SE2430125A1

SE2430125A1 - A method, uses of the same, a pulp composition and a system

Info

Publication number: SE2430125A1
Application number: SE2430125A
Authority: SE
Inventors: Mikko Nikamaa
Original assignee: Metsae Board Oyj
Priority date: 2021-08-17
Filing date: 2022-08-17
Publication date: 2024-03-13
Also published as: CN117881845A; CA3228125A1; WO2023021244A1; FI20215862A1

Abstract

According to an example aspect of the present invention, there is provided a method comprising: providing a pulp composition; screening the pulp composition to obtain an accept fraction and a reject fraction; and dewatering the accept fraction output from the screening by a screw press.

Description

A method, uses of the same, a pulp composition, and a system FIELD [0001] The present invention relates to processes used in manufacturing of pulp. BACKGROUND [0002] In the known pulping methods, chipped Wood may first be impregnated With Chemicals. The impregnated chips are then directed to primary refining, Which may consist of several consecutive primary refiners. After the reﬁning, the consistency of the pulp is typically decreased and latency removed. After the latency removal, the pulp is screened to an accept and a reject fraction. The accept fraction may be directed to a disc filter, Wherein the consistency of the pulp is increased, and then further to bleaching and Washing steps. The reject fraction is typically stored in reject storage silos and treated in a separate reject treatment line involving one or more reject refiners.

[0003] The present invention is aimed at improving the known pulping methods. SUMMARY OF THE INVENTION [0004] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0005] According to a first aspect of the present invention, there is provided a method comprising: providing Wood chips; impregnating the Wood chips With an impregnating composition to obtain impregnated Wood chips; refining the impregnated Wood chips in at least one refiner to obtain a refined pulp composition; screening the refined pulp composition to obtain an accept fraction and a reject fraction; and directing at least part of the reject fraction from the screening step back to said impregnating step or to a step preceding said impregnating step.

[0006] from the following bulleted list: Various embodiments of the first aspect may comprise one or more features The impregnating composition is an aqueous composition comprising one or more of the following: NaOH, NagSOg, White liquor, such as oxidised white liquor, green liquor, such as oxidised green liquor, and HgOg. In said refining, the refining energy consumption is in the range 0.2 to 1.5 MWh/t.

After the ref1ning step, the pulp composition has a Pulmac shiVe content of less than 10%, such as less than 5%.

After the ref1ning step, the pulp composition has Canadian Standard Freeness (CSF) in the range 285 to 750, for example 285 to 470, or 350 to 750.

In the screening step at least 80 wt-%, such as at least 95 wt-% of the reﬁned pulp composition becomes directed to the accept fraction.

The Pulmac shiVe content of the accept fraction is not more than 10 percentage points lower, such as not more than 5 percentage points lower than the Pulmac shiVe content of the incoming ref1ned pulp composition fed to the screening.

The CSF of the accept fraction differs from the CSF of the incoming ref1ned pulp composition fed to the screening by not more than 120%.

The method further comprises dewatering the accept fraction output from the screening. Said dewatering is carried out by a screw press and/or by a disc filter. The dewatering comprises dewatering carried out by a screw press.

The pulp composition, such as the accept fraction, that is fed to the screw press has a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%. The dewatering comprises dewatering carried out by a disc filter.

The pulp composition, such as the accept fraction, that is fed to the disc filter has a consistency of at least 0.5%, such as 1.0 to l.5%.

In the dewatering, the pulp composition is dewatered to a consistency of at least %, such as at least 30%. 0 The dewatered pulp composition is fed to a bleaching step, optionally after decreasing the consistency of the pulp composition to less than 15%, such as to less than 10%. 0 The consistency of the accept fraction is first increased to above 20% and then decreased to about 8 to 12%, preferably to about 10%, for example to clean the pulp. 0 The reject fraction is fed to the impregnating step at a consistency in the range 4 to %, such as 4 to 10%.

[0007] of the method according to the first aspect in the manufacturing of bleached or unbleached According to a second aspect of the present invention, there is provided use therrnomechanical pulp.

[0008] composition, obtained by the method according to the ﬁrst aspect. Preferably, the pulp According to a third aspect of the present invention, there is provided a pulp composition comprises BCTMP.

