FI20255213A1 - A screen support assembly and a screen plate - Google Patents

Abstract

A screen assembly for a pulp treatment vessel, the screen assembly includes a screen plate (310a, 310b, 510, 710, 710a, 710b) disposed substantially parallel to an inner wall of the pulp treatment vessel and having a plurality of openings (312, 712a, 712b) configured to pass liquor from a pulping process while preventing passage of pulp; and a support structure including an inclined support plate (530, 635, 665) disposed between the inner wall of the pulp treatment vessel and the screen plate (310a, 310b, 510, 710, 710a, 710b), the inclined support plate (530, 635, 665) being inclined at an acute angle with respect to the screen plate (310a, 310b, 510, 710, 710a, 710b) from an upper portion (512) of the screen plate (310a, 310b, 510, 710, 710a, 710b) to a lower portion (514) of the screen plate (310a, 310b, 510, 710, 710a, 710b); and multiple of support elements (455, 535) disposed on the inclined support plate (530, 635, 665), the multiple support elements (455, 535) extending between the inner wall of the pulp treatment vessel and the screen plate (310a, 310b, 510, 710, 710a, 710b).

Description

A SCREEN SUPPORT ASSEMBLY AND A SCREEN PLATE

BACKGROUND

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to being prior art by inclusion in this section.

Wood chips and other cellulosic fibrous material are treated in impregnation vessels and digesters to chemically separate fibers in the chips and material by, for example, removing lignin. A digester is a vessel in which comminuted cellulosic material, such as wood chips, are treated with heat, liquid, and chemicals to convert the chips to pulp. A continuous digester vessel is typically an upright cylinder with an upper inlet to receive chips in a continuous flow. The chips flow slowly through the digester vessel, 30 to 100 meters tall, in a generally downward direction.

As the chips move through the continuous digester, the lignin’s binding fibers — together in the chips release the fibers and the chips are converted to pulp.

The pulp is removed through a bottom outlet of the digester. Chips are continually added to a continuous digester while the chips already in the digester vessel are processed and pulp is discharged from the bottom of the vessel. In a batch digester, chips are first loaded in a vessel, the loaded chips are processed as a batch and thereafter the processed chips are discharged to empty the vessel. In a batch digester the chips tend to remain in substantially the same location in the vessel.

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S Chemicals, e.g., cooking liguor, in a digester process the chips, cause 8 lignin's to unbind fibers and convert the chips to pulp. The chemicals are s 25 included in cooking liquor that is continuously pumped into and out of batch

E and continuous digesters. Screens, such as screen plates, are used in

O conventional digesters to produce chemical cellulose pulp, e.g., kraft pulp, a for both continuous and batch digesters. Screens are filters that allow liguor

O to be extracted from a digester but prevent the extraction of fibrous material.

There are several types of screens plates used in digester applications. The screen plate types commonly used are perforated screen plates with circular holes, stave screen plates, profile bar screen plates, and slotted screen plates.

Screen plates are generally arranged around an inner circumference of a digester. An inner surface of the screen is exposed to the chip slurry in the digester and an outer surface of the screen forms a wall to a liquor extraction chamber. The screen may have multiple rows of narrow slots through which liquor (but not fiber) is extracted from the chip slurry and flows into the extraction chamber.

There are several types of screens used in said applications. The screen types commonly used are perforated screen plates with circular holes, stave screens, profile bar screens and slotted screen plates. Typical problems with the existing screens are: (i) limited open area which restricts the flows through the screen openings; (ii) tendency to accumulate various types of scale deposits on the screen. The scaling, such as calcium carbonate precipitation, is due to chemical reactions of liquor and raw material. This increases the limitation of the screen open area; (iii) accumulation of scaling deposit behind the screen in channel between vessel wall and the screen plate. This reduces flow capacity of the screen. There is need to clean screens and channel behind the screen periodically. — With longer maintenance intervals for vessels there is a need for screen assembly that has reduced scaling formation and stay in operation for longer period than current design and is easier to open for cleaning during

LO maintenance.

