A method for preparing pulp from bamboo chips

Abstract

This invention discloses a method for preparing pulp from bamboo strips, comprising the following steps: 1) adding bamboo strips to a twin-screw extruder for kneading to obtain kneaded bamboo strips; 2) adding the kneaded bamboo strips to a rotary multi-tank digester, then adding sodium hydroxide, sodium sulfate, and water for sulfate cooking, followed by washing, dewatering by extrusion, and screening with a flat sieve to obtain pulp. The method for preparing pulp from bamboo strips of this invention has advantages such as high pulp yield, low kappa number, and low reagent dosage, making it suitable for large-scale industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of pulping and papermaking, and in particular to a method for preparing pulp from bamboo chips. Background Art

[0002] The papermaking industry is an important basic industry of the national economy. The consumption level of paper and paperboard is one of the indicators of a country's modernization level and civilization. In recent years, the use of paper instead of plastic has brought new opportunities to the papermaking industry. Kraft pulping is an alkaline pulping process that uses a mixed solution of sodium hydroxide and sodium sulfide to treat wood chips to produce pulp. The pulp produced by the cooking process is washed and screened to obtain good pulp, which is then bleached (or unbleached) and sent to a paper machine to make paper products. However, the existing kraft pulping has problems such as low pulp yield, high kappa number of pulp, and large amount of reagents, which makes it difficult to fully meet the growing practical application requirements.

[0003] Therefore, it is of great significance to develop a pulping process with high pulp yield, low kappa number of pulp and small amount of reagents. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing pulp from bamboo chips.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing pulp from bamboo chips, comprising the following steps:

[0007] 1) adding bamboo chips into a twin-screw extruder kneading machine for kneading to obtain kneaded bamboo chips;

[0008] 2) The kneaded bamboo chips are added to a rotary multi-tank cooking pot, and then sodium hydroxide, sodium sulfate and water are added to perform sulfate cooking, followed by washing, extrusion dehydration and flat screen screening to obtain pulp.

[0009] Preferably, in step 1), the bamboo strip has a length of 15 mm to 42 mm and a thickness of 3 mm to 6 mm.

[0010] Preferably, the bamboo chips in step 1) are wet bamboo chips with a moisture content of 35% to 45%.

[0011] Preferably, the degree of kneading treatment in step 1) is 30% to 90%. The degree of kneading treatment (%) = m1 / m0×100%, m1 is the mass of the bamboo pieces in a filamentous state after kneading treatment, and m0 is the initial mass of the bamboo pieces before kneading treatment.

[0012] Preferably, in step 2), the mass ratio of the kneaded bamboo chips, sodium hydroxide and sodium sulfate is 12-17:1.2-1.4:1.

[0013] Preferably, in step 2), the cooking liquor ratio of the kraft cooking is 1:3-5, and the sulfidation degree is 15%-25%.

[0014] Preferably, the heating process of the sulfate cooking in step 2) is: first, heating from room temperature to 100°C-120°C at a heating rate of 1.5°C / min-2.5°C / min, keeping warm for 25min-35min, then heating to 140°C-160°C at a heating rate of 1.5°C / min-2.5°C / min, keeping warm for 15min-25min, then heating to 165°C-170°C at a heating rate of 0.5°C / min-1.5°C / min, and keeping warm for 80min-100min.

[0015] Preferably, the kraft cooking in step 2) is carried out under the condition that the pressure in the rotary multi-tank cooking pot is ≤ 0.8 MPa.

[0016] Preferably, the residual alkali concentration of the black liquor produced by the kraft cooking in step 2) is 10.5 g / L to 12.0 g / L.

[0017] Preferably, in step 2), the sieve slot width of the flat sieve is 0.1 mm to 0.2 mm.

[0018] The beneficial effects of the present invention are as follows: the method for preparing pulp from bamboo chips of the present invention has the advantages of high pulp yield, low kappa number of pulp, small amount of reagent used, etc., and is suitable for large-scale industrial application.

[0019] Specifically: The present invention adopts a twin-screw extrusion kneading machine to first roll the bamboo slices into threads, so that the fibers in the bamboo slices are dissociated according to different degrees of dissociation, and then a rotary multi-tank cooker is used to perform sulfate cooking on the bamboo threads, which solves the problem of low pulp yield caused by uneven liquid penetration in traditional sulfate cooking, greatly improves the pulp yield, and at the same time reduces the Kappa number and the amount of chemicals used in the pulp, thereby improving the delignification degree of the pulp. DETAILED DESCRIPTION

[0020] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0021] Embodiment 1:

[0022] A method for preparing pulp from bamboo chips, comprising the following steps:

[0023] 1) adding wet bamboo chips with a length of 15 mm to 42 mm, a thickness of 3 mm to 6 mm and a moisture content of 38% to a twin-screw extruder kneading machine (SL185 model of Hebei Tianzheng Screening Pulping Equipment Co., Ltd., with a motor power of 110 kW) for kneading treatment, with a compression ratio of 1:2 and a kneading degree of 30% to obtain kneaded bamboo chips;

