CA2285148A1 - Chemimechanical or mechanical pulp manufacture with reduced energy consumption - Google Patents
Chemimechanical or mechanical pulp manufacture with reduced energy consumption Download PDFInfo
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- CA2285148A1 CA2285148A1 CA002285148A CA2285148A CA2285148A1 CA 2285148 A1 CA2285148 A1 CA 2285148A1 CA 002285148 A CA002285148 A CA 002285148A CA 2285148 A CA2285148 A CA 2285148A CA 2285148 A1 CA2285148 A1 CA 2285148A1
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- Prior art keywords
- stage
- temperature
- carried out
- softening temperature
- raw material
- 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.)
- Abandoned
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/02—Pretreatment of the raw materials by chemical or physical means
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Processing Of Solid Wastes (AREA)
- Paper (AREA)
Abstract
Energy consumption is reduced when producing chemimechanical or mechanical pulp from pieces of pulp raw material, such as wood chips, sawdust, straw chaff or bagasse chaff, in a refiner, by subjecting the pieces of pulp raw material to bulk-density reducing plastic deformation between compression rolls prior to refining said material, this plastic deformation being continued until a reduction in bulk density of 35-65% is reached.
Description
CHEMIMECHANICAL OR MECHANICAL PULP MANUFACTURE WITH REDUCED
ENERGY CONSUMPTION
The present invention relates to a method of reducing energy consumption in the chemimechanical or mechanical manufacture of pulp from pieces of pulp raw material, such as wood chips, straw chaff or bagasse chaff, in refiners.
A large number methods of compressing pulp raw materials with the intention of lowering energy consumption in the manufacture of chemimechanical and mechanical pulp have been proposed earlier in the art. For instance, axial precompression of wood has been proposed (Frazier, W.C. and . Williams, G.J., (1982), "Reduction of specific energy in mechanical pulping by axial precompression of wood", Pulp and Paper Can., 86:6, 87) and screw compression of chips (Hartler, N., (1995), "Aspects on curled and microcompressed fibres", Nordic Pulp Paper Res. J., 1,4). The energy gains achieved, however, have been moderate in relation to investment costs and in relation to the energy consumed by screw compression. With the intention of facilitating suction of chemical solution into chips, it has also been suggested that the chips are compressed between rolls and the compressed chips immersed directly into the chemical solution for expansion therein.
An object of the present invention is to provide a novel and advantageous method of reducing energy consumption in chemimechanical (e. g. CTMP) or mechanical (e. g. TMP) pulp manufacturing processes in refiners.
ENERGY CONSUMPTION
The present invention relates to a method of reducing energy consumption in the chemimechanical or mechanical manufacture of pulp from pieces of pulp raw material, such as wood chips, straw chaff or bagasse chaff, in refiners.
A large number methods of compressing pulp raw materials with the intention of lowering energy consumption in the manufacture of chemimechanical and mechanical pulp have been proposed earlier in the art. For instance, axial precompression of wood has been proposed (Frazier, W.C. and . Williams, G.J., (1982), "Reduction of specific energy in mechanical pulping by axial precompression of wood", Pulp and Paper Can., 86:6, 87) and screw compression of chips (Hartler, N., (1995), "Aspects on curled and microcompressed fibres", Nordic Pulp Paper Res. J., 1,4). The energy gains achieved, however, have been moderate in relation to investment costs and in relation to the energy consumed by screw compression. With the intention of facilitating suction of chemical solution into chips, it has also been suggested that the chips are compressed between rolls and the compressed chips immersed directly into the chemical solution for expansion therein.
An object of the present invention is to provide a novel and advantageous method of reducing energy consumption in chemimechanical (e. g. CTMP) or mechanical (e. g. TMP) pulp manufacturing processes in refiners.
