Preparation method of low-dirt-degree and high-strength bleached sulfate mixed broadleaf wood wet wood pulp and pulp board

Abstract

The invention belongs to the technical field of pulp paper production, and particularly relates to a preparation method of low-dirt-degree and high-strength bleached sulfate mixed broadleaf wood wet wood pulp and pulp board. According to the invention, the acacia mangium chips and the eucalyptus chips are mixed and prepared, so that a foundation is laid for obtaining subsequent high-quality products; mixed wood chips are pre-impregnated in impregnation liquid with the effective alkali content being 4-8 g / L, so that the wood chips can react quickly in the cooking stage, and resin in broadleaf wood is eliminated; the wood chips are cooked, knotted, screened and washed, so that impurities in the slurry can be eliminated again; and by performing oxygen delignification treatment and bleaching on the coarse pulp, the quality of the pulp is improved. Therefore, the mixed broadleaf wood wet wood pulp and wood pulp board prepared by the preparation method disclosed by the invention are excellent in various indexes, low in dust degree, high in tension resistance, tear-resistant and breakage-resistant, and high-quality mixed wood pulp is provided for customers of paper for daily use.

Description

Technical Field

[0001] The invention belongs to the technical field of pulp and paper production, and in particular relates to a preparation method of low-dust and high-strength bleached kraft mixed broadleaf wet wood pulp and pulp board. Background Art

[0002] In recent years, as people's environmental awareness has increased, the country has continuously strengthened the protection and control of forest resources. At the same time, as people's living standards continue to improve, people's demand for paper products has also gradually increased. In this context, wood, as the main raw material for wood pulp production, can no longer be maintained in a stable single-species raw material production mode.

[0003] Wood pulp can be divided into hardwood pulp and softwood pulp. As for hardwood, the kraft pulping method is mostly used. Compared with softwood, it has the characteristics of less consumption of cooking chemicals, higher yield, higher whiteness and lower consumption of bleaching chemicals, so it is often used to make wood pulp. However, the presence of resin deposition in hardwood pulp often leads to poor strength of wet wood pulp and pulp board and higher dust content, which is not conducive to obtaining high-quality products and it is difficult to meet customers' demand for wood pulp and pulp board. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing low-dust, high-strength bleached sulfate mixed hardwood wet pulp and pulp board, which not only reduces the dustiness of the pulp, but also improves the strength of the pulp, thereby facilitating the acquisition of high-quality wet pulp and pulp board.

[0005] The present invention provides a method for preparing low-dust and high-strength bleached kraft mixed hardwood wet pulp, comprising the following steps:

[0006] Mixing acacia wood chips and eucalyptus wood chips to obtain mixed wood chips;

[0007] pre-impregnating the mixed wood chips in an impregnation liquid to obtain pre-impregnated wood chips;

[0008] Cooking the pre-impregnated wood chips with white liquor to obtain a rough pulp;

[0009] The crude pulp is sequentially subjected to de-sectioning, screening and washing to obtain washed crude pulp;

[0010] The washed brown pulp is subjected to oxygen delignification treatment to obtain pulp;

[0011] The pulp is subjected to D0 stage bleaching, EO stage bleaching, D1 stage bleaching and D2 stage bleaching in sequence to obtain the mixed hardwood wet pulp;

[0012] The impregnation liquid includes white liquor and / or black liquor; the effective alkali content in the impregnation liquid is 4-8g / L.

[0013] Preferably, during the mixing and preparing, the mass ratio of acacia wood chips to eucalyptus wood chips is 5-8:2-5;

[0014] The varieties of the acacia wood chips include: Acacia mangium and / or Acacia crassicarpa;

[0015] The species of the eucalyptus chips preferably include one or more of fast-growing eucalyptus, small-leaved eucalyptus, bright-fruited eucalyptus, blue eucalyptus, dunn's eucalyptus and straight-stem eucalyptus.

[0016] Preferably, the pre-impregnation temperature is 80-110° C.; the pre-impregnation time is 60-80 min.

[0017] Preferably, during the cooking, the concentration of sodium hydroxide in the white liquor is 100-108 g / L, and the amount of white liquor is 250-350 kg / adt;

[0018] The cooking time is 200 to 300 minutes.

[0019] Preferably, the knot removal comprises: performing first-stage knot removal and second-stage knot removal on the rough pulp in sequence to obtain the good pulp;

[0020] During the first stage of the de-slagging process, the slag removal rate is 5% to 15%.

[0021] Preferably, the oxygen delignification treatment comprises: sequentially performing a first stage oxygen delignification treatment and a second stage oxygen delignification treatment on the washed brown pulp;

[0022] In the one-stage oxygen delignification treatment, the amount of oxygen used is 10-11 kg / adt, and the amount of sodium hydroxide used is 8-15 kg / adt;

[0023] In the two-stage oxygen delignification treatment, the amount of oxygen used is 15-20 kg / adt.

[0024] Preferably, in the D0 stage bleaching process, the amount of chlorine dioxide used is 10-15 kg / adt, and the amount of sulfuric acid used is 2-4 kg / adt;

[0025] In the EO stage bleaching process, the amount of sodium hydroxide used is 7-10 kg / adt, and the amount of oxygen used is 3.5-4.5 kg / adt;

[0026] In the D1 stage bleaching process, the amount of chlorine dioxide used is 3-6 kg / adt;

[0027] In the D2 stage bleaching process, the dosage of chlorine dioxide is 1-2 kg / adt.

[0028] The present invention provides a mixed hardwood wet pulp prepared by the preparation method of the above technical solution, wherein the mixed hardwood wet pulp has a tensile index of >75Nm / g and a tear index of >7.0Nm / g. 2 / g, bursting index>4.5kPa m 2 / g, dichloromethane extract <0.3wt%, dust density <3.0mm 2 / m 2 , whiteness ≥88%ISO

[0029] The present invention provides a method for preparing a low-dust, high-strength bleached kraft mixed hardwood pulp board, comprising the following steps:

[0030] The mixed hardwood wet pulp is prepared by the preparation method described in the above technical solution;

[0031] The mixed hardwood wet pulp is papermade to obtain a mixed hardwood pulp board.

[0032] The present invention provides a mixed hardwood pulp board prepared by the preparation method described in the above technical solution, characterized in that the mixed hardwood pulp board has a tensile index of >72Nm / g and a tear index of >6.8mNm 2 / g, bursting index>4.0kPa m 2 / g, dichloromethane extract <0.4wt%, dust density <1.0mm 2 / m 2 , whiteness ≥88% ISO.

[0033] The present invention provides a method for preparing low-dust, high-strength bleached sulfate mixed broadleaf wet wood pulp. By mixing acacia wood chips and eucalyptus wood chips for material preparation, a foundation is laid for subsequent high-quality products; by pre-impregnating the mixed wood chips in an impregnation solution with an effective alkali content of 4 to 8 g / L, it is beneficial for the wood chips to react quickly in the cooking stage and eliminate the resin in the broadleaf wood; by cooking, de-knotting, screening and washing the wood chips, it is beneficial to eliminate impurities in the pulp again; by oxygen delignification treatment, D0 stage bleaching, EO stage bleaching, D1 stage bleaching and D2 stage bleaching of the coarse pulp, the quality of the pulp is improved, and the wet wood pulp prepared in this way has a tensile index of >75Nm / g and a tear index of >7.0m Nm 2 / g, bursting index>4.5kPa.

[0034] Based on the above technical advantages, the present invention also provides a method for preparing a low-dust, high-strength bleached sulfate mixed hardwood pulp board. By strictly controlling various parameters in the preparation process, a mixed acacia and eucalyptus pulp board is obtained, and the dustiness of the pulp board is less than 1.0 mm. 2 / m 2, but the tensile index is >72Nm / g, providing high-quality mixed wood pulp for household paper customers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0036] Figure 1 A technical roadmap provided for the present invention. DETAILED DESCRIPTION

[0037] The invention provides a method for preparing low-dust and high-strength bleached sulfate mixed hardwood wet pulp, comprising the following steps: mixing acacia wood chips and eucalyptus wood chips to obtain mixed wood chips; pre-impregnating the mixed wood chips in an impregnation liquid to obtain impregnated wood chips; steaming the pre-impregnated wood chips with white liquor to obtain coarse pulp; de-knotting, screening and washing the coarse pulp in sequence to obtain washed coarse pulp; performing oxygen delignification treatment on the washed coarse pulp to obtain pulp; performing D0 stage bleaching, EO stage bleaching, D1 stage bleaching and D2 stage bleaching on the pulp in sequence to obtain the mixed hardwood wet pulp; the impregnation liquid comprises white liquor and / or black liquor; and the effective alkali content in the impregnation liquid is 4-8 g / L.

