A process system for preparing biochar by pyrolysis and carbonization of agricultural waste rape straw

Abstract

The application relates to the field of solid waste treatment, and discloses a process system for preparing biochar by pyrolysis and carbonization of agricultural waste rape straw, which comprises a pretreatment unit, a staged pyrolysis and carbonization unit, a gas-solid separation unit, an activation and modification unit and a carbon storage unit connected in sequence, the pretreatment unit pretreats the rape straw through drying, crushing and steam explosion; the staged pyrolysis and carbonization unit divides the inner cavity of a multistage pyrolysis reactor into an upper constant temperature zone and a lower temperature rising zone through a separation ring, so that pyrolysis gas distribution and gradient circulation are realized; the gas-solid separation unit separates pyrolysis gas through a cyclone separator and a bag-type dust collector; the activation and modification unit performs phosphorus modification through a phosphoric acid impregnation and a co-pyrolysis reactor; and the carbon storage unit cools, grades and quality detects the product, the application can realize pyrolysis gas distribution and gradient circulation utilization, improve system thermal energy utilization rate, increase the cation exchange capacity of modified biochar to 77-80 cmol / kg, effectively improve the carbon yield, stabilize the product quality, realize the full-process continuous production from raw material pretreatment to finished product output, and the like.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically a process system for preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks. Background Technology

[0002] The pyrolysis and carbonization of rapeseed stalks to prepare biochar is an important technological approach for realizing the high-value utilization of agricultural waste, carbon sequestration and emission reduction, and soil improvement. This technology converts rapeseed stalks into biochar rich in fixed carbon by pyrolysis under anaerobic conditions through a stepped heating process, while simultaneously producing combustible gas as the system's energy source. In the entire pyrolysis and carbonization process system, the pretreated rapeseed stalk material enters the staged pyrolysis and carbonization unit, and is then transported to the multi-stage pyrolyzer via a segmented feeder. After completing the pyrolysis reaction in the heating zone, the carbonization process is completed in the isothermal zone. Finally, high-quality biochar is obtained through gas-solid separation and activation modification. In this process, the multi-stage pyrolyzer is the core device for realizing staged pyrolysis, and its structural design directly determines the system's pyrolysis efficiency, char product quality, and the level of stepped utilization of pyrolysis gas distribution.

[0003] However, in existing technologies, multi-stage pyrolyzers still employ a single reaction chamber design, with the heating zone and the isothermal zone functionally coupled within the same space. Their airflow and temperature fields interfere with each other, making it difficult to achieve cascaded recycling of the pyrolysis gas distribution. The pyrolysis gas generated in the heating zone is directly discharged, lacking a heat and mass exchange mechanism with the isothermal zone. Similarly, the activation exhaust gas cannot enter the gas distribution system to participate in the cascaded recycling, resulting in low pyrolysis gas distribution efficiency and a system thermal energy utilization rate of less than 40%. Furthermore, because the heating and isothermal zones share the same space, the temperature field distribution is uneven, and the pyrolysis process lacks precise control methods. The large fluctuation range of the heating rate and the significant temperature deviation in the isothermal zone make it difficult to guarantee the consistency of the pyrolysis reaction process. This structural defect further restricts the stability of char yield and product quality. The char yield is usually only 25% to 30%, and the fixed carbon content of the product fluctuates by more than 15%, which cannot meet the needs of large-scale production of high-quality biochar. The limitations of the existing pyrolyzer structure have become the core bottleneck restricting the overall performance improvement of the pyrolysis carbonization process system. It is urgent to achieve effective separation of the heating zone and the isothermal zone and the cascade utilization of pyrolysis gas through structural innovation in order to break through the technical bottlenecks of pyrolysis efficiency and product quality stability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a process system for preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks. This system solves the problems of low pyrolysis efficiency of rapeseed stalks, large fluctuations in char yield and fixed carbon content, insufficient product quality stability, high activation and modification costs, and difficulty in achieving continuous production.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a process system for preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks, the system comprising a pretreatment unit, a staged pyrolysis and carbonization unit, a gas-solid separation unit, an activation and modification unit, and a biochar storage unit connected sequentially along the material flow direction; The staged pyrolysis carbonization unit includes a multi-stage pyrolyzer, and a partition ring is provided inside the multi-stage pyrolyzer. The partition ring divides the inner cavity of the multi-stage pyrolyzer into a lower heating zone and an upper constant temperature zone. The partition ring is provided with a vent for the pyrolysis gas to pass through. The multi-stage pyrolyzer is provided with a gas distribution channel that communicates with the heating zone; The activated exhaust gas generated by the activation and modification unit is channeled into the gas distribution channel through a pipeline to achieve a stepped circulation of pyrolysis gas and activated exhaust gas.

[0006] The multi-stage pyrolyzer includes an outer cylinder, an inner cylinder, and a partition ring. A first annular airflow channel is formed between the outer and inner cylinders. A pyrolysis reaction chamber is formed inside the inner cylinder, and a main air inlet is provided at the bottom. The partition ring is located between the outer and inner cylinders, dividing the pyrolysis reaction chamber into an upper constant-temperature zone and a lower heating zone. The partition ring is fixed to the outer cylinder by bolts and sealed with a graphite gasket. The main air inlet is connected to the bottom of the segmented feeder through a first gas distribution channel, which is equipped with a gas flow meter and an oxygen concentration detector. Several vent holes are provided on the partition ring. The vent holes adopt a trapezoidal hole design, with the larger end facing upwards and the smaller end facing downwards. During operation, the heating rate of the lower heating zone is 10°C per minute, the pyrolysis temperature is controlled at 500°C, the holding time is 30 minutes, and the temperature deviation of the upper constant-temperature zone is controlled within ±5°C.

[0007] Preferably, in the pretreatment unit, the dryer adopts a belt dryer structure, the hot air temperature is controlled at 80 to 120℃, the hot air speed is controlled at 2 to 3 m / s, the conveyor belt is a stainless steel mesh belt with a width of 1.2m and a length of 10m, and the drying capacity is 500kg / h; the steam explosion tank has an explosion pressure of 2.5MPa, an explosion temperature of 210℃, an explosion holding time of 2 minutes, a volume of 3m³, a processing capacity of 100 to 150kg per batch, a tank body material of wear-resistant alloy steel, and a metal spiral wound gasket is used to connect the pressure relief valve to the tank body.

[0008] Preferably, in the staged pyrolysis carbonization unit, the segmented feeder adopts a double-helix propulsion structure. The inner helix is ​​used to transport materials, and the outer helix is ​​used to form a sealed gas seal to prevent pyrolysis gas from leaking out. The feeding speed is 5 to 15 kg / h, and the helical blades are made of wear-resistant alloy material with a surface hardness of HRC60 or higher. The number and arrangement of the vent holes are optimized through computational fluid dynamics simulation to ensure the best gas-solid countercurrent contact effect. The temperature control system uses a proportional-integral-differential algorithm for closed-loop control, and thermocouple arrays are arranged in multiple positions in the reaction chamber to achieve accurate temperature measurement.