[0024] 2) Add the kneaded bamboo chips into a rotary multi-tank cooking pot, add sodium hydroxide, sodium sulfate and water, and then run it idle for 10 minutes, and then perform sulfate cooking. The mass ratio of the kneaded bamboo chips, sodium hydroxide and sodium sulfate is 12.8:1.3:1, the cooking liquid ratio is 1:4, and the sulfidation degree is 20%. The heating process of sulfate cooking is: first, the temperature is increased from room temperature to 110°C at a heating rate of 1.8°C / min, and the temperature is kept for 30 minutes, then the temperature is increased to 150°C at a heating rate of 2.0°C / min, and the temperature is kept for 20 minutes, and then the temperature is increased to 168°C at a heating rate of 1.0°C / min, and the temperature is kept for 90 minutes. During the entire sulfate cooking process, the pressure in the rotary multi-tank cooking pot is maintained at ≤0.8MPa, and then washing (the residual alkali concentration of the black liquor is 10.9g / L) and extrusion dehydration are performed, and then screening is performed using a flat screen with a screen gap width of 0.15mm to obtain pulp.

[0025] According to the test, the pulp yield in this embodiment is 36% and the Kappa number is 12.7.

[0026] Embodiment 2:

[0027] A method for preparing pulp from bamboo chips, comprising the following steps:

[0028] 1) adding wet bamboo chips with a length of 15 mm to 42 mm, a thickness of 3 mm to 6 mm and a moisture content of 38% to a twin-screw extruder kneading machine (SL185 model of Hebei Tianzheng Screening Pulping Equipment Co., Ltd., with a motor power of 110 kW) for kneading treatment, with a compression ratio of 1:3 and a kneading degree of 50% to obtain kneaded bamboo chips;

[0029] 2) Add the kneaded bamboo chips into a rotary multi-tank cooking pot, add sodium hydroxide, sodium sulfate and water, and then run it idle for 10 minutes, and then perform sulfate cooking. The mass ratio of the kneaded bamboo chips, sodium hydroxide and sodium sulfate is 14.9:1.3:1, the cooking liquid ratio is 1:4, and the sulfidation degree is 20%. The heating process of sulfate cooking is: first, the temperature is increased from room temperature to 110°C at a heating rate of 1.8°C / min, and the temperature is kept for 30 minutes, then the temperature is increased to 150°C at a heating rate of 2.0°C / min, and the temperature is kept for 20 minutes, and then the temperature is increased to 168°C at a heating rate of 1.0°C / min, and the temperature is kept for 90 minutes. During the entire sulfate cooking process, the pressure in the rotary multi-tank cooking pot is maintained at ≤0.8MPa, and then washing (the residual alkali concentration of the black liquor is 11.2g / L) and extrusion dehydration are performed, and then screening is performed using a flat screen with a screen gap width of 0.15mm to obtain pulp.

[0030] According to the test, the pulp yield in this embodiment is 41% and the Kappa number is 11.5.

[0031] Embodiment 3:

[0032] A method for preparing pulp from bamboo chips, comprising the following steps:

[0033] 1) adding wet bamboo chips with a length of 15 mm to 42 mm, a thickness of 3 mm to 6 mm and a moisture content of 38% to a twin-screw extruder kneading machine (SL185 type, Hebei Tianzheng Screening Pulping Equipment Co., Ltd., with a motor power of 110 kW) for kneading treatment, with a compression ratio of 1:4 and a kneading degree of 70% to obtain kneaded bamboo chips;

[0034] 2) Add the kneaded bamboo chips into a rotary multi-tank cooking pot, add sodium hydroxide, sodium sulfate and water, and then run it idle for 10 minutes, and then perform sulfate cooking. The mass ratio of the kneaded bamboo chips, sodium hydroxide and sodium sulfate is 15.5:1.3:1, the cooking liquid ratio is 1:4, and the sulfidation degree is 20%. The heating process of sulfate cooking is: first, the temperature is increased from room temperature to 110°C at a heating rate of 1.8°C / min, and the temperature is kept for 30 minutes, then the temperature is increased to 150°C at a heating rate of 2.0°C / min, and the temperature is kept for 20 minutes, and then the temperature is increased to 168°C at a heating rate of 1.0°C / min, and the temperature is kept for 90 minutes. During the entire sulfate cooking process, the pressure in the rotary multi-tank cooking pot is maintained at ≤0.8MPa, and then washing (the residual alkali concentration of the black liquor is 11.5g / L) and extrusion dehydration are performed, and then screening is performed using a flat screen with a screen gap width of 0.15mm to obtain pulp.

[0035] According to the test, the pulp yield in this embodiment is 42% and the Kappa number is 10.7.

