CA1164259A - Bleaching system for pulp reject treatment - Google Patents
Bleaching system for pulp reject treatmentInfo
- Publication number
- CA1164259A CA1164259A CA000380005A CA380005A CA1164259A CA 1164259 A CA1164259 A CA 1164259A CA 000380005 A CA000380005 A CA 000380005A CA 380005 A CA380005 A CA 380005A CA 1164259 A CA1164259 A CA 1164259A
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- CA
- Canada
- Prior art keywords
- pulp material
- reject
- stream
- bleaching chemical
- pulp
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
BLEACHING SYSTEM FOR PULP REJECT TREATMENT
ABSTRACT OF THE DISCLOSURE
An apparatus and method of treating reject pulp material without regard to accept pulp material with sufficient bleaching chemicals is disclosed. Reject pulp material is screened from the main pulp material stream and is separately refined and mixed with sufficient bleaching chemicals. The reject pulp material, as treated, is reintroduced to the accept material stream.
This commingled pulp stream is further mixed with sufficient bleaching chemical before proceeding to other unit one rations.
ABSTRACT OF THE DISCLOSURE
An apparatus and method of treating reject pulp material without regard to accept pulp material with sufficient bleaching chemicals is disclosed. Reject pulp material is screened from the main pulp material stream and is separately refined and mixed with sufficient bleaching chemicals. The reject pulp material, as treated, is reintroduced to the accept material stream.
This commingled pulp stream is further mixed with sufficient bleaching chemical before proceeding to other unit one rations.
Description
2 S ~
BI~EACHING SYSTEM FOR PULP REJECT TREATMENT
BACKGROUND AND SIJMMARY OF THE INVENTION
The present invention relates to the bleaching of pulp materia] obtained when fibrous substances are chemically acted upon. More specifically, the present invention relates to the separate treatment of reject pulp material con-sisting of a high concentration of lignin, e.g.
undercooked material, bark, knots and the like, by a bleaching chemical and subsequently reintro-ducing it into the main pulp or accept pulpstream.
The removal of reject material consisting of high concentration of lignin, such as, under-cooked material, bark, knots and the like, has posed a problem in pulp bleaching processes. The conventional method of handling the reject material prior to bleaching has been either to screen it out from the acceptable material and discard it or to screen it out, grind or refine the material into sufficiently small pieces and then reintroduce it into the main or accept pulp stream. The latter process, however, does not adequately delignify the reject pulp material and, as a consequence, when this refined reject pulp material is returned to the main or accept pulp stream and subJected to the chemical bleaching process, there normally is an insufficient quàntity of bleaching chemical alloted to it. The reject material, even though conventionally refined, represents a higher demand for bleaching chemical and competes with surrounding organic material for the bleaching chemical. If the reject material is not sufficiently refined, then the bleaching chemical in the vicinity of the 2 ~ 9 -reject material is exhausted too quickly or too much bleaching chemical is consummed by the accept pulp material causing pulp degradation. Thus, the prior systems utilize proce~ses which are designed S toward ~he bleaching of the average quality of pulp material taking into consideration both reject and accept pulp material.
The conventional methods of bleaching pulp material utilizes either C12, ClO2 or a combination thereof. Also, the bleaching may conventionally be accomplished in stages to facilitate the bleaching process and the further delignification of the reject pulp material. The conventional bleaching methods discussed above, normally require low consistency pulp material, e.g. 2%~4% concentration of fiber, and lower reaction temperatures. These conventional process parameters greatly increase the retention time necessary for sufficient bleachiang and delignification. Retention times in the range of about 20-60 minutes are normally expected.
In accordance with the present invention, reject pulp material containing a high concen-tration of lignin is treated in such a way that the higher lignin content is taken into account, without regard to the accept pulp material. In this regard, a sufficient quantity of bleaching chemical is added directly to the separated reject pulp material such that competition with the accept pulp material for the bleaching chemical will not occur. According to the present invention, pulp material having a consistency of about 8~ to 12%, preferably 10%, is screened to remove the reject pulp material. The reject pulp material is then mechanically refined~ and mixed :L ~ 642~9 with a sufficient quantity of bleaching chemical, pre~erably C12 and/or ClO2, prior to being returned to the accept pulp material stream for further processing. Since higher consistency pulp material and a correspondingly higher reaction temperature are utilized, the retention time necessary to sufficiently bleach and delignify the reject pulp material is greatly reduced over that of the conventional methods. Retention times associated with this aspect of the present invention are about 1 minute.