[0009] Preferably, in the multi-stage pyrolyzer, the large end of the vent hole on the partition ring faces upward to allow the rising pyrolysis gas to pass smoothly, and the small end faces downward to prevent material blockage; the inlet of the first gas distribution channel is connected to the outlet of the multi-stage pyrolyzer and the activation and modification unit respectively, and is used to collect pyrolysis gas and activation tail gas to obtain pyrolysis gas distribution, so as to realize the cascade recycling of pyrolysis gas distribution.

[0010] Preferably, the chemical activation tank includes a tank body, an impregnation and stirring assembly, and a liquid-solid separation assembly. The tank body is lined with a corrosion-resistant inner lining made of polytetrafluoroethylene (PTFE). The impregnation and stirring assembly includes a stirring shaft and spiral blades. The stirring shaft is driven by a motor with a power of 2.2 kW and an adjustable speed range of 30 to 120 rpm. The spiral blades are made of stainless steel, and the blade angle is optimized to ensure thorough turbulent mixing of the phosphoric acid solution and rapeseed stalks and maintain a reaction temperature of 60 to 80°C. The tank body is equipped with a jacketed heating system using heat transfer oil as the heating medium. The liquid-solid separation assembly is located at the bottom of the tank and includes a filter plate and a filter press mechanism. The filter plate is made of ceramic with a pore size of 0.1 to 0.2 mm, used to separate excess phosphoric acid solution and send the separated phosphoric acid solution to a phosphoric acid storage tank for recycling via a phosphoric acid recovery pump. After impregnation, the moisture content of the material is controlled at 60% to 70%, and it is sent to a drying zone at 60 to 80°C to dry until the moisture content is below 15%. The drying zone uses a fluidized bed drying method.

[0011] Preferably, the co-pyrolysis reactor includes a reaction cylinder, a phosphate feeding mechanism, and a temperature control system. A second air inlet is provided at the bottom of the reaction cylinder for introducing nitrogen to form a protective atmosphere. The nitrogen purity is not less than 99.99%, and the flow rate is precisely controlled by a mass flow meter. The phosphate feeding mechanism is located on the side wall of the reaction cylinder and includes a salt storage bin and a metering auger. The salt storage bin has a capacity of 50 liters, a moisture-proof cover and a desiccant pack at the top, and an arch-breaking device at the bottom. The metering auger is driven by a servo motor with a speed accuracy of up to [insert accuracy here]. With a speed of ±0.1 revolutions per minute, precise phosphate addition can be achieved, with the addition error controlled within ±2%. The temperature control system includes a circumferentially arranged electric heating element and a thermocouple array. The electric heating element is made of silicon carbide rod and is distributed in the circumference and axial direction of the reaction cylinder, with a total power of 50 kW. The thermocouple array uses K-type thermocouples and has a total of 5 temperature measuring points, distributed at different heights in the reaction zone, to accurately control the reaction temperature within the range of 300 to 600℃ and maintain it for 80 minutes of co-pyrolysis time. The temperature control accuracy can reach ±2℃.

[0012] Preferably, the activation and modification unit further includes an alkali modification component, which includes an alkali preparation tank and an alkali spraying device. The alkali preparation tank is used to prepare a 2 mol / L sodium hydroxide solution and maintain it at 100°C for 12 hours to introduce acidic oxygen-containing functional groups. The preparation tank has an enamel liner, a volume of 500 liters, and is heated by steam with a steam pressure controlled at 0.3 to 0.5 MPa. A frame stirrer is used for stirring at a speed of 20 to 50 revolutions per minute. The alkali spraying device is located at the top of the cooling chamber and includes a spray pipe and an atomizing nozzle. The spray pipe is made of stainless steel and is evenly arranged along the cross-section of the cooling chamber. The atomizing nozzle is an ultrasonic atomizing nozzle with an atomization particle size of 10 to 50 μm, which can make the alkali solution evenly cover the surface of the biochar. The alkali spraying volume is precisely controlled by a metering pump. After treatment, the biochar is washed with water until neutral and dried. The water washing adopts a multi-stage countercurrent washing method.

[0013] Preferably, the biochar storage unit further includes a quality testing component and a packaging component. The quality testing component includes an elemental analyzer, a BET surface area analyzer, and a pH meter, used to detect the fixed carbon content, carbon mass fraction, nitrogen mass fraction, potassium mass fraction, pH value, and cation exchange capacity of the biochar sample. The elemental analyzer uses infrared detection principle with a detection accuracy of up to 0.01%. The BET surface area analyzer uses nitrogen adsorption method with a surface area detection range of 0.5 to 2000 m² per gram. The pH meter uses glass electrode method with a measurement accuracy of ±0.01 pH. The packaging component is located at the outlet of the biochar storage chamber and is sealed using a vacuum packaging machine with a vacuum degree of up to -0.09 MPa. The packaging material is a nylon-polyethylene composite film.

[0014] Preferably, in the gas-solid separation unit, the cyclone separator cylinder is made of wear-resistant stainless steel, and the inner wall is lined with wear-resistant material to prevent wear on the cylinder by high-speed particulate airflow, achieving a separation efficiency of over 95%; the bag filter has a filtration accuracy of 1 to 10 μm, uses pulse cleaning, and the cleaning frequency is automatically adjusted according to the dust concentration, achieving a total separation efficiency of over 99.5%; the clean pyrolysis gas is sent to the subsequent processing system, and the solid particles are returned to the multi-stage pyrolyzer for secondary pyrolysis through the return pipe.

[0015] Preferably, the charcoal storage bin is used to store graded biochar and to label it according to a fixed carbon content greater than 45% and a carbon element mass fraction greater than 53%. The charcoal storage bin is equipped with multiple layers of partitions, each partition corresponding to a grade area, and automatic classification and storage are achieved through a material level sensor. The grading screen is connected to a vibrating feeder, and the vibration frequency is adjustable to achieve effective grading of biochar particles of different sizes. The grading particle size is set to four grades: less than 1 mm, 1 to 3 mm, 3 to 5 mm, and greater than 5 mm.

[0016] This invention provides a process system for preparing biochar by pyrolysis and carbonization of agricultural waste, rapeseed stalks. It has the following beneficial effects: 1. This invention pretreats rapeseed stalks by setting up a steam explosion tank. The stalks are steam-exploded for 2 minutes at 210℃ and 2.5MPA to destroy the fiber structure. The depressurization process after the explosion is controlled within 3 to 5 seconds, so that the material fibers are fully torn during the rapid depressurization process. The specific surface area of ​​the pretreated material can be increased by more than 50%, which effectively solves the technical problem of low pyrolysis efficiency caused by the dense fiber structure of rapeseed stalks, and creates favorable conditions for subsequent pyrolysis and carbonization.

