CN106468029B

CN106468029B - Preparation method of high-strength low-dust bleached sulfate hardwood pulp, wood pulp board and preparation method thereof

Info

Publication number: CN106468029B
Application number: CN201511031223.5A
Authority: CN
Inventors: 刘若飞; 陈德海; 肖光彩; 李雪峰; 张守国; 杨恒; 李书杰
Original assignee: Asia Symbol Shandong Pulp And Paper Co ltd
Current assignee: Asia Symbol Shandong Pulp And Paper Co ltd
Priority date: 2015-12-31
Filing date: 2015-12-31
Publication date: 2021-06-22
Anticipated expiration: 2035-12-31
Also published as: CN106468029A

Abstract

The invention provides a preparation method of bleached sulfate hardwood pulp, a wood pulp board and a preparation method thereof. The preparation method of the wood pulp comprises the following steps: preparing broad-leaved wood chips to obtain wood; cooking timber in white liquor to obtain coarse pulp, wherein the cooked kappa number is 16.0-20.0; the coarse pulp is subjected to joint removal, screening, washing, oxygen delignification and bleaching in sequence to obtain wood pulp; bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching; the dosage of chlorine dioxide in chlorine dioxide bleaching is 10-15 kg/adt; the bleaching agent in the alkaline bleaching is NaOH, and the using amount of the NaOH is 10-15 kg/adt; the bleaching agent in the first-stage bleaching is chlorine dioxide, and the dosage of the bleaching agent is 3-4 kg/adt; the bleaching agent used in the second-stage bleaching is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent is 0.3-0.7 kg/adt. The wood pulp is manufactured by papermaking to obtain the wood pulp board with high strength and low dust degree.

Description

Preparation method of high-strength low-dust bleached sulfate hardwood pulp, wood pulp board and preparation method thereof

Technical Field

The invention relates to the technical field of papermaking, in particular to a preparation method of high-strength low-dust bleached sulfate hardwood pulp, a wood pulp board and a preparation method thereof.

Background

The paper making industry is an important basic raw material industry closely related to the development of national economy and social career, and the consumption level of paper and paperboard is a mark for measuring the modernization level and the civilization degree of the country. According to statistics, the total output of paper and paperboard in China currently reaches 8640 ten thousand tons, the total consumption amount reaches 8569 ten thousand tons, and China becomes a genuine big country for producing and consuming paper and paper products.

Bleached kraft pulp is classified by tree into hardwood pulp and softwood pulp. The hardwood pulp adopts raw material hardwood, which has shorter fiber, low lignin content, less content of hybrid cells and short growth period, is a main tree species for the integrated construction of wood pulp and paper in China, is one of good pulping and papermaking raw materials, and is distributed in the southwest, south China and the like.

In recent years, with the rapid development of the paper industry in China, people have higher and higher requirements on the strength and the dust degree of paper boards prepared from hardwood pulp, but the existing bleached sulfate hardwood pulp boards cannot meet the market demand.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for preparing high-strength low-dust bleached sulfate hardwood pulp, a wood pulp sheet and a preparation method thereof.

The invention provides a bleached sulfate hardwood pulp board, which has a tensile index of more than or equal to 72N.m/g and a burst index of more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree is less than or equal to 1.3mm²/m²The whiteness is 89-90% ISO and the methylene dichloride extract is less than or equal to 0.6%.

The invention provides a preparation method of bleached sulfate hardwood pulp, which comprises the following steps:

a) preparing broad-leaved wood chips to obtain wood;

b) cooking the wood in white liquor to obtain coarse pulp, wherein the cooked kappa number is 16.0-20.0;

c) removing knots, screening, washing, oxygen delignification and bleaching the brown stock to obtain bleached sulfate hardwood pulp;

the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching;

the dosage of chlorine dioxide in the chlorine dioxide bleaching process is 10-15 kg/adt;

the bleaching agent used in the alkali bleaching process is NaOH, and the dosage of the NaOH is 10-15 kg/adt;

the bleaching agent used in the first-stage bleaching process is chlorine dioxide, and the dosage of the bleaching agent used in the first-stage bleaching process is 3-4 kg/adt;

the bleaching agent used in the secondary bleaching process is chlorine dioxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.7 kg/adt.

Preferably, the mass concentration of the pulp in the chlorine dioxide bleaching process is 10-15%; the reaction temperature is 70-80 ℃; the pH value is 2.0-3.0.

Preferably, the mass concentration of the pulp in the alkali bleaching process is 10-15%; the oxygen consumption is 3.0-5.0 kg/adt, the reaction temperature is 70-80 ℃, and the pH value is 10.0-12.0.

Preferably, the mass concentration of the pulp in the first-stage bleaching process is 10-15%; the reaction temperature is 70-80 ℃, and the pH value is 4.0-6.0.

Preferably, the mass concentration of the pulp in the secondary bleaching process is 10-15%; the reaction temperature is 70-80 ℃, and the pH value is 4.0-6.0.

Preferably, the hardwood chips are selected from one or more of acacia chips, eucalyptus chips and hardwood chips.

Preferably, the removing segment in the step c) specifically comprises the following steps:

performing primary section removing on the coarse pulp, enabling the fine pulp obtained by the primary section removing to enter a screening process, performing secondary section removing after diluting the tailings of the primary section removing, enabling the fine pulp obtained by the secondary section removing to enter the screening process, and returning the tailings obtained by the secondary section removing to the cooking process after diluting, cleaning and dehydrating;

the pulp inlet concentration of the first-section joint removal is 3.0-5.0 wt%, the pulp inlet pressure is 180-310 KPa, the slag discharge rate is 5-20%, and the first-section joint removal pressure difference is 10-30 KPa; the slurry inlet concentration of the two-section joint removal is 3.0-5.0 wt%, the slurry inlet pressure is 180-220 KPa, the slag discharge rate is 10-30%, and the pressure difference of the two-section joint removal is 10-30 KPa.

Preferably, the screening section in step c) specifically comprises the following steps:

the method comprises the following steps of (1) carrying out first-stage screening on the coarse pulp subjected to section removal, enabling the fine pulp obtained by the first-stage screening to enter a washing process, diluting the tailings obtained by the first-stage screening and then carrying out second-stage screening, returning the fine pulp obtained by the second-stage screening to the first-stage screening process, diluting the tailings obtained by the second-stage screening and then carrying out third-stage screening, returning the fine pulp obtained by the third-stage screening to the second-stage screening process, diluting the tailings obtained by the third-stage screening and then carrying out fourth-stage screening, and returning the;

the pulp inlet concentration of the first section of screening is 2.0-4.1 wt%, the pulp inlet pressure is 180-300 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the two-stage screening is 1.6-1.8 wt%, the pulp inlet pressure is 100-260 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the three-stage screening is 0.8-2.5 wt%, the pulp inlet pressure is 100-200 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the four-stage screening is 1.0-1.5 wt%, the pulp inlet pressure is 100-200 KPa, and the screening pressure difference is 10-60 KPa.

The invention provides a preparation method of a bleached sulfate hardwood pulp board, which comprises the following steps:

the bleached sulfate hardwood pulp prepared by the preparation method in the technical scheme is manufactured by paper to obtain the bleached sulfate hardwood pulp board.

Compared with the prior art, the invention provides a preparation method of bleached sulfate hardwood pulp and a wood pulp board prepared by the method. The preparation method of the bleached sulfate hardwood pulp provided by the invention comprises the following steps: a) preparing broad-leaved wood chips to obtain wood; b) cooking the wood in white liquor to obtain coarse pulp, wherein the cooked kappa number is 16.0-20.0; c) removing knots, screening, washing, oxygen delignification and bleaching the brown stock in sequence to obtain bleached sulfate hardwood pulp; the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching; the dosage of chlorine dioxide in the chlorine dioxide bleaching process is 10-15 kg/adt; the bleaching agent used in the alkali bleaching process is NaOH, and the dosage of the NaOH is 10-15 kg/adt; the first stage bleachingThe bleaching agent used in the process is chlorine dioxide, and the dosage of the bleaching agent used in the first-stage bleaching is 3-4 kg/adt; the bleaching agent used in the secondary bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.7 kg/adt. The wood pulp prepared by the preparation method is manufactured by paper making to obtain the wood pulp board with high strength and low dust degree. The experimental results show that: the tensile index of the wood pulp board provided by the invention is more than or equal to 72N.m/g, and the burst index is more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree is less than or equal to 1.3mm²/m²The whiteness is 89-90% ISO and the methylene dichloride extract is less than or equal to 0.6%.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a flow chart of a process for producing bleached kraft hardwood pulp sheet according to an embodiment of the present invention.

Detailed Description

In the invention, the tensile index of the bleached sulfate hardwood pulp board is more than or equal to 72N.m/g, and preferably 72-76 N.m/g. In a particular embodiment of the invention, the average value of the tensile index of the bleached sulphate hardwood pulp board is in particular 72N.m/g, 73N.m/g or 76 N.m/g. The tensile index of the bleached sulfate hardwood pulp board is determined by a TAPPI T494 method.

In the present invention, the bleached sulfate hardwood pulp sheets are resistantThe burst index is more than or equal to 4.0KPa.m²G, preferably 4.0KPa.m²/g～5.7KPa.m²(ii) in terms of/g. In a particular embodiment of the invention, the average value of the burst index of the bleached sulphate hardwood pulp board is in particular 4.5kpa.m²/g、5.0KPa.m²G or 5.7KPa.m²(ii) in terms of/g. The method adopts standard TAPPI T403-2010 to bleach the burst index of the sulfate hardwood pulp board.

In the invention, the tearing index of the bleached sulfate hardwood pulp board is more than or equal to 6.6mN.m²Per g, preferably 6.6mN.m²/g～8.5mN.m²(ii) in terms of/g. In a particular embodiment of the invention, the average value of the tear index of the bleached sulphate hardwood pulp board is in particular 6.6mn.m²/g、7.2mN.m²G or 8.5mN.m²(ii) in terms of/g. The invention adopts standard TAPPI T414-2013 to bleach the tearing index of sulfate hardwood pulp board.

In the invention, the dust degree of the bleached sulfate hardwood pulp board is less than or equal to 1.3mm²/m²Preferably 1.0mm²/m²～1.3mm²/m². In a particular embodiment of the invention, the bleached kraft hardwood pulp board has an average value of specifically 1.1mm of dirt count²/m²、1.0mm²/m²Or 1.3mm²/m². The invention uses standard TAPPI T213-2010 to bleach the dust degree of sulfate hardwood pulp board.

In the present invention, the whiteness of the bleached sulfate hardwood pulp sheet is 89% ISO to 90% ISO, preferably 89.0% ISO to 89.9% ISO. In a specific embodiment of the invention, the average value of the whiteness of the bleached sulfate hardwood pulp sheet is specifically 89.3% ISO or 89.9% ISO. The invention adopts ISO 2470: 1999 determination of paper, cardboard and pulp-diffuse reflectance factor (ISO Brightness) whiteness of bleached sulfate hardwood pulp sheets was performed.

In the invention, the methylene chloride extract of the bleached sulfate hardwood pulp board is less than or equal to 0.6 percent, and preferably 0.16 to 0.6 percent. In particular embodiments of the invention, the average value of the methylene chloride extract of the bleached sulfate hardwood pulp sheet is in particular 0.36%, 0.25% or 0.16%. The present invention employs standard TAPPI T204-2010 for bleaching the methylene chloride extract of sulfate hardwood pulp sheets.

a) preparing broad-leaved wood chips to obtain wood;

c) removing knots, screening, washing, oxygen delignification and bleaching the brown stock in sequence to obtain bleached sulfate hardwood pulp;

the bleaching agent used in the secondary bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.7 kg/adt.

The invention prepares the wood by preparing the broad-leaved wood chips. In the invention, the process of preparing timber from broadleaf wood chips through stock preparation comprises the following steps: the broadleaf strands are screened. The broad-leaved wood chips are one or more of acacia wood chips, eucalyptus wood chips and hardwood wood chips, and preferably acacia wood chips and eucalyptus wood chips. The mass ratio of the acacia wood chips to the eucalyptus wood chips is preferably 0.5-2: 1, and more preferably 1: 1. The water content of the broad-leaved wood chips is preferably 35-50 wt%. Screening to obtain wood chips with the size meeting the requirement, namely wood; crushing the wood chips with the size larger than the specified size after screening, and returning to the screening process for secondary screening after crushing; and discharging the wood chips with the size smaller than the specified size, namely wood chips, after screening. In the present invention, the wood chips discharged outside may beUsed as fuel in fluidized bed boilers. The compression degree of the wood is preferably 10-15%; the virtual volume density of the wood is preferably 160-230 kg/m³. The proportion of bark and/or sapwood in the total wood is preferably less than or equal to 1 wt%; the proportion of the timber with the thickness of 3mm in the total timber is preferably less than or equal to 1 wt%; the proportion of the timber with the thickness of 3-7 mm in the total timber is preferably less than or equal to 6 wt%; the proportion of the timber with the thickness of 8-12 mm in the total timber is preferably less than or equal to 8 wt%; the proportion of the timber with the thickness of 13-45 mm in the total timber is preferably more than or equal to 55 wt%; the proportion of the timber with the thickness of more than or equal to 45mm in the total timber is preferably less than or equal to 2 wt%.

After obtaining the wood, the wood is steamed in white liquor to obtain coarse pulp, and the steamed kappa number is 16.0-20.0. In the invention, the white liquor is preferably NaOH and Na₂And (3) mixed solution of S. In the invention, the process of cooking the wood in white liquor to obtain the brown stock specifically comprises the following steps:

b1) impregnating the timber to obtain impregnated timber;

the dipping temperature is 80-110 ℃;

b2) the impregnated wood is steamed and boiled in white liquor under high pressure to obtain coarse pulp;

the temperature of the high-pressure cooking is 140-160 ℃; the pressure of the high-pressure cooking is 0.2-0.7 MPa; the liquid-material ratio of the high-pressure cooking is 1.5-7 m³Bdt; the boiling kappa number is 16.0-20.0.

