Preparation method of chemical pulp from golden bamboo grass fiber raw material by circulating cooking of black liquor calcified alkali liquor

Abstract

The invention provides a method for preparing chemical pulp by circulating and boiling golden bamboo grass fiber raw materials with black liquor calcified alkali liquor, belonging to the technical field of papermaking. The method comprises the following steps: adding sodium hydroxide solid particles and golden bamboo grass into a cooking pot, wherein the mass of sodium hydroxide is 20% of the mass of golden bamboo grass, adding water, wherein the mass ratio of water to the mass of golden bamboo grass is 6:1, boiling, draining to obtain softened golden bamboo grass, subjecting the crude pulp to five times of pressing and four times of pulp washing alternately to obtain chemical pulp, and post-treating the pulp, wherein the chemical pulp is subjected to pulping treatment to obtain good pulp. The invention adopts pulping waste liquor for recycling after calcification, so that 30%-32% of the alkali liquor used in the boiling of golden bamboo grass comes from the recycled alkali liquor, and 68%-70% comes from the newly added alkali liquor. The wastewater recycled after the pulping waste liquor is calcified accounts for 80%-81% of the total wastewater. The recycling and reuse of the wastewater reduces discharge, reduces the cost of conventional chemical pulp wastewater treatment, and reduces the production cost of pulping.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, in particular to a method for preparing chemical pulp by circulating black liquor calcified alkali liquor to cook golden bamboo grass fiber raw materials. Background Art

[0002] At present, pulp mills mainly produce two types of pulp: chemical pulp and chemimechanical pulp. Each type of pulp has its own process characteristics: chemimechanical pulp is a two-stage pulping method that combines chemical pretreatment with mechanical pulping. This method is suitable for raw materials containing more lignin. Chemical pulp refers to the pulp made by treating plant fiber raw materials with chemical agents under specific conditions to dissolve most of the lignin and separate the fibers from each other. Chemical pulp has the advantage of making the single fibers in the raw materials fully loose and separated into pulp with higher cellulose purity. Golden bamboo grass is a perennial crop with high yield, high protein, high calories, and high fiber yield. In addition to the relatively high content of pentosan and 1% NaOH extract, the other chemical compositions of the raw materials can basically meet the needs of pulping and papermaking, and it is a relatively good raw material for pulping and papermaking.

[0003] Black liquor is a waste liquid produced during the chemical pulping process. It is rich in lignin, hemicellulose, organic matter, sodium and other salt ions. Direct discharge will pollute the natural environment, so the black liquor must be treated before discharge. In order to achieve high-value utilization of black liquor resources and recover lignin and caustic soda in black liquor, a variety of methods are used to treat pulping black liquor. In the current production process, the concentration-incineration method is generally used to treat black liquor to recover heat and sodium. This technology is to evaporate and burn the black liquor to convert the sodium salt of organic matter in the black liquor into N 2 CO 3 , dissolved and then causticized with lime to produce white liquor (NaOH, N 2 S), and sent back to the cooking section for recycling. This technology not only eliminates the pollution of black liquor, utilizes the heat of organic matter in black liquor, but also recovers pulping chemicals - white liquor. This alkali recovery technology is perfect in theory and mature in production practice. However, there are still problems with this recovery technology. First, the investment is large, and second, when recovering alkali, a large amount of alkaline waste residue - white mud is produced, which constitutes serious secondary pollution.

[0004] The other is black liquor gasification recovery technology, which is a new method for recovering alkali and energy. The process is as follows: first, the black liquor is transported to a high-temperature gasifier, where the black liquor is gasified to generate fuel gas, which is then transported to a gas turbine for combustion to generate electricity. At the same time, the heat of the exhaust gas in the gas turbine is used to produce high-pressure steam, which is then transported to a steam turbine for a second power generation. For the domestic papermaking industry, black liquor gasification technology will greatly improve the level of black liquor treatment. However, there are also many difficulties in black liquor gasification that need to be solved, such as difficulties in fluidized bed operation, material corrosion of equipment and reactors, carbon conversion rate and mirabilite reduction problems in low-temperature gasification of black liquor, and increased gasification load. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing chemical pulp by circulating black liquor calcified alkali liquor to cook golden bamboo grass fiber raw material, so as to solve the technical problems of low pulping rate, high black liquor and wastewater discharge and high pulping cost in the existing pulping process.

[0006] This improved technology uses calcification to treat black liquor and recovers the precipitation by-product lignin calcium (an organic anion adsorbent) and alkali solution; it avoids the energy consumption of concentration and combustion in traditional alkali recovery methods and reduces the production of "white mud".