[0038] In the present invention, unless otherwise specified, the methods and materials used are conventionally selected.

[0039] The invention mixes acacia wood chips and eucalyptus wood chips and then screens them to obtain mixed wood chips. In the present invention, the varieties of the acacia wood chips preferably include: Acacia mangium Willd. and / or Acacia crassicarpa Benth., more preferably Acacia mangium and Acacia crassicarpa; the origin of the Acacia mangium is preferably Vietnam; the origin of the Acacia crassicarpa is preferably Hainan; the varieties of the eucalyptus wood chips preferably include: one or more of Eucalyptus robusta Smith, Eucalyptus parvula LAS Johnson & K.D. Hill, Eucalyptus nitens (H. Deane & Maiden) Maiden, Eucalyptus globulus Labill., Eucalyptus dunnii Maiden and Eucalyptus maidenii, further preferably Eucalyptus dunnii Maiden and Eucalyptus dunnii, more preferably Eucalyptus nitens. The origin of the fast-growing eucalyptus of the present invention is preferably Hainan; the origin of the small-leaved eucalyptus is preferably Hainan; the origin of the bright-fruited eucalyptus is preferably Australia or Chile; the origin of the blue eucalyptus is preferably Chile; the origins of the dunn's eucalyptus and straight-stem eucalyptus are preferably Uruguay. The above-mentioned definition of special origins and special products is conducive to improving the quality of the corresponding products.

[0040] When mixed according to the present invention, the mass ratio of acacia chips and eucalyptus chips is 5-8:2-5, preferably 1:1, 3:2, 7:3 or 4:1, more preferably 1:1; when the acacia chips are composed of Acacia mangium and Acacia crassicarpa, the mass ratio of Acacia mangium and Acacia crassicarpa is preferably 9-15:1, more preferably 9:1, 11:1, 13:1 or 15:1; when the eucalyptus chips are composed of different types of eucalyptus, the total amount of eucalyptus chips can meet the demand. In a specific embodiment of the present invention, the eucalyptus chips are obtained by mixing eucalyptus radiata from Chile, eucalyptus radiata from Australia and eucalyptus dunn from Uruguay in a mass ratio of 2:1:1, or by mixing eucalyptus radiata from Chile and eucalyptus dunn from Uruguay in a mass ratio of 2:1, or by mixing eucalyptus radiata from Chile and eucalyptus dunn from Uruguay in a mass ratio of 3:2.

[0041] In the present invention, the mixed wood chips preferably include one or more of bark, oversized chips, overthick chips, qualified chips, oversized chips and sawdust; the mass percentage of the bark in the mixed wood chips is preferably ≤1.0%, more preferably 0.4% to 0.7%; the oversized chips are preferably chips with a diameter of >45mm; the mass percentage of the oversized chips in the mixed wood chips is preferably ≤2.0%, more preferably 0.2% to 1.6%; the overthick chips are preferably chips with a thickness of >8mm; the mass percentage of the overthick chips in the mixed wood chips is preferably ≤8.0%, more preferably ≤5.0%; the qualified chips are preferably chips with a diameter of 7 to 45mm and a thickness of <8mm; the mass percentage of the qualified chips in the mixed wood chips is preferably ≥83%, more preferably ≥85%; the oversized chips are preferably chips with a diameter of <7mm; the mass percentage of the oversized chips in the mixed wood chips is preferably ≤6.0%, more preferably ≤4%; the mass percentage of the sawdust in the mixed wood chips is preferably ≤1.0%, more preferably ≤0.5%. The moisture content of the mixed wood chips of the present invention is preferably 46% to 52%, more preferably 47% to 50%. By limiting the composition and moisture content of the mixed wood chips, a foundation is laid for the subsequent acquisition of low dustiness and high strength bleached kraft mixed hardwood wet pulp.

[0042] After obtaining the mixed wood chips, the present invention pre-impregnates the mixed wood chips to obtain pre-impregnated mixed wood chips. The present invention preferably performs the pre-impregnation in an impregnation tower; the pre-impregnation process preferably involves immersing the mixed wood chips in an impregnation liquid; the impregnation liquid includes white liquor and / or black liquor; in the impregnation liquid, there is no special requirement for the addition ratio of white liquor and black liquor, and the impregnation liquid with an effective alkali content of 4 to 8 g / L is the standard, and preferably the impregnation liquid with an effective alkali content of 6 to 8 g / L is appropriate. The white liquor in the impregnation liquid of the present invention preferably includes NaS (sodium sulfide) and NaOH (sodium hydroxide); the concentration of NaOH in the white liquor is preferably 100 to 108 g / L; the sulfidation degree of the white liquor is preferably 34% to 37%, further preferably 35% to 36%, and more preferably 35.89%, 35.3%, 35.43% or 35%; the black liquor is extracted by the extraction sieve plate inside the cooking tower. The pre-impregnation temperature of the present invention is preferably 80-110° C., more preferably 95-110° C.; the pre-impregnation time is preferably 60-80 min, more preferably 70-80 min.

[0043] To obtain the pre-impregnated mixed wood chips, the present invention preferably adds white liquor from the cooking section through the white liquor inlet at the top of the cooking tower, and performs upper cooking on the pre-impregnated mixed wood chips in the upper cooking zone of the cooking tower to obtain unpulped wood chips. In the present invention, the composition and sulfidation degree of the white liquor in the cooking section are the same as those of the white liquor in the impregnation liquid, which will not be described in detail here; the dosage of the white liquor in the cooking section is preferably 250-350 kg / adt, more preferably 300-320 kg / adt; the temperature of the upper cooking zone is preferably 140-155°C, more preferably 147-152°C or 150-155°C; the pressure of the upper cooking zone is preferably 2-5 bar, more preferably 5 bar; when performing the upper cooking, the residual effective alkali content in the black liquor is preferably 11-15 g / L, further preferably 12-15 g / L, more preferably 12-13 g / L or 13-15 g / L; the liquid-to-solid ratio of the upper cooking zone is preferably 3.5-7.0 m 3 / bdt (cubic meter / absolute dry ton), more preferably 4.0 to 4.5 m 3 / bdt or 6.0~7.0m 3 / bdt.

[0044] After obtaining the unpulped wood chips, the present invention preferably performs lower cooking on the unpulped wood chips in the lower cooking zone of a cooking tower to obtain pulp. In the present invention, the temperature of the lower cooking zone is preferably 150-165°C, more preferably 150-160°C or 155-160°C; the pressure of the lower cooking zone is preferably 5-7 bar, more preferably 6 bar; when performing the lower cooking, the residual effective alkali content in the black liquor is (preferably 4-8 g / L, more preferably 7-8 g / L. After upper cooking and lower cooking, the mixed wood chips complete the entire cooking process; the time of the entire cooking process is preferably 200-300 min, more preferably 220-260 min.

[0045] After obtaining the slurry, the present invention preferably performs countercurrent washing on the slurry in the tower washing zone, and then sprays the slurry at the discharge port at the bottom of the tower to obtain a coarse slurry. When the present invention performs the countercurrent washing, the washing dilution factor is preferably 0.5 to 2.5 adt / m 3 , more preferably 1.5 to 2.5 adt / m 3 , more preferably 2.0 adt / m 3 , 2.1adt / m 3 or 2.2adt / m 3 The discharge port temperature of the countercurrent washing is preferably <95°C, more preferably 88-90°C.

[0046] When the spraying is carried out in the present invention, the mass concentration of the spray line slurry is preferably 8% to 15%, more preferably 8% to 10%, 10% to 12% or 12% to 14%; the residual effective alkali content in the spray line is preferably 2% to 5%, more preferably 2% to 4% or 2% to 3%; at this time, the Kappa number of the slurry is preferably 16 to 18, further preferably 16.5 to 17.5, more preferably 16.84, 17.1, 17.35 or 17.5.

