Low-carbon pulping black liquor zero-emission treatment system

Abstract

The utility model belongs to the technical field of papermaking wastewater treatment, and relates to a low-carbon pulping black liquor zero-discharge treatment system which comprises a raw water tank, an air flotation flocculation precipitation system, a pretreatment system, an oxidation decolorization system, an ultrafiltration system, a nanofiltration / reverse osmosis system, an ED concentration system and an MVR evaporation system, the system further comprises a dosing system, a recycling water tank, a sludge filter pressing system and an ionic membrane electrolysis system. The zero-emission treatment system for the low-carbon pulping black liquor disclosed by the utility model adopts a treatment process combining chemical treatment as a main process and physical treatment as an auxiliary process; the treated materials are completely recycled, so that complete zero emission is realized; the occupied area is small and is 1 / 5 of that of a traditional process; inorganic solids can be decomposed and synthesized again through an electrolysis system, so that complete utilization is realized; and full-automatic operation can be realized.

Description

Technical Field

[0001] This utility model belongs to the field of papermaking wastewater treatment technology, and relates to a low-carbon pulping black liquor zero-emission treatment system. Background Technology

[0002] Black liquor refers to wastewater from papermaking, such as that generated by the "Nafis Eco-Pulping" technology from the UK. The "Nafis Eco-Pulping" technology uses agricultural straw or annual gramineous plants (such as reeds) as raw materials to extract cellulose from the straw. This cellulose can be directly used to manufacture various paper products, from high-strength corrugated paper to household paper, as well as molded paper packaging and industrial packaging. This technology completely overcomes the high energy consumption and high cost bottlenecks of traditional straw pulping processes, representing an innovative, low-carbon, and eco-friendly pulping method.

[0003] Currently, most pulping wastewater treatment methods employ biological processes. To accommodate these processes, the wastewater needs to be diluted approximately tenfold, increasing both the workload and the amount of solid waste generated by flotation sedimentation. This significantly increases the land area and energy consumption of the treatment process, and ironically, generates a large amount of hazardous waste. Furthermore, the treated water is discharged into river basins and the ocean, causing significant environmental pollution. Current pulping technology consumes 15-20 tons of water per ton of pulp, consuming vast amounts of water resources and causing substantial environmental pollution. Existing technologies cannot effectively treat the high-COD, high-temperature, and high-SS-content pulping wastewater generated from straw pulp papermaking. Therefore, a low-carbon, zero-discharge treatment system for pulping black liquor is proposed. Utility Model Content

[0004] To solve the above-mentioned technical problems, this utility model provides a low-carbon pulping black liquor zero-emission treatment system. The technical solution adopted by this utility model is as follows:

[0005] A low-carbon pulping black liquor zero-discharge treatment system includes a raw water tank, an air flotation flocculation sedimentation system, a pretreatment system, an oxidation decolorization system, an ultrafiltration system, a nanofiltration / reverse osmosis system, an ED concentration system, and an MVR evaporation system connected in sequence; a dosing system is connected to the air flotation flocculation sedimentation system.

[0006] The product water outlets of the nanofiltration / reverse osmosis system, ED concentration system, and MVR evaporation system are connected to the reclaimed water tank; the sludge discharge outlet of the air flotation flocculation sedimentation system, the sludge discharge outlet of the pretreatment system, and the mother liquor discharge outlet of the MVR evaporation system are connected to the sludge defiltration system; the filtrate outlet of the sludge defiltration system is connected to the raw water tank; and the ion-exchange membrane electrolysis system is connected to the oxidation decolorization system.