[0009] system configured to execute the method according to the first aspect.

According to a fourth aspect of the present invention, there is provided a

[0010] method comprising: providing a pulp composition; screening the pulp composition to According to a f1fth aspect of the present invention, there is provided a obtain an accept fraction and a reject fraction; and deWatering the accept fraction output from the screening by a screw press. [001 1] from the following bulleted list: Various embodiments of the fifth aspect may comprise one or more features 0 The method comprises before the screening step: providing Wood chips; refining the Wood chips in at least one ref1ner to obtain a ref1ned pulp composition; directing the ref1ned pulp composition to said screening. 0 The method comprises before the screening step: providing a pulp composition comprising mechanical pulp, such as groundWood pulp; directing the pulp composition comprising mechanical pulp to said screening.

The pulp composition, such as the accept fraction, that is fed to the screw press has a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%.

The dewatering is carried out both during the screening and in the subsequent SCTCW pfCSS.

In the dewatering, the pulp composition is deWatered to a consistency of at least %, such as at least 30%.

The deWatered pulp composition is fed to a bleaching step, optionally after decreasing the consistency of the pulp composition to less than 15%, such as to less than 10%.

The consistency of the accept fraction is first increased to above 20% and then decreased to about 8 to 12%, preferably to about 10%, for example to clean the pulp composition.

The screening comprises screening carried out by a first screening device and screening carried out by a subsequent second screening device.

The consistency of the pulp composition in the output of the first screening device is lower than the consistency of the pulp composition in the output of the second screening device.

In the screening step at least 50 Wt-%, such as at least 80 Wt-% of the reﬁned pulp composition becomes directed to the accept fraction.

The method comprises directing the reject fraction from the screening step to a reject treatment line.

The rej ect treatment line comprises at least a step of refining the reject fraction by a reject refiner.

The method comprises directing an output of the reject treatment line to said screw press, and preferably said output has a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%. 0 The method further comprises, before the screening step, impregnating the Wood chips With an impregnating composition to obtain impregnated Wood chips, and ref1ning the impregnated Wood chips in at least one refiner. 0 The impregnating composition is an aqueous composition comprising one or more of the following: NaOH, NagSOg, White liquor, such as oxidised White liquor, green liquor, such as oxidised green liquor, and HgOg. 0 The method comprises directing at least part of the reject fraction from the screening step back to said impregnating step or to a step preceding said impregnating step.

[0012] According to a sixth aspect of the present invention, there is provided use of the method according to the f1fth aspect in the manufacturing of chemitherrnomechanical pulp or bleached chemitherrnomechanical pulp.

[0013] According to a seventh aspect of the present invention, there is provided use of the method according to the f1fth aspect in the manufacturing of mechanical pulp, such as groundWood pulp, pressure groundWood pulp, stone groundWood pulp, or therrnomechanical pulp.

[0014] According to an eighth aspect of the present invention, there is provided a pulp composition, obtained by the method according to the f1fth aspect. Preferably, the pulp composition comprises BCTMP.

[0015] According to a ninth aspect of the present invention, there is provided a system configured to execute the method according to the fifth aspect.

[0016] Advantages of the invention

[0017] An advantage of the present invention is that the amount of reject generated in the screening step may be decreased.

[0018] A further advantage of the present invention is that relatively high CSF levels may be used throughout the process.

[0019] dispensed With.

A further advantage of the present invention is that a disc filter may be

[0020] A further advantage of the present inVention is that tailoring of the pulping process for the purpose of preparing Various pulp end compositions may be facilitated.

[0021] An advantage of the present inVention is that energy saVings may be attained as the process involves less equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIGURES l and 2 illustrate the method in accordance With at least some embodiments of the present inVention; and

[0023] least some embodiments of the present invention.

FIGURE 3 illustrates the screening step in the method in accordance With at EMBODIMENTS [0024] As used herein, the terrn “pulp” typically refers to Wood pulp. [0025] As used herein, the terrn “accept” refers to the fraction that has been accepted to be fed to the succeeding step in the process, such as to the succeeding step in the main line process.