[0047] After obtaining the crude pulp, the present invention preferably performs a stage of de-segmenting on the crude pulp to obtain tailings after the stage of de-segmenting. When the present invention performs the stage of de-segmenting, the inlet concentration of the crude pulp is preferably 3% to 6%, more preferably 4.0% to 4.5%; the inlet pressure is preferably 1.5 to 3.2 bar, more preferably 2.7 to 3.1 bar; the pressure difference of the de-segmenting is preferably 1.5 to 3.0 bar, more preferably 2.5 to 3.0 bar. When performing the stage of de-segmenting, the slag discharge rate is preferably controlled at 5% to 15%, more preferably 8% to 13% or 10% to 11.5%.

[0048] After obtaining the tailings after the first stage of de-knotting, the present invention preferably performs a second stage of section washing on the tailings after the first stage of de-knotting to obtain good pulp. When the present invention performs the second stage of section washing, the inlet concentration of the tailings is preferably 3% to 6%, more preferably 4.0% to 4.5%, and the liquid level of the liquid level box is preferably 7% to 15%, more preferably 8% to 11%; when performing the second stage of section washing, the discharge concentration of the good pulp is preferably controlled at 1.0% to 2.2%, more preferably 1.4% to 1.6%.

[0049] After obtaining the good pulp, the present invention preferably performs one-stage screening, two-stage screening and three-stage screening on the good pulp in sequence to obtain the screened good pulp. When the present invention performs one-stage screening, the pulp inlet concentration of the good pulp is preferably 3.0%-4.5%, and more preferably 3.7%-4.0%; the pulp inlet pressure is preferably 1.5-3.5 bar, and more preferably 2.7-3.2 bar; the pressure difference of the one-stage screening is preferably 1.5-3.0 bar, and more preferably 2.5-3.0 bar; when the two-stage screening is performed, the pulp inlet pressure is preferably 1.5-3.2 bar, and more preferably 2.7-3.1 bar; the pressure difference of the two-stage screening is preferably 1.5-3.0 bar, and more preferably 2.5-3.0 bar; when the three-stage screening is performed, the pulp inlet pressure is preferably 1.5-3.2 bar, and more preferably 2.7-3.1 bar; the pressure difference of the three-stage screening is preferably 1.5-3.0 bar, and more preferably 2.5-3.0 bar; the above screening is beneficial to remove impurities in the good pulp.

[0050] After obtaining the selected acceptable pulp, the present invention preferably performs a first washing and a second washing on the selected acceptable pulp in sequence to obtain wood pulp. When performing the first washing, the washing dilution factor is preferably controlled to be 1.5 to 2.5 m 3 / adt, more preferably 1.8 to 2.3 m 3 / adt; When performing the second washing, the washing dilution factor is preferably controlled at 2.5 to 4m 3 / adt, more preferably 2.8 to 3.5 m 3 / adt; After the second washing treatment, the pulp brightness of the acceptable pulp is preferably ≥30% ISO, more preferably ≥35% ISO.

[0051] After obtaining the wood pulp, the present invention preferably performs a one-stage oxygen delignification treatment on the wood pulp to obtain a one-stage oxygen delignified wood pulp. In the present invention, during the one-stage oxygen delignification treatment, the amount of oxygen used is preferably 10-11 kg / adt, more preferably 10.2-10.4 kg / adt or 10.9-11.2 kg / adt; the amount of NaOH used is preferably 5-10 kg / adt, more preferably 6-8 kg / adt or 7-7.6 kg / adt; the temperature is preferably 85-100°C, further preferably 90-100°C, more preferably 97°C, 98°C or 100°C; the pressure of oxygen in the one-stage oxygen delignification pipeline is preferably 7.5-8.5 bar, more preferably 7.8-8.2 bar; the residence time of the wood pulp in the one-stage oxygen delignification pipeline is preferably 5-10 min, more preferably 8-10 min.

[0052] After obtaining the one-stage oxygen delignified wood pulp, the present invention preferably performs a two-stage oxygen delignification treatment on the one-stage oxygen delignified wood pulp to obtain a two-stage oxygen delignified wood pulp. In the present invention, during the two-stage oxygen delignification treatment, the amount of oxygen used is preferably 15-20 kg / adt, more preferably 10-12 kg / adt or 11.5-13 kg / adt; the temperature is preferably 90-100°C, more preferably 95-100°C, more preferably 97°C or 98°C; the pressure at the top of the tower is preferably ≥5 bar, more preferably 5.5-6.5 bar; the residence time of the one-stage oxygen delignified wood pulp in the two-stage oxygen delignification tower is preferably 60-90 min, more preferably 60-70 min, more preferably 60 min. The above-mentioned one-stage oxygen delignification and two-stage oxygen delignification are beneficial to oxygen oxidation, remove lignin in the pulp, and improve the whiteness of the pulp.

[0053] The second stage oxygen delignified wood pulp is obtained. The present invention preferably washes the second stage oxygen delignified wood pulp to obtain washed wood pulp. When the present invention performs the washing, the washing dilution factor is preferably controlled to be 1.5 to 2.5 m 3 / adt, more preferably 2 to 2.5 m3 / adt.

[0054] After obtaining the washed wood pulp, the present invention preferably sequentially subjects the washed wood pulp to chlorine dioxide bleaching (D0), oxygen alkali extraction (EO), one-stage chlorine dioxide bleaching (D1) and two-stage chlorine dioxide bleaching (D2).

[0055] The chlorine dioxide bleaching treatment of the present invention preferably includes sequentially performing chlorine dioxide bleaching and D0 post-bleaching washing on the washed wood pulp to obtain D0 bleached wood pulp. When the chlorine dioxide bleaching is performed in the present invention, the amount of chlorine dioxide is preferably 10 to 15 kg / adt, more preferably 11 to 12 kg / adt, more preferably 11.68 kg / adt, 11.20 kg / adt or 11.22 kg / adt; the amount of H2SO4 is preferably 2 to 4 kg / adt, more preferably 2.5 to 3.2 kg / adt, more preferably 3 kg / adt; the reaction residence time is preferably 60 to 80 min, more preferably 70 to 75 min, more preferably 70 min. When the D0 post-bleaching washing is performed in the present invention, the washing dilution factor is preferably controlled to be 0.8 to 1.2 m 3 / adt, more preferably 0.8 to 1.0 m 3 / adt, preferably 0.9m 3 / adt.

[0056] The oxygen-alkaline extraction treatment of the present invention preferably includes oxygen-alkaline extraction and EO post-bleaching washing of the D0 bleached wood pulp in sequence to obtain EO bleached wood pulp. When the oxygen-alkaline extraction is performed in the present invention, the amount of sodium hydroxide used is preferably 7-10 kg / adt, and more preferably 7.5-8.5 kg / adt; the amount of oxygen used is preferably 3.5-4.5 kg / adt, and more preferably 3.8-4.3 kg / adt; the reaction temperature is preferably 70-85°C, and more preferably 75-80.5°C; the reaction residence time is preferably 60-80 min, and more preferably 70-75 min, and more preferably 70 min. When the EO post-bleaching washing is performed in the present invention, the washing dilution factor is preferably controlled to be 0.8-1.2 m 3 / adt, preferably 1.0m 3 / adt or 0.9m 3 / adt.

[0057] The one-stage chlorine dioxide bleaching treatment of the present invention preferably includes sequentially performing one-stage chlorine dioxide bleaching and D1 washing on the EO bleached wood pulp to obtain D1 bleached wood pulp. When the present invention performs the one-stage chlorine dioxide bleaching, the amount of chlorine dioxide used is preferably 3 to 6 kg / adt, more preferably 4 to 5 kg / adt or 5.19 kg / adt; the reaction residence time in the tower is preferably 70 to 100 min, more preferably 85 to 90 min, and more preferably 90 min. When the present invention performs the D1 post-bleaching washing, the washing dilution factor is preferably controlled to -0.2 to -1.0 m 3 / adt, more preferably -1.5 to -1.0m 3 / adt.

[0058] The two-stage chlorine dioxide bleaching treatment of the present invention preferably includes sequentially performing a first-stage chlorine dioxide bleaching and a D2 post-bleaching washing on the D1 bleached wood pulp to obtain a mixed broadleaf wet wood pulp. When the present invention performs the two-stage chlorine dioxide bleaching, the amount of chlorine dioxide used is preferably 1 to 2 kg / adt, more preferably 1.2 to 1.5 kg / adt or 2 kg / adt; the reaction residence time in the tower is preferably 70 to 100 min, more preferably 85 to 90 min, and more preferably 90 min. When the present invention performs the D2 post-bleaching washing, the washing dilution factor is preferably controlled to -0.4 to 0 m 3 / adt, preferably 0m 3 / adt.