[0007] The recovered alkali liquor (accounting for 80%-81% of the total wastewater) is recycled for cooking, which reduces the input of water resources in the cooking process and increases the pulp yield due to the sugars and fine fibers in the filtrate; it reduces the load of wastewater treatment in traditional alkali recovery methods and traditional black liquor gasification methods, realizes the recycling of wastewater, and achieves the purpose of energy conservation and emission reduction.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing chemical pulp by circulating black liquor calcified alkali liquor to cook golden bamboo grass fiber raw materials, the method comprising the following steps:

[0010] Step 1: adding sodium hydroxide solid particles and golden bamboo grass into a cooking pot, wherein the mass of sodium hydroxide is 20% of the mass of golden bamboo grass, adding water, wherein the mass ratio of water to the mass of golden bamboo grass is 6:1, cooking, and draining to obtain softened golden bamboo grass;

[0011] Step 2: The crude pulp is subjected to five pressings and four washings alternately to obtain chemical pulp;

[0012] Step 3: Post-processing of pulp: chemical pulp is processed by pulping to obtain good pulp.

[0013] Furthermore, the specific process of step 1 is:

[0014] Step 1.1: Cutting: Use absolutely dry golden bamboo grass as raw material and cut the golden bamboo grass through a cutting machine;

[0015] Step 1.2: Loading: Take an appropriate amount of absolutely dried golden bamboo grass and put it into a digester, add sodium hydroxide, the mass of sodium hydroxide added is 20% of the total mass of absolutely dried golden bamboo grass, and add water to make the material-liquid ratio 1:6;

[0016] Step 1.3: Steaming: Heat the steaming vessel to steam the absolutely dried golden bamboo grass therein, heat the steaming vessel for 2 hours, so that the temperature inside the steaming vessel increases from room temperature to 165°C, and keep the steaming vessel warm at 165°C for 2 hours.

[0017] Step 1.4: Draining: After cooking, crude pulp and black liquor are obtained. After draining and separation, the water content of the crude pulp is 85%, and the black liquor is calcified.

[0018] Furthermore, in step 1.2, 30%-32% of the sodium hydroxide is derived from the alkalization recycling of the pulping black liquor, and 68%-70% of the sodium hydroxide is added.

[0019] Furthermore, the water in step 1.2 includes 77%-81% of circulating black liquor and 19%-23% of newly added clean water.

[0020] Furthermore, the specific process of step 2 is:

[0021] Step 2.1: primary pressing: using a twin-screw press to press the medium-consistency pulp to obtain primary pressed pulp and primary pressed waste liquid; wherein the primary pressed pulp includes dry pulp and residual black liquor, and the primary pressed waste liquid is used in the pulping process after being calcified;

[0022] Step 2.2: Primary pulp washing: Use a spiral trough or an inclined trough to send the primary pressed pulp to the pulp washing tank; continuously add all the waste liquid produced by the four pressings to the primary pressed pulp, and stir it with a stirrer to disperse the pulp clumps in the primary pressed pulp, so that the black liquor entrained in the primary pressed pulp is fully dissolved in water to form an 8% primary washed medium-consistency pulp;

[0023] Step 2.3: Secondary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by the primary washing to obtain secondary pressed pulp with a concentration of 30% and secondary pressed waste liquid, wherein the secondary pressed pulp includes dry pulp and black liquor, and the solid concentration of the secondary pressed waste liquid is 1.7%;

[0024] Step 2.4: Secondary pulp washing: discharge the secondary pressed pulp obtained by the secondary pressing into the pulp washing tank; add all the waste liquid from the fifth pressing, stir with a stirrer, so that the black liquor entrained in the secondary pressed pulp is fully dissolved in water, and once again form an 8% secondary washed medium-consistency pulp;

[0025] Step 2.5: tertiary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by secondary washing to obtain 30% tertiary pressed pulp and tertiary pressed waste liquid, wherein the concentration of the tertiary pressed waste liquid is 0.46%;

[0026] Step 2.6: Three-time pulp washing: The three-time pressed pulp obtained by three-time pressing is discharged into a pulp washing tank, and clean water is added to the three-time pressed pulp, and stirred with a stirrer to fully dissolve the black liquor entrained in the three-time pressed pulp in the water to form a three-time washed medium-consistency pulp with a concentration of 8%;

