Abstract
A screen assembly for a digester, impregnation vessel or other treatment vessel for separation of cooking liquor or treatment liquor from lignocellulosic material, typically in a form of chips, in the production of chemical cellulose pulp, which screen assembly includes a plurality of screen panels (17) of woven wire mesh cloth and attachment device configured to attach the screen panels to a support frame of the digester or vessel.
Claims
1. A screen assembly for a digester, impregnation vessel or other treatment vessel for separation of cooking liquor or treatment liquor from lignocellulosic material in the production of chemical cellulose pulp, wherein the screen assembly comprises: a plurality of screen panels, wherein each of the screen panels include a screen formed of woven, non-welded wire mesh cloth, and the plurality of screen panels are configured to allow passage of the cooking liquor or the treatment liquor and retain the lignocellulosic material, and an attachment device configured to attach the plurality of screen panels to a support frame, wherein the attachment device includes side clamps, an upper end clamp, a lower end clamp, fastening bolts or studs and a fastening plate for each of the screen panels.
2. The screen assembly according to claim 1, wherein the screen in each of the screen panels has openings, wherein a width of each of the openings is in a range of 1 mm to 7 mm and a length of each of the openings is in a range of 1 mm to 50 mm.
3. The screen assembly according to claim 1, wherein the screen of each of the screen panels has openings, each of the openings are a square or rectangular opening, and which each of the openings have a width of 1 mm-7 mm and a length of 1 to 50 mm.
4. The screen assembly according to claim 1, wherein the woven, non-welded wire mesh cloth is formed of screen wire that is round in cross section.
5. The screen assembly according to claim 4, wherein the woven, non-welded wire mesh cloth includes a screen wire having a diameter in a range of 0.5 mm to 7 mm.
6. The screen assembly according to claim 1, wherein the screen for each of the screen panels has rectangular, quadratic, triangular or rhombus apertures.
7. The screen assembly according to claim 1, wherein each of the screen panels has straight, bent or folded edges.
8. The screen assembly according to claim 7, wherein the edges of the screen panels are reinforced with metal or another material.
9. The screen assembly according to claim 1, wherein said woven wire, non-welded mesh cloth includes a weave of at least one of: a plain weave, a double crimp weave, a single intermediate crimp weave, a double intermediate crimp weave, a lock crimp weave, a twill weave, a dutch weave, a dutch twill weave, a reverse dutch weave, and a reverse dutch twill weave.
10. The screen assembly according to claim 1, wherein the screen in each of the screen panels has a surface area that is at least 45% open.
11. The screen assembly according to claim 1, wherein the woven, non-welded wire mesh cloth includes a plurality of layers of woven wire, non-welded mesh cloth.
12. The screen assembly according to claim 1, wherein each of the screen panels is flexible.
13. The screen assembly according to claim 1, wherein the support frame includes a screen support frame structure of the digester, the impregnation vessel or the other treatment vessel.
14. The screen assembly of claim 1, wherein the woven wire, non-welded mesh cloth screen of each of the screen panels has a first side edge, and a second side edge, opposite to the first side edge, wherein the fastening plate is a first fastening plate aligned with and secured to the first side edge, and the screen assembly further comprises a second fastening plate aligned with and secured to the second side edge.
15. The screen assembly of claim 1, wherein each of the screen panels includes a first curved lip at the first side edge, and a second curved lip at the second side edge, and the screen assembly further comprises: a first clamp; a first sealing rod attached to the first fastening plate, wherein the first curved lip is clamped between the first clamp and the first sealing rod, a second clamp; a second sealing rod attached to the second fastening plate, wherein the second curved lip is clamped between the second clamp and the second sealing rod.
16. The screen assembly of claim 14, wherein each of the screen panels includes a first curved lip at the first side edge, and a second curved lip at the second side edge, and the screen assembly further comprises: a first clamp; a first sealing rod attached to the first fastening plate, wherein the first curved lip is clamped between the first clamp and the first sealing rod, a second clamp; a second sealing rod attached to the second fastening plate, wherein the second curved lip is clamped between the second clamp and the second sealing rod.
17. A screen assembly for a digester, an impregnation vessel or another treatment vessel, wherein the screen assembly is configured to separate cooking liquor or treatment liquor from lignocellulosic material, in the production of chemical cellulose pulp, wherein the screen assembly comprises: screen panels each including a woven wire, non-welded mesh cloth screen, and an attachment assembly configured to attach the screen panels to a support frame of the digester, impregnation vessel or the other support vessel, wherein the attachment assembly includes side clamps, an upper end clamp, a lower end clamp, fastening bolts or studs, and a fastening plate for each of the screen panels.
18. The screen assembly of claim 17, wherein the woven wire, non-welded mesh cloth screen of each of the screen panels has a first side edge, and a second side edge, opposite to the first side edge, wherein the fastening plate is a first fastening plate aligned with and secured to the first side edge, and the screen assembly further comprises a second fastening plate aligned with and secured to the second side edge.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the following the invention is described in more detail by reference to the accompanying drawings wherein.
