in an axial direction is covered by each of the limiting plates by more than 50%, particularly more than 80% of the radial extension of the gap. This arrangement results in good pressure rates and high extraction of liquid in that region while still allowing from time to time the outlet of the pressed material, particularly in the side regions, close to the side walls 63 of the cavity.

[0126] The location of the gap 65 is shown in figure 4 although in figure 4 the vision on the gap 65 is obscured by a front panel 67, which is also shown in figure 3. Therefore, with respect to the gap, it is also referred to other figures 2, particularly figure 6.

[0127] Fig. 5 shows a detail of the profile view shown in figure 3, wherein the cross-sectional plane A-A is marked, which will be shown in figure 6. Also, the axial width W of the limiting plates 33 is shown.

[0128] Fig. 6 shows the cross-sectional view A-A which is indicated in figure 5. The limiting plates 33 are shown in a frontal view.

[0129] The first limiting plate 35 and the second limiting plate 37 each comprises a plate body 69 which is bounded by a forward surface 71, a rearward surface 73 and a circumferential surface 75. The rearward surface 73 cannot be directly seen in figure 6. The rearward surface 73 is, for example, shown in figures 2, 3 and 4. However, one can imagine, that the rearward surface 73 is on the side of the limiting plate that is opposite to the forward surface 71. As can be seen in figures 2, 3 and 4 the rearward surface extends in an angle, here particularly perpendicular to the rotation axis and, thus, also in the same angle to the surface of the shaft.

[0130] Thereby, the material flow limiting plates 33, 35, 37 are located at an end of the helicoid structure 13 facing the outlet opening 7 such that the path 27 is limited in an axial direction particularly without completely closing said path 27. Therefore, it is still possible to advance material from the inlet opening through the axial section of the limiting plates 33 to the outlet opening 7 on the other side of the limiting plates 33.

[0131] As can be seen in figure 6 the plate body 69 covers more than half of the gap 65 of the meshing region 57 between the two screw conveyors such that passage of pressed material in axial direction is blocked at least partially. In this particular embodiment, the plate body 69 even covers more than 75%, particularly more than 90% of the gap 65 at the axial position of the limiting plate 33.

[0132] Further, figure 6 shows that the material flow limiting plate 33 of the first rotatable screw conveyor 23 extends from a starting position 77 of the first rotatable screw conveyor 23 in circumferential direction covering an angle between 1° and 359°. The angle of the first screw conveyor 23 is also called the first angle.

[0133] In this second embodiment of the screw press 1 shown here in figure 6, the first rotatable screw conveyor 23 particularly extends in counterclockwise direction. Therein, the covered angle of the first material flow limiting plate 33 is particular between 150° to 190°, being approximately 160° to 175°. It is preferred that the second material flow limiting plate 37 also covers an angle between 1° and 359°, which is called the second angle. Preferably, as in this second embodiment, the second angle equals the first angle of the first limiting plate 35. Thereby, the strain on the limiting plates 33 is balanced and lifetime of the screw press 1, particularly its limiting plates 33 is increased.

[0134] Figures 7 to 10 show in detail the embodiment according to the B-mounting setup.

[0135] As will be apparent when looking at fig. 7, the starting position 77 of the first rotatable screw conveyor 9, 23 in circumferential direction is located where the last turn of the helicoid structure 13 ends in axial direction, preferably in counterclockwise direction. Here in figure 7, the first helicoid 59 of the helicoid structure 13 of the first screw conveyor 23 converges with the first limiting plate 33 exactly at the starting position 77.

[0136] When converging, the first helicoid 59 and the first limiting plate 35 preferably comprise the same height relative to the shaft surface respectively to the rotation axis R which causes good pressure rates for extracting liquid from the material particularly towards the end of the first helicoid 59. It is noted that in figure 7 only one rotation axis R is shown, as both rotation axes R1, R2 are parallel to each other such that the second rotations axis R2 is essentially behind the first rotation axis R1.

