FI123861B - Clamp screw drainage device, its screw and screw operation - Google Patents

Abstract

A screw for a compression dewatering device comprising an elongated shaft having axially spaced apart first and second ends, a conveying section at the first end of the shaft, having a single helical screw flight rigidly projecting from the shaft, a flightless transition section axially adjacent the conveying section, and a dewatering section axially adjacent the transition section, having a double helical screw flight rigidly projecting from the shaft. Another embodiment is a compression screw having a perforated tubular dewatering wall intermediate the ends, followed by an imperforate spool wall at the discharge end. The screw includes a central shaft, a conveying sectio n extending axially from the inlet end of the shaft, having a single helical screw flight rigidly projecting from the shaft, a flightless plug section extendin g axially from the discharge end of the shaft, within the spool wall, and a dewatering section adjacent the plug section, having a double helical screw flight rigidly projecting from the shaft. A flightless transition section is situated betwe en the conveying section and the dewatering section. A gravity feed device is operatively associated with the inlet end for depositing bulk solids materia l through the feed opening onto the conveying screw, and a drive system isoper atively connected to the inlet end of the screw for rotating the screw in the housing.

Description

BACKGROUND OF THE INVENTION BACKGROUND OF THE INVENTION

The present invention relates to dewatering of wood by-products in the manufacture of pulp slurry which is fed to a mechanical refiner or chemical digester to process the fibers into pulp.

In the most important overall processes, i.e. the production of fiberboard (MDF), chipboard (PB), or heat-pulp pulp (TMP), the dewatering screw is intended to remove liquids (extracts) from the raw material and form a pressure plug before the material is fed into the digester or pulverizer. The raw material is typically sawdust, wood chips or wood chips, which are generally considered as bulk solids. Except for washing or pre-steaming, no pre-treatment is required before dewatering. In MDF or PB processes, refining is usually followed by an air dryer, and the amount of heat or energy required to reach the target dryness of the powdered material (dryer load) is inversely measured by measuring the efficiency of the pre-refining dewatering device. Even when there is no active drying following the dewatering device, the energy efficiency of the main process can be correlated with the dewatering efficiency. In the TMP-20 process, the extracts removed from the raw material contribute to the darkening of the final product. Removal of extractives can therefore reduce the amount of bleaching chemicals needed to achieve the desired brightness.

For years, efforts have been made to increase the efficiency of the dewatering of the feed material and thus reduce the total energy consumption or chemical costs, especially the cost of the final drying or bleaching steps. Typical of these efforts has been to reduce variations in the initial moisture content (which

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fluctuations due, for example, to storage conditions and seasonal variations) and

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increasing the compression ratio of the drainage portion of the screwdriver. Typical equipment

σ> 30 is described in US Patent 5,320,034 and International Publication WO

o § 92/13710, which are incorporated herein by reference. Here, the compression ratio o to the cross-sectional area of the discharge.

^ (CR) is defined as the ratio of the cross-sectional area of the inlet of the dewatering device 2

Dewatering of bulk solids has been particularly difficult. Dewatering of bulk suspensions of the order of 4-5% consistency is relatively easy, while dewatering bulk materials having a consistency of more than 25% has caused difficulties. The problems result from the difficulty in controlling the relative friction between the screw shaft, screw 5 threads, and the clamping wall wall. In particular, it is desirable that the friction in the axial direction of the wall be lower than in the tangential direction of the wall so that the material under the action of the screw threads moves as well as compressed in the axial direction and does not rotate between the individual threads.

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It is also known that when very high compression ratios are required, single-threaded screws naturally have an uneven load and reach a point where the yield decreases, so that a certain increase in the applied energy (by increasing the torque of the screw) contributes little to dewatering. Thus, single-threaded screws are suitable for al-15 dense consistency feed materials, or, for bulk solids, only for modest compression levels. Double screws are known to be suitable for harder press environments, especially for bulk solids. However, double-threaded screws have necessitated forced supply as described in U.S. Patent No. 5,320,034, which has resulted in the need for a second drive and increased total energy consumption for a given drainage level.

Summary of the Invention

The present invention is directed to a new screw and a new dewatering device utilizing it which achieve a higher level of dewatering and reliability with the same energy consumption of the screw drive as with conventional devices.