To this end, it is proposed in accordance with the invention that when proceeding in the manner described in the introduction, the pieces of pulp raw material are subjected to bulk-density reducing plastic deformation between compression rolls prior to refining the material, this plastic deformation being continued until a reduction in bulk density of 35-65% is achieved. It has been found quite surprisingly that the compression treatment proposed in accordance with the invention, this compression treatment having a low energy-input requirement (e.g. in the order of 30 kWh per tonne of pulp raw material), can result in energy savings of several hundred kWh in the subsequent refining process.
Co-acting rolls are suitably driven at different peripheral speeds, conveniently with a speed difference of 5-50%, e.g.
30-50%, between the rolls. The latter may advantageously present a shallow pattern for establishing a certain amount of friction against the pulp raw material, so as to facilitate introduction of the raw material into the roll nip. When the moisture content of the pulp raw material is very low or uneven, it may be beneficial to steam said material prior to compression treatment, to obtain a more uniform product.
In order to obtain uniform quality, it is also advantageous to orientate the pieces of pulp raw material in a similar fashion, preferably so that the fibre direction will define only small angles with the axial direction of the rolls. For instance, it is desirable that the fibre direction of at least the major part of the pieces of pulp raw material defines an angle of less than 45° with the roll axes prior to said material passing between the rolls.
From an energy aspect, the inventive method of procedure will preferably be independent of whether or not the refining stages that follow compression of the material are effected at a temperature above or below the lignin softening temperature, although a particular advantage is afforded when the first refining stage is carried out at a temperature above the lignin softening temperature, since this enables fibre shortening that accompanies refining of the compressed chips at temperature beneath the lignin softening temperature to be avoided. This is thought to be due to the fact that compression of the material between the rolls causes microcracks to form in the fibre walls in the wood, meaning that separation of the fibres in the disc refiner takes place in the fibre walls and not in the lignin-rich centre lamellae, even at temperatures above the lignin softening temperature (above 150°C). Thus, the invention enables significant advantages to be achieved when refining is carried out in at least two stages, wherein the first and the second stage are both carried out at temperatures above the lignin softening temperature, or wherein the first stage is carried out at a temperature above the lignin softening temperature and the second stage is carried out at a temperature beneath the lignin softening temperature.
Significant advantages can be achieved with a roll-precompression of the kind concerned, even when refining in one stage at high temperature, roughly in accordance with the original Asplund method. The invention also enables significant advantages to be achieved when the first stage is carried out at a temperature beneath the lignin softening temperature and the second stage is carried out at a temperature above the lignin softening temperature in accordance with SE-B-470 555, or the second stage is also carried out at a temperature beneath the lignin softening temperature as in the case of traditional TMP production.
The aforesaid advantages will be evident from the following Tables, which illustrate results obtained when applying the invention on a laboratory scale on pine chips. Precompression was carried out on chips of normal size, between generally smooth rolls having a diameter of about 300 mm and a roll nip 'smaller than 0.5 mm. The rolls rotated at respective speeds of 20 and 40 rpm and gave a bulk density reduction of 60% at an energy input of less than 30 kWh/tonne chips.
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Column No. 1 in the Table shows in the left sub-column a conventional chemimechanical process, a CTMP process, in which two refining stages were both carried out at 130°C, i.e. beneath the lignin softening temperature. At a total refining energy of 1850 kWH/tonne chips, there was obtained a freeness or dewatering capacity of 350, expressed as Canadian Standard Freeness. It will be seen from the centre column in column 1 that only 1150 kWh/tonne was required to achieve the same dewatering capacity with chips pretreated by roll-compression, in other words energy corresponding to almost 700 kWh/tonne can be saved when producing a corresponding pulp when the chips have been precompressed in the manner proposed by the present invention. A certain amount of fibre shortening occurs, as made evident by a lower tear index, although this need not always imply a drawback. With a total refining energy input of 1500 kWh (right sub-column) there was obtained with an unchanged tear index a lower dewatering capacity and significantly increased tensile index, at an energy saving of above 300 kWh/tonne.