[0059] The present invention provides a mixed hardwood wet pulp prepared by the preparation method of the above technical solution, which has the characteristics of low dustiness and high strength; the tensile index of the mixed hardwood wet pulp is greater than 75Nm / g, and the tear index is greater than 7.0Nm / g. 2 / g, bursting index>4.5kPa m 2 / g, dichloromethane extract <0.3wt%, dust density <3.0mm 2 / m 2 , Whiteness ≥88% ISO.

[0060] Based on the above technical advantages, the present invention also provides a method for preparing a low-dust, high-strength bleached sulfate mixed hardwood pulp board, the steps of which are: preparing mixed hardwood wet pulp using the preparation method described in the above technical solution; papermaking the mixed hardwood wet pulp to obtain a mixed hardwood pulp board. In the present invention, the papermaking process preferably includes screening the mixed hardwood wet pulp, pulp flow, double-wire pressing, three-roller two-pressing, shoe pressing and drying in sequence, so as to obtain a pulp board with low dust and high tensile index.

[0061] The present invention also provides a mixed hardwood pulp board prepared by the preparation method of the above technical solution, wherein the mixed hardwood pulp board has a tensile index of >72Nm / g and a tear index of >6.8Nm / g. 2 / g, bursting index>4.0kPa m 2 / g, dichloromethane extract <0.4wt%, dust density <1.0mm 2 / m 2 , whiteness ≥88% ISO.

[0062] In order to further illustrate the present invention, the preparation method of a low-dust, high-strength bleached sulfate mixed hardwood wet pulp and pulp board provided by the present invention is described in detail below in combination with the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present invention.

[0063] For the detection of various technical indicators in the present invention, refer to the standards in Table 1.

[0064] Table 1 Detection methods of various technical indicators in the present invention

[0065]

[0066]

[0067] Example 1

[0068] A method for preparing low dust content, high strength bleached kraft mixed hardwood wet pulp (see flow chart for reference) Figure 1 ), the steps are:

[0069] (1) Material preparation: Acacia wood chips are obtained by mixing Acacia mangium from Vietnam and Acacia crassicarpa from Hainan in a mass ratio of 9:1;

[0070] The eucalyptus chips are obtained by mixing eucalyptus globulus from Chile and eucalyptus globulus from Australia in a mass ratio of 3:2;

[0071] The acacia wood chips and eucalyptus wood chips are mixed in a mass ratio of 1:1, and the wood chips are passed through a shaking screen system to obtain mixed wood; the moisture content of the mixed wood is 49.44%, and the percentages of various substances in the mixed wood are as follows: the content of bark is 0.47%, the content of oversized pieces is 1.31%, the content of overthick pieces is 7.42%, the content of qualified pieces is 85.99%, the content of undersized pieces is 4.41% and the content of sawdust is 0.4%.

[0072] (2) Pre-impregnation: The mixed wood in step (1) is transported by a conveyor belt to a pre-impregnation tower filled with an impregnation solution (the effective alkali content of the impregnation solution is 7.29 g / L) at a temperature of 97° C. and immersed for 70 minutes to obtain pre-impregnated wood chips.

[0073] (3) Cooking: The pre-impregnated wood chips in step (2) are transferred from a high-pressure feeder to a cooking tower. The cooking tower is a continuous cooking type. The wood chips move from top to bottom (first into the upper cooking zone, then into the lower cooking zone, the countercurrent washing zone and the spraying discharge port in sequence). After cooking, the wood chips are decomposed into coarse pulp, which is discharged by a scraper at the bottom of the tower and then transported to the spray pot for storage. During the entire cooking process, the white liquor sulfidation degree is 35.89%, the white liquor consumption is 290 kg / adt, and the cooking time is 240 min.

[0074] Among them, in the upper cooking zone: the cooking temperature is 150-155℃, the cooking pressure is 2-5bar, the liquid ratio is 4.3, and the residual alkali content of the black liquor is 13.03g / L; in the lower cooking zone: the cooking temperature is 155-160℃, the cooking pressure is 5-7bar, and the residual alkali content of the black liquor is 8.0g / L; in the countercurrent washing zone: the washing dilution factor is 2.1adt / m 3 , the discharge port temperature is 85-95°C; spraying treatment area: the spraying line slurry concentration is 12.1%, the spraying line residual alkali is 2.27% and the slurry Kappa number is 16.84.

[0075] (4) De-knotting, screening and washing: The coarse pulp in step (3) is transferred to a de-knotting machine for a first-stage de-knotting to remove larger tree knots, thereby obtaining good pulp; the removed larger tree knots are subjected to a node washing process, the pulp on the tree knots is washed off in turn, and the washed pulp is subjected to a desander process, and then returned for de-knotting again; the good pulp is subjected to a first-stage screening, a second-stage screening and a third-stage screening in turn, and the screened pulp is obtained and washed twice to obtain a pulp having the following parameters:

[0076] Knot removal treatment: the pulp inlet concentration is 4.5%, the pulp inlet pressure is 3 bar, the knot removal pressure difference is 2.9 bar and the slag discharge rate is 10.5% (the slag discharge rate refers to the mass percentage of pulp slag discharged during screening or purification in the pulp); Knot washing treatment: the pulp inlet concentration is 4.1%, the liquid level in the liquid level box is 11% and the good pulp discharge concentration is 1.46%; one-stage screening: the pulp inlet concentration is 4.0%, the pulp inlet pressure is 3.00 bar and the screening pressure difference is 2.80 bar; two-stage screening: the pulp inlet pressure is 3.10 bar and the screening pressure difference is 2.90 bar; three-stage screening: the pulp inlet pressure is 3.00 bar and the screening pressure difference is 2.90 bar;

[0077] In one washing, the pulp concentration is 4.3% and the washing dilution factor is 2.2m 3 / adt, the squeeze pressure is 75kNm, the pulp concentration is 25%; during the secondary washing, the pulp concentration is 2.1%, and the washing dilution factor is 2.8m 3 / adt, the slurry squeezing pressure is 97.3kNm, the slurry concentration is 31.86%, the slurry whiteness is 36.3%, and the diluted riser slurry concentration is 13%.

[0078] (5) Oxygen delignification treatment: The pulp obtained in step (4) is transported to the oxygen delignification section, and the first oxygen delignification treatment (U-shaped tube), the second oxygen delignification treatment and the washing treatment are carried out in sequence. After the washing treatment is completed, the pulp is transported to the unbleached pulp storage tower for storage, and the washing wastewater is transported to the storage tank for storage and reuse. The specific parameters in this process are:

[0079] The first stage of oxygen delignification treatment: reaction pulp concentration is 13%, oxidation white liquor consumption is 10.1kg / adt, NaOH consumption is 7.6kg / adt, initial reaction pH is 11.5, oxygen consumption is 10.9kg / adt, pipeline oxygen pressure is 8.1bar, reaction temperature is 100℃ and residence time is 10min; the second stage of oxygen delignification treatment: reaction pulp concentration is 13%, oxygen consumption is 16.3kg / adt, reaction tower top pressure is 5.7bar, reaction temperature is 97℃, residence time is 60min, bleaching liquor reaction end point pH is 10.53, bleaching kappa number is 9.87 and bleaching pulp brightness (ISO) is 54.82%; washing treatment: pulp inlet concentration is 7.9%, washing dilution factor is 2.47m 3 / adt, the slurry pressure is 100 kNm and the slurry concentration is 26.97%.

[0080] (6) Bleaching treatment: This process includes chlorine dioxide bleaching (D0), oxygen alkali extraction (EO), one-stage chlorine dioxide bleaching (D1) and two-stage chlorine dioxide bleaching (D2) to prepare mixed hardwood wet pulp, specifically:

[0081] Before entering the D0 bleaching treatment, the pulp in the unbleached pulp storage tower in step 5 needs to be washed again. The amount of chlorine dioxide in the D0 stage is determined according to the pulp Kappa number measured in step (5). During the second washing treatment, the pulp concentration is 8.0% and the washing dilution factor is 2.66m 3 / adt, the slurry pressure is 102kNm and the slurry concentration is 23.42%.

