System and method for preparing biochar from sludge

Abstract

The invention provides a system and method for preparing biochar from sludge, the system comprises a dewatering device, a drum dryer, a spiral granulator, a pyrolyzing furnace, a cooling device, a crusher and a vibrating screen which are connected in sequence, the dewatering device is used for primarily dewatering the sludge, the drum dryer is used for drying the sludge subjected to primary dewatering, and the spiral granulator is used for granulating the sludge subjected to primary dewatering. The spiral granulator is used for enabling the dried sludge to form sludge particles, the pyrolyzing furnace is a stepped pyrolyzing furnace and is used for performing stepped pyrolysis on the sludge particles to form biochar particles, the cooling device is used for cooling the biochar particles, the crusher is used for crushing the biochar particles, and the vibrating screen is used for screening the crushed biochar particles. According to the invention, the problems of discharge and stacking of the domestic sludge of urban residents are solved, the sludge is converted into a biochar material with multiple purposes, and resource utilization of the sludge is realized.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment and resource recycling technology, and in particular to a system and method for preparing biochar from sludge. Background Technology

[0002] The sludge produced by urban wastewater treatment plants mainly consists of sludge discharged along with domestic sewage from urban residents. This sludge exists primarily in the form of sediment in the wastewater and originates mainly from the daily activities of urban residents, such as those generated during the operation of catering, hotels, and shopping malls. With the expansion of urban scale and the increase in population, urban sludge is showing a trend of increasing year by year.

[0003] Currently, the main treatment method for domestic sewage sludge produced by municipal sludge treatment plants is landfill. Other treatment methods include drying and incineration, composting, and ultrasonic sludge disintegration technology. Sludge landfilling is divided into separate landfilling and mixed landfilling. Currently, the most common method is to mix dewatered sludge with municipal solid waste for landfilling, which is the most prevalent method for sludge treatment. However, this method requires a large land area and generates a large amount of leachate during landfilling. The leachate contains heavy metals and pathogens, increasing the burden on leachate treatment and easily causing secondary pollution. Sludge must undergo dewatering treatment before landfilling, generally through mechanical dewatering and the addition of additives to control the sludge moisture content to around 65-70%. Directly landfilling dewatered sludge cake is a waste of resources. In addition, the following difficulties may exist in landfill operation: (1) Landfills usually use a layer of garbage and a layer of soil for compaction to ensure space utilization efficiency, but the high water content and high viscosity of sludge often cause the compaction machinery to slip or even sink into it, increasing the difficulty of operation; (2) The rheological properties of sludge make the landfill body easy to deform and landslide, forming man-made swamps, which brings safety hazards to the landfill; (3) The high water content of sludge significantly increases the amount of leachate to be treated in the landfill. Due to the small size of sludge particles, it often clogs the leachate collection system and drainage pipes, increasing the load on the landfill dam, making it difficult for the safety and management of the landfill, and the cost of cleaning the collection system is high. With the increasing scarcity of land resources and the rapid increase in sludge production, landfill technology is gradually becoming unable to meet the long-term development needs of sludge treatment. Sludge incineration technology has the advantage of rapidly reducing sludge volume, eliminating the need for storage equipment under harsh weather conditions, and simultaneously recovering heat and killing pathogens. However, due to the high moisture content of sludge (typically around 30% for dewatered sludge) and its low calorific value, direct incineration requires a large amount of auxiliary fuel, resulting in high operating costs. Furthermore, the incineration process may be accompanied by problems such as exhaust gas, noise, vibration, and heat radiation, limiting the widespread application of this technology. Sludge composting technology essentially utilizes aerobic microorganisms in the sludge for aerobic fermentation. Through a mixed microbial community, various organic substances are oxidized and decomposed, transforming them into humus easily absorbed by plants. The final products of the reaction are carbon dioxide, water, and heat. The large amount of heat maintains the material at a sustained high temperature above 60°C, effectively reducing the moisture content and removing pathogens, parasite eggs, and weed seeds. After 10-15 days of composting fermentation, the moisture content of the material can be reduced to around 25%. Part of the composted material can be recycled as a microbial culture medium, and the other part can be used as nutrient soil. However, this technology requires a large area, has a long composting cycle, is prone to producing odors, and is difficult to operate unmanned. Ultrasonic sludge breaking technology is a novel approach for sludge stabilization, volume reduction, and resource recovery. It can be applied to sludge digestion pretreatment to improve digestion efficiency, or to break down excess sludge and recycle it for further treatment to reduce sludge discharge. This technology utilizes the energy of ultrasound to create localized high-temperature, high-pressure conditions through cavitation in a very short time. This, coupled with strong shock waves and free microjets, bombards microbial cells, causing the cell walls of microorganisms in the sludge to rupture. After cell wall rupture, intracellular contents dissolve, and solid COD is converted into soluble COD, thereby accelerating the hydrolysis rate of the sludge. However, this technology is costly and difficult to apply to large-scale sludge treatment scenarios, thus limiting its application in urban sludge treatment. Currently, efforts are being made to treat sludge in a way that addresses both disposal and resource utilization, allowing it to continue to benefit humanity. Preparing sludge into biochar through specific methods can alleviate the pressure of sludge stockpiling and transform it into a functional material with multiple uses. However, existing sludge biochar preparation technologies still have limitations in terms of energy consumption control, process complexity, product multifunctionality, and raw material adaptability. Summary of the Invention