(2) FIG. 1 illustrates a batch digester during liquor filling (left) and during liquor circulation (right) and typical process locations where the new screen assembly may be applied.
(3) FIG. 2 illustrates typical process locations in a continuous digester, where the new screen assembly may be applied.
(4) FIGS. 3 and 4 illustrate an attachment of an embodiment of the mesh screen in a batch digester displacement strainer.
(5) FIG. 5 illustrates an installation of a mesh screen assembly and a mesh screen panel for a batch digester displacement strainer.
(6) FIG. 6 illustrates a fastening of a mesh screen in a batch digester displacement strainer.
(7) FIG. 7 illustrates a woven non-welded wire mesh.
(8) FIG. 8 illustrates a screen support frame in a continuous digester.
(9) FIGS. 9, 10a, 10b, 10c, 11 and 12a, 12b and 12c illustrate other fastenings of a mesh screen in strainers of a batch digester and a continuous digester and other treatment vessels.
(10) FIG. 13 illustrates a mesh screen panel as installed in a continuous digester.
DETAILED DESCRIPTION OF THE DRAWINGS
(11) FIG. 1 illustrates a batch digester 1 for cooking during liquor filling (left) and during liquor circulation (right). A typical displacement batch cooking starts with the digester being filled with cellulosic material, such as chips, through an inlet 2. The filling of the digester is followed by impregnation and hot displacement of the cellulosic material in the digester. Liquors are discharged from the digester through displacement screens 3 to line 4. Liquors can also be discharged through circulation screens during any liquor filling of the digester. After the digester is filled with cellulosic material and liquor, the material in the batch digester is heated to the cooking temperature, typically 130-180° C., and the cooking process is performed. Liquor is pulled through circulation screens 6 and is circulated during the heating and cooking stage. The cooking process is ended with a cold displacement and the pulp is discharged from the digester by pump 8. The screens according to the present invention can be used as circulation screens 3 and displacement screens 6 in batch digesters.
(12) FIG. 2 is a side view of an impregnation vessel 11 and a continuous vertical pressurized digester 10 for processing cellulosic fiberous material, e.g., wood chips, into fiber pulp. A slurry of comminuted cellulosic fibrous material and cooking chemical is introduced through line 12 at the top of the impregnation vessel. The impregnated material is discharged at the bottom of the impregnation vessel and introduced to the top of the digester. The material is cooked in the pressurized digester typically at a temperature of 130-180° C. The slurry of fully-cooked pulp and spent cooking liquor is discharged at the bottom and fed to line 16. The digester 10 comprises a cylindrical shell that typically forms a column of, for example, 100 feet (30 meters) tall. Within the cylindrical shell are several cylindrical screen assemblies 9, 13, 14 and 15. In continuous digesters said screens are typically cooking screens 9, extraction screens 13, 14 and washing screens 15, as shown in FIG. 2. Some systems have a pressurized or non-pressurized impregnation vessel 11 which may have screens for liquor separation.
(13) Known screens may include screen plates assembled to form a cylindrical screen, such as screens 13 and 14. The screen plates are attached to a frame 22 on the inner wall of the digester shell, as shown in FIG. 8. The frame 22, for example, comprises metal bars, angle irons, or corresponding structural elements which are connected directly to the digester shell, although the frame 22 may be distinct and detachable from the digester. Each screen forms generally an annular ring around the inside wall of the cylindrical shell of the digester 10.
(14) FIGS. 3 to 6 illustrate a screen assembly according to the present invention which is used as a batch digester displacement screen or strainer. The location of the displacement screen is described in connection with FIG. 1 above. The assembly comprises a plurality of screen panels 17 of a woven non-welded wire mesh. A fastening system of the woven wire mesh panels comprises side clamps 18, an upper end clamp 21, a lower end clamp 19, fastening bolts 27 and fastening plates 28. FIG. 3 shows also a support frame 22 for the screen assembly. The frame 22 is located on the inner wall of the digester 10. The side clamps 18 and the end clamps 19, 21 are attached to the fastening plates with the bolts 27, as shown in FIG. 4. FIG. 6 shows a detail view of the fastening system for screen panels. The fastening plate 28 is attached by welding to the bars or ribs of the support frame 22. The adjacent screen panels 17 are disposed between the fastening plate 28 and the side clamp 18. The side clamp 18 is attached to the fastening plate with fastening bolts 27 or studs. The fastening bolt 27 is attached to the fastening plate by welding. Alternatively, the fastening plate may have a threaded bore for receiving a fastening bolt. The side edges of the woven wire mesh screen section are bent, as shown in FIG. 6. The bent side edges of two adjacent screen sections are placed between the side clamp 18 and the fastening plate 28, which are attached with bolts. The side edges can also be straight or folded doubly. The straight, bent or folded edges may be reinforced.