S

3 SUMMARY

X 25 — This invention relates to a treatment vessel for producing pulp, and more

E particularly, but not exclusively, to a screen assembly for a treatment vessel © for producing pulp. > 10 According to various aspects of the present disclosure, a screen assembly

N for a pulp treatment vessel is provided. In some aspects, the screen assembly may include a screen plate disposed substantially parallel to an inner wall of the pulp treatment vessel. The screen plate may have a plurality of openings configured to pass liquor from a pulping process while preventing passage of pulp. The screen assembly may further include a support structure. The support structure may include an inclined support plate disposed between the inner wall of the pulp treatment vessel and the screen plate. The inclined support plate may be inclined at an acute angle with respect to the screen plate from an upper portion of the screen plate to a lower portion of the screen plate. The support structure may further include multiple of support elements disposed on the inclined support plate. The multiple support elements may extend between a surface of the inclined support plate and the screen plate.

According to various aspects of the present disclosure, a support structure for a screen plate for a pulp treatment vessel is provided. In some aspects, the support structure may include an inclined support plate disposed between an inner wall of the pulp treatment vessel and the screen plate. The inclined support plate is inclined at an acute angle with respect to the screen plate from an upper portion of the screen plate to a lower portion of the screen plate. The support structure may further include multiple support elements disposed on the inclined support plate. The multiple support elements may extend between a surface of the inclined support plate and the screen plate.

According to various aspects of the present disclosure, a screen plate for a pulp treatment vessel is provided. In some aspects, the screen plate may

S include a plurality of openings configured to pass liguor from a pulping 0 25 process while preventing passage of pulp. The plurality of openings of the = screen plate may be configured to form more open area at an upper portion = of the screen plate than at a lower portion of the screen plate. A hinge may a be disposed on the screen plate. The hinge may be configured to be 2 attached to a frame of the treatment vessel configured to mount the screen 5 30 plate. The hinge is configured to enable the screen plate to be movable. ” BRIEF DESCRIPTION OF THE DRAWINGS

Aspects and features of the various embodiments will be more apparent by describing examples with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an example of a digester according to various aspects of the present disclosure;

FIG. 2 is a diagram illustrating an example of a frame 230 forming a structure for supporting screens in a screen zone of the digester according to various aspects of the present disclosure;

FIG. 3 is a perspective view of an example of screen plates mounted in a frame of a digester according to various aspects of the present disclosure;

FIG. 4 is a side view of an example of a typical screen plate mounted in a frame of a digester;

FIG. 5A is a side view of an example of a screen plate assembly according to various aspects of the present disclosure;

FIG. 5B is a side view of an example of a support plate assembly according — to various aspects of the present disclosure;

FIG. 5C is a perspective view illustrating an example of a support plate assembly installed in a frame of a digester according to various aspects of the present disclosure;

FIG. 6A is a perspective view of an example of a support plate assembly showing a curvature of the support plate assembly according to various

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N aspects of the present disclosure;

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8 FIG. 6B is a front view of an example of the support plate assembly

J illustrating the plurality of support elements on the first side of the support

E plate assembly according to various aspects of the present disclosure; 2 25 FIG. 6C is a front view of an example of the support plate assembly (O illustrating horizontal support elements according to various aspects of the

S present disclosure;

FIG. 6D is a front view of an example of the support plate assembly illustrating vertical support elements according to various aspects of the present disclosure;

FIG. 7 is a perspective view of an example of screen plates installed in a 5 frame of a digester according to various aspects of the present disclosure; and

FIG. 8 is a diagram illustrating an example of a slot pattern for a screen plate according to various aspects of the present disclosure.

DETAILED DESCRIPTION

While certain embodiments are described, these embodiments are presented by way of example only and are not intended to limit the scope of protection. The apparatuses, methods, and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes in the form of the example methods and systems described herein may be made without departing from the scope of protection.

In a digester for the pulping industry, screen plates may be utilized in a cooking process for separating cooking liquor and comminuted lignocellulosic particles. The screen plates may be applied in continuous digesters, batch digesters, impregnation vessels, and other pulp treatment vessels where the screen plates are used for separation of liquor and 10 comminuted cellulosic materials.