[0017] 2. This invention divides the pyrolysis reaction chamber into an upper constant temperature zone and a lower heating zone by setting a partition ring inside the multi-stage pyrolyzer. It also connects to the bottom of the segmented feeder through the first gas distribution channel to achieve the oxygen-limited gas distribution required for segmented pyrolysis. At the same time, it collects the activated tail gas to participate in the cascade recycling, which greatly improves the pyrolysis gas distribution efficiency and the system thermal energy utilization rate. This solves the technical bottleneck of existing technologies where it is difficult to achieve cascade recycling of pyrolysis gas distribution and the system thermal energy utilization rate is less than 40%.

[0018] 3. This invention features trapezoidal ventilation holes on the separator ring, with the larger end facing upwards to facilitate the smooth passage of pyrolysis gas and the smaller end facing downwards to prevent material blockage. Combined with proportional-integral-differential algorithm closed-loop control and multi-position thermocouple array temperature measurement, the heating rate of the lower heating zone is controlled at 10℃ per minute, and the temperature deviation of the upper constant temperature zone is controlled within ±5℃. This effectively ensures the consistency of the pyrolysis reaction process and significantly improves the stability of product quality.

[0019] 4. This invention uses a chemical activation tank for phosphoric acid solution impregnation, followed by co-pyrolysis in a co-pyrolysis reactor with calcium dihydrogen phosphate monohydrate or potassium dihydrogen phosphate added at a mass ratio of 5:1 to obtain phosphorus-modified biochar. Simultaneously, acidic oxygen-containing functional groups are introduced through an alkaline modification component, enabling the modified biochar to achieve a cation exchange capacity of 77 to 80 cmol / kg, which is more than 30% higher than that of unmodified biochar, effectively improving the soil amendment performance and environmental protection application value of the product.

[0020] 5. This invention achieves gas-solid separation by setting up a cyclone separator and a bag filter. The solid particles are sent back to a multi-stage pyrolyzer for secondary pyrolysis, which can further increase the char yield by about 2% to 3%. At the same time, the built-in water-cooled jacket structure of the cooling chamber enables rapid cooling to prevent over-carbonization, with a cooling rate of 50 to 100°C per minute. The particles are classified by a grading sieve and tested by a quality detection component. Qualified products are sent to the char storage silo for automatic classification and storage. This realizes continuous production throughout the entire process from raw material pretreatment to finished product output, effectively improving the char yield and stabilizing product quality. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall system architecture of the present invention; Figure 2 This is a schematic diagram of the core principle framework of the staged pyrolysis carbonization unit of the present invention; Figure 3 This is a schematic diagram of the structural framework of the pretreatment unit and the gas-solid separation unit of the present invention; Figure 4 This is a schematic diagram illustrating the interaction and data flow between the activation modification unit and the carbon storage unit of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example: Please see the appendix Figure 1 -Appendix Figure 4This invention provides a process system for preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks. This embodiment is specifically applied to the process scenario of preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks. The process scenario deploys a complete process system. The system as a whole includes five core functional modules along the material flow direction: a pretreatment unit, a staged pyrolysis and carbonization unit, a gas-solid separation unit, an activation and modification unit, and a char storage unit. When the system is running, the central controller acts as the coordinating core of the entire process system. It collects the process parameter data of each unit in real time through a sensor network and generates adjustment commands according to the preset control strategy to realize continuous production from rapeseed stalk raw material to finished biochar product.

[0024] The pretreatment unit is located at the front end of the system. It receives the rapeseed stalk raw material to be processed and performs drying, crushing, and steam explosion pretreatment. The core components of the pretreatment unit include three devices arranged in series: a dryer, a crusher, and a steam explosion tank. The dryer adopts a belt dryer structure with a stainless steel mesh belt conveyor inside. The mesh belt is designed to be 1.2m wide and 10m long, with a drying capacity of 500kg / h. The dryer's hot air generator produces hot air with a temperature controlled between 80 and 120℃ and a speed controlled between 2 and 3m / s. The rapeseed stalk raw material is evenly spread on the stainless steel mesh belt through the feed hopper and is dried under the counter-current flow of hot air. After the moisture content is reduced to below 15%, it is conveyed to the crusher by the first conveyor belt. The inlet of the crusher is connected to the end of the first conveyor belt. The crusher is equipped with a high-speed rotating blade assembly and a fixed screen. The blades cut and crush the dried rapeseed stalks to a particle size of 20 to 100 mesh. The crushed rapeseed stalk powder is then conveyed to the steam explosion tank by the second conveyor belt. The steam explosion rupture tank is made of wear-resistant alloy steel with a volume of 3m³. Each processing volume is controlled within the range of 100-150kg. The tank is equipped with a steam heating jacket and a pressure sensor. The sealing connection between the tank and the pressure relief valve uses a metal spiral wound gasket structure. A safety valve and a pressure regulating valve are located on the top of the steam explosion rupture tank. The opening of the pressure regulating valve can be precisely adjusted by the control system to achieve precise control of the pressure relief rate. During operation, the steam explosion rupture tank first raises the internal temperature to 210℃ through the steam heating jacket. Simultaneously, the pressure sensor monitors the internal pressure in real time. When the pressure reaches 2.5MPa, it enters the pressure holding stage, which is maintained for 2 minutes. After the pressure holding period, the control system drives the pressure regulating valve to open rapidly, completing the pressure relief process within 3-5 seconds. The enormous energy carried by the high-pressure steam inside the tank is released instantaneously, causing the material fibers to be thoroughly torn during the rapid pressure reduction. After the steam explosion pretreatment is completed, the pretreated material is discharged through the pressure relief valve and falls into the buffer silo below, awaiting the next process.