In the present invention, the wood obtained in step a) is first subjected to step b1) to obtain impregnated wood. The step b1) is as follows: the wood is impregnated to obtain impregnated wood. The impregnation liquid is white liquor and/or cooking black liquor generated by high-pressure cooking. The dipping temperature is preferably 80-110 ℃, and more preferably 90-100 ℃; in particular embodiments of the invention, the temperature of the impregnation is 100 ℃, 95 ℃ or 90 ℃. Discharging the impregnation black liquor generated in the wood impregnation process. In the invention, the discharged impregnation black liquor is preferably recycled, the discharged impregnation black liquor can be filtered and evaporated to obtain concentrated black liquor, and the concentrated black liquor can be used as a raw material for producing white liquor. The present invention preferably steams the wood prior to wood impregnation. In the present invention, steaming refers to placing the wood in an atmosphere of high temperature steam, preferably hot steam generated by the impregnation fluid during the impregnation process.

In the present invention, the steaming and impregnation are preferably performed in an impregnation tower including an upper and a lower layer structure, the upper layer being a steaming section and the lower layer being an impregnation section.

In the present invention, the wood is first steamed in a steaming section, the steaming steam being derived from rising steam generated by the impregnation fluid in the impregnation section. The steamed wood falls into the impregnation section where it is impregnated. The dipping section is provided with an extraction sieve plate for extracting the dipping black liquor generated in the dipping process. And extracting the impregnation black liquor by using an extraction sieve plate, filtering, evaporating filtrate obtained by filtering to obtain concentrated black liquor, and feeding filter residue obtained by filtering into a high-pressure cooking process. The filtration of the impregnated black liquor is preferably carried out in a black liquor filter and the evaporation of the filtrate is preferably carried out in an evaporation plant.

The impregnated wood obtained in step b1) is subjected to step b2) to obtain a brown stock. The step b2) is as follows: and (3) steaming and boiling the impregnated wood in white liquor at high pressure to obtain coarse pulp.

In the present invention, the impregnated wood is preferably fed to the autoclaving process from a carrier fluid. The carrier fluid is preferably an impregnation fluid used in the impregnation process. In the present invention, the impregnated wood is preferably fed to the high-pressure cooking process through a discharge device, a high-pressure feeder and a separator.

In the invention, the impregnated wood obtained by impregnation enters a discharging device filled with a carrier fluid from an impregnation section, then enters a high-pressure feeder along with the carrier fluid, the impregnated wood and the carrier fluid are conveyed to a separator by the high-pressure feeder, the impregnated wood and the carrier fluid are separated in the separator, the carrier fluid obtained by separation is recycled, and the impregnated wood obtained by separation enters a high-pressure cooking process.

In the autoclaving process, the wood and the white are impregnatedThe liquid is mixed and steamed under high pressure to obtain coarse pulp. The white liquor is NaOH and Na₂And (3) mixed solution of S. The concentration of NaOH in the white liquid is preferably 125-145 g/L, more preferably 130-135 g/L, and in the specific embodiment of the invention, the concentration of NaOH in the white liquid is 132g/L or 130 g/L; the sulfuration degree of the white liquor is preferably 30-35%, and more preferably 32-34%; in a particular embodiment of the invention, the degree of vulcanisation of the white liquor is particularly 32.5% or 32%. The temperature of the high-pressure cooking is preferably 140-160 ℃, more preferably 146-152 ℃, and in the specific embodiment of the invention, the temperature of the high-pressure cooking is specifically 152 ℃, 148 ℃ or 146 ℃. The pressure of the high-pressure cooking is preferably 0.2-0.7 MPa, and more preferably 0.25-0.5 MPa; in a specific embodiment of the invention, the pressure of the autoclaving is specifically 0.32MPa, 0.25MPa or 0.3 MPa. The liquid-material ratio of the high-pressure cooking is preferably 1.5-7 m³And/bdt. In the present invention, it is preferable that the impregnated wood is first subjected to primary autoclaving to obtain primary digested wood pulp, and then the primary digested wood pulp is subjected to secondary autoclaving to obtain brown stock. The process of carrying out first-stage high-pressure cooking and second-stage high-pressure cooking on the impregnated wood comprises the following specific steps: the impregnated wood is mixed with white liquor and subjected to a first stage of high pressure cooking. The temperature of the first-stage high-pressure cooking is preferably 140-160 ℃, and more preferably 148-150 ℃; the pressure is preferably 0.2-0.7 MPa, and more preferably 0.25-0.4 MPa; the liquid-material ratio is preferably 3.5-7.0 m³/bdt, more preferably 4.2 to 4.5m³Bdt; in a specific embodiment of the invention, the feed-liquid ratio is specifically 4.5m³/bdt、4.2m³/bdt or 4.4m³And/bdt. Discharging first-stage cooking black liquor generated by first-stage high-pressure cooking out of the cooking system. In the invention, the first-stage cooking black liquor discharged from the cooking system is preferably recycled, and can be used as impregnation liquor to return to the impregnation process; can also be used as a carrier fluid for conveying the impregnated wood; the concentrated black liquor can be obtained after filtration and evaporation, and can be used as a raw material for producing white liquor. The impregnated wood is subjected to a first stage of high pressure cooking to obtain a first stage of cooked wood pulp. And mixing the first-stage cooked wood pulp with white liquor to perform second-stage high-pressure cooking. The second mentionedThe temperature of the high-pressure cooking is preferably 140-160 ℃, and more preferably 160 ℃; the pressure is preferably 0.5-0.7 MPa, in the specific embodiment of the invention, the pressure is specifically 0.65MPa or 0.64MPa, and the liquid-material ratio is preferably 1.5-3.0 m³Bdt; in the embodiment of the invention, the feed-liquid ratio is specifically 2.0m³/bdt or 1.9m³/bdt. Discharging the second-stage black liquor generated by the second-stage high-pressure cooking out of the cooking system. In the present invention, it is preferable to use the second stage black liquor discharged from the cooking system to exchange heat with the white liquor which is not introduced into the cooking system, so as to recover the heat of the second stage black liquor. In the invention, the heat-exchanged second-stage cooking black liquor is preferably recycled, and can be filtered and evaporated to obtain concentrated black liquor, and the concentrated black liquor can be used as a raw material for producing white liquor.

The first-stage cooked wood pulp is subjected to second-stage high-pressure cooking to obtain coarse pulp. The brown stock is subjected to step b3) to obtain brown stock. The step b3) is as follows: and washing the coarse pulp to obtain the coarse pulp. The washing dilution factor is preferably 0.5-2.5 m³A/adt, more preferably 0.5 to 1.3m³In the examples of the invention, the dilution factor of the wash is in particular 1.3m³/adt or 0.5m³And/adt. The kappa number of the coarse pulp is preferably 16.0-20.0. And discharging washing waste liquid generated by washing out from a washing system. In the present invention, it is preferable to use the washing waste liquid discharged from the washing system to exchange heat with the white liquor which has not entered the cooking system, to recover the heat of the washing waste liquid. In the invention, the washing waste liquid after heat exchange is preferably recycled, the washing waste liquid after heat exchange can be filtered and evaporated to obtain concentrated black liquor, and the concentrated black liquor can be used as a raw material for producing white liquor.

In the present invention, the separation of the impregnated wood and carrier fluid, the first stage autoclaving, the second stage autoclaving and the brown stock washing are preferably carried out in a digester. The cooking tower comprises a separator, an upper cooking section, a lower cooking section and a washing section, wherein the separator, the upper cooking section, the lower cooking section and the washing section are distributed from top to bottom along the vertical direction of the cooking tower. The separator is arranged at the top of the cooking tower. The upper cooking section and the lower cooking section are separated by an upper extraction sieve plate. The lower cooking section and the washing section are separated by a lower extraction sieve plate.

In the invention, the impregnated wood and the carrier flow are conveyed into a separator at the top of the cooking tower through a high-pressure feeder, the separator separates the impregnated wood and the carrier flow, and the carrier flow obtained by separation returns to a discharging device, the high-pressure feeder or an impregnation section of the impregnation tower; the separated impregnated wood is fed to an upper cooking stage. The upper cooking section is provided with a white liquor inlet, and white liquor enters the upper cooking section through the white liquor inlet. The impregnated wood and white liquor are mixed in an upper cooking section and subjected to a first-stage high-pressure cooking. The first-stage black liquor generated in the first-stage high-pressure cooking process is extracted out of the cooking tower through an upper extraction sieve plate. The extracted black liquor can be used as a current-carrying return discharging device; can also be used as impregnation liquid to return to the impregnation section of the impregnation tower; and the filter residue can also be conveyed to a black liquor filter, filtrate obtained by filtering is conveyed to an evaporation device, and filter residue obtained by filtering is conveyed to a discharger. The extracted section of cooking black liquor is preferably heat exchanged with white liquor that has not entered the cooking tower before entering the black liquor filter. The impregnated wood is subjected to a first stage of high pressure cooking to obtain a first stage of cooked wood pulp. And the first-stage cooked wood pulp enters a lower cooking stage. The lower cooking section is also provided with a white liquor inlet, and white liquor enters the lower cooking section through the white liquor inlet. The first stage cooked wood pulp and the white liquor are mixed in the lower cooking stage for second stage high pressure cooking. The second-stage cooking black liquor generated in the second-stage high-pressure cooking process is extracted out of the cooking tower through a lower extraction sieve plate. Preferably, the extracted two-stage cooking black liquor is conveyed to a black liquor filter, filtrate obtained by filtering is conveyed to an evaporation device, and filter residue obtained by filtering is conveyed to a discharger. The extracted two-stage cooking black liquor is preferably heat exchanged with white liquor that does not enter the cooking tower before entering the black liquor filter.

And the first-stage wood pulp cooking lower cooking stage is subjected to second-stage high-pressure cooking to obtain coarse pulp. The brown stock enters a washing section. And a washing liquid inlet in the washing section is arranged at the bottom of the washing section, washing liquid enters a washing section of the cooking tower from the washing liquid inlet after being pressurized to carry out countercurrent washing on coarse pulp, washing waste liquid generated by washing is extracted out of the cooking tower through a lower extraction sieve plate, the extracted washing waste liquid is preferably conveyed to a black liquid filter, filtrate obtained by filtering is conveyed to an evaporation device, and filter residue obtained by filtering is conveyed to a discharger. The extracted washing waste liquor is preferably heat exchanged with white liquor not entering the digester before entering the black liquor filter. And discharging the pulp obtained after the wood pulp is washed from a pulp discharge port of the cooking tower. In the present invention, the temperature of the washing liquid entering the digester is preferably less than 80 ℃ in order to ensure that the brown stock temperature at the discharge outlet of the digester is less than 90 ℃. In the invention, the strength performance of the slurry can be maintained at a better level by controlling the temperature of the slurry at the slurry outlet, and the flash evaporation of the slurry in the discharging process can be prevented.

In the present invention, the pulp discharged from the cooking tower is preferably stored in a cooking blow-down pot, on top of which an atmospheric diffusion scrubber is arranged for further washing of the brown stock. When the diffusion washer operates normally, the slurry falls into a spraying groove at the bottom of a spraying pot after being washed by the normal-pressure diffusion washer; when the diffusion scrubber fails, the slurry directly enters the blow-down tank. The slurry is diluted in a blow tank and then conveyed to a subsequent working section. The coarse pulp concentration in the spraying groove is diluted to 3.0-4.6 wt% and then conveyed to 3 parallel-connected first-stage knot removers.

After the brown stock is obtained, the brown stock is subjected to joint removal, screening, washing, oxygen delignification and bleaching in sequence to obtain bleached sulfate hardwood pulp; the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching; the dosage of chlorine dioxide in the chlorine dioxide bleaching process is 10-15 kg/adt; the bleaching agent used in the alkali bleaching process is NaOH, and the dosage of the NaOH is 10-15 kg/adt; the bleaching agent used in the first-stage bleaching process is chlorine dioxide, and the dosage of the bleaching agent used in the first-stage bleaching process is 3-4 kg/adt; the bleaching agent used in the secondary bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.6 kg/adt.

In the invention, the coarse pulp removing and joint saving section specifically comprises the following steps:

the pulp inlet concentration of the first-section node removal is 3.0-5.0 wt%, the pulp inlet pressure is preferably 180-310 KPa, and more preferably 280-310 KPa; the slag discharge rate is 5-20%, and in the specific embodiment of the invention, the slag discharge rate is 19% or 18%; the first-section pressure difference for removing the pressure difference is 10-30 KPa, more preferably 20-25 KPa, in the specific embodiment of the invention, the first-section pressure difference for removing the pressure difference is 25KPa or 23 KPa; the slurry inlet concentration of the two-stage joint removal is 3.0-5.0 wt%, the slurry inlet pressure is 180-220 KPa, the slag discharge rate is 10-30%, and the pressure difference of the two-stage joint removal is 10-30 KPa, more preferably 20-25 KPa.

In the invention, the coarse pulp enters a section of section removal process after being diluted. The slurry inlet concentration of the first-stage section is preferably 3.0-4.3 wt%, more preferably 3.5-4.0%, the slurry inlet pressure is preferably 190-220 KPa, more preferably 195-198 KPa, the slag discharge rate is preferably 5-30%, more preferably 25-30%, in the specific embodiment of the invention, the slag discharge rate is specifically 28% or 27%, and the section-removing pressure difference is preferably 10-30 KPa, more preferably 20-27 KPa. The good pulp of the first-section joint removal enters a screening process, and the tailings of the first-section joint removal enter a second-section joint removal process after being diluted. The first-stage removal is therefore preferably carried out in a first-stage removal machine, which preferably consists of 3 removal machines connected in parallel. And diluting the tailings of the first-stage section removal, and then carrying out second-stage section removal, wherein the slurry inlet concentration of the second-stage section removal is preferably supplemented by 3.0-5.0 wt%, the slurry inlet pressure is preferably supplemented by 180-220 KPa, the slag discharge rate is preferably supplemented by 10-30%, and the operation pressure difference is preferably supplemented by 10-30 KPa. The good pulp of the second-stage knot removal enters a screening process, and the tailings of the second-stage knot removal return to a cooking process after dilution, impurity removal, cleaning and dehydration, and preferably return to a dipping process in the cooking process. In the invention, the tailings of the second-stage knot removal can also be stored without returning to the cooking process after dilution, impurity removal, cleaning and dehydration. The two-stage debulking is carried out in a preferred two-stage debulking machine.

In some embodiments of the present invention, it is preferable to dilute and wash the tailings of the second stage of section removal, the good pulp after section washing enters the screening process, and the tail pulp after section washing returns to the cooking process after dilution, cleaning and dehydration, and preferably returns to the impregnation process in the cooking process. The washing is preferably carried out in a washing machine, the pulp inlet concentration of the washing machine is preferably 0.5-1.0 wt%, and the tail pulp discharge concentration is preferably 28-30 wt%. A screen drum is arranged in the section washing machine, a spiral is arranged in the screen drum, tailing diluent of two-section removal sections is upwards conveyed by the spiral after entering the screen drum, dewatering is carried out through a hole screen in the conveying process, washing liquid is sprayed onto dewatered tailings from the end of the spiral shaft, fibers in the tailings are separated, and tailings after dewatering and washing are discharged from the top of the screen drum. In the process of washing knots, the good pulp passes through the sieve pores and enters a screening process.

