Digester and cooking pulping process based thereon

Abstract

The present application relates to a digester and a cooking pulping process based on the same, belonging to the field of bamboo pulp papermaking, comprising a tank body, the tank body having a feeding port and a discharging port, characterized in that the discharging port comprises a bottom discharging port opened in the bottom of the tank body and a liquid discharge port opened in the upper side of the tank body and located above the bottom discharging port, the bottom discharging port is connected with a conveyor, the liquid discharge port is connected to the feeding port through a circulating system outside the tank, the circulating system comprises a circulating pump, the input end of the circulating pump is connected with the liquid discharge port through a pipeline, and the output end of the circulating pump is connected with the feeding port through a pipeline; the bamboo chip is aged by using the above-mentioned digester, and the problems of high equipment cost, low yield of pulping method, high energy consumption, high manufacturing cost and low finished product index in the prior art are solved, and the original strength of the fiber is preserved to the maximum extent.

Description

Technical Field

[0001] This invention relates to the field of bamboo pulp papermaking, and more specifically to a digester for pulping and a pulping process based thereon. Background Technology

[0002] Currently, over 90% of the world's total pulp production is made from wood, with the remainder primarily using the stalks of various gramineous plants such as rice straw, wheat straw, bamboo, reeds, sugarcane bagasse, as well as cotton and hemp as pulping raw materials. Developed countries in Europe and America have widely adopted unbleached paper since the 1990s, rarely using bleached white paper. With my country's economic development and rising living standards, the consumption of timber and wood products is substantial, with China ranking second globally in consumption of engineered wood products, pulp, paper, and paperboard. my country's annual timber production is less than 100 million cubic meters, while commercial timber consumption reaches 150 million cubic meters annually, resulting in a severe timber resource deficit. Existing timber reserves are far from meeting demand and will continue to be a long-term problem. Currently, the raw material for papermaking, wood pulp, relies on imports, and the self-sufficiency rate of domestically produced finished wood pulp is low, leading to high manufacturing costs. Wood chip raw materials are relatively scarce, resulting in low yields and small production capacity that cannot meet the demands of papermaking.

[0003] Bamboo pulp production is a promising industry, as bamboo has immense recycling value. Planting bamboo once yields benefits for a century. Once a bamboo forest matures, it can be harvested in about three years, and can be harvested annually while preserving at least 10 bamboo stalks, ensuring other ecological benefits remain unaffected. Large, clumping bamboo in southern regions can form forests in 2-3 years and reach maturity in 3-4 years. Planting bamboo on a barren mountain can transform it into an oasis within a year.

[0004] Currently, bamboo pulping technology is relatively mature. Generally, the raw bamboo chips are first steamed and matured to dissolve the lignin. The matured bamboo then undergoes processes such as shredding, pulping, grinding, and rinsing. Existing bamboo pulping processes typically involve mixing bamboo chips with an alkaline solution of 15-18% by mass at a solid-liquid ratio of 1:5. The bamboo chips are then immersed in the alkaline solution and subjected to high-temperature (≥150℃) and high-pressure steaming. This process suffers from low yield, high manufacturing costs, and a narrow range of applications. After maturation, the soaked bamboo is vented under pressure from the bottom of the pot to a venting pot for recovery. This process involves not only high temperature and pressure but also a large amount of alkaline solution, posing significant safety hazards. Furthermore, during steaming, the steam comes into direct contact with the wood (bamboo) material, dissolving lignin while simultaneously damaging the fiber strength, resulting in low burst strength and low breaking strength of the finished pulp. The steamers used are high-temperature and high-pressure equipment, leading to high energy consumption and equipment costs. Most importantly, the pulp yield is low, generally only around 50%. Summary of the Invention