O a Chemicals, e.g., cooking liquor, in a digester process the chips by causing = lignin’s to unbind fibers and convert the chips to pulp. Screen plates are = 25 filters that allow liquor to be extracted from a digester but prevent the

E extraction of fibrous material. Screen plates are generally arranged around 2 an inner circumference of a digester. An inner surface of the screen plate is i exposed to the chip slurry in the digester and an outer surface of the screen

N forms a wall to a liquor extraction chamber. A screen plate may have multiple rows of narrow slots through which liquor, but not fiber, is extracted from the chip slurry. The liquor flows into the extraction chamber.

Screen plates tend to accumulate various types of scale deposits, such as calcium carbonate precipitation, on the screen plate due to chemical reactions of liquor and raw material. These scale deposits reduce flow capacity of the screen plate requiring periodic cleaning of the screen plates and the channels behind the screen plates. To achieve longer intervals between maintenance for digesters, there is a need for screen plates that have reduced scaling formation and stay in operation for longer period than current design and are easier to open for cleaning during maintenance.

Aspects of the present disclosure provide a novel screen assembly for digesters and other treatment vessels that includes a supporting structure which also provides guidance for liquor flow and a newly designed screen plate. The novel screen assemblies disclosed herein are applicable to continuous digesters, batch digesters, impregnation vessels, and other treatment vessels where the screen plates are used for separation of liquor and comminuted cellulosic materials.

FIG. 1 is a diagram illustrating an example of a digester 100 according to various aspects of the present disclosure. Referring to FIG. 1, the digester 100 includes an outer wall 110 enclosing screen zones 120. The digester 100 includes several screen zones 120 at various vertical locations along the digester 100. The screen zones 120 are arranged around an inner 10 circumference of the digester 100. Material to be digested, e.g., chips, are

N deposited within the inner circumference of the digester 100 and cooking 3 25 liquor added to promote the digestion process. The digester 100 may s typically be 30 to 100 meters tall and may have three to five or more screen

E zones 120. Screen plates provided in the screen zones 120 around the inner cn circumference allow the liguor to be extracted from the digester 100 but 0 prevent the extraction of fibrous material, e.g., pulp, which is subsequently

O 30 extracted from the bottom of the digester 100.

FIG. 2 is a diagram illustrating an example of a frame 230 forming a structure for supporting screens in a screen zone of the digester according to various aspects of the present disclosure. The digester 100 may include a frame 230 mounted to an inner surface 210 of the outer wall 110 forming a generally annular ring around the inner circumference of digester 100. The frame 230 may be formed, for example, with metal bars, angle irons, or corresponding structural elements. In some cases, the frame 230 may be connected directly to the inner surface 210 of the outer wall 110. In other cases, the frame 230 may be distinct and detachable from the digester. The frame 230 is configured to form liquor collection chambers 235 between the inner surface 210 of the outer wall 110 and screen plates (not shown) mounted to the frame 230. Liquor collected in the collection chambers 235 drains into collection headers 240 below the collection chambers 235 through extraction nozzles (not shown) to be collected and processed. The extracted liquor may be circulated back to the digester with added chemicals and heat or sent to other processes.

FIG. 3 is a perspective view of an example of screen plates 310a, 310b mounted in a frame of a digester according to various aspects of the present disclosure. As used herein, an individual screen plate of the screen plates 310a, 310b may be referred to as a screen plate 310. As illustrated in FIG. 3, the screen plates 310a, 310b are attached to the frame 230 forming collection chambers 235 between the inner surface 210 of the outer wall 110, the screen plates 310a, 310b, and the frame 230. The screen plates 310 10 provide a series of openings 312 to enable liquor to flow through the

N 25 openings in the screen plates 350 to be separated from the pulp and 3 collected in the collection chambers 235 and collection headers 240 for