[0025] The staged pyrolysis and carbonization unit is the core functional module of this invention, used to complete the staged pyrolysis and carbonization reaction of rapeseed stalks. The core components of the staged pyrolysis and carbonization unit include a segmented feeder and a multi-stage pyrolyzer. The segmented feeder is located above the feed inlet of the multi-stage pyrolyzer. The feeding speed of the segmented feeder is designed to be 5 to 15 kg / h. The segmented feeder adopts a double-helix propulsion structure. The inner helical shaft is arranged along the feeding direction. The helical blades are made of wear-resistant alloy material with a surface hardness of HRC60 or higher. The inner helix is ​​used to push the rapeseed stalk powder material forward. The outer helical shaft is sleeved on the outer circumference of the inner helical shaft. The pitch and direction of rotation of the outer helix are specially designed to form a reverse airflow in the feeding channel when rotating. A sealed gas seal effectively prevents the high-temperature pyrolysis gas inside the multi-stage pyrolyzer from leaking outwards along the feed channel. The bottom outlet of the segmented feeder is connected to the top inlet of the multi-stage pyrolyzer via a feed pipe made of high-temperature resistant stainless steel, with an insulation layer on the outer wall to reduce heat loss. The multi-stage pyrolyzer is the core device for achieving segmented pyrolysis. The overall structure of the multi-stage pyrolyzer includes three main components: an outer cylinder, an inner cylinder, and a partition ring. The outer cylinder is made of high-temperature resistant alloy steel, and electric heating elements and temperature sensors are installed on the outer wall to provide the heat required for the pyrolysis reaction and monitor the cylinder wall temperature in real time. The inner cylinder is coaxially arranged inside the outer cylinder, forming a first annular airflow channel between the inner and outer cylinders. The inner cylinder forms a pyrolysis reaction chamber. A main air inlet is located at the bottom of the inner cylinder, connected to the bottom of the segmented feeder via a first gas distribution channel. The main air inlet is used to introduce an oxygen-limiting atmosphere. A gas flow meter and an oxygen concentration detector are installed on the first gas distribution channel. The gas flow meter monitors the volumetric flow rate of the introduced gas in real time, and the oxygen concentration detector monitors the oxygen content in the gas distribution in real time, ensuring that the pyrolysis process takes place under oxygen-deficient conditions. A partition ring is located between the outer and inner cylinders, and is fixed to them by bolts. A graphite gasket is used to seal the connection. The partition ring divides the pyrolysis reaction chamber axially into two functional areas: an upper isothermal zone and a lower heating zone. The partition ring is equipped with… The device is equipped with several vents, which are trapezoidal in shape with the larger end facing upwards and the smaller end facing downwards. The diameter of the larger end is larger than that of the smaller end. This trapezoidal design allows the pyrolysis gas rising from the heating zone to smoothly enter the constant temperature zone, while preventing solid materials above from clogging the vents. The number and arrangement of the vents have been optimized through computational fluid dynamics simulation to ensure that the temperature and airflow distribution in the separation ring region achieve the best gas-solid countercurrent contact effect between the pyrolysis gas and the solid materials. When the multi-stage pyrolyzer is working, the heating rate of the lower heating zone is controlled at 10℃ per minute, the pyrolysis temperature is controlled at 500℃, and the holding time is 30 minutes. The temperature deviation of the upper constant temperature zone is controlled within ±5℃.

[0026] The gas-solid separation unit is located at the rear end of the staged pyrolysis carbonization unit. It separates solid particles from the pyrolysis gas to obtain clean pyrolysis gas. The core components of the gas-solid separation unit include a cyclone separator and a bag filter. The cyclone separator's cylinder is made of wear-resistant stainless steel, and the inner wall is lined with a wear-resistant lining to prevent wear from the high-speed particulate airflow. The inlet of the cyclone separator is connected to the hot gas outlet of the multi-stage pyrolysis unit via a hot gas duct. The hot gas duct is insulated to prevent condensation caused by temperature drop during transport. After the pyrolysis gas carrying solid particles enters the cyclone separator, the solid particles are thrown against the cylinder wall by centrifugal force and spiral down the cylinder wall to the dust collection hopper at the bottom. The clean pyrolysis gas is discharged from the top outlet. The separation efficiency of the cyclone separator is [not specified]. With a filtration efficiency exceeding 95%, the bag filter's inlet is connected to the solid outlet of the cyclone separator via a dust conveying pipe. The bag filter's filtration accuracy is designed to be 1 to 10 μm. Several filter bags are installed inside the bag filter, and the accumulated dust is periodically removed using a pulse cleaning method. The cleaning frequency of the bag filter is automatically adjusted based on the dust concentration sensor signal; the cleaning frequency increases when the dust concentration increases and decreases when the dust concentration decreases. The overall separation efficiency of the bag filter can reach over 99.5%. The clean pyrolysis gas, after two stages of gas-solid separation, is sent to the subsequent processing system. The solid particles separated by the cyclone separator and bag filter are transported through a return pipe to a multi-stage pyrolyzer for secondary pyrolysis. Secondary pyrolysis can further increase the carbon yield by approximately 2% to 3%.

[0027] The activation and modification unit is located at the rear end of the gas-solid separation unit. It is used to chemically activate and modify the pyrolysis products to improve product quality. The core components of the activation and modification unit include a chemical activation tank, a co-pyrolysis reactor, and an alkali modification component. The chemical activation tank has a corrosion-resistant lining made of polytetrafluoroethylene (PTFE), which effectively resists the corrosion of phosphoric acid solution. The impregnation feed pipe of the chemical activation tank is connected to the storage silo of the pretreatment unit to receive rapeseed stalk material after steam explosion pretreatment. A jacketed heating system is installed outside the tank, with heat transfer oil circulating in the jacket as the heating medium. The heating power of the thermal system is adjusted in stages via electric heating elements. The chemical activation tank is equipped with an impregnation and stirring assembly, which includes a stirring shaft and spiral blades. The stirring shaft is driven by a 2.2 kW motor with an adjustable speed range of 30 to 120 rpm. The spiral blades are made of stainless steel, and their angles are optimized to create a thorough turbulent mixing effect. During the impregnation process, a 10% to 40% concentration phosphoric acid solution is added to the chemical activation tank along with rapeseed stalks at a liquid-to-solid ratio of 3:1. The control system maintains the tank temperature between 60 and 80°C, and the impregnation and stirring time is 30 to 60 seconds. After impregnation for several minutes, a liquid-solid separation assembly is installed at the bottom of the tank. This assembly includes a filter plate and a pressure filter mechanism. The filter plate is made of ceramic material with a pore size of 0.1 to 0.2 mm, used to separate excess phosphoric acid solution. The separated phosphoric acid solution is then sent to a phosphoric acid storage tank for recycling via a phosphoric acid recovery pump. The moisture content of the material after impregnation is controlled at 60% to 70%, and it is then sent to a fluidized bed drying zone for gradient drying. The hot air temperature in the fluidized bed drying zone is controlled at 60 to 80°C. After drying until the moisture content of the material is below 15%, it proceeds to the next process. The chemical activation tank is also connected to a multi-stage pyrolyzer via pipeline. The activated tail gas generated by the chemical activation tank is transported to the first gas distribution channel of the multi-stage pyrolyzer through the tail gas pipeline. After mixing with the gas introduced into the main air inlet, it participates in the cascade recycling of pyrolysis gas distribution. The introduction of activated tail gas has a dual synergistic effect: on the one hand, the sensible heat carried by the tail gas is used to preheat the ambient temperature gas distribution at the main air inlet, effectively reducing the initial heating energy consumption of the multi-stage pyrolyzer; on the other hand, the high-temperature water vapor rich in the tail gas can act as a weak activator in the pyrolysis reactor, participating in the in-situ pore-forming and micro-pore-expanding reaction on the surface of biochar, thereby improving the system's thermal energy utilization rate while further improving the pore structure of biochar.

