Low cost environment-friendly papermaking pulping process

Abstract

This invention provides a low-cost and environmentally friendly papermaking pulping process, comprising the following steps: S1. Pretreatment of papermaking fiber plant raw materials. S2. Oxy-alkali cooking: The pretreated papermaking fiber plant raw materials are mixed with an aqueous sodium carbonate solution, and cooked for 0.5–5 hours using oxygen as an oxidant. Then, sodium hydroxide is added, and cooking continues for 0.3–2 hours. Finally, the pulp and black liquor are separated by pressing. S3. Black liquor treatment: The black liquor is mixed with fiber waste, pressed, and burned as biomass fuel. S4. Recovery and causticization. This papermaking pulping process uses sodium carbonate and a small amount of sodium hydroxide for staged oxy-alkali pulping, and the generated black liquor is mixed with fiber waste and burned to recover sodium carbonate and heat, reducing the causticization rate and pulping costs.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a low-cost and environmentally friendly papermaking pulping process. Background Technology

[0002] With increasing industrialization, industrial pollution has become increasingly serious, threatening human survival and the development of modern civilization. Paper mill wastewater is one of the major sources of industrial pollution, severely damaging the ecological environment. As people increasingly value environmental protection, the treatment of wastewater from the paper industry is also receiving more and more attention.

[0003] Black liquor is a waste liquid produced in the pulping stage of papermaking. It is dark black, viscous, has a foul odor, and is extremely difficult to treat. Its main components are lignin and carbohydrate degradation products, and it contains a significant amount of residual caustic soda. Its COD emissions account for 90% of the total pollutant emissions from the entire papermaking process. Currently, the main methods for treating black liquor from alkaline pulping and papermaking include: alkali recovery treatment, flocculation and sedimentation treatment, evaporation and concentration, and anaerobic biological treatment. Among these, alkali recovery technology is the most economical and effective method for treating papermaking black liquor. This method involves extracting papermaking black liquor containing organic solids, inorganic solids, and a small amount of residual caustic soda, concentrating it in an evaporator, and then burning it in a special boiler. The organic solids in the black liquor are converted into heat energy, and the sodium, residual caustic soda, and alkali-containing inorganic solids that combine with it are converted into sodium carbonate. The sodium carbonate reacts with slaked lime to produce caustic soda and white mud. The caustic soda is recovered and used for pulping, and the white mud is burned to produce lime. After digestion, it is used to produce caustic soda again. The caustic soda lost in the production process is replenished by adding conversion substances during the production process to achieve self-sufficiency.

[0004] In my country, alkali recovery technology has proven effective in addressing black liquor pollution from large-scale wood-based alkali pulping plants. However, it struggles to achieve ideal results in controlling black liquor pollution from numerous smaller pulp and paper mills that use grass fibers as raw materials. The black liquor discharged from grass fiber pulping contains low-calorific-value combustible organic compounds such as cellulose and hemicellulose, making heat balance difficult to achieve. During alkali conversion combustion, heavy oil or natural gas must be used continuously to supplement calorific value and aid combustion, increasing energy consumption and operating costs for alkali recovery. This is particularly problematic for small enterprises with a pulping capacity of less than 10,000 tons, where insufficient black liquor volume makes it difficult to maintain balance using traditional processes and small furnaces, hindering long-term continuous production. Furthermore, pulping typically uses caustic soda for delignification, requiring the caustic soda residue to be causticized into NaOH, which is then reused in cooking. Currently, there is no mature and reliable method for treating the calcium carbonate (white mud) produced during causticization, leaving it to be discarded or buried, causing secondary pollution and increasing recovery costs. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a low-cost and environmentally friendly papermaking pulping process. This process uses sodium carbonate and a small amount of sodium hydroxide for segmented oxygen-alkali pulping, and mixes the generated black liquor with fiber waste for combustion to recover sodium carbonate and heat, thereby reducing the causticization rate and pulping costs.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0007] S2. Oxy-alkali cooking: The pretreated papermaking fiber plant raw material is mixed with sodium carbonate aqueous solution and cooked for 0.5 to 5 hours with oxygen as oxidant. Then sodium hydroxide is added and cooking is continued for 0.3 to 2 hours. Finally, the pulp and black liquor are separated.