[0005] This invention addresses the aforementioned problems in the prior art by providing a cooker and a cooking and pulping process based thereon, thereby solving the problems of high equipment cost, low pulping yield, high energy consumption, high manufacturing cost, and low finished product quality in the prior art. Moreover, it preserves the original strength of the fiber to the greatest extent, making the product more widely applicable and suitable for the production of food containers, toilet paper, high-grade packaging paper products, etc.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] On one hand, the present invention provides a cooking apparatus, including a tank having a feeding port and a discharging port. The discharging port is characterized in that it includes a bottom discharging port at the bottom of the tank and a drain port on the tank above the bottom discharging port. The bottom discharging port is connected to a conveyor, and the drain port is connected to the feeding port through an external circulation system. The circulation system includes a circulation pump, the input end of which is connected to the drain port through a pipeline, and the output end of which is connected to the feeding port through a pipeline.

[0008] The cooking appliance is an atmospheric pressure device.

[0009] Furthermore, the pipeline is also equipped with a circulation tank and a heat exchanger.

[0010] Furthermore, the tank is a vertical tank with a tapered lower part, and the bottom outlet is located at the bottom of the tapered section.

[0011] Furthermore, a sieve plate is provided on the inner wall of the tank at the position corresponding to the drain port, and the shape of the sieve plate is consistent with the shape of the inner wall of the tank.

[0012] Furthermore, the sieve plate is a conical sieve plate that runs vertically through the top and bottom.

[0013] Furthermore, at least one set of air cannons is provided on the outer wall of the tank and on the upper side of the bottom discharge port. Each set of air cannons includes a preset number of air cannons arranged along the circumference of the tank, and the output end of the air cannons extends into the tank.

[0014] Furthermore, the conveyor is a screw conveyor.

[0015] On the other hand, the present invention provides a cooking and pulping process, characterized in that the above-mentioned cooking device is used to mature bamboo strips. The bamboo strip maturation process is as follows: bamboo strips and alkali solution are put into the tank at a preset solid-liquid ratio, the circulation system is turned on, so that the alkali solution flowing out of the tank enters the tank again through the circulation system to realize the circulation of alkali solution, and the temperature is kept to mature the bamboo strip material.

[0016] Furthermore, the cured bamboo strips are discharged through the bottom outlet by the conveyor. When the bamboo strips are discharged, air cannons are activated in sequence to send the bamboo strips from the tank into the bottom conveyor.

[0017] Furthermore, the solid-liquid ratio, i.e., the mass ratio of bamboo strips to alkaline solution, is controlled at 1:0.6-0.65. The alkaline solution is a sodium hydroxide solution, and the temperature of the alkaline solution is controlled to be no lower than 85°C and no higher than 95°C during the circulation process. The sodium hydroxide solution is preferably a 10-11% sodium hydroxide solution.

[0018] The beneficial effects of this invention are:

[0019] 1. This invention uses a self-made cooker, which is equipped with a bottom discharge port and a liquid discharge port, and uses an external circulation system to circulate the liquid inside and outside the tank, making it possible to achieve high solid-liquid ratio process conditions inside the tank.

[0020] 2. The present invention further enables the solid material in the tank to be quickly discharged through the bottom outlet after the liquid material is discharged by means of an air cannon.

[0021] 3. This invention further utilizes the aforementioned cooking equipment in conjunction with a specific cooking and pulping process for bamboo pulping. This enables flexible cooking and pulping using a low-temperature cold fermentation method with relatively low temperatures (85-95℃) and a high solid-liquid ratio. The process conditions are mild, significantly improving pulp yield compared to existing technologies. It also reduces energy consumption and water consumption, saving water resources. Furthermore, the resulting bamboo pulp product exhibits minimal fiber loss, maximizing the preservation of the original fiber strength. This facilitates the application of bamboo fiber products in other fields, such as food containers, toilet paper, and high-grade packaging paper production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of a cooking appliance according to an embodiment of the present invention;

[0023] Figure 2 This is a three-dimensional structural diagram of a tank according to an embodiment of the present invention.