[0026] accepted to be fed to the succeeding step in the process, such as to the fraction that has As used herein, the terrn “reject” refers to the fraction that has not been been rejected from continuing in the main line process.

[0027] In the present context, the terrn “reject fraction” typically refers to the reject fraction from the screening step.

[0028] according to ISO 5267-2.

In the present context, Canadian Standard Freeness (CSF) is measured

[0029] In the present context, brightness is measured according to brightness 457 nm, ISO 2470. [0030] In the present context, shive content refers to shive content “Pulmac (0.l mm)”.

[0031] In some embodiments of the present inVention it has been surprisingly observed that in a pulping process it may be possible to entirely dispense with a separate reject treatment line.

[0032] observed that a disc filter may be replaced by a screw press in a dewatering step of a In some embodiments of the present inVention it has been surprisingly pulping process.

[0033] Typically, the present method may be incorporated in a pulp manufacturing process. [0034] In one embodiment, the present method comprises: providing wood chips; impregnating the wood chips with an impregnating composition to obtain impregnated wood chips; ref1ning the impregnated wood chips in at least one ref1ner to obtain a ref1ned pulp composition; screening the refined pulp composition to obtain an accept fraction and a reject fraction; and directing at least part of the reject fraction from the screening step back to said impregnating step or to a step preceding said impregnating step.

[0035] In another embodiment, the present method comprises: providing wood chips; ref1ning the wood chips in at least one ref1ner to obtain a ref1ned pulp composition; screening the ref1ned pulp composition to obtain an accept fraction and a reject fraction; and dewatering the accept fraction by a screw press.

[0036] mixtures thereof, or hardwood, such as birch, poplar, aspen, alder, maple, eucalypt tropical The wood to be chipped may comprise softwood, such as spruce or pine or hardwood, or mixtures thereof, or it may comprise a mixture of softwood and hardwood.

[0037] The impregnating composition may be an aqueous composition comprising one or more of the following: NaOH, NagSOg, white liquor, such as oxidised white liquor, green liquor, such as oxidised green liquor, and HgOg.

[0038] that has been softened in the impregnating step. As a result of the mechanical forces in During the refining, the wood fibres become released from the wood material reﬁning, the fibres are shortened, the ﬁbre diameter is decreased, and the fibres become f1brillated. The f1brillating (extemal fibrillating) involves breaking of the smooth f1bre surface to make it hairy by introduction of microfibrils on the f1bre surface. Also intemal fibrillating typically occurs, which increases flexibility of the fibres. As to the quality of the obtained ref1ned mass, a low shive content, high strength, and a sufficient f1bre length may be aimed at.

[0039] The ref1ner that is used for ref1ning the Wood chips may be a high- consistency ref1ner or a low-consistency ref1ner. In the case of a high-consistency ref1ner, the consistency of the pulp to be ref1ned is typically 20 to 60%. In the case of a low- consistency refiner, the consistency of the pulp to be ref1ned is typically 3 to 5%.

[0040] The ref1ner may be a ﬂat disc ref1ner or a conical disc ref1ner.

[0041] The ref1ner may be a one-disc or a tWo-disc ref1ner. Preferably the ref1ner is a one-disc ref1ner comprising a stator and a rotor.

[0042] The distance between the blades of the ref1ner may be in the range 0.1 to 1.0 mm.

[0043] In said ref1ning, the refining energy consumption may be in the range 0.2 to 1.5 MWh/t.

[0044] After the ref1ning step, the pulp may have a Pulmac shive content of less than %, such as less than 10%, for example less than 5%.

[0045] may have Canadian Standard Freeness (CSF) of at least 285, such as at least 350, for After the ref1ning step, i.e. in the output of the last refiner, the ref1ned pulp example at least 400. In some embodiments, the ref1ned pulp may have Canadian Standard Freeness of less than 750, such as less than 470.

[0046] (CSF) in the range 285 to 470. Such pulp may be suitable for the manufacturing of CTMP In one embodiment, the refined pulp may have Canadian Standard Freeness that is usable as a material of lightWeight coated printing paper.

[0047] In one embodiment, the refined pulp may have Canadian Standard Freeness (CSF) in the range 350 to 750. Such pulp may be suitable for the manufacturing of BCTMP that is usable as a material of folding boxboard.