[0027] Step 2.7: four-time pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by three washings to obtain four-time pressing pulp with a concentration of 30% and four-time pressing waste liquid, wherein the solid concentration of the four-time pressing waste liquid is 0.12%, and the waste liquid is transferred back to the first pulp washing tank to wash the first-time pressing pulp;

[0028] Step 2.8: Four-time pulp washing: the four-time pressed pulp obtained by four-time pressing is discharged into a pulp washing tank, and clean water is added to the four-time pressed pulp, and stirred with a stirrer to fully dissolve the black liquor entrained in the four-time pressed pulp in the water to form a four-time washed medium-consistency pulp with a concentration of 8%;

[0029] Step 2.9: Fifth pressing: The 8% medium-concentration pulp obtained by four washings is pressed by a belt filter press to obtain fifth-pressed pulp with a concentration of 30% and fifth-pressed waste liquid, wherein the solid concentration of the fifth-pressed waste liquid is 0.03%, and it is transferred back to the secondary pulp washing tank to wash the secondary pressed pulp.

[0030] Furthermore, the specific process of step 3 is:

[0031] Step 3.1: Dilution of medium-consistency pulp: Transfer the medium-consistency pulp to the pre-tapping tank, add clean water or the squeezing waste liquid generated in the above-mentioned squeezing process to dilute and stir it to form a uniform low-concentration pulp with a concentration of 2%-5%.

[0032] Step 3.2: Beating: Use a PFI beater to beat the 2%-5% low-concentration slurry three times in series to beat the slurry to a beating degree of 33°SR-37°SR. After beating, transfer it to the post-beating pool.

[0033] Step 3.3: Slurry preparation: After beating, the low-concentration slurry, starting from 10%, is added to the original papermaking slurry, mixed thoroughly, and then sent to the papermaking workshop;

[0034] Step 3.4: Papermaking: Use papermaking equipment to produce corresponding paper products.

[0035] Pulping, washing and post-treatment of pulp. In the circulating pulping, the amount of sodium hydroxide accounts for 20% of the raw material weight, of which 30%-32% of the sodium hydroxide comes from the alkalization recycling of the pulping black liquor, and the additional 68%-70%; the material-liquid ratio of the golden bamboo grass (absolutely dry) and water is 1:6, of which the water includes 77%-81% of the circulating black liquor and 19%-23% of the additional clean water; the coarse pulp is processed by five pressings and four washings; the black liquor reacts with the first pressing black liquor and lime to remove the lignin therein, generate lignin calcium precipitation, and at the same time, regenerate into low-concentration sodium hydroxide. The outstanding advantages of this method: saving 30%-32% of the sodium hydroxide dosage, increasing the pulping rate by 4%, and reducing the discharge of the pulping black liquor by 80%-81% through recycling. It not only reduces production energy consumption, but also reduces the content of harmful chemical components in the black liquor after cooking and the difficulty of wastewater treatment, and recycles the regenerated alkali solution, thereby greatly reducing the manufacturing cost.

[0036] Compared with the traditional black liquor treatment method, the present invention makes process improvements in two aspects: the black liquor is treated by calcification, and lignin calcium is recovered without producing "white mud"; the calcified filtrate is used for circulating cooking, which not only reduces the input of water resources and the amount of new alkali, but also reduces the load of the wastewater treatment process and improves the pulp yield. In the whole process, the present invention can fully recover resources such as lignin calcium and alkali liquor, reduce the input of water and chemical agents in the circulating cooking process, and achieve the effect of energy saving and emission reduction.

[0037] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0038] (1) The present invention uses pulping waste liquid for recycling after calcification, so that 30%-32% of the alkali liquid used in the cooking of golden bamboo grass comes from the recycled alkali liquid, and 68%-70% comes from the newly added alkali liquid.

[0039] (2) In the technical solution of the present invention, the recycled wastewater after calcification of pulping wastewater accounts for 80%-81% of the total wastewater. The recycling of the wastewater reduces emissions, reduces the cost of conventional chemical pulp wastewater treatment and reduces the production cost of pulping.

[0040] (3) The pulp produced by the technical solution of the present invention maintains a yield of about 50%, which is about 8% higher than the yield of traditional chemical pulping. The alkali liquid produced by the pulping black liquor after calcification contains some fine fibers, sugars, and organic substances, which react with the fibers to increase the quality of the pulp and improve the pulp yield.