[0028] The co-pyrolysis reactor is located at the rear end of the chemical activation tank. It receives the material after phosphate impregnation and drying, and adds phosphate in a specific ratio for co-pyrolysis. The reactor's internal chamber contains a phosphate addition assembly, including a salt storage bin and a metering auger. The salt storage bin, with a capacity of 50 liters, is located above the side wall of the reactor chamber. It is equipped with a moisture-proof cover and desiccant pack at the top to prevent phosphate from absorbing moisture and clumping, and an arch-breaking device at the bottom to ensure smooth phosphate flow. The metering auger is located at the outlet below the salt storage bin and is driven by a servo motor with a rotational speed accuracy of ±0.1 rpm, enabling precise control of the phosphate addition amount, with an error within ±2%. The co-pyrolysis reactor adds calcium dihydrogen phosphate monohydrate or phosphoric acid at a rapeseed stalk to phosphate mass ratio of 5:1. The reaction vessel contains potassium dihydrogen phosphate. A second air inlet is located at the bottom of the reaction vessel to introduce nitrogen gas to form a protective atmosphere. The nitrogen purity is required to be no less than 99.99%. The nitrogen flow rate is precisely controlled by a mass flow meter. The temperature control system of the co-pyrolysis reactor includes an array of electric heating elements and thermocouples arranged in a circular pattern. The electric heating elements are made of silicon carbide rods and are distributed in the circumferential and axial positions of the reaction vessel, with a total power of 50 kW. The thermocouple array uses K-type thermocouples and has 5 temperature measuring points. The temperature measuring points are distributed at different heights in the reaction zone to accurately monitor the temperature distribution at each point in the reaction zone. When the co-pyrolysis reactor is working, the control system precisely controls the reaction temperature within the range of 300 to 600°C and maintains it for 80 minutes of co-pyrolysis time. The temperature control accuracy can reach ±2°C. The carbon outlet of the co-pyrolysis reactor is connected to the cooling chamber of the carbon storage unit through a cooling feed pipe.

[0029] The alkali modification component is located at the rear end of the activation modification unit and is used to further modify the biochar with alkali to introduce acidic oxygen-containing functional groups. The alkali modification component includes an alkali preparation tank and an alkali spraying device. The alkali preparation tank is used to prepare a 2 mol / L sodium hydroxide solution. The alkali preparation tank has an enamel-lined liner, a volume of 500 liters, and is heated by steam with a steam pressure controlled at 0.3 to 0.5 MPa. A frame stirrer is used for stirring, with a rotation speed controlled at 20 to 50 rpm. The alkali preparation tank is equipped with a temperature sensor and a level sensor. The temperature sensor monitors the alkali temperature and maintains it at 100°C for 12 hours to complete the functional group introduction reaction. The level sensor monitors the alkali level. The liquid level is maintained to ensure the normal operation of the preparation process. The alkali spraying device is located at the top of the cooling chamber. The alkali spraying device includes spray pipes and atomizing nozzles. The spray pipes are made of stainless steel and are evenly arranged along the cross-section of the cooling chamber. Multiple atomizing nozzles are installed on the spray pipes. The atomizing nozzles are ultrasonic atomizing nozzles, and the atomized particle size is controlled within the range of 10 to 50 μm, which can make the alkali solution evenly cover the surface of the biochar. The alkali spraying volume is precisely controlled by a metering pump. The flow rate of the metering pump can be adjusted according to the processing volume and the concentration of the alkali solution. After the alkali modification treatment is completed, the system performs a multi-stage countercurrent water washing program to remove residual alkali solution. The water washing adopts a multi-stage countercurrent washing method to save water. After the water washing is completed, drying is performed.

[0030] The char storage unit is located at the rear end of the activation and modification unit. It is used for cooling, grading, quality inspection, packaging, and storing the modified biochar. The core components of the char storage unit include a cooling chamber, a grading screen, a char storage chamber, quality inspection components, and packaging components. The inlet of the cooling chamber is connected to the char outlet of the co-pyrolysis reactor. The cooling chamber adopts a built-in water-cooled jacket structure. Cooling water is circulated within the jacket to rapidly cool the biochar and prevent over-carbonization. The cooling water flow rate is precisely controlled by an electric regulating valve, with the cooling time controlled at 5 to 10 minutes and the cooling rate reaching 50 to 100°C per minute. A grading screen is installed below the cooling chamber, and the grading screen is connected to the cooling chamber via a vibrating feeder. The vibrating feeder can be adjusted to effectively classify biochar particles of different sizes. The grading screen is set to four grades: less than 1mm, 1 to 3mm, 3 to 5mm, and greater than 5mm. Biochar of different sizes falls into the corresponding collection hoppers. The biochar storage silo is equipped with multiple partitions, each partition corresponding to a grade area. The biochar storage silo monitors the material storage amount in each grade area through a material level sensor to achieve automatic classification and storage of biochar. The classification standard of the biochar storage silo is a fixed carbon content greater than 45% and a carbon element mass fraction greater than 53%. Qualified products are sent to the biochar storage silo for storage.

[0031] The quality testing component is located on the conveyor channel between the grading sieve and the biochar storage bin. This component includes an elemental analyzer, a BET surface area analyzer, and a pH meter. The elemental analyzer uses infrared detection with an accuracy of 0.01%, used to determine the fixed carbon content, carbon mass fraction, nitrogen mass fraction, and potassium mass fraction in biochar samples. The BET surface area analyzer uses nitrogen adsorption, with a surface area detection range of 0.5 to 2000 m² / gram, used to determine the specific surface area and pore volume of biochar. The pH meter uses a glass electrode method, with a high measurement accuracy. The pH value is ±0.01 for determining the pH value of biochar samples. The quality testing component also includes a cation exchange capacity measuring device to determine the cation exchange capacity index of biochar. After quality testing, qualified products are sent to the biochar storage silo for classified storage, while unqualified products are returned for reprocessing through the return pipe. The packaging component is located at the outlet of the biochar storage silo and is sealed using a vacuum packaging machine with a vacuum degree of -0.09 MPa. The packaging material is a nylon-polyethylene composite film with good barrier properties. The packaging specifications can be adjusted according to customer needs, generally from 10 to 50 kg per bag.