[0008] Preferably, in step S1, when the papermaking fiber is a wood fiber raw material, the specific pretreatment process of the papermaking fiber plant raw material is as follows: crush the papermaking fiber raw material, then soak it in water to absorb water and swell, and finally press and separate the fibers.

[0009] Preferably, the water absorption and swelling is achieved by soaking at 20–90°C for 0.5–10 hours.

[0010] Preferably, in step S2, the amount of sodium carbonate used is 10% to 50% and the amount of sodium hydroxide used is 1% to 5% based on the dry weight of the pretreated papermaking fiber plant raw material; by weight, the ratio of the pretreated papermaking fiber to the sodium carbonate aqueous solution is 1:2 to 10.

[0011] Preferably, in step S2, the cooking temperature is 100–180°C.

[0012] Preferably, in step S2, the black liquor is mixed with fiber waste and burned as biomass fuel to obtain a melt.

[0013] Preferably, the main component of the molten material after combustion is sodium carbonate, which is dissolved into an aqueous sodium carbonate solution. The sodium carbonate aqueous solution with a weight ratio of 1% to 20% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining aqueous sodium carbonate solution are then reused in step S2.

[0014] Preferably, the fiber waste is waste obtained from the pretreatment of papermaking fiber plant raw materials.

[0015] Preferably, the black liquor is mixed with fiber waste, extruded, and then conveyed to a combustion furnace for combustion, wherein the extrusion is performed by screw extrusion.

[0016] Preferably, the excess black liquor after extrusion is recovered and mixed with fiber waste.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: The low-cost and environmentally friendly papermaking pulping process of this invention uses sodium carbonate and a small amount of sodium hydroxide for segmented oxygen-alkali pulping, and mixes and burns the generated black liquor with fiber waste to recover sodium carbonate and heat, which greatly reduces the causticization rate or avoids the causticization process of alkali recovery (the loss of sodium in the process is all compensated by sodium hydroxide), thus reducing pulping costs.

[0018] This invention presents a low-cost, environmentally friendly papermaking pulping process that uses sodium carbonate and a small amount of sodium hydroxide for segmented oxygen-alkali pulping. First, inexpensive sodium carbonate, with its weak alkalinity and low cellulose-damaging effect, is used for oxygen-alkali removal of easily removable lignin. Only the remaining small amount of difficult-to-remove lignin is removed using a small amount of the corresponding, more expensive, strong alkali, sodium hydroxide, for oxygen-alkali delignin removal. Compared to sodium carbonate alone, this method improves the delignin removal effect and shortens the cooking time. Compared to sodium hydroxide alone, it reduces cellulose damage, increases pulp yield and fiber strength, and reduces or completely avoids the complex, costly, and environmentally polluting causticizing process in the later stages. Normally, 85% of sodium carbonate is causticized to NaOH, which is then recycled for cooking. Currently, there is no mature and reliable method for treating the calcium carbonate (white mud) produced during the causticizing reaction, causing secondary pollution. This application only requires causticizing 1% to 10% of the sodium carbonate in the later stages. Compared to directly mixing sodium carbonate and sodium hydroxide, this method improves efficiency. Treating with sodium carbonate first makes it difficult to remove lignin later, so a small amount of sodium hydroxide is then used for treatment, which can save energy and improve efficiency.

[0019] This invention provides a low-cost, environmentally friendly papermaking pulping process that mixes black liquor with fiber waste, compresses it, and then burns it as biomass fuel, thereby improving the recovery rate and reducing costs. The cellulose, hemicellulose, and other combustible organic matter contained in black liquor has a low calorific value, making it difficult to achieve heat balance during combustion. During alkali conversion combustion, heavy oil or natural gas must be used for extended periods to supplement the calorific value and assist combustion, thus increasing the energy consumption and operating costs of alkali recovery. This application mixes black liquor with raw material fibrous plant waste and then burns it, which not only improves waste utilization but also reduces the use of heavy oil, further lowering costs.

[0020] The low-cost and environmentally friendly papermaking pulping process of this invention improves the delignification effect and shortens the time when the fibrous plant is wood chip. When the fibrous plant is wood chip, the delignification is incomplete. The fibrous plant is first crushed, then soaked in water to absorb water and swell, then pressed and separated into fibers, and then subjected to oxygen-alkali cooking for delignification. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Example

[0022] A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0023] Wheat straw is selected as the raw material. The wheat straw is crushed and impurities are removed, and then papermaking fibers and fiber waste are obtained. The fiber waste consists of straw leaves and straw residue obtained by removing impurities, crushing or sieving wheat straw.

[0024] S2. Oxy-alkali cooking: Papermaking fibers are mixed with sodium carbonate aqueous solution and cooked in an intermittent digester using oxygen as an oxidant. Steam is introduced into the digester and the pressure is increased to 0.3 MPa within 30 minutes. The steam supply is then cut off, and oxygen is introduced to the total pressure. Oxygen is continued to be introduced to maintain the total pressure in the digester at 2 MPa and the temperature is maintained for 2 hours. Then sodium hydroxide is added, and the temperature is maintained for another 1 hour. Finally, the pulp in the digester is sprayed out and the pulp and black liquor are separated by extrusion.

[0025] Based on the dry weight of the papermaking fiber, the amount of sodium carbonate is 20% and the amount of sodium hydroxide is 2%; by weight, the ratio of the papermaking fiber to the sodium carbonate aqueous solution is 1:4.

[0026] S3. Black liquor treatment: The black liquor is mixed with fiber waste, extruded, and then transported to an alkali recovery furnace for combustion as biomass fuel to recover heat and molten material. The extrusion is performed using a screw extruder. Excess black liquor after extrusion is recovered and mixed with fiber waste again.

[0027] S4. Recycling and Causticization: The main component of the molten material after combustion is sodium carbonate, which is dissolved into a sodium carbonate aqueous solution. The sodium carbonate aqueous solution with a volume ratio of 10% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining sodium carbonate aqueous solution are then reused in step S2. Example

[0028] A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0029] Cotton stalks are selected as raw material. The stalks are cleaned, crushed, and then sieved to obtain papermaking fibers and fiber waste. The fiber waste consists of residue obtained from the cleaning, crushing, and sieving of wheat straw.

[0030] S2. Oxy-alkali cooking: Papermaking fibers are mixed with sodium carbonate aqueous solution and cooked in a digester. Oxygen is used as the oxidant. Oxygen is introduced into the digester until the oxygen pressure reaches 1 MPa. The oxygen supply is then cut off, and the pulp and black liquor are added to the digester. The mixture is heated to 130°C within 30 minutes. Oxygen is introduced to maintain the pressure in the digester at 2 MPa. The temperature is maintained for 4 hours. Then sodium hydroxide is added, and the digestion is continued for another hour. Finally, the pulp and black liquor are separated by pressing.

[0031] Based on the dry weight of the papermaking fiber, the amount of sodium carbonate is 25% and the amount of sodium hydroxide is 2%; by weight, the ratio of the papermaking fiber to the sodium carbonate aqueous solution is 1:7.

[0032] S3. Black liquor treatment: The black liquor is mixed with fiber waste, extruded, and then transported to an alkali recovery furnace for combustion as biomass fuel to recover heat and molten material. The extrusion is performed using a vortex extrusion process. Excess black liquor after extrusion is recovered and mixed with fiber waste again.

[0033] S4. Recycling and Causticization: The main component of the molten material after combustion is sodium carbonate, which is dissolved into a sodium carbonate aqueous solution. The sodium carbonate aqueous solution with a volume ratio of 7% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining sodium carbonate aqueous solution are then reused in step S2. Example

[0034] A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0035] Cotton linters are selected as raw material. The cotton stalks are cleaned of impurities, crushed, and then sieved to obtain papermaking fibers and fiber waste. The fiber waste is the waste obtained from cleaning, crushing, and sieving cotton linters.

[0036] S2. Oxy-alkali cooking: Papermaking fibers are mixed with sodium carbonate aqueous solution and cooked in a digester with oxygen as the oxidant. Oxygen is introduced into the digester until the oxygen pressure reaches 1 MPa. The oxygen supply is then cut off, and the pulp and black liquor are added to the digester. The mixture is heated to 110°C within 30 minutes. Oxygen is introduced to maintain the pressure in the digester at 2 MPa. The mixture is kept at this temperature for 2 hours. Then sodium hydroxide is added, and the digestion is continued for another 0.5 hours. Finally, the pulp and black liquor are separated by pressing.

[0037] Based on the dry weight of the papermaking fiber, the amount of sodium carbonate is 15% and the amount of sodium hydroxide is 1%; by weight, the ratio of the papermaking fiber to the sodium carbonate aqueous solution is 1:10.

[0038] S3. Black liquor treatment: The black liquor is mixed with fiber waste, extruded, and then transported to an alkali recovery furnace for combustion as biomass fuel to recover heat and molten material. The extrusion is performed using a vortex extrusion process. Excess black liquor after extrusion is recovered and mixed with fiber waste again.

[0039] S4. Recycling and Causticization: The main component of the molten material after combustion is sodium carbonate, which is dissolved into a sodium carbonate aqueous solution. The sodium carbonate aqueous solution with a volume ratio of 7% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining sodium carbonate aqueous solution are then reused in step S2. Example

[0040] A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0041] Larch, a coniferous tree, was selected as the raw material. The larch wood chips were cleaned of impurities, crushed, and sieved. They were then soaked in water to absorb water and swell, and finally pressed to separate the fibers. The water absorption and swelling process involved soaking the wood at 30°C for 8 hours.

[0042] The fiber waste is the waste obtained from removing impurities, crushing and sieving larch wood chips.

[0043] S2. Oxy-alkali cooking: Papermaking fibers are mixed with sodium carbonate aqueous solution and cooked in a digester. Oxygen is used as the oxidant. Oxygen is introduced into the digester until the oxygen pressure reaches 1 MPa. The oxygen supply is then cut off, and the pulp and black liquor are added to the digester. The mixture is heated to 140°C within 30 minutes. Oxygen is introduced to maintain the pressure in the digester at 2 MPa. The temperature is maintained for 5 hours. Then sodium hydroxide is added, and the digestion is continued for another 2 hours. Finally, the pulp and black liquor are separated by pressing.

[0044] Based on the dry weight of the papermaking fiber, the amount of sodium carbonate is 30% and the amount of sodium hydroxide is 3%; by weight, the ratio of the pretreated papermaking fiber to the sodium carbonate aqueous solution is 1:5.

[0045] S3. Black liquor treatment: The black liquor is mixed with fiber waste, extruded, and burned as biomass fuel. The extrusion is performed using a vortex extrusion method. Excess black liquor after extrusion is recovered and mixed with fiber waste again.

[0046] S4. Recycling and Causticization: The main component of the molten material after combustion is sodium carbonate, which is dissolved into a sodium carbonate aqueous solution. The sodium carbonate aqueous solution with a volume ratio of 10% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining sodium carbonate aqueous solution are then reused in step S2. Example

[0047] A low-cost, environmentally friendly papermaking pulping process includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber.

[0048] Broadleaf maple wood is selected as the raw material. The maple wood chips are cleaned of impurities, crushed, and sieved. Then, they are soaked in water to absorb water and swell, and finally pressed to separate the fibers. The water absorption and swelling process involves soaking at 40℃ for 5 hours.

[0049] The fiber waste is the waste obtained from removing impurities, crushing and sieving maple wood chips.

[0050] S2. Oxy-alkali cooking: Papermaking fibers are mixed with sodium carbonate aqueous solution and cooked in a digester. Oxygen is used as the oxidant. Oxygen is introduced into the digester until the oxygen pressure reaches 1 MPa. The oxygen supply is then cut off, and the pulp and black liquor are added to the digester. The mixture is heated to 140°C within 30 minutes. Oxygen is introduced to maintain the pressure in the digester at 2 MPa. The temperature is maintained for 5 hours. Then sodium hydroxide is added, and the digestion is continued for another 2 hours. Finally, the pulp and black liquor are separated by pressing.

[0051] Based on the dry weight of the papermaking fiber, the amount of sodium carbonate is 30% and the amount of sodium hydroxide is 3%; by weight, the ratio of the pretreated papermaking fiber to the sodium carbonate aqueous solution is 1:5.

[0052] S3. Black liquor treatment: The black liquor is mixed with fiber waste, extruded, and burned as biomass fuel. The extrusion is performed using a vortex extrusion method. Excess black liquor after extrusion is recovered and mixed with fiber waste again.

[0053] S4. Recycling and Causticization: The main component of the molten material after combustion is sodium carbonate, which is dissolved into a sodium carbonate aqueous solution. The sodium carbonate aqueous solution with a volume ratio of 10% is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining sodium carbonate aqueous solution are then reused in step S2.

[0054] Comparative Example 1 A papermaking pulping process, using wheat straw as raw material, differs from Example 1 in that, in step S2, oxygen-alkali cooking, sodium hydroxide is not added, and the amount of sodium carbonate added is 22% based on the dry weight of the paper fiber. The process involves cooking at a constant temperature for 4 hours, with the other steps remaining the same.

[0055] Comparative Example 2 A papermaking pulping process, using maple wood as raw material, differs from Example 5 in that, in step S2, oxygen-alkali cooking, sodium hydroxide is not added, and the amount of sodium carbonate added is 33% based on the dry weight of the paper fibers. The cooking is carried out at a constant temperature for 2.5 hours, with the other steps remaining the same.

[0056] Comparative Example 3 A papermaking pulping process, using maple as raw material, differs from Example 5 in that, in step S1, the pretreatment of papermaking fiber plant raw materials, only the maple wood chips are cleaned, crushed, and sieved; soaking in water and pressing to separate the fibers are not performed. All other steps remain the same.

[0057] Comparative Example 4 A papermaking pulping process, using wheat straw as raw material, differs from Example 1 in that, in step S2, oxygen-alkali cooking, sodium carbonate is not added, and the amount of sodium hydroxide added is 22% based on the dry weight of the paper fibers. The process involves cooking at a constant temperature for 4 hours, with the other steps remaining the same.

[0058] Comparative Example 5 A papermaking pulping process uses wheat straw as raw material. Compared with Example 5, in step S3, black liquor treatment, the black liquor is evaporated and directly added to the alkali recovery furnace for combustion and recovery. The other steps are the same.

[0059] Experimental example: Using wheat straw as an example, we can verify the difference between boiling it with sodium carbonate and sodium hydroxide.

[0060] The freeness, yield, and brightness (quantitative value of 55.54 g / m³) of the pulps prepared in Example 1 and Comparative Example 1 were measured respectively. 2 ), tensile strength (quantitative value 75.17 g / m²) 2 ) and kappa value (standard GB / T 1546-2004).

[0061] Table 1 Analysis of straw pulp indexes Experimental Example Beating degree °SR Whiteness% Yield % Tensile strength kN / m Card value causticization rate % Example 1 18.0±0.5 43.0 44 3.77±0.1 10.9±0.1 10 Comparative Example 1 17.0±0.5 42.0 38 3.81±0.1 15.4±0.1 0 Comparative Example 4 15.0±0.5 40.0 40 3.42±0.1 9.7±0.1 More than 90 As can be seen from Table 1, the pulping process in Example 1, which uses a segmented addition of sodium carbonate and sodium hydroxide for oxy-alkali cooking, can improve the whiteness, yield, and beating degree.

[0062] Compared to the control group, which only added sodium carbonate, this method improved yield and whiteness while significantly reducing kappa number under the same cooking time. Treating with sodium carbonate first makes lignin removal more difficult later; therefore, using a small amount of sodium hydroxide can save energy and improve efficiency.

[0063] Compared to Comparative Example 4, adding only sodium hydroxide, under the same cooking time, can improve whiteness and yield, and also improve pulping degree, thereby improving the transparency of the pulp.

[0064] Compared to Comparative Example 4, the causticization rate of black liquor recovery in Example 1 was reduced in the later stage. Only a portion of the sodium carbonate solution needed to be causticized to meet the requirements of oxygen-alkali cooking, which simplified the process and greatly reduced the cost.

[0065] Taking broadleaf maple as an example, the effect of pretreatment soaking and fiber separation was verified. The yield and kappa number (standard GB / T 1546-2004) of the slurries prepared in Example 5 and Comparative Examples 2-3 were determined respectively.

[0066] Table 2 Analysis of Wood Pulp Indicators Experimental Example Yield % Card value Example 1 42 12.7±0.1 Comparative Example 2 40 17.6±0.1 Comparative Example 3 36 24.5±0.1 As can be seen from Table 1, the pulping process in Example 1, which involves first soaking the wood chip raw material in water to absorb water and swell, then pressing and separating the fibers, and then adding sodium carbonate and sodium hydroxide in stages for oxy-alkali cooking, can improve the yield, reduce the kappa number, and improve the delignification effect.