[0004] The purpose of this invention is to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a system and method for preparing biochar from sewage sludge, which not only solves the discharge and treatment problems caused by urban sewage sludge, but also transforms sewage sludge into biochar material with multiple uses through optimized process flow, thereby achieving resource utilization.

[0005] One embodiment of the present invention provides a system for preparing biochar from sludge, comprising: a dewatering device, a drum dryer, a spiral granulator, a pyrolysis furnace, a cooling device, a crusher, and a vibrating screen. The dewatering device is used to initially remove moisture from the sludge; the feed end of the drum dryer is connected to the discharge end of the dewatering device, and the drum dryer is used to dry the initially dewatered sludge; the feed end of the spiral granulator is connected to the discharge end of the drum dryer, and the spiral granulator is used to form sludge particles from the dried sludge; the feed end of the pyrolysis furnace is connected to the discharge end of the spiral granulator, and the pyrolysis furnace is a stepped pyrolysis furnace used to perform stepped pyrolysis of the sludge particles to form biochar particles; the feed end of the cooling device is connected to the discharge end of the pyrolysis furnace, and the cooling device is used to cool the biochar particles; the feed end of the crusher is connected to the discharge end of the cooling device, and the crusher is used to crush the biochar particles; the feed end of the vibrating screen is connected to the discharge end of the crusher, and the vibrating screen is used to screen the crushed biochar particles.

[0006] In some embodiments, a discharge screen is connected to the discharge port of the spiral granulator.

[0007] In some embodiments, the pyrolysis furnace has a low-temperature chamber, a medium-temperature chamber and a high-temperature chamber connected in sequence. The temperature range of the low-temperature chamber is 200℃-300℃, the temperature range of the medium-temperature chamber is 400℃-500℃, and the temperature range of the high-temperature chamber is 600℃-700℃.

[0008] In some embodiments, the system for preparing biochar from sludge further includes a combustion chamber having an air inlet and an exhaust outlet, the air inlet of which is connected to the exhaust outlet of the pyrolysis furnace to combust the pyrolysis gas discharged from the pyrolysis furnace.

[0009] In some embodiments, the low-temperature chamber, the medium-temperature chamber, and the high-temperature chamber are each connected to a heat exchanger. The air inlet and exhaust outlet of the combustion chamber are connected through a circulation pipeline. The heat exchanger is connected to the circulation pipeline. The heat exchanger includes a low-temperature chamber heat exchanger, a medium-temperature chamber heat exchanger, and a high-temperature chamber heat exchanger. The low-temperature chamber heat exchanger is located in the low-temperature chamber, the medium-temperature chamber heat exchanger is located in the medium-temperature chamber, and the high-temperature chamber heat exchanger is located in the high-temperature chamber. The exhaust outlet of the combustion chamber is sequentially connected to the high-temperature chamber heat exchanger, the medium-temperature chamber heat exchanger, and the low-temperature chamber heat exchanger to heat the high-temperature chamber, the medium-temperature chamber, and the low-temperature chamber in sequence.