[0137] The second helicoid 61 of the second screw conveyor 25 converges correspondingly with the second limiting plate 37, wherein the second limiting plate 37 preferably comprises the same height as the second helicoid 61 at least in the region of convergence.

[0138] It is preferred that this starting position 77 is rather close to a circumferential end 79 of the limiting plate. However, the circumferential end 79 can also be offset from the starting position 77, wherein the offset is preferably small, i.e. smaller than 15°, preferably smaller than 5°.

[0139] In figure 7 on the right side, the starting position 77 of the first screw conveyor 23 can be well seen, wherein the viewer can also see the small offset between the starting position 77 and the circumferential end 79 of the limiting plate. In the opposite circumferential direction towards the opposing circumferential end 81 the first limiting plate 35 extends over the above-mentioned first angle of preferably between 150° and 190°, wherein said first angle is measured between the starting position 77 and the opposing circumferential end 81. Correspondingly, the second angle is measured between the starting position 77 on the second limiting plate 37 and the opposing circumferential end 81 of said second limiting plate 37, wherein the second angle preferably equals the first angle in absolute values.

[0140] Figure 7 further shows that the first limiting plate 33 extends from its starting position 77 over the first angle in counterclockwise direction, wherein the second limiting plate extends from its starting position 77 over the second angle in clockwise direction. It is generally preferred that the two angles, the first angle and the second angle, extend in opposite directions starting from their respective starting positions 77, as this allows improved rotational dynamics, particularly when two or more rotatable screw conveyors 9 are provided. Particularly, this facilitates the meshing of the helicoids 59,61 while allowing the free rotation of both.

[0141] The material flow limiting plates 33 as shown in figure 7 comprise a plurality of reinforcement ribs 83 to support the rearward surface 73 when the material is pressed against said rearward surface 73. The rearward surface 73 faces into the direction of the inlet opening 5 and, thus, in operation mode, the material is pressed against said rearward surface 73.

[0142] The reinforcement ribs 83 are preferably located on the backside of the rearward surface 73, particularly between the forward surface 71 and an adjacent supporting surface 85, which can be a further circumferential surface. It is particularly preferred that the forward surface 71 is perpendicular to the supporting surface 85. Thereby, stability of the limiting plate 33 is improved.

[0143] The reinforcement rib 83 in figure 7 is particularly comprises a portion formed as a triangular wedge with a slanted surface, enclosing an angle with the rotation axis R, wherein said angle is between 20° and 60°, preferably smaller than 45°.

[0144] Fig. 8 shows the rotatable screw conveyor 9 from the side in an - relative to the other figures - enlarged view, wherein the starting position 77 is located at the very left of figure 8. Here it can be seen that the helicoid of the helicoid structure 13 comprises on its radially outer end a circumferential surface 87. Said circumferential surface 87 of the helicoid aligns with the circumferential surface 75 of the limiting plate 33 at the starting position 77. This results from the limiting plate 33 and the circumferential surface 87 of the helicoid both having the same height relative to the surface 89 of the shaft 11.

[0145] In operation mode, when rotating the shaft 11 around the rotation axis R - in figure 8 from left to right - a forward surface 91 of the helicoid of the helicoid structure 13 pushes material forward in the direction of the material flow limiting plate 33, thus, causing an accumulation of material in the frontal region close to the limiting plate 33. Thereby, the pressure is high and reduction of liquid from the material is improved.

[0146] In this detailed view of figure 8, the reinforcement ribs 83 between the supporting surface 85 and the forward surface of the limiting plate 33 and the slanted surfaces 93 of the triangular portion of said reinforcement ribs 83 can be well seen. The slanted surface 93 encloses an angle with the rotation axis R that is smaller than 45°, preferably 30°.

[0147] Further, the circumferential surface 75 of the limiting plate 33 is perpendicular to the forward surface 71 and to another forward surface 95, axially distanced to the forward surface 71. Said other forward surface 95 is particularly used for fixation of the limiting plate 33 to the shaft 11 and is therefore also called fixation surface 95.

