A multi-section zoned tunnel kiln and a continuous carbonization method

Abstract

This invention relates to the field of biomass carbonization equipment and continuous pyrolysis control technology, specifically to a multi-section zoned tunnel kiln and a continuous carbonization method. The multi-section zoned tunnel kiln includes a kiln body, which, along the material flow direction, consists of a pre-drying zone, an isothermal drying zone, a slow-heating dehydroxylation zone, a main pyrolysis zone, a densification zone, and an inerting cooling zone. Kiln cars transport raw materials through each zone sequentially. The continuous carbonization method involves kiln cars carrying logs passing through each zone sequentially; adjusting the temperature and oxygen concentration of each zone within a set range; and creating a controlled pressure difference along the material flow direction in the tunnel kiln body by adjusting the opening degree of the exhaust valve group and the recirculation ratio of the recirculation gas inlet in each zone. The slow-heating dehydroxylation zone of this invention provides sufficient temperature buffering and stress release for the logs before they enter the high-temperature main pyrolysis zone, effectively avoiding cracking defects caused by excessively rapid heating or a sudden increase in internal moisture pressure.

Description

Technical Field

[0001] This invention relates to the field of biomass carbonization equipment and continuous pyrolysis control technology, and more specifically, to a multi-stage zoned tunnel kiln and a continuous carbonization method. Background Technology

[0002] In chrysanthemum charcoal production, logs are prone to cracking during continuous carbonization due to excessively rapid heating or insufficient release of internal stress, affecting the integrity of the charcoal and the yield. Existing continuous tunnel kilns are typically only roughly divided into drying, pyrolysis, and cooling sections based on temperature, lacking targeted zoning treatment for the migration of internal moisture and stress release processes in logs. In particular, they lack a separate slow-heating dehydroxylation zone, resulting in logs not being able to fully release internal stress before entering the high-temperature pyrolysis zone, leading to a high risk of cracking and poor consistency in charcoal quality. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-segment zoned tunnel kiln and a continuous carbonization method, which can solve the above-mentioned technical problems.

[0004] In a first aspect, the present invention provides a multi-section zoned tunnel kiln, comprising: The tunnel kiln body comprises, along the material running direction, a pre-drying zone, an isothermal drying zone, a slow-heating dehydroxylation zone, a main pyrolysis zone, a densification zone, and an inertization cooling zone. The kiln car is used to transport raw materials sequentially through the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone.

[0005] In an optional implementation, a track is also included; The kiln car is positioned on the track.

[0006] In an optional implementation, a detection system is also included; The detection system is configured to detect the temperature and oxygen concentration of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone.

[0007] In an optional implementation, a double gate chamber is also provided; The double gate chambers are located at one or both ends of the tunnel kiln body to isolate the interior and exterior atmospheres of the tunnel kiln body during feeding or discharging.

[0008] In an optional implementation, a circulating fan system is also included; The circulating fan system is configured to circulate gas within the tunnel kiln body.

[0009] In an optional embodiment, the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone are all equipped with an exhaust valve group and a reflux gas inlet.

[0010] Secondly, the present invention provides a continuous carbonization method in which a kiln car carrying logs passes sequentially through a pre-drying zone, an isothermal drying zone, a slow-heating dehydroxylation zone, a main pyrolysis zone, a densification zone, and an inerting cooling zone. The temperature and oxygen concentration of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone are adjusted within a set range; Adjusting the opening degree of the exhaust valve group of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone, and the reflux ratio of the reflux gas inlet, so that the tunnel kiln body forms a controlled pressure difference along the material running direction.

[0011] In an optional implementation, the kiln cars adopt a step-by-step operation mode, and multiple kiln cars move forward as a whole by a set pitch after completing one process cycle, so that the dwell time ratio in each zone remains constant.

[0012] In an optional implementation, when the temperature and oxygen concentration in the main pyrolysis zone deviate from the set range simultaneously, the reflux ratio and exhaust volume are first adjusted to restore the oxygen concentration to the set range. After the oxygen concentration is restored to the set range, the output power of the heating module is then adjusted.

[0013] In an optional implementation, the carbonized material is carried into the kiln tail double gate chamber by the kiln car, and then removed from the tunnel kiln body after atmosphere conditioning and cooling.