[0041] (4) The performance of hand-made paper made from the pulp produced by the technical solution of the present invention was tested. The physical properties of the paper made from the conventional chemical pulping method in terms of bursting index were similar to those of the paper made from the good pulp made from the conventional chemical pulping method, and the tear index, tensile index, and tear length index were better than those of the paper made from the good pulp made from the conventional chemical pulping method. The reason is that after delignification of the cooking black liquor, fine fibers, sugars, and organic substances remain in the recycled alkali liquor. These substances adhere to the surface of the golden bamboo grass fiber during the cyclic cooking process, improving the strength of the fiber and enhancing the mechanical properties of the paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of the steps of the present invention;

[0043] Figure 2 It is a detailed structural diagram of the process of the present invention;

[0044] Figure 3 It is a curve comparison diagram of the pulp yield of the present invention and the pulp yield of the traditional pulping method;

[0045] Figure 4 It is a partial performance comparison diagram of paper made from pulp produced by the present invention and pulp produced by a traditional pulping method. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are only for the purpose of enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0047] like Figure 1-2 As shown, the method for preparing chemical pulp by circulating the black liquor calcified alkali liquor to cook the golden bamboo grass fiber raw material comprises the following steps:

[0048] Step S10, pulping: adding sodium hydroxide solid particles and absolutely dried golden bamboo grass into a cooking pot, using 20% ​​alkali, supplementing water to make the material-liquid ratio 1:6, heating at a cooking temperature of 26° C. for 2 hours, keeping the temperature at 165° C. for 2 hours, and draining to obtain softened golden bamboo grass;

[0049] The specific steps in this step are as follows:

[0050] S11 Cutting: Use golden bamboo grass as raw material, cut the golden bamboo grass through a cutting machine, and cut the size according to actual needs.

[0051] S12 Loading: Put an appropriate amount of absolutely dried golden bamboo grass into the digester, add sodium hydroxide, the mass of sodium hydroxide added is 20% of the total mass of absolutely dried golden bamboo grass, and add water to make the material-liquid ratio 1:6.

[0052] S13 Steaming: heating the steaming vessel to steam the absolutely dried golden bamboo grass therein. The heating condition here is to slowly heat the steaming vessel for 2 hours through calculation so that the temperature inside the steaming vessel is about 165°C, and to keep the steaming vessel warm at this temperature for 2 hours so that the temperature inside the steaming vessel is maintained at about 165°C.

[0053] S14 Draining: After cooking, crude pulp and black liquor are obtained. After draining and separation, the water content of the crude pulp is 85%. After calcification, the black liquor is used in the golden bamboo grass cooking pulping process to achieve the purpose of saving costs and improving the pulping rate of pulping.

[0054] Step S20, pulp washing: the crude pulp is subjected to five pressings and four pulp washings to obtain chemical pulp, wherein the four pressings and the three pulp washings are performed alternately. The crude pulp is subjected to five pressings and four pulp washings to obtain chemical pulp, wherein the five pressings and the four pulp washings are performed alternately, and the steps specifically include:

[0055] S21, primary pressing: using a twin-screw press to press medium-consistency pulp to obtain primary pressing pulp and primary pressing waste liquid; wherein the primary pressing pulp includes dry pulp and residual black liquor; the primary pressing waste liquid is used in the pulping process after being calcified;

[0056] S22, primary pulp washing: the primary pressed pulp is sent to the pulp washing tank by a spiral trough or an inclined trough; all the waste liquid produced by the four pressings is continuously added to the primary pressed pulp, and the pulp is stirred by a stirrer to disperse the pulp clumps in the primary pressed pulp, so that the black liquor entrained in the primary pressed pulp is fully dissolved in water to form a primary washed medium-consistency pulp of 8%;

[0057] S23, secondary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by the primary washing to obtain secondary pressed pulp with a concentration of 30% and secondary pressed waste liquid, wherein the secondary pressed pulp includes dry pulp and black liquor, and the solid concentration of the secondary pressed waste liquid is 1.7%;

[0058] S24, secondary pulp washing: discharge the secondary pressed pulp obtained by secondary pressing into a pulp washing tank; add all the waste liquid from the fifth pressing; stir with a stirrer to fully dissolve the black liquor entrained in the secondary pressed pulp in water, and once again form a secondary washed medium-consistency pulp of 8%;

[0059] S25, tertiary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by secondary washing to obtain 30% tertiary pressed pulp and tertiary pressed waste liquid, wherein the concentration of the tertiary pressed waste liquid is 0.46%;

[0060] S26, three-time pulp washing: the three-time pressed pulp obtained by three-time pressing is discharged into a pulp washing tank, and clean water is added to the three-time pressed pulp, and stirred with a stirrer to make the black liquor entrained in the three-time pressed pulp fully dissolved in the water to form a three-time washed medium-consistency pulp with a concentration of 8%;