[0148] The limiting plate 33 comprises another plurality of additional reinforcement ribs 97 which are placed on the fixation surface 95. These additional reinforcement ribs 97 are essentially rectangular-like shaped, wherein they comprise a chamfered edge 99 at their radially outer end which - when installed in the screw press 1 - faces the outlet opening 7 rather than the inlet opening 5.

[0149] Fig. 9 shows another perspective view of the two rotatable screw conveyors 9 according to the second embodiment. When comparing this view to the view in figure 4, this view is from the opposite direction, which is a view from below when the screw conveyors 9 are installed in the screw press 1 shown in figure 3 and 4.

[0150] In this view of figure 9 is it particularly pointed out that - at the opposing circumferential end 81 - there is an axial distance D between the limiting plate 33 and the last winding of the helicoid structure 13, here in particular the helicoid 59. For high extraction rates of liquid this distance D is preferably 176 mm or 237 mm.

[0151] Fig. 10 shows two rotatable screw conveyors 9 of a screw press 1 according to a third embodiment, wherein said third embodiment is different from the previously shown embodiments by providing a second helicoid on each of the screw conveyors 9. This means that the first screw conveyor 23 comprises two first helicoids 59, wherein a primary helicoid 101 of the two first helicoids 59 extends up to the first limiting plate 35 of the first screw conveyor 23, particularly up to the starting position 77. The other of the two first helicoids 59, which is a secondary helicoid 103, ends in axial direction in a distance to the first limiting plate 35, wherein said distance is indicated by a dashed double arrow E. Said distance E is preferably smaller than 350 mm, preferably smaller than 300 mm. Further preferred, the secondary helicoid 103 is not in the exact middle between of two primary helicoid 101 windings. The secondary helicoid is preferably closer to the helicoid winding of the primary helicoid 101 which is closer to the inlet opening 5. It is particularly preferred to have the secondary helicoid located at about one third of the distance between two primary helicoid 101 windings.

[0152] The second screw conveyor 25 also comprises two second helicoids, namely a primary second helicoid 105 and a secondary second helicoid 107. The arrangement of the primary second helicoid 105 and the secondary second helicoid 107 is preferably analogous to the first screw conveyor 23.

[0153] Furthermore, the secondary helicoids 103 comprise a smaller height than the primary helicoids 101. The primary helicoids 101 preferably comprise a height equal to the height of the limiting plates 33. The heights of the secondary helicoid 103 are preferably at most half the height of the primary helicoids 101. This causes extraction rates to be very high.

[0154] The limiting plate of the second screw conveyor 25 is not visible in figure 10 as it is hidden behind the protrusions 41 of the screw conveyors 9.

[0155] Fig. 11 and Fig. 12 (A-mounting setup) show two rotatable screw conveyors of a screw press 1 according to a fourth embodiment from two different perspectives.

[0156] Therein, the limiting plates 33 are mounted differently compared to the mounting of the third embodiment. As can been in figure 11, the larger part of the limiting plates is mounted such that it looks like an extension of the helicoid structure 13, without the axial propagation of the helicoid structure 13. In other words, following a non-rotating helicoid from the inlet opening 5 to the outlet opening 7 and, thus, in the direction of the limiting plate 33, the limiting plates 33 - in circumferentially direction - extend from the starting position 77 over the angle between 1° and 359°, in particular 40 to 190°, in particular 90 to 190°, particularly 150° to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in a direction that corresponds to the winding direction of the helicoid. In a particularly preferred embodiment, the angle is from 90 to 185°, preferably from 150 to 180°, in particular 165° or 170°.

[0157] This means - starting from the starting position 77 of the screw conveyor 9 - the limiting plates 33 extend over their respective first resp. second angles in a direction that is opposite to the rotational direction T1, T2 of the respective screw conveyors 9: the first screw conveyor 23 extends from its starting position 77 (which is also called first starting position 109) in figure 11 in clockwise direction over the first angle, which is an angle between 150° and 190°, wherein the second screw conveyor 25 extends from its starting position 77 (which is also called second starting position 111) in figure 11 in counterclockwise direction over the second angle, which is an angle between 150° and 190°.