[0014] The beneficial effects of this invention are: This invention divides the tunnel kiln body along the material flow direction into a pre-drying zone, an isothermal drying zone, a slow-heating dehydroxylation zone, a main pyrolysis zone, a densification zone, and an inerting cooling zone. This allows logs to sequentially complete moisture migration, internal stress release, pyrolysis reaction, structural densification, and low-oxygen cooling under continuous operation. In particular, the independently designed slow-heating dehydroxylation zone provides sufficient temperature buffering and stress release for the logs before they enter the high-temperature main pyrolysis zone, effectively preventing cracking defects caused by excessively rapid heating or a sudden increase in internal moisture pressure. The decoupled and independently controllable functions of each zone, combined with the sequential conveying method of kiln cars, significantly improve the integrity of the charcoal end faces and batch consistency, thus achieving the technical effect of low cracking rate and high-quality stable output in continuous production. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the overall longitudinal section structure of a multi-segment zoned tunnel kiln provided in an embodiment of the present invention; Figure 2 Temperature curves of each section of a multi-segmented tunnel kiln provided in this embodiment of the invention; Figure 3 A schematic diagram of the pressure difference distribution in each section of a multi-section tunnel kiln provided in an embodiment of the present invention; Figure 4 A schematic diagram of the airflow organization and reflux pipeline of a multi-section zoned tunnel kiln provided in an embodiment of the present invention; Figure 5 A schematic diagram of the structure of the double gate chamber at the kiln head of a multi-segment zoned tunnel kiln provided in an embodiment of the present invention; Figure 6 The control logic diagram of the multi-segment zoned tunnel kiln provided in the embodiments of the present invention; Figure 7 The sensor control logic diagram of a multi-segment zoned tunnel kiln provided in this embodiment of the invention; Figure 8 The execution end control logic diagram of the multi-segment partitioned tunnel kiln provided in the embodiment of the present invention.

[0017] Icons: 1-Pre-drying zone; 2-Isothermal drying zone; 3-Slow heating dehydroxylation zone; 4-Main pyrolysis zone; 5-Densification zone; 6-Inerting cooling zone; 7-Kiln head double gate chamber; 8-Kiln tail double gate chamber; 9-Kiln car; 10-Railway; 11-Heating module; 12-Exhaust valve group; 13-Temperature sensor; 14-Oxygen concentration sensor; 15-Pressure sensor; 16-Outer gate; 17-Inner gate. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] The following is combined with Figures 1-8 The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] Example 1 This embodiment describes in detail a multi-section, zoned tunnel kiln for producing chrysanthemum charcoal. For example... Figure 1As shown, the tunnel kiln includes a tunnel kiln body, a kiln head double gate chamber 7 structure located at the inlet end of the tunnel kiln body, a kiln tail double gate chamber 8 structure located at the outlet end of the tunnel kiln body, and a pre-drying zone 1, an isothermal drying zone 2, a slow-heating dehydroxylation zone 3, a main pyrolysis zone 4, a densification zone 5 (also known as a high-temperature polishing / densification zone 5), and an inerting cooling zone 6 arranged sequentially along the material running direction within the tunnel kiln body. In addition, the tunnel kiln also includes a track 10, a kiln car 9, a detection system, a circulating fan system, an inlet and outlet valve group 12, a return gas inlet, and a heating module 11, among other components.

[0026] The tunnel kiln body is a horizontal, rectangular, sealed container constructed of refractory materials, insulation materials, and a steel structure shell. Its interior is divided into six continuous functional zones along its length (i.e., the material flow direction). Each zone is separated by a heat-resistant partition wall, with an arched passageway in the center of each partition wall for the kiln car 9 and material to pass through. The six zones are arranged according to the carbonization process of the material: - Pre-drying zone 1: Used for initial heating of logs to evaporate the free water on the surface. The temperature in this zone is controlled between 120 and 180°C, mainly utilizing the residual heat of the reflux kiln gas for heating.

[0027] - Isothermal Drying Zone 2: Used to allow moisture inside the logs to migrate outwards and distribute evenly under relatively constant temperature conditions. The temperature in this zone is controlled between 180 and 220°C, and the heating rate is strictly limited (≤2°C / min) to avoid rapid temperature fluctuations that could cause the surface of the logs to crack.

[0028] - Slow-heating dehydroxylation zone 3: This zone controls the heating rate and extends the residence time, allowing the logs to complete the hydroxyl removal reaction and redistribute internal stress. The temperature in this zone gradually increases from approximately 220°C to 320–340°C, with the heating rate controlled at ≤1.5°C / min, and the residence time is generally 15–25 hours. This zone is one of the core improvements of this invention, specifically designed to reduce the risk of cracking in the logs during subsequent high-temperature pyrolysis.

[0029] - Main pyrolysis zone 4: Used to complete the main pyrolysis reaction of logs in a low-oxygen environment, producing charcoal and volatiles. The temperature in this zone is controlled at 480-520℃, and the oxygen concentration is controlled at ≤3%. The low-oxygen environment is achieved through a high proportion of kiln gas reflux (70%-85%).

[0030] - Densification Zone 5: Used for short-term high-temperature treatment of charcoal materials, causing further shrinkage and rearrangement of the charcoal structure, increasing density and improving the chrysanthemum texture on the end face. The temperature in this zone is controlled at 650–720℃, the residence time is 1–3 hours, and the oxygen concentration is ≤2%.

[0031] - Inerting Cooling Zone 6: Used for slow cooling of charcoal materials in a low-oxygen environment to prevent oxidation caused by contact with air. The temperature in this zone gradually decreases from approximately 650℃ to below 180℃ at a cooling rate of ≤5℃ / min, maintaining a slight positive pressure to prevent air backflow.

[0032] The length ratios of the aforementioned zones are optimized based on raw material characteristics and production capacity requirements. For example, for processing logs with a diameter of 8–12 cm and a moisture content of 30%–40%, the total effective length of the tunnel kiln body can be set to 118 meters, where the pre-drying zone 1 is 12 meters long, the isothermal drying zone 2 is 16 meters long, the slow-heating dehydroxylation zone 3 is 24 meters long, the main pyrolysis zone 4 is 32 meters long, the densification zone 5 is 10 meters long, and the inerting cooling zone 6 is 24 meters long. It should be noted that the above lengths are only examples and can be adjusted according to the production scale in actual applications.

[0033] Two parallel tracks 10 are fixedly laid along the length of the bottom surface inside the tunnel kiln body. The tracks 10 are made of light rail or I-beams, and the track gauge matches the wheel gauge of the kiln cars 9. Multiple kiln cars 9 are arranged sequentially on the tracks 10 to form a train. The kiln cars 9 are steel flat plate structures with four wheels installed at the bottom. The wheels are placed on the tracks 10 and can roll along the tracks 10. The upper surface of the kiln cars 9 is used to load logs. The logs are stacked in a staggered manner, with ventilation channels left between adjacent logs to facilitate airflow through the material layer evenly. A guide baffle and limiting structure can also be installed above the kiln cars 9 to guide the airflow in a set direction and limit the displacement of the logs during operation.

[0034] The kiln cars 9 adopt a stepping operation mode, meaning that after completing a set process cycle, all kiln cars 9 are pushed forward by a set pitch as a whole by a stepping drive mechanism (such as a hydraulic cylinder or an electric screw pusher). The stepping pitch is usually slightly larger than the length of the kiln car 9; for example, if the length of the kiln car 9 is 2 meters, the stepping pitch is 2.2 meters, leaving a small gap between adjacent kiln cars 9. Compared with uniform continuous sliding, stepping operation can significantly reduce the periodic disturbance of airflow inside the kiln, which is beneficial to maintaining the stability of the atmosphere inside each zone and the reliability of the pressure difference gradient.

[0035] The tunnel kiln body has a kiln head double gate chamber 7 at the inlet and a kiln tail double gate chamber 8 at the outlet. The kiln head double gate chamber 7 includes an outer gate 16, an inner gate 17, and a sealed buffer chamber located between the outer gate 16 and the inner gate 17. The sealed buffer chamber has an independent atmosphere regulating channel, which is connected to a return gas pipeline system or a nitrogen source, allowing low-oxygen gas to be introduced into the chamber. The outer gate 16 and the inner gate 17 are respectively connected to an interlocking control mechanism, ensuring that they cannot be opened simultaneously; that is, when the outer gate 16 is open, the inner gate 17 is locked closed; when the inner gate 17 is open, the outer gate 16 must be closed. The kiln tail double gate chamber 8 has a structure symmetrical to the kiln head double gate chamber 7, also including an inner gate 17, an outer gate 16, and a sealed buffer chamber, used to isolate external air during the discharge process.

[0036] The function of the double gate chamber 7 at the kiln head is as follows: During the feeding process, the kiln car 9 first enters the buffer chamber. After the outer gate 16 closes, the atmosphere inside the chamber is replaced to match the oxygen concentration at the inlet of the pre-drying zone 1. Then, the inner gate 17 opens, and the kiln car 9 enters the kiln. This structure effectively prevents outside air from flowing back into the tunnel kiln body during the feeding operation. The double gate chamber 8 at the kiln tail has a similar function, preventing outside air from entering the kiln when high-temperature carbon material exits, while providing a low-oxygen cooling environment for the carbon material.

[0037] The detection system includes multiple temperature sensors 13, oxygen concentration sensors 14, and pressure sensors 15, which are distributed in each zone and communicate with the central controller.

[0038] - The temperature sensor 13 is preferably a type K or type S thermocouple, with its measuring end extending into the internal space of the partition and installed on the top or side wall of the partition for real-time monitoring of the gas temperature in each partition. At least two temperature sensors 13 are provided in each partition, located near the partition inlet and outlet respectively, to monitor the temperature change along the material flow direction.