In Column No. 2, the left sub-column and the centre sub-column show refining of uncompressed chips at a temperature of 175°C, i.e. a temperature well above the lignin softening temperature, at a respective energy input of 1620 and 1800 kWh/tonne. These two tests can be considered to illustrate a conventional Asplund method. The pulp obtained in the left sub-column cannot be used for paper manufacture. Subsequent to precompression of the chips in accordance with the invention, there is obtained according to column 3 a pulp which is fully comparable with modern TMP at a low total refining energy. Division of the refining step into two mutually sequential steps at 175°C and an unchanged total refiner energy input gives the same results as those shown in column No. 2.
The left sub-column of column No. 3 illustrates the manufacture of TMP in accordance with SE-B-470 555. As evident from the centre sub-column after precompression of the chips in accordance with the invention corresponding results are obtained with a 200 kWh/tonne lower total refiner energy input, with the exception of a certain degree of fibre shortening. According to sub-column 3, an essentially unchanged refiner energy input results in a lower dewatering capacity and higher tensile index. As evident from column No.
' 2, right sub-column, an increase in the temperature in the first refining stage results in lower energy consumption, higher tensile index and higher index.
The left sub-column of column No. 4 illustrates conventional two-stage TMP manufacture in refiners at temperatures beneath the lignin softening temperature. Subsequent to precompression in accordance with the present invention, there is obtained according to the centre sub-column the same dewatering capacity at a refiner energy saving of more than 600 kWh/tonne pulp. The tensile index and tear index values are lower, however. According to the right sub-column, unchanged refiner energy results in a decreased dewatering capacity and increased tensile index.
The two left sub-columns of column No. 5 illustrate TMP
manufacture in two refiner stages, of which the first stage is carried out at a temperature in the region of or immediately above the lignin softening temperature, whereas the second stage is carried out at temperatures that lie beneath the lignin softening temperature. The two right sub-columns illustrate the same TMP manufacture subsequent to precompression of the chips in accordance with the invention.
It is evident that significant savings in refiner energy can be made while retaining the dewatering capacity essentially unchanged and obtaining improved tensile index and tear index values.
It will be understood that the invention is not restricted to the aforedescribed exemplifying embodiments thereof and that it can be implemented in any desired manner within the scope of the inventive concept as defined in the following Claims.
It can be mentioned in this connection that relative movement between the compression rolls can also be achieved by mutual axial displacement of the rolls and can replace or be combined with the relative movement that is achieved by rotating the rolls at different speeds, as described above.
Co-acting rolls are suitably driven at different peripheral speeds, conveniently with a speed difference of 5-50%, e.g.
30-50%, between the rolls. The latter may advantageously present a shallow pattern for establishing a certain amount of friction against the pulp raw material, so as to facilitate introduction of the raw material into the roll nip. When the moisture content of the pulp raw material is very low or uneven, it may be beneficial to steam said material prior to compression treatment, to obtain a more uniform product.
In order to obtain uniform quality, it is also advantageous to orientate the pieces of pulp raw material in a similar fashion, preferably so that the fibre direction will define only small angles with the axial direction of the rolls. For instance, it is desirable that the fibre direction of at least the major part of the pieces of pulp raw material defines an angle of less than 45° with the roll axes prior to said material passing between the rolls.
From an energy aspect, the inventive method of procedure will preferably be independent of whether or not the refining stages that follow compression of the material are effected at a temperature above or below the lignin softening temperature, although a particular advantage is afforded when the first refining stage is carried out at a temperature above the lignin softening temperature, since this enables fibre shortening that accompanies refining of the compressed chips at temperature beneath the lignin softening temperature to be avoided. This is thought to be due to the fact that compression of the material between the rolls causes microcracks to form in the fibre walls in the wood, meaning that separation of the fibres in the disc refiner takes place in the fibre walls and not in the lignin-rich centre lamellae, even at temperatures above the lignin softening temperature (above 150°C). Thus, the invention enables significant advantages to be achieved when refining is carried out in at least two stages, wherein the first and the second stage are both carried out at temperatures above the lignin softening temperature, or wherein the first stage is carried out at a temperature above the lignin softening temperature and the second stage is carried out at a temperature beneath the lignin softening temperature.
