FI74493B - FOERFARANDE FOER FRAMSTAELLNING AV MEKANISK MASSA, ISYNNERHET KEMIMEKANISK MASSA UTAV RAOMATERIAL AV VED. - Google Patents

Description

74493

Method for producing mechanical pulp, in particular chemimechanical pulp, from wood raw material

The invention relates to a method for producing a mechanical pulp according to the preamble of claim 1.

With regard to the state of the art, reference is made to the following publications: 1. Leask, R.A., Proceedings of the International Mechanical Pulping Conference, Helsinki 1977, vol. 1.

2. Atack, D., Heitner, C., and Karnis, A., Ultra-high yield Pulping of eastern black spruce. Part 2. Svensk Papperstidning 83 (1980): 5, 133-141.

3. Kurra, S., Virkola, N.-E. and Lindholm, C.-A., Effects of uneven impregnation in Chemi-mechanical Pulping, Proceedings of the International Mechanical Pulping Conference, May 6-10, 1985,

Stockholm, pp. 162.

Manufacturing processes for high-yield pulps, especially mechanical (including chemimechanical) pulps, have been the subject of growing interest in recent years. Mechanical pulp usually means pulp that has been substantially defibered, e.g. in a grinder (RMP) or by means of a grindstone (groundwood, GWD). The defibering can also be carried out on chips preheated to 105 ° to 130 ° C, in which case hot-rubbing (TMP) is used. The term chemimechanical pulp (CMP and CTMP), in turn, as used in the context of this invention, means a mechanical pulp which has been defibered in a depressurized or pressurized state using slightly delignifying chemicals. The chemicals are usually impregnated (impregnated) into the chips. The pulps to be produced are ideally suited for the production of tissue papers, but they do not have the same technical pulp properties as chemical pulps, especially sulphate pulp. This is mainly due to their lower strength and flexibility properties and poorer ability to form hydrogen bridges. One important reason for the insufficient paper properties of mechanical pulps is that the proportion of long fibers in the pulps is lower than the corresponding proportion of chemical pulps.

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It is known that the properties of the mechanical pulp improve as the water content of the chips increases [1]. In the manufacture of chemimechanical pulps, the impregnation of the cooking liquid is usually carried out in the liquid phase. It is known that the strengths of a chemimechanical pulp improve with an increase in the intensity of chemical treatment, but the optical properties deteriorate [2]. With the help of chemical treatment, mainly sulfonation, e.g. improves the flexibility of the fibers of the chemimechanical pulp. It is also known that the uniformity of impregnation improves the properties of the pulp [3]. Means have been developed to achieve uniform impregnation of cooking liquids, such as pressing the chips into a constant moisture and simultaneously removing air from inside the chips.

The object of the invention is to eliminate the drawbacks associated with known mechanical, in particular chemimechanical, masses and to provide a new method for producing a mass having good strength properties.

The present invention takes advantage of the finding that the properties of the individual chip particles are not the same, but the chip is divided into two fractions in water: the surface fraction and the bottom fraction. The reasons for the fractionation of chips are manifold, e.g. it is affected by differences in density and hydrophobicity. On the other hand, according to the screening studies, no change in the size distribution of the chips has been observed due to the effect of fractionation. Due to the variety and unexplained causes, the phenomenon has so far not been exploited in the production of pulp, but on the contrary has been avoided. However, fractionation of the chips is simple and can be performed accurately and reproducibly. In connection with our invention, we have found that the phenomenon should be exploited, and our invention is based on subjecting the chips to water fractionation at a suitable stage before rubbing. In the production of a chemimechanical pulp, the fractionation is carried out either before or after the chemical treatment.

The present invention therefore relates to a process for preparing a mechanical pulp, in particular a chemimechanical pulp, by separating two fractions, a surface residue and a submerged fraction, from the chips by means of water. The fraction more suitable for the production of the pulp is then normally produced into pulp, while the other fraction is subjected to post-milling, or it is used, for example, in the production of chemical pulp.

3,74493 To be precise, the method according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

According to an embodiment of the invention, the fractionation of the chips is performed in connection with the washing of the chips. In this case, it is possible to proceed in such a way that the chips obtained from the search are first washed, after which the washed chips are fed into the fractionation tank. However, it is also possible to carry out the washing and fractionation of the chips in succession or even simultaneously in the fractionation tank itself. In the first case, the washed chips are fed into a water basin with a water content of 3 to 10 times, preferably about 4 times the amount of chips in units of weight. The chips introduced into the basin are allowed to separate into surface and bottom fractions by standing with water + chips for about 1 to 30 minutes, preferably about 5 to 10 minutes. The standing time depends mainly on the size of the chip particles and the water temperature. When using ordinary raw water (ie lake water), the water temperature varies according to the season, usually 5e ... 20 * C. The chipping of the chips can be performed in the same basin as the actual fractionation, e.g. by mixing water and the chips for some time, after which the chips are allowed to be fractionated by standing.