According to another aspect of this invention, the treated reject pulp material is combined with untreated accept pulp material.
This combined pulp material stream is then further mixed with a sufficient quantity of bleaching chemical, preferably C12 and/or ClO2, prior to proceeding with conventional unit operations~
According to yet another aspect of this invention, the addition of a sufficient quantity of bleaching chemical when mixed with either the reject pulp material or a combination of the reject and accept pulp materials is controlled by sensing the residual chlorine present in the efluent mixing stream. In this regard, only the amount of bleaching chemical demanded by the specific lignin content being treated will be used thereby curtailing bleaching chemical waste and pulp degradation. The means used for sensing bleaching chemical residue can be connected to a control valve or the like in the bleaching chemical stream to vary the flow rate of the bleaching chemical as demand for it varies.
64L~59 Therefore, according to the present invention a method and apparatus are provided for bleaching pulp material whereby the reject pulp material is independently treated with a bleaching chemical greatly decreasing the retention time necessary for proper bleaching and delignification of the pulp material and reducing the number of steps necessary for the bleaching of pulp material (thereby reducing the cost of such operation and producing bleached pulp material in a more efficient manner). Additionally, the present invention provides controls for the addition of bleaching chemical in a bleaching and deligni-fication operation such that the amount of bleaching chemical used will be minimized while the amount of pulp material treated in such an operation will be maximized.
RRIEF DESCRIPTION OF THE DRAWINGS
FIGURES lA and lB illustrate exemplary prior art systems for the treatment of reject pulp material; and FIGURE 2 is a diagramatic showing of an embodiment of an exemplary assembly according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
_ FIGURES lA and lB illustrate exemplary prior art proposals for dealing with the treatment of reject material in the bleaching stage operation. Each system includes a stock tank 1 holding pulp at a consistency of about 2-4%, a pump means 2, a means for separating the reject ~ :~ 6~2~
material 3, a second stock tank 4, a second pump means 5, a means for mixing the pulp material with a sufficient quantity of bleaching chemical 6, and a bleaching vessel 7. Referring specifically to FIGURE lA, the pulp material enters ~he screening means 3 and the reject pulp material stream 8 re-sulting from this process is conveyed to a waste disposal unit 9 and discarded. The accept material stream 10 is conveyed to a thickened stock tank 4 where the effluent therefrom is diluted with dilution stream 11. This diluted pulp material is then conveyed by a second pump means 5 to a mixing means 6 where bleaching chemi-cal stream 12 is added thereto. The pulp material, as mixed with bleaching chemical stream 12 is then conveyed from the mixing means 6 to a bleaching vessel 7.
Referring specifically to FIGURE lB, the pulp material of about 2-4% consistency is introduced to screening means 2 from ~ank 1, and the reject material 8 as a result of this process enters a second screening means 13~ The accept material 14 from the second screening means 13 is reintroduced downstream from the main screening means 2 while the reject material 15 from the second screening means passes to a third screening means 16. The accept material 17 is reintroduced downsteam of the second screening means 13. The reject material 8 from the third screening means 16 is introduced to a thickener 19 and subse-quently is refined by refiner 20 and reintroduced downstream of the third screening means 16. This cyclical operation is intended in the prior to provide a means of fully refining the pulp material prior to bleaching. From the main screen means 3, the accepts 10 flow to a stock tank 4.
The effl~lent from the stock tank is diluted with diluti~n stream 11 and subsequently introduced into a nuxing means 6 with a sufficient quantity of bleaching chemical 12. The effluent from the mixing means ;s then introduced into an upflow bleaching vessel 7. The ef1uent fr~m bleaching ~essel 7 is subsequently transported to a pulp washing system.