[0067] Compared to the control group, which only added sodium carbonate, the yield was improved and the kappa number was significantly reduced under the same cooking time. Treating with sodium carbonate first makes lignin removal more difficult later; using a small amount of sodium hydroxide afterwards can save energy and improve efficiency.

[0068] Compared to control example 3, soaking in water to absorb moisture and swell, followed by pressing and separating the fibers, can improve the penetration of alkali during the alkaline boiling process and enhance the delignification effect.

[0069] As can be seen from Table 1, the pulping process of this application significantly reduces costs. Using sodium carbonate and a small amount of sodium hydroxide for staged oxygen-alkali pulping, and then causticizing a small amount of sodium carbonate during black liquor recovery, reduces costs to some extent. Furthermore, while conventional black liquor combustion requires the addition of heavy oil, this application directly burns a mixture of black liquor and raw material waste, reducing the cost of heavy oil, improving heat recovery, and also recycling the raw material waste, further reducing costs.

[0070] In summary, using sodium carbonate and a small amount of sodium hydroxide for segmented oxygen-alkali pulping, and mixing and burning the resulting black liquor with fiber waste to recover sodium carbonate and heat, reduces the causticization rate, which can improve equipment efficiency, improve pulping quality, and reduce pulping costs.

[0071] The above description is a detailed explanation of preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical concept presented in the present invention should fall within the patent scope covered by the present invention.

Claims

1. A low-cost and environmentally friendly papermaking pulping process, characterized in that, Includes the following steps: S1. Pretreatment of plant raw materials for papermaking fiber; S2. Oxy-alkali cooking: The pretreated papermaking fiber plant raw material is mixed with sodium carbonate aqueous solution and cooked for 0.5 to 5 hours with oxygen as oxidant. Then sodium hydroxide is added and cooking is continued for 0.3 to 2 hours. Finally, the pulp and black liquor are separated.

2. The low-cost and environmentally friendly papermaking pulping process according to claim 1, characterized in that, In step S1, when the papermaking fiber is wood fiber raw material, the specific process for pretreatment of the papermaking fiber plant raw material is as follows: crush the papermaking fiber raw material, then soak it in water to absorb water and swell, and finally press and separate the fibers.

3. The low-cost and environmentally friendly papermaking pulping process according to claim 2, characterized in that, The water absorption and swelling process involves soaking the product at 20–90°C for 0.5–10 hours.

4. The low-cost and environmentally friendly papermaking pulping process according to claim 1, characterized in that, In step S2, based on the dry weight of the pretreated papermaking fiber plant raw material, the amount of sodium carbonate is 10% to 50%, and the amount of sodium hydroxide is 1% to 5%; by weight, the ratio of the pretreated papermaking fiber to the sodium carbonate aqueous solution is 1:2 to 10.

5. The low-cost and environmentally friendly papermaking pulping process according to claim 1, characterized in that, In step S2, the cooking temperature is 100-180°C.

6. The low-cost and environmentally friendly papermaking pulping process according to claim 1, characterized in that, In step S2, the black liquor is mixed with fiber waste and burned as biomass fuel to obtain a melt.

7. The low-cost and environmentally friendly papermaking pulping process according to claim 6, characterized in that, The main component of the molten material after combustion is sodium carbonate, which is dissolved into an aqueous sodium carbonate solution. The sodium carbonate solution, with a weight ratio of 1% to 20%, is causticized to obtain sodium hydroxide. The causticized sodium hydroxide and the remaining aqueous sodium carbonate solution are then reused in step S2.

8. The low-cost and environmentally friendly papermaking pulping process according to claim 6, characterized in that, The fiber waste is waste obtained from the pretreatment of papermaking fiber plant raw materials.

9. The low-cost and environmentally friendly papermaking pulping process according to claim 6, characterized in that, The black liquor is mixed with fiber waste, extruded, and then fed into a combustion furnace for combustion. The extrusion is performed using a screw extrusion process.

10. The low-cost and environmentally friendly papermaking pulping process according to claim 9, characterized in that, Excess black liquor after extrusion is recovered and mixed with fiber waste.