After the selected standing time, the surface and bottom fractions are separated. Separation of the surface chip fraction can be performed, for example, by overflowing the surface water and the wood chips therein and possibly enhancing the overflow by means of an impeller. The water is then separated from the chips in a manner known per se, e.g. with a diagonal screw or a water separation screen. The submerged chip fraction, in turn, can be separated from the bottom remaining, e.g., by sucking and pumping a layer of groundwater from the bottom of the basin. This operation can be intensified by using a screw conveyor or a slowly rotating scraper.

In addition to the above, the water fractionation of the chips can, of course, also be carried out continuously. Surface water and groundwater are then discharged from the basin as more water and wood chips are fed into it. In this case, the fractionation tank is preferably elongate in shape, with water and chips being fed to one end thereof. The surface and bottom chips move with the flow of water to the other end of the basin, from where they are then removed, e.g. as described above.

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After fractionation, the chip fractions are used separately as starting materials for pulping. The surface fraction then gives a mechanical pulp with better strength properties. The bottom fraction chips can be post-milled or used to make a chemical pulp.

In a preferred embodiment of the invention, the fractionation is carried out in connection with Kemi-mechanical pulping. It has been found that the qualitative differences between the chip fractions have a particularly favorable effect on the properties of the chemimechanical pulps prepared from the fractions.

In our experiments, we have prepared chemimechanical pulp by grinding fractionated chips from both fractions. When the specific energy consumption of the chips is kept at the same level, the properties of the pulp made from the surface chips are either better or worse than those of the pulp made from the unfractionated or submerged fraction, depending on whether the fractionation was performed before or after sulfonation. It has been found that when the fractionation of the chips is carried out before sulfonation, the pulp made from surface chips is more ground and has better properties than the pulp made from bottom chips. Instead, when the sulfonated chips were fractionated, the pulp made from surface chips was coarser and inferior in properties to the pulp made from bottom chips.

The chips are thus fractionated either before or after chemical treatment (sulfonation). In the former case, the procedure is completely as described above, i.e. the chips are fed to the fractionation tank, after which the surface fraction is made into a benign pulp after chemical treatment, while the bottom fraction is treated by some optional method. In the second case, the whole washed chip is subjected to a chemical treatment, after which the impregnated chip particles are subjected to the fractionation treatment described above. As mentioned above, the impregnated chips give the pulp with the best properties if the bottom fraction is used as the pulp starting material.

The invention provides considerable advantages. Thus, with the method presented, it is possible to produce a better pulp from a part of the chips than from the whole chips or the remaining chips, as the examples below clearly show. A worse mass can be post-milled or used as a coarser mass for purposes other than a better mass.

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The invention will now be examined in more detail by means of a few application examples which illustrate the implementation of the invention in connection with the production of chemimechanical pulp and hot milling.

EXAMPLE 1

Fresh spruce chips made of spruce (400 kg) were poured into water (wood: water = 1: 4), whereupon immediately some of the chips (54%) remained on the surface and some (46%) sank to the bottom. After the operation, the dry matter contents of the fractions were as follows: surface chips: 50%, bottom chips 37% and unfractionated reference chips: 48%. The wood chips left on the surface were separated from the wood chips that had sunk to the bottom. The separated fractions were again immersed in water and it was found that the proportions of the fractions were as indicated above with 95% accuracy.

The chips of the separated fractions and the unfractionated reference chip were treated with sodium sulphite solution under the following conditions: - Na 2 SO 3 content 30 g / l, - DTPA content 1 Z, - liquid / wood ratio 6: 1, - pre-evaporation 95-100 ° C / 20 min, - impregnation 25 - 30 ° C / 15 min, - steam phase treatment 130 ° C / 10 min.

Sulfonation conditions were kept as similar as possible in all treatments.

The sulfonate content of the different chip fractions was obtained: surface chip 0.55%, bottom chip 0.67%, unfractionated chip 0.65%. The specific energy consumption of wood chips under pressure grinding varied between 1.1 and 2.3 MWh / t.

Table 1 shows the dry and wet strengths as well as the optical properties and freeness of pulp sheets made of surface and bottom chips corresponding to the specific energy consumption of 1900 kWh / t. In addition, the table shows the properties of the whole pulp mass when the specific energy consumption was 1900 kWh / t.