(15) FIG. 5 shows a complete screen assembly 3 according to the present invention. The screen is formed of a plurality of woven non-welded wire mesh screen panels 17. A single screen panel 17 is also shown in FIG. 5. The conical screen assembly is typically used as a displacement strainer in the upper part of a batch digester.
(16) FIG. 7 shows a woven non-welded wire mesh, which can preferably be used in the new screen assembly. The screen can have different types of weaves. In FIG. 7 the screen has a plain weave. The screen has rectangular apertures, which have a width 40 of 1 mm-7 mm and a length 41 of 1-50 mm, typically 10 mm-50 mm. The diameter of the screen wires 42 is from 0.5 mm to 7 mm.
(17) FIG. 8 illustrates a screen support frame 22 which is located on the inner wall of the digester shell 10. The frame 22 comprises metal bars, angle irons, or corresponding structural elements.
(18) FIGS. 9 and 10a, 10b and 10c illustrate a fastening system for screen panels. This can be used in batch digesters and in continuous digesters and in other treatment vessels in a digester plant of a pulp mill. FIG. 10a shows a side clamp 23. The side clamp is formed of an elongated plate 23. There are key hole type slots 20 in the side clamp which slots have an enlarged portion 31 and a narrow portion 32. FIG. 10b shows a front view of the fastening system comprising the side clamp 23. FIG. 10c depicts a cross-sectional view of the fastening system taken along lines 10c-10c of FIG. 10b. FIG. 9 shows a detailed cross-sectional view of the fastening system taken along lines 9-9 in FIG. 10b. In FIG. 9 a straight fastening plate 30 is attached by welding to the support frame 22. FIG. 10c illustrates welds (solid black zones 36) which attach the fastening plate 30 to the frame 22. The fastening plate is provided with an opening 39 for a fastening bolt 29, which is also welded to the frame 22. The bent side edges of screen panels 24 are placed against the fastening plate. Sealing rods 35 may be welded to the front face of the fastening plate 30 and along the length of the fastening plate. The sealing rods form a surface against on which seats an edge region of the screen panel. A curved lip 37 at the edge region of the screen panel curves around the sealing rod and hooks the screen panel to the fastening plate. The screen panels are pressed against the fastening plate by means of the side clamp 23. The edge region of the screen panels are sandwiched between the sealing rods and the side clamp.
(19) Each fastening bolt comprises a head portion, a narrow neck portion and a lower portion (shank). The diameter of the neck portion is smaller than that of the head or the lower portion. In order to install the side clamp the head portion of the bolt is inserted through the enlarged portion 31 of the keyhole slot. Then the side clamp is slid downwards on the neck portion of the bolt so that the neck of the bolt enters the narrow portion 32 of the slots, as shown in FIG. 10b. This means that the side clamp and thus also the screen panels are rigidly affixed.
(20) There is a gap 33 between the fastening plate 30 and the side clamp 23, in which gap the side edges of the screen panels are located. This embodiment is advantageous especially when a new screen is installed to an existing frame of a digester. The empty gap provides more space for the installation action.
(21) FIGS. 11 and 12a, 12b and 12c illustrate another fastening system for screen panels. This can be used also in batch digesters and in continuous digesters and in other treatment vessels in a digester plant of a pulp mill. Especially this embodiment is suitable to a circulation screen assembly of a batch digester. FIG. 12a shows a side clamp 23. The side clamp is formed of an elongated plate 23. As described in connection of FIGS. 9 and 10a, 10b and 10c, there are key hole type slots 20 in the side clamp. FIG. 12b shows a front view of the fastening system comprising the side clamp 23. FIG. 10c depicts a cross-sectional view of the fastening system taken along lines 12c-12c of FIG. 12b. FIG. 11 shows a detailed cross-sectional view of the fastening system taken along lines 11-11 in FIG. 12b. In FIG. 11 fastening plate 26 is bent against the support frame 22 and attached by welding to the frame 22. FIG. 12c illustrates welds (black zones 36) which attach the fastening plate 26 to the frame 22. The fastening plate is provided with an opening 34 for a fastening bolt 25, which is also welded to the frame 22. The bent side edges of screen panels 24 are placed against the fastening plate and the panels are pressed against the fastening plate by means of the side clamp 23. Each fastening bolt 25 comprises a head portion, a narrow neck portion and a lower portion (shank). The diameter of the neck portion is smaller than that of the head or the lower portion. In order to install the side clamp the head portion of the bolt is inserted through the enlarged portion 31 of the keyhole slot 20. Then the side clamp is slid downwards on the neck portion of the bolt so that the neck of the bolt enters the narrow portion 32 of the slots, as shown in FIG. 12b. This means that the side clamp and thus also the screen panels are rigidly affixed.
(22) FIG. 13 shows a part of the inner wall of a continuous digester and a part of a support frame 22 attached to the inner wall. A wire mesh screen panel 24 is connected to the frame, as described in connection with FIGS. 9-12.
(23) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.