[0158] Fig. 13 shows a semi-transparent view of two rotatable screw conveyors according to the fifth embodiment. According to this fifth embodiment the limiting plates are mounted as they are according to the fourth embodiment shown in figures 11 and 12. In contrast to the fourth embodiment, the screw conveyors 9 of the fifth embodiment each comprise two particularly different helicoids.

[0159] Like the screw conveyors 9 of the third embodiment, the first screw conveyor 23 comprises a primary first helicoid 101 and a secondary first helicoid 103, wherein the second screw conveyor 25 comprises a primary second helicoid 105 and a secondary second helicoid 107. This allows high extraction rates for the liquid, leaving the pressed material with a low residual liquid.

[0160] Due to the semi-transparent view, it is possible to see the extent of the holes 51 and how the fixation elements 53 are inserted in the holes 51.

[0161] Fig. 14 shows a limiting plate 33. Particularly it shows one of a plurality of segments 113, which can be combined to a single limiting plate 33.

[0162] As can be seen in the other figures, particularly figures 7 and 11, the limiting plates 33 of the first, second, third, fourth and fifths embodiment preferably comprise several of such segments 113. In particular a limiting plate 33 according to one of the embodiments comprises two segments 113. Thereby, it is possible to exchange single segments 113 and / or fixation elements 53 individually. Thus, heavily burdened segments 113 can be exchanged without exchanging the whole limiting plate 33 made of several segments 113. Therefore, maintenance is facilitated, and material requirements are reduced.

[0163] The segments 113 comprise a plurality of through hole 115 which allow access to the fixation holes 51 of the screw conveyor 9 when the segment 113 is mounted to the screw conveyor 9. By putting the fixation elements 53 through the through holes 115 and fixating them into the holes 51, the segment 113 can be mounted to the screw conveyor 9.

[0164] The segments 113 according to the embodiment shown in figure 14 does not comprise any reinforcement ribs. However, as was shown in other figures, providing reinforcement ribs 83, 97 to the limiting plates 33, respectively the segment 113 is preferred to increase stability of the segment 113.

[0165] The segments 113 comprise the circumferential surface 75, the forward surface 71 and the rearward surface 73, which is on the side of the segment 113 facing away from the viewer. The segment 113 further comprises the supporting surface 85, which can be used for placing reinforcement ribs 83, 91 to support the plate body 69 and particularly the rearward surface 71 when the pressure of the pressed material during pressing of the material is applied. Further, the segment comprises the fixation surface 95, in which the through holes 115 are located.

[0166] The segment 113 is formed like a step with adjacent surfaces being perpendicular to each other. In particular, the rearward surface 73 is perpendicular to the circumferential surface 75 and the circumferential surface 75 is perpendicular to the forward surface 71. Further, the forward surface 71 is perpendicular to the supporting surface 85, which is preferably perpendicular to the fixation surface 95. Thus, the fixation surface 95 is preferably parallel to the forward surface 71 and parallel to the rearward surface 73. Further, it is preferred that the circumferential surface 75 is bound concentrically to the supporting surface 85.

[0167] Overall, this segment 113 provides a limiting plate 33 with a very high stability, wherein it is also easy to mount and replace to the screw conveyor 9.

[0168] The limiting plates 33 according to the first, second, third, fourth and fifth embodiment are preferably identically formed. The screw conveyors 9 according to the second and fourth embodiment are preferably formed identically. Further, it is preferred that the screw press 1 according to the fourth embodiment is different from the screw press 1 according to the second embodiment particularly only in that the limiting plates 33 are mounted on a different location in circumferential direction.

[0169] Further, it is preferred that the screw press 1 according to the third and fifth embodiments is different from the screw press 1 according to the second and fourth embodiment only in that the screw conveyors 9 according to the third and fifth embodiment each comprise more than one helicoid, wherein the screw conveyors 9 according to the second and fourth embodiment preferably only comprise one single helicoid per screw conveyor 9.