[0010] In some embodiments, the system for preparing biochar from sludge further includes an exhaust gas treatment device connected to the exhaust port of a cryogenic chamber heat exchanger.

[0011] In some embodiments, the exhaust gas treatment device includes a cyclone separator, a bag filter and an activated carbon adsorption tower. The cyclone separator has an air inlet, an exhaust outlet and an ash discharge outlet. The air inlet of the cyclone separator is connected to the exhaust outlet of the low-temperature chamber heat exchanger. The cyclone separator is used to remove larger particles from the exhaust gas. The ash discharge outlet of the cyclone separator is connected to an ash hopper. A bag filter dust collector has an air inlet and an air outlet. The air inlet of the bag filter dust collector is connected to the air outlet of the cyclone separator. The bag filter dust collector is used to remove smaller particles from the exhaust gas. The activated carbon adsorption tower has an air inlet and an exhaust outlet. The air inlet of the activated carbon adsorption tower is connected to the exhaust outlet of the bag filter. The activated carbon adsorption tower is used to adsorb harmful gases in the exhaust gas. The exhaust outlet of the activated carbon adsorption tower is connected to an exhaust stack to discharge the exhaust gas after adsorbing harmful gases.

[0012] In some embodiments, the discharge end of the vibrating screen is connected to the feed end of the crusher to return biochar particles larger than the standard particle size to the crusher for further crushing.

[0013] In some embodiments, the discharge end of the drum dryer is inclined downwards.

[0014] Another embodiment of the present invention provides a method for preparing biochar from sludge, which utilizes the above-described system for preparing biochar from sludge and includes the following steps: S1. The sludge is dewatered using a dewatering device to reduce its moisture content to 40%-50%. S2. The dewatered sludge is transported to a drum dryer for drying, reducing the moisture content of the sludge to 10%-15%. S3. The dried sludge is transported to a spiral granulator for granulation to form sludge particles. S4. The sludge particles are transported to a pyrolysis furnace for staged pyrolysis to obtain biochar particles. S5. The biochar granules are conveyed to a cooling device for cooling. S6. The cooled biochar granules are conveyed to the crusher for crushing, and the crushed material is screened by a vibrating screen to separate biochar granules of different particle sizes. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 This is a schematic diagram of the system for preparing biochar from sludge according to an embodiment of the present invention; Figure label: 1. Dehydration device; 2. Rotary drum dryer; 3. Spiral granulator; 4. Pyrolysis furnace; 5. Combustion chamber; 6. Tail gas treatment device; 7. Cooling device; 8. Crusher; 9. Vibrating screen. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0017] The system and method for preparing biochar from sludge according to embodiments of the present invention are described below with reference to the accompanying drawings.

[0018] like Figure 1 As shown, one embodiment of the present invention proposes a system for preparing biochar from sludge, comprising: a dewatering device 1, a drum dryer 2, a spiral granulator 3, a pyrolysis furnace 4, a cooling device 7, a crusher 8, and a vibrating screen 9. The dewatering device 1 is used to initially remove moisture from the sludge; the feed end of the drum dryer 2 is connected to the discharge end of the dewatering device 1, and the drum dryer 2 is used to dry the initially dewatered sludge; the feed end of the spiral granulator 3 is connected to the discharge end of the drum dryer 2, and the spiral granulator 3 is used to precipitate the dried sludge. Sludge is formed into sludge particles; the feed end of pyrolysis furnace 4 is connected to the discharge end of spiral granulator 3. Pyrolysis furnace 4 is a stepped pyrolysis furnace, used for the stepped pyrolysis of sludge particles to form biochar particles; the feed end of cooling device 7 is connected to the discharge end of pyrolysis furnace 4, and cooling device 7 is used to cool biochar particles; the feed end of crusher 8 is connected to the discharge end of cooling device 7, and crusher 8 is used to crush biochar particles; the feed end of vibrating screen 9 is connected to the discharge end of crusher 8, and vibrating screen 9 is used to screen the crushed biochar particles.

[0019] The system of this invention not only solves the problem of sewage sludge discharge and storage in urban areas, but also transforms the sludge into biochar materials with multiple uses, realizing the resource utilization of sludge. The biochar materials prepared by the system of this invention have abundant porous structures and active surface functional groups, and can be widely used in soil improvement, solid waste disposal, heavy metal adsorption, and other fields, expanding the application scenarios of sludge resource utilization. The operation process is simple and suitable for large-scale promotion.

[0020] Compared with existing ultrasonic sludge breaking technology and hydrothermal carbonization technology, the system of this invention does not require complex chemical reagents or high-pressure equipment, thus reducing operating costs and technical barriers. At the same time, it generates no secondary pollution throughout the process, meeting environmental protection requirements and providing a feasible solution for the long-term development of sludge treatment.

[0021] Furthermore, the dewatering device 1 is a mechanical extrusion dewatering device. After the sludge enters the pressing chamber of the mechanical extrusion dewatering device, it is subjected to extrusion, and the water is squeezed out of the sludge and discharged through the drainage pipe.

[0022] Furthermore, adjacent devices are transported by a conveying device, which can be a conveyor belt, a conveyor vehicle, a conveying pipeline, etc., and can be selected according to actual needs.

[0023] Furthermore, the cooling device 7 employs a combination of water cooling and air cooling. The cooling device 7 includes a water-cooled chamber, water-cooled piping, and a cooler. The water-cooled piping is arranged inside the cooling chamber, using circulating cooling water to remove heat. The cooler is located at the top of the cooling chamber, accelerating the cooling process of the biochar particles by blowing air downwards. After being processed by the cooling device 7, the temperature of the biochar particles drops below 50°C, facilitating subsequent processing.

[0024] Furthermore, the crusher 8 is a hammer crusher, and a screen plate is connected to the discharge end of the crusher 8. The screen plate is used to control the particle size of the biochar particles to below 8 mm.

[0025] Furthermore, the vibrating screen 9 includes a first screen, a second screen, and a third screen arranged vertically. The first screen is located at the top layer with an aperture of 8 mm, the second screen is located in the middle layer with an aperture of 5 mm, and the third screen is located at the bottom layer with an aperture of 2 mm.

[0026] The vibrating screen 9 works by using a vibrating motor to drive the reciprocating motion of each layer of screens, causing biochar particles to be sorted step by step on the screens. Powder particles smaller than 2 mm are collected through the bottom third screen and can be used to prepare composite materials or as fillers. Biochar particles with a diameter between 2 and 5 mm are collected through the middle second screen, and biochar particles with a diameter between 5 and 8 mm are collected through the top first screen. Particles larger than 8 mm are discharged from the discharge end of the vibrating screen 9 and fed back into the crusher 8 for secondary crushing.

[0027] In some embodiments, a discharge screen is connected to the discharge port of the spiral granulator 3. The discharge screen is used to expel sludge particles by extrusion, forming sludge particles with a particle size of 7-10 mm. The sludge particles after being extruded and screened by the discharge screen have high density and uniformity, making subsequent pyrolysis more uniform.

[0028] In some embodiments, the pyrolysis furnace 4 has a low-temperature chamber, a medium-temperature chamber and a high-temperature chamber connected in sequence. The temperature range of the low-temperature chamber is 200℃-300℃, the temperature range of the medium-temperature chamber is 400℃-500℃, and the temperature range of the high-temperature chamber is 600℃-700℃.

[0029] The embodiments of the present invention significantly reduce the energy consumption of the pyrolysis process by employing staged pyrolysis technology, while also improving the yield and performance of biochar.

[0030] The sludge particles first enter the low-temperature chamber, where water evaporates and some volatile substances are released. Then, the sludge particles are conveyed into the medium-temperature chamber, where the temperature promotes the decomposition of organic matter, generating small-molecule gases and tar. Finally, the sludge particles enter the high-temperature chamber, where the function is to further stabilize the carbon framework structure and activate surface functional groups.

[0031] Furthermore, the low-temperature cavity, medium-temperature cavity, and high-temperature cavity are each equipped with a temperature control system. The temperature control system monitors the temperature inside the cavity in real time through thermocouples and automatically adjusts the heating power.

[0032] Furthermore, the material is conveyed through a conveyor belt within the pyrolysis furnace 4, and the residence time of the material in each chamber can be adjusted, thereby regulating the pore structure and surface properties of the biochar.

[0033] In some embodiments, the system for preparing biochar using sludge further includes a combustion chamber 5 having an air inlet and an exhaust outlet. The air inlet of the combustion chamber 5 is connected to the exhaust outlet of the pyrolysis furnace 4 to combust the pyrolysis gas discharged from the pyrolysis furnace 4.

[0034] In some embodiments, the low-temperature chamber, the intermediate-temperature chamber, and the high-temperature chamber are each connected to a heat exchanger. The inlet and outlet of the combustion chamber 5 are connected via a circulation pipeline, and the heat exchangers are connected to the circulation pipeline. The heat exchangers include a low-temperature chamber heat exchanger, an intermediate-temperature chamber heat exchanger, and a high-temperature chamber heat exchanger. The low-temperature chamber heat exchanger is located inside the low-temperature chamber, the intermediate-temperature chamber heat exchanger is located inside the intermediate-temperature chamber, and the high-temperature chamber heat exchanger is located inside the high-temperature chamber. The outlet of the combustion chamber 5 is sequentially connected to the high-temperature chamber heat exchanger, the intermediate-temperature chamber heat exchanger, and the low-temperature chamber heat exchanger to heat the high-temperature chamber, the intermediate-temperature chamber, and the low-temperature chamber in sequence. This allows for the full utilization of the heat from the pyrolysis gas to perform staged heating of the pyrolysis furnace 4, thereby reducing energy consumption.

[0035] Furthermore, the high-temperature cavity heat exchanger, the medium-temperature cavity heat exchanger, and the low-temperature cavity heat exchanger are each connected to a gas flow rate regulating device, which can regulate the gas flow rate and thus the temperature of each heat exchanger.

[0036] It should be noted that heating devices are installed in the high-temperature chamber, medium-temperature chamber, and low-temperature chamber, and heat exchangers provide supplementary heating, which can reduce the energy consumption of the heating devices and make full use of the heat of the pyrolysis gas.

[0037] In some embodiments, the system for preparing biochar from sludge further includes an exhaust gas treatment device 6, which is connected to the exhaust port of the low-temperature chamber heat exchanger. By providing the exhaust gas treatment device 6, the pyrolysis gas after heat exchange is purified to meet emission standards.

[0038] In some embodiments, the exhaust gas treatment device 6 includes a cyclone separator, a bag filter and an activated carbon adsorption tower. The cyclone separator has an air inlet, an exhaust outlet and an ash discharge outlet. The air inlet of the cyclone separator is connected to the exhaust outlet of the low-temperature chamber heat exchanger. The cyclone separator is used to remove larger particles in the exhaust gas. The ash discharge outlet of the cyclone separator is connected to an ash hopper. A bag filter dust collector has an air inlet and an air outlet. The air inlet of the bag filter dust collector is connected to the air outlet of the cyclone separator. The bag filter dust collector is used to remove smaller particles from the exhaust gas. The activated carbon adsorption tower has an air inlet and an exhaust outlet. The air inlet of the activated carbon adsorption tower is connected to the exhaust outlet of the bag filter. The activated carbon adsorption tower is used to adsorb harmful gases in the exhaust gas. The exhaust outlet of the activated carbon adsorption tower is connected to an exhaust stack to discharge the exhaust gas after adsorbing harmful gases.

[0039] Furthermore, the interior of a baghouse dust collector includes several filter bags.

[0040] In some embodiments, the discharge end of the vibrating screen 9 is connected to the feed end of the crusher 8 to return biochar particles larger than the standard particle size to the crusher 8 for further crushing.

[0041] In some embodiments, the discharge end of the drum dryer 2 is inclined downwards, which allows the material to move automatically toward the discharge end for easy discharge.

[0042] Furthermore, the drum dryer 2 includes an inclined rotating drum with guide plates inside to promote sludge agitation and uniform heating. A heating jacket is provided outside the rotating drum for heating it.

[0043] Another embodiment of the present invention provides a method for preparing biochar from sludge, which utilizes the above-described system for preparing biochar from sludge and includes the following steps: S1. The sludge is dewatered by dewatering device 1 to reduce the moisture content of the sludge to 40%-50%; S2. The dewatered sludge is transported to the drum dryer 2 for drying, so that the moisture content of the sludge is reduced to 10%-15%; S3. The dried sludge is transported to the spiral granulator 3 for granulation to form sludge particles; S4. The sludge particles are transported to pyrolysis furnace 4 for staged pyrolysis to obtain biochar particles. S5. The biochar granules are conveyed to the cooling device 7 for cooling. S6. The cooled biochar granules are conveyed to the crusher 8 for crushing, and the crushed material is screened by the vibrating screen 9 to separate biochar granules of different particle sizes.

[0044] In the method of this invention, sludge is used as the sole raw material, without the need for any auxiliary components. The method of this invention, through staged pyrolysis technology, significantly reduces energy consumption in the pyrolysis process while improving the yield and performance of biochar. Furthermore, the pyrolysis gas generated during the pyrolysis process is effectively recovered and utilized, forming an energy closed loop and further saving energy costs.

[0045] The method described in this invention not only solves the problems of sewage sludge discharge and disposal in urban areas, but also transforms the sludge into biochar materials with multiple uses, realizing the resource utilization of sludge. Biochar materials possess abundant porous structures and active surface functional groups, and can be widely used in soil improvement, solid waste disposal, heavy metal adsorption, and other fields, expanding the application scenarios of sludge resource utilization. The operation process is simple and suitable for large-scale promotion.

[0046] Compared with existing ultrasonic sludge breaking technology and hydrothermal carbonization technology, the method of this invention does not require complex chemical reagents or high-pressure equipment, thus reducing operating costs and technical barriers. Furthermore, this method generates no secondary pollution throughout the entire process, meeting environmental protection requirements and providing a feasible solution for the long-term development of sludge treatment.

[0047] The present invention will be further illustrated by specific embodiments below.

[0048] Example 1 In a real-world scenario of sludge resource utilization, a city's wastewater treatment plant generates 10 tons of domestic sewage sludge with a moisture content of 80% daily. After processing by this system, approximately 1.1 tons of biochar can be obtained.

[0049] First, the sludge is transported from the wastewater treatment plant to a mechanical extrusion dewatering unit. After entering the unit, the sludge is squeezed out by the pressing action of the pressing chamber, and the water is discharged through the drainage pipe. At this point, the sludge's moisture content drops from 80% to 40%-50%. The pre-dewatered sludge is then conveyed to a drum dryer 2, where the moisture content is further reduced to 10%-15%. Next, the dried sludge particles are directly conveyed to a screw granulator 3. The screw granulator 3 compresses the sludge particles, forming a dense granular structure. The discharge screen at the outlet of the screw granulator 3 ensures that the diameter of the final granulated sludge particles remains stable within the range of 7-10 mm.

[0050] The granulated sludge particles are conveyed into a stepped pyrolysis furnace via a conveyor belt. The sludge particles first enter the low-temperature zone, where, within a temperature range of 200℃-300℃, moisture evaporates and some volatile substances are released. Subsequently, the sludge particles enter the medium-temperature zone via a conveyor belt, where, in an environment of 400℃-500℃, organic matter undergoes decomposition, generating small-molecule gases and tar. Finally, the sludge particles enter the high-temperature zone, where, under conditions of 600℃-700℃, the carbon skeleton structure is further stabilized, and surface functional groups are activated. This segmented pyrolysis method significantly reduces energy consumption while improving the yield and performance of biochar. Furthermore, the pyrolysis gas generated during the pyrolysis process is collected through pipelines and reused in combustion chamber 5. The high-temperature gas obtained from combustion in combustion chamber 5 is sequentially transported to the high-temperature chamber, medium-temperature chamber, and low-temperature chamber, maintaining the temperatures of these chambers and forming an energy closed loop.

[0051] After pyrolysis, the biochar particles are discharged from the outlet of the stepped pyrolysis furnace and enter the cooling device 7. After treatment by the cooling device 7, the temperature of the biochar particles drops to below 50℃, facilitating subsequent crushing and screening operations. The cooled biochar particles are then conveyed to a hammer crusher for crushing. The screen plate at the discharge port of the hammer crusher can be adjusted or replaced with the required aperture, controlling the particle size of the crushed biochar particles to be below 8 mm.

[0052] The crushed biochar particles are conveyed to a vibrating screen 9 for sieving. The vibrating screen 9 employs a multi-layer screen structure, comprising a first screen, a second screen, and a third screen arranged vertically. The first screen is located at the top layer with an 8 mm aperture, the second screen is located in the middle layer with a 5 mm aperture, and the third screen is located at the bottom layer with a 2 mm aperture. A vibrating motor drives each screen in reciprocating motion, causing the biochar particles to be sorted step-by-step on the screens. Powder with a particle size smaller than 2 mm is collected through the bottom third screen and can be used to prepare composite materials or as a filler. Biochar particles with a particle size between 2 and 5 mm are collected through the middle second screen, biochar particles with a particle size between 5 and 8 mm are collected through the top first screen, and particles larger than 8 mm are discharged from the discharge end of the vibrating screen 9 and re-feeded to the crusher 8 for secondary crushing. This sieving process ensures that the particle size distribution of the biochar particles meets the needs of different application fields.

[0053] After heat exchange, the pyrolysis gas is introduced into the exhaust gas treatment device 6 by an induced draft fan for purification. The exhaust gas treatment device 6 includes a cyclone separator, a bag filter, and an activated carbon adsorption tower. The inlet of the cyclone separator is connected to the exhaust port of the low-temperature chamber heat exchanger. The cyclone separator removes larger particles from the exhaust gas, and its ash discharge port is connected to an ash hopper. The inlet of the bag filter is connected to the exhaust port of the cyclone separator. The bag filter removes smaller particles from the exhaust gas. The inlet of the activated carbon adsorption tower is connected to the exhaust port of the bag filter. The activated carbon adsorption tower is filled with activated carbon particles, which remove harmful gases from the exhaust gas through adsorption. After purification by the exhaust gas treatment device 6, the exhaust gas meets emission standards and is discharged into the atmosphere through an exhaust stack. This exhaust gas treatment process design ensures the environmental friendliness of the system during operation.

[0054] Through the above steps, this system achieves efficient resource utilization of sludge. The final biochar product can be used for soil improvement, and when applied to farmland, it can improve soil water retention and fertility; it can also be used for solid waste disposal and heavy metal adsorption, for example, as an adsorbent to remove heavy metal ions in industrial wastewater treatment. The implementation of this system not only solves the problems of sludge discharge and storage but also achieves resource utilization of sludge, while reducing energy consumption and operating costs.

[0055] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0056] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0059] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A system for preparing biochar using sludge, characterized in that, include: A dewatering device, used to initially remove moisture from sludge; A drum dryer, wherein the feed end of the drum dryer is connected to the discharge end of the dewatering device, and the drum dryer is used to dry sludge that has been preliminarily dewatered; A spiral granulator, wherein the feed end of the spiral granulator is connected to the discharge end of the drum dryer, and the spiral granulator is used to form sludge particles from dried sludge. The pyrolysis furnace is connected to the discharge end of the spiral granulator. The pyrolysis furnace is a stepped pyrolysis furnace used to perform stepped pyrolysis of sludge particles to form biochar particles. A cooling device, the feed end of which is connected to the discharge end of the pyrolysis furnace, is used to cool the biochar particles; A crusher, wherein the feed end of the crusher is connected to the discharge end of the cooling device, and the crusher is used to crush biochar particles; A vibrating screen, the feed end of which is connected to the discharge end of the crusher, is used to screen the crushed biochar particles.