[0007] This invention provides a low-carbon pulping black liquor zero-discharge treatment system. First, the produced pulping black liquor is collected and pumped to a raw water tank for mixing and water quality adjustment. Then, it enters an air flotation flocculation sedimentation system. A dosing system adds chemicals such as enzyme catalysts, flocculants, and acids to the air flotation flocculation sedimentation system, achieving 80%-90% solid-liquid separation through comprehensive chemical treatment. The clarified liquid is pumped into a pretreatment system to remove 95% of impurities, including larger suspended solids, colloids, and organic matter (microorganisms). After pretreatment, the purified water enters an oxidation decolorization system for further reduction of COD and color, thus meeting the water quality requirements of the ultrafiltration system. The ultrafiltration system effectively removes particles, colloids, and bacteria from the water. The ultrafiltration system produces water that is pressurized by a high-pressure pump and then enters a nanofiltration / reverse osmosis system for concentration and desalination, selectively removing macromolecules, organic matter, heavy ions, and some charged ions from the aqueous solution. The concentrated water produced by the nanofiltration / reverse osmosis system enters an ED concentration system for further concentration. The water produced by the nanofiltration / reverse osmosis system and the ED concentration system, once meeting the required water quality, enters a reclaimed water tank. The concentrate from the ED concentration system enters an MVR evaporation system for further concentration. Some of the salt produced after evaporation in the MVR evaporation system is processed by an ion-exchange membrane electrolysis system to produce alkali, hydrochloric acid, and sodium hypochlorite solution. The alkali and hydrochloric acid are used in the production process, while the sodium hypochlorite enters an oxidation decolorization system. The remaining salt can be sold externally, and the resulting steam condensate enters a reclaimed water tank for reuse.

[0008] The sludge produced by the air flotation flocculation sedimentation system and the sludge separated by the pretreatment system are collected, settled, concentrated, and dewatered by the sludge dewatering system. The filtrate is returned to the raw water tank for reprocessing, and the sludge cake (containing a large amount of organic matter) is incinerated or sold as lignin.

[0009] Furthermore, the pretreatment system, the ultrafiltration system, and the nanofiltration / reverse osmosis system are provided with pipes for reflux to the air flotation flocculation sedimentation system.

[0010] The ultrafiltration system has an ultrafiltration recovery rate of approximately 95%, meaning the water production rate is 95%. The remaining 5% of the concentrate is mostly recycled back to the air flotation flocculation sedimentation system for further treatment. The concentrate from the pretreatment system and the nanofiltration / reverse osmosis system is also recycled.

[0011] Furthermore, the ED concentration system is equipped with a freshwater return pipe that returns the freshwater to the nanofiltration / reverse osmosis system.

[0012] The freshwater from the ED concentration system still has a relatively high salt content and needs to be re-entered into the nanofiltration / reverse osmosis system for desalination treatment.

[0013] Furthermore, the sludge dewatering system includes a sludge thickening tank and a plate and frame filter press.

[0014] The sludge generated by the air flotation flocculation sedimentation system and the sludge separated from the pretreatment system first enter the sludge thickening tank of the sludge filter press system. The sludge thickening tank settles, thickens, and stabilizes the sludge, and is also an important facility for sludge treatment and storage. After the sludge is mixed in the sludge thickening tank, it is pumped to the plate and frame filter press for dewatering.

[0015] Furthermore, the pretreatment system includes a bag filter and a solid-liquid separation filter.

[0016] The bag filter of the pretreatment system can remove some of the larger suspended solids, colloids, organic matter (microorganisms) in the water with a filtration accuracy of about 100 microns. The effluent enters the solid-liquid separator through a booster pump. The solid-liquid separator contains a special filter element that can retain particulate matter larger than 0.2 microns for further filtration. The separated impurities accumulate on the surface of the filter element to form a filter cake layer. After backflushing, the filter cake falls off and is discharged into the sludge thickening tank through the residue discharge port.

[0017] Furthermore, the air flotation flocculation sedimentation system includes an integrated air flotation flocculation sedimentation machine.

[0018] The integrated air flotation, flocculation, and sedimentation system is a highly efficient wastewater treatment device that combines air flotation, flocculation, and sedimentation technologies to remove suspended solids, grease, and other impurities from water.

[0019] Furthermore, the ultrafiltration system includes a security filter and an ultrafiltration membrane assembly.

[0020] When water enters the ultrafiltration membrane module of the ultrafiltration system, it first passes through a security filter to remove trace impurities, colloids, and microorganisms remaining from the previous treatment unit, ensuring the quality of the water entering the ultrafiltration membrane module. Then, it enters the ultrafiltration membrane module, where, under low pressure, some small-molecule solutes such as inorganic salt ions and water molecules can pass through the ultrafiltration membrane, while large molecules exceeding a certain molecular weight are retained as a concentrate, effectively removing particles, colloids, bacteria, pyrogens, and organic matter from the water.