Referring specifically to FIGURE 2, an exemplary embodiment of an assembly according to the present invention is illustrated wherein medium consistency pulp (i.e. ab~ut B-12~) is transported from a stock tank 1 by a pump 2 and is introduced into a means f~r screening the reject material 3t SUC~ as that disclosed by ~.S. Patent
BI~EACHING SYSTEM FOR PULP REJECT TREATMENT
BACKGROUND AND SIJMMARY OF THE INVENTION
The present invention relates to the bleaching of pulp materia] obtained when fibrous substances are chemically acted upon. More specifically, the present invention relates to the separate treatment of reject pulp material con-sisting of a high concentration of lignin, e.g.
undercooked material, bark, knots and the like, by a bleaching chemical and subsequently reintro-ducing it into the main pulp or accept pulpstream.
The removal of reject material consisting of high concentration of lignin, such as, under-cooked material, bark, knots and the like, has posed a problem in pulp bleaching processes. The conventional method of handling the reject material prior to bleaching has been either to screen it out from the acceptable material and discard it or to screen it out, grind or refine the material into sufficiently small pieces and then reintroduce it into the main or accept pulp stream. The latter process, however, does not adequately delignify the reject pulp material and, as a consequence, when this refined reject pulp material is returned to the main or accept pulp stream and subJected to the chemical bleaching process, there normally is an insufficient quàntity of bleaching chemical alloted to it. The reject material, even though conventionally refined, represents a higher demand for bleaching chemical and competes with surrounding organic material for the bleaching chemical. If the reject material is not sufficiently refined, then the bleaching chemical in the vicinity of the 2 ~ 9 -reject material is exhausted too quickly or too much bleaching chemical is consummed by the accept pulp material causing pulp degradation. Thus, the prior systems utilize proce~ses which are designed S toward ~he bleaching of the average quality of pulp material taking into consideration both reject and accept pulp material.
The conventional methods of bleaching pulp material utilizes either C12, ClO2 or a combination thereof. Also, the bleaching may conventionally be accomplished in stages to facilitate the bleaching process and the further delignification of the reject pulp material. The conventional bleaching methods discussed above, normally require low consistency pulp material, e.g. 2%~4% concentration of fiber, and lower reaction temperatures. These conventional process parameters greatly increase the retention time necessary for sufficient bleachiang and delignification. Retention times in the range of about 20-60 minutes are normally expected.
In accordance with the present invention, reject pulp material containing a high concen-tration of lignin is treated in such a way that the higher lignin content is taken into account, without regard to the accept pulp material. In this regard, a sufficient quantity of bleaching chemical is added directly to the separated reject pulp material such that competition with the accept pulp material for the bleaching chemical will not occur. According to the present invention, pulp material having a consistency of about 8~ to 12%, preferably 10%, is screened to remove the reject pulp material. The reject pulp material is then mechanically refined~ and mixed :L ~ 642~9 with a sufficient quantity of bleaching chemical, pre~erably C12 and/or ClO2, prior to being returned to the accept pulp material stream for further processing. Since higher consistency pulp material and a correspondingly higher reaction temperature are utilized, the retention time necessary to sufficiently bleach and delignify the reject pulp material is greatly reduced over that of the conventional methods. Retention times associated with this aspect of the present invention are about 1 minute.
According to another aspect of this invention, the treated reject pulp material is combined with untreated accept pulp material.
This combined pulp material stream is then further mixed with a sufficient quantity of bleaching chemical, preferably C12 and/or ClO2, prior to proceeding with conventional unit operations~
According to yet another aspect of this invention, the addition of a sufficient quantity of bleaching chemical when mixed with either the reject pulp material or a combination of the reject and accept pulp materials is controlled by sensing the residual chlorine present in the efluent mixing stream. In this regard, only the amount of bleaching chemical demanded by the specific lignin content being treated will be used thereby curtailing bleaching chemical waste and pulp degradation. The means used for sensing bleaching chemical residue can be connected to a control valve or the like in the bleaching chemical stream to vary the flow rate of the bleaching chemical as demand for it varies.