Screening the coarse pulp after removing knots, wherein the screening specifically comprises the following steps:

and (3) carrying out first-stage screening on the coarse pulp subjected to section removal, enabling the good pulp obtained by the first-stage screening to enter a washing process, diluting the tailings obtained by the first-stage screening and then carrying out second-stage screening, returning the good pulp obtained by the second-stage screening to the first-stage screening process, diluting the tailings obtained by the second-stage screening and then carrying out third-stage screening, returning the good pulp obtained by the third-stage screening to the second-stage screening process, diluting the tailings obtained by the third-stage screening and then carrying out fourth-stage screening, and returning the good pulp obtained by the. The concentration of the pulp entering in the first stage of screening is preferably 2.0-4.0 wt%, more preferably 3.5-4.0 wt%, and in the embodiment of the invention, the concentration is specifically 4 wt% or 3.8 wt%; the pulp inlet pressure is preferably 180-300 KPa, and is specifically 180KPa or 190KPa in the embodiment of the invention; the screening pressure difference is preferably 10-60 KPa, and is specifically 40KPa in the embodiment of the invention; the pulp inlet concentration of the secondary screening is preferably 1.6-3 wt%, more preferably 2.5-3.0 wt%, and in the specific embodiment of the invention, the pulp inlet concentration of the secondary screening is specifically 2.8 wt% or 2.9 wt%; the pulp inlet pressure is preferably 100-260 KPa, more preferably 250-260 KPa, and the screening pressure difference is preferably 10-60 KPa, more preferably 25-30 KPa; the pulp inlet concentration of the three-stage screening is preferably 0.8-2.1 wt%, more preferably 2.0-2.1 wt%, the pulp inlet pressure is preferably 100-200 KPa, more preferably 200-180 KPa, the screening pressure difference is preferably 10-60 KPa, more preferably 30-35 KPa, and is specifically 30KPa or 35KPa in the embodiment of the invention; the pulp inlet concentration of the four-stage screening is 1.0-1.5 wt%, in the embodiment of the invention, 1.2 wt% or 1.3 wt%, the pulp inlet pressure is 100-200 KPa, more preferably 180-190 KPa, and the screening pressure difference is 10-60 KPa, more preferably 20-30 KPa, in the embodiment of the invention, the screening pressure difference is 20KPa, 25KPa or 30 KPa.

In the invention, the coarse pulp after the nodes are removed is diluted and then is subjected to a first-stage screening. The pulp inlet concentration of the first stage of screening is preferably 2.0-4.1 wt%, more preferably 4.0-4.1 wt%, the pulp inlet pressure is preferably 180-300 KPa, more preferably 180-195 KPa, and the screening pressure difference is preferably 10-60 kPa, more preferably 40-45 KPa. And (4) the good pulp obtained by the first-stage screening enters a washing procedure, and the tailings obtained by the first-stage screening are diluted and then subjected to second-stage screening. The pulp inlet concentration of the secondary screening is preferably 1.6-3.0 wt%, and more preferably 2.9 wt%; the slurry inlet pressure is preferably 100-260 KPa, and more preferably 250-260 KPa; the screening pressure difference is preferably 10 to 60kPa, and more preferably 25 to 30 KPa. And (4) returning the good pulp obtained by the second-stage screening to the first-stage screening process, and diluting the tailings obtained by the second-stage screening to perform third-stage screening. The pulp inlet concentration of the three-stage screening is preferably 0.8-2.5 wt%, and more preferably 2.1 wt%; the pulp inlet pressure is preferably 100-200 KPa, and more preferably 180 KPa; the screening pressure difference is preferably 10-60 kPa. And returning the good pulp obtained by the third-stage screening to the second-stage screening process, and diluting the tailings obtained by the third-stage screening to perform fourth-stage screening. In the invention, the tailings obtained by the two-stage screening are diluted and then preferably subjected to sand removal, and the good pulp subjected to sand removal is subjected to three-stage screening. The desanding is performed in a desander. The sand remover is a centrifugal purification device, tailings of the second-stage screen enter the sand remover in a tangential direction after being diluted, the tailings rotate at a high speed in the sand remover, sand particles with large specific gravity fall into the lower end of the sand remover in the rotation process, then enter the collector, and slurry with small specific gravity leaves from the top of the sand remover and enters the third-stage screening process. Diluting tailings obtained by the three-stage screening, and then carrying out four-stage screening, wherein the pulp inlet concentration of the four-stage screening is preferably 1.0-1.5 wt%, and more preferably 1.3 wt%; the pulp inlet pressure is 100-200 KPa, and more preferably 190 KPa; the screening pressure difference is preferably 10-60 KPa, and more preferably 25 KPa. The good pulp screened in the fourth section returns to the third screening process, and the tailings screened in the fourth section are discharged. The invention preferably presses the tailings discharged from the four-section screening, the dried tailings are discharged, and the filtrate obtained by pressing is recovered for later use. The pressing is preferably carried out in a screw press.

In certain embodiments of the present invention, it is preferred to dilute and wash the tailings of the four stage screening. And returning the good pulp obtained by washing the slag to the four-section screening process, and discharging the tailings after washing the slag. Slag washing is preferably carried out in a slag washing machine, and the pulp feeding concentration of the slag washing machine is preferably 0.5-1.0 wt%, and more preferably 0.8-1.0 wt%. The temperature of the washing liquid used in the slag washing process is preferably 70-90 ℃. The structure and the working principle of the slag washing machine are the same as those of the washing machine, and the details are not repeated.

In the present invention, the screening of the brown stock is preferably carried out in a pressure screen. The pressure screen is composed of a screen drum and a rotor in the screen drum, wood pulp liquid to be screened enters the top of the screen drum, good pulp passes through the screen drum, and tailings are discharged from the bottom of the screen drum. Whether the pressure screen operates normally can be judged through the pressure difference between the pulp inlet and the pulp outlet in the operation process of the pressure screen, the normal operation pressure difference of the pressure screen is 10-60 kPa, if a screen cylinder starts to be blocked, the pressure difference is increased, and the pulp flow is reduced. If the screen drum is blocked, the blockage condition can be relieved by reducing the pulp inlet amount.

And washing the coarse pulp after screening, wherein the washing specifically comprises the following steps:

firstly, carrying out primary washing on the screened coarse pulp, wherein the dilution factor of the primary washing is preferably 0.8-2.0 m³And/adt. And diluting the first-stage washed wood pulp obtained by the first-stage washing, and then carrying out second-stage washing, wherein first-stage washing waste liquid generated by the first-stage washing is discharged. In the present invention, the source of the washing liquid used in the first-stage washing is not particularly limited, and it is preferably a secondary washing waste liquid generated in the second-stage washing. In the invention, the discharged first-stage washing waste liquid is preferably recycled, and the discharged first-stage washing waste liquid can be returned to the cooking procedure to be used as washing liquid for washing coarse pulp. The one-stage washing is carried out in a washing apparatusPreferably, the washing apparatus is 3 parallel twin roll washers. The pulp inlet concentration of the double-roller pulp washer is preferably 3.0-4.2 wt%, and the pulp outlet concentration of the double-roller pulp washer is preferably 26-30 wt%.

And diluting the first-stage washed wood pulp obtained by the first-stage washing, and then carrying out second-stage washing. The dilution factor of the two-stage washing is preferably 0.8-2.0 m³And/adt. Diluting the second-stage washing wood pulp obtained by the second-stage washing, and then entering an oxygen delignification procedure, and discharging second-stage washing waste liquid generated by the second-stage washing. In the present invention, the source of the washing liquid used in the secondary washing is not particularly limited, and is preferably washing waste liquid generated in the secondary oxygen delignification wood pulp washing. In the invention, the discharged second-stage washing waste liquid is preferably recycled, and the discharged second-stage washing waste liquid can be used as a washing liquid for first-stage washing and returned to the first-stage washing process. The secondary washing is carried out in a washing apparatus, preferably 2 twin-roll washers connected in parallel. The pulp inlet concentration of the double-roller pulp washer is preferably 3.0-4.2 wt%, and the pulp outlet concentration of the double-roller pulp washer is preferably 26-30 wt%. And diluting the two-stage washed wood pulp obtained by the two-stage washing, and then, entering an oxygen delignification process, wherein the concentration of the diluted wood pulp is preferably 10-12 wt%.

And the screened brown pulp enters an oxygen delignification process after being subjected to primary washing and secondary washing. In the present invention, the oxygen delignification refers to the removal of lignin dissolved in brown stock in the presence of oxygen and an oxygen delignification agent. The purity of the oxygen is preferably greater than 93%; the oxygen delignification agent is white liquor or NaOH.

In the present invention, the process of oxygen delignification of the brown stock comprises the following steps:

c1) the brown stock is subjected to primary oxygen delignification to obtain primary oxygen delignification wood pulp;

the pulp inlet concentration of the first-stage oxygen delignification is 10-12 wt%, the pulp outlet concentration is 10-12 wt%, and the time is 20-30 min; the pressure is 600-800 KPa, preferably 650KPa, the temperature is 90-95 ℃, preferably 94 ℃, the pH value is 10.8-11.5, the oxygen consumption is 10-22 kg/add, and the oxygen delignification agent consumption is 15-26 kg/add;

c2) the first-stage oxygen delignification wood pulp is subjected to second-stage oxygen delignification to obtain second-stage oxygen delignification wood pulp;

the pulp inlet concentration of the two-stage oxygen delignification is 10-12 wt%, the pulp outlet concentration is 10-12 wt%, and the time is 40-60 min; the pressure is 300-600 KPa, the temperature is 98-110 ℃, the pH value is 10-11, the oxygen consumption is 2-10 kg/adt, and the oxygen delignification agent consumption is 0-5 kg/adt;

c3) washing the second-stage oxygen delignified wood pulp to obtain bleached sulfate hardwood pulp;

the dilution factor of the washing is 2.0-2.5 m³The/adt; the kappa number of the bleached sulfate hardwood pulp is 8.5-11.5.

In the present invention, the oxygen delignification refers to the removal of lignin dissolved in brown stock in the presence of oxygen and an oxygen delignification agent. The purity of the oxygen is preferably greater than 93%; the oxygen delignification agent is white liquor or NaOH.

In the present invention, the brown stock is first subjected to step c1) to obtain a primary oxygen delignified wood pulp. The step c1) is as follows: and performing primary oxygen delignification on the brown stock to obtain primary oxygen delignified wood pulp. The process of obtaining the primary oxygen delignified wood pulp by the brown stock through the primary oxygen delignification is specifically as follows: mixing the coarse pulp, the oxygen delignification agent and oxygen to carry out primary oxygen delignification. The concentration of the slurry entering the primary oxygen delignification is preferably 10-12 wt%; the preferable pulp outlet concentration is 10-12 wt%; the time is preferably 20-25 min; the pressure is preferably 600 to 800KPa, more preferably 630 to 700KPa, in the embodiment of the invention, the pressure is specifically 650KPa, 700KPa or 630 KPa; the temperature is preferably 90-95 ℃, and more preferably 93 ℃; the pH value is preferably 10.8-11.5, more preferably 11-11.2, and in the specific embodiment of the invention, the pH value is specifically 11.0; the dosage of the oxygen is preferably 10-20 kg/adt, more preferably 18-20 kg/adt, and in the specific embodiment of the invention, the dosage of the oxygen is specifically 20 kg/adt; the dosage of the oxygen delignification agent is preferably 15-26 kg/adt, more preferably 20-24 kg/adt, and in the embodiment of the invention, the dosage is specifically 23.5 kg/adt. The present invention preferably deaerates the brown stock to remove gases from the brown stock prior to mixing the brown stock, the oxygen delignification agent and the oxygen. And obtaining the primary oxygen delignification wood pulp after the primary oxygen delignification is finished.

The primary oxygen delignified wood pulp is subjected to step c2) to obtain a secondary oxygen delignified wood pulp. The step c2 is as follows: and the first-stage oxygen delignified wood pulp is subjected to second-stage oxygen delignification to obtain second-stage oxygen delignified wood pulp. The process of obtaining the second-stage oxygen delignified wood pulp by the first-stage oxygen delignified wood pulp through the second-stage oxygen delignification is as follows: the primary oxygen delignification wood pulp, the oxygen delignification agent and oxygen are mixed for secondary oxygen delignification. The pulp inlet concentration of the two-stage oxygen delignification is preferably 10-12 wt%; the preferable pulp outlet concentration is 10-12 wt%; the time is preferably 40-60 min, and more preferably 55-60 min; the pressure is preferably 300 to 600KPa, more preferably 310 to 330KPa, in the embodiment of the invention, the pressure is specifically 320KPa or 310 KPa; the temperature is preferably 98-110 ℃, more preferably 100-105 ℃, and in the specific embodiment of the invention, the temperature is specifically 104 ℃ or 103.5 ℃; the pH value is preferably 10-11, preferably 10.2-10.5; the dosage of the oxygen is preferably 3-10 kg/adt, and more preferably 3.5-5 kg/adt; the dosage of the oxygen delignification agent is preferably 0-5 kg/adt. The present invention preferably deaerates the primary oxygen delignification prior to mixing the primary oxygen delignification wood pulp, the oxygen delignification agent and the oxygen to remove gases from the primary oxygen delignification wood pulp. And after the second-stage oxygen delignification is finished, obtaining the second-stage oxygen delignification wood pulp.

The secondary oxygen delignified wood pulp is subjected to step c3) to obtain bleached kraft hardwood pulp. The step c3) is as follows: and washing the two-stage oxygen delignified wood pulp to obtain bleached sulfate hardwood pulp. The invention preferably deaerates the secondary oxygen delignified wood pulp prior to washing the secondary oxygen delignified wood pulp to remove gases from the secondary oxygen delignified wood pulp. The washing dilution factor is preferably 2-2.5 m³And/adt. The kappa number of the bleached sulfate hardwood pulp is preferably 8.5-11.5.