[0021] Furthermore, the ultrafiltration membrane module is a hollow fiber ultrafiltration membrane module.

[0022] Hollow fiber ultrafiltration membrane modules adopt advanced external pressure membrane separation technology, which separates at room temperature and low pressure. It has the advantages of low energy consumption, high filtration accuracy, large water production, and strong anti-fouling ability. It can effectively filter out harmful substances such as bacteria, colloids, suspended solids, rust, and macromolecular organic matter in water.

[0023] Furthermore, the reverse osmosis nanofiltration membrane in the nanofiltration / reverse osmosis system is an alkali-resistant nanofiltration membrane.

[0024] Alkali-resistant nanofiltration membranes allow solvent molecules, certain low-molecular-weight solutes, or low-valence ions to pass through. The surface separation layer is composed of polyelectrolytes and has a certain rejection rate for inorganic salts. Alkali-resistant nanofiltration membranes possess excellent film-forming properties, thermal stability, chemical stability, resistance to acid and alkali corrosion and microbial attack, chlorine resistance, as well as high water flux, high salt rejection rate, and resistance to colloidal and suspended solids fouling.

[0025] Furthermore, the MVR evaporation system includes an MVR evaporator and a centrifuge.

[0026] The MVR evaporator performs evaporation, concentration, and crystallization. The feed liquid with a certain concentration is supersaturated and crystallized in a cooling crystallizer. The resulting slurry with a certain solid-liquid ratio enters a centrifuge for solid-liquid separation to obtain sodium chloride solid product. The centrifugal mother liquor can be sent back to the evaporator by a feed pump into a mother liquor tank. The evaporated mother liquor is also discharged quantitatively to the sludge dewatering system.

[0027] This utility model provides a low-carbon pulping black liquor zero-emission treatment system, which adopts a treatment process that combines chemical treatment as the main method and physical treatment as a supplement. The treated materials are completely recycled and reused to achieve complete zero emissions. It occupies a small area, only 1 / 5 of the traditional process. Inorganic solids can be decomposed and synthesized through an electrolysis system to achieve complete utilization. It can achieve fully automated operation. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the zero-emission treatment system for low-carbon pulping black liquor of this utility model.

[0029] Explanation of markings in the diagram:

[0030] 1. Raw water tank; 2. Air flotation flocculation sedimentation system; 3. Pretreatment system; 4. Oxidation decolorization system; 5. Ultrafiltration system; 6. Nanofiltration / reverse osmosis system; 7. ED concentration system; 8. MVR evaporation system; 9. Reclaimed water tank; 10. Sludge defiltration system; 11. Ion membrane electrolysis system; 12. Chemical dosing system. Detailed Implementation

[0031] To better understand the purpose, structure, and function of this utility model, a more detailed description of this utility model is provided below with reference to the accompanying drawings.

[0032] Example:

[0033] like Figure 1As shown, a low-carbon pulping black liquor zero-discharge treatment system includes a raw water tank 1, an air flotation flocculation sedimentation system 2, a pretreatment system 3, an oxidation decolorization system 4, an ultrafiltration system 5, a nanofiltration / reverse osmosis system 6, an ED concentration system 7, and an MVR evaporation system 8 connected in sequence; a dosing system 12 is connected to the air flotation flocculation sedimentation system 2; the product water outlets of the nanofiltration / reverse osmosis system 6, the ED concentration system 7, and the MVR evaporation system 8 are connected to a recycled water tank 9; the sludge discharge outlet of the air flotation flocculation sedimentation system 2, the sludge discharge outlet of the pretreatment system 3, and the mother liquor discharge outlet of the MVR evaporation system 8 are connected to a sludge dewatering system 10; the filtrate outlet of the sludge dewatering system 10 is connected to the raw water tank 1; and the ion-exchange membrane electrolysis system 11 is connected to the oxidation decolorization system 4. The pretreatment system 3, the ultrafiltration system 5, and the nanofiltration / reverse osmosis system 6 are provided with pipelines for reflux to the air flotation flocculation sedimentation system 2; the ED concentration system 7 is provided with a freshwater reflux pipeline for reflux to the nanofiltration / reverse osmosis system 6.