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In one preferred embodiment, the invention is directed to dewatering

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clamp screw comprising an elongated shaft having an axial direction

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the first end and the second end spaced apart, the transport portion 30 at the first end of the shaft where one threaded screw thread protrudes outwardly from the shaft, a non-threaded transition portion in the axial direction near the transport portion, and a drainage portion, axially adjacent to the transport portion and having a double-threaded screw thread which protrudes outwardly from the shaft.

In another preferred embodiment, the invention relates to a screw for mounting on a drainage press screw apparatus having a sheath, a feed head, an outlet end, and an actuator for rotating the screw inside the sheath. The screw includes a central shaft having an inlet end and an outlet end mounted on the inlet end and outlet end of the jacket, a transport portion at the shaft inlet end having a single threaded screw that protrudes from the shaft and a water outlet 10 near the shaft out of the shaft. There is a threadless transition between the transport section and the drainage section.

In another embodiment, the invention relates to a press screw dewatering device comprising an elongated jacket having a feed head and an outlet end on the jacket shaft. The jacket includes an axially perforated tubular drainage wall between the ends, followed by an unpunched choke portion at the outlet end. The screw passes coaxially with the shaft axis and includes a central shaft having an inlet end and an outlet end rotatable from the inlet end and outlet end of the diaper, a transport portion extending axially from the inlet end of the shaft and having inside the throttle wall, and in the vicinity of the plug portion, a dewatering portion having a double screw thread which rises fixedly from the shaft. There is a threadless transition between the transport portion and the drainage portion. The feed end is operatively connected to a gravity feed device to push bulk solids through the inlet to the transport screw, and the screw feed end is operatively connected to a transmission system for rotating the screw within the shell.

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As is well known in the case of dewatering apparatuses, the effective current range between the drainage portion of the shell wall and the screw shaft decreases towards the outlet end. In a further embodiment of the preferred embodiment, the wall of the drainage section has irregularities or elevations intended to provide greater resistance to the tangential flow along the wall than to the axial flow along the wall.

The significantly improved dewatering efficiency according to the invention is probably the result of the synergy achieved by combining the best features of a single-screw screw with the best features of a double-screw screw while providing an efficient transition between them. A single-screw screw would produce an unbalanced radial pressure wave (when looking at the drainage section in the axial section). An unbalanced wave forces the screw to turn 10 instead of staying centrally inside the shell. As the compression ratio increases with a single-threaded screw, power dissipates and rotates the screw at the expense of material handling. The double thread has a balanced pressure wave and therefore does not rotate due to deflection. The ability to handle a higher compression ratio results in an immediate process advantage over single-threaded screws. However, various unexplained problems may arise in the feed, especially fluctuations in production speed, loss of production, fluctuations in discharge consistency, and loss of plug holding capacity (pressure sealing). The root cause of this phenomenon is not obvious, but through significant insights, the present inventors have realized that the problem was caused by the rotation of the material at the feed portion of the device.

The hybrid single / double threaded screw structure of the present invention by itself solves the problem of said forward supply problem and high compression ratio. At the feed portion, a simple thread receives the material to be fed by weight and conveys it axially forward. the press

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With the twisting portion, the twin thread achieves a high compression ratio without directing the energy to deflection or unwanted rotation.

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The threaded transition portion distributes the material evenly over the double-threaded portion and

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additionally produces a favorable pressure wave.

σ> 30 § Brief Description of the Drawings o ^ The preferred embodiment will be described below with reference to the accompanying drawings, of which:

Fig. 1 is a longitudinal sectional view of a press screw drainage device according to an embodiment of the invention;

Figures 2A and B schematically show the relationship of a screw according to the invention to a compression sheath for a tapered sheath and a straight sheath and a tapered screw shaft 5 respectively;

Figures 3A, B and C are schematic views of a feed silo and a press diaper and associated cross-sectional views showing optional anti-rotation ridges protruding from the bottom of the silo and from the wall of the press mantle;