[0170] Figure 15 shows the built-up of pressure in bar over the length of the press 1 in the absence of a material flow limiting plate 33 (indicated by filled triangles), in the presence of the present A-mounting setup (indicated by filled circles) and in the presence of the present B-mounting setup (indicated filled squares). It is evident that in the absence of a material flow limiting plate 33 the pressure over the length of the press does not build up such as for the screw press 1 of the present invention. Further, it is evident that the present B-mounting setup provides for a further pressure improvement over the present A-mounting setup.EXAMPLE: Processes comparing the screw presses of the present invention with a conventional screw press without limiting discs (without material flow limiting plate): Test 1:

[0171] Using the B-mounting setup (figures 7 to 10) of the present invention, comparative methods for the preparation of a pressed sugar beet pulp have been conducted comprising the following steps: a) providing a sugar beet pulp to be pressed, b) pressing the pulp provided in step a) with a screw press (1) according to the present invention (B-mounting setup) and - in a comparative pressing method - with a conventional screw press having the identical construction but without limiting discs, and c) obtaining the pressed sugar beet pulp according to both methods.

[0172] The use of the screw press of the present invention (B-mounting setup) advantageously resulted in increased values for the dry substance content (32.5 % dry matter) of the obtained pressed sugar beet pulp versus 30,8 % dry matter obtained using a conventional screw press without limiting discs, while the flow rate of the pressed pulp remained almost constant: 10,19 t / h for a screw press according to the invention and 10,27 t / h for a conventional screw press without limiting disc (each for 1300 rpm). The torque (average) increased from 769 Nm for the conventional screw press without limiting discs to 806 Nm using the screw press according to the invention. A significant increase of pressure in the pressing zone closest to the outlet could be observed using the process of the present invention (B-mounting setup) in comparison to the method using the conventional screw press (with high speed 1300 rpm (rotation per minute): 23-25 % and with low speed 900 rpm:10-12 %).Test 2:

[0173] Using the A-mounting setup (figures 11 and 12) and the B-mounting setup (figures 7 to 10) of the present invention, comparative methods for the preparation of a pressed sugar beet pulp have been conducted comprising the following steps: a) providing a sugar beet pulp to be pressed, b) pressing the pulp provided in step a) with two different screw presses (1) according to the present invention (namely with the A- and B-mounting setups) and - in a further comparative pressing method - with a conventional screw press having the identical construction but without limiting discs, and c) obtaining the pressed sugar beet pulp according to the three different methods.

[0174] The use of the screw presses of the present invention advantageously resulted in increased values for the dry substance content (32.7 % dry matter) of the pressed sugar beet pulp obtained using the screw press with the B-mounting setup versus 31,8 % dry matter of the pressed sugar beet pulp obtained using the screw press with the A-mounting setup versus 31,1 % dry matter of the pressed sugar beet pulp obtained using the screw press using the conventional screw press without limiting discs (each for 1300 rpm).

[0175] Figure 15 shows the built-up of pressure over the length of the press in the absence of a material flow limiting plate 33 with a pressure building up to about 8 bar, in the presence of the present A-mounting setup with a pressure building up to about 9 bar and in the presence of the present B-mounting setup with a pressure building up to about 12 bar.List of reference signs:

[0176] 1screw press 3enclosure 5inlet opening 7outlet opening 9rotatable screw conveyor 11shaft 13helicoid structure 15first bearing 17second bearing 19chamber for liquid 20discharge opening for liquid 21cavity 23first screw conveyor 25second screw conveyor 27path 29first section 31second section 32interior chamber of the shaft 33limiting plate 35first limiting plate 37second limiting plate 39end (outlet side) 41mounting protrusion 43mounting part 45first segment 47distance holding element 49end face 51holes 53fixation element 55power and control system 57meshing region 59first helicoid of first conveyor 61second helicoid of second conveyor 63side wall of cavity 65gap 67front panel 69plate body 71forward surface 73rearward surface 75circumferential surface 77starting position 79circumferential end of limiting plate 81opposing circumferential end 83reinforcement rib 85supporting surface 87circumferential surface of the helicoid 89surface of the shaft 91forward surface of the helicoid 93slanted surface of the reinforcement rib 95fixation surface 97reinforcement rib 99chamfered edge 101primary first helicoid 103secondary first helicoid 105primary second helicoid 107secondary second helicoid 109first starting position 111second starting position 113segment 115through hole Rrotation axis R1rotation axis R2rotation axis ADirection for advancing the material Waxial width of the limiting plates Daxial distance between limiting plate and last turn of helicoid Edistance between secondary helicoid and limiting plate T1rotational direction ("turning direction") of first conveyor T2rotational direction ("turning direction") of second conveyor

Claims

1. A screw press (1) for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, comprising: - an enclosure (3) comprising: - at least one inlet opening (5), - at least one outlet opening (7), - at least one rotatable screw conveyor (9) enclosed by the enclosure (3) for pressing the liquid-containing solid material and for advancing the liquid-containing solid material from the inlet opening (5) towards the outlet opening (7), the screw conveyor (9) comprising: - a shaft (11) with a rotation axis (R), and - a helicoid structure (13) wound circumferentially around the shaft (11) longitudinally extending at least from the at least one inlet opening (5) towards the at least one outlet opening (7); the screw conveyor (9) and the enclosure (3) defining a path (27) for the forced material advancement from the inlet opening (5) to the outlet opening (7), characterized in that the at least one screw conveyor (9) comprises - a material flow limiting plate (33) comprising a plate body (69) bounded by a forward surface (71), a rearward surface (73) and preferably a circumferential surface (75), which material flow limiting plate (33) is located at an outlet opening (7) facing end (39) of the helicoid structure (13) such that the path (27) is limited in an axial direction and wherein the material flow limiting plate (33) is fixed to the shaft (11) of the screw press (1), wherein the rearward surface (73) is extending in an angle, preferably perpendicular to the rotation axis (R), and wherein the material flow limiting plate (33) of the rotatable screw conveyor (9) extends from a starting position (77, 109) of the rotatable screw conveyor (9, 23) in circumferential direction over an angle of 40 to 190°, wherein the starting position (77, 109) of the rotatable screw conveyor (9, 23) in circumferential direction is located where the last turn of the helicoid structure (13) ends in axial direction.

2. The screw press (1) according to claim 1, wherein at least one helicoid (103, 109) of the helicoid structure (13) ends axially distanced from the material flow limiting plate (33).

3. The screw press (1) according to claim 1 or 2, wherein the screw press (1) comprises at least two rotatable screw conveyors (9), in particular two rotatable screw conveyors (9), in particular with their rotational axes (R1, R2) parallel to each other.

4. The screw press (1) according to claim 3, wherein the material flow limiting plate (33) of a second rotatable screw conveyor (9, 25) extends from a starting position (77, 111) of the second rotatable screw conveyor (9, 25) in circumferential direction - preferably in clockwise direction - over a second angle of 1 to 359°, in particular 40 to 190°, in particular 90 to 190°, in particular 150 to 190°, in particular 60 to 180°, in particular 90 to 175°, in particular 120 to 170°, in particular 165° or 170°, wherein preferably the starting position (77, 111) of the second rotatable screw conveyor (9, 25) in circumferential direction is located where the last turn of the helicoid structure (13) ends in axial direction, preferably in counterclockwise direction.

5. The screw press (1) according to any one of the preceding claims, wherein the radial outer end of the material flow limiting plate (33) is located in a radial distance to the rotation axis (R), that equals the distance between the rotation axis (R) and the outer end of the helicoid structure (13), particularly the helicoids, at least at the end - in axial direction - of the helicoid that faces the material flow limiting plate (33).

6. The screw press (1) according to any one of claims 3 or 4, wherein the two screw conveyors (9) are configured to rotate in opposite directions to each other.

