CN106468030B

CN106468030B - Preparation method of sulfate acacia wood pulp, wood pulp board and preparation method thereof

Info

Publication number: CN106468030B
Application number: CN201511031650.3A
Authority: CN
Inventors: 刘若飞; 陈德海; 肖光彩; 杨恒; 张守国; 李雪峰; 董元锋
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: CN106468030A

Abstract

The invention provides a preparation method of sulfate acacia wood pulp, a wood pulp board and a preparation method of the wood pulp board. The preparation method of the sulfate acacia wood pulp comprises the following steps: preparing the acacia wood chips into wood, wherein the density of the acacia wood chips is 135-160 kg/m³(ii) a Cooking timber in white liquor containing NaOH and Na to obtain coarse pulp₂S mixed solution; the kraft acacia wood pulp is obtained by sequentially carrying out nodulation removal, screening, washing, oxygen delignification and bleaching on the brown pulp, wherein the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching. The wood pulp prepared by the preparation method is manufactured by paper making to obtain the sulfate acacia wood pulp board with high strength and low content of dichloromethane extract. The experimental results show that: the tensile index of the sulfate jequirity wood pulp board is more than or equal to 65N.m/g, and the dust degree is less than or equal to 2.0mm²/m²The whiteness is 89.0-91.0% ISO and the dichloromethane extract is less than or equal to 0.45%.

Description

Preparation method of sulfate acacia wood 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 sulfate acacia wood pulp, a wood pulp board and a preparation method of the wood pulp board.

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.

The sulfate wood pulp is one kind of wood pulp, and is prepared with various kinds of coniferous tree and broad-leaved tree as material and through cooking in sulfate process. The kraft pulp is stronger and contains more hemicellulose than sulfite pulp and alkali pulp, so the yield is higher. Depending on the raw materials and the processing, it can be used to make wrapping paper, fine paper, etc.

At present, the market share of sulfate wood pulp is low, and particularly, the preparation methods of sulfate acacia wood pulp and sulfate pure acacia wood pulp boards are not reported at present.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for preparing kraft acacia wood pulp, a wood pulp sheet and a method for preparing the same, wherein the wood pulp sheet provided by the present invention has high strength and low content of methylene chloride extract.

The invention provides a sulfate acacia wood pulp board, which has a tensile index of more than or equal to 65N.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 less than or equal to 2.0mm²/m²The whiteness is 89.0-91.0% ISO and the dichloromethane extract is less than or equal to 0.45%.

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

a) preparing raw materials for acacia wood chips to obtain wood, wherein the density of the acacia wood chips is 135-160 kg/m³；

b) Cooking the wood in white liquor to obtain coarse pulp, wherein the white liquor is NaOH and Na₂S mixed solution;

c) sequentially removing knots, screening, washing, oxygen delignification and bleaching the brown stock to obtain the kraft acacia wood 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 12-15 kg/adt;

the bleaching agent in the alkali bleaching process comprises NaOH and oxygen, wherein the dosage of the NaOH is 10-15 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt;

the bleaching agent in the first-stage bleaching process comprises chlorine dioxide and oxygen, wherein the dosage of the chlorine dioxide is 3-4 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt;

the bleaching agent in the secondary bleaching process comprises chlorine dioxide and NaOH; the dosage of the chlorine dioxide is 0.5-1.0 kg/adt, and the dosage of the NaOH is 0.5-1.5 kg/adt.

Preferably, the mass concentration of the slurry in the chlorine dioxide bleaching process is 10-15%, the reaction temperature is 75-90 ℃, and the reaction time is 100-130 min.

Preferably, the mass concentration of the slurry in the alkali bleaching process is 10-15%, the reaction temperature is 75-90 ℃, and the reaction time is 100-130 min.

Preferably, the mass concentration of the pulp in the first-stage bleaching process is 10-15%, the reaction temperature is 60-80 ℃, and the reaction time is 160-190 min.

Preferably, the mass concentration of the slurry in the two-stage bleaching process is 10-15%, the reaction temperature is 65-80 ℃, and the reaction time is 100-130 min.

Preferably, in step a), the proportion of the wood with the thickness of more than or equal to 8mm in the total wood is less than or equal to 8 wt%, the proportion of the bark and/or the rotten wood in the total wood is less than or equal to 1 wt%, and the moisture content of the wood is less than 55 wt%.

Preferably, the step b) specifically comprises the following steps:

b1) impregnating the timber to obtain impregnated timber;

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

Preferably, the oxygen delignification section of the step c) comprises the following steps:

c1) subjecting the washed pulp to primary oxygen delignification to obtain primary oxygen delignified wood pulp;

the dosage of the oxygen delignification agent adopted in the first-stage oxygen delignification is 15-30 kg/adt;

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

the dosage of the oxygen delignification agent adopted in the two-stage oxygen delignification is 0-5 kg/adt;

c3) washing the two-stage oxygen delignification wood pulp to obtain sulfate pure acacia wood pulp;

the dilution factor of the washing is 2.0-2.5 m³/adt。

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

and (3) making the sulfate acacia wood pulp prepared by the preparation method in the technical scheme by using a paper machine to obtain the sulfate acacia wood pulp board.

The invention provides a preparation method of sulfate acacia wood pulp and a wood pulp board prepared from the wood pulp. The preparation method of the sulfate acacia wood pulp provided by the invention comprises the following steps: a) preparing raw materials for acacia wood chips to obtain wood, wherein the density of the acacia wood chips is 135-160 kg/m³(ii) a b) Cooking the wood in white liquor to obtain coarse pulp, wherein the white liquor is NaOH and Na₂S mixed solution; c) sequentially removing knots, screening, washing, oxygen delignification and bleaching the brown stock to obtain the kraft acacia wood 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 12-15 kg/adt; the bleaching agent in the alkali bleaching process comprises NaOH and oxygen, the dosage of the NaOH is preferably 10-15 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt; the bleaching agent in the first-stage bleaching process comprises chlorine dioxide and oxygen, wherein the dosage of the chlorine dioxide is 3-4 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt; the bleaching agent in the secondary bleaching process comprises chlorine dioxide and NaOH; the dosage of the chlorine dioxide is 0.5-1.0 kg/adt, and the dosage of the NaOH is 0.5-1.5 kg/adt. The wood pulp prepared by the preparation method is manufactured by paper making to obtain the sulfate acacia wood pulp board with high strength and low content of dichloromethane extract. The experimental results show that: the tensile index of the wood pulp board provided by the invention is not less than65N.m/g, burst index not less than 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree less than or equal to 2.0mm²/m²The whiteness is 89.0-91.0% ISO and the dichloromethane extract is less than or equal to 0.45%.

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 production process of a sulfate acacia wood pulp sheet according to an embodiment of the present invention.

Detailed Description

In the invention, the tensile index of the sulfate acacia wood pulp board is more than or equal to 65N.m/g, and preferably 66-68 N.m/g. In a particular embodiment of the invention, the average value of the tensile index of the sulphate jequirity pulp sheet is in particular 66n.m/g, 66n.m/g or 68 n.m/g. The tensile index of the bleached sulfate hardwood pulp board is determined by a TAPPI T494 method.

In the invention, the burst index of the sulfate acacia wood pulp board is more than or equal to 4.0KPa.m²G, preferably 4.6KPa.m²/g～4.9KPa.m²(ii) in terms of/g. In a particular embodiment of the invention, the average burst index of the sulphate acacia wood pulp sheet is in particular 4.9kpa.m²/g、4.8KPa.m²G or 4.6KPa.m²(ii) in terms of/g. The burst index of the sulfate acacia wood pulp board is carried out by adopting standard TAPPI T403-2010.

In the present invention, the sulfate acacia wood pulp sheetThe tearing index is more than or equal to 6.6mN.m²Per g, preferably 6.6mN.m²/g～7.3mN.m²(ii) in terms of/g. In a particular embodiment of the invention, the average value of the tear index of the sulphate acacia wood pulp sheet is in particular 7.2mn.m²/g、6.7mN.m²G or 6.8mN.m²(ii) in terms of/g. The invention adopts standard TAPPI T414-2013 to carry out the tearing index of the sulfate acacia wood pulp board.

In the invention, the dust degree of the sulfate acacia wood pulp board is less than or equal to 2.0mm²/m²Preferably 1.3mm²/m²～1.8mm²/m². In a particular embodiment of the invention, the sulphate hardwood pulp board has an average value of the dust degree of in particular 1.3mm²/m²、1.5mm²/m²Or 1.4mm²/m². The invention uses standard TAPPI T213-2010 for dust count of sulfate acacia wood pulp board.

In the present invention, the whiteness of the sulfate jequirity pulp sheet is 89.0% ISO-89.8% ISO, preferably 89.2% ISO-89.8% ISO. In a particular embodiment of the invention, the average value of the whiteness of the sulphate jequirity pulp sheet is in particular 89.5% ISO, 89.7% ISO or 89.2% ISO. The invention adopts GB/T8940.2 paper pulp whiteness measuring method to process the whiteness of the sulfate acacia wood pulp board.

In the invention, the dichloromethane extract of the sulfate acacia wood pulp board is less than or equal to 0.45 percent, and preferably 0.39 to 0.45 percent. In particular embodiments of the present invention, the average value of the methylene chloride extract of the sulfate acacia wood pulp sheet is in particular 0.44%, 0.45% or 0.39%. The present invention utilizes standard TAPPI T204-2010 for the dichloromethane extraction of sulfate acacia wood pulp sheets.

the dosage of chlorine dioxide in the chlorine dichloride bleaching process is 12-15 kg/adt;

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

The method comprises the steps of preparing raw materials for acacia wood chips to obtain wood, wherein the density of the acacia wood chips is 135-160 kg/m³. In the present invention, the acacia wood chips are subjected to step a) to obtain wood. The step a) is as follows: the acacia wood chips are prepared to obtain the wood. The process of obtaining the timber from the acacia wood chips through material preparation specifically comprises the following steps: the acacia wood chips were screened. The acacia wood chips are one or more of acacia wood chips in Indonesia, acacia wood chips in Vietnam and acacia wood chips in south Africa, and are preferably acacia wood chips in Indonesia and acacia wood chips in Vietnam. The mass ratio of the Indonesia acacia wood chips to the Vietnam acacia wood chips is preferably 0.5: 1-2: 1, and more preferably 1: 1. In certain embodiments of the present invention, the acacia chips are specifically acacia senii, acacia vietnamensis and acacia nanensis in a mass ratio of 1:1: 1; in certain embodiments of the present invention, the acacia chips are specifically acacia senii and acacia vietnamese in a mass ratio of 1: 1. In the invention, the moisture content of the acacia wood chips is preferably 30-55 wt%, and more preferably 40-55 wt%. Screening to obtain wood chips with the size and thickness meeting the requirements, namely wood materials; pulverizing the wood chips with size and/or thickness larger than the specified size, and returning to the sieving step for another timeScreening; and discharging the wood chips with the size smaller than the specified size, namely wood chips, after screening. In the invention, the discharged wood chips can be used as fuel for the circulating fluidized bed boiler. The compression degree of the wood is preferably 10-15%; the density of the wood is 135-160 kg/m³Preferably 140 to 158kg/m³. The proportion of bark and/or sapwood in the wood in the total wood is preferably less than or equal to 1 wt%. The proportion of the timber with the size less than 3mm in the total timber is preferably less than or equal to 2 wt%; the proportion of 3-7 mm-sized timber in the total timber is preferably less than or equal to 6 wt%; the proportion of 7-13 mm-sized timber in the total timber is preferably less than or equal to 20 wt%; the proportion of the timber with the size of more than 45mm in the total timber is preferably less than or equal to 2 wt%. The proportion of the timber with the thickness of more than or equal to 8mm in the total timber is preferably less than or equal to 8 wt%.

The wood obtained in step a) is subjected to step b) to obtain brown stock. The step b) is as follows: cooking the wood in white liquor to obtain coarse pulp; the white liquor is NaOH and Na₂And (3) mixed solution of S. The process of cooking wood in white liquor to obtain brown stock specifically comprises the following steps:

b1) impregnating the timber to obtain impregnated timber;

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

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 95-105 ℃, more preferably 100-103 ℃, in the embodiment of the invention, the temperature is specifically 100 ℃ or 101 ℃, and the liquid-solid ratio during dipping is preferably 4: 1-5: 1. 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 high-pressure cooking process, the impregnated wood is mixed with white liquor and subjected to high-pressure cooking to obtain coarse pulp. The white liquor is NaOH and Na₂And (3) mixed solution of S. The concentration of NaOH in the white liquor is preferably 133-143 g/L, and in some embodiments of the inventionIn particular 133 g/L; the white liquor preferably has a degree of sulfidation of 30-35%, specifically 32.5% or 31.5% in some embodiments of the invention. The temperature of the high-pressure cooking is preferably 145-158 ℃, more preferably 150-155 ℃, and in some embodiments of the invention is 153 ℃; the pressure of the high-pressure cooking is preferably 0.3-0.5 MPa, more preferably 0.35-0.4 MPa, and in some embodiments of the invention is specifically 0.36 MPa; the liquid-solid ratio of the high-pressure cooking is preferably 2.0-5.0 m³/bdt, more preferably 4.0 to 5.0m³/bdt, specifically 4.6m in certain embodiments of the invention³Bdt; the boiling kappa number is preferably 16.0-20.0. 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 145-165 ℃, more preferably 150-161 ℃, and in some embodiments of the invention specifically 153 ℃ or 161 ℃; the pressure is preferably 0.2-0.7 MPa, and the liquid-material ratio is preferably 4.0-5.0 m³And/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 temperature of the two-stage high-pressure cooking is preferably 145-160 ℃, more preferably 155-160 ℃, and particularly 159 ℃ in certain embodiments of the invention; the pressure is preferably 0.2-0.7 MPa, and in some embodiments of the invention is specifically 0.65MPa or 0.35 MPa; the liquid-material ratio is preferably 2.0-2.5 m³And/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 preferred to use a two-stage cooking black liquor with no cooking systemThe white liquor entering the cooking system exchanges heat to recover the heat of the second-stage cooking 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 washed. The washing dilution factor is preferably 1.0-2.5 m³A/adt, more preferably 1.0 to 1.5m³The/adt, in some embodiments of the invention is specifically 1.0 or 1.2m³And/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.

The brown stock obtained in step b) is subjected to step c) to obtain kraft acacia wood pulp. The step c) is as follows: the kraft acacia wood pulp is obtained by the brown stock through the steps of removing knots, screening, washing, oxygen delignification and bleaching, and the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching.

Preferably, the step c) specifically comprises the following steps:

c1) removing knots of the coarse pulp through a second section to obtain the coarse pulp after removing knots;

c2) screening the coarse pulp subjected to section removal in four sections to obtain screened coarse pulp;

c3) washing the screened coarse pulp for the second section to obtain washed coarse pulp;

c4) subjecting the washed brown stock to oxygen delignification to obtain oxygen delignified brown stock;

c5) and the brown pulp after oxygen delignification is subjected to chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching in sequence to obtain the kraft pulp.

In the invention, the removing specifically comprises the following steps:

the coarse pulp is subjected to primary section removing, the fine pulp obtained by the primary section removing enters a screening process, the tailings of the primary section removing are subjected to secondary section removing after being diluted, the fine pulp of the secondary section removing enters the screening process, and the tailings of the secondary section removing return to the cooking process after being diluted, cleaned and dehydrated.

The slurry inlet concentration of the first-stage section is preferably 3.0-5.0 wt%, the pressure is preferably 0.2-0.6 MPa, more preferably 0.3-0.4 MPa, and in the embodiment of the invention, the concentration is specifically 0.3MPa or 0.33 MPa; the slag discharge rate is preferably 15-25%, and in some embodiments of the invention, the slag discharge rate is specifically 17% or 19%; the slurry inlet concentration of the two-stage section is preferably 3.0-5.0 wt%, the pressure is preferably 0.2-0.6 MPa, and the slag discharge rate is preferably 25-35%.

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 removal is preferably 3.0-4.3 wt%, and more preferably 3.5-4.1 wt%; the slurry inlet pressure is preferably 0.1-0.3 MPa, and the slag discharge rate is preferably 20-22%. 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 3.3-4.6 wt%, the slurry inlet pressure is preferably 180-200 KPa, and the slag discharge rate is preferably 25-30%, and more preferably 27%. 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:

the coarse pulp after section removal is subjected to first-stage screening, the fine pulp obtained by the first-stage screening enters a washing process, the tailings obtained by the first-stage screening are diluted and then subjected to second-stage screening, the fine pulp obtained by the second-stage screening returns to the first-stage screening process, the tailings obtained by the second-stage screening are diluted and then subjected to third-stage screening, the fine pulp obtained by the third-stage screening returns to the second-stage screening process, the tailings obtained by the third-stage screening are diluted and then subjected to fourth-stage screening, the fine pulp obtained by the fourth-stage screening returns to the third-stage screening process, and the. The pulp inlet concentration of the first-stage screening is 3.0-4.0 wt%, 4; the pressure is 180 to 300KPa, more preferably 180 to 200 KPa; the slag discharge rate is 15-20%; the pulp inlet concentration of the secondary screening is preferably 2.5-4.0 wt%, and more preferably 2.8-3.2 wt%; the slurry inlet pressure is 200-250 KPa, specifically 250KPa or 240KPa in some embodiments of the present invention; the slag discharge rate is 15-25%; the pulp inlet concentration of the three-stage screening is preferably 2.0-3.0 wt%, and in some embodiments of the invention specifically 2.1 wt%; the pressure is preferably 100 to 200KPa, more preferably 150 to 200KPa, in some embodiments of the invention specifically 200KPa or 190 KPa; the slag discharge rate is 20-30%; the pulp inlet concentration of the four-stage screening is 1.0-2.0 wt%, the pressure is 100-200 KPa, and in some embodiments of the invention, 175KPa or 180KPa is particularly adopted; the slag discharge rate is 25-35%.

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. And diluting the tailings obtained by the three-stage screening, and then carrying out four-stage screening, preferably squeezing the tailings discharged by the four-stage screening, discharging the squeezed dry tailings, and recovering the filtrate obtained by squeezing 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:

the washing section is a two-stage washing, and the washing filtrate is a counter-current washing. The wash filtrate of the first stage comes from the second stage and the second stage in turn comes from the oxygen stripping stage. The excessive filtrate in the first section is pumped to a dilute black liquor buffer tank by a filtrate tank and then sent to a cooking section. 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 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 pulp inlet concentration of the primary oxygen delignification is 10-15 wt%, and the pulp outlet concentration is preferably 10-15 wt%, and more preferably 11 wt%; the time is 20-30 min; the pressure is preferably 600 to 800KPa, more preferably 650 to 750 KPa; the temperature is preferably 90-100 ℃, and more preferably 94-96 ℃; the pH value is 10.5-11.5, the oxygen consumption is preferably 10-25 kg/adt, and more preferably 23 kg/adt; the oxygen delignification agent adopted in the first-stage oxygen delignification process comprises NaOH; the dosage of the oxygen delignification agent adopted in the first-stage oxygen delignification process is preferably 15-30 kg/adt, more preferably 20-25 kg/adt, and in the embodiment of the invention, the dosage is specifically 25 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 10-15 wt%, the pulp outlet concentration is 10-15 wt%, and the time is preferably 40-60 min, more preferably 60 min; the pressure is 300 to 600KPa, the temperature is 100 to 110 ℃, and the pH value is preferably 10.0 to 11.0, more preferably 10.5 to 10.8; the oxygen consumption is 3-10 kg/adt, more preferably 3-5 kg/adt, and the oxygen delignification agent adopted in the two-stage oxygen delignification process comprises NaOH; the dosage of the oxygen delignification agent adopted in the two-stage oxygen delignification process is 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 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 2.0-2.5 m³And/adt. The kappa number of the bleached kraft acacia wood 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-off 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.

And discharging the two-section oxygen delignified wood pulp in the oxygen delignification blow-off pot from a discharge hole of the blow-off pot, and conveying the two-section oxygen delignified wood pulp to a pulp washer. 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%, the pulp outlet concentration is preferably 20-30 wt%, and the dilution factor is preferably 2-2.5 m³The pulp inlet pressure is preferably 500-600 kPa, the rotating speed is preferably 1.0-10.0 rpm, and the filtrate conductivity is preferably 0-1000 us/cm. And after washing is finished, obtaining the wood pulp after oxygen delignification.

Bleaching the pulp after oxygen delignification to obtain the sulphate acacia wood pulp, wherein the bleaching sequentially comprises chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching.

In the present invention, the bleaching is elemental chlorine-free bleaching (ECF bleaching). In the invention, the aim of bleaching is 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); the sulphate acacia wood pulp is obtained by the bleaching of the second stage (stage D2).

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 DHT stage slurry concentration is preferably 10% to 15%, and in some embodiments specifically 10%; the reaction time is preferably 100-130 min, the reaction temperature is preferably 75-90 ℃, the pH value is preferably 2.0-3.0, and more preferably 2.5-2.8; the dosage of the chlorine dioxide is 12-15 kg/adt, preferably 12.5-14.5 kg/adt.

In the present invention, the pulp still contains a small amount of lignin after the DHT bleaching stage. 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 mass concentration of the Eop section slurry is preferably 10-15%, the reaction time is preferably 100-130 min, the reaction temperature is preferably 75-90 ℃, and the pH value is 10.0-12.0. The bleaching agent in the alkali bleaching process comprises NaOH and oxygen, wherein the amount of the NaOH is 10-15 kg/adt, preferably 11-14 kg/adt, more preferably 12-14 kg/adt, and in some embodiments of the invention, the amount of the NaOH is specifically 13.5 kg/adt; the dosage of the oxygen is preferably 3.0-5.0 kg/adt, and more preferably 4.5 kg/adt; the bleaching agent preferably further comprises H₂O₂(ii) a Said H₂O₂The amount is preferably 0 to 1.0 kg/adt.

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 bleaching agent in the primary bleaching process comprises chlorine dioxide and oxygen, wherein the dosage of the chlorine dioxide is 3-4 kg/adt, and preferably 3.6-4.0 kg/adt; the amount of oxygen is 3.0-5.0 kg/adt, preferably 3.5-4.5 kg/adt. In the invention, the mass concentration of the pulp in the first-stage bleaching process is preferably 10-15%, and more preferably 10.5-14.5%; the reaction temperature is preferably 60-80 ℃, and more preferably 65-76 ℃; the reaction time is preferably 160-190 min, and more preferably 165-185 min. The invention preferably employs H in a single bleaching stage₂SO₄And adjusting the required pH value, wherein the preferable dosage of the sulfuric acid is 0.5-1.0 kg/adt, so that the preferable pH value is 4.0-6.0, and more preferably 4.5-5.5.

In the present invention, the purpose of the secondary bleaching is to increase to the final target whiteness and avoid the reversion of the pulp. In the present invention, the bleaching agent in the secondary bleaching process comprises chlorine dioxide and NaOH; the dosage of the chlorine dioxide is 0.5-1.0 kg/adt, preferably 0.6-0.9 kg/adt; the amount of NaOH is 0.5-1.5 kg/adt, preferably0.8-1.3 kg/adt is selected. In the invention, the mass concentration of the pulp in the secondary bleaching process is preferably 10-15%; if ClO is generated in the two-stage bleaching process₂Excessive residue, which leads to a reduction in the whiteness of the bleached pulp, requires SO passage₂To eliminate oxidizing residual chlorine in the second-stage bleaching process; the SO₂The dosage of the composition is preferably 0-1.0 kg/adt, and more preferably 0.1-0.8 kg/adt; the reaction temperature is preferably 65-80 ℃, and more preferably 68-77 ℃; the reaction time is preferably 100-130 min, and more preferably 105-125 min; the pH value is preferably 4.0-6.0.

In the invention, the sulfate pure acacia wood pulp is manufactured into the sulfate acacia wood pulp board, and the manufacturing preferably comprises the following steps:

and the sulfate pure acacia wood pulp is subjected to fine screening, wood pulp flow conveying, forming, squeezing and drying in sequence to obtain the sulfate acacia wood pulp board.

Wherein the screening specifically comprises the steps of:

the method comprises the following steps of performing first-stage screening on sulfate acacia wood pulp, diluting good pulp obtained by the first-stage screening, then feeding the good pulp into a wood pulp feeding process, diluting tailings obtained by the first-stage screening, then performing second-stage screening, returning the good pulp obtained by the second-stage screening to the first-stage screening process, diluting tailings obtained by the second-stage screening, then performing third-stage screening, returning good pulp obtained by the third-stage screening to the second-stage screening process, diluting tailings obtained by the third-stage screening, then performing fourth-stage screening, returning the good pulp obtained by the fourth-stage screening to the third-stage screening process, and diluting tailings obtained by the fourth-stage screening, and then performing first.

The bleached sulfate acacia wood pulp is firstly subjected to primary screening, the pulp inlet concentration of the primary screening 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 conducted, and the flow of the wood pulp is preferably 2000-2800L/s 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 4.0-8.0 KN/m; the tension of the press felt in the heavy pressing process is 3.0-4.0 KN/m. The dryness of the wet wood pulp sheet is preferably greater than 45%.

In the invention, the formed wood pulp is firstly subjected to twin-wire pressing, the tension of the wire in the twin-wire pressing process is preferably 4.0-8.0 KN/m, and the twin-wire pressing is preferably carried out in a twin-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 through the double-net, and the tension of the press felt in the heavy squeezing process is preferably 3.0-3.5 KN/m. 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 pure acacia wood 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 pure acacia wood pulp board provided by the invention can be used for producing the bleached sulfate pure acacia wood pulp board with the tensile index of more than or equal to 65N.m/g and the burst index of more than or equal to 4.0KPa.m²The tear index is more than or equal to 6.6mN.m²G, dust degree less than or equal to 2.0mm²/m²The whiteness is 89.4 +/-0.4 percent ISO, DCM extract is less than or equal to 0.45 percent, and the quantitative of a pulp plate is 850-1270 g/m²The moisture content is less than 10 wt%.

The method for preparing the bleached sulfate pure acacia wood pulp board provided by the invention is described in detail below with reference to the accompanying drawings, referring to fig. 1, wherein fig. 1 is a production process flow chart of the bleached sulfate pure acacia wood 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. After washing, the sulfate acacia wood pulp is obtained by sequentially carrying out chlorine dioxide bleaching, alkali bleaching, primary bleaching and secondary bleaching. And conveying the sulfate acacia wood pulp to a pulp board papermaking machine, and papermaking in the pulp board papermaking machine to obtain the sulfate acacia wood pulp board.

In order to further illustrate the present invention, the method for preparing sulfate acacia wood pulp, the wood pulp sheet and the method for preparing the same according to the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.

Example 1

Preparation of bleached sulfate 100% Indonesia wood pulp board:

and screening the Indonesia acacia chips with the moisture content of 40-55 wt% in a screening device to obtain qualified wood. The compression degree of the qualified timber is 10-15%, and the density of the qualified timber is 135-160 kg/m³(ii) a 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 size less than 3mm in the total timber is less than or equal to 2 wt%; the proportion of the timber with the size of 3-7 mm in the total timber is less than or equal to 6 wt%; the proportion of the timber with the size of 7-13 mm in the total timber is less than or equal to 20 wt%; the proportion of the timber with the thickness of more than 45mm in the total timber is less than or equal to 2 wt%; the proportion of the timber with the thickness of more than or equal to 8mm in the total timber is less than or equal to 8wt 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 101 ℃. 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. Mixing the soaked wood with white liquor at the upper cooking section, wherein the concentration of NaOH in the white liquor is 133g/LThe white liquor has a degree of vulcanization of 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 4.6m³And/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 153 ℃, and the high-pressure cooking pressure is controlled at 0.36 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 2.3m³And/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 159 ℃, and the high-pressure cooking pressure is controlled at 6.5 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 1.2m³And/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.

Conveying coarse slurry discharged from the cooking tower to a normal-pressure diffusion washer positioned at the top of the blowing pot, washing the coarse slurry by the normal-pressure diffusion washer, then dropping the coarse slurry into a blowing groove at the bottom end of the blowing pot, diluting the concentration of the coarse slurry in the blowing groove to 4.5 wt%, and then conveying the coarse slurry to 3 parallel-connected first-stage knot removers.

The coarse pulp is subjected to section removal in a section of a section removing machine, the pulp inlet pressure of the section removing machine is set to be 0.3MPa, and the slag discharge rate is 17%. 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) 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 second-stage knotter is 190kPa, and the slag discharge rate is 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 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 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 2.8 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 slurry inlet concentration of the three-section pressure sieve is 2.1 wt%, the slurry 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%, the vacuum of the first twin-roll washer was not lower than-30 kPa, and the speed of the first twin-roll washer was 8 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 double-roller pulp washer is 30 wt%, the vacuum degree of the two-stage double-roller pulp washer is not lower than-30 kPa, and the operation rotating speed is 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 consumption is 23kg/adt, the NaOH consumption is 25kg/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 11 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 secondary oxygen delignification, the oxygen consumption is 3kg/adt, the NaOH consumption is 0kg/adt, the pH value of the reaction system is maintained at 10.5, the pressure is maintained at 350kPa, 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 secondary 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 7.5 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.5m³The/adt, the feed pressure was 540kPa, and the operating speed was 9 rpm.

Bleaching adopts a multi-stage bleaching mode, and sequentially passes through four bleaching processes of a DHT stage, an Eop stage, a D1 stage and a D2 stage.

The concentration of the DHT section slurry is 10%, the dosage of chlorine dioxide is 14kg/adt, the reaction temperature is 76 ℃, and the pH value is 2.6.

The concentration of the slurry in the Eop section is 10 percent, the dosage of NaOH is 13.5kg/adt, the dosage of oxygen is 4.5kg/adt, the reaction temperature is 78 ℃, and the pH value is 10.5.

D1 stage, slurry concentration 10%, chlorine dioxide 4kg/adt, temperature 76 deg.C, pH 4.5.

The concentration of the slurry in the D2 stage is 10 percent, the chlorine dioxide is 0.5kg/adt, the temperature is 77 ℃, and the pH value is 5.5.

And bleaching the obtained product in the last D2 stage to obtain sulfate acacia wood pulp, wherein the whiteness reaches 89.3-89.8% 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 specification of the iron wire used for the baling line is 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 53-59%. The bleached sulfate wood pulp sulfate acacia wood pulp board produced is detected, and the result is as follows: the tensile index is 66N.m/g and the burst index is 4.9KPa.m²(g) tear index 7.2mN.m²(g) the dust degree is 1.3mm²/m²The brightness of the pulp is 89.5 percent ISO, the methylene dichloride extract is 0.44 percent sulfate acacia wood pulp, and the quantitative ratio of the pulp is 850-1270 g/m²The moisture content is less than 10 wt%.

Example 2

Preparing a bleached sulfate Indonesia acacia-Vietnam acacia pulp board:

mixing the Indonesia abrus wood chips with the moisture content of 40-55 wt% and the Vietnam abrus wood chips with the moisture content of 40-55 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 bulk 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 133g/L, and the vulcanization degree of the white liquor is 31.5%. 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 4.6m³And/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 153 ℃, and the high-pressure cooking pressure is controlled at 0.35 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 the lower cooking stage, the temperature of the high-pressure cooking is controlled at 161 ℃, and the pressure of the high-pressure cooking 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 to 1.0m³And/adt. And conveying the coarse pulp obtained by washing to a cooking blow-down boiler. Two-stage cooking produced by two-stage high-pressure cookingThe black liquor and the washing waste liquor generated by washing are extracted out of the cooking tower through a lower extraction sieve plate, and the extracted two-stage cooking black liquor and the washing waste liquor exchange heat with the white liquor which does not enter the cooking tower and are then conveyed to a black liquor filter.

Conveying coarse slurry discharged from the cooking tower to a normal-pressure diffusion washer positioned at the top of the blowing pot, washing the coarse slurry by the normal-pressure diffusion washer, then dropping the coarse slurry into a blowing groove at the bottom end of the blowing pot, diluting the concentration of the coarse slurry in the blowing groove to 4.4 wt%, and then conveying the coarse slurry to 3 parallel-connected 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 330kPa, the operation pressure difference is 26kPa, 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 3.6 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 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 slurry inlet concentration of the first-stage pressure sieve is 4.1 wt%, the slurry inlet pressure is 185kPa, 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-section pressure screen is 2.7 wt%, the slurry inlet pressure is 240kPa, and the operation pressure difference is 10-60 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 1.2 wt%, the pulp inlet pressure is 175KPa, and the screening pressure difference is 22 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 29 wt%, the vacuum of the first twin-roll washer was not lower than-30 kPa, and the rotational speed was 8 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 double-roller pulp washer is 30 wt%, the vacuum degree of the two-stage double-roller pulp washer is not lower than-30 kPa, and the operation rotating speed is 9 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 670kPa, 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 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. The oxygen consumption in the second-stage oxygen delignification process is 4kg/adt, the NaOH consumption is 0kg/adt, the pH value of the reaction system is maintained at 10.5, the pressure is maintained at 360kPa, the temperature is maintained at 102 ℃, the pulp outlet concentration is set to be 11 wt%, and the wood pulp is subjected to second-stage oxygen delignificationThe residence time in the lignin column was set at 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 the oxygen delignified wood pulp after washing. The pulp inlet concentration of the pulp washer is 7.8 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.3m³The/adt, the feed pressure was 530kPa, and the operating speed was 9.5 rpm.

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

The concentration of the DHT section slurry is 10.5 percent, the dosage of chlorine dioxide is 13.5kg/adt, the reaction temperature is 75 ℃, and the pH value is 2.6.

The concentration of the slurry in the Eop section is 10.5 percent, the dosage of NaOH is 13.5kg/adt, the dosage of oxygen is 4.5kg/adt, the reaction temperature is 79 ℃, and the pH value is 10.5.

The concentration of the slurry in the D1 stage is 10.5 percent, the chlorine dioxide is 4kg/adt, the temperature is 76 ℃, and the pH value is 4.6.

The concentration of the slurry in the D2 stage is 10.5 percent, the chlorine dioxide is 0.6kg/adt, the temperature is 76 ℃, and the pH value is 5.6.

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 acacia wood pulp is first diluted and then fed into a section of 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 acacia wood pulp board. The working speed of the drying box is set to be 60-140 m/min.

And (3) cutting the bleached sulfate acacia wood 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 specification of the iron wire used for the baling line is 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 53-59%. The produced sulfate acacia wood pulp board is detected, and the result is as follows: the tensile index is 66N.m/g and the burst index is 4.8KPa.m²(g) tear index 6.7mN.m²(g) the dust degree is 1.5mm²/m²The whiteness is 89.7 percent ISO, the dichloromethane extract is 0.45 percent, and the pulp sheet ration is 850-1270 g/m²The moisture content is less than 10 wt%.

Example 3

Preparing a bleached sulfate Indonesia jequirity-Vietnam jequirity-south Africa jequirity wood pulp board:

feeding Indonesia wood chips with the moisture content of 40-55 wt%, Vietnam wood chips with the moisture content of 40-55 wt% and south Africa wood chips with the moisture content of 40-55 wt% into a screening device according to the mass ratio of 1:1:1And (5) screening 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 was impregnated in the impregnation section of the impregnation tower at a impregnation temperature of 102 ℃. 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 135g/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 4.5m³And/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 157 ℃, and the pressure of the high-pressure cooking is controlled at 0.36 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. Part of the extracted black liquor is conveyed to a discharger, and part of the black liquor is conveyed to wood soakingAnd one part of the soaking tower 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 162 ℃, 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 to 1.0m³And/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.

Conveying coarse slurry discharged from the cooking tower to a normal-pressure diffusion washer positioned at the top of the blowing pot, washing the coarse slurry by the normal-pressure diffusion washer, then dropping the coarse slurry into a blowing groove at the bottom end of the blowing pot, diluting the concentration of the coarse slurry in the blowing groove to 4.6 wt%, and then conveying the coarse slurry to 3 parallel-connected 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 set to be 26kPa, and the slag discharge rate is set to be 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 3.6 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 190kPa, the operation pressure difference is set to be 25kPa, and the slag discharge rate is set 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 sieve is 4 wt%, the pulp inlet pressure is 200kPa, and the operation pressure difference is 45 kPa. And (3) diluting the good pulp concentration of the first-stage pressure screen to 3.2 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 3.0 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 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 3.6 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 3.5 wt%, the vacuum of the first twin-roll washer was not lower than-30 kPa, and the rotational 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 double-roller pulp washer is 29 wt%, the vacuum degree of the two-stage double-roller pulp washer is not lower than-30 kPa, and the operation rotating speed is 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 19kg/adt, the NaOH dosage is 23kg/adt, the pH value of the reaction system is maintained at 10.8, the pressure is maintained at 650kPa, the temperature is maintained at 94 ℃, the pulp outlet concentration is set to be 11 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 secondary oxygen delignification, the oxygen consumption is 6kg/adt, the NaOH consumption is 0kg/adt, the pH value of the reaction system is maintained at 10.8, the pressure is maintained at 350kPa, the temperature is maintained at 103 ℃, the pulp outlet concentration is set to be 11 wt%, and the retention time of wood pulp in a secondary 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 the bleached sulfate acacia wood pulp after washing. The pulp inlet concentration of the pulp washer is 7.5 wt%, the pulp outlet concentration is 30 wt%, and the dilution factor is 2.4m³The/adt, the feed pressure was 530kPa, and the operating speed was 10 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.

The concentration of the DHT section slurry is 115 percent, the dosage of chlorine dioxide is 14kg/adt, the reaction temperature is 75 ℃, and the pH value is 2.6.

The concentration of the slurry in the Eop section is 11 percent, the dosage of NaOH is 14kg/adt, the dosage of oxygen is 4kg/adt, the reaction temperature is 79 ℃, and the pH value is 10.6.

The concentration of the slurry in the D1 stage was 11%, the chlorine dioxide content was 4kg/adt, the temperature was 78 ℃ and the pH was 4.7.

The concentration of the slurry in the D2 stage was 11%, the chlorine dioxide content was 0.6kg/adt, the temperature was 77 ℃ and the pH was 5.6.

And bleaching the obtained product in the last D2 stage to obtain the sulfate acacia wood pulp, wherein the whiteness reaches 89.2-89.8% ISO. The obtained bleached sulfate acacia wood pulp is conveyed to a pulp board papermaking machine.

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 1.0-1.2 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.

And (3) cutting the bleached sulfate acacia wood 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 yield of the sulfate acacia wood pulp board produced by the method provided by the embodiment is calculated, and the result is 53-59%. The bleached sulfate wood pulp sulfate acacia wood pulp board produced is detected, and the result is as follows: the tensile index is 68N.m/g and the burst index is 4.6KPa.m²(iv) g, tear index 6.8mN.m²(g) the dust degree is 1.4mm²/m²The whiteness is 89.2 percent ISO, the dichloromethane extract is 0.39 percent, and the pulp sheet ration is 850-1270 g/m²The moisture content is less than 10 wt%.

From the above examples, the present invention provides a method for preparing sulfate acacia wood pulp and a wood pulp sheet prepared from the wood pulp. The preparation method of the sulfate acacia wood pulp provided by the invention comprises the following steps: a) preparing raw materials for acacia wood chips to obtain wood, wherein the density of the acacia wood chips is 135-160 kg/m³(ii) a b) Cooking the wood in white liquor to obtain coarse pulp, wherein the white liquor is NaOH and Na₂S mixed solution; c) sequentially removing knots, screening, washing, oxygen delignification and bleaching the brown stock to obtain the kraft acacia wood 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 12-15 kg/adt; the bleaching agent in the alkali bleaching process comprises NaOH and oxygen, wherein the dosage of the NaOH is 10-15 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt; the bleaching agent in the first-stage bleaching process comprises chlorine dioxide and oxygen, wherein the dosage of the chlorine dioxide is 3-4 kg/adt, and the dosage of the oxygen is 3.0-5.0 kg/adt; the bleaching agent in the secondary bleaching process comprises chlorine dioxide and NaOH; the dosage of the chlorine dioxide is 0.5-1.0 kg/adt, and the dosage of the NaOH is 0.5-1.5 kg/adt. The wood pulp prepared by the preparation method is manufactured by paper making to obtain the sulfate acacia wood pulp board. The experimental results show that: the tensile index of the wood pulp board provided by the invention is more than or equal to 65N.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 less than or equal to 2.0mm²/m²The whiteness is 89.0-91.0% ISO and the dichloromethane extract is less than or equal to 0.45%.

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 sulfate acacia wood pulp comprises the following steps:

the bleaching agent in the secondary bleaching process comprises chlorine dioxide and NaOH; the dosage of the chlorine dioxide is 0.5-1.0 kg/adt, and the dosage of the NaOH is 0.5-1.5 kg/adt;

the tensile index of the sulfate acacia wood pulp board is more than or equal to 65N.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 less than or equal to 2.0mm²/m²The whiteness is 89.0-91.0% ISO and the dichloromethane extract is less than or equal to 0.45%;

the mass concentration of the slurry in the chlorine dioxide bleaching process is 10-15%, the reaction temperature is 75-90 ℃, and the reaction time is 100-130 min;

the mass concentration of the slurry in the alkali bleaching process is 10-15%, the reaction temperature is 75-90 ℃, and the reaction time is 100-130 min;

the mass concentration of the pulp in the first-stage bleaching process is 10-15%, the reaction temperature is 60-80 ℃, and the reaction time is 160-190 min;

in the two-stage bleaching process, the mass concentration of the pulp is 10-15%, the reaction temperature is 65-80 ℃, and the reaction time is 100-130 min;

in the step a), the proportion of the timber with the thickness of more than or equal to 8mm in the total timber is less than or equal to 8 wt%, the proportion of the bark and/or the rotten timber in the total timber is less than or equal to 1 wt%, and the moisture content of the timber is less than 55 wt%;

the step b) specifically comprises the following steps:

b1) impregnating the timber to obtain impregnated timber;

the oxygen delignification working section in the step c) comprises the following steps:

c3) washing the two-stage oxygen delignification wood pulp to obtain sulphate acacia wood pulp;

the dilution factor of the washing is 2.0-2.5 m³/adt。

2. A preparation method of sulfate acacia wood pulp board comprises the following steps:

making the sulfate acacia wood pulp prepared by the preparation method of claim 1 into paper to obtain the sulfate acacia wood pulp board.