Fig. 4 is a perspective view of a half portion of a two-piece compression jacket shell showing a fluid venting hole and an irregular inner wall surface for increasing tangential friction; and Fig. 5 is a cross-sectional view of the compression jacket of Fig. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 is a longitudinal partial sectional view of a dewatering device 10 and associated components according to an embodiment of the invention. The dewatering device 10 comprises one, two, three or more physical jacket portions which are fixedly connected to each other at their ends to form a substantially tubular jacket. For example, the feed portion 12 forms a silo, followed by a press portion 14. The feed portion is sometimes perforated to discharge bulk water, but does not actively remove water by squeezing. Functionally, the feed section of the silo receives feed material which is conveyed to the drainage section of the compression section. The functional zones are primarily determined by the ratio of the inner screw 18 of the central screw 16 and the co 25 to the surrounding shell. The screw has inlet and outlet ends mounted to rotate inside the jacket, ö o The movable or feed portion at the inlet end of the screw receives gravity | 20 a silo aperture 30 formed in the feed portion 12 of the feed material casing. Traditionally, a transmission system, such as a motor 22, is mounted on the end surface of the feed portion 12 such that it is coupled to the screw feed end.

o The single screw thread carries the material. The thread has a steady pitch (what is the distance from the brush to the brush) and preferably extends axially for at least two pitches.

The press portion 14 is fixed to the feed portion and its inner wall 18 is substantially conical in shape and tapering in the direction of material transport. Thus, the cross sectional area of the effective flow of the compression portion is reduced in the transport direction, whereby the material is compressed so that water and other extractable substances are squeezed out of the material and pass through the shell wall through desired holes or other perforations.

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Figures 2A and B are more detailed views of preferred embodiments of screw 16, with alternative embodiments of compression portions A and B. The screw has a central axis 30A, 30B defining an axial line of the screw. The shaft feed end is adapted to be connected to the transmission system 22 and the shaft discharge end 15 is adapted to enter inside the plug portion 24 of the jacket. It may be advantageous for the screw to be substantially coaxially mounted within the housing to be rotated there by the drive transmission system. The screw structure having a single thread 32A, 32B extends solidly from the shaft in the axial direction of the feed portion of the jacket, and preferably by about one thread pitch to the press portion of the jacket, where al-20 bumping occurs and some dewatering between the thread and the wall. This effectively seals the material caused either by the tapering of the wall of the tapered sheath (option A) or the outwardly expanding cone of the shaft of the screw inside the cylindrical wall of the cylindrical sheath (option B). Preferably, the entry cone angle of the compression sheath of variant A is greater than 25 ° than the total cone angle along the perforated walls of the compression sheath.

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The conveyor screw thread terminates abruptly, preferably not at the edge, which is substantially

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radially relative to the axis centreline. At an axial distance that corresponds

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at least about one-eighth of the thread pitch, the shaft has no screw thread.

σ> 30 This threadless portion 34A, 34B can be regarded as a transition between the actual carrying portion of the screw o g and the actual drainage portion of the screw. Typically, the axial dimension of the transition portion 34A, 34B should be at least about one inch (2.5 cm).

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The dewatering portion 36A, 36B has a double helix on the shaft where each helix rises in a fixed spiral with the same or different pitch as a single screw helix, but the helix helices are 180 degrees out of sync with each other. Preferably, the threads of this portion extend across the axis for at least two full inclines of at least 720 degrees. At the end of the transition portion, each double thread terminates sharply at the leading edge e2, which is substantially radial to the centerline of the axis. Preferably, the twin threads are at least about 45 degrees out of sync with the simple, threaded thread.

As can be seen from the screw portion 16 of the compression portion shown in Fig. 1, which has a longitudinal section along the centerline of the shaft, one thread of the double thread is symmetrical with respect to the corresponding and opposite section of the other thread.

Between the clamping portion and the outlet end, the screw is threadless 38A, 38B and is surrounded by a choke 24, which may be integrated into or attached to the clamping portion of the jacket as a separate choke portion. The material that has passed through the dewatering forms a pressure plug in the thrust portion that extends along the shaft until it exits the outlet chamber or sheath 26 (see Figure 1), typically at atmospheric pressure, whereby the ma-20 material expands rapidly before further processing.