[0024] Figure 3 This is a three-dimensional structural schematic diagram of a sieve plate according to an embodiment of the present invention;

[0025] Figure 4 This is a scanning electron microscope image of the cooked bamboo strips obtained using a cooking apparatus according to an embodiment of the present invention.

[0026] In the diagram: 1. Tank body, 2. Feeding port, 3. Discharge port, 31. Bottom discharge port, 32. Drain port, 4. Conveyor, 5. Circulation system, 51. Circulation pump, 52. Pipeline, 53. Circulation tank, 54. Heat exchanger, 6. Screen plate, 61. Filter hole, 7. Air cannon, 8. Column. Detailed Implementation

[0027] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] like Figures 1-3 As shown, the cooking apparatus in this embodiment is an atmospheric pressure device, which includes a tank 1 equipped with an internal circulation heating system. The tank 1 has a feeding port 2 and a discharging port 3, which are located at the top and bottom of the tank, respectively. The discharging port 3 includes a bottom discharging port 31 and a drain port 32. The bottom discharging port 31, i.e., the bamboo chip outlet, is located at the bottom of the tank 1, and the drain port 32 is located on the side wall of the tank 1 and above the bottom discharging port 31. The bottom discharging port 31 is connected to a conveyor 4 for conveying solid materials such as cooked bamboo chips. In this embodiment, the conveyor 4 is a screw conveyor 4. The drain port 32 is connected to the feeding port 2 through an external circulation system 5 for forming a circulation of liquid materials inside and outside the tank.

[0030] In this embodiment, the tank 1 is a vertical tank, which facilitates increased contact with the bamboo strips during the circulation of the alkali solution. Its lower part is tapered to allow the material inside the tank to settle downwards. The bottom outlet 31 is located at the bottom of the tapered section for easy discharge of the material. Several columns 8 are connected to the bottom of the tank 1.

[0031] Specifically, in this embodiment, the main component is made of Q235 steel plate and processed into a tank with a diameter of 12 meters and a height of 29 meters. The bottom is cut with a 6-meter high taper.

[0032] The cooker in this embodiment is used for cooking and pulping bamboo strips, specifically for the maturation of the bamboo strips. During use, the raw bamboo strips and alkali solution are added to tank 1 at a solid-liquid ratio. The circulation system 5 is then activated, allowing the alkali solution flowing out of tank 1 to re-enter the tank through the circulation system 5, thus circulating the alkali solution, maintaining its temperature, and maturing the bamboo strips. A gate valve is installed at the bottom outlet 31. After all the alkali solution in the tank has been discharged, the gate valve is opened, and the maturated bamboo strips are discharged through the bottom outlet 31 by the conveyor 4 for subsequent pulping processes.

[0033] Specifically, washed bamboo strips are transported to the top of the tank via a conveyor belt and enter the tank through four feeding ports. Simultaneously, a diluted alkali solution (10% sodium hydroxide solution by mass) is injected into the tank via an alkali pump. When the alkali solution is more than half full, the internal circulation heating system is activated to heat the solution to meet process requirements. Once the bamboo is full and the alkali solution is injected at a solid-liquid ratio of 1:0.6, the constant temperature heating system continues heating to above 85°C but not exceeding 95°C. At the same time, the circulation system is activated to circulate the alkali solution back to feeding port 2 and maintain this temperature for 24 hours. After confirming the bamboo is properly cured, a bamboo sample is taken, and the alkali solution is discharged from the hopper and transferred to the next hopper for continued use until residual alkali is absorbed. After the alkali solution is emptied from the tank, the bottom discharge valve is opened, and air cannons are activated in different sequences to feed the bamboo strips from the hopper into the bottom screw conveyor. The conveyor then transports the bamboo strips to subsequent processing stages for further processing, producing high-quality finished bamboo pulp.

[0034] In another embodiment, the solid-liquid ratio of the added bamboo chips and alkali solution is controlled to be 1:0.65, and the temperature of the alkali solution is controlled to be no lower than 85°C and no higher than 95°C during the circulation process.