Significant advantages can be achieved with a roll-precompression of the kind concerned, even when refining in one stage at high temperature, roughly in accordance with the original Asplund method. The invention also enables significant advantages to be achieved when the first stage is carried out at a temperature beneath the lignin softening temperature and the second stage is carried out at a temperature above the lignin softening temperature in accordance with SE-B-470 555, or the second stage is also carried out at a temperature beneath the lignin softening temperature as in the case of traditional TMP production.
The aforesaid advantages will be evident from the following Tables, which illustrate results obtained when applying the invention on a laboratory scale on pine chips. Precompression was carried out on chips of normal size, between generally smooth rolls having a diameter of about 300 mm and a roll nip 'smaller than 0.5 mm. The rolls rotated at respective speeds of 20 and 40 rpm and gave a bulk density reduction of 60% at an energy input of less than 30 kWh/tonne chips.
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Column No. 1 in the Table shows in the left sub-column a conventional chemimechanical process, a CTMP process, in which two refining stages were both carried out at 130°C, i.e. beneath the lignin softening temperature. At a total refining energy of 1850 kWH/tonne chips, there was obtained a freeness or dewatering capacity of 350, expressed as Canadian Standard Freeness. It will be seen from the centre column in column 1 that only 1150 kWh/tonne was required to achieve the same dewatering capacity with chips pretreated by roll-compression, in other words energy corresponding to almost 700 kWh/tonne can be saved when producing a corresponding pulp when the chips have been precompressed in the manner proposed by the present invention. A certain amount of fibre shortening occurs, as made evident by a lower tear index, although this need not always imply a drawback. With a total refining energy input of 1500 kWh (right sub-column) there was obtained with an unchanged tear index a lower dewatering capacity and significantly increased tensile index, at an energy saving of above 300 kWh/tonne.
In Column No. 2, the left sub-column and the centre sub-column show refining of uncompressed chips at a temperature of 175°C, i.e. a temperature well above the lignin softening temperature, at a respective energy input of 1620 and 1800 kWh/tonne. These two tests can be considered to illustrate a conventional Asplund method. The pulp obtained in the left sub-column cannot be used for paper manufacture. Subsequent to precompression of the chips in accordance with the invention, there is obtained according to column 3 a pulp which is fully comparable with modern TMP at a low total refining energy. Division of the refining step into two mutually sequential steps at 175°C and an unchanged total refiner energy input gives the same results as those shown in column No. 2.
The left sub-column of column No. 3 illustrates the manufacture of TMP in accordance with SE-B-470 555. As evident from the centre sub-column after precompression of the chips in accordance with the invention corresponding results are obtained with a 200 kWh/tonne lower total refiner energy input, with the exception of a certain degree of fibre shortening. According to sub-column 3, an essentially unchanged refiner energy input results in a lower dewatering capacity and higher tensile index. As evident from column No.
' 2, right sub-column, an increase in the temperature in the first refining stage results in lower energy consumption, higher tensile index and higher index.
The left sub-column of column No. 4 illustrates conventional two-stage TMP manufacture in refiners at temperatures beneath the lignin softening temperature. Subsequent to precompression in accordance with the present invention, there is obtained according to the centre sub-column the same dewatering capacity at a refiner energy saving of more than 600 kWh/tonne pulp. The tensile index and tear index values are lower, however. According to the right sub-column, unchanged refiner energy results in a decreased dewatering capacity and increased tensile index.