As shown in Figure 3, one or more anti-rotation structures, such as longitudinal ridges, may be provided on the shell wall. Section A-A shows anti-rotation ridges on the lower concave wall of the feed portion of the 40 diaper £ 25. Preferably, the anti-rotation ridges 42 are

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provided on the inlet of the compression sheath as shown in B-B and on the wall of the sheath which surrounds the transition portion of the screw. As is well known in the art, ridges, pins, pits, and other technical structures can be used to prevent rotation. The anti-rotation ridges, the sharp edges of the screw threads at the beginning and end of the transition portion 30, and the material entering the drainage section at two radially opposite points, ensure that the material entering the drainage section is uniform throughout. This improves the propagation of the material by preventing excessive accumulation or agglomeration of the material by the feed portion and the transition portion of the shell. In addition, this ensures the total balance of the material mass and the compression forces acting on the shaft and the threads during the dewatering of the material. In this way, compression ratios of 4: 1 or more can be achieved.

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Figure 4 schematically illustrates a tapered dewatering compression sheath halve 44 shown in Figure 2A. Two such sheath halves are known to be secured together in opposing holes 46 by bolts to be tightened. Preferably, the compression sheath includes a conical liner 48 which acts as an inner wall having multiple orifices 50 for collecting extractable material to be removed to a collection point in a manner generally known in the art. In the embodiment shown, the lining structure comprises ridges 52 and grooves 54 which serve to prevent rotation and facilitate dewatering. Preferably, the sharp inlet angle of the inlet relative to the rest of the compression sheath is clearly shown at 56. Figure 5 shows a cross-section of a half of the sheath from which the fluid drainage holes are omitted for clarity.

The invention has been described in connection with a dewatering of a bulk solid according to a preferred embodiment. However, this new screw, which combines a single thread 20 for supply and initial transport and a double thread for dewatering, is also useful when used in a variety of diapers for dewatering a variety of materials, including suspensions of low consistency. Such a screw is particularly suitable for retrofitting to existing dewatering devices, the size of the original screw and the curtain surface of the threaded ridges can be readily realized by the invention.

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^ replacement screw. Even if the transmission system is not altered in any way, greater compression and better dewatering are achieved at the same time the screw is operated.

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energy consumption.

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Claims (19)