[0035] In this embodiment, a sieve plate 6 is provided on the inner wall of the tank 1 at the position corresponding to the drain port 32. The sieve plate has several filter holes 61 for filtering out solid materials when the liquid is discharged through the drain port 32. The shape of the sieve plate 6 is consistent with the inner wall of the tank 1. The sieve plate is placed inside the tank and fits snugly against the inner wall. This sieve plate effectively filters out bamboo chips inside the tank during the process of discharging the alkali solution into the circulation system. In this embodiment, the sieve plate 6 is a vertically continuous conical sieve plate, see... Figure 2 and Figure 3 As shown, this ensures a good fit with the inner wall of the tank, resulting in excellent filtration. At the same time, the sieve plate 6 does not affect the discharge of solid material through the bottom outlet 31.

[0036] In other embodiments, the circulation system 5 includes a circulation pump 51, which serves as the power source for the circulation of the alkali solution. Its input end is connected to the drain port 32 via a pipe 52, and its output end is connected to the feed port 2 via a pipe 52. This pump circulates the alkali solution discharged from the drain port to the feed port at the top of the tank, thus achieving alkali solution circulation. A circulation tank 53 and a heat exchanger 54 are also installed on the pipe 52 to control the temperature of the alkali solution circulating to the feed port.

[0037] In other embodiments, multiple sets of air cannons 7 are also provided on the outer wall of the tank body 1 and above the bottom discharge port 31. This embodiment has three sets of air cannons, see Figure 1As shown, the lowest layer of air cannons is located at the bottom of the tank, above the bottom discharge port; the middle layer of air cannons is located at the top of the lower cone of the tank; and the upper layer of air cannons is located in the lower middle part of the tank. Each group of air cannons 7 includes multiple air cannons 7 arranged circumferentially along the tank body. The air cannons 7 are installed on the outer wall of the tank and their output ends extend into the tank. Specifically, in this embodiment, three 100L air cannons are installed 1.3 meters above the cone discharge port, nine 170L air cannons are installed 1.3 meters below the cone apex, and six 300L air cannons are installed 4.5 meters above the bottom of the cylindrical surface, for a total of 18 air cannons. The function of the air cannons is to quickly and evenly discharge the cured bamboo strips in the tank through the bottom discharge port into the screw conveyor after the alkali solution is discharged, and then enter the subsequent processing steps through the screw conveyor. After the bamboo strips have matured and the alkali solution has been discharged, the air cannon 7 is activated to send the bamboo strips from the tank into the bottom conveyor 4, and then discharge the matured bamboo strips.

[0038] Comparative Example 1

[0039] This comparative example uses an existing vertical industrial high-pressure steamer, which uses high-temperature steam ≥150℃ and 18%~20% alkaline sodium hydroxide solution to mix with bamboo strips, with a solid-liquid ratio of 1:5, and steaming for 5 hours to mature the bamboo strip material.

[0040] The matured bamboo materials from Example 1 and Comparative Example 1 were subjected to conventional subsequent processes such as shredding, pulping, grinding, and rinsing to obtain slurry after slag removal and rinsing. The slurry after slag removal and rinsing was then dewatered into pulp boards by a double-mesh filter press, and then cut into pulp boards by a slitting machine, and finally packaged into finished bamboo pulp boards.

[0041] Table 1 shows a comparison of the performance of the steamer (flexible steamer) in Example 1 and the steamer (vertical steamer) in Comparative Example 1.