[0048] Before directing the ref1ned pulp to the screening, a latency removal step is typically present. During the latency removal, curling of the ﬁbres is reduced and the f1bres become straightened.

[0049] In one embodiment, the ref1ned pulp composition that is fed to the screening step may have a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%.

[0050] the pulp has a consistency of at least 2%, such as at least 3%, for example 2 to 5%, During the screening step or at least in the accept output of the screening step preferably 3 to 4%. An advantage of having such a high consistency at least in the accept output of the screening is that the accept fraction may be directly feedable to a screw press after the screening. In lower consistencies, the mass ﬂow rate might be too high to be handled by a screw press.

[0051] at least 90 wt-%, preferably at least 95 wt-% of the refined pulp composition becomes In the screening step, at least 50 wt-%, for example at least 80 wt-%, such as directed to the accept fraction.

[0052] Preferably, the composition and properties of the refined pulp are not substantially altered as a result of the screening. In other words, the amount of reject separated from the pulp in the screening step is preferably minimised.

[0053] 50 percentage points lower, such as not more than 10 percentage points lower, for example The Pulmac shive content of the accept fraction is preferably not more than not more than 5 percentage points lower than the Pulmac shive content of the incoming refined pulp fed to the screening.

[0054] 10%, such as less than 5%, preferably less than 1%.

For example, the Pulmac shive content of the accept fraction may be less than

[0055] The CSF of the accept fraction may differ from the CSF of the incoming refined pulp fed to the screening by not more than 120%,

[0056] pulp feeds are combined to the accept fraction that is output from the screening step. Thus, In some embodiments, in steps succeeding the screening step, no incoming the steps downstream of the screening step, typically dewatering and bleaching, receive as an input only the accept fraction from the screening. Therefore, preferably the properties and composition of only this sole accept fraction need to be adjusted if the input of post- screening steps needs adjustment.

[0057] In one embodiment, the dewatering may be carried out in a screw press. In this embodiment, the fraction that is fed from the screening to the dewatering step preferably has a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%. Preferably said fraction consists of the accept fraction from the screening.

[0058] embodiment, the fraction that is fed from the screening to the dewatering step preferably In one embodiment, the dewatering may be carried out by a disc filter. In this has a consistency of 0.5 to 2%, such as 1.0 to 1.5%. Preferably said fraction consists of the accept fraction from the screening.

[0059] screening and in a subsequent screw press or disc filter. Thus, part of water removal may In one embodiment, the dewatering may be carried out both during the take place already in the screening step, for example by using at least two screening devices arranged in series and by configuring the latter screening device to partly dewater the pulp composition.

[0060] fraction in steps succeeding the screening step. An advantage of not using a disc filter is In a preferred embodiment, a disc filter is not used for dewatering the accept that CSF of the pulp may be adjusted to higher levels throughout the process, as cake- forming problems may be avoided. Such cake-forming problems might be encountered in methods that use a disc filter.

[0061] consistency may be increased to high levels, such as to 15 to 40%, for example to at least An advantage of using a screw press for the dewatering is that the %, preferably to at least 30%. The ability to effectively remove water from the screened pulp, if needed, may be advantageous.

[0062] at least 20%, such as at least 30%.

The accept fraction from the screening may be dewatered to a consistency of

[0063] The method may comprise: providing wood chips; impregnating the wood chips with an impregnating composition to obtain impregnated wood chips; refining the impregnated wood chips in at least one refiner to obtain a refined pulp composition; screening the refined pulp composition to obtain an accept fraction and a reject fraction; and dewatering the accept fraction output from the screening by a screw press, wherein the accept fraction that is fed to the screw press has a consistency of at least 3%, and wherein 11 in the deWatering, the pulp composition is typically dewatered to a consistency of at least %.

[0064] decreasing the consistency of the accept fraction to less than 15%, such as to less than %.

The dewatered accept fraction may be fed to a bleaching step, optionally after

[0065] to above 20% and then decreased to about 8 to 12%, preferably to about 10%, for example In some embodiments, the consistency of the accept fraction is first increased to clean the pulp.