9 A screw (16) for mounting on a press screw dewatering device (10), the screw (16) having an elongated shaft (30A, 30B) having spaced apart feed and drain ends; a transport portion (32A, 32B) at the feed end of the shaft (30A, 30B) having a single screw thread; a dewatering section (36A, 36B), wherein the dewatering section (36A, 36B) has a double screw thread and a 10 threaded transition section (34A, 34B) between the transport section (32A, 32B) and the dewatering section (36A, 36B), characterized by , that the transition portion (34A, 34B) has an axial length of at least 25 mm and the thread of the transport portion (32A, 32B) has a phase difference of at least 45 degrees with respect to both threads of the dewatering portion (36A, 36B). 15 Screw (16) according to claim 1, characterized in that the thread of the transport portion (32A, 32B) extends axially along the axis (30A, 30B) by at least two turns. Screw (16) according to claim 1 or 2, characterized in that the thread of the transport portion (32A, 32B) has a uniform pitch and the thread extends axially along the axis (30A, 30B) by at least two pitches. Screw (16) according to one of the preceding claims, characterized in that the double screw thread of the dewatering section (36A, 36B) comprises a first thread extending at least two turns along the axial line of the shaft (30A, 30B). along the axial line of the axis (30A, 30B), and having a second tr rising substantially equal to said first ascent and being ak-30. symmetrical with respect to said first thread (30A, 30B), o Screw (16) according to one of the preceding claims, characterized in that the thread of the transport portion (32A, 32B) has a pitch and the transition portion (34A, 34B) 10 has a length which is at least one-eighth of the pitch of the transport portion (32A, 32B). Screw (16) according to one of the preceding claims, characterized in that the thread of the transport portion (32A, 32B) has a trailing edge (e1) substantially radial with respect to the axial line of the shaft (30A, 30B) and a drainage portion (36A, 36B). ), the first and second threads have leading edges (e2) that are substantially radial with respect to the center line of the shaft (30A, 30B). Screw (16) according to one of the preceding claims, characterized in that the screw (16) has a threaded plug portion (38A, 38B) adjacent the drainage portion (36A, 36B) and extending to the outlet end of the shaft (30A, 30B). A press screw drainage device (10) for bulk material comprising: an elongated diaper having an inlet end and an outlet end having a perforated tubular drainage wall in the direction of the shaft (30A, 30B), a screw (16) having an axial line extending coaxially. with the axial line of the diaper and having a central axis (30A, 30B) having an inlet and outlet end rotatably supported on respective inlet and outlet ends of the diaper, a transport portion (32A, 32B) beginning at the inlet end and having a screw (16) the central shaft (30A, 30B) has a single screw thread, the drainage section (36A, 36B), wherein the drainage section (36A, 36B) has a double screw thread on the central axis (30A, 30B) of the screw (16) which With the earth wall (18) to remove water from the material, the CNJ threadless transition portion (34A, 34B) between the transport portion (32A, 32B) and the drainage portion (36A, 36B); O-weight feeder operatively connected to the sheath feed end CC for transferring bulk solids through the inlet (28) to the screw transport portion S 30 (32A, 32B) and a transmission system (22) operatively connected to the central shaft (30A, 30B) of the screw 16) for rotation within the housing; characterized in that the transition portion (34A, 34B) has an axial length of at least 25 mm and the thread of the transport portion (32A, 32B) has a phase difference of at least 45 degrees with respect to each thread of the dewatering portion (36A, 36B). A press screw drainage device (10) according to claim 8, characterized in that the conveying portion (32A, 32B) of the screw (16) extends into the perforated wall of the jacket, preferably by about one thread pitch. A press screw drainage device (10) according to claim 8 or 9, characterized in that the jacket tapers inwardly around at least a portion of the screw transport portion (32A, 32B). A press screw drainage device (10) according to claim 8, 9 or 10, characterized in that the sheath of the transport section (32A, 32B) has protruding members 15 (40, 42) for providing greater resistance to the tangential flow of the material than to the axial flow. A press screw drainage device (10) according to claim 11, characterized in that said means (40) 20 protruding from the diaper of the transport portion (32A, 32B) are located on the inwardly tapering portion of the diaper. A press screw drainage device (10) according to claim 9, wherein the members (42) projecting from the sheath in the direction of the screw are located on the inwardly tapering portion of the sheath. CO - 25 o CM Press screw drainage device (10) according to one of Claims 8 to 13, characterized in that, beside the drainage section (36A, 36B), the outlet end O has a threaded plug portion (38A, 38B), the portion 24 of which is not perforated. 't σ> 30 δ CD O O C \ l 12 Press screw drainage device (10) according to one of claims 8 to 14, characterized in that the double screw thread of the drainage section (36A, 36B) comprises a first thread extending at least two turns along the axial line of the shaft (30A, 30B), and a second thread extending at least two turns along the axial line of the axis (30A, 30B) and having a second pitch substantially equal to said first pitch and symmetrical with said first thread (30A, 30B). . Press screw drainage device (10) according to one of Claims 8 to 15, characterized in that the thread of the transport section (32A, 32B) has an end edge (e1) substantially radial with respect to the center line of the shaft (30A, 30B) and a dewatering section (36A, 36B) the first and second threads have leading edges (e2) that are substantially radial with respect to the center line of the shaft (30A, 30B). 15 A press screw drainage device (10) according to any one of claims 8 to 16, characterized in that the perforated wall of the jacket has means (42) protruding towards the screw (16) to provide greater friction for the tangential flow of the material than for the axial flow of the material. 20 A press screw drainage device according to any one of claims 8 to 17, characterized in that the conveying portion (32A, 32B) has means (40) projecting towards the screw (16) to provide greater friction for the tangential flow of the material than for the axial flow of the material. CO - 25 o CVJ Use of a clamping screw (16), wherein the screw (16) has a single thread having a feed and initial transport or transport section (32A, 32B) and a double thread or dewatering section (36A, 36B) with dewatering to remove material from the CC, such as wood by-products, to feed material to a mechanical mill or chemical digester, and between them a threadless transition (34A, 34B), characterized in that the transition portion has an axial length of at least 25 mm. and the thread of the transport portion (32A, 32B) has a phase difference of at least 45 degrees with respect to each thread of the dewatering portion (36A, 36B). 13