[0082] The D0 stage is a process in which chlorine dioxide (ClO2) is used as an oxidant to oxidize and dissolve lignin under acidic and high-temperature conditions, remove colored groups, improve the whiteness of the pulp, and achieve a bleaching effect. The parameters of this process are: reaction pulp concentration is 12%, reaction temperature is 76°C, chlorine dioxide dosage is 11.68kg / adt, sulfuric acid dosage is 3kg / adt, riser residence time is 10min, tower residence time is 70min, bleaching liquid reaction end point pH is 2.47, bleached pulp kappa is 3.01, and bleached pulp whiteness is 67.8%; the washing parameters of the D0 stage are: washing dilution factor is 1m 3 / adt, the squeeze pressure is 80kNm and the pulp concentration is 23.1%;

[0083] The EO stage is a process in which a small amount of oxygen is added under alkaline high temperature conditions, and the oxygen selectively reacts with the chlorinated lignin and residual lignin in the pulp to remove the lignin. The liquid used to adjust the alkaline environment is sodium hydroxide (its concentration is ≥150g / L). The parameters of the process are: reaction pulp concentration is 11.4%, oxygen consumption is 4.1kg / adt, NaOH consumption is 8.1kg / adt, reaction tower top pressure is 4.3bar, reaction temperature is 80.3℃, residence time is 70min, bleached pulp Kappa number is 2.77, bleached pulp whiteness is 75.96%, and bleaching liquid reaction end point pH is 10.32; EO stage washing parameters are: washing dilution factor is 1m 3 / adt, the squeeze pressure is 78kNm and the pulp concentration is 25.88%;

[0084] The D1 bleaching process mainly adds a small amount of chlorine dioxide bleaching agent to increase the pulp whiteness close to the target value. The specific parameters are: reaction pulp concentration is 11.6%, reaction temperature is 76.1℃, chlorine dioxide dosage is 5.19kg / adt, riser residence time is 10min, tower residence time is 90min, bleaching liquid reaction end point pH is 3.93, bleaching liquid reaction end point residual chlorine is 2.3mg / L, and pulp whiteness after bleaching is 86.2%; D1 washing parameters are: washing dilution factor is -2m 3 / adt, the squeeze pressure is 90kNm and the pulp concentration is 26.54%;

[0085] The purpose of D2 bleaching is to bleach the pulp to the target value by adding a small amount of chlorine dioxide bleaching agent, while avoiding the pulp from yellowing. The specific parameters are: reaction pulp concentration is 11.8%, reaction temperature is 77.8℃, chlorine dioxide dosage is 2kg / adt, riser residence time is 10min, tower residence time is 90min, bleaching liquid reaction end point pH is 4.38, bleaching liquid reaction end point residual chlorine is 1.78mg / L, and pulp whiteness after bleaching is 88.2%; D1 washing parameters are: washing dilution factor is 0m 3 / adt, the slurry pressure is 60kNm and the slurry concentration is 24.57%.

[0086] A method for preparing a low-dust, high-strength bleached kraft mixed hardwood pulp board, comprising the following steps:

[0087] The bleached pulp (mixed hardwood wet pulp in step 6) is subjected to pulping treatment. The process is to first remove impurities through screening, then send the pulp to the wire part for forming through the headbox, and after pressing, dehydration and drying, the mixed hardwood pulp board is obtained with the following parameters:

[0088] The screening process includes one-stage screening, two-stage screening, three-stage screening, four-stage screening and five-stage screening. The parameters of each stage screening are as follows: in the first stage screening, the pulp concentration is 3% and the pulp pressure is 3.8 bar; in the second stage screening, the pulp concentration is 2.8% and the pulp pressure is 3.98 bar; in the third stage screening, the pulp concentration is 2.6% and the pulp pressure is 4.5 bar; in the fourth stage screening, the pulp concentration is 2.31% and the pulp pressure is 4.4 bar; in the fifth stage screening, the pulp concentration is 1.9% and the pulp pressure is 2.89 bar.

[0089] The inlet concentration of the slurry during flow conveying is: 1.62%;

[0090] Double-wire pressing is used during pressing, and the felt tension is 5.1KN / m;

[0091] The parameters for three rolls and two presses are: 1st press pressure is 37KN / m, 2nd press pressure is 125KN / m, and the finished pulp concentration is 45%;

[0092] The shoe pressure is 820KN / m;

[0093] The parameters of dehydration and drying are: paper feeding speed is 145m / min, drying temperature is 130℃, pulp board moisture is 11.8%, pulp board basis weight is 2900g / m 2 .

[0094] Example 2

[0095] The preparation method of mixed hardwood wet pulp is the same as the preparation steps in Example 1, the only difference is the parameter settings in each step, specifically:

[0096] (1) Material preparation: Acacia wood chips are obtained by mixing Acacia mangium from Vietnam and Acacia crassicarpa from Hainan in a mass ratio of 11:1;

[0097] The eucalyptus chips are obtained by mixing eucalyptus globulus from Chile, eucalyptus globulus from Australia and eucalyptus dunnii from Uruguay in a mass ratio of 2:1:1;

[0098] The acacia wood chips and eucalyptus wood chips are mixed in a mass ratio of 3:2, and the wood chips are passed through a shaking screen system to obtain mixed wood; the moisture content of the mixed wood is 48.3%, and the percentages of various substances in the mixed wood are as follows: the content of bark is 0.5%, the content of oversized pieces is 1.3%, the content of overthick pieces is 9.4%, the content of qualified pieces is 85.7%, the content of undersized pieces is 2.7% and the content of sawdust is 0.5%.

[0099] (2) Pre-impregnation: The mixed wood in step (1) is transported by a conveyor belt to a pre-impregnation tower filled with an impregnation solution (the effective alkali content of the impregnation solution is 7.2 g / L) at a temperature of 96° C. and immersed for 70 minutes to obtain pre-impregnated wood chips.

[0100] (3) Cooking: During the entire cooking process, the sulfidation degree of the white liquor was 35.3%, the white liquor consumption was 305 kg / adt, and the cooking time was 240 min;

[0101] In the upper cooking zone: the cooking temperature is 150-155℃, the cooking pressure is 2-5bar, the liquid ratio is 4.2, and the residual alkali content of the black liquor is 13.27g / L; in the lower cooking zone: the cooking temperature is 155-160℃, the cooking pressure is 5-7bar, and the residual alkali content of the black liquor is 7.9g / L; in the countercurrent washing zone: the washing dilution factor is 2.0adt / m 3 , the discharge port temperature is 85-95°C; spraying treatment area: the spraying line slurry concentration is 11.5%, the spraying line residual alkali is 2.2% and the slurry Kappa number is 17.1.

[0102] (4) De-knotting, screening and washing: The specific parameters are as follows: first stage de-knotting: the pulp inlet concentration is 4.1%, the pulp inlet pressure is 3 bar, the pressure difference of de-knotting is 2.9 bar and the slag discharge rate is 10.2%; second stage cleaning: the pulp inlet concentration is 4.2%, the liquid level in the liquid level box is 10% and the good pulp discharge concentration is 1.5%; first stage screening: the pulp inlet concentration is 3.9%, the pulp inlet pressure is 2.8 bar and the screening pressure difference is 2.72 bar; second stage screening: the pulp inlet pressure is 2.9 bar and the screening pressure difference is 2.90 bar; third stage screening: the pulp inlet pressure is 2.9 bar and the screening pressure difference is 2.8 bar;

[0103] In one washing, the pulp concentration is 4.5% and the washing dilution factor is 2.1m 3 / adt, the squeeze pressure is 70.2kNm, and the pulp concentration is 27.3%; during the secondary washing, the pulp concentration is 2.0%, and the washing dilution factor is 3.0m 3 / adt, the slurry squeezing pressure is 74kNm, the slurry concentration is 28%, the slurry whiteness is 33.3%, and the diluted riser slurry concentration is 11.4%.