The two left sub-columns of column No. 5 illustrate TMP
manufacture in two refiner stages, of which the first stage is carried out at a temperature in the region of or immediately above the lignin softening temperature, whereas the second stage is carried out at temperatures that lie beneath the lignin softening temperature. The two right sub-columns illustrate the same TMP manufacture subsequent to precompression of the chips in accordance with the invention.
It is evident that significant savings in refiner energy can be made while retaining the dewatering capacity essentially unchanged and obtaining improved tensile index and tear index values.
It will be understood that the invention is not restricted to the aforedescribed exemplifying embodiments thereof and that it can be implemented in any desired manner within the scope of the inventive concept as defined in the following Claims.
It can be mentioned in this connection that relative movement between the compression rolls can also be achieved by mutual axial displacement of the rolls and can replace or be combined with the relative movement that is achieved by rotating the rolls at different speeds, as described above.
Claims (10)
1. A method of reducing energy consumption in the chemimechanical or mechanical manufacture of pulp from pieces of pulp raw material, such as wood chips, sawdust, straw chaff or bagasse chaff, in refiners, characterised by subjecting the pieces of pulp raw material to a bulk-density reducing plastic deformation between compression rolls prior to refining said material, said plastic deformation being continued until a reduction in bulk density of 35-65% has been achieved.
2. A method according to Claim 1, characterised by rotating co-acting rolls at different peripheral speeds, suitably at a speed difference of 5-50%, for instance 30-50%.
3. A method according to Claim 1 or 2, characterised by using rolls that exhibit solely a shallow pattern for generating friction against the pulp raw material.
4. A method according to any one of Claims 1-3, characterised by carrying out said deformation process on steamed pulp raw material.
5. A method according to any one of Claims 1-4, characterised by orientating the pieces of pulp raw material prior to their passage through the rolls, so that the fibre direction of at least the major part of said pieces will define with the roll axes an angle of less than 45°.
6. A method according to any one of Claims 1-5, characterised by carrying out said refining process in at least one first and one second stage at a temperature above the lignin softening temperature.
7. A method according to any one of Claims 1-5, characterised by carrying out the refining process in at least one first and one second stage, wherein said first stage is carried out at a temperature beneath the lignin softening temperature and the second stage is carried out at a temperature above the lignin softening temperature.
8. A method according to any one of Claims 1-5, characterised in that the refining process is carried out in one stage at a temperature above the lignin softening temperature.
9. A method according to any one of Claims 1-5, characterised in that the refining process is carried out at least in one first and one second stage at a temperature beneath the lignin softening temperature.
10. A method according to any one of Claims 1-5, characterised in that the refining process is carried out at least in one first and one second stage, wherein the first stage is carried out at a temperature above the lignin softening temperature and the second stage is carried out at a temperature beneath the lignin softening temperature.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9702194A SE9702194L (en) | 1997-06-09 | 1997-06-09 | Chemical mechanical or mechanical pulping with reduced energy consumption |
| CA002285148A CA2285148A1 (en) | 1997-06-09 | 1999-10-05 | Chemimechanical or mechanical pulp manufacture with reduced energy consumption |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9702194A SE9702194L (en) | 1997-06-09 | 1997-06-09 | Chemical mechanical or mechanical pulping with reduced energy consumption |
| CA002285148A CA2285148A1 (en) | 1997-06-09 | 1999-10-05 | Chemimechanical or mechanical pulp manufacture with reduced energy consumption |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2285148A1 true CA2285148A1 (en) | 2001-04-05 |
Family
ID=25681238
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002285148A Abandoned CA2285148A1 (en) | 1997-06-09 | 1999-10-05 | Chemimechanical or mechanical pulp manufacture with reduced energy consumption |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2285148A1 (en) |
| SE (1) | SE9702194L (en) |
-
1997
- 1997-06-09 SE SE9702194A patent/SE9702194L/en unknown
-
1999
- 1999-10-05 CA CA002285148A patent/CA2285148A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| SE9702194L (en) | 1998-12-10 |
| SE9702194D0 (en) | 1997-06-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |