Pulping and cooking system

Abstract

This invention relates to the field of pulping and cooking, and discloses a pulping and cooking system, including a cooking pot, a pumping unit, and a receiving tank. The receiving tank includes a white liquor tank, a warm black liquor tank, and a hot black liquor tank. The white liquor tank contains white liquor, the warm black liquor tank contains warm black liquor, and the hot black liquor tank contains hot black liquor. The cooking pot is connected to the white liquor tank, the warm black liquor tank, and the hot black liquor tank, respectively, to reduce cooking time and increase pulp yield.

Description

Technical Field

[0001] This invention relates to the field of pulping and cooking, and more specifically to pulping and cooking systems. Background Technology

[0002] The papermaking process mainly includes pulping, washing and screening, bleaching, and papermaking. Among them, the pulping process mainly involves cooking the cooking materials together with white liquor containing sodium hydroxide and sodium sulfide. The cooking materials are cooked to remove lignin, thus becoming pulp. The white liquor is cooked to obtain black liquor, which has a lower alkali concentration than the white liquor. In the subsequent washing and screening process, the water remaining after washing and screening is the washing liquor.

[0003] The cooking material can be either wood or bamboo. However, existing pulping methods generally follow the wood pulping process. In fact, bamboo pulping and wood pulping have many fundamental differences. Bamboo has a much lower chemical structure uniformity than wood, a lower lignin content, and a much higher hemicellulose content. In addition, bamboo has a dense structure and a waxy layer on its surface, making it difficult for cooking liquor from traditional wood processing to penetrate. Bamboo pulp produced directly using the wood pulp replacement cooking process suffers from long cooking times and low pulp yield. Summary of the Invention

[0004] The present invention aims to provide a pulping and cooking system to reduce cooking time and increase pulp yield.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a pulping and cooking system, including a cooking pot, a pumping unit, and a receiving tank, the receiving tank including a white liquor tank, a warm black liquor tank, and a hot black liquor tank, the white liquor tank containing white liquor, the warm black liquor tank containing warm black liquor, and the hot black liquor tank containing hot black liquor, the cooking pot being connected to the white liquor tank, the warm black liquor tank, and the hot black liquor tank respectively; the cooking pot is connected to the white liquor tank, the warm black liquor tank, and the hot black liquor tank, the cooking pot is equipped with a heating and heat preservation unit, and the cooking pot is divided into a first cooking pot and a second cooking pot according to the cooking stages;

[0006] The first cooking pot can pre-soak bamboo strips, replace warm black liquor with hot black liquor, and replace part of the hot black liquor with white liquor; the second cooking pot can cook bamboo strips, and the heating and heat preservation unit can heat the second cooking pot to 140-154℃; the second cooking pot can turn black liquor into washing liquor, and according to the temperature of the replaced black liquor, the pumping unit can discharge hot black liquor into the hot black liquor tank and warm black liquor into the warm black liquor tank.

[0007] The beneficial effects of this plan are:

[0008] 1. Due to the dense structure of bamboo strips, after loading the bamboo strips into the first cooking pot, they are pre-soaked in warm black liquor. This ensures full contact between the bamboo strips and the liquor, allowing it to penetrate the interior and opening up channels for heat transfer. This results in faster heating in later stages, less steam usage, and a higher pulp yield. (Based on a cooking pot of 400m³...) 3 It is calculated that 15 batches of pulp can be produced per day.

[0009] 2. Compared to gradually heating the first cooking pot, in this scheme, the first cooking pot directly replaces the warm black liquor with hot black liquor, resulting in a faster temperature increase. The temperature difference at the contact point between the hot and warm black liquor is the greatest, which removes the wax layer on the surface of the bamboo strips faster and more thoroughly. At the same time, the wax layer and the warm black liquor are also replaced together, completing the cleaning of impurities. Meanwhile, since some of the warm black liquor has penetrated into the bamboo strips during the pre-soaking process, the warm black liquor inside the bamboo strips cannot be immediately replaced. It can only be replaced by heat exchange, where the warm black liquor gradually heats up to become hot black liquor. This avoids the damage to the fibers inside the bamboo strips caused by the rapid temperature increase and improves the pulp yield.

[0010] 3. In the first cooking pot, some of the hot black liquor is replaced with white liquor to maintain the pH value.

[0011] 4. In the second cooking pot, the heating and heat preservation unit can heat the cooking pot to 140-150℃ and maintain it for 1 hour. According to the temperature of the displaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank and the warm black liquor into the warm black liquor tank.