[0104] (5) Oxygen delignification treatment: The specific parameters in this process are:

[0105] The first stage of oxygen delignification treatment: reaction pulp concentration is 11.4%, oxidation white liquor consumption is 10.8kg / adt, NaOH consumption is 7.2kg / adt, initial reaction pH is 11.4, oxygen consumption is 10.0kg / adt, pipeline oxygen pressure is 8.0bar, reaction temperature is 97℃ and residence time is 10min; the second stage of oxygen delignification treatment: reaction pulp concentration is 11.5%, oxygen consumption is 17.6kg / adt, reaction tower top pressure is 6.4bar, reaction temperature is 97℃, residence time is 60min, bleaching liquor reaction end point pH is 10.5, bleaching kappa number is 9.7 and bleaching pulp brightness (ISO) is 52.7%; washing treatment: pulp inlet concentration is 8.0%, washing dilution factor is 2.2m 3 / adt, the squeeze pressure is 92.1kNm and the pulp concentration is 27.8%;

[0106] (6) Bleaching treatment: During the second washing process, the pulp concentration is 8.0% and the washing dilution factor is 2.52m 3 / adt, the pulping pressure is 95.2kNm and the pulping concentration is 26.1%.

[0107] The parameters of D0 section are: reaction pulp concentration of 11.7%, reaction temperature of 75℃, chlorine dioxide dosage of 11.2kg / adt, H2SO4 dosage of 3kg / adt, residence time in riser of 10min, residence time in tower of 70min, pH of bleaching liquid reaction end point of 2.8, Kappa number of bleached pulp of 2.9, and whiteness of bleached pulp of 69.2%; the washing parameters of D0 section are: washing dilution factor of 0.9m 3 / adt, the squeeze pressure is 86.7kNm and the pulp concentration is 28.5%;

[0108] The parameters of the EO section are: reaction pulp concentration of 12%, oxygen consumption of 4.0kg / adt, NaOH consumption of 7.6kg / adt, reaction tower top pressure of 4.3bar, reaction temperature of 80℃, residence time of 70min, bleached pulp Kappa number of 2.4, bleached pulp whiteness of 76%, bleaching liquid reaction end point pH of 10.3; the washing parameters of the EO section are: washing dilution factor of 0.84m 3 / adt, the squeeze pressure is 73.1kNm and the pulp concentration is 25.7%;

[0109] The parameters of D1 section are: reaction pulp concentration of 12%, reaction temperature of 75℃, chlorine dioxide dosage of 4.7kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4.2, residual chlorine of bleaching liquid reaction end point of 2.4mg / L, and whiteness of pulp after bleaching of 86.7%; the washing parameters of D1 section are: washing dilution factor of -1.9m 3 / adt, the squeeze pressure is 83.8kNm and the pulp concentration is 26.7%;

[0110] The parameters of D2 section are: reaction pulp concentration of 12%, reaction temperature of 75.7℃, chlorine dioxide dosage of 1.3kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4.8, residual chlorine of bleaching liquid reaction end point of 1.9mg / L, and whiteness of pulp after bleaching of 88.3%; the washing parameters of D1 section are: washing dilution factor of -0.22m 3 / adt, the pulping pressure is 84.2kNm and the pulping concentration is 23.6%.

[0111] The preparation method of the mixed hardwood pulp board is the same as the preparation steps in Example 1, the only difference being the parameter settings in each step, specifically:

[0112] During the first stage screening, the pulp concentration is 3% and the pulp pressure is 4.0 bar; during the second stage screening, the pulp concentration is 2.8% and the pulp pressure is 4.8 bar; during the third stage screening, the pulp concentration is 2.6% and the pulp pressure is 4.2 bar; during the fourth stage screening, the pulp concentration is 2.31% and the pulp pressure is 3.6 bar; during the fifth stage screening, the pulp concentration is 1.9% and the pulp pressure is 2.9 bar;

[0113] The inlet concentration of the slurry during flow conveying is: 1.65%;

[0114] Double-wire pressing is used during pressing, and the felt tension is 5.7KN / m;

[0115] The parameters of three-roll two-press are: 1st press pressure is 44.2KN / m, 2nd press pressure is 138KN / m, and the finished pulp concentration is 43%;

[0116] The shoe pressure is 866KN / m;

[0117] The parameters of dehydration and drying are: paper feeding speed is 145m / min, drying temperature is 143℃, pulp board moisture is 12.5%, pulp board basis weight is 2900g / m 2 .

[0118] Example 3

[0119] The preparation method of mixed hardwood wet pulp is the same as the preparation steps in Example 1, the only difference is the parameter settings in each step, specifically:

[0120] (1) Material preparation: Acacia wood chips are obtained by mixing Acacia mangium from Vietnam and Acacia crassicarpa from Hainan in a mass ratio of 13:1;

[0121] The eucalyptus chips are obtained by mixing eucalyptus radiata from Chile and eucalyptus dunnii from Uruguay in a mass ratio of 2:1;

[0122] The acacia wood chips and eucalyptus wood chips prepared above were mixed in a mass ratio of 7:3, and the wood chips were passed through a shaking screen system to obtain mixed wood; the moisture content of the mixed wood was 49.68%, and the percentages of various substances in the mixed wood were as follows: the content of bark was 0.39%, the content of oversized pieces was 1.62%, the content of overthick pieces was 9.91%, the content of qualified pieces was 84.66%, the content of undersized pieces was 2.97%, and the content of sawdust was 0.45%.

[0123] (2) Pre-impregnation: The mixed wood in step (1) is transported by a conveyor belt to a pre-impregnation tower filled with an impregnation solution (the effective alkali content of the impregnation solution is 7.05 g / L) at a temperature of 103° C. and immersed for 70 minutes to obtain pre-impregnated wood chips.

[0124] (3) Cooking: During the entire cooking process, the sulfidation degree of the white liquor was 35.43%, the white liquor consumption was 309 kg / adt, and the cooking time was 240 min;

[0125] In the upper cooking zone: the cooking temperature is 150-155℃, the cooking pressure is 2-5bar, the liquid ratio is 4.1, and the residual alkali content of the black liquor is 12.26g / L; in the lower cooking zone: the cooking temperature is 155-160℃, the cooking pressure is 5-7bar, and the residual alkali content of the black liquor is 8g / L; in the countercurrent washing zone: the washing dilution factor is 2.2adt / m 3 , the discharge port temperature is 85-95°C; spraying treatment area: the spraying line slurry concentration is 12%, the spraying line residual alkali is 2.14% and the slurry Kappa number is 17.35.

[0126] (4) De-knotting, screening and washing: The specific parameters are as follows: first stage de-knotting: the pulp inlet concentration is 4.3%, the pulp inlet pressure is 2.9 bar, the pressure difference of de-knotting is 2.8 bar and the slag discharge rate is 11%; second stage cleaning: the pulp inlet concentration is 4.0%, the liquid level in the liquid level box is 10.5% and the good pulp discharge concentration is 1.5%; first stage screening: the pulp inlet concentration is 3.7%, the pulp inlet pressure is 3.00 bar and the screening pressure difference is 2.85 bar; second stage screening: the pulp inlet pressure is 2.6 bar and the screening pressure difference is 2.5 bar; third stage screening: the pulp inlet pressure is 2.9 bar and the screening pressure difference is 2.8 bar;

[0127] In one washing, the pulp concentration is 4.3% and the washing dilution factor is 2.0m 3 / adt, the squeeze pressure is 76kNm, and the pulp concentration is 28.4%; during the secondary washing, the pulp concentration is 2.0%, and the washing dilution factor is 3.46m 3 / adt, the slurry squeezing pressure is 70kNm, the slurry concentration is 27.8%, the slurry whiteness is 34%, and the diluted riser slurry concentration is 12.8%.

[0128] (5) Oxygen delignification treatment: The specific parameters in this process are:

[0129] The first stage of oxygen delignification treatment: reaction pulp concentration is 12.8%, oxidation white liquor consumption is 10.2kg / adt, NaOH consumption is 6.8kg / adt, initial reaction pH is 11.6, oxygen consumption is 11.2kg / adt, pipeline oxygen pressure is 8.1bar, reaction temperature is 98℃ and residence time is 10min; the second stage of oxygen delignification treatment: reaction pulp concentration is 12.8%, oxygen consumption is 16.8kg / adt, reaction tower top pressure is 5.8bar, reaction temperature is 98℃, residence time is 60min, bleaching liquor reaction end point pH is 10.6, bleaching kappa number is 9.9 and bleaching pulp brightness (ISO) is 53.3%; washing treatment: pulp inlet concentration is 8.1%, washing dilution factor is 2.0m 3 / adt, the squeeze pressure is 90kNm and the pulp concentration is 26.3%;

[0130] (6) Bleaching treatment: During the second washing process, the pulp concentration is 8.0% and the washing dilution factor is 2.56m 3 / adt, the pulping pressure is 98.6kNm and the pulping concentration is 26.3%.