[0036] Embodiment 4:

[0037] A method for preparing pulp from bamboo chips, comprising the following steps:

[0038] 1) adding wet bamboo chips with a length of 15 mm to 42 mm, a thickness of 3 mm to 6 mm and a moisture content of 38% to a twin-screw extruder kneading machine (SL185 model of Hebei Tianzheng Screening Pulping Equipment Co., Ltd., with a motor power of 110 kW) for kneading treatment, with a compression ratio of 1:5 and a kneading degree of 90% to obtain kneaded bamboo chips;

[0039] 2) Add the kneaded bamboo chips into a rotary multi-tank cooking pot, add sodium hydroxide, sodium sulfate and water, and then run it idle for 10 minutes, and then perform sulfate cooking. The mass ratio of the kneaded bamboo chips, sodium hydroxide and sodium sulfate is 16.1:1.3:1, the cooking liquid ratio is 1:4, and the sulfidation degree is 20%. The heating process of sulfate cooking is: first, the temperature is increased from room temperature to 110°C at a heating rate of 1.8°C / min, and the temperature is kept for 30 minutes, then the temperature is increased to 150°C at a heating rate of 2.0°C / min, and the temperature is kept for 20 minutes, and then the temperature is increased to 168°C at a heating rate of 1.0°C / min, and the temperature is kept for 90 minutes. During the entire sulfate cooking process, the pressure in the rotary multi-tank cooking pot is maintained at ≤0.8MPa, and then washing (the residual alkali concentration of the black liquor is 11.9g / L) and extrusion dehydration are performed, and then screening is performed using a flat screen with a screen gap width of 0.15mm to obtain pulp.

[0040] According to the test, the pulp yield in this embodiment is 44% and the Kappa number is 9.6.

[0041] Comparative Example:

[0042] A method for preparing pulp from bamboo chips, comprising the following steps:

[0043] Wet bamboo chips with a length of 15 mm to 42 mm, a thickness of 3 mm to 6 mm and a moisture content of 38% were added to a rotary multi-tank cooking pot, and then sodium hydroxide, sodium sulfate and water were added and the pot was idling for 10 minutes, and then sulfate cooking was performed. The mass ratio of wet bamboo chips, sodium hydroxide and sodium sulfate was 11.5:1.3:1, the cooking liquid ratio was 1:4, and the sulfidation degree was 20%. The heating process of sulfate cooking was as follows: first, the temperature was raised from room temperature to 11 at a heating rate of 1.8°C / min. The temperature was set at 0℃, kept warm for 30min, then heated to 150℃ at a heating rate of 2.0℃ / min, kept warm for 20min, then heated to 168℃ at a heating rate of 1.0℃ / min, kept warm for 90min. During the whole kraft cooking process, the pressure in the rotary multi-tank cooking pot was kept ≤0.8MPa, and then washed (the residual alkali concentration of the black liquor was 10.9g / L) and squeezed for dehydration, and then screened with a flat screen with a screen gap width of 0.15mm to obtain pulp.

[0044] According to the test, the pulp yield in this embodiment is 36% and the Kappa number is 15.6.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing pulp from bamboo chips, characterized in that: Here are the steps: 1) adding bamboo chips into a twin-screw extruder kneading machine for kneading to obtain kneaded bamboo chips; 2) Add the kneaded bamboo chips into a rotary multi-tank cooking pot, add sodium hydroxide, sodium sulfate and water, and then perform kraft cooking, followed by washing, squeezing dehydration and flat screen screening to obtain pulp; Step 1) the bamboo chips are wet bamboo chips with a moisture content of 35% to 45%; Step 1) The compression ratio of the kneading process in the machine is one of 1:2, 1:3, 1:4, and 1:5; Step 1) The degree of rubbing treatment is 30% to 90%; Step 2) The mass ratio of the kneaded bamboo pieces, sodium hydroxide and sodium sulfate is 12-17:1.2-1.4:1; Step 2) The cooking liquor ratio of the kraft cooking is 1:3-5 and the sulfidation degree is 15%-25%; Step 2) The heating process of the kraft cooking is as follows: firstly, the temperature is raised from room temperature to 100°C to 120°C at a heating rate of 1.5°C / min to 2.5°C / min, and the temperature is kept at that temperature for 25min to 35min; then, the temperature is raised to 140°C to 160°C at a heating rate of 1.5°C / min to 2.5°C / min, and the temperature is kept at that temperature for 15min to 25min; then, the temperature is raised to 165°C to 170°C at a heating rate of 0.5°C / min to 1.5°C / min, and the temperature is kept at that temperature for 80min to 100min; Step 2) The kraft cooking is carried out under the condition that the pressure in the rotary multi-tank cooking pot is ≤ 0.8 MPa.

2. The method according to claim 1, characterized in that: Step 1) The length of the bamboo piece is 15 mm to 42 mm, and the thickness is 3 mm to 6 mm.

3. The method according to claim 1, characterized in that: Step 2) The residual alkali concentration of the black liquor produced by the kraft cooking is 10.5 g / L to 12.0 g / L.

4. The method according to claim 1, characterized in that: Step 2) The sieve slot width of the flat sieve is 0.1 mm to 0.2 mm.