64L~59 Therefore, according to the present invention a method and apparatus are provided for bleaching pulp material whereby the reject pulp material is independently treated with a bleaching chemical greatly decreasing the retention time necessary for proper bleaching and delignification of the pulp material and reducing the number of steps necessary for the bleaching of pulp material (thereby reducing the cost of such operation and producing bleached pulp material in a more efficient manner). Additionally, the present invention provides controls for the addition of bleaching chemical in a bleaching and deligni-fication operation such that the amount of bleaching chemical used will be minimized while the amount of pulp material treated in such an operation will be maximized.
RRIEF DESCRIPTION OF THE DRAWINGS
FIGURES lA and lB illustrate exemplary prior art systems for the treatment of reject pulp material; and FIGURE 2 is a diagramatic showing of an embodiment of an exemplary assembly according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
_ FIGURES lA and lB illustrate exemplary prior art proposals for dealing with the treatment of reject material in the bleaching stage operation. Each system includes a stock tank 1 holding pulp at a consistency of about 2-4%, a pump means 2, a means for separating the reject ~ :~ 6~2~
material 3, a second stock tank 4, a second pump means 5, a means for mixing the pulp material with a sufficient quantity of bleaching chemical 6, and a bleaching vessel 7. Referring specifically to FIGURE lA, the pulp material enters ~he screening means 3 and the reject pulp material stream 8 re-sulting from this process is conveyed to a waste disposal unit 9 and discarded. The accept material stream 10 is conveyed to a thickened stock tank 4 where the effluent therefrom is diluted with dilution stream 11. This diluted pulp material is then conveyed by a second pump means 5 to a mixing means 6 where bleaching chemi-cal stream 12 is added thereto. The pulp material, as mixed with bleaching chemical stream 12 is then conveyed from the mixing means 6 to a bleaching vessel 7.
Referring specifically to FIGURE lB, the pulp material of about 2-4% consistency is introduced to screening means 2 from ~ank 1, and the reject material 8 as a result of this process enters a second screening means 13~ The accept material 14 from the second screening means 13 is reintroduced downstream from the main screening means 2 while the reject material 15 from the second screening means passes to a third screening means 16. The accept material 17 is reintroduced downsteam of the second screening means 13. The reject material 8 from the third screening means 16 is introduced to a thickener 19 and subse-quently is refined by refiner 20 and reintroduced downstream of the third screening means 16. This cyclical operation is intended in the prior to provide a means of fully refining the pulp material prior to bleaching. From the main screen means 3, the accepts 10 flow to a stock tank 4.
The effl~lent from the stock tank is diluted with diluti~n stream 11 and subsequently introduced into a nuxing means 6 with a sufficient quantity of bleaching chemical 12. The effluent from the mixing means ;s then introduced into an upflow bleaching vessel 7. The ef1uent fr~m bleaching ~essel 7 is subsequently transported to a pulp washing system.
Referring specifically to FIGURE 2, an exemplary embodiment of an assembly according to the present invention is illustrated wherein medium consistency pulp (i.e. ab~ut B-12~) is transported from a stock tank 1 by a pump 2 and is introduced into a means f~r screening the reject material 3t SUC~ as that disclosed by ~.S. Patent
3,886,035 tQ Laaks~ The reject material 8 is transp~rted to a refiner 21 and the refined reject material is then introduced into a first mixer 22, such as that disclosed by U.S. Patent 4,093,506 to Richter~
together with a sufficient quantity of bleaching chemical 23. The ef~luent 24 of the mixture ~s subsequently reintroduced to the accept~ material 10 at feed point 25. The bleached reject material and the unbleached accept material flow concur-rently to a second mixing means 26 (&uch as in U~S. Patent 4,093,506) wherein a ~ufficient ~uantity of bleaching chemical is introduced through conduit 24'. The effluent of the second mixing means is then transp~rted to a pulp washing system. In the effluent of b~th the first mixing means and the second mixing meanst a means 27' for 6ensing the residual bleaching chemical present therein is ~se~ as a means of controlling the 3. 16~5~
quantity of bleaching chemical in each respective chemical stream. The sensing means 27, 27' is interlocked to a solenoid-opera~ed control valve 28, 28' which varies the flow rate of the bleaching chemical as necessary. The sensing means utilized by the present invention can be a conventional device which measures oxidation-reduction potential. That is, the sensing means 27, 27' may be of a type which measures the difference in emf, or voltage, between a reference electrode and a measuring electrode It will thus be seen that according to the present invention a simple and effective method and apparatus for bleaching pulp, taking into account the relatively high liquor content of reject material, has been provided. The pulp produced according to the invention has little "dirt" compared to pulp produced according to prior art methods and apparatus.