[0066] The reject fraction from the screening may be fed back to the impregnating step or to a step preceding the impregnating step. Preferably the reject fraction is fed to the impregnating step or to a step preceding the impregnating step at a consistency in the range 2 to 45%. In one example, the pulp composition, such as the reject fraction, fed to the impregnating step has a consistency in the range 4 to 10%.

[0067] to a step preceding the refining step. In that Way problems related to maintaining an Advantageously, the reject is not fed directly to the refining step but instead appropriate consistency in the ref1ner may be avoided. In this embodiment, the consistency of the reject may be allowed to vary in a broader range.

[0068] step preceding the impregnating step is that the reject fraction may receive a further An advantage related to feeding the reject to the impregnating step or to a impregnation before continuing to the refining.

[0069] or to a step preceding the impregnating step Without separate deWatering of the reject In preferred embodiments, the reject fraction is fed to the impregnating step fraction and/or Without separate ref1ning of the reject fraction. For example, the reject fraction may be fed directly from the screening reject output to the impregnating step or to a step preceding the impregnating step.

[0070] a step immediately preceding the impregnating step, typically Without any refining of the In some embodiments, the reject fraction is fed to the impregnating step or to reject fraction.

[0071] chips.

The step preceding the impregnating step may be a step of Washing the Wood 12

[0072] preferably substantially all of it, directly back to the impregnating step or to a step The method may comprise leading at least a part of the reject fraction, immediately preceding the impregnating step.

[0073] The method may comprise leading substantially all of the reject fraction directly back to the impregnating step, preferably without any ref1ning of said reject fraction.

[0074] In some embodiments, at least part of the reject fraction, such as substantially all of the reject fraction, may be directed from the screening to a reject treatment line that is separate from the main line, i.e. does not form part of the main line.

[0075] The reject treatment line may include a reject ref1ner.

[0076] dewatering the reject, ref1ning the reject by the rej ect ref1ner, and screening the rej ect to an The reject treatment may comprise one or more of the following steps: accept and a rej ect of the rej ect treatment line.

[0077] as at least two screening devices.

The reject treatment line may comprise one or more screening devices, such

[0078] may have a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably 3 to 4%.

The pulp composition input to the screening step of the reject treatment line

[0079] the main line, for example to the main line dewatering step, thus to become combined with An output, such as an accept of the reject treatment line may be fed back to the accept output from the main line screening.

[0080] may have a consistency of at least 2%, such as at least 3%, for example 2 to 5%, preferably In one embodiment, the accept that is output from the reject treatment line 3 to 4%. An advantage is that the accept of the reject treatment line can then be fed directly to a screw press in the mainline.

[0081] In one embodiment, an accept from a reject treatment line is directed to the main line dewatering step, such as to the screw press for example at a consistency of at least 2%. 13

[0082] It is preferred to adjust the consistency of the accept that is output from the reject treatment line to the range 2 to 5%.

[0083] back to the impregnating step and another part of the reject from the screening step is In one embodiment, a part of the reject from the screening step is directed directed to the rej ect treatment line.

[0084] selected from the following group: mechanical pulp, therrnomechanical pulp (TMP) The present inVention may be applicable for the manufacturing of pulp chemitherrnomechanical pulp (CTMP), bleached chemitherrnomechanical pulp (BCTMP), semichemical pulp, groundWood pulp (GW), pressure groundWood pulp (PGW), stone groundWood pulp (SGW), and combinations thereof

[0085] The pulp may be bleached or unbleached.

[0086] pulp or bleached chemitherrnomechanical pulp.

Preferably, the method is for the manufacturing of chemitherrnomechanical

[0087] pulp, groundWood pulp (GW), pressure groundWood pulp (PGW), stone groundWood pulp (SGW) or therrnomechanical pulp (TMP).

In some embodiments, the method is for the manufacturing of mechanical

[0088] BCTMP obtained by some embodiments of the present method may be applicable as a material of one or more layers of paperboard, such as folding boxboard, or of paper, such as printing paper or Writing paper or tissue paper.

[0089] for the manufacturing of paperboard With the fo lloWing characteristics: In one embodiment, the method is for preparation of such pulp that is adapted

[0090] Preferably the brightness of the paperboard is larger than 84%.