[0061] S27, fourth pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by three washings to obtain a fourth-pressed pulp with a concentration of 30% and a fourth-pressed waste liquid, wherein the solid concentration of the fourth-pressed waste liquid is 0.12%, and the waste liquid is transferred back to the first-pressed pulp washing tank to wash the first-pressed pulp;

[0062] S28, four-time pulp washing: discharging the four-time pressed pulp obtained by four-time pressing into a pulp washing tank, adding clean water to the four-time pressed pulp, and stirring with a stirrer to fully dissolve the black liquor entrained in the four-time pressed pulp in the water to form a four-time washed medium-consistency pulp with a concentration of 8%;

[0063] S29, fifth pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by four washings to obtain a fifth-pressed pulp with a concentration of 30% and a fifth-pressed waste liquid, wherein the solid concentration of the fifth-pressed waste liquid is 0.03%, and the waste liquid is transferred back to the secondary pulp washing tank to wash the secondary pressed pulp;

[0064] Step S30, pulp post-treatment: the chemical pulp is subjected to pulping treatment to obtain good pulp.

[0065] The specific steps in this step are as follows:

[0066] S31 medium-concentration pulp dilution: The medium-concentration pulp is transferred to the pre-beating tank, diluted with clean water or the squeezing waste liquid generated in the above-mentioned squeezing process and stirred to form a uniform low-concentration pulp with a concentration of 2%-5%.

[0067] S32 beating: use PFI beating machine to beat the 2%-5% low concentration slurry to a beating degree of 33°SR-37°SR for three times in series. After beating, transfer it to the post-beating pool.

[0068] S33 pulping: The low-concentration pulp after beating is added to the original papermaking pulp, starting from 10%, and after being fully mixed, it is sent to the papermaking workshop.

[0069] S34 Papermaking: Use papermaking equipment to produce corresponding paper products.

[0070] The method for preparing chemical pulp of golden bamboo grass fiber raw material by circulating cooking of black liquor calcified alkali liquor is described in detail below through a specific embodiment.

[0071] Example 1

[0072] Step S10, pulping includes:

[0073] S11 Slicing: 7 tons of golden bamboo grass is used as raw material and the golden bamboo grass is sliced ​​through a cutting machine.

[0074] S12 Soaking: Put the absolutely dried golden bamboo grass into a cooking vessel and add sodium hydroxide. The mass of the added sodium hydroxide is 20% of the total mass of the absolutely dried golden bamboo grass, that is, 1.4 tons of sodium hydroxide and 42 tons of clean water. The mass after adding is 50.4 tons.

[0075] S13 Steaming: heating the steaming vessel to steam the absolutely dried golden bamboo grass therein. The heating condition here is to slowly heat the steaming vessel for 2 hours through calculation so that the temperature inside the steaming vessel is about 165°C, and to keep the steaming vessel warm at this temperature for 2 hours so that the temperature inside the steaming vessel is maintained at about 165°C.

[0076] S14 Draining: After cooking, crude pulp and black liquor are obtained. After draining and separation, the water content of crude pulp is 85%. After calcification, black liquor is used in the golden bamboo grass cooking pulping process to achieve the purpose of saving costs and improving the pulping rate. At this time, the total weight of black liquor is 25.56 tons and the solid content is 3.39 tons.

[0077] Step S20 pulp washing includes:

[0078] S21, primary pressing: using a twin-screw press to press medium-concentration pulp, a concentration of 30% and a mass of 12.42 tons of primary pressing pulp and primary pressing waste liquid are obtained; wherein the primary pressing pulp contains 3.5 tons of dry pulp, 8.92 tons of black liquor, 0.755 tons of black liquor solids, and the entrained black liquor solids account for 21.58% of the dry pulp. Also obtained is 12.42 tons of primary pressing waste liquid, containing 0.754 tons of solids, and the solid concentration of the primary pressing waste liquid is 6.9%. After calcification, the primary pressing waste liquid is used in the pulping process to improve the pulp yield of pulping.