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent assemblies and methods.
together with a sufficient quantity of bleaching chemical 23. The ef~luent 24 of the mixture ~s subsequently reintroduced to the accept~ material 10 at feed point 25. The bleached reject material and the unbleached accept material flow concur-rently to a second mixing means 26 (&uch as in U~S. Patent 4,093,506) wherein a ~ufficient ~uantity of bleaching chemical is introduced through conduit 24'. The effluent of the second mixing means is then transp~rted to a pulp washing system. In the effluent of b~th the first mixing means and the second mixing meanst a means 27' for 6ensing the residual bleaching chemical present therein is ~se~ as a means of controlling the 3. 16~5~
quantity of bleaching chemical in each respective chemical stream. The sensing means 27, 27' is interlocked to a solenoid-opera~ed control valve 28, 28' which varies the flow rate of the bleaching chemical as necessary. The sensing means utilized by the present invention can be a conventional device which measures oxidation-reduction potential. That is, the sensing means 27, 27' may be of a type which measures the difference in emf, or voltage, between a reference electrode and a measuring electrode It will thus be seen that according to the present invention a simple and effective method and apparatus for bleaching pulp, taking into account the relatively high liquor content of reject material, has been provided. The pulp produced according to the invention has little "dirt" compared to pulp produced according to prior art methods and apparatus.
While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment thereof, it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent assemblies and methods.
Claims (13)
1. A method for treating unbleached pulp flowing in a continuous stream and having a consistency of about 8-12%
throughout treatment, comprising the steps of:
a) screening the pulp in the continuous stream to provide a reject stream and an accept stream, the reject stream containing material having relatively high lignin content compared to material in the accept stream;
b) refining the reject pulp material;
c) mixing the reject pulp material with sufficient bleaching chemical at a mixing station to effect a desired degree of delignification thereof;
d) while it is flowing in the reject stream, determining the residual bleaching chemical in the reject pulp material stream downstream of the mixing station;
e) controlling the quantity of bleaching chemical added in step c) in response to the determination in step d) of the amount of residual bleaching chemical;
f) feeding the delignified reject pulp material to the accept stream at a feed point; and g) mixing the pulp material in the accept stream combined with the delignified reject pulp material, downstream of the feed point, with sufficient bleaching chemical to effect a desired degree of delignification thereof.
throughout treatment, comprising the steps of:
a) screening the pulp in the continuous stream to provide a reject stream and an accept stream, the reject stream containing material having relatively high lignin content compared to material in the accept stream;
b) refining the reject pulp material;
c) mixing the reject pulp material with sufficient bleaching chemical at a mixing station to effect a desired degree of delignification thereof;
d) while it is flowing in the reject stream, determining the residual bleaching chemical in the reject pulp material stream downstream of the mixing station;
e) controlling the quantity of bleaching chemical added in step c) in response to the determination in step d) of the amount of residual bleaching chemical;
f) feeding the delignified reject pulp material to the accept stream at a feed point; and g) mixing the pulp material in the accept stream combined with the delignified reject pulp material, downstream of the feed point, with sufficient bleaching chemical to effect a desired degree of delignification thereof.
2. A method of treating pulp material as recited in claim 1 wherein said pulp material is of about 10% consistency.
3. A method of treating pulp material as recited in claim 1 wherein steps c) and e) are practiced by adding Cl2 during mixing.
4. A method of treating pulp material as recited in claim 1 wherein steps c) and e) are practiced by adding ClO2 during mixing.