[0032] The system's control logic is uniformly coordinated by a central controller, which is located in the system's control room and connected to the actuators and sensors of each unit via cables. The central controller integrates a data acquisition module, a control strategy module, a communication interface module, and a display and operation module. The data acquisition module collects process parameter data from each unit in real time through a sensor network, including temperature data from temperature sensors, pressure data from pressure sensors, flow data from flow sensors, concentration data from concentration sensors, and level data from level sensors. The control strategy module generates adjustment commands based on preset control algorithms and process parameter setpoints. The control strategy module integrates proportional-integral-derivative control algorithms, sequential control logic, and interlocking protection logic. The communication interface module supports data communication with a higher-level monitoring system, enabling remote monitoring and management of production data. The display and operation module has a human-machine interface for displaying the system's operating status and process parameter curves. Operators can set parameters and perform operation control through the human-machine interface.

[0033] The system's workflow and the collaborative operation of its modules are as follows: First, rapeseed stalks are transported to a temporary storage area by transport vehicles. This area is equipped with a weighbridge and a sampling device. The weighbridge automatically records the weight of the incoming material, and the sampling device randomly samples the stalks for subsequent moisture content testing and fiber structure analysis. Operators then load the rapeseed stalks into the feed hopper of the pretreatment unit using a loader. The feed hopper is equipped with a uniform distribution device to ensure the rapeseed stalks are evenly distributed on the conveyor belt. After entering the dryer, the dryer's internal hot air generator produces hot air at 100°C. The hot air velocity... The hot air is controlled at 2.5 m / s, and the rapeseed stalks come into countercurrent contact with each other on the stainless steel mesh belt. The moisture content of the rapeseed stalks gradually decreases from the initial 30% to 40% to below 15%. The dried rapeseed stalks are then conveyed to the pulverizer via the first conveyor belt. The blade assembly inside the pulverizer rotates at a high speed of 3000 revolutions per minute, cutting and pulverizing the rapeseed stalks into powder with an 80-mesh sieve particle size. The pulverized rapeseed stalk powder is then conveyed to the feed inlet of the steam explosion tank via the second conveyor belt. After the feed is completed, the steam explosion tank closes its lid and starts the steam heating program.

[0034] Temperature sensors inside the steam explosion tank monitor the tank temperature in real time. When the temperature reaches 210℃ and the pressure reaches 2.5MPa, the control system enters the pressure holding time stage, which lasts for 2 minutes. After the pressure holding time ends, the control system sends a rapid opening command to the pressure regulating valve. The pressure regulating valve adjusts the valve core opening to the maximum position within 0.5s. The high-pressure steam inside the tank is quickly released into the buffer tank through the pressure relief channel. After the pressure relief process lasts for 3 to 5 seconds, the pressure inside the tank drops to atmospheric pressure. The tank cover is then opened to remove the pretreated material. The specific surface area of ​​the pretreated material is more than 50% higher than that of the raw material, and the fiber structure is fully torn and loosened.

[0035] Pre-treated materials are fed into the multi-stage pyrolyzer via a segmented feeder. The inner spiral of the segmented feeder pushes the material forward at 15 revolutions per minute, while the outer spiral forms a reverse sealing gas seal at 20 revolutions per minute. After entering the top feed port of the multi-stage pyrolyzer through the feed pipe, the material falls into the constant temperature zone above the separator ring. During the operation of the multi-stage pyrolyzer, the lower heating zone is heated by electric heating elements. A temperature sensor array monitors the temperature distribution data of the heating zone in real time. The control system calculates the temperature deviation according to the proportional-integral-differential algorithm and adjusts the output power of the electric heating elements to precisely control the heating rate of the heating zone at 10°C per minute. After the heating zone reaches the pyrolysis temperature of 500°C, it enters the heat preservation stage for 30 minutes. During the heating process, the main air inlet introduces oxygen-limited gas into the heating zone through the first gas distribution channel. The gas flow meter shows that the nitrogen flow rate is 8 liters per minute, and the oxygen concentration detector shows that the oxygen concentration is maintained at about 1.5% to meet the conditions for oxygen-deficient pyrolysis.

[0036] The trapezoidal vents on the partition ring allow the pyrolysis gas generated in the heating zone to pass smoothly into the upper constant-temperature zone, while preventing solid materials from falling from the constant-temperature zone into the heating zone. Within the constant-temperature zone, the pyrolysis gas exchanges heat and mass with the solid materials. The control system calculates the temperature distribution uniformity using multi-point temperature measurement data from a thermocouple array and precisely controls the constant-temperature zone temperature within the range of 495 to 505℃, with a temperature deviation within ±5℃. The main components of the pyrolysis gas include hydrogen, carbon monoxide, carbon dioxide, and methane, with a gas production rate of approximately 1.5 to 2.0 m³ per kg of biomass. After the pyrolysis reaction is complete, the biochar semi-finished product and the pyrolysis gas are discharged from different outlets of the multi-stage pyrolyzer.

[0037] Pyrolysis gas enters the cyclone separator through a hot gas duct. Inside the cyclone separator, the pyrolysis gas forms a high-speed rotating airflow. Solid particles are thrown against the cylinder wall by centrifugal force and spiral down the cylinder wall to the ash collection hopper. The separation efficiency of the cyclone separator is over 95%. The pyrolysis gas falling from the top of the cyclone separator enters the bag filter through the ash conveying pipe. The filter bags in the bag filter capture residual dust particles. The pulse cleaning device periodically removes the accumulated ash on the filter bags according to the dust concentration sensor signal. The total separation efficiency of the bag filter is over 99.5%. The clean pyrolysis gas is sent from the top outlet of the bag filter to the subsequent treatment system for utilization. The solid particles collected by the cyclone separator and the bag filter are returned to the multi-stage pyrolysis unit through the return pipe for secondary pyrolysis. Secondary pyrolysis can further increase the carbon yield by about 2% to 3%.

[0038] The semi-finished biochar discharged from the multi-stage pyrolyzer enters the chemical activation tank through a cooling feed pipe. The control system of the chemical activation tank raises the temperature inside the tank to 70°C and then starts the phosphoric acid impregnation process. A 10% concentration phosphoric acid solution is pumped into the chemical activation tank through a metering pump at a liquid-to-solid ratio of 3:1. The speed of the stirring motor is set to 80 revolutions per minute to create a sufficient turbulent mixing effect. After impregnation and stirring continue for 45 minutes, the control system starts the filter press mechanism to separate the liquid and solids. The ceramic filter plate retains the solid material, and the phosphoric acid solution passes through the filter plate into the filtrate collection tank and is sent to the phosphoric acid storage tank by the phosphoric acid recovery pump for recycling and reuse. After impregnation, the moisture content of the material is controlled at 65%. Then, it is fed into the fluidized bed drying zone through a feeder. The hot air temperature in the fluidized bed drying zone is controlled at 70°C. The hot air comes into countercurrent contact with the material for drying treatment, and the moisture content of the material is gradually reduced to below 15%.