J reuse. = > While two screen plates 310a, 310b are illustrated in FIG. 3, it should be 2 appreciated that screen plates are disposed to form a generally annular ring 5 30 around the inner circumference of digester 100. ” FIG. 4 is a side view of an example of a typical screen plate 310 mounted in a frame of a digester. As illustrated in FIG. 4, screen plates 310 are mounted to the frame 230 and form collection chambers 235 between the inner surface 210 of the outer wall 110 of the digester 100 and the screen plates 310. Support beams 455 attached to the screen plates 310 support the screen plates 310 and maintain the space between the outer wall 110 and the screen plates 310 for the collection chambers 235. Liquor flows through the openings 312 in the screen plates 310 (see FIG. 3) to be separated from the pulp and collected in the collection chambers 235 and collection headers 240 for reuse.

Existing screen plate/support beam configurations are prone to various problems. For example, problems with the existing screen plate/support beam configurations include a tendency to accumulate various types of scale deposits on the screen plate which decreases the screen plate open area, and accumulation of scaling deposits behind the screen plate in the collection chamber between digester wall and the screen plate. In addition, the support beams are long making the screen plates hard to handle during installation and removal, for example, to perform maintenance on the digester.

Aspects of the present disclosure provide a novel screen plate assembly including a screen plate and an inclined support plate for a digester. The support plate may incorporate support beams configured to support the screen plate. The screen plate may be configured with different slot patterns (e.g., openings) in different areas of the screen plate. The inclined support plate and slot patterns of the screen plate may promote more uniform liquor s flow through the surface of the screen plate which may reduce scaling 3 25 deposits on the screen plate and in the collection chamber.

X FIG. 5A is a side view of an example of a screen plate assembly 500

E according to various aspects of the present disclosure. The screen plate cn assembly 500 may include a screen plate 510 and a support plate assembly 0 525. The support plate assembly 525 may include an inclined support plate

O 30 530 and a plurality of support elements 535. The plurality of support elements 535 may be substantially cylindrical beams. The inclined support plate 530 may be inclined from an upper portion 512 to a lower portion 514 of the screen plate 510 at an acute angle a with respect to the screen plate 510. The angle a depends at least in part on the height of the screen plate 510 and the depth of the collection chamber behind the screen plate 510. A distance “d” between the inclined support plate 530 and the upper portion 512 of the screen plate 510 may be less than a distance “D” between the inclined support plate 530 and the lower portion 514 of the screen plate 510.

The inclined support plate 530 may equalize the liquor flow velocity by promoting increased liquor flow through the screen plate 510 at the upper portion 512 of the screen plate 510 where the fluid pressure is lower than at the lower portion 514 of the screen plate 510. The equalized liquor flow velocity may reduce the accumulation of scale deposits on the screen plate and in the collection chamber.

In some implementations, the plurality of support beams 535 of the support plate assembly may extend only between a first surface of the support plate and the inner surface of the screen plate. In these implementations, the attachment between the support plate assembly and the frame enables the support beams 535 to support the screen plate.

FIG. 5B is a side view of an example of a support plate assembly 525 according to various aspects of the present disclosure. As illustrated in FIG. 6, the inclined support plate 530 may incorporate a plurality of support beams 535 configured to support the screen plate 510. The plurality of support beams 535 may be attached to the inclined support plate 530 at an acute angle B with respect to the inclined support plate 530 such that the s plurality of support beams 535 is substantially perpendicular to the inner a 25 — surface 210 of the outer wall 110 of the digester and the inner surface 516 = of the screen plate 510. The angle B may depends at least in part on the = height of the screen plate 510 and the depth of the collection chamber a behind the screen plate 510. The plurality of support elements 535 may be 5 attached to the inclined support plate 530 by welding or by other means. 5 30 The plurality of support beams 535 may extend from the inner surface 210 of the outer wall 110 of the digester to an inner surface 516 of the screen plate 510. The plurality support beams 535 provide support for the screen plate 510 against pressure exerted by the material (e.g., chips, pulp) being digested within the digester. Each of the plurality of support beams 535 may have a same length “L.” The length “L” of the plurality of support beams 535 may depend on the dimensions of the digester. In some implementations, the screen plate may be inclined with respect to the support plate. In such implementations, the support beams may have different lengths. The plurality of support beams 535 may be configured such that they do not interfere with the slot patterns (e.g., openings) in the screen plate 510.