Preferably the density of the paperboard is in the range 0.5 - 1.3 g/cm3.

[0091] adapted for the manufacturing of paper With the following characteristics: In another embodiment, the method is for preparation of such pulp that is

[0092] the brightness of the paper is larger than 77%.

Preferably the density of the paper is in the range 0.7 - l.4 g/cm3. Preferably 14

[0093] method according to any of the embodiments described above or their any combinations.

The present invention also concerns a system conf1gured to execute the The system may form part of a pulp mill. The system may comprise one or more of the following devices: a wood chipping device, a wood chip impregnating system, one or more primary ref1ners, one or more pulp screening devices, one or more reject ref1ners, a reject screening device, a pulp dewatering device, such as a disc filter or a screw press, a pulp bleaching system.

[0094] Tuming now to the drawings:

[0095] some embodiments of the present invention. The process comprises the following steps: FIGURE 1 illustrates process steps in a method in accordance with at least chipping 10, impregnating 11, ref1ning 12, screening 13, dewatering 14, optional bleaching 15, and optional washing 16. The screening produces as outputs an accept fraction and a reject fraction. The accept fraction continues in the main line and is directed from the screening 13 to the dewatering 14. The reject fraction, if existing, or at least a part of the reject fraction, is fed from the screening 13 back to a step preceding the ref1ning step, for example to the impregnating step 11, as shown by an arrow in FIG. 1. Here, the dewatering 14 may comprise a screw press or a disc filter.

[0096] some embodiments of the present invention. Here, the main line comprises the steps of FIGURE 2 illustrates process steps in a method in accordance with at least chipping 20, optional impregnating 21, ref1ning 22, screening 23, dewatering 24, optional bleaching 25, and optional washing 26. The method further includes a reject treatment line 27 which is separate from the main line. The reject fraction obtained in the screening 23 is directed to the reject treatment line 27. The reject treatment line may comprise a reject reﬁning step and/or a reject screening step. An output, such as an accept fraction from the reject treatment line 27 may be directed back to the main line, such as to the dewatering 24. Here, the dewatering 24 preferably comprises a screw press.

[0097] least some embodiments of the present invention. The incoming pulp composition P is fed FIGURE 3 illustrates the screening step in the method in accordance with at to the screening step 33. The screening produces as outputs an accept fraction A and a reject fraction R. The accept fraction A is accepted to continue in the mainline process to the next step, the dewatering by a screw press 34. The reject fraction R is rejected from continuing in the mainline process and instead directed either to a reject treatment line or backWards in the mainline, for example to an impregnating step (not shown here).

[0098] preferably at least 3.5%, for example 3.5 to 4.5%.

The consistency of the incoming pulp P, Which may be ref1ned pulp, is

[0099] The consistency of the accept fraction A is preferably at least 3%, such as 3.5 to 4%.

[00100] The consistency of the reject fraction is preferably at least 4%, such as at least 4.5%.

[00101] EXAMPLE

[00102] A pulping process comprising direct feeding of the reject from the screening to the impregnating Was tested. The process main line included chipping, impregnating, ref1ning, screening, dewatering by a disc filter, and bleaching. The consistency of the pulp composition input to the bleaching Was about 10%. The accept from the screening Was directed to the disc filter. The reject from the screening Was directed either to a conventional rej ect treatment line or altematively back to the impregnating step.

[00103] bypassed and the reject from the screening Was fed back to the impregnating step. Tests 1 In Test 1 and Test 2 processes, the conventional reject treatment line Was and 2 Were conducted on different days.

[00104] The Reference process did not include any back-feeding of the reject but instead the reject from the screening Was directed to the conventional reject treatment line comprising a reject ref1ner. 16

[00105] that Was output from the disc filter (i.e. at a point between the disc filter and the bleaching).

We measured the Canadian Standard Freeness (CSF) of the pulp composition The results are presented in Table l. The results show that the CSF of the pulp composition in Test 1 and 2 processes Were successfully maintained at the same level as the CSF of the pulp composition in the Reference process.