[0039] The dried material is fed into the co-pyrolysis reactor through the feed pipe. The co-pyrolysis reactor is heated under a nitrogen protective atmosphere. When the temperature of the reaction zone reaches the set value, the arch-breaking device at the bottom of the salt storage bin begins to vibrate to prevent phosphate agglomeration. The metering auger, driven by a servo motor, precisely delivers the phosphate material. The servo motor speed is set to 30 revolutions per minute. Calcium dihydrogen phosphate monohydrate is mixed with rapeseed stalks at a mass ratio of 5:1 through the metering auger and falls into the reaction cylinder. The temperature control system of the co-pyrolysis reactor precisely controls the reaction temperature at 450℃ and maintains the co-pyrolysis time for 80 minutes. During the co-pyrolysis process, nitrogen gas with a purity of 99.99% is continuously introduced through the second air inlet as a protective atmosphere. The nitrogen flow rate is controlled at 4 liters per minute to maintain an inert atmosphere in the reaction zone.

[0040] After co-pyrolysis is completed, the discharge valve at the bottom of the reaction cylinder is opened, and the co-products enter the cooling chamber through the cooling feed pipe. Cooling water with a flow rate of 80 liters per minute is circulated into the jacket of the cooling chamber. The biochar exchanges heat with the cooling water in the cooling chamber, and the cooling rate reaches 70°C per minute. The biochar cooled to room temperature is evenly distributed on the grading screen by a vibrating feeder. The vibration frequency of the grading screen is set to 50 Hz per minute. Under the action of vibration and gravity, the biochar is stratified according to particle size and passes through screens with different apertures. Fine particles smaller than 1 mm pass through the first layer of screens and fall into the corresponding collection hopper. Medium and fine particles of 1 to 3 mm pass through the second layer of screens and fall into the collection hopper. Medium and coarse particles of 3 to 5 mm pass through the third layer of screens and fall into the collection hopper. Coarse particles larger than 5 mm are intercepted by the third layer of screens and fall into the collection hopper.

[0041] After grading, the biochar was transported through pipelines to a quality testing unit for index analysis. An elemental analyzer analyzed the biochar samples, revealing a fixed carbon content of 46% to 48%, a carbon element mass fraction of 54% to 56%, a nitrogen element mass fraction of 1% to 2%, and a potassium element mass fraction of 4% to 5%. A BET surface area analyzer showed a specific surface area of ​​180 to 220 m² / g and a pore volume of 0.18 to 0.22 cm³ / g. A pH meter reading showed a pH value of 8.5 to 9. 0.5 is alkaline, and the cation exchange capacity test results show that the cation exchange capacity is 78 to 80 cmol / kg. The control system calculates the product quality index based on the quality test data. When the fixed carbon content is greater than 45% and the carbon element mass fraction is greater than 53%, it is judged as a qualified product and the corresponding grade classification label is output. Qualified products are sent to the corresponding partition area of ​​the charcoal storage silo by grade classification through the conveying device. The material level sensor monitors the material storage amount in each partition area in real time. Biochar that fails the quality test is returned to the chemical activation tank for reprocessing through the return pipe.

[0042] The alkaline modification process is as follows: After the biochar in the cooling chamber has completed its initial cooling, the alkaline spraying device is activated to perform alkaline modification treatment on the surface of the biochar. The alkaline preparation tank is pre-prepared with a 2 mol / L sodium hydroxide solution and heated to 100°C for 12 hours to complete the functional group introduction reaction. Ultrasonic atomizing nozzles atomize the alkaline solution into droplets with a particle size of 10 to 50 μm and spray them evenly onto the surface of the biochar. The spray pipes are evenly arranged along the cross-section of the cooling chamber to ensure uniform alkaline coverage. The alkaline spraying rate is precisely controlled by a metering pump at a rate of [missing information - likely a unit of measurement]. The system processes 5 liters of water. After processing, it performs a multi-stage countercurrent water washing program to remove residual alkali. The water washing adopts a three-stage countercurrent washing method. The first stage uses fresh deionized water for washing, and the second and third stages use the wash water generated from the previous stage for countercurrent washing to save water. After the countercurrent water washing is completed, hot air drying is carried out. The drying temperature is controlled at 90℃. After drying to constant weight, the modified biochar product is obtained. The cation exchange capacity of the modified biochar reaches 77 to 80 cmol / kg, which is more than 30% higher than that of the unmodified biochar.

[0043] Qualified biochar products are conveyed to the packaging assembly for sealing via a conveyor device. The vacuum packaging machine packs the biochar into nylon-polyethylene composite film bags, and the sealing vacuum degree is controlled at -0.09MPA to ensure good barrier performance. The packaging machine is equipped with a weight measuring device to ensure that the weight of each bag meets the specifications. The packaging specification is set at 25kg per bag. The packaged biochar products are sent to the finished product warehouse via conveyor belt for storage and shipment management.

[0044] The specific working process of the system control logic is as follows: Before the system starts, the central controller completes the initialization parameter settings of each unit, including setting the dryer hot air temperature to 100℃ and the hot air speed to 2.5m / s, setting the steam explosion tank explosion pressure to 2.5MPa, the explosion temperature to 210℃, and the explosion holding time to 2 minutes, setting the staged pyrolyzer heating zone heating rate to 10℃ per minute, the pyrolysis temperature to 500℃, the holding time to 30 minutes, the upper limit of the constant temperature zone temperature deviation to 5℃, the lower limit of the deviation to -5℃, the chemical activation tank immersion temperature to 70℃, the immersion time to 45 minutes, and the liquid-to-solid ratio to 3:1, the co-pyrolysis reactor co-pyrolysis temperature to 450℃, the co-pyrolysis time to 80 minutes, the nitrogen flow rate to 4 liters per minute, the cooling water flow rate of the cooling chamber to 80 liters per minute, and the grading screen vibration frequency to 50 Hz, etc.

[0045] During system operation, the central controller continuously collects real-time data from each sensor and performs limit judgments. When the temperature data collected by the temperature sensor exceeds the set range, the control system triggers the proportional-integral-derivative adjustment program to calculate the adjustment amount and output the adjustment command. When the pressure data collected by the pressure sensor exceeds the safety threshold, the control system triggers the interlock protection program to stop the operation of the corresponding equipment and issue an alarm signal. When the flow data collected by the flow sensor deviates from the set value, the control system performs flow compensation through the regulating valve. When the material level sensor detects that the material level has reached the high limit, the control system stops the feeding equipment and starts the relevant actuators to regulate the material level.