In the present invention, the brown stock is preferably subjected to oxygen delignification in a system consisting of: the system comprises an oxygen delignification feeding trough, a medium concentration pump, a first gas mixer, a first chemical mixer, a first-stage oxygen delignification tower, a second gas mixer, a second chemical mixer, a second-stage oxygen delignification tower, an oxygen delignification blow-out pot and a pulp washer. The oxygen delignification feeding trough is connected with the middle-concentration pump liquid inlet, the middle-concentration pump liquid outlet is connected with the first gas mixer liquid inlet, the first gas mixer liquid outlet is connected with the first chemical mixer liquid inlet, the first chemical mixer liquid outlet is connected with the bottom end feed inlet of one section oxygen delignification tower, the top end discharge outlet of the one section oxygen delignification tower is connected with the second gas mixer liquid inlet, the second gas mixer liquid outlet is connected with the second chemical mixer liquid inlet, the second chemical mixer liquid outlet is connected with the bottom end feed inlet of the two section oxygen delignification tower, the top end discharge outlet of the two section oxygen delignification tower is connected with the oxygen delignification blow-off pot feed inlet, and the oxygen delignification blow-off pot discharge outlet is connected with the pulp washer feed inlet.

In the invention, the brown stock is conveyed to an oxygen-removing feeding trough, and the brown stock in the oxygen-removing feeding trough is pumped to a feed inlet of a first-stage oxygen delignification tower by a medium-concentration pump. And an oxygen delignification agent feeding port is arranged on a pipeline connecting the feeding tank and the medium concentration pump, the oxygen delignification agent is added into the brown stock through the feeding port, the adding amount of the oxygen delignification agent is adjusted according to the pH value of the pulp in the first-stage oxygen delignification tower, and the pH value of the pulp in the first-stage oxygen delignification tower is kept between 10.8 and 11.5. The medium consistency pump is equipped with a de-aeration system for removing gas from the brown stock. In the process that the coarse pulp is pumped to the feed inlet of the first-stage oxygen delignification tower by the medium-concentration pump, the coarse pulp sequentially passes through the first gas mixer and the first chemical mixer. The first gas mixer is provided with an oxygen inlet and a steam inlet, oxygen is added into the brown stock through the oxygen inlet, and medium-pressure steam is added into the brown stock through the steam inlet. The medium-pressure steam is used for increasing the temperature of the coarse pulp, the adding amount of the medium-pressure steam is adjusted according to the pulp inlet temperature, and the pulp inlet temperature is kept at 90-95 ℃. The first chemical mixer is used for uniformly mixing the oxygen delignification agent and the brown stock. When the medium concentration pump is shut down, in order to prevent the coarse slurry from flowing back to the oxygen-removing feeding trough from the pipeline, the liquid inlet and outlet valves of the chemical mixer are closed. The slurry mixed with oxygen and the oxygen delignification agent enters a first-section oxygen delignification tower through a feed inlet of the first-section oxygen delignification tower. The first-section oxygen delignification tower is provided with two pressure sensors, the internal pressure of the oxygen delignification tower is measured by using the two pressure sensors, and the normal pressure at the top of the oxygen delignification tower is 600-800 kPa. After the reaction of the coarse pulp in the first-stage oxygen delignification tower is finished, the coarse pulp is discharged from a discharge port at the top end of the first-stage oxygen delignification tower and enters a liquid inlet of a second gas mixer. And a discharge device is arranged at the discharge outlet at the top end of the first section of oxygen delignification tower, and the discharge device is provided with a degassing system. In the invention, the deaeration of the brown stock after the primary oxygen delignification is beneficial to improving the delignification effect of the brown stock in the secondary oxygen delignification tower.

And (3) after the reaction of the coarse pulp in the first-stage oxygen delignification tower is finished, obtaining the first-stage oxygen delignification wood pulp. And the first-stage oxygen delignified wood pulp is discharged from a discharge hole at the top end of the first-stage oxygen delignified tower and conveyed to a liquid inlet of a second gas mixer. The second gas mixer is provided with an oxygen inlet and a steam inlet, oxygen is added into one section of oxygen delignification wood pulp through the oxygen inlet, and medium-pressure steam is added into one section of oxygen delignification wood pulp through the steam inlet. The adding amount of the medium-pressure steam is adjusted according to the pulp inlet temperature, and the pulp inlet temperature is kept at 98-110 ℃. And the first-stage oxygen delignified wood pulp is discharged from a liquid outlet of the second gas mixer and enters a second chemical mixer. And an oxygen delignification agent feeding port is arranged on a connecting pipeline of the second gas mixer and the second chemical mixer, the oxygen delignification agent is added into the first-stage oxygen delignification wood pulp through the feeding port, the adding amount of the oxygen delignification agent is adjusted according to the pH value of the pulp in the second-stage oxygen delignification tower, and the pH value of the pulp in the second-stage oxygen delignification tower is kept between 10 and 11. And mixing the first-stage oxygen delignified wood pulp and the oxygen delignification agent in a second chemical mixer, and uniformly mixing the first-stage oxygen delignified wood pulp and the oxygen delignification agent, and then feeding the mixture into a second-stage oxygen delignification tower through a feed inlet at the bottom end of the second-stage oxygen delignification tower. The two-section oxygen delignification tower is provided with two pressure sensors, the internal pressure of the oxygen delignification tower is measured by using the two pressure sensors, and the normal pressure at the top of the oxygen delignification tower is 300-600 kPa. And the second-stage oxygen delignified wood pulp is obtained after the reaction of the first-stage oxygen delignified wood pulp in the second-stage oxygen delignified tower is finished, and is discharged from a discharge port at the top end of the second-stage oxygen delignified tower and enters an oxygen delignified blow-on pot.

Discharging the two-stage oxygen delignified wood pulp from the discharge port of the oxygen delignification spraying pot, and conveying the two-stage oxygen delignified wood pulp to washingA slurry machine. A degassing system is provided on the connecting line between the oxygen delignification blow-off pot and the washer for removing gases from the secondary oxygen delignified wood pulp. In the invention, the pulp inlet concentration of the pulp washer is preferably 7-11 wt%, more preferably 7-9 wt%, and the pulp outlet concentration is preferably 11-30 wt%, more preferably 25-30 wt%; the preferred dilution factor is 2-2.5 m³/adt, more preferably 2.2m³/adt～2.3m³The/adt; the pulp inlet pressure is preferably 30-50 kPa, and more preferably 30-40 kPa; the rotation speed is preferably 1.0-9.5 rpm, more preferably 8.0-9.5 rpm, and in the embodiment of the present invention, the rotation speed is specifically 8.0rpm, 8.5rpm or 9.5 rpm; the electric conductivity of the filtrate is preferably 0-1000 us/cm. And obtaining the bleached sulfate hardwood pulp after the washing is finished.

And bleaching the pulp after oxygen delignification to obtain bleached sulfate hardwood pulp.

The bleaching aims to remove residual lignin and impurities in the pulp, such as non-fiber components, extractable substances and the like, so as to meet the quality indexes of the pulp such as whiteness, whiteness stability, strength, smoothness and the like and achieve the required whiteness and quality requirements.

A more selective chemical is used in the bleaching stage to bleach the pulp to the desired brightness. In the invention, the bleaching adopts a multi-stage bleaching mode, and the bleaching comprises chlorine dioxide bleaching (DHT stage), alkali bleaching (Eop stage), primary bleaching (D1 stage) and secondary bleaching (D2 stage); after the bleaching of the second stage (stage D2), the whiteness of the pulp reaches 89.0-91.0% ISO.

In the present invention, the pulp after oxygen delignification still contains part of the lignin in the chlorine dioxide bleaching stage. To achieve the final brightness it is necessary to remove the residual lignin from the pulp. The DHT bleaching stage enables lignin removal for increased brightness. The objective of the DHT bleaching stage is to reduce the residual lignin to a certain extent to facilitate the subsequent bleaching treatment, while at the same time increasing the brightness of the pulp. The concentration of the slurry in the chlorine dioxide bleaching section is 10% -15%, preferably 10-12%, in the specific embodiment of the invention, the concentration of the slurry in the chlorine dioxide bleaching section is 10%, 11% or 11.5%; the dosage of chlorine dioxide is preferably 10-15 kg/adt, more preferably 11-14 kg/adt, and in the specific embodiment of the invention, the dosage of chlorine dioxide is specifically 13kg/adt, 13.5kg/adt or 14 kg/adt; the reaction temperature is 70-80 ℃, more preferably 74-76 ℃, and in the specific embodiment of the invention, the reaction temperature is specifically 75 ℃ or 74 ℃; the pH value is preferably 2.0-3.0, more preferably 2.3-2.6, and in the embodiment of the invention, the pH value is specifically 2.5, 2.3 or 2.6.

The pulp after the DHT bleaching stage still contains a small amount of lignin. The pulp is further delignified in the Eop bleaching stage to increase brightness. In the present invention, the purpose of the alkaline bleaching stage is to reduce the residual lignin to a certain extent, facilitating the subsequent bleaching treatment, while at the same time increasing the brightness of the pulp. In the invention, the concentration of the slurry in the alkaline bleaching section is 10-15%, preferably 11-13%, and in a specific embodiment of the invention, the concentration of the slurry in the alkaline bleaching section is specifically 13%, 11% or 11.5%; the bleaching agent used in the alkali bleaching process is NaOH, and the dosage of the NaOH is 10-15 kg/adt, 13kg/adt and 13.5 kg/adt; the dosage of the oxygen is 3.0-5.0 kg/adt, preferably 4.0-4.5 kg/adt, and in the specific embodiment of the invention, the dosage of the oxygen is specifically 4.5kg/adt or 4.0 kg/adt; the reaction temperature is 70-80 ℃, more preferably 77-79 ℃, and in the specific embodiment of the invention, the reaction temperature is 78 ℃, 78.5 ℃ or 79 ℃; the pH value is 10.0 to 12.0, and more preferably 10.5 to 11.

In the present invention, the purpose of the primary bleaching stage is to increase the brightness stage, increase the brightness of the pulp to a desired value and maintain the viscosity of the pulp. In the invention, the concentration of the first-stage bleached pulp is 10-15%, and more preferably 10-11%; the bleaching agent used in the first-stage bleaching process is chlorine dioxide, the dosage of the bleaching agent used in the first-stage bleaching process is 3-4 kg/adt, more preferably 3.5-4 kg/adt, and in the specific embodiment of the invention, the dosage of the bleaching agent used in the first-stage bleaching process is specifically 4kg/adt or 3.5 kg/adt; the temperature of the first-stage bleaching is 70-80 ℃, in the specific embodiment of the invention, the temperature of the first-stage bleaching is specifically 75 ℃ or 77 ℃; the pH value is 4.0-6.0, preferably 4.2-4.8, and in the specific embodiment of the invention, the pH value is specifically 4.5 or 4.6.

In the present invention, the purpose of the secondary bleaching stage is to increase to the final target whiteness and to avoid yellowing of the pulp. In the invention, the bleaching agent used in the second-stage bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the second-stage bleaching is 0.3-0.7 kg/adt, more preferably 0.5-0.7 kg/adt; the concentration of the pulp in the two-stage bleaching section is 10-15%, more preferably 10-11%, in the specific embodiment of the invention, the concentration of the pulp is 10% or 11%; the temperature of the second-stage bleaching is 70-80 ℃, more preferably 72-78 ℃, and in the specific embodiment of the invention, the temperature of the second-stage bleaching is specifically 75 ℃; the pH value is preferably 4.0 to 6.0, more preferably 4.5 to 5.5, and in an embodiment of the present invention, the pH value is specifically 5 or 5.5.

In the invention, the bleached sulfate hardwood pulp is subjected to screening, pulp flow conveying, forming, squeezing and drying in sequence to obtain the bleached sulfate hardwood pulp board.

In the present invention, the step of screening the wood pulp comprises:

bleached sulfate broad-leaved wood pulp carries out one section screening, and the good pulp that one section screening obtained gets into wood pulp drifting process after diluting, and the tailings that one section screening obtained carries out the second-stage screening after diluting, and the good pulp that the second-stage screening obtained returns one section screening process, and the tailings that the second-stage screening carries out one section slagging-off after diluting, and the good pulp that one section slagging-off obtained returns the second-stage screening process, and the tailings that one section slagging-off obtained carries out the second-stage slagging-off after diluting, and the good pulp that the second-stage slagging-off obtained returns one section slagging-.

The bleached sulfate hardwood pulp is firstly screened for the first time, the pulp inlet concentration of the screening for the first time is preferably 2.8-3.2 wt%, and the pulp inlet pressure is preferably 0.6 MPa. Diluting the good pulp obtained by the first-stage screening, then feeding the good pulp into a wood pulp flow process, and diluting the tailings obtained by the first-stage screening, and then carrying out second-stage screening. The first-stage screening is preferably carried out in a first-stage pressure screen, and the pulp inlet capacity of the first-stage pressure screen is preferably 512 adt/d. Diluting tailings obtained by the first-stage screening, and then, carrying out second-stage screening, wherein the slurry inlet concentration of the second-stage screening is preferably 2.0-2.3 wt%, the slurry inlet pressure is preferably 0.15-0.35 MPa, and the slurry outlet concentration is preferably 1.1-1.3 wt%. Good pulp obtained by the second-stage screening returns to the first-stage screening, and tailings obtained by the second-stage screening are diluted and subjected to first-stage deslagging. The secondary screening is preferably carried out in a secondary pressure screen, the pulp inlet capacity of the secondary pressure screen is preferably 192adt/d, and the pulp outlet capacity of the secondary pressure screen is preferably 152 adt/d. And diluting tailings obtained by the second-stage screening, and then carrying out first-stage deslagging, wherein the slurry inlet concentration of the first-stage deslagging is preferably 1.1-1.3 wt%, and the slurry outlet concentration is preferably 1-1.2 wt%. Good pulp obtained by first-stage deslagging returns to second-stage screening, and tailings obtained by first-stage deslagging are subjected to second-stage deslagging after being diluted. The one-section deslagging is preferably carried out in 8 parallel deslagging devices, the total pulp inlet capacity of the 8 parallel deslagging devices is preferably 48adt/d, and the total pulp outlet capacity is preferably 37 adt/d. And diluting the tailings subjected to the first-stage deslagging, and then performing second-stage deslagging, wherein the pulp inlet concentration of the second-stage deslagging is preferably 0.5 wt%, the good pulp obtained by the second-stage deslagging is returned to the first-stage deslagging, and the tailings subjected to the second-stage deslagging are discharged. The two-stage deslagging is preferably carried out in 2 parallel deslagging devices, and the total pulp inlet capacity of the 2 parallel deslagging devices is preferably 12 adt/d.