[0012] 5. Compared to washing the bamboo strips with washing liquor after they come out of the second digester, in this method, the washing liquor is directly replaced with washing liquor in the second digester. The bamboo strips are cleaned using the high temperature remaining in the second digester. At high temperatures, the adhesion of impurities is lower, and the bamboo strips are easier to wash clean. At the same time, directly replacing the black liquor with washing liquor can quickly stop the reaction between the black liquor and the bamboo strips, preventing excessive reaction that would result in a low pulp yield.

[0013] 6. Based on the temperature of the black liquor displaced from the second digester, the hot black liquor is discharged into the hot black liquor tank and the warm black liquor is discharged into the warm black liquor tank. The alkali and temperature in the black liquor are recovered and utilized, saving energy and protecting the environment, and improving production efficiency. At the same time, the black liquor is discharged into different tanks according to the temperature to form a temperature gradient for use in the next batch of the first digester.

[0014] Preferably, as an improvement, the first cooking pot uses a mixed liquor to pre-soak the bamboo strips. The mixed liquor includes white liquor and warm black liquor, and the ratio of white liquor to warm black liquor allows the pH value of the mixed liquor to be maintained at a stable value. Soaking the bamboo strips with a mixed liquor at a stable value can prevent fiber precipitation in the bamboo strips. This setting prevents fiber precipitation and improves the pulp yield.

[0015] Preferably, as an improvement, the pumping unit pumps the warm black liquor displaced from the first digester to a warm black liquor tank. This configuration allows the warm black liquor to be reused in the next first digester, recovering and utilizing the alkali and temperature within the warm black liquor, thus saving energy, protecting the environment, and improving production efficiency.

[0016] Preferably, as an improvement, the heating and insulation unit includes steam, a circulation pipe, and a heater on the circulation pipe. The circulation pipe is connected to the cooking pot, and high-pressure steam circulates between the circulation pipe and the cooking pot. With this configuration, steam is introduced into the circulation pipe, the heater heats the steam, and the heated steam returns to the cooking pot to increase its temperature.

[0017] Preferably, as an improvement, a heat exchanger is also included. The excess hot black liquor displaced by the white liquor and the second cooking pot flows into the heat exchanger, where it exchanges heat with the white liquor to become warm black liquor. This arrangement recovers the heat energy from the hot black liquor, saving energy and protecting the environment, while reducing the heating cost of the white liquor.

[0018] Preferably, as an improvement, after the first digester replaces the warm black liquor with hot black liquor, it can also replace a portion of the hot black liquor with white liquor. With this setup, alkali, the main substance reacting with bamboo chips, is present. The alkali concentration of the white liquor is much higher than that of the hot black liquor. Compared to directly replacing the warm black liquor with a mixture of white and hot black liquor, in this scheme, the first digester first replaces the warm black liquor with hot black liquor, and then replaces a portion of the hot black liquor with white liquor. The white liquor and the replaced portion of the hot black liquor do not come into contact, eliminating concerns about the white liquor diffusing into the hot black liquor and causing waste due to the hot black liquor being replaced out of the first digester. This ensures the alkali concentration during the next heating and cooking step, improves delignification efficiency, and ultimately increases pulping efficiency.

[0019] Preferably, as an improvement, it also includes an alkali recovery system, which converts excess black liquor displaced from the second digester into white liquor through a causticizing reaction. With this setup, some alkali remains in the black liquor, which is then converted into white liquor through the causticizing reaction.

[0020] Preferably, as an improvement, when cooking bamboo strips in the second cooking pot, the heating and heat preservation unit heats the second cooking pot to 140°C. With this setting, the lower the temperature, the more fiber is obtained in the bamboo strips, and the higher the pulp yield. Experiments have shown that under the pressure inside the cooking pot, after the hot black liquor replaces the warm black liquor, the temperature inside the cooking pot is around 140°C. Compared to cooking at 150°C, maintaining a temperature of 140°C results in a higher pulp yield and greater economic benefits. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of Example 1;

[0022] Figure 2 This is a flowchart of Example 1. Detailed Implementation

[0023] The following detailed description illustrates the specific implementation method:

[0024] The reference numerals in the accompanying drawings include: 1. Cooking pot; 2. Heat exchanger; 3. Warm black liquor tank; 4. Hot black liquor tank; 5. Washing liquor tank; 6. Cold white liquor tank; 7. Hot white liquor tank; 8. Water pump; 9. Pumping valve; 10. Alkali recovery system.