FIG. 5C is a perspective view illustrating an example of a support plate assembly 525 installed in a frame of a digester according to various aspects of the present disclosure. As illustrated in FIG. 5C, the inclined support plate 530 is inclined from an upper portion of the collection chamber 235 to a lower portion of the collection chamber 235 formed by the frame 230. It is also shown in FIG. 5C, the plurality of support beams 535 extend further from the — surface of the inclined support plate 530 at the lower portion than from the surface of the inclined support plate 530 at the upper portion due to the inclination of the inclined support plate 530.

The support plate assembly 525 may be easily removable from the frame 230. For example, the support plate assembly 525 may be attached to the frame 230 with bolts. The support plate assembly 525 may have a large size, for example 2 m wide by 3 m tall. The support plate assembly 525 may be fabricated in multiple pieces, for example 2-4 pieces or another number e of pieces, to facilitate handling during installation and removal.

S FIG. 6A is a perspective view of an example of a support plate assembly 525 8 25 showing a curvature of the support plate assembly according to various 3 aspects of the present disclosure. FIG. BA illustrates a first side 610 of the

E support plate assembly 525 and a second side 620 of the support plate cn assembly 525. The first side 610 of the support plate assembly 525 may face 0 the screen plate (e.g., the screen plate 510) and the second side 620 of the

O 30 support plate assembly 525 may face the inner surface 210 of the outer wall 110 of the digester. The plurality of support beams 535 may extend substantially perpendicularly from the inner surface 210 of the outer wall 110 of the digester to the inner surface 516 of the screen plate 510.

As shown in FIG. 6A, the inclined support plate assembly 525 conforms to a curvature of the digester with the inclined support plate 530 having a concave surface on the first side 610 of the support plate assembly 525 facing the screen plate and a convex surface 622 on the second side 620 of the support plate assembly 525 facing the inner surface 210 of the outer wall 110 of the digester. Conformity a curvature of the inclined support plate 532 the curvature of the digester enables the plurality of support beams 535 to be disposed substantially perpendicularly to both the inner surface 210 of the outer wall 110 of the digester and the inner surface 516 of the screen plate 510 to provide support for the screen plate 510 against the forces exerted by the digesting material.

FIG. 6B is a front view of an example of the support plate assembly 525 illustrating the plurality of support beams on the first side of the support plate assembly according to various aspects of the present disclosure. As can be seen on the first side 610 of the support plate assembly 525 in FIG. 6B, the orientation of the plurality of support beams 535 changes to remain substantially perpendicular to the inner surface 210 of the outer wall 110 of the digester and the inner surface 516 of the screen plate 510 according to the curvature of the inclined support plate 530.

In some implementations, the support elements may be continuous support 10 bars extending horizontally from a side edge of the support plate to an

N opposing side edge of the support plate. FIG. 6C is a front view of an 3 25 example of the support plate assembly 630 illustrating horizontal support s elements according to various aspects of the present disclosure. The

E plurality of horizontal support elements may be horizontal support bars 640. cn The horizontal support bars 640 of the support plate assembly 630 may 0 extend only between the first side 637 of the support plate 635 and the inner

O 30 surface of the screen plate (e.g. the screen plate 510) In these implementations, the attachment between the support plate assembly 630 and the frame (e.g., the frame 230) enables the horizontal support bars 640 to support the screen plate.

In some implementations, the support plate 635 may be a support frame attached to end portions 642 of the horizontal support bars 640. In such implementations, the plurality of horizontal support bars 640 may extend from the inner surface 210 of the outer wall 110 of the digester to an inner surface 516 of the screen plate. In such implementations, each of the horizontal support bars 640 may have the same width in a direction from the inner surface of the wall of the digester to the inner surface of the screen plate. In some implementations, the screen plate may be inclined with respect to the support plate. In such implementations, the support elements may have different widths.