5. A method of treating pulp material as recited in claim 1 wherein steps c) and e) are practiced by adding a combination of Cl2 and ClO2 during mixing.
6. A method as recited in claim 1 wherein step f) is practiced so that the feed point is downstream of where said screening step a) is practiced.
7. A method as recited in claims 1 or 6 wherein step c) is practiced by adding bleaching chemical selected from the group consisting essentially of C12, ClO2, and mixtures of Cl2 and ClO2; and wherein step c) is practiced by retaining the bleaching chemical and refined reject pulp material together about one minute.
8. A method as recited in claim 1 comprising the further steps of: h) determining the residual bleaching chemical in the accept stream after step g) plus a predetermined retention time; and i) controlling the quantity of bleaching chemical added in step g) in response to the determination of step h) of the amount of residual bleaching chemical.
9. Apparatus for treating pulp material, comprising:
means for transporting pulp material in a continuous stream;
means for screening the pulp stream to divide the pulp into a reject stream with material having a relatively high lignin content, and an accept stream;
means for refining the reject pulp material;
first means for mixing the reject pulp material with bleaching chemical, first means for controlling the quantity of bleaching chemical added to said first mixing means, comprising: means for sensing residual bleaching chemical in the reject stream;
and means for controlling the flow of bleaching chemical to said first mixing means in response to said sensing means;
means for feeding the bleached reject pulp material to the accept pulp material stream at a feed point;
second means for mixing the pulp material in the accept stream combined with the treated reject pulp material with bleaching chemicals, said second mixing means being located downstream of said feed point; and means for controlling the quantity of bleaching chemical added to said second mixing means.
means for transporting pulp material in a continuous stream;
means for screening the pulp stream to divide the pulp into a reject stream with material having a relatively high lignin content, and an accept stream;
means for refining the reject pulp material;
first means for mixing the reject pulp material with bleaching chemical, first means for controlling the quantity of bleaching chemical added to said first mixing means, comprising: means for sensing residual bleaching chemical in the reject stream;
and means for controlling the flow of bleaching chemical to said first mixing means in response to said sensing means;
means for feeding the bleached reject pulp material to the accept pulp material stream at a feed point;
second means for mixing the pulp material in the accept stream combined with the treated reject pulp material with bleaching chemicals, said second mixing means being located downstream of said feed point; and means for controlling the quantity of bleaching chemical added to said second mixing means.
10. An apparatus as recited in claim 9 wherein said means for screening the pulp material is capable of screening pulp material having a consistency of about 8-12%, and wherein said first and second means for mixing the reject pulp material with a bleaching chemical are capable of mixing pulp material having a consistency of about 8-12%.
11. An apparatus as recited in claim 9 wherein said second means for controlling the quantity of bleaching chemical comprises means for sensing residual bleaching chemical; and means for controlling the flow of bleaching chemical to said second mixing means in response to said sensing means.
12. An apparatus as recited in claim 9 wherein said means for controlling the flow of bleaching chemical to said first or second mixing means comprises a solenoid-operated control valve.
13. Apparatus as recited in claim 9 wherein said feed point is downstream of said screening means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US18985380A | 1980-09-22 | 1980-09-22 | |
| US189,853 | 1988-05-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1164259A true CA1164259A (en) | 1984-03-27 |
Family
ID=22699031
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000380005A Expired CA1164259A (en) | 1980-09-22 | 1981-06-17 | Bleaching system for pulp reject treatment |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1164259A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006128950A1 (en) * | 2005-05-03 | 2006-12-07 | M-Real Oyj | Process for producing mechanical pulp suitable for paper or cardboard making |
-
1981
- 1981-06-17 CA CA000380005A patent/CA1164259A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006128950A1 (en) * | 2005-05-03 | 2006-12-07 | M-Real Oyj | Process for producing mechanical pulp suitable for paper or cardboard making |
| NO343830B1 (en) * | 2005-05-03 | 2019-06-17 | Metsae Board Oyj | Process for making mechanical pulp suitable for making paper or cardboard |
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