[0025] Example 1

[0026] Example 1 is basically as follows Figure 1 The pulping and cooking system includes a cooking pot 1, a pumping unit, a heat exchanger 2, a receiving tank, and an alkali recovery system 10. The receiving tank has heat insulation function, and the side walls of the receiving tank are equipped with insulation cotton. The receiving tank includes a white liquor tank, a black liquor tank, and a washing liquor tank 5. The white liquor tank includes a cold white liquor tank 6 and a hot white liquor tank 7. The cold white liquor tank 6 contains cold white liquor, and the hot white liquor tank 7 contains hot white liquor. The black liquor tank includes a warm black liquor tank 3 and a hot black liquor tank 4. The warm black liquor tank 3 contains warm black liquor, and the hot black liquor tank 4 contains hot black liquor. The washing liquor tank 5 contains washing liquor. The cooking pot 1 is equipped with a cooking inlet pipe at the upper end and a washing inlet pipe at the lower end. It has a grate and a cooking liquid outlet pipe. All liquids must pass through the grate for filtration before entering the cooking liquid inlet pipe. The cooking liquid inlet pipe is connected to the cold white liquor tank 6, the hot white liquor tank 7, the warm black liquor tank 3, the hot black liquor tank 4, and the washing liquor tank 5. The cooking liquid outlet pipe is connected to the warm black liquor tank 3 and the hot black liquor tank 4. The heat exchanger 2 is equipped with a first heat exchange tube and a second heat exchange tube that can perform heat exchange. The first heat exchange tube is connected to the hot black liquor tank 4, the heat exchanger 2, and the warm black liquor tank 3 in sequence. The second heat exchange tube is connected to the alkali recovery system 10, the heat exchanger 2, and the hot white liquor tank 7 in sequence. The cold white liquor tank 6 is directly connected to the alkali recovery system 10.

[0027] The temperature of the hot black liquor is 80℃-90℃, and the temperatures of the warm black liquor tank 3 and the hot white liquor are both 50℃-55℃. The cooking pot 1 is equipped with a heating and heat preservation unit, which includes steam, a circulation pipe, and a heater on the circulation pipe. The circulation pipe is connected to the cooking pot 1, and high-pressure steam circulates between the circulation pipe and the cooking pot 1. The cooking pot 1 is divided into a first cooking pot and a second cooking pot according to the cooking stage. In this embodiment, the first and second cooking pots use the same cooking pot 1. The first cooking pot 1 can pre-soak bamboo strips in a mixed liquor, which includes cold white liquor and warm black liquor. The ratio of cold white liquor to warm black liquor can maintain the pH value of the mixed liquor at a stable value. Soaking bamboo strips in a mixed liquor at a stable value can prevent fiber precipitation in the bamboo strips. The first cooking pot 1 can replace warm black liquor with hot black liquor and can also replace part of the hot black liquor with hot white liquor.

[0028] The second cooking pot 1 can cook bamboo strips, and the heating and heat preservation unit can heat the second cooking pot 1 to 150℃-154℃; the second cooking pot 1 can turn black liquor into washing liquor, and according to the temperature of the displaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank 4 and discharge the warm black liquor into the warm black liquor tank 3.

[0029] Steam cooker 1 has a volume of 400m³ 3 A vertical cooker with a height of 10-20m is provided. The cooker 1 is equipped with a valve on the top of the cooker. The pumping unit includes several pumping pipes, water pumps 8 and valves. In this embodiment, the pumping of liquid is completed by controlling the opening and closing of water pumps 8 and valves through the pumping unit. The cooking liquid inlet pipe, cooking liquid outlet pipe, first heat exchange pipe and second heat exchange pipe are all pumping pipes. In this embodiment, the liquid is replaced by pumping the liquid into the cooker 1 from the cooking liquid inlet pipe and pumping the liquid out of the cooker 1 from the cooking liquid outlet pipe.

[0030] Flowchart as follows Figure 2 As shown, the specific implementation steps are as follows:

[0031] 1. Loading into the pot: Place the bamboo strips from the bamboo and wood yard into the steaming pot 1, and distribute the bamboo strips evenly in the steaming pot 1.

[0032] 2. Warm charging and pre-soaking in warm black liquor: Pump warm black liquor into the cooking pot 1, close the valve on top of the pot, and continue pumping warm black liquor until the pressure inside the pot reaches the specified pressure value, which is the optimal pressure value that cooking pot 1 can withstand. When fresh bamboo strips come into contact with the warm black liquor, the residual alkali is quickly consumed. Therefore, a portion of cold white liquor needs to be added to maintain a certain pH value to prevent fiber precipitation in the bamboo strips. Simultaneously, low-pressure steam is introduced into the circulation pipe and heated by a heater.

[0033] 3. Hot charging: First, the warm black liquor in the cooking pot 1 is replaced with hot black liquor. The replaced warm black liquor enters the warm black liquor tank 3 through the grate. Then, part of the hot black liquor in the cooking pot 1 is replaced with hot white liquor.