In some implementations, the support elements may be continuous bars extending vertically from an upper portion of the support plate to a lower — portion of the support plate. FIG. 6D is a front view of an example of the support plate assembly 650 illustrating vertical support elements according to various aspects of the present disclosure: The plurality of vertical support elements may be vertical support bars 660. The vertical support bars 660 of the support plate assembly 650 may extend only between the first side 667 of the support plate 665 and the inner surface of the screen plate (e.g., the screen plate 510). In these implementations, the attachment between the support plate assembly 650 and the frame (e.g., the frame 230) enables the e vertical support bars 660 to support the screen plate.

S In some implementations, the support plate 665 may be a support frame 8 25 attached to end portions 662 of the vertical support bars 660. In such s implementations, the plurality of vertical support bars 660 may extend from

E the inner surface 210 of the outer wall 110 of the digester to an inner surface cn 516 of the screen plate. In such implementations, each of the vertical 0 support bars 660 may have the same width in a direction from the inner

O 30 — surface of the wall of the digester to the inner surface of the screen plate. In some implementations, the screen plate may be inclined with respect to the support plate. In such implementations, the support elements may have different widths.

In some implementations, the screen plate and support plate assembly may be treated to provide a non-stick surface. For example, the screen plate and support plate assembly may be coated with Teflon® or another non-stick coating. Alternatively or additionally, the surfaces of the screenplay and support plate assembly may be electropolished. The non-stick surface can reduce scale formation on the screen plate and support plate assembly.

Aspects of the present disclosure provide a novel screen plate for separating liquor and comminuted cellulosic materials in a digester. Conventional screen plates are prone to clogging due to scale accumulation caused by uneven liquor flow velocity through the screen plate. The uneven flow velocity can result from lower fluid pressure at the upper portion of the screen plate than at the lower portion of the screen plate. The novel screen plate includes portions of the screen plate having different open areas to compensate for differences in fluid pressure.

FIG. 7 is a perspective view of an example of screen plates 710a, 710b installed in a frame of a digester according to various aspects of the present disclosure. As used herein, an individual screen plate of the screen plates 710a, 710b may be referred to as a screen plate 710. Each screen plate 710, 710b may be, for example, the screen plate 510 illustrated in FIG. 5A.

The screen plates 710a, 710b provide a series of slots, or openings, 712a, s 712b to enable liquor to flow through the openings 712a, 712b in the screen 3 plates 710a, 710b to be separated from the pulp and collected in the + 25 collection chambers 235 and collection headers 240 for reuse. Each screen = plate 710 may include multiple areas of slots or openings providing different - amounts of open area to permit liguor to flow more uniformly through the 2 screen plate 710 into the collection chamber 235. In general, the multiple 5 areas of slots or openings provide more open area to permit liguor flow at

N 30 the upper portions of the screen plate 710 with the areas of slots or openings providing progressively less open area towards the lower portions of the screen plate 710.

The screen plates 710a, 710b are attached to the frame 230 forming collection chambers 235 between the inner surface 210 of the outer wall 110 and screen plates 710a, 710b. Hinges 714a, 714b may be provided along in the edge of the screen plates 710a, 710b to enable opening the screen plates 710a, 710b for maintenance and access to the collection chambers (e.g., the collection chamber 235) and support plate assembly (e.g., the support plate assembly 525). — While two screen plates 710a, 710b are illustrated in FIG. 7, it should be appreciated that screen plates are disposed to form a generally annular ring around the inner circumference of digester. As shown in FIG. 7, the screen plates 710a, 710b conform to a curvature of the digester.

The screen plate 710 may have a large size, for example 2 m wide by 3 m — tall. The screen plate 710 may be fabricated in multiple pieces, for example 2-4 pieces or another number of pieces, to facilitate handling during installation and removal.