[0034] The sludge dewatering system 10 includes a sludge thickening tank and a plate and frame filter press; the pretreatment system 3 includes a bag filter and a solid-liquid separation filter; the air flotation flocculation sedimentation system 2 includes an integrated air flotation flocculation sedimentation machine; the ultrafiltration system 5 includes a security filter and an ultrafiltration membrane module; the ultrafiltration membrane module is a hollow fiber ultrafiltration membrane module; the reverse osmosis nanofiltration membrane in the nanofiltration / reverse osmosis system 6 is an alkali-resistant nanofiltration membrane; and the MVR evaporation system 8 includes an MVR evaporator and a centrifuge.

[0035] In operation, the produced black liquor is first collected and pumped to raw water tank 1 for water quality adjustment through mixing. Then it enters the air flotation flocculation sedimentation system 2. The dosing system 12 adds chemicals such as enzyme catalysts, flocculants, and acid to the air flotation flocculation sedimentation system 2, and 80%-90% solid-liquid separation is achieved through comprehensive chemical treatment. The clarified liquid is pumped into the pretreatment system 3. The bag filter can remove some of the larger suspended solids, colloids, organic matter (microorganisms), etc. in the water, with a filtration accuracy of about 100 microns. The effluent is pumped into the solid-liquid separator by a booster pump. The solid-liquid separator contains special filter elements that can retain particles larger than 0.2 microns for further filtration. The separated impurities accumulate on the surface of the filter elements to form a filter cake layer. After backflushing, the filter cake falls off and is discharged into the sludge thickening tank through the residue discharge port. After passing through the pretreatment system 3, 95% of the impurities in the water have been removed. The purified water produced by the pretreatment system 3 enters the oxidation and decolorization system 4 for further treatment, reducing COD and color, so that the water quality indicators meet the influent requirements of the ultrafiltration system 5. The water treated by the oxidation and decolorization system 4 first enters the security filter of the ultrafiltration system 5 to remove trace impurities, colloids, and microorganisms remaining in the previous treatment unit, ensuring the water quality entering the ultrafiltration membrane module. Then it enters the ultrafiltration membrane module. Under low pressure, some small molecule solutes such as inorganic salt ions and water molecules can pass through the ultrafiltration membrane, while large molecules exceeding a certain molecular weight are retained as a concentrate, which can effectively remove particles, colloids, bacteria, pyrogens, and organic matter in the water. The ultrafiltration recovery rate of the ultrafiltration system 5 is about 95%, that is, the water production ratio is 95%, and the remaining 5% of the concentrate is mostly recycled back to the air flotation flocculation sedimentation system 2 for recycling. The permeate from ultrafiltration system 5 is pressurized by a high-pressure pump and then enters nanofiltration / reverse osmosis system 6 for concentration and desalination, selectively removing macromolecules, organic matter, heavy ions, and some charged ions from the aqueous solution. The concentrate from nanofiltration / reverse osmosis system 6 enters ED concentration system 7 for further concentration. The concentrate from nanofiltration / reverse osmosis system 6 is recycled. The permeate from nanofiltration / reverse osmosis system 6 and ED concentration system 7, once meeting the required water quality, enters recycled water tank 9. The freshwater from ED concentration system 7, due to its still relatively high salt content, needs to re-enter nanofiltration / reverse osmosis system 6 for desalination. The concentrate from ED concentration system 7 enters the MVR evaporator of MVR evaporation system 8 for evaporation, concentration, and crystallization. The slurry with a certain solid-liquid ratio, obtained by supersaturation crystallization in a cooling crystallizer, enters a centrifuge for solid-liquid separation to obtain sodium chloride solid product. The centrifugal mother liquor can be sent back to the evaporator by a raw material pump into a mother liquor tank. The evaporated mother liquor is quantitatively discharged to the sludge thickening tank of sludge dewatering system 10. After evaporation in the MVR evaporation system 8, some of the salt produced is converted into alkaline solution, hydrochloric acid, and sodium hypochlorite solution through the ion-exchange membrane electrolysis system 11. The alkaline solution and hydrochloric acid are then used in the production process, while the sodium hypochlorite is used in the oxidation and decolorization system 4. The remaining salt can be sold externally, and the steam condensate generated is sent to the reuse water tank 9 for reuse.