2. The system for preparing biochar from sludge according to claim 1, characterized in that, The discharge screen is connected to the discharge port of the spiral granulator.

3. The system for preparing biochar from sludge according to claim 1, characterized in that, The pyrolysis furnace has a low-temperature chamber, a medium-temperature chamber and a high-temperature chamber connected in sequence. The temperature range of the low-temperature chamber is 200℃-300℃, the temperature range of the medium-temperature chamber is 400℃-500℃, and the temperature range of the high-temperature chamber is 600℃-700℃.

4. The system for preparing biochar from sludge according to claim 3, characterized in that, It also includes a combustion chamber having an air inlet and an exhaust outlet, wherein the air inlet of the combustion chamber is connected to the exhaust outlet of the pyrolysis furnace to burn the pyrolysis gas discharged from the pyrolysis furnace.

5. The system for preparing biochar from sludge according to claim 4, characterized in that, The low-temperature chamber, the medium-temperature chamber, and the high-temperature chamber are each connected to a heat exchanger. The air inlet and exhaust outlet of the combustion chamber are connected through a circulation pipeline. The heat exchanger is connected to the circulation pipeline. The heat exchanger includes a low-temperature chamber heat exchanger, a medium-temperature chamber heat exchanger, and a high-temperature chamber heat exchanger. The low-temperature chamber heat exchanger is located inside the low-temperature chamber, the medium-temperature chamber heat exchanger is located inside the medium-temperature chamber, and the high-temperature chamber heat exchanger is located inside the high-temperature chamber. The exhaust outlet of the combustion chamber is sequentially connected to the high-temperature chamber heat exchanger, the medium-temperature chamber heat exchanger, and the low-temperature chamber heat exchanger to heat the high-temperature chamber, the medium-temperature chamber, and the low-temperature chamber in sequence.

6. The system for preparing biochar from sludge according to claim 4, characterized in that, It also includes an exhaust gas treatment device, which is connected to the exhaust port of the low-temperature chamber heat exchanger.

7. The system for preparing biochar from sludge according to claim 6, characterized in that, The exhaust gas treatment device includes a cyclone separator, a bag filter, and an activated carbon adsorption tower. The cyclone separator has an air inlet, an exhaust outlet, and an ash discharge outlet. The air inlet of the cyclone separator is connected to the exhaust outlet of the low-temperature chamber heat exchanger. The cyclone separator is used to remove larger particles from the exhaust gas. The ash discharge outlet of the cyclone separator is connected to an ash hopper. The bag filter has an air inlet and an exhaust outlet. The air inlet of the bag filter is connected to the exhaust outlet of the cyclone separator. The bag filter is used to remove smaller particles from the exhaust gas. The activated carbon adsorption tower has an air inlet and an exhaust outlet. The air inlet of the activated carbon adsorption tower is connected to the exhaust outlet of the bag filter. The activated carbon adsorption tower is used to adsorb harmful gases in the exhaust gas. The exhaust outlet of the activated carbon adsorption tower is connected to an exhaust stack to discharge the exhaust gas after adsorbing harmful gases.

8. The system for preparing biochar from sludge according to claim 1, characterized in that, The discharge end of the vibrating screen is connected to the feed end of the crusher so that biochar particles larger than the standard particle size can be returned to the crusher for further crushing.

9. The system for preparing biochar from sludge according to claim 1, characterized in that, The discharge end of the drum dryer is inclined downwards on one side.

10. A method for preparing biochar using sludge, characterized in that, The system for preparing biochar from sludge according to any one of claims 1-9 comprises the following steps: S1. The sludge is dewatered using a dewatering device to reduce its moisture content to 40%-50%. S2. The dewatered sludge is transported to a drum dryer for drying, reducing the moisture content of the sludge to 10%-15%. S3. The dried sludge is transported to a spiral granulator for granulation to form sludge particles. S4. The sludge particles are transported to a pyrolysis furnace for staged pyrolysis to obtain biochar particles. S5. The biochar granules are conveyed to a cooling device for cooling. S6. The cooled biochar granules are conveyed to the crusher for crushing, and the crushed material is screened by a vibrating screen to separate biochar granules of different particle sizes.

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