FIG. 8 is a diagram illustrating an example of a slot pattern 800 for a screen plate according to various aspects of the present disclosure. The screen plate may be, for example, the screen plates 710a, /10b described with respect to FIG. 7. The slot pattern 800 may have multiple portions of slots, or openings, and the slots or openings in each portion may provide a s different amount of open area to permit liguor to flow through the screen a plate into the collection chamber 235. As used herein, the terms “slots” and = 25 “openings” may be used interchangeably.

E FIG. 8 illustrates four portions 810-840 of slots in the slot pattern 800. It

O should be appreciated that more or fewer than four portions of slots in the a slot pattern 800 may be provided without departing from the scope of the

O present disclosure. Each portion 810-840 may include multiple rows of slots.

Forexample, in FIG. 8, the first portion of slots 810 includes eight rows 812a- 812h of slots, the second portion of slots 820 may include seven rows 822a-

822g of slots, the third portion of slots 830 may include seven rows 832a- 832g of slots, and the fourth portion of slots 840 may include seven rows 842a-842g of slots. It should be appreciated that more or fewer rows of slots may be provided in each portion 810 to 840 of the slot pattern 800 without departing from the scope of the present disclosure.

As illustrated in FIG. 8, the slots in each row of the slot pattern 800 may have substantially same dimensions except for the first slot and the last slot on each end of a row. The total open area of a portion the slot pattern may be varied by varying the separation between the slots in a row and/or the separation between the rows in a portion of the slot pattern. In some implementations, the openings may have shapes other than slots, for example, but not limited to, circles, rectangles, etc., or combinations of slots and other shapes. In some implementations, the open area in a portion of the slot pattern may be varied by varying the number and/or shape of the openings.

The variation in open area for the portions 810-840 of slots in the slot pattern 800 can provide more uniform liquor flow velocities through the screen plate 710 and in the collection chamber 235 thereby reducing the formation of scale on the screen plate 710, the support plate assembly 525, and the collection chamber 235.

While FIG. 8 illustrates a slot pattern having rows of continuous slots, other slot patterns may be implemented without departing from the scope of the 10 present disclosure. For example, the slot pattern in a row of slots may be

N interrupted with blank portions having no slots.

O

= 25 While the terms “digester” and “pulp treatment vessel” have been used = throughout the description, it should be understood that these terms i encompass continuous digesters, batch digesters, impregnation vessels, 2 and other pulp treatment vessels where the screen plates are used for i separation of liquor and comminuted cellulosic materials to which

N 30 embodiments according to the present disclosure are applicable. Further,

the various embodiments according to the present disclosure are applicable to newly manufactured digesters as well as to retrofits of existing digesters.

The examples and embodiments described herein are for illustrative purposes only. Various modifications or changes in light thereof will be apparent to persons skilled in the art. These are to be included within the spirit and purview of this application, and the scope of the appended claims, which follow.

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Claims (14)

1. A screen plate (310a, 310b, 510, 710, 710a, 710b) for a pulp treatment vessel (100), the screen plate (310a, 310b, 510, 710, 710a, 710b) comprising: -a plurality of openings (312, 712a, 712b) configured to pass liquor from a pulping process while preventing passage of pulp, the plurality of openings (312, 712a, 712b) of the screen plate (310a, 310b, 510, 710, 710a, 710b) configured to form more open area at an upper portion (512) of the screen plate (310a, 310b, 510, 710, 710a, 710b) than at a lower portion (514) of the screen plate (310a, 310b, 510, 710, 710a, 710b).

2. The screen plate (310a, 310b, 510, 710, 710a, 710b) of claim 1, wherein a hinge (714a, 714b) is disposed on the screen plate (310a, 310b, 510, 710, 710a, 710b) and wherein; -the hinge (/14a, 714b) is configured to be attached to a frame of the pulp treatment vessel configured to mount the screen plate (310a, 310b, 510, 710, 7104, /10b), and -the hinge (714a, 714b) is configured to enable the screen plate (310a, 310b, 510, 710, 710a, 710b) to be movable.

3. The screen plate (310a, 310b, 510, 710, 710a, 710b) of claim 1 or 2, LO wherein each opening (312, 712a, 712b) of the plurality of openings (312, N & 712a, 712b) between a first opening (312, 712a, 712b) and a last opening in 3 a row have substantially same dimensions.