[0046] In the processing link, the cascade circulation control logic of pyrolysis gas distribution is as follows: The control system collects data from the gas flow meter and oxygen concentration detector on the first gas distribution channel in real time, and calculates the recycling rate of pyrolysis gas distribution. The recycling rate is calculated as the ratio of the total volumetric flow rate of the collected pyrolysis gas and activation tail gas to the volumetric flow rate of the gas distribution introduced into the main inlet. When the recycling rate is lower than the target value, the control system increases the reuse ratio of activation tail gas by adjusting the opening of the tail gas return valve. When the recycling rate is higher than the target value, the control system reduces the opening of the tail gas return valve to reduce the reuse ratio of activation tail gas. By dynamically adjusting the tail gas reuse ratio, the control system realizes the cascade circulation of pyrolysis gas distribution, effectively improving the system's thermal energy utilization rate to over 60%.

[0047] In the processing chain, the calculation and classification logic of the product quality index is as follows: The quality inspection component sends the inspection data to the central controller. The central controller calculates the product quality index according to the preset weighting coefficients. The formula for calculating the product quality index is: Product quality index = Fixed carbon content multiplied by the first weighting coefficient + Carbon element mass fraction multiplied by the second weighting coefficient + Cation exchange capacity multiplied by the third weighting coefficient. The first, second, and third weighting coefficients are set according to the product application scenario. For example, when modified biochar is mainly used for soil improvement and heavy metal adsorption, the process places more emphasis on the cation exchange capacity of modified biochar. In this case, the first weighting coefficient... The first weighting factor can be set to 0.3, the second weighting factor to 0.2, and the third weighting factor to 0.5. When used as solid fuel, the first weighting factor can be adjusted to 0.6, the second weighting factor to 0.3, and the third weighting factor to 0.1. When the product quality index is greater than the preset grading threshold, the control system outputs a grade classification identifier and automatically allocates the product to the corresponding storage partition area. The grade classification standard includes three levels: Grade 1, Grade 2, and Grade 3. Grade 1 products have a fixed carbon content greater than 48% and a carbon element mass fraction greater than 55%, Grade 2 products have a fixed carbon content greater than 45% and a carbon element mass fraction greater than 53%, and Grade 3 products are other qualified products.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process system for preparing biochar by pyrolysis and carbonization of agricultural waste rapeseed stalks, characterized in that, The system includes a pretreatment unit, a staged pyrolysis and carbonization unit, a gas-solid separation unit, an activation and modification unit, and a carbon storage unit connected sequentially along the material flow direction. The staged pyrolysis carbonization unit includes a multi-stage pyrolyzer, and a partition ring is provided inside the multi-stage pyrolyzer. The partition ring divides the inner cavity of the multi-stage pyrolyzer into a lower heating zone and an upper constant temperature zone. The partition ring is provided with a vent for the pyrolysis gas to pass through. The multi-stage pyrolyzer is provided with a gas distribution channel that communicates with the heating zone; The activated exhaust gas generated by the activation and modification unit is channeled into the gas distribution channel through a pipeline to achieve a stepped circulation of pyrolysis gas and activated exhaust gas.

2. The process system according to claim 1, characterized in that, The vent hole on the separator ring is a trapezoidal hole, with the larger end of the trapezoidal hole facing upwards and the smaller end facing downwards; the staged pyrolysis carbonization unit also includes a segmented feeder disposed above the multi-stage pyrolyzer. The segmented feeder adopts a double-helix propulsion structure. The inner helix of the segmented feeder is used to transport materials, and the outer helix is ​​used to form a reverse sealing gas seal.

3. The process system according to claim 1, characterized in that, The pretreatment unit includes a dryer, a pulverizer, and a steam explosion tank connected in sequence. The steam explosion tank is equipped with a pressure regulating valve and a control system, which is used to hold the material under pressure at 210℃ and 2.5MPA, and then quickly release the pressure within 3 to 5 seconds by controlling the pressure regulating valve to perform the tearing treatment of the rapeseed stalk fiber structure.

4. The process system according to claim 1, characterized in that, The multi-stage pyrolyzer is equipped with a thermocouple array and a control system. The control system performs closed-loop control based on a proportional-integral-derivative algorithm to control the heating rate of the heating zone at 10°C per minute to the target pyrolysis temperature, and adjusts the heating element according to the temperature measurement data of the thermocouple array to maintain the temperature deviation of the constant temperature zone within ±5°C.

5. The process system according to claim 1, characterized in that, The gas-solid separation unit includes a cyclone separator and a bag filter connected in sequence, used to separate the pyrolysis gas discharged from the multi-stage pyrolysis unit; the solid outlets of the cyclone separator and the bag filter are connected to the multi-stage pyrolysis unit through a return pipe, used to send the separated solid particles back to the multi-stage pyrolysis unit for secondary pyrolysis.

6. The process system according to claim 1, characterized in that, The activation and modification unit includes a chemical activation tank and a fluidized bed drying zone; the chemical activation tank is equipped with an impregnation and stirring assembly for mixing phosphoric acid solution with pretreated rapeseed stalk material to form an impregnation system; the bottom of the chemical activation tank is equipped with a liquid-solid separation assembly for separating and recovering excess phosphoric acid solution; the fluidized bed drying zone is used for gradient drying of the impregnated material.

7. The process system according to claim 6, characterized in that, The activation and modification unit also includes a co-pyrolysis reactor connected to the rear end of the fluidized bed drying zone; the co-pyrolysis reactor is provided with an inlet for introducing nitrogen to form a protective atmosphere, and a metering auger feeder for precise addition of phosphate, for performing co-pyrolysis reaction in the range of 300 to 600°C.

8. The process system according to claim 1, characterized in that, The activation and modification unit further includes an alkali modification component; the alkali modification component includes an alkali spraying device disposed on the upper part of the biochar storage unit; the alkali spraying device is equipped with an ultrasonic atomizing nozzle for spraying alkali solution with an atomized particle size of 10 to 50 μm onto the surface of biochar to introduce acidic oxygen-containing functional groups, and after spraying, it undergoes multi-stage countercurrent water washing and drying.

9. The process system according to claim 1, characterized in that, The biochar storage unit includes a cooling chamber and a grading screen located below the cooling chamber; the cooling chamber adopts a built-in water-cooled jacket structure to perform rapid cooling; the grading screen is connected through a vibrating feeder to classify the cooled biochar according to particle size and drop it into the corresponding collection hopper.

10. The process system according to claim 1, characterized in that, The process system is also equipped with a quality detection component and a central controller; the quality detection component includes a detector for detecting the fixed carbon content, carbon element mass fraction and cation exchange capacity of biochar samples; the central controller has a built-in algorithm model for calculating the product quality index based on the detection data and weight coefficients. When the product quality index is greater than a preset threshold, it outputs a grade classification identifier and triggers the automatic classification and storage mechanism of the carbon storage unit.

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