[0036] The sludge produced by the air flotation flocculation sedimentation system 2 and the sludge separated by the pretreatment system 3 first enter the sludge thickening tank of the sludge dewatering system 10. The sludge thickening tank settles, thickens, and stabilizes the sludge, and is also an important facility for sludge treatment and storage. After the sludge is mixed in the sludge thickening tank, it is pumped to the plate and frame filter press for dewatering. The filtrate is returned to the raw water tank 1 for reprocessing, and the sludge cake (containing a large amount of organic matter) is incinerated or sold as lignin.

[0037] This utility model provides a low-carbon pulping black liquor zero-emission treatment system, which adopts a treatment process that combines chemical treatment as the main method and physical treatment as a supplement. The treated materials are completely recycled and reused to achieve complete zero emissions. It occupies a small area, only 1 / 5 of the traditional process. Inorganic solids can be decomposed and synthesized through an electrolysis system to achieve complete utilization. It can achieve fully automated operation.

[0038] It is understood that this utility model has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this utility model. Furthermore, under the teachings of this utility model, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this utility model.

Claims

1. A low-carbon pulping black liquor zero-emission treatment system, characterized in that, It includes a raw water tank, an air flotation flocculation sedimentation system, a pretreatment system, an oxidation decolorization system, an ultrafiltration system, a nanofiltration / reverse osmosis system, an ED concentration system, and an MVR evaporation system connected in sequence; a dosing system is connected to the air flotation flocculation sedimentation system; The product water outlets of the nanofiltration / reverse osmosis system, ED concentration system, and MVR evaporation system are connected to the reclaimed water tank; the sludge discharge outlet of the air flotation flocculation sedimentation system, the sludge discharge outlet of the pretreatment system, and the mother liquor discharge outlet of the MVR evaporation system are connected to the sludge defiltration system; the filtrate outlet of the sludge defiltration system is connected to the raw water tank; and the ion-exchange membrane electrolysis system is connected to the oxidation decolorization system.

2. The low-carbon pulping black liquor zero-emission treatment system according to claim 1, characterized in that, The pretreatment system, the ultrafiltration system, and the nanofiltration / reverse osmosis system are provided with pipelines for reflux to the air flotation flocculation sedimentation system.

3. The low-carbon pulping black liquor zero-emission treatment system according to claim 2, characterized in that, The ED concentration system is equipped with a freshwater return pipeline for recirculating the nanofiltration / reverse osmosis system.

4. The low-carbon pulping black liquor zero-emission treatment system according to claim 1 or 2, characterized in that, The sludge dewatering system includes a sludge thickening tank and a plate and frame filter press.

5. The low-carbon pulping black liquor zero-emission treatment system according to claim 3, characterized in that, The pretreatment system includes a bag filter and a solid-liquid separation filter.

6. The low-carbon pulping black liquor zero-emission treatment system according to claim 1, characterized in that, The air flotation flocculation sedimentation system includes an integrated air flotation flocculation sedimentation machine.

7. The low-carbon pulping black liquor zero-emission treatment system according to claim 1, characterized in that, The ultrafiltration system includes a security filter and an ultrafiltration membrane assembly.

8. The low-carbon pulping black liquor zero-emission treatment system according to claim 7, characterized in that, The ultrafiltration membrane module is a hollow fiber ultrafiltration membrane module.

9. The low-carbon pulping black liquor zero-emission treatment system according to claim 8, characterized in that, The reverse osmosis nanofiltration membrane in the nanofiltration / reverse osmosis system is an alkali-resistant nanofiltration membrane.

10. The low-carbon pulping black liquor zero-emission treatment system according to claim 1, characterized in that, The MVR evaporation system includes an MVR evaporator and a centrifuge.

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