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4. The screen plate (310a, 310b, 510, 710, 710a, 710b) of claim 1, wherein & 25 the open area in a portion of the screen plate (310a, 310b, 510, 710, 710a, 2 710b) is determined by a separation between openings (312, 712a, 712b) in i each row of the portion of the screen plate (310a, 310b, 510, 710, 710a, oo N 710b) or by a separation between rows of openings (812a-812h, 822a-822g,

832a-8329) in the portion of the screen plate (310a, 310b, 510, 710, 710a, 710b).

5. The screen plate (310a, 310b, 510, 710, 710a, 710b) of claim 1, wherein the screen plate (310a, 310b, 510, 710, 710a, 710b) comprises a plurality of areas of openings (312, 712a, 712b), wherein each area of the plurality of areas of openings (312, 712a, 712b) comprises one or more rows of openings (812a-812h, 822a-822g, 832a-832¢g), and wherein each area of the plurality of areas of openings (312, 712a, 712b) provides a different amount of open area.

6. The screen plate (310a, 310b, 510, 710, 710a, 710b) of claim 5, wherein the plurality of areas of openings (312, 712a, 712b) provides progressively less open area from an upper portion (512) of the screen plate (310a, 310b, 510, 710, 710a, 710b) to a lower portion (514) of the screen plate (310a, 310b, 510, 710, 710a, 7106).

7. A screen assembly for a pulp treatment vessel, the screen assembly having a screen plate (310a, 310b, 510, 710, 710a, 710b) according to any of claims 1 to 6 and a support structure comprising: -an inclined support plate (530, 635, 665) disposed between the inner wall of the pulp treatment vessel and the screen plate (310a, 310b, 510, 710, 710a, 710b), wherein the inclined support plate (530, 635, 665) is inclined at an acute angle with respect to the screen plate (310a, 310b, 510, 710, 710a, /10b) from an upper portion (512) of the screen plate (310a, 310b, s 510, 710, 710a, 710b) to a lower portion (514) of the screen plate (310a, a 310b, 510, 710, 710a, 710b); and O s 25 —-multiple support elements (455, 535) disposed on the inclined support plate E (530, 635, 665), the multiple support elements (455, 535) extending between O a first surface of the inclined support plate (530, 635, 665) and the screen a plate (310a, 310b, 510, 710, 710a, 710b). N

N 8. The screen assembly of claim 7, wherein the multiple support elements (455, 535) comprise substantially cylindrical beams.

9. The screen assembly of claim 7, wherein the multiple support elements (455, 535) comprise horizontal support bars (640).

10. The screen assembly of claim 7, wherein the multiple support elements (455, 535) comprise vertical support bars (660).

11. The screen assembly of claim 7, wherein screen plate (310a, 310b, 510, 710, 710a, 710b) and the inclined support plate (530, 635, 665) are formed with a curvature corresponding to a curvature of a wall (110) of the pulp treatment vessel (100).

12. The screen assembly of claim 7, wherein each of the multiple support elements (455, 535) are arranged on the inclined support plate (530, 635, 665) to be positioned between the plurality of openings (312, 712a, 712b) on the screen plate (310a, 310b, 510, 710, 710a, /10b).

13. The screen assembly of claim 12, wherein the inclined support plate (530, 635, 665) is inclined such that the inclined support plate (530, 635, 665) is disposed closer to an upper portion (512) of the screen plate (310a, 310b, 510, 710, 710a, 710b) than to a lower portion (514) of the screen plate (310a, 310b, 510, 710, 710a, 710b).

14. The screen assembly of claim 12, wherein a distance between a lower portion of the inclined support plate (530, 635, 665) and a lower portion (514) of the screen plate (310a, 310b, 510, 710, 710a, 710b) is greater than the distance between an upper portion of the inclined support plate (530, 635, 10 665) and an upper portion (512) of the screen plate (310a, 310b, 510, 710, & 710a, 710b). O <Q < = 25 a O oN LO LO N oo Al