[0042] Table 1

[0043] Performance Comparison Table of New Steamer and Vertical Steamer

[0044]

[0045] As can be seen from the data in the table above, the pulping yields of bamboo pulp matured using the cookers and maturation processes of Example 1 and Comparative Example 1 were 50% and 70%, respectively. This demonstrates that the cooker and maturation process of this invention significantly improves pulping yield compared to existing technologies. Furthermore, the reaction conditions of this invention are milder, eliminating the need for high-pressure equipment; atmospheric pressure equipment suffices. The bamboo pulp produced by the low-temperature cold fermentation method (85-95℃ in this invention compared to ≥150℃ in existing technologies) not only consumes less energy and uses less alkali—compared to the 15-18% concentration of alkali solution required by existing technologies, this invention only requires approximately 10% concentration (the alkali usage in Table 1 represents the mass fraction of alkali used)—but also results in less fiber loss, maximizing the preservation of the original fiber strength and expanding its application range. The equipment and process are pollution-free, produce fewer dissolved substances, and require less clean water, with only 3 tons of water consumed per ton of pulp, significantly saving water resources.

[0046] A scanning electron microscope (SEM) image of the finished bamboo pulp board made from the fibers obtained using the cooking apparatus and bamboo curing process of Example 1 is shown below. Figure 4 Its performance indicators are shown in Table 2.

[0047] Table 2

[0048]

Claims

1. A cooking and pulping process, characterized in that, Bamboo strips are matured using a steamer, and the matured bamboo strips are then subjected to subsequent processes of shredding, pulping, grinding, and rinsing to obtain a pulp after slag removal and rinsing. The cooker is used for cooking bamboo strips with sodium hydroxide alkali solution to make pulp. The cooker is an atmospheric pressure device. The cooker includes a tank (1). The tank (1) is a vertical tank. The tank (1) has a feeding port (2) and a discharging port (3). The discharging port (3) includes a bottom discharging port (31) opened at the bottom of the tank (1) and a drain port (32) opened on the tank (1) and located on the upper side of the bottom discharging port (31). The bottom discharging port (31) is connected to a conveyor (4). The drain port (32) is connected to the feeding port (2) through a circulation system (5) outside the tank. The circulation system (5) includes a circulation pump (51). Its input end is connected to the drain port (32) through a pipeline (52). Its output end is connected to the feeding port (2) through a pipeline (52). The process of bamboo rinsing is as follows: bamboo rinsing and alkaline solution are put into tank (1) according to a preset solid-liquid ratio. The solid-liquid ratio, i.e. the mass ratio of bamboo rinsing and alkaline solution, is controlled at 1:0.6-0.

65. The alkaline solution is sodium hydroxide solution. The circulation system (5) is turned on so that the alkaline solution flowing out of tank (1) re-enters the tank through the circulation system (5) to realize the circulation of alkaline solution. During the circulation process, the temperature of alkaline solution is controlled to be no lower than 85℃ and no higher than 95℃. The temperature is kept warm to rinsing the bamboo rinsing.

2. The cooking and pulping process according to claim 1, characterized in that, The pipeline (52) is also equipped with a circulation tank (53) and a heat exchanger (54).

3. The cooking and pulping process according to claim 1, characterized in that, The tank (1) is a vertical tank with a tapered bottom and a bottom outlet (31) located at the bottom of the tapered bottom.

4. The cooking and pulping process according to claim 1 or 3, characterized in that, A sieve plate (6) is provided on the inner wall of the tank (1) at the position corresponding to the drain port (32), and the shape of the sieve plate (6) is consistent with the shape of the inner wall of the tank (1).

5. The cooking and pulping process according to claim 4, characterized in that, The sieve plate (6) is a conical sieve plate that runs vertically through the top and bottom.

6. The cooking and pulping process according to claim 1, characterized in that, At least one set of air cannons (7) is also provided on the outer wall of the tank (1) and on the upper side of the bottom discharge port (31). Each set of air cannons (7) includes a preset number of air cannons (7) arranged around the tank (1), and the output end of the air cannons (7) extends into the tank.

7. The cooking and pulping process according to claim 1, characterized in that, The conveyor (4) is a screw conveyor (4).

8. The cooking and pulping process according to claim 1, characterized in that, After the bamboo strips have matured, they are discharged from the bottom outlet (31) by the conveyor (4). When the bamboo strips are discharged, the air cannon (7) is activated in sequence to send the bamboo strips from the tank into the bottom conveyor (4).

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