7. The screw press (1) according to any one of claims 4 to 6, wherein the limiting plate (33, 35) of the first screw conveyor (23) extends over the first angle - starting from the starting position (77, 109) - in a direction that corresponds to the opposite of the rotational direction of the shaft (11) of the first screw conveyor (23), and / or wherein the limiting plate (33, 37) of the second screw conveyor (25) extends over the second angle - starting from the respective starting position (77, 111) - in a direction that corresponds to the opposite of the rotational direction of the shaft (11) of the second screw conveyor (25).

8. The screw press (1) according to any one of claims 4 to 6, wherein the limiting plate (33, 35) of the first screw conveyor (23) extends over the first angle - starting from the starting position (77, 109) - in a direction that corresponds to the rotational direction of the shaft (11) of the first screw conveyor (23), and / or wherein the limiting plate (33, 37) of the second screw conveyor (25) extends over the second angle - starting from the respective starting position (77, 111) - in a direction that corresponds to the rotational direction of the shaft (11) of the second screw conveyor (25).

9. The screw press (1) according to any one of claims 3 to 8, wherein the helicoid structures (13) of the rotatable screw conveyors (9) are arranged to each other so that the rotatable screw conveyors (9) mesh and are freely rotatable.

10. The screw press (1) according to any one of the preceding claims, wherein the material flow limiting plate (33) comprises reinforcement ribs (83, 97), in particular between the forward surface (71) and an adjacent supporting surface (85) and / or on a fixation surface (95) of the limiting plate (33).

11. The screw press (1) according to any one of the preceding claims, wherein the shaft (11) comprises at least one at least partially hollow tubular body section which has along its circumferential surface a plurality of holes and / or wherein the enclosure (3) comprises at least one section with a plurality of holes.

12. The screw press (1) according to any one of claims 4 to 11, wherein - in helicoid pitch direction - between the starting position (77) of the first or second rotatable screw conveyor (23, 25) and the middle of the last turn of the helicoid structure (13) a fraction 1 / x of the helicoid pitch of the last turn of the helicoid structure (13), in particular a distance in a range from 100 to 300 mm, in particular 170 to 240 mm, in particular 176 mm or 237 mm, is provided, wherein x is a natural number of 1 to 100, in particular 2.

13. A rotatable screw conveyor (9) for pressing a liquid-containing solid material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, in particular for use in a screw press (1) according to one of the preceding claims, comprising: - a shaft (11) with a rotation axis (R), and - a helicoid structure (13) wound circumferentially around the shaft (11) in axial direction of the shaft (11) defining a material advancement direction; characterized in that the rotatable screw conveyor (9) comprises - a material flow limiting plate (33) comprising a plate body (69) bounded by a forward surface (71), a rearward surface (73) and a preferably a circumferential surface (75), which material flow limiting plate (33) is located at a material advancement direction end (39) of the shaft (11), and wherein the material flow limiting plate (33) is fixed to the shaft (11), wherein the rearward surface (73) is extending in an angle, preferably perpendicular to the rotation axis (R).

14. The rotatable screw conveyor (9) according to claim 13, wherein the material flow limiting plate (33) of the rotatable screw conveyor (9) extends from a starting position (77) of the rotatable screw conveyor (9) in circumferential direction over an angle of 40 to 190°, wherein the starting position (77) of the rotatable screw conveyor (9) in circumferential direction is located where the last turn of the helicoid structure (13) ends in axial direction.

15. A method for the preparation of a pressed material, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, comprising the following steps: a) providing a material to be pressed, preferably chicory root pulp or sugar beet pulp, in particular sugar beet pulp, b) pressing the material provided in step a) with a screw press (1) according to any one of claims 1 to 14, and c) obtaining a pressed material.

16. The method according to claim 15, wherein the pressed material obtained in step c) has an average dry substance content of more than 31,1 % at 1300 rpm of a rotatable screw conveyor (9) with two screws and / or wherein a dry substance improvement of 1 to 2 wt.-% points is achieved.

17. A pressed material prepared according to a method according to claim 15 or 16.

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