After wood pulp is screened, wood pulp flow is carried out, and the flow of the wood pulp is preferably 9500-2450L/min in the wood pulp flow process; the concentration of the wood pulp is preferably 1.6-2.2 wt%. The flow of wood pulp is preferably carried out in a headbox, which is preferably of a closed high turbulence design. The wood pulp delivered to the forming wire is firstly sprayed to form, and then is squeezed to obtain the wet wood pulp board. The squeezing specifically comprises the following steps:

the formed wood pulp is sequentially subjected to double-net squeezing and heavy-duty squeezing to obtain a wet wood pulp board;

the tension of a press felt in the double-net pressing process is 4-8N/mm; the tension of the press felt in the heavy pressing process is 3-3.5N/mm. The dryness of the wet wood pulp sheet is preferably greater than 45%.

In the invention, the formed wood pulp is firstly subjected to double-wire pressing, the wire tension in the double-wire pressing process is preferably 4-8N/mm, and the double-wire pressing is preferably carried out in a double-wire press. The double-wire press is 3750mm in wire width, 3600mm in working width, 24100-24200 mm in bottom wire length and 24100-24200 mm in top wire length.

The wood pulp is heavily squeezed after being squeezed by the two nets, and the tension of the squeezing felt in the heavy squeezing process is preferably 3-3.5N/mm. The heavy pressing is preferably carried out in a heavy pressing machine, the heavy pressing machine comprises two transmission pressing rolls, the surfaces of the pressing rolls are covered with soft rubber, the thickness of the soft rubber is preferably 22.5mm, and the hardness of the soft rubber is preferably 8-10. The size of the press roll is preferably phi 1200X 3700 mm. The working width of the heavy-duty squeezer is 3600mm, the width of the blanket is 3750mm, the length of the top blanket is 13500mm, and the length of the bottom blanket is 13500 mm.

And drying the wet wood pulp board obtained after the wood pulp is squeezed to obtain the bleached sulfate hardwood pulp board. The drying is preferably carried out in a drying box, and the working speed of the drying box is preferably 60-140 m/min.

The preparation method of the bleached sulfate hardwood pulp board can produce the bleached sulfate hardwood pulp board with the tensile index of more than or equal to 72N.m/g and the bursting index of more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree is less than or equal to 1.3mm²/m²Bleached sulfate broad-leaved wood pulp board with whiteness of 89-90% ISO and DCM extract of less than or equal to 0.6%, wherein the quantitative content of the pulp board is 850-1270 g/m²The moisture content is less than 10 wt%.

The preparation method of the bleached sulfate hardwood pulp board provided by the invention is described in detail below with reference to the attached drawings, and with reference to fig. 1, fig. 1 is a production process flow chart of the bleached sulfate hardwood pulp board provided by the embodiment of the invention, and the steps are as follows:

the wood chips are firstly screened in a screening device, the qualified wood obtained by screening enters a wood dipping tower for dipping, and the wood chips obtained by screening are conveyed to a fluidized bed boiler for incineration. The method comprises the steps of soaking qualified wood in a wood soaking tower, conveying the soaked wood to a cooking tower through a discharger and a high-pressure feeder, conveying soaking black liquor generated by soaking to a black liquor filter, filtering the soaking black liquor in the black liquor filter, conveying filtrate obtained by filtering to an evaporation device for evaporation, and obtaining concentrated black liquor after evaporation. The discharger and the high-pressure feeder need to convey the impregnated wood under the action of a current carrying, wherein the current carrying is an impregnating solution.

The impregnated wood is conveyed with a carrier flow into a digester which includes a separator, an upper digester section, a lower digester section and a washing section. The impregnated wood and the carrier fluid are separated in a separator of the cooking tower, the separated impregnated wood enters an upper cooking section, and the separated carrier fluid returns to a high-pressure feeder, a discharger or a wood impregnating tower. The impregnated wood is cooked in the upper cooking section, the cooked wood pulp enters the lower cooking section, the black liquor produced in cooking is extracted out of the cooking tower by the upper extraction sieve plate arranged in the upper cooking section, and the extracted black liquor can be returned to a discharger or a wood impregnating tower as the upper extraction black liquor or can enter a black liquor filter. And the first section of cooked wood pulp obtained in the upper cooking section enters a lower cooking section, the first section of cooked wood pulp is cooked in the lower cooking section, and the second section of cooked wood pulp obtained in the cooking enters a washing section. And washing the second-stage cooked wood pulp in a washing section of the cooking tower to obtain coarse pulp, and conveying the coarse pulp to a cooking blow-down pot. The second stage black liquor and washing waste liquor are extracted from the digestion tower by the lower extraction sieve plate between the lower digestion section and the washing section, and the extracted second stage black liquor and washing waste liquor are used as the lower extraction black liquor to enter the black liquor filter.

The coarse pulp is diluted to proper concentration in a cooking blow-down boiler and then conveyed to 3 parallel first-stage knot breakers, the good pulp of the first-stage knot breaker is conveyed to 3 parallel first-stage pressure sieves, and the tailings of the first-stage knot breaker are diluted and then enter a second-stage knot breaker. Good pulp of the second-stage knotter is conveyed to 3 parallel first-stage pressure sieves, and tailings of the second-stage knotter enter a heavy impurity slag remover after being diluted. The good pulp of the heavy impurity slag separator enters a coarse screen, and the tailings of the heavy impurity slag separator are conveyed to a slag collecting bin. And washing and dewatering the good pulp of the heavy impurity slag separator in a coarse screen to obtain drier knots, and returning the drier knots to the wood dipping tower or conveying the drier knots to a knot collecting bin.

The good pulp of the first-section knot removing machine is screened in 3 first-section pressure sieves which are connected in parallel, the good pulp of the first-section pressure sieves is diluted and then conveyed to 3 first-section double-roller pulp washers which are connected in parallel, and the tailings of the first-section pressure sieves are diluted and then conveyed to a second-section pressure sieve. And the good pulp of the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and the tailings of the second-stage pressure screen enter the third-stage pressure screen after being diluted. Good pulp of the three-section pressure screen returns to a feed inlet of the two-section pressure screen, and tailings of the three-section pressure screen enter the four-section pressure screen after being diluted. The good pulp of the four-section pressure screen enters a feed inlet of the three-section pressure screen, and the tailings of the four-section pressure screen enter a screw press. And squeezing tailings of the four-section pressure screen in a screw press, conveying dry slag obtained by squeezing to a slag bin, and conveying filtrate obtained by squeezing to a filtrate storage tank.

The good pulp of the first-section pressure screen is washed in 3 parallel first-section double-roller pulp washers, the washing waste liquid generated in the washing process is used as the washing liquid of the washing section of the cooking tower to return to the cooking tower, and the washed good pulp enters 2 parallel second-section double-roller pulp washers after being diluted. Washing waste liquid generated by the two-section double-roller pulp washer is used as washing liquid of the one-section double-roller pulp washer to return to the one-section double-roller pulp washer, and good pulp obtained by washing the two-section double-roller pulp washer is conveyed to the one-section oxygen delignification tower.

And (3) carrying out primary oxygen delignification on the good pulp obtained by washing the two-section double-roller pulp washer in a primary oxygen delignification tower to obtain primary oxygen delignification wood pulp. And conveying the first-stage oxygen delignified wood pulp to a second-stage oxygen delignification tower for second-stage oxygen delignification, and obtaining second-stage oxygen delignified wood pulp after the second-stage oxygen delignification. And conveying the two-stage oxygen delignified wood pulp to a pulp washer for washing. Washing waste liquid generated by washing of the pulp washer is used as washing liquid of the two-section double-roller pulp washer to return to the two-section double-roller pulp washer. And obtaining the bleached sulfate hardwood pulp after the washing is finished. And conveying the bleached sulfate hardwood pulp to a pulp sheet papermaking machine, and papermaking in the pulp sheet papermaking machine to obtain the bleached sulfate hardwood pulp sheet.

To further illustrate the present invention, the method of making a high strength, low dusting bleached kraft hardwood pulp, wood pulp sheets and methods of making the same provided by the present invention are described in detail below with reference to the examples, which should not be construed as limiting the scope of the invention.

Example 1

Preparing a bleached sulfate acacia wood pulp board:

and screening the acacia chips with the moisture content of 35-50 wt% in a screening device to obtain qualified wood. The compression degree of the qualified timber is 10-15%, and the virtual volume density is 160-190 kg/m³. The ratio of bark and/or saplings in the qualified timber in the total timber is less than or equal to 1 wt%; the proportion of the timber with the thickness of 3mm in the total timber is less than or equal to 1 wt%; the proportion of the timber with the thickness of 3-7 mm in the total timber is less than or equal to 6 wt%; the proportion of the timber with the thickness of 8-12 mm in the total timber is less than or equal to 8 wt%; the proportion of the timber with the thickness of 13-45 mm in the total timber is more than or equal to 55 wt%; the proportion of the timber with the thickness of more than or equal to 45mm in the total timber is less than or equal to 2wt percent.

Qualified wood passes through a wood chip buffer and a wood chip meter and then enters a steaming section of a wood impregnation tower, and rising steam generated by boiling liquid in the impregnation tower is used for steaming and degassing the wood. The steamed wood is soaked in a soaking section of a soaking tower, and the soaking temperature is 100 ℃. In the dipping process, the generated dipping black liquor is extracted by an extraction sieve plate in a dipping tower, the extracted dipping black liquor is conveyed to a black liquor filter, filtrate obtained by filtering is conveyed to an evaporation device, and the filtrate is evaporated in the evaporation device to obtain concentrated black liquor; and conveying filter residues obtained by filtering to a discharger and finally conveying to a cooking tower.

The impregnated wood and impregnation liquor after impregnation are conveyed to a separator at the top of the cooking tower by a discharger and a high-pressure feeder. Separating the wood and the steeping liquor in a top separator, and returning the steeping liquor obtained by separation to a discharger; the separated impregnated wood is fed into the upper cooking section of the cooking tower. The impregnated wood is mixed with white liquor in an upper cooking section, wherein the concentration of NaOH in the white liquor is 132g/L, and the degree of vulcanization of the white liquor is 32%. The white liquor passes throughThe white liquor inlet of the upper cooking section is added into the upper cooking section. The liquid-material ratio of the upper cooking section is controlled to be 4.5m³And/bdt. The impregnated wood is subjected to one-section high-pressure cooking in the upper cooking section, the temperature of the high-pressure cooking is controlled at 152 ℃, and the pressure of the high-pressure cooking is controlled at 0.32 MPa. The first stage black liquor generated by the first stage high pressure cooking is extracted out of the cooking tower through an upper extraction sieve plate. The addition of white liquor is regulated by detecting the concentration of residual alkali in the first stage of black liquor. One part of the extracted section of black liquor is conveyed to a discharger, one part of the extracted section of black liquor is conveyed to a wood impregnating tower, and the other part of the extracted section of black liquor is conveyed to a black liquor filter.

The impregnated wood is cooked in the upper cooking section to obtain a first section of cooked wood pulp, and the first section of cooked wood pulp is conveyed to the lower cooking section. The first stage cooked wood pulp is mixed with white liquor in the lower stage. The white liquor is added into the lower cooking section through a white liquor inlet of the lower cooking section, and the liquor-material ratio of the lower cooking section is controlled to be 2.0m³And/bdt. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in the lower cooking stage, wherein the high-pressure cooking temperature is controlled at 160 ℃, and the high-pressure cooking pressure is controlled at 0.65 MPa. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in the lower cooking stage to obtain second-stage cooked wood pulp, and the second-stage cooked wood pulp is conveyed to the washing stage. The second stage cooked wood pulp is contacted with the washing liquid in countercurrent in the washing stage. The dilution factor of the washing was controlled at 1.3m³And/adt. And conveying the coarse pulp obtained by washing to a cooking blow-down boiler. The second-stage black liquor and waste washing liquor produced by washing and produced by second-stage high-pressure cooking are extracted out of the cooking tower by means of lower extraction sieve plate, and the extracted second-stage black liquor and waste washing liquor are heat-exchanged with white liquor which is not fed into the cooking tower, and transferred into black liquor filter.

The coarse pulp concentration in the blowing tank is diluted to 4.5 wt% and then conveyed to 3 parallel first-stage knot removers.

The coarse pulp is subjected to section removal in a first-section removing machine, the pulp inlet pressure of the removing machine is set to be 300kPa, the operation pressure difference is 25kPa, and the slag discharge rate is 18%. The good pulp of the first-stage knotter is diluted and then conveyed to 3 first-stage pressure sieves which are connected in parallel, and the tailings of the first-stage knotter are diluted into tailings liquid with the concentration of 3.5 wt% and then enter the second-stage knotter. And (3) after diluting the tailings of the first-section knotting machine into tailings liquid, continuously knotting in a second-section knotting machine, setting the slurry inlet pressure of the knotting machine to be 195kPa, the operation pressure difference to be 20kPa and the slag discharge rate to be 28%. Good pulp of the second-stage knotter is conveyed to 3 first-stage pressure sieves connected in parallel, and tailings in the second-stage knotter are diluted and then enter a heavy impurity slag remover. The good pulp of the heavy impurity slag separator enters a coarse screen, and the tailings of the heavy impurity slag separator are conveyed to a slag collecting bin. The good pulp of the heavy impurity slag separator is washed and dewatered in a coarse screen to obtain dry knots, and the knots are returned to a wood dipping tower or conveyed to a knot collecting bin.

The fine pulp in the first-stage economizer is diluted and then enters 3 parallel first-stage pressure sieves. The pulp inlet concentration of the first-stage pressure screen is 4 wt%, the pulp inlet pressure is 180kPa, and the operation pressure difference is 40 kPa. And (3) diluting the good pulp concentration of the first-stage pressure screen to 1.0-1.23.5 wt%, and then conveying the diluted good pulp to 3 first-stage double-roller pulp washers connected in parallel, wherein tailings of the first-stage pressure screen are conveyed to a second-stage pressure screen after being diluted. The slurry inlet concentration of the two-stage pressure screen is 2.8 wt%, the slurry inlet pressure is 250kPa, and the operation pressure difference is 20 kPa. The good pulp of the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and the tailings of the second-stage pressure screen enter a desander after being diluted. And discharging the impurities separated by the sand remover, diluting the fine slurry obtained by the sand remover, and then feeding the fine slurry into a three-section pressure screen. The pulp inlet concentration of the three-section pressure sieve is 0.8-1.02.0 wt%, the pulp inlet pressure is 200kPa, and the operation pressure difference is 30 kPa. Good pulp of the three-section pressure screen returns to a feed inlet of the two-section pressure screen, and tailings of the three-section pressure screen enter the four-section pressure screen after being diluted. The pulp inlet concentration of the four-section pressure sieve is 1.2 wt%, the pulp inlet pressure is 180KPa, and the screening pressure difference is 20 KPa. The good pulp of the four-section pressure screen enters a feed inlet of the three-section pressure screen, and the tailings of the four-section pressure screen enter a screw press. And squeezing tailings of the four-section pressure screen in a screw press, conveying dry slag obtained by squeezing to a slag bin, and conveying filtrate obtained by squeezing to a filtrate storage tank.

The fine pulp concentration of the first-stage pressure sieve is diluted to 3.5 wt%, and then the fine pulp is conveyed to 3 parallel first-stage double-roller pulp washers, and the pulp is washed in the first-stage double-roller pulp washer. The pulp concentration of the first twin-roll washer was 28 wt% and the operating speed was 8.0 rpm. And (3) returning washing waste liquid generated in the washing process as washing liquid of a washing section of the cooking tower to the cooking tower, and feeding the washed good pulp into 2 two-section double-roller pulp washers connected in parallel after the concentration of the good pulp is diluted to 7 wt%. The pulp concentration of the two-stage two-roll washer was 30 wt% and the operation speed was 9.0 rpm. Washing waste liquid generated by the two-section double-roller pulp washer is used as washing liquid of the one-section double-roller pulp washer to return to the one-section double-roller pulp washer, and good pulp obtained by washing the two-section double-roller pulp washer is conveyed to the one-section oxygen delignification tower.

And (3) carrying out primary oxygen delignification on the good pulp obtained by washing the two-section double-roller pulp washer in a primary oxygen delignification tower. In the first-stage oxygen delignification process, the oxygen consumption is 20kg/adt, the NaOH consumption is 23kg/adt, the pH value of the reaction system is maintained at 10.8-11.5, the pressure is maintained at 650kPa, the temperature is maintained at 94 ℃, the pulp outlet concentration is set to be 10 wt%, and the retention time of wood pulp in the first-stage oxygen delignification tower is set to be 30 min. And obtaining the primary oxygen delignified wood pulp after the primary oxygen delignification. And conveying the first-stage oxygen delignified wood pulp to a second-stage oxygen delignification tower for second-stage oxygen delignification. In the process of the second-stage oxygen delignification, the consumption of oxygen is 3kg/adt, the consumption of the oxygen delignification agent NaOH is 0kg/adt, the pH value of the reaction system is maintained at 10.5, the pressure is maintained at 320kPa, the temperature is maintained at 104 ℃, the pulp outlet concentration is set to be 11 wt%, and the retention time of wood pulp in a second-stage oxygen delignification tower is set to be 60 min. And obtaining the second-stage oxygen delignification wood pulp after the second-stage oxygen delignification. And (3) conveying the two-stage oxygen delignified wood pulp to a pulp washer, washing in the pulp washer, and obtaining the bleached kraft wood pulp kraft acacia wood pulp after the washing is finished. The pulp inlet concentration of the pulp washer is 7 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.2m³The/adt, the feed pressure was 40kPa, and the running speed was 8.0 rpm.

The bleaching adopts a multi-stage bleaching mode, namely four-stage bleaching processes of a DHT stage, an Eop stage, a D1 stage and a D2 stage.

In the DHT section, the slurry still contains part of lignin after oxygen delignification. To achieve the final brightness it is necessary to remove the residual lignin from the pulp. The DHT bleaching stage enables lignin removal for increased brightness. The objective of the DHT bleaching stage is to reduce the residual lignin to a certain extent to facilitate the subsequent bleaching treatment, while at the same time increasing the brightness of the pulp. The concentration of the DHT section slurry is 10 percent, the dosage of chlorine dioxide is 13kg/adt, the reaction temperature is 75 ℃, and the pH value is 2.5.

The Eop section, the pulp after the DHT bleaching section still contains a small amount of lignin. The pulp is further delignified in the Eop bleaching stage to increase brightness. This stage is the alkaline extraction stage and aims to reduce the residual lignin to a certain extent to facilitate the subsequent treatment by bleaching and at the same time increase the brightness of the pulp. The concentration of the slurry in the Eop section is 10%, the dosage of NaOH is 13kg/adt, the dosage of oxygen is 4.5kg/adt, the reaction temperature is 78 ℃, and the pH value is 10.5.

Stage D1, stage D1 bleaching stage is the whiteness-enhancing stage. The goal of the D1 bleaching stage is to increase the brightness of the pulp to a desired value and to maintain the viscosity of the pulp. The mass concentration of the slurry in the D1 stage is 10%, the chlorine dioxide is 4kg/adt, the temperature is 75 ℃, and the pH value is 4.5.

Stage D2, the final bleaching stage may be stage D2 or stage hydrogen peroxide. The final bleaching stage is increased to the final target brightness and avoids yellowing of the pulp. The mass concentration of the slurry in the D2 stage is 10%, the chlorine dioxide is 0.5kg/adt, the temperature is 75 ℃, and the pH value is 5.0.

Bleaching the obtained product in the last D2 stage to obtain bleached sulfate acacia wood pulp with whiteness reaching 89.0-91.0% ISO. The obtained bleached sulfate acacia wood pulp is conveyed to a pulp board papermaking machine. The pulp board making machine consists of a first-stage pressure screen, a second-stage pressure screen, a first-stage slag separator, a second-stage slag separator, a pulp flow box, a net part, a double-net squeezer, a heavy squeezer and a drying box. Bleached kraft pulp kraft acacia wood pulp is first diluted and then fed into a first pressure screen. The pulp inlet capacity of the first-stage pressure screen is 512adt/d, the pulp inlet concentration is 2.8-3.2 wt%, and the operation pressure is 0.6 MPa. Good pulp obtained by the first-stage pressure screen flows into a pulp box after being diluted, and tailings of the first-stage pressure screen are subjected to second-stage pressure screen after being diluted. The two-section pressure screen has the pulp inlet capacity of 192adt/d, the pulp inlet concentration of 2.0-2.3 wt%, the pulp outlet concentration of 1.1-1.3 wt%, the operation pressure of 0.15-0.35 MPa and the good pulp outlet capacity of 152 adt/d. Good pulp obtained by the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and tailings of the second-stage pressure screen enter 8 parallel first-stage slag separators after being diluted. The total pulp inlet capacity of the first-stage slag remover is 48adt/d, the pulp inlet concentration is 1.1-1.3 wt%, the total good pulp outlet capacity is 37adt/d, and the pulp outlet concentration is 1-1.2 wt%. And the good pulp obtained by the first-stage slag remover returns to a feed inlet of the second-stage pressure screen, and the tailings after first-stage slag removal are diluted and then subjected to 2 parallel second-stage slag removal. The total pulp inlet capacity of the two-stage slag separator is preferably 12adt/d, and the pulp inlet concentration is 0.5 wt%. Good pulp obtained by the second-stage slag remover returns to the feeding hole of the first-stage slag remover, and tailings obtained by the second-stage slag removal are discharged.

Diluting the good pulp obtained by the first-stage pressure screen, and then feeding the good pulp into a pulp box, wherein the flow range of the pulp box is 9500-2450L/min; the slurry concentration is 1.6-2.2 wt%. The wood pulp is conveyed to the net part by the head box, and the wood pulp enters the twin-wire presser and the heavy presser in sequence after being formed in the net part, so that the wet wood pulp board with the dryness of more than 45 percent is obtained. And conveying the wet wood pulp board into a drying box for drying to obtain the bleached sulfate wood pulp sulfate acacia wood pulp board. The working speed of the drying box is set to be 60-140 m/min.

The bleached sulfate wood pulp sulfate acacia wood pulp board is subjected to plate cutting and packaging to obtain a pulp board finished product. The specification of the finished product is as follows: the gram weight is 900-1270 g/m²The weight of a single package is 250kg, and the size of a finished pulp board is 5 multiplied by 685 multiplied by 800 mm; the iron wire specification used by the baling line is respectively as follows: phi 2.18 mm and phi 2.3mm, and the tensile strength is 980-1200N/mm respectively²、1000～1250N/mm²。

The yield of the sulfate acacia wood pulp board produced by the method provided by the embodiment is calculated, and the result is 48-53%. The bleached sulfate wood pulp sulfate acacia wood pulp board produced is detected, and the result is as follows: the tensile index is 73N.m/g and the burst index is 4.5KPa.m²(g) tear index 6.6mN.m²(g) the dust degree is 1.1mm²/m²The whiteness of the bleached sulfate hardwood pulp board is 89.3 percent ISO, the dichloromethane extract is 0.36 percent, and the quantitative content of the pulp board is 850-1270 g/m²The moisture content is less than 10 wt%.

Example 2

Preparation of bleached sulfate 50 wt% acacia wood-50 wt% eucalyptus pulp board

Mixing the acacia wood chips with the moisture content of 35-50 wt% and the eucalyptus wood chips with the moisture content of 35-50 wt% according to the mass ratio of 1:1, and screening in a screening device to obtain qualified wood. The compression degree of the qualified timber is 10-15%, and the virtual volume density is 160-190 kg/m³. The ratio of bark and/or saplings in the qualified timber in the total timber is less than or equal to 1 wt%; wood material with thickness of 3mmThe proportion of the wood in the total wood is less than or equal to 1 wt%; the proportion of the timber with the thickness of 3-7 mm in the total timber is less than or equal to 6 wt%; the proportion of the timber with the thickness of 8-12 mm in the total timber is less than or equal to 8 wt%; the proportion of the timber with the thickness of 13-45 mm in the total timber is more than or equal to 55 wt%; the proportion of the timber with the thickness of more than or equal to 45mm in the total timber is less than or equal to 2wt percent.

Qualified wood passes through a wood chip buffer and a wood chip meter and then enters a steaming section of a wood impregnation tower, and rising steam generated by boiling liquid in the impregnation tower is used for steaming and degassing the wood. The steamed wood is soaked in a soaking section of a soaking tower, and the soaking temperature is 95 ℃. In the dipping process, the generated dipping black liquor is extracted by an extraction sieve plate in a dipping tower, the extracted dipping black liquor is conveyed to a black liquor filter, filtrate obtained by filtering is conveyed to an evaporation device, and the filtrate is evaporated in the evaporation device to obtain concentrated black liquor; and conveying filter residues obtained by filtering to a discharger and finally conveying to a cooking tower.

The impregnated wood and impregnation liquor after impregnation are conveyed to a separator at the top of the cooking tower by a discharger and a high-pressure feeder. Separating the wood and the steeping liquor in a top separator, and returning the steeping liquor obtained by separation to a discharger; the separated impregnated wood is fed into the upper cooking section of the cooking tower. The impregnated wood is mixed with white liquor at an upper cooking section, wherein the concentration of NaOH in the white liquor is 132g/L, and the degree of vulcanization of the white liquor is 32%. The white liquor is added into the upper cooking section through a white liquor inlet of the upper cooking section. The liquid-material ratio of the upper cooking section is controlled to be 4.2m³And/bdt. The impregnated wood is subjected to one-section high-pressure cooking in the upper cooking section, the high-pressure cooking temperature is controlled at 148 ℃, and the high-pressure cooking pressure is controlled at 0.25 MPa. The first stage black liquor generated by the first stage high pressure cooking is extracted out of the cooking tower through an upper extraction sieve plate. The addition of white liquor is regulated by detecting the concentration of residual alkali in the first stage of black liquor. One part of the extracted section of black liquor is conveyed to a discharger, one part of the extracted section of black liquor is conveyed to a wood impregnating tower, and the other part of the extracted section of black liquor is conveyed to a black liquor filter.

The impregnated wood is cooked in the upper cooking section to obtain a first section of cooked wood pulp, and the first section of cooked wood pulp is conveyed to the lower cooking section. Mixing the first-stage cooked wood pulp with white liquor in the lower cooking stage. The white liquor is added into the lower cooking section through a white liquor inlet of the lower cooking section, and the liquor-material ratio of the lower cooking section is controlled to be 1.9m³And/bdt. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in the lower cooking stage, wherein the high-pressure cooking temperature is controlled at 160 ℃, and the high-pressure cooking pressure is controlled at 0.64 MPa. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in the lower cooking stage to obtain second-stage cooked wood pulp, and the second-stage cooked wood pulp is conveyed to the washing stage. The second stage cooked wood pulp is contacted with the washing liquid in countercurrent in the washing stage. The dilution factor of the washing was controlled at 0.5m³And/adt. And conveying the coarse pulp obtained by washing to a cooking blow-down boiler. The second-stage black liquor and waste washing liquor produced by washing and produced by second-stage high-pressure cooking are extracted out of the cooking tower by means of lower extraction sieve plate, and the extracted second-stage black liquor and waste washing liquor are heat-exchanged with white liquor which is not fed into the cooking tower, and transferred into black liquor filter.

The coarse pulp concentration in the blowing tank is diluted to 4.4 wt% and then conveyed to 3 parallel first-stage knot removers.

The coarse pulp is subjected to section removal in a first-section sluicing machine, the pulp inlet pressure of the sluicing machine is set to be 310kPa, the operation pressure difference is 23kPa, and the slag discharge rate is 19%. The good pulp of the first-stage knotter is diluted and then conveyed to 3 first-stage pressure sieves which are connected in parallel, and the tailings of the first-stage knotter are diluted into tailings liquid with the concentration of 3.8 wt% and then enter the second-stage knotter. And (3) continuously removing the joints in the second-stage knotter after the tailings of the first-stage knotter are diluted into tailings liquid, wherein the slurry inlet pressure of the knotter is set to be 200kPa, the operation pressure difference is set to be 20kPa, and the slag discharge rate is set to be 29%. Good pulp of the second-stage knotter is conveyed to 3 first-stage pressure sieves connected in parallel, and tailings in the second-stage knotter are diluted and then enter a heavy impurity slag remover. The good pulp of the heavy impurity slag separator enters a coarse screen, and the tailings of the heavy impurity slag separator are conveyed to a slag collecting bin. The good pulp of the heavy impurity slag separator is washed and dewatered in a coarse screen to obtain dry knots, and the knots are returned to a wood dipping tower or conveyed to a knot collecting bin.

The fine pulp in the first-stage economizer is diluted and then enters 3 parallel first-stage pressure sieves. The slurry inlet concentration of the first-stage pressure sieve is 4.1 wt%, the slurry inlet pressure is 195kPa, and the operation pressure difference is 40 kPa. And (3) diluting the good pulp concentration of the first-stage pressure screen to 3.5 wt%, and then conveying the diluted good pulp to 3 first-stage double-roller pulp washers connected in parallel, wherein tailings of the first-stage pressure screen are conveyed to a second-stage pressure screen after being diluted. The slurry inlet concentration of the two-stage pressure screen is 2.9 wt%, the slurry inlet pressure is 260kPa, and the operation pressure difference is 25 kPa. The good pulp of the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and the tailings of the second-stage pressure screen enter a desander after being diluted. And discharging the impurities separated by the sand remover, diluting the fine slurry obtained by the sand remover, and then feeding the fine slurry into a three-section pressure screen. The slurry inlet concentration of the three-section pressure screen is 2.1 wt%, the slurry inlet pressure is 180kPa, and the operation pressure difference is 35 kPa. Good pulp of the three-section pressure screen returns to a feed inlet of the two-section pressure screen, and tailings of the three-section pressure screen enter the four-section pressure screen after being diluted. The pulp inlet concentration of the four-section pressure sieve is 1.3 wt%, the pulp inlet pressure is 190KPa, and the screening pressure difference is 25 KPa. The good pulp of the four-section pressure screen enters a feed inlet of the three-section pressure screen, and the tailings of the four-section pressure screen enter a screw press. And squeezing tailings of the four-section pressure screen in a screw press, conveying dry slag obtained by squeezing to a slag bin, and conveying filtrate obtained by squeezing to a filtrate storage tank.

The fine pulp concentration of the first-stage pressure sieve is diluted to 3.6 wt%, and then the fine pulp is conveyed to 3 parallel first-stage double-roller pulp washers, and the pulp is washed in the first-stage double-roller pulp washer. The pulp concentration of the first twin-roll washer was 29 wt% and the operating speed was 8.0 rpm. And (3) returning washing waste liquid generated in the washing process as washing liquid of a washing section of the cooking tower to the cooking tower, and feeding the washed good pulp into 2 two-section double-roller pulp washers connected in parallel after the concentration of the good pulp is diluted to 7.5 wt%. The pulp concentration of the two-stage two-roll washer was 30 wt% and the operation speed was 8.5 rpm. Washing waste liquid generated by the two-section double-roller pulp washer is used as washing liquid of the one-section double-roller pulp washer to return to the one-section double-roller pulp washer, and good pulp obtained by washing the two-section double-roller pulp washer is conveyed to the one-section oxygen delignification tower.

And (3) carrying out primary oxygen delignification on the good pulp obtained by washing the two-section double-roller pulp washer in a primary oxygen delignification tower. In the first-stage oxygen delignification process, the oxygen dosage is 20kg/adt, the NaOH dosage is 23.5kg/adt, the pH value of the reaction system is maintained at 11.0, the pressure is maintained at 700kPa, the temperature is maintained at 93 ℃, the pulp outlet concentration is set to be 11.5 wt%, and the retention time of wood pulp in the first-stage oxygen delignification tower is set to be 25 min. And obtaining the primary oxygen delignified wood pulp after the primary oxygen delignification. First stage oxygenAnd conveying the delignified wood pulp to a second-stage oxygen delignification tower for second-stage oxygen delignification. In the two-stage oxygen delignification process, the oxygen consumption is 3.5kg/adt, the NaOH consumption is 0kg/adt, the pH value of the reaction system is maintained at 10.5, the pressure is maintained at 310kPa, the temperature is maintained at 103.5 ℃, the pulp outlet concentration is set to be 10-12 wt%, and the retention time of wood pulp in the two-stage oxygen delignification tower is set to be 60 min. And obtaining the second-stage oxygen delignification wood pulp after the second-stage oxygen delignification. And conveying the two-stage oxygen delignified wood pulp into a pulp washer for washing, and obtaining bleached sulfate wood pulp sulfate which is 50 wt% of acacia wood-50 wt% of eucalyptus wood pulp after washing. The pulp inlet concentration of the pulp washer is 7 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.2m³The pressure of the slurry inlet was 30kPa, and the running speed was 8.5 rpm.

In the DHT section, the slurry still contains part of lignin after oxygen delignification. To achieve the final brightness it is necessary to remove the residual lignin from the pulp. The DHT bleaching stage enables lignin removal for increased brightness. The objective of the DHT bleaching stage is to reduce the residual lignin to a certain extent to facilitate the subsequent bleaching treatment, while at the same time increasing the brightness of the pulp. The concentration of the DHT section slurry is 11 percent, the dosage of chlorine dioxide is 13.5kg/adt, the reaction temperature is 75 ℃, and the pH value is 2.3.

The Eop section, the pulp after the DHT bleaching section still contains a small amount of lignin. The pulp is further delignified in the Eop bleaching stage to increase brightness. This stage is the alkaline extraction stage and aims to reduce the residual lignin to a certain extent to facilitate the subsequent treatment by bleaching and at the same time increase the brightness of the pulp. The concentration of the slurry in the Eop section is 11 percent, the dosage of NaOH is 13.5kg/adt, the dosage of oxygen is 4.0kg/adt, the reaction temperature is 78.5 ℃, and the pH value is 10.5.

Stage D1, stage D1 bleaching stage is the whiteness-enhancing stage. The goal of the D1 bleaching stage is to increase the brightness of the pulp to a desired value and to maintain the viscosity of the pulp. The concentration of the slurry in the D1 stage is 11%, the chlorine dioxide is 3.5kg/adt, the temperature is 75 ℃, and the pH value is 4.6.

Stage D2, the final bleaching stage may be stage D2 or stage hydrogen peroxide. The final bleaching stage is increased to the final target brightness and avoids yellowing of the pulp. The concentration of the slurry in the D2 stage is 11%, the chlorine dioxide is 0.6kg/adt, the temperature is 75 ℃, and the pH value is 5.5.

Bleaching the obtained product in the last D2 stage to obtain bleached sulfate acacia wood pulp with whiteness reaching 89.0-91.0% ISO. The obtained bleached sulfate acacia wood pulp is conveyed to a pulp board papermaking machine.

The pulp board making machine consists of a first-stage pressure screen, a second-stage pressure screen, a first-stage slag separator, a second-stage slag separator, a pulp flow box, a net part, a double-net squeezer, a heavy squeezer and a drying box. Bleached kraft pulp sulfate 50 wt% acacia wood-50 wt% eucalyptus pulp is first diluted and then fed into a first pressure screen. The pulp inlet capacity of the first-stage pressure screen is 512adt/d, the pulp inlet concentration is 2.8-3.2 wt%, and the operation pressure is 0.6 MPa. Good pulp obtained by the first-stage pressure screen flows into a pulp box after being diluted, and tailings of the first-stage pressure screen are subjected to second-stage pressure screen after being diluted. The two-section pressure screen has the pulp inlet capacity of 192adt/d, the pulp inlet concentration of 2.0-2.3 wt%, the pulp outlet concentration of 1.1-1.3 wt%, the operation pressure of 0.15-0.35 MPa and the good pulp outlet capacity of 152 adt/d. Good pulp obtained by the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and tailings of the second-stage pressure screen enter 8 parallel first-stage slag separators after being diluted. The total pulp inlet capacity of the first-stage slag remover is 48adt/d, the pulp inlet concentration is 1.1-1.3 wt%, the total good pulp outlet capacity is 37adt/d, and the pulp outlet concentration is 1-1.2 wt%. And the good pulp obtained by the first-stage slag remover returns to a feed inlet of the second-stage pressure screen, and the tailings after first-stage slag removal are diluted and then subjected to 2 parallel second-stage slag removal. The total pulp inlet capacity of the two-stage slag separator is preferably 12adt/d, and the pulp inlet concentration is 0.5 wt%. Good pulp obtained by the second-stage slag remover returns to the feeding hole of the first-stage slag remover, and tailings obtained by the second-stage slag removal are discharged.

Diluting the good pulp obtained by the first-stage pressure screen, and then feeding the good pulp into a pulp box, wherein the flow range of the pulp box is 9500-2450L/min; the slurry concentration is 1.6-2.2 wt%. The wood pulp is conveyed to the net part by the head box, and the wood pulp enters the twin-wire presser and the heavy presser in sequence after being formed in the net part, so that the wet wood pulp board with the dryness of more than 45 percent is obtained. And conveying the wet wood pulp board into a drying box for drying to obtain the bleached sulfate wood pulp board with the sulfate of 50 wt% of acacia wood and 50 wt% of eucalyptus wood pulp. The working speed of the drying box is set to be 60-140 m/min.

Bleached sulfate wood pulp sulfate 50 wt% acacia wood-50 wt% eucalyptus wood pulp board is subjected to board cutting and packaging to obtain a pulp board finished product. The specification of the finished product is as follows: the gram weight is 900-1270 g/m²The weight of a single package is 250kg, and the size of a finished pulp board is 5 multiplied by 685 multiplied by 800 mm; the iron wire specification used by the baling line is respectively as follows: phi 2.18 mm and phi 2.3mm, and the tensile strength is 980-1200N/mm respectively²、1000～1250N/mm²。

The yield of 50 wt% acacia wood-50 wt% eucalyptus pulp board produced by the method provided by the embodiment is calculated, and the result is 53-59%. The test of the produced bleached sulfate wood pulp sulfate 50 wt% acacia wood-50 wt% eucalyptus wood pulp board shows that: tensile index of 73N.m/g and burst index of 5.0KPa.m²(g) tear index 7.2mN.m²(g) the dust degree is 1.0mm²/m²The whiteness of the bleached sulfate hardwood pulp board is 89.3 percent ISO, the dichloromethane extract is 0.25 percent, and the quantitative content of the pulp board is 850-1270 g/m²The moisture content is less than 10 wt%.

Example 3

Preparation of bleached sulfate eucalyptus pulp board

And screening the eucalyptus pieces with the water content of 35-50 wt% in a screening device to obtain qualified wood. The compression degree of the qualified timber is 10-15%, and the virtual volume density is 160-190 kg/m³. The ratio of bark and/or saplings in the qualified timber in the total timber is less than or equal to 1 wt%; the proportion of the timber with the thickness of 3mm in the total timber is less than or equal to 1 wt%; the proportion of the timber with the thickness of 3-7 mm in the total timber is less than or equal to 6 wt%; the proportion of the timber with the thickness of 8-12 mm in the total timber is less than or equal to 8 wt%; the proportion of the timber with the thickness of 13-45 mm in the total timber is more than or equal to 55 wt%; the proportion of the timber with the thickness of more than or equal to 45mm in the total timber is less than or equal to 2wt percent.

Qualified wood passes through a wood chip buffer and a wood chip meter and then enters a steaming section of a wood impregnation tower, and rising steam generated by boiling liquid in the impregnation tower is used for steaming and degassing the wood. The steamed wood is soaked in a soaking section of a soaking tower, and the soaking temperature is 90 ℃. In the dipping process, the generated dipping black liquor is extracted by an extraction sieve plate in a dipping tower, the extracted dipping black liquor is conveyed to a black liquor filter, filtrate obtained by filtering is conveyed to an evaporation device, and the filtrate is evaporated in the evaporation device to obtain concentrated black liquor; and conveying filter residues obtained by filtering to a discharger and finally conveying to a cooking tower.

The impregnated wood and impregnation liquor after impregnation are conveyed to a separator at the top of the cooking tower by a discharger and a high-pressure feeder. Separating the wood and the steeping liquor in a top separator, and returning the steeping liquor obtained by separation to a discharger; the separated impregnated wood is fed into the upper cooking section of the cooking tower. The impregnated wood is mixed with white liquor in an upper cooking section, wherein the concentration of NaOH in the white liquor is 130g/L, and the degree of vulcanization of the white liquor is 32.5%. The white liquor is added into the upper cooking section through a white liquor inlet of the upper cooking section. The liquid-material ratio of the upper cooking section is controlled to be 4.4m³And/bdt. The impregnated wood is subjected to one-section high-pressure cooking in the upper cooking section, the temperature of the high-pressure cooking is controlled at 146 ℃, and the pressure of the high-pressure cooking is controlled at 0.25 MPa. The first stage black liquor generated by the first stage high pressure cooking is extracted out of the cooking tower through an upper extraction sieve plate. The addition of white liquor is regulated by detecting the concentration of residual alkali in the first stage of black liquor. One part of the extracted section of black liquor is conveyed to a discharger, one part of the extracted section of black liquor is conveyed to a wood impregnating tower, and the other part of the extracted section of black liquor is conveyed to a black liquor filter.

The impregnated wood is cooked in the upper cooking section to obtain a first section of cooked wood pulp, and the first section of cooked wood pulp is conveyed to the lower cooking section. The first stage cooked wood pulp is mixed with white liquor in the lower stage. The white liquor is added into the lower cooking section through a white liquor inlet of the lower cooking section, and the liquor-material ratio of the lower cooking section is controlled to be 2.1m³And/bdt. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in a lower cooking stage, wherein the high-pressure cooking temperature is controlled at 158 ℃, and the high-pressure cooking pressure is controlled at 0.62 MPa. And the first-stage cooked wood pulp is subjected to second-stage high-pressure cooking in the lower cooking stage to obtain second-stage cooked wood pulp, and the second-stage cooked wood pulp is conveyed to the washing stage. The second stage cooked wood pulp is contacted with the washing liquid in countercurrent in the washing stage. The dilution factor of the washing was controlled at 0.7m³And/adt. And conveying the coarse pulp obtained by washing to a cooking blow-down boiler. Extracting the black liquor and waste washing liquid from two-stage high-pressure digestion via lower extracting sieve plate to obtain the black liquor and waste washing liquidThe second stage of the black liquor and the washing waste liquor exchange heat with the white liquor which does not enter the cooking tower and then are conveyed to the black liquor filter.

The coarse pulp concentration in the blowing tank is diluted to 4.6 wt% and then conveyed to 3 parallel first-stage knot removers.