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table 1

Surface chip Base chip Full chip

Tensile index [Nm / g] 26 20 22

Tear index [mNm2 / g] 5.5 4.9 5.5

Original brand strength: - tensile index [Nm / g] 1.35 1.3 1.2 - breaking work [mJ / g] 64 54 52 - elongation [%] 4.9 4.3 A, 3

Light scattering coefficient [n »2 /] cg] 48 42 45

Light absorption coefficient [m 2 / kg] 1.9 1.6 1.6

Freeness [ml] 280 380 330 EXAMPLE 2

The spruce chips were sulfonated under the sulfonation conditions set forth in Example 1. After the chemical treatment, the chip fraction remaining on the surface in water (proportion 29%) and the bottom-sinking fraction (proportion 71%) were separated from the chips. The dry matter content of the surface chips after sulfonation and water separation was 36% and that of the bottom chips 33%, respectively. After sulfonation alone, the dry matter content of the whole chip was 42%.

In Table 2, in the previous example, the wet and dry strengths of both the optical properties and the freeness of the pulp sheets made from different chip fractions and the whole chip correspond to the specific energy consumption of 1900 kWh / t.

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Table 2

Surface chip Base chip Full chip

Tensile index [Nm / g] 19 31 27

Tear index [mNm ^ / g] 4.2 6.3 6.0

Original wet strength: - tensile index [Nm / g] 1.1 1.45 1.35 - breaking work [mJ / g] 43 83 63 - elongation [%] 4.1 5.3 5.1

Light scattering coefficient [m2 / kg 46 43 48

Light absorption coefficient [m * / kg] 2.1 2.1 2.3

Freeness [ml] 430 220 270

Table 3 compares the properties of pulps made from surface chips and bottom chips in the above examples. In the case of Example 1, it has been calculated what percentage of the properties of the pulps made from surface chips differ in their values from the properties of the pulps made from the bottom chips and the pulps made from the whole chips, respectively.

Correspondingly, in the case of Example 2, the percentage deviations of the properties of the pulps made from bottom chips from the properties of the pulps made from surface chips and the whole chips, respectively, have been calculated.

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Table 3

Eg 1 surface chip mass Example 2 bottom chip mass superiority [%] in relation to superiority [%] in relation to bottom chip size.

Traction index +30 +18 +63 +15

Tear index +12 0 +50 +5

Rest. wet strength:! - traction index +4 +12 +32 +7 - breaking work +19 +23 +93 +32 - elongation +14 +14 +22 +4

Light scattering coefficient +14 +7 +4 0

Valonabs. coefficient +19 +19 0 -9

Freeness -26 -15 -49 -19

According to Table 3, when fractionation is performed before sulfonation, the pulp made from surface chips is finer (freeness lower) and the properties of the pulp are better than the pulp made from bottom chips. When the chips are fractionated after sulfonation, the pulp made from surface chips is coarser and has poorer properties than the pulp made from bottom chips. The order in which the treatments are carried out is thus essential for the properties of the pulp. The properties of the pulps made from the whole chip are between the properties of the pulps made from the chip fraction.

Comparing the properties of pulps made from surface and bottom chips by comparing the values of the properties corresponding to the same freeness level (300 ml) with the specific energy consumption used to make that pulp gives indicators describing the pulps at the same freeness level and specific energy consumption level. The freeness of the masses collected in Table 4 was thus 300 ml and in the case where fractionation was performed before sulfonation, the specific energy consumption was EOK surface = 1.85 MWh / t, EOK bottom = 2.05 MWh / t, EOK size * 2.0 MWh / t and respectively when sulfonation was performed before fractionation EOK surface = 2.1 MWh / t, EOK bottom = 1.7 MWh / t and EOK size = 1.8 MWh / t.

Pulp prepared in Example 1: Fractionation of chips before sulfonation and grinding.

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Table 4

Surface chip Base chip Full chip

Veto index / EOK 15 14 14

Tear Index / EOK 2.9 2.8 2.8

Original wet strength: - tensile index / EOK 0.73 0.66 0.68 - breaking work / EOK 34 30 28 - elongation / EOK 2.5 2.2 2.3

Light scattering coefficient / EOK 25 22 23

Light absorption coefficient / EOK 1.0 0.9 0.9

Pulp prepared in Example 2: Fractionation of chips after sulfonation and grinding.

Table 5

Surface chip Base chip Full chip

Veto index / EOK 11 16 15

Tear Index / EOK 2.3 2.6 3.2

Original wet strength: - tensile index / EOK 0.62 0.80 0.71 - breaking work / EOK 28 39 32 - elongation / EOK 2.2 2.8 2.6

Light scattering coefficient / EOK 24 26 26

Light absorption coefficient / EOK 1.1 1.1 1.3

Table 6 shows how many percent of the pulp chips differ from the base chips and the whole chips, respectively (Example 1), and in the case of Example 2, what percentage of the chips pulps differ from the surface chips.