[0079] S22, primary pulp washing: the primary pressed pulp is sent to the pulp washing tank by a spiral trough or an inclined trough; all the waste liquid produced by four pressings is continuously added to the primary pressed pulp, with a total mass of 44.5 tons; and the pulp is stirred by a stirrer to disperse the pulp clumps in the primary pressed pulp, so that the black liquor entrained in the primary pressed pulp is fully dissolved in water to form a medium-consistency pulp of 8% primary washing;

[0080] S23, secondary pressing: The 8% medium-concentration pulp obtained by the primary washing is pressed by a belt filter press to obtain a secondary pressing pulp with a concentration of 30% and a mass of 11.87 tons and secondary pressing waste liquid, wherein the secondary pressing pulp contains 3.5 tons of dry pulp, 8.37 tons of waste liquid, 201.48 kg of black liquor solids, and the entrained black liquor solids account for 5.8% of the dry pulp, the mass of the secondary pressing waste liquid is 32.63 tons, containing 553.85 kg of solids, and the solid concentration of the secondary pressing waste liquid is 1.7%. 32.63 tons of secondary pressing waste liquid are transferred to the flocculation sedimentation tank.

[0081] S24, secondary pulp washing: discharge the secondary pressed pulp obtained from the secondary pressing into the pulp washing tank; add all the waste liquid from the five pressings, with a total mass of 43.95 tons; stir with a stirrer to fully dissolve the black liquor entrained in the secondary pressed pulp in water, and once again form a secondary washed medium-consistency pulp of 8%;

[0082] S25, three-time pressing: the 8% medium-concentration pulp obtained by the second washing is pressed by a belt filter press to obtain a three-time pressing pulp with a concentration of 30% and a mass of 11.73 tons and a three-time pressing waste liquid, wherein the three-time pressing pulp contains 3.5 tons of dry pulp, 8.23 ​​tons of waste liquid, 53.74 kg of black liquor solids, and the entrained black liquor solids account for 1.5% of the dry pulp, the mass of the second pressing waste liquid is 32.22 tons, containing 147.74 kg of solids, and the solid concentration of the three-time pressing waste liquid is 0.46%. 32.22 tons of the three-time pressing waste liquid are transferred to the flocculation sedimentation tank.

[0083] S26, three-time pulp washing: the three-time pressed pulp obtained by three-time pressing is discharged into a pulp washing tank, and clean water is added to the three-time pressed pulp, with a total mass of 43.8 tons; and the three-time pressed pulp is stirred by a stirrer to fully dissolve the black liquor entrained in the three-time pressed pulp in water to form a three-time washed medium-consistency pulp with a concentration of 8%;

[0084] S27, four times pressing: use a belt filter press to press the 8% medium-concentration pulp obtained by three washings to obtain a concentration of 30%, a mass of 11.68 tons of four-time pressing pulp and four-time pressing waste liquid, wherein the four-time pressing pulp contains 3.5 tons of dry pulp, 8.18 tons of waste liquid, 14.31 kg of black liquor solids, and the entrained black liquor solids account for 0.41% of the dry pulp. The mass of the secondary pressing waste liquid is 32.12 tons, containing 39.41 kg of solids, and the solid concentration of the four-time pressing waste liquid is 0.12%. It is then transferred back to the primary pulp washing tank to wash the primary pressing pulp;

[0085] S28, four-time pulp washing: the four-time pressed pulp obtained by four-time pressing is discharged into a pulp washing tank, and clean water is added to the four-time pressed pulp, with a total mass of 43.76 tons; and the pulp is stirred with a stirrer to fully dissolve the black liquor entrained in the four-time pressed pulp in water, forming a four-time washed medium-consistency pulp with a concentration of 8%;

[0086] S29, five times pressing: use a belt filter press to press the 8% medium-concentration pulp obtained by four washings to obtain a five-time pressing pulp and five-time pressing waste liquid with a concentration of 30% and a mass of 11.67 tons, wherein the five-time pressing pulp contains 3.5 tons of dry pulp, 8.17 tons of waste liquid, 3.82 kg of black liquor solids, and the entrained black liquor solids account for 0.11% of the dry pulp. The mass of the secondary pressing waste liquid is 32.09 tons, containing 10.51 kg of solids, and the solid concentration of the five-time pressing waste liquid is 0.03%. It is then transferred back to the secondary pulp washing tank to wash the secondary pressing pulp;

[0087] Step S30 slurry post-treatment includes:

[0088] S31 medium-concentration pulp dilution: The medium-concentration pulp is transferred to the pre-beating tank, diluted with clean water or the squeezing waste liquid generated in the above-mentioned squeezing process and stirred to form a uniform low-concentration pulp with a concentration of 2%-5%.

[0089] S32 beating: using a double-disc pulping machine for beating, three times in series, the 2%-5% low-concentration pulp is beaten to a beating degree range of 33°SR-37°SR. After beating, it is transferred to the post-beating pool.