[0131] The parameters of D0 section are: reaction pulp concentration is 11.9%, reaction temperature is 74℃, chlorine dioxide dosage is 12.22kg / adt, H2SO4 dosage is 3kg / adt, riser residence time is 10min, tower residence time is 70min, bleaching liquid reaction end point pH is 2.7, bleached pulp Kappa number is 3.13, bleached pulp whiteness is 70.1%; D0 section washing parameters are: washing dilution factor is 1m 3 / adt, the squeeze pressure is 84.7kNm and the pulp concentration is 25%;

[0132] The parameters of the EO section are: reaction pulp concentration of 11.9%, oxygen consumption of 4.0kg / adt, NaOH consumption of 8.0kg / adt, reaction tower top pressure of 4.5bar, reaction temperature of 80.5℃, residence time of 70min, bleached pulp Kappa number of 2.83, bleached pulp whiteness of 75.8%, bleaching liquid reaction end point pH of 10.2; EO section washing parameters are: washing dilution factor of 0.9m 3 / adt, the squeeze pressure is 72.6kNm and the pulp concentration is 25.3%;

[0133] The parameters of D1 section are: reaction pulp concentration of 11.3%, reaction temperature of 75.7℃, chlorine dioxide dosage of 4.9kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4.0, residual chlorine of bleaching liquid reaction end point of 2.6mg / L, whiteness of pulp after bleaching of 87.0%; washing parameters of D1 section are: washing dilution factor of -1.2m 3 / adt, the squeeze pressure is 84.2kNm and the pulp concentration is 27.5%;

[0134] The parameters of D2 section are: reaction pulp concentration of 11.3%, reaction temperature of 75℃, chlorine dioxide dosage of 1.3kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4.6, residual chlorine of bleaching liquid reaction end point of 1.6mg / L, whiteness of pulp after bleaching of 88.1%; the washing parameters of D1 section are: washing dilution factor of -0.36m 3 / adt, the squeeze pressure is 82kNm and the pulp concentration is 23.2%.

[0135] The preparation method of the mixed hardwood pulp board is the same as the preparation steps in Example 1, the only difference being the parameter settings in each step, specifically:

[0136] During the first stage screening, the pulp concentration is 3.1% and the pulp pressure is 4.0 bar; during the second stage screening, the pulp concentration is 2.9% and the pulp pressure is 4.5 bar; during the third stage screening, the pulp concentration is 2.6% and the pulp pressure is 4.0 bar; during the fourth stage screening, the pulp concentration is 2.38% and the pulp pressure is 4.0 bar; during the fifth stage screening, the pulp concentration is 1.9% and the pulp pressure is 2.78 bar;

[0137] The inlet concentration of the slurry during flow conveying is: 1.62%;

[0138] Double-wire pressing is used during pressing, and the felt tension is 5.1KN / m;

[0139] The parameters of three-roll two-press are: 1st press pressure is 41KN / m, 2nd press pressure is 133KN / m, and the finished pulp concentration is 44.2%;

[0140] The shoe pressure is 840KN / m;

[0141] The parameters of dehydration and drying are: paper feeding speed is 140m / min, drying temperature is 136℃, pulp board moisture is 11.8%, pulp board basis weight is 2900g / m 2 .

[0142] Example 4

[0143] The preparation method of mixed hardwood wet pulp is the same as the preparation steps in Example 1, the only difference is the parameter settings in each step, specifically:

[0144] (1) Material preparation: Acacia wood chips are obtained by mixing Acacia mangium from Vietnam and Acacia crassicarpa from Hainan in a mass ratio of 15:1;

[0145] The eucalyptus wood chips are from Chile;

[0146] The acacia wood chips and eucalyptus wood chips are mixed in a mass ratio of 8:2, and the wood chips are passed through a shaking screen system to obtain mixed wood; the moisture content of the mixed wood is 45%, and the percentages of various substances in the mixed wood are as follows: the content of bark is 0.3%, the content of oversized pieces is 1.43%, the content of overthick pieces is 8.31%, the content of qualified pieces is 86.56%, the content of undersized pieces is 3%, and the content of sawdust is 0.4%.

[0147] (2) Pre-impregnation: The mixed wood in step (1) is transported by a conveyor belt to a pre-impregnation tower filled with an impregnation solution (the effective alkali content of the impregnation solution is 7.05 g / L) at a temperature of 100° C. and immersed for 70 minutes to obtain pre-impregnated wood chips.

[0148] (3) Cooking: During the entire cooking process, the sulfidation degree of the white liquor was 35%, the white liquor consumption was 320 kg / adt, and the cooking time was 240 min;

[0149] In the upper cooking zone: cooking temperature is 150-155℃, cooking pressure is 2-5bar, liquid ratio is 4.1 and the residual alkali content of black liquor is 13g / L; in the lower cooking zone: cooking temperature is 155-160℃, cooking pressure is 5-7bar, and the residual alkali content of black liquor is 8.0g / L; in the countercurrent washing zone: the washing dilution factor is 2.2adt / m 3 , the discharge port temperature is 85-95°C; spraying treatment area: the spraying line slurry concentration is 11.8%, the spraying line residual alkali is 2.34% and the slurry Kappa number is 17.5.

[0150] (4) De-knotting, screening and washing: The specific parameters are as follows: first stage de-knotting: the pulp inlet concentration is 4.4%, the pulp inlet pressure is 2.9 bar, the de-knotting pressure difference is 2.8 bar and the slag discharge rate is 11.2%; second stage cleaning: the pulp inlet concentration is 4.3%, the liquid level in the liquid level box is 11.3% and the good pulp discharge concentration is 1.48%; first stage screening: the pulp inlet concentration is 3.8%, the pulp inlet pressure is 3.00 bar and the screening pressure difference is 2.90 bar; second stage screening: the pulp inlet pressure is 2.7 bar and the screening pressure difference is 2.60 bar; third stage screening: the pulp inlet pressure is 3.00 bar and the screening pressure difference is 2.90 bar;

[0151] In one washing, the pulp concentration is 4.4% and the washing dilution factor is 2.2m 3 / adt, the squeeze pressure is 74kNm, the pulp concentration is 26.4%; during the secondary washing, the pulp concentration is 2.2%, and the washing dilution factor is 3.5m 3 / adt, the slurry squeezing pressure is 70kNm, the slurry concentration is 26.7%, the slurry whiteness is 35.6%, and the diluted riser slurry concentration is 11.9%.

[0152] (5) Oxygen delignification treatment: The specific parameters in this process are:

[0153] The first stage of oxygen delignification treatment: reaction pulp concentration is 11.9%, oxidation white liquor consumption is 10.5kg / adt, NaOH consumption is 7.0kg / adt, initial reaction pH is 11.4, oxygen consumption is 11kg / adt, pipeline oxygen pressure is 8.1bar, reaction temperature is 98℃ and residence time is 10min; the second stage of oxygen delignification treatment: reaction pulp concentration is 12.8%, oxygen consumption is 17.2kg / adt, reaction tower top pressure is 6.0bar, reaction temperature is 98℃, residence time is 60min, bleaching liquor reaction end point pH is 10.3, bleaching kappa number is 10 and bleaching pulp brightness (ISO) is 52.3%; washing treatment: pulp inlet concentration is 8.0%, washing dilution factor is 2.0m 3 / adt, the squeeze pressure is 91kNm and the pulp concentration is 27.2%;

[0154] (6) Bleaching treatment: During the second washing process, the pulp concentration is 8.0% and the washing dilution factor is 2.6m 3 / adt, the squeeze pressure is 97.8kNm and the pulp concentration is 27%.