Table 6 10 74493

Eg 1 surface chip mass Example 2 bottom chip mass superiority [%] in relation to superiority [%] in relation to bottom chip chip.surface chip chip.applied to mass to mass mass

Veto index / EOK +7 +7 +45 +7

Tear index / EOK +4 +4 +56 -19

Rest. wet strength: - tensile index / EOK +11 +7 +29 +13 - fracture work / EOK +13 +21 +39 +22 - elongation / EOK +14 +9 +27 +8 j Light emitter / EOK +14 +9 + 8 0 | Valonabs.kerr./EOK +25 +11 0 -15 EXAMPLE 3

Fresh log spruce chips (400 kg) were poured into water (wood: water = 1: 4), leaving some of the chips (55%) on the surface and some (45%) sinking to the bottom. After the operation, the dry matter contents of the fractions were as follows: surface chips: 45% and bottom chips 36%. The dry matter content of the unfractionated control chip was 44%.

From the separated fractions, hot milling (TMP) was prepared to different freeness levels by changing the specific energy consumption. Table 7 shows the properties at a freeness level of 150 ml according to the commonly used method.

Table 7 n 74493

Surface chips Bottom chips Whole chips Tensile index [Nm / g] 2 ^

Tear index [mNm ^ / g] 5.3, »

Original wet strength: - tensile index [Nm / g] '' - breaking work [mj / g] - elongation [%] 5 »> *

Light scattering coefficient [m ^ / fcg] ^ 1 '

Light absorption coefficient [m ^ / kg] 2,3 2 * '

Specific energy consumption [MWh / 1] 1> ^ 5, 35,

From an economic point of view, when comparing masses, it is interesting to relate the properties of the masses to the same energy consumption. Table 8 shows the key figures that describe the masses at the same freeness level and with the same specific energy consumption value.

Table 8

Surface chip Base chip Full chip

Veto index / EOK 20 20 18

Tear Index / EOK 3.7 3.9 3.5

Original wet strength: - tensile index / EOK 0.90 0.96 0.84 - breaking work / EOK 47 50 44 - elongation / EOK 3.9 4.2 3.7

Light scattering coefficient / EOK 42 43 38

Light absorption coefficient / EOK 1.6 1.7 1.5

~ '------- 1' '- I' I

Table 9 compares the best pulp made from bottom chips with the pulp made from both surface chips and whole chips based on the values in Table 8. The differences are expressed as percentages.

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Table 9 Superiority of base chip mass [%] in relation to surface chip total mass

Tensile index 0 +11

Tear index +7 +15

Rest. wet strength: - tensile index +7 +14 - breaking work +6 +14 - elongation +8 +14

Valonsir.kerr. +2 +13

Valonabs.kerr. +6 +13

Within the framework of the invention, it is also possible to consider solutions that differ from the above examples. Thus, fractionation can also be carried out using, in addition to ordinary raw water or purified water, e.g. water containing a chemical. This has either been added to the water to promote fractionation, or it has migrated into it with the chips. Instead of water, another suitable liquid of suitable density, such as an alcohol, can also be used.

Claims (9)

1. A method for the preparation of mechanical pulp from wood frame material, according to which the process is to decompose the frame material into chips which are deflected essentially mechanically, characterized in that - they are fractionated by adding the wood in water, allowing it to spread into a surface fraction and a bottom fraction , and by removing the fractions separately from the water, and - the ice fractions are subjected to continued treatment separately from each other for the production of pulp. Process according to claim 1, characterized in that a liquid / water ratio of between 1: 3 and 1:10 is used, preferably about 1: 4. Method according to claim 1 or 2, characterized in that the fractionation is carried out in a sedimentation pool, the sedimentation time used being between 1 and 30 minutes. 4. Method according to claim 1 or 2, characterized in that the fractionation is carried out in a continuously functioning flow-through pool. . ·. Process according to any of the preceding claims for the production of mechanical pulp with good shelf strength characteristics, characterized in that for the production of the desired pulp, only the chip fraction which is better suited for the production of mechanical pulp is defibrated. Process according to claim 5, characterized in that the second fraction is refined and / or used for the preparation of ceramic pulp. Method according to claim 5 or 6 for the production of thermo-mechanical pulp, characterized in that the bottom fraction is used for the defibration. 8. A method according to claim 5 or 6 for the preparation of chemical-mechanical pulp, in which the process of water fractionation is carried out before