[0090] S33 pulping: The low-concentration pulp after beating is added to the original papermaking pulp, starting from 10%, and after being fully mixed, it is sent to the papermaking workshop.

[0091] S34 Papermaking: Use papermaking equipment to produce corresponding paper products.

[0092] That is, the black liquor reacts directly with lime to generate lignin calcium precipitate and low-concentration sodium hydroxide solution. Thereby, lignin is removed from the waste liquid, sodium hydroxide is regenerated from the waste liquid, and the alkaline filtrate can be directly reused for wood chip cooking; compared with the black liquor gasification recovery technology, the calcification treatment of black liquor reduces the load and energy consumption of wastewater treatment by directly reusing it after calcification; compared with the traditional concentration-incineration method, there is no energy consumption for concentrating and burning black liquor, and no by-product "white mud" is produced. The pulp yield of this method is improved, thereby improving the utilization rate of the company's raw materials, increasing production capacity, and improving the company's economic benefits. However, lignin calcium by-product will be produced in the process of recovering alkali. Lignin calcium by-product is an anionic adsorbent that can be used in the fields of sewage treatment and soil improvement. Such as Figure 3As shown, the pulp produced by the technical solution of the present invention maintains a yield of about 50%, which is about 8% higher than that of traditional chemical pulping.

[0093] See also Figure 3 The present invention calculates the pulp yield by using Example 1 and compares it with the pulp yield after pulping by the traditional chemical pulping method to obtain Figure 3 In the curve graph. Figure 3 Curve A in the figure is the pulp yield of golden bamboo grass after pulping by the pulping method of the present invention, curve B is the average pulp yield of golden bamboo grass after pulping by the pulping method of the present invention, and curve C is the pulp yield of golden bamboo grass after pulping by the conventional chemical pulping method. It can be seen from the curves in the figure that the pulp yield of the pulping method of the present invention exceeds the pulp yield of the pulping by the conventional chemical pulping method, and compared with the conventional chemical pulping method, the circulating cooking process is added, thereby greatly reducing the production cost.