[0155] The parameters of D0 section are: reaction pulp concentration is 11.5%, reaction temperature is 75℃, chlorine dioxide dosage is 12kg / adt, H2SO4 dosage is 3kg / adt, riser residence time is 10min, tower residence time is 70min, bleaching liquid reaction end point pH is 2.6, bleached pulp Kappa number is 3.00, bleached pulp whiteness is 70%; D0 section washing parameters are: washing dilution factor is 1m 3 / adt, the squeeze pressure is 83.5kNm and the pulp concentration is 24.8%;

[0156] The parameters of the EO section are: reaction pulp concentration of 11.8%, oxygen consumption of 4.1kg / adt, NaOH consumption of 8.10kg / adt, reaction tower top pressure of 4.8bar, reaction temperature of 80.0℃, residence time of 70min, bleached pulp Kappa number of 2.6, bleached pulp whiteness of 76%, bleaching liquid reaction end point pH of 10.4; EO section washing parameters are: washing dilution factor of 0.88m 3 / adt, the squeeze pressure is 74.8kNm and the pulp concentration is 27.8%;

[0157] The parameters of D1 section are: reaction pulp concentration of 12.4%, reaction temperature of 74℃, chlorine dioxide dosage of 4.9kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4, residual chlorine of bleaching liquid reaction end point of 2.5mg / L, whiteness of pulp after bleaching of 86.8%; washing parameters of D1 section are: washing dilution factor of -1.1m 3 / adt, the squeeze pressure is 86.2kNm and the pulp concentration is 28%;

[0158] The parameters of D2 section are: reaction pulp concentration of 11.3%, reaction temperature of 75℃, chlorine dioxide dosage of 1.5kg / adt, residence time in riser of 10min, residence time in tower of 90min, pH of bleaching liquid reaction end point of 4.6, residual chlorine of bleaching liquid reaction end point of 1.8mg / L, and whiteness of pulp after bleaching of 88.5%; the washing parameters of D1 section are: washing dilution factor of -0.35m 3 / adt, the squeeze pressure is 79kNm and the pulp concentration is 22.2%.

[0159] The preparation method of the mixed hardwood pulp board is the same as the preparation steps in Example 1, the only difference being the parameter settings in each step, specifically:

[0160] During the first stage screening, the pulp concentration is 3% and the pulp pressure is 4 bar; during the second stage screening, the pulp concentration is 2.8% and the pulp pressure is 4.2 bar; during the third stage screening, the pulp concentration is 2.6% and the pulp pressure is 4.7 bar; during the fourth stage screening, the pulp concentration is 2.31% and the pulp pressure is 4.1 bar; during the fifth stage screening, the pulp concentration is 1.9% and the pulp pressure is 2.77 bar;

[0161] The inlet concentration of the slurry during flow conveying is: 1.66%;

[0162] Double-wire pressing is used during pressing, and the felt tension is 5.3KN / m;

[0163] The parameters of three-roll two-press are: 1st press pressure is 46KN / m, 2nd press pressure is 140KN / m, and the finished pulp concentration is 45%;

[0164] The shoe pressure is 835KN / m;

[0165] The parameters of dehydration and drying are: paper feeding speed is 135m / min, drying temperature is 132℃, pulp board moisture is 11.8%, pulp board basis weight is 2900g / m 2 .

[0166] The mixed hardwood wet pulp prepared in Examples 1 to 4 was respectively tested for corresponding indicators. The results are shown in Table 2.

[0167] Table 2 Test data of corresponding indicators of different mixed hardwood wet pulp

[0168]

[0169] It can be seen from Table 2 that the mixed hardwood wet pulp prepared by the technical solution provided by the present invention has low dustiness and high strength performance, low resin content and high whiteness; the specific indicators are: tensile index>75Nm / g, tear index>7.0m Nm 2 / g, bursting index>4.5kPa m 2 / g, dichloromethane extract <0.3wt%, dust density <3.0mm 2 / m 2 , Whiteness ≥88% ISO.

[0170] The mixed hardwood pulp boards prepared in Examples 1 to 4 were respectively tested for corresponding indicators. The results are shown in Table 3.

[0171] Table 3 Test data of corresponding indicators of different mixed hardwood pulp boards

[0172]

[0173]

[0174] It can be seen from Table 3 that the mixed hardwood pulp board prepared by the technical solution provided by the present invention has the following indicators: tensile index>72Nm / g, tear index>6.8m Nm 2 / g, bursting index>4.0kPa m 2 / g, dichloromethane extract <0.4wt%, dust density <1.0mm 2 / m 2 , whiteness ≥ 88% ISO and pulp basis weight 2500~3000g / m 2 It can be seen that the mixed hardwood pulp board prepared by the present invention has low dustiness and high paper strength.

[0175] In summary, it can be seen that after adopting the technical solution provided by the present invention, not only the production process is stable, but also the strength and dust indexes of the wet wood pulp and pulp board obtained thereby are more excellent, which can meet the quality requirements of the product.

[0176] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing low dust content, high strength bleached kraft mixed hardwood wet pulp, characterized in that: The steps include: Mixing acacia wood chips and eucalyptus wood chips to obtain mixed wood chips; pre-impregnating the mixed wood chips in an impregnation liquid to obtain pre-impregnated wood chips; Cooking the pre-impregnated wood chips with white liquor to obtain a rough pulp; The crude pulp is sequentially subjected to de-sectioning, screening and washing to obtain washed crude pulp; The washed brown pulp is subjected to oxygen delignification treatment to obtain pulp; The pulp is subjected to D0 stage bleaching, EO stage bleaching, D1 stage bleaching and D2 stage bleaching in sequence to obtain the mixed hardwood wet pulp; The impregnation liquid includes white liquor and / or black liquor; the effective alkali content in the impregnation liquid is 4-8g / L.

2. The preparation method according to claim 1, characterized in that: When the mixing and preparing is performed, the mass ratio of the acacia wood chips to the eucalyptus wood chips is 5-8:2-5; The varieties of the acacia wood chips include: Acacia mangium and / or Acacia crassicarpa; The varieties of the eucalyptus chips include one or more of fast-growing eucalyptus, small-leaved eucalyptus, bright-fruited eucalyptus, blue eucalyptus, dunn's eucalyptus and straight-stem eucalyptus.

3. The preparation method according to claim 1, characterized in that: The pre-impregnation temperature is 80-110° C.; the pre-impregnation time is 60-80 minutes.

4. The preparation method according to claim 1, characterized in that: When the cooking is performed, the concentration of sodium hydroxide in the white liquor is 100-108 g / L, and the amount of the white liquor is 250-350 kg / adt; The cooking time is 200 to 300 minutes.

5. The preparation method according to claim 1, characterized in that: The knot removal comprises: performing first-stage knot removal and second-stage knot removal on the rough pulp in sequence to obtain the good pulp; During the first stage of the de-slagging process, the slag removal rate is 5% to 15%.

6. The preparation method according to claim 1, characterized in that: The oxygen delignification treatment comprises: sequentially performing a first stage oxygen delignification treatment and a second stage oxygen delignification treatment on the washed brown pulp; In the one-stage oxygen delignification treatment, the amount of oxygen used is 10-11 kg / adt, and the amount of sodium hydroxide used is 8-15 kg / adt; In the two-stage oxygen delignification treatment, the amount of oxygen used is 15-20 kg / adt.

7. The preparation method according to claim 1, characterized in that: In the D0 stage bleaching process, the amount of chlorine dioxide used is 10-15 kg / adt, and the amount of sulfuric acid used is 2-4 kg / adt; In the EO stage bleaching process, the amount of sodium hydroxide used is 7-10 kg / adt, and the amount of oxygen used is 3.5-4.5 kg / adt; In the D1 stage bleaching process, the amount of chlorine dioxide used is 3-6 kg / adt; In the D2 stage bleaching process, the dosage of chlorine dioxide is 1-2 kg / adt.

8. The mixed hardwood wet pulp prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The tensile index of the mixed hardwood wet pulp is >75Nm / g, and the tear index is >7.0Nm / g 2 / g, bursting index>4.5kPa m 2 / g, dichloromethane extract <0.3wt%, whiteness ≥88%ISO, dustiness <3.0mm 2 / m 2 .

9. A method for preparing a low dustiness, high strength bleached kraft mixed hardwood pulp board, characterized in that: The steps include: Mixed hardwood wet pulp is prepared by the preparation method according to any one of claims 1 to 7; The mixed hardwood wet pulp is papermade to obtain a mixed hardwood pulp board.

10. The mixed hardwood pulp board prepared by the preparation method according to claim 9, characterized in that: The tensile index of the mixed hardwood pulp board is >72Nm / g, and the tear index is >6.8Nm / g. 2 / g, bursting index>4.0kPa m 2 / g, dichloromethane extract <0.4wt%, whiteness ≥88%ISO, dustiness <1.0mm 2 / m 2 .

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