[0034] 4. Heating and maintaining temperature: While replacing the liquid in steps 2-3, the low-pressure steam in the cooking pot 1 has been heated to medium-pressure steam, and the temperature inside the cooking pot 1 has reached about 140°C. Continue to raise the temperature by 10-15°C so that the temperature inside the cooking pot 1 reaches 150°C-154°C. In this embodiment, it is more appropriate to reach 150°C. Maintain the temperature at 150°C for 1 hour, and control the pressure inside the pot at 0.5 MPa.

[0035] 5. Replacement: Open the valve on the top of the pot to release the pressure, and the temperature inside the cooking pot 1 drops to 100°C. Replace the black liquor in the cooking pot 1 with washing liquor. Pump the hot black liquor with a higher temperature that was replaced in the early stage to the hot black liquor tank 4. Pump the warm black liquor with a lower temperature that was replaced in the later stage to the warm black liquor tank 3. Pump the excess warm black liquor to the alkali recovery system 10. The alkali recovery system 10 converts the black liquor into white liquor through a causticization reaction. A portion of the white liquor and the hot black liquor exchange heat in the heat exchanger 2 and then enter the hot white liquor tank 7. The remaining white liquor enters the cold white liquor tank 6. The hot black liquor that has undergone heat exchange becomes warm black liquor and enters the warm black liquor tank 3.

[0036] 6. Placing in the pot: The slurry formed from the softened bamboo strips is pumped into the spraying pot for the next process.

[0037] Example 2

[0038] The difference between Example 2 and Example 1 is that in step 4, the heater no longer raises the temperature inside the cooking pot, but maintains the temperature at 140°C for cooking, and the cooking time is increased by 10%.

[0039] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing bamboo pulp using a pulping and cooking system, characterized in that: The system includes a cooking pot, a pumping unit, and a receiving tank. The receiving tank includes a white liquor tank, a warm black liquor tank, and a hot black liquor tank. The white liquor tank contains white liquor, the warm black liquor tank contains warm black liquor, and the hot black liquor tank contains hot black liquor. The cooking pot is connected to the white liquor tank, the warm black liquor tank, and the hot black liquor tank. The cooking pot is equipped with a heating and heat preservation unit. The cooking pot is divided into a first cooking pot and a second cooking pot according to the cooking stages. The first cooking pot can pre-soak bamboo strips, and the second cooking pot can cook the bamboo strips. Includes the following steps: Step 1, Loading the pot: Place the bamboo strips from the bamboo and wood yard into the steaming pot, and distribute the bamboo strips evenly in the steaming pot; Step 2, Warm charging and pre-soaking in warm black liquor: Pump the warm black liquor into the cooking pot, close the valve on the top of the pot, and continue pumping the warm black liquor until the pressure inside the pot reaches the specified pressure value, which is the optimal pressure value that the cooking pot can withstand; when fresh bamboo strips come into contact with the warm black liquor, the residual alkali is quickly consumed; therefore, a portion of cold white liquor needs to be added to maintain a certain pH value to prevent fiber precipitation in the bamboo strips. At the same time, low-pressure steam is introduced into the circulation pipe and heated by a heater. Step 3, Hot charging: First, replace the warm black liquor in the cooking pot with hot black liquor. The replaced warm black liquor enters the warm black liquor tank through the grate. Then, replace part of the hot black liquor in the cooking pot with hot white liquor. The temperature of the hot black liquor is 80℃-90℃, and the temperature of the warm black liquor tank and the temperature of the hot white liquor are both 50℃-55℃. Step 4, Heating and Maintaining Temperature: While the liquid is being replaced in Steps 2-3, the low-pressure steam in the cooking pot has been heated to medium-pressure steam, and the temperature inside the cooking pot has reached about 140℃. The temperature is maintained at 140℃ for cooking, and the cooking time is 66 minutes. The pressure inside the pot is controlled at 0.5 MPa. Step 5, Replacement: Open the valve on the top of the pot to release the pressure, and the temperature inside the cooking pot drops to 100°. Replace the black liquor in the cooking pot with washing liquor. Pump the hot black liquor with a higher temperature that was replaced in the early stage to the hot black liquor tank. Pump the warm black liquor with a lower temperature that was replaced in the later stage to the warm black liquor tank. Pump the excess warm black liquor to the alkali recovery system. The alkali recovery system converts the black liquor into white liquor through a causticization reaction. A portion of the white liquor and the hot black liquor exchange heat in the heat exchanger and then enter the hot white liquor tank. The remaining white liquor enters the cold white liquor tank. The hot black liquor that has undergone heat exchange becomes warm black liquor and enters the warm black liquor tank. Step 6, Placing in the pot: Pump the slurry formed from the softened bamboo strips into the spraying pot, and proceed to the next process.

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