[0094] See also Figure 4 The paper was made from the good pulp obtained in Example 1, and the performance was compared with that of the paper made from the good pulp obtained by conventional chemical pulping method and the paper made from the good pulp obtained by conventional chemical mechanical pulping method. Figure 4 The curve diagram in the figure. Curve A is a paper made from good pulp obtained by conventional chemical pulping, and curve B is a paper made from good pulp obtained by the pulping method of the present invention. From the curves in the above figure, it can be seen that the paper prepared by the present application has similar physical properties to the paper made from good pulp obtained by conventional chemical pulping in terms of burst resistance index, and its tear index, tensile index, breaking length and other indexes are better than the physical properties of the paper made from good pulp obtained by conventional chemical pulping. The reason is that after delignification, fine fibers, sugars and organic substances remain in the recycled alkali solution of the cooking black liquor and the primary pressing wastewater. These substances adhere to the surface of the wood chip fibers during the cyclic cooking process, improve the strength of the fibers, and enhance the mechanical properties of the paper.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing chemical pulp from golden bamboo grass fiber raw material by circulating cooking with black liquor calcified alkali liquor, characterized in that: The method comprises the following steps: Step 1: adding sodium hydroxide solid particles and golden bamboo grass into a cooking pot, wherein the mass of sodium hydroxide is 20% of the mass of golden bamboo grass, adding water, wherein the mass ratio of water to the mass of golden bamboo grass is 6:1, cooking, and draining to obtain softened golden bamboo grass; Step 2: The crude pulp is subjected to five pressings and four washings alternately to obtain chemical pulp; Step 3: Post-treatment of pulp: chemical pulp is processed by beating to obtain good pulp; The specific process of step 1 is: Step 1.1: Cutting: Use absolutely dry golden bamboo grass as raw material and cut the golden bamboo grass through a cutting machine; Step 1.2: Loading: Take an appropriate amount of absolutely dried golden bamboo grass and put it into a digester, add sodium hydroxide, the mass of sodium hydroxide added is 20% of the total mass of absolutely dried golden bamboo grass, and add water to make the material-liquid ratio 1:6; Step 1.3: Steaming: heating a steaming vessel to steam the absolutely dried golden bamboo grass therein, heating the steaming vessel for 2 hours, so that the temperature in the steaming vessel rises from room temperature to 165° C., and keeping the steaming vessel at 165° C. for 2 hours; Step 1.4: Draining: After cooking, crude pulp and black liquor are obtained. After draining and separation, the water content of the crude pulp is 85%, and the black liquor is calcified; The specific process of step 2 is: Step 2.1: primary pressing: using a twin-screw press to press the medium-consistency pulp to obtain primary pressed pulp and primary pressed waste liquid; wherein the primary pressed pulp includes dry pulp and residual black liquor, and the primary pressed waste liquid is used in the pulping process after being calcified; Step 2.2: Primary pulp washing: Use a spiral trough or an inclined trough to send the primary pressed pulp to the pulp washing tank; continuously add all the waste liquid produced by the four pressings to the primary pressed pulp, and stir it with a stirrer to disperse the pulp clumps in the primary pressed pulp, so that the black liquor entrained in the primary pressed pulp is fully dissolved in water to form an 8% primary washed medium-consistency pulp; Step 2.3: Secondary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by the primary washing to obtain secondary pressed pulp with a concentration of 30% and secondary pressed waste liquid, wherein the secondary pressed pulp includes dry pulp and black liquor, and the solid concentration of the secondary pressed waste liquid is 1.7%; Step 2.4: Secondary pulp washing: discharge the secondary pressed pulp obtained by the secondary pressing into the pulp washing tank; add all the waste liquid from the fifth pressing, stir with a stirrer, so that the black liquor entrained in the secondary pressed pulp is fully dissolved in water, and once again form an 8% secondary washed medium-consistency pulp; Step 2.5: tertiary pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by secondary washing to obtain 30% tertiary pressed pulp and tertiary pressed waste liquid, wherein the concentration of the tertiary pressed waste liquid is 0.46%; Step 2.6: Three-time pulp washing: The three-time pressed pulp obtained by three-time pressing is discharged into a pulp washing tank, and clean water is added to the three-time pressed pulp, and stirred with a stirrer to fully dissolve the black liquor entrained in the three-time pressed pulp in the water to form a three-time washed medium-consistency pulp with a concentration of 8%; Step 2.7: four-time pressing: using a belt filter press to press the 8% medium-concentration pulp obtained by three washings to obtain four-time pressing pulp with a concentration of 30% and four-time pressing waste liquid, wherein the solid concentration of the four-time pressing waste liquid is 0.12%, and the waste liquid is transferred back to the first pulp washing tank to wash the first-time pressing pulp; Step 2.8: Four-time pulp washing: the four-time pressed pulp obtained by four-time pressing is discharged into a pulp washing tank, and clean water is added to the four-time pressed pulp, and stirred with a stirrer to fully dissolve the black liquor entrained in the four-time pressed pulp in the water to form a four-time washed medium-consistency pulp with a concentration of 8%; Step 2.9: Fifth pressing: The 8% medium-concentration pulp obtained by four washings is pressed by a belt filter press to obtain fifth-pressed pulp with a concentration of 30% and fifth-pressed waste liquid, wherein the solid concentration of the fifth-pressed waste liquid is 0.03%, and it is transferred back to the secondary pulp washing tank to wash the secondary pressed pulp.

2. The method for preparing chemical pulp of golden bamboo grass fiber raw material by circulating cooking of black liquor calcified alkali liquor according to claim 1, characterized in that: In step 1.2, 30%-32% of the sodium hydroxide is derived from the alkalization recycling of pulping black liquor, and 68%-70% of the sodium hydroxide is added.

3. The method for preparing chemical pulp of golden bamboo grass fiber raw material by circulating cooking of black liquor calcified alkali liquor according to claim 1, characterized in that: The water in step 1.2 includes 77%-81% of recycled black liquor and 19%-23% of newly added clean water.

4. The method for preparing chemical pulp of golden bamboo grass fiber raw material by circulating cooking of black liquor calcified alkali liquor according to claim 1, characterized in that: The specific process of step 3 is: Step 3.1: Medium-concentration pulp dilution: transfer the medium-concentration pulp to the pre-beating tank, add clean water or the squeezing waste liquid generated in the above squeezing process to dilute and stir it to form a uniform low-concentration pulp with a concentration of 2%-5%; Step 3.2: beating: use a PFI beating machine to beat the 2%-5% low-concentration slurry to a beating degree range of 33°SR-37°SR for three times in series, and then transfer it to the post-beating pool after beating; Step 3.3: Slurry preparation: After beating, the low-concentration slurry, starting from 10%, is added to the original papermaking slurry, mixed thoroughly, and then sent to the papermaking workshop; Step 3.4: Papermaking: Use papermaking equipment to produce corresponding paper products.

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