The coarse pulp is subjected to section removal in a first-section sluicing machine, the pulp inlet pressure of the sluicing machine is set to be 310kPa, the operation pressure difference is 23kPa, and the slag discharge rate is 18%. The good pulp of the first-stage knotter is diluted and then conveyed to 3 first-stage pressure sieves which are connected in parallel, and the tailings of the first-stage knotter are diluted into tailings liquid with the concentration of 3.8 wt% and then enter the second-stage knotter. And (3) continuously removing the joints in the second-stage knotter after the tailings of the first-stage knotter are diluted into tailings liquid, setting the slurry inlet pressure of the knotter to be 198kPa, the operation pressure difference to be 27kPa and the slag discharge rate to be 27%. Good pulp of the second-stage knotter is conveyed to 3 first-stage pressure sieves connected in parallel, and tailings in the second-stage knotter are diluted and then enter a heavy impurity slag remover. The good pulp of the heavy impurity slag separator enters a coarse screen, and the tailings of the heavy impurity slag separator are conveyed to a slag collecting bin. The good pulp of the heavy impurity slag separator is washed and dewatered in a coarse screen to obtain dry knots, and the knots are returned to a wood dipping tower or conveyed to a knot collecting bin.

The fine pulp in the first-stage economizer is diluted and then enters 3 parallel first-stage pressure sieves. The pulp inlet concentration of the first-stage pressure screen is 3.8 wt%, the pulp inlet pressure is 190kPa, and the operation pressure difference is 10-60 kPa. And (3) diluting the good pulp concentration of the first-stage pressure screen to 3.6 wt%, and then conveying the diluted good pulp to 3 first-stage double-roller pulp washers connected in parallel, wherein tailings of the first-stage pressure screen are conveyed to a second-stage pressure screen after being diluted. The slurry inlet concentration of the two-stage pressure screen is 2.7 wt%, the slurry inlet pressure is 260kPa, and the operation pressure difference is 45 kPa. The good pulp of the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and the tailings of the second-stage pressure screen enter a desander after being diluted. And discharging the impurities separated by the sand remover, diluting the fine slurry obtained by the sand remover, and then feeding the fine slurry into a three-section pressure screen. The slurry inlet concentration of the three-section pressure screen is 2.1 wt%, the slurry inlet pressure is 190kPa, and the operation pressure difference is 35 kPa. Good pulp of the three-section pressure screen returns to a feed inlet of the two-section pressure screen, and tailings of the three-section pressure screen enter the four-section pressure screen after being diluted. The pulp inlet concentration of the four-section pressure sieve is 1.3 wt%, the pulp inlet pressure is 170KPa, and the screening pressure difference is 25 KPa. The good pulp of the four-section pressure screen enters a feed inlet of the three-section pressure screen, and the tailings of the four-section pressure screen enter a screw press. And squeezing tailings of the four-section pressure screen in a screw press, conveying dry slag obtained by squeezing to a slag bin, and conveying filtrate obtained by squeezing to a filtrate storage tank.

The fine pulp concentration of the first-stage pressure sieve is diluted to 3.4 wt%, and then the fine pulp is conveyed to 3 parallel first-stage double-roller pulp washers, and the pulp is washed in the first-stage double-roller pulp washer. The pulp concentration of the first twin-roll washer was 29 wt% and the operating speed was 8.0 rpm. And (3) returning washing waste liquid generated in the washing process as washing liquid of a washing section of the cooking tower to the cooking tower, and feeding the washed good pulp into 2 two-section double-roller pulp washers connected in parallel after the concentration of the good pulp is diluted to 7 wt%. The pulp concentration of the two-stage two-roll washer was 31 wt% and the operation speed was 8.0 rpm. Washing waste liquid generated by the two-section double-roller pulp washer is used as washing liquid of the one-section double-roller pulp washer to return to the one-section double-roller pulp washer, and good pulp obtained by washing the two-section double-roller pulp washer is conveyed to the one-section oxygen delignification tower.

And (3) carrying out primary oxygen delignification on the good pulp obtained by washing the two-section double-roller pulp washer in a primary oxygen delignification tower. In the first-stage oxygen delignification process, the oxygen consumption is 22kg/adt, the NaOH consumption is 24kg/adt, the pH value of a reaction system is maintained at 10.8-11.5, the pressure is maintained at 630kPa, the temperature is maintained at 93 ℃, the pulp outlet concentration is set to be 10-12 wt%, and the residence time of wood pulp in a first-stage oxygen delignification tower is set to be 30 min. And obtaining the primary oxygen delignified wood pulp after the primary oxygen delignification. And conveying the first-stage oxygen delignified wood pulp to a second-stage oxygen delignification tower for second-stage oxygen delignification. In the process of the two-stage oxygen delignification, the oxygen dosage is 2.5kg/adt, the NaOH dosage is 0kg/adt, the pH value of the reaction system is maintained at 10.5, the pressure is maintained at 320kPa, the temperature is maintained at 103 ℃, the pulp outlet concentration is set to be 12 wt%, and the retention time of wood pulp in a two-stage oxygen delignification tower is set to be 60 min. And obtaining the second-stage oxygen delignification wood pulp after the second-stage oxygen delignification. And conveying the two-stage oxygen delignified wood pulp to a pulp washer for washing, and obtaining bleached sulfate wood pulp sulfate eucalyptus pulp after washing. The pulp inlet concentration of the pulp washer is 7 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.0-2.52.3 m³/adt, the pulp inlet pressure is 30kPa,the running speed was 9.5 rpm.

The concentration of the DHT section slurry is 11.5 percent, the dosage of chlorine dioxide is 14kg/adt, the reaction temperature is 74 ℃, and the pH value is 2.6.

The concentration of the slurry in the Eop section is 11.5 percent, the dosage of NaOH is 13.5kg/adt, the dosage of oxygen is 4.0kg/adt, the reaction temperature is 79 ℃, and the pH value is 10.5.

The concentration of the slurry in the D1 stage is 11%, the chlorine dioxide is 4kg/adt, the temperature is 77 ℃, and the pH value is 4.6.

The concentration of the slurry in the D2 stage is 11%, the chlorine dioxide is 0.7kg/adt, the temperature is 75 ℃, and the pH value is 5.5.

The obtained bleached sulfate wood pulp sulfate eucalyptus pulp is conveyed to a pulp sheet papermaking machine. The pulp board making machine consists of a first-stage pressure screen, a second-stage pressure screen, a first-stage slag separator, a second-stage slag separator, a pulp flow box, a net part, a double-net squeezer, a heavy squeezer and a drying box. Bleached kraft pulp kraft acacia wood pulp is first diluted and then fed into a first pressure screen. The pulp inlet capacity of the first-stage pressure screen is 512adt/d, the pulp inlet concentration is 2.8-3.2 wt%, and the operation pressure is 0.6 MPa. Good pulp obtained by the first-stage pressure screen flows into a pulp box after being diluted, and tailings of the first-stage pressure screen are subjected to second-stage pressure screen after being diluted. The two-section pressure screen has the pulp inlet capacity of 192adt/d, the pulp inlet concentration of 2.0-2.3 wt%, the pulp outlet concentration of 1.1-1.3 wt%, the operation pressure of 0.15-0.35 MPa and the good pulp outlet capacity of 152 adt/d. Good pulp obtained by the second-stage pressure screen returns to the feeding hole of the first-stage pressure screen, and tailings of the second-stage pressure screen enter 8 parallel first-stage slag separators after being diluted. The total pulp inlet capacity of the first-stage slag remover is 48adt/d, the pulp inlet concentration is 1.1-1.3 wt%, the total good pulp outlet capacity is 37adt/d, and the pulp outlet concentration is 1.0-1.2 wt%. And the good pulp obtained by the first-stage slag remover returns to a feed inlet of the second-stage pressure screen, and the tailings after first-stage slag removal are diluted and then subjected to 2 parallel second-stage slag removal. The total pulp inlet capacity of the two-stage slag separator is preferably 12adt/d, and the pulp inlet concentration is 0.5 wt%. Good pulp obtained by the second-stage slag remover returns to the feeding hole of the first-stage slag remover, and tailings obtained by the second-stage slag removal are discharged.

Diluting the good pulp obtained by the first-stage pressure screen, and then feeding the good pulp into a pulp box, wherein the flow range of the pulp box is 9500-2450L/min; the slurry concentration is 1.6-2.2 wt%. The wood pulp is conveyed to the net part by the head box, and the wood pulp enters the twin-wire presser and the heavy presser in sequence after being formed in the net part, so that the wet wood pulp board with the dryness of more than 45 percent is obtained. And conveying the wet wood pulp board into a drying box for drying to obtain the bleached sulfate wood pulp sulfate eucalyptus pulp board. The working speed of the drying box is set to be 60-140 m/min.

And (3) cutting the bleached sulfate wood pulp sulfate eucalyptus pulp board, and packaging to obtain a pulp board finished product. The specification of the finished product is as follows: the gram weight is 900-1270 g/m²The weight of a single package is 250kg, and the size of a finished pulp board is 5 multiplied by 685 multiplied by 800 mm; the iron wire specification used by the baling line is respectively as follows: phi 2.18 mm and phi 2.3mm, and the tensile strength is 980-1200N/mm respectively²、1000～1250N/mm²。

The method provided by the embodiment of the invention calculates the yield of the sulfate eucalyptus pulp board produced by the method, and the result is 53-59%. The detection is carried out on the produced bleached sulfate wood pulp sulfate eucalyptus pulp board, and the result is as follows: the tensile index is 76N.m/g and the burst index is 5.7KPa.m²(g) the tear index is 8.5mN.m²(g) the dust degree is 1.0mm²/m²The whiteness of the bleached sulfate hardwood pulp board is 89.9 percent ISO, the dichloromethane extract is 0.16 percent, and the quantitative content of the pulp board is 850-1270 g/m²The moisture content is less than 10 wt%.

From the above examples, it can be seen that compared with the prior art, the present invention provides a method for preparing bleached sulfate hardwood pulp and a wood pulp sheet prepared thereby. The preparation method of the bleached sulfate hardwood pulp provided by the invention comprises the following steps: a) preparing broad-leaved wood chips to obtain wood; b) cooking the wood in white liquor to obtain coarse pulp, wherein the cooked kappa number is 16.0-20.0; c) removing knots, screening, washing, oxygen delignification and bleaching the brown stock in sequence to obtain bleached sulfate hardwood pulp; the bleaching is in turn carried outComprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching; the dosage of chlorine dioxide in the chlorine dioxide bleaching process is 10-15 kg/adt; the bleaching agent adopted by the alkali bleaching is NaOH, and the dosage of the NaOH is 10-15 kg/adt; the bleaching agent used in the first-stage bleaching process is chlorine dioxide, and the dosage of the bleaching agent used in the first-stage bleaching process is 3-4 kg/adt; the bleaching agent used in the secondary bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.7 kg/adt. The wood pulp prepared by the preparation method is manufactured by paper making to obtain the wood pulp board with high strength and low dust degree. The experimental results show that: the tensile index of the wood pulp board provided by the invention is more than or equal to 72N.m/g, and the burst index is more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree is less than or equal to 1.3mm²/m²The whiteness is 89-90% ISO and the methylene dichloride extract is less than or equal to 0.6%.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing bleached sulfate hardwood pulp board, comprising:

manufacturing bleached sulfate hardwood pulp to obtain a bleached sulfate hardwood pulp board;

the preparation method of the bleached sulfate hardwood pulp comprises the following steps:

a) preparing broad-leaved wood chips to obtain wood; the broad-leaved wood chips are selected from one or more of acacia wood chips, eucalyptus wood chips and hardwood wood chips; the compression degree of the wood is 10-15%; the virtual volume density of the wood is 160-230 kg/m³. The proportion of bark and/or saplings in the wood in the total wood is less than or equal to 1 wt%; the proportion of timber with the thickness of 3mm in the total timber is less than or equal to 1 wt%; the proportion of timber with the thickness of 3-7 mm in the total timber is less than or equal to 6 wt%; middle thickness of the woodThe proportion of 8-12 mm timber in the total timber is less than or equal to 8 wt%; the proportion of the timber with the thickness of 13-45 mm in the total timber is more than or equal to 55 wt%; the proportion of the timber with the thickness of more than or equal to 45mm in the total timber is preferably less than or equal to 2 wt%;

b) cooking the wood in white liquor to obtain coarse pulp, wherein the cooked kappa number is 16.0-20.0; the white liquor is NaOH and Na₂S mixed solution;

the dosage of chlorine dioxide in the chlorine dioxide bleaching process is 10-15 kg/adt; the mass concentration of the pulp in the chlorine dioxide bleaching process is 10-15%; the reaction temperature is 70-80 ℃; the pH value is 2.0-3.0;

the bleaching agent used in the alkali bleaching process is NaOH, and the dosage of the NaOH is 10-15 kg/adt; the mass concentration of the pulp in the alkali bleaching process is 10-15%; the dosage of oxygen is 3.0-5.0 kg/adt, the reaction temperature is 70-80 ℃, and the pH value is 10.0-12.0;

the bleaching agent used in the first-stage bleaching process is chlorine dioxide, and the dosage of the bleaching agent used in the first-stage bleaching process is 3-4 kg/adt; the mass concentration of the pulp in the first-stage bleaching process is 10-15%; the reaction temperature is 70-80 ℃, and the pH value is 4.0-6.0;

the bleaching agent used in the secondary bleaching process is chlorine dioxide or hydrogen peroxide, and the dosage of the bleaching agent used in the secondary bleaching process is 0.3-0.7 kg/adt; the mass concentration of the pulp in the second-stage bleaching process is 10-15%; the reaction temperature is 70-80 ℃, and the pH value is 4.0-6.0;

the tensile index of the bleached sulfate hardwood pulp board is more than or equal to 72N.m/g, and the burst index is more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree is less than or equal to 1.3mm²/m²The whiteness is 89-90% ISO and dichloromethaneThe extract is less than or equal to 0.6 percent;

the joint removing section in the step c) specifically comprises the following steps:

the pulp inlet concentration of the first-section joint removal is 3.0-5.0 wt%, the pulp inlet pressure is 180-310 KPa, the slag discharge rate is 5-20%, and the first-section joint removal pressure difference is 10-30 KPa; the slurry inlet concentration of the two-section joint removal is 3.0-5.0 wt%, the slurry inlet pressure is 180-220 KPa, the slag discharge rate is 10-30%, and the pressure difference of the two-section joint removal is 10-30 KPa;

the screening section in the step c) comprises the following steps:

the pulp inlet concentration of the first section of screening is 2.0-4.1 wt%, the pulp inlet pressure is 180-300 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the two-stage screening is 1.6-3.0 wt%, the pulp inlet pressure is 100-260 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the three-stage screening is 0.8-2.5 wt%, the pulp inlet pressure is 100-200 KPa, and the screening pressure difference is 10-60 KPa; the pulp inlet concentration of the four-stage screening is 1.0-1.5 wt%, the pulp inlet pressure is 100-200 KPa, and the screening pressure difference is 10-60 KPa.