CSF measurement l measurement 2 Reference 529 534 Test 1 526 521 Test 2 539 540 [00106] It is to be understood that the embodiments of the invention disclo sed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as Would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terrninology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

C

[00107] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection With the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[00108] elements, and/or materials may be presented in a common list for convenience. However, As used herein, a plurality of items, structural elements, compositional these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group Without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along With altematives for the various components thereof. It is understood that such 17 embodiments, examples, and altematives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[00109] combined in any suitable manner in one or more embodiments.

Furtherrnore, the described features, structures, or characteristics may be In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[00110] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[00111] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise CL 77 explicitly stated. Furthermore, it is to be understood that the use of a or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[00112] of pulp, such as CTMP or BCTMP.

The present invention is industrially applicable at least in the manufacturing ACRONYMS LIST TMP therrnomechanical pulp CTMP BCTMP GW PGW SGW CSE , 20 11,21 12, 22 13, 23, 33 14, 24, 34 , 25 16, 26 27 18 chemitherrnomechanical pulp bleached chemitherrnomechanical pulp groundwood pulp pressure groundwood pulp stone groundwood pulp Canadian Standard Freeness REFERENCE SIGNS LIST chipping impregnating reﬁning screening deWatering bleaching Washing reject treatment

Claims

1. A method comprising: providing wood chips; impregnating the wood chips with an impregnating composition to obtain impregnated wood chips; ref1ning the impregnated wood chips in at least one ref1ner to obtain a ref1ned pulp composition, wherein the refined pulp composition has Canadian Standard Freeness (CSF) ofat least 350; screening the ref1ned pulp composition to obtain an accept fraction and a reject fraction; feeding the accept fraction output from the screening to a screw press at a consistency of 3 to 4%; and dewatering the accept fraction output from the screening by the screw press to a consistency of at least 20%, wherein the dewatering step provides as an output a pulp composition.

2. The method according to any of the preceding claims, wherein the dewatering is carried out both during the screening and in the subsequent screw press.

3. The method according to any of the preceding claims, wherein in the dewatering, the pulp composition is dewatered to a consistency of at least 30%.

4. The method according to any of the preceding claims, wherein the dewatered pulp composition is fed to a bleaching step, optionally aﬁer decreasing the consistency of the pulp composition to less than 15%, such as to less than 10%.

5. The method according to any of the preceding claims, wherein the consistency of the accept fraction is first increased to above 20% and then decreased to about 8 to 12%, preferably to about 10%, for example to clean the pulp composition.

6. The method according to any of the preceding claims, wherein the screening comprises screening carried out by a first screening device and screening carried out by a subsequent second screening device, and preferably the consistency of the pulp composition in the output of the ﬁrst screening device is lower than the consistency of the pulp composition in the output of the second screening device.

7. The method according to any of the preceding claims, wherein in the screening step at least 50 wt-%, such as at least 80 wt-% of the refined pulp composition becomes directed to the accept fraction.

8. The method according to any of the preceding claims, comprising directing the reject fraction from the screening step to a reject treatment line comprising at least a step of ref1ning the reject fraction by a rej ect ref1ner.

9. The method according to claim 9, comprising directing an output of the rej ect treatment line to said screw press, and preferably said output has a consistency of at least 2%, such as at least 3%, for exampleto 5%, preferably 3 to 4%.

l0. The method according to any of the preceding claims, wherein the impregnating composition is an aqueous composition comprising one or more of the following: NaOH, NagSOg, white liquor, such as oxidised white liquor, green liquor, such as oxidised green liquor, and H2O

ll. The method according to any of the preceding claims, comprising directing at least part of the reject fraction from the screening step back to said impregnating step or to a step preceding said impregnating step.

l2. Use of the method according to claim l in the manufacturing of chemitherrnomechanical pulp or bleached chemitherrnomechanical pulp.

l3. A pulp composition, obtained by a pulp manufacturing process incorporating the method according to any of claims l to ll.

14. A system conﬁgured to execute the method according to any of c1ain1s 1 to 11, the system forniing part of a pu1p n1i11 and coniprising: a Wood chipping device, a Wood chip inipregnating system, one or more primary reﬁners, one or more pu1p screening devices, a pu1p dewatering device Which is a screw press, and optiona11y a pu1p bleaching system.