[0039] - The oxygen concentration sensor 14 is preferably a zirconia oxygen analyzer, whose sampling probe is installed near the exhaust pipe or return gas inlet of each zone to monitor the oxygen concentration in the zone in real time. At least one oxygen concentration sensor 14 is installed in each zone.

[0040] - Pressure sensor 15 employs a differential pressure transmitter, with its two pressure taps located on opposite sides of the partition wall between adjacent zones, for measuring the pressure difference between zones. Alternatively, an absolute pressure sensor 15 can be installed at the top of each zone to obtain pressure difference data by calculating the pressure difference between adjacent zones.

[0041] To achieve independent airflow organization and pressure regulation in each zone, each zone is equipped with a circulating fan, an intake and exhaust valve group 12, and a return air inlet.

[0042] The circulating fan is a high-temperature resistant centrifugal fan. Its inlet is connected to the gas circulation channel inside the partition via a pipe, and its outlet is connected to the heating module 11, the equalizing box, and the diffuser plate in sequence via pipes before returning to the partition. The circulating fan drives the gas circulation within the partition, ensuring a uniform distribution of temperature and oxygen concentration fields. It should be noted that the gas driven by the circulating fan is not fresh outside air, but a mixture of low-oxygen kiln gas introduced through the return gas inlet and the existing gas within the partition.

[0043] The intake and exhaust valve assembly 12 includes an electrically adjustable valve and an exhaust pipe. The opening degree of the electrically adjustable valve is controlled by a central controller. One end of the exhaust pipe is connected to the interior of the partition, and the other end is connected to the main exhaust pipe. The exhaust gas is discharged after purification treatment. By adjusting the opening degree of the intake and exhaust valve assembly 12, the discharge rate of the exhaust gas in the partition can be controlled, thereby changing the pressure of the partition.

[0044] The reflux gas inlet is connected to the main reflux gas pipe via a pipeline. The main reflux gas pipe draws high-temperature, low-oxygen kiln gas from the top of the main pyrolysis zone 4 or densification zone 5, and after dust removal, cooling (if necessary), and mixing, it is sent to the zones requiring gas replenishment through the reflux gas inlets of each zone. Each reflux gas inlet is equipped with a flow regulating valve to independently control the reflux gas replenishment ratio of that zone. Through the coordinated regulation of the reflux gas inlet and the inlet / outlet valve group 12, a micro-pressure gradient distributed along the material flow direction can be formed between the zones, causing the gas in the kiln to flow in a directional manner and suppressing the backflow of outside air.

[0045] Each zone is equipped with a heating module 11, but the heating methods may differ between zones. The pre-drying zone 1 and isothermal drying zone 2 primarily utilize the waste heat from the reflux kiln gas for heating, supplemented by low-power electric heating tubes for temperature fine-tuning. The slow-heating dehydroxylation zone 3 and main pyrolysis zone 4 employ direct heating with electric heating tubes or gas-fired radiant tubes to meet higher heat load requirements. The densification zone 5 uses high-power electric heating tubes for short-term, high-temperature intensive heating. The inerting cooling zone 6 does not have a heating module 11; gradual cooling is achieved solely through a circulating fan and reflux kiln gas.

[0046] Example 2 This embodiment describes in detail a method for continuous carbonization using the aforementioned multi-section zoned tunnel kiln. The method includes steps such as feeding, walking beam operation, zoned process control, atmosphere priority control, and discharge.

[0047] Step 1: Feeding.

[0048] The logs are loaded onto the kiln cars 9 in a staggered manner, with each car carrying a roughly consistent amount of logs, and the stacking height not exceeding the upper edge of the kiln car's side panels. After loading, the kiln cars 9 move along the feeding track 10 to the outer gate 16 of the kiln head double gate chamber 7. The feeding process is as follows: 1. The outer gate 16 is opened, and the kiln car 9 enters the sealed buffer chamber; 2. When the outer gate 16 is closed, the interlock control mechanism locks the outer gate 16. 3. Low-oxygen kiln gas or nitrogen is introduced into the buffer chamber through the atmosphere conditioning channel to replace the air in the chamber and reduce the oxygen concentration in the chamber to a set value (e.g., ≤5%). 4. After the pressure detection device confirms that the pressure inside the cavity is basically consistent with the inlet pressure of the pre-drying zone 1, the inner gate 17 is opened; 5. Kiln car 9 enters the pre-drying zone 1 of the tunnel kiln body from the buffer chamber; 6. The inner gate 17 closes, completing one feeding cycle.

[0049] Step 2: Step-by-step operation.

[0050] After kiln cars 9 enter the pre-drying zone 1, all kiln cars 9 move forward as a whole under the drive of the stepping mechanism. At the end of each process cycle, the stepping mechanism pushes the kiln car 9 column forward by a set pitch (e.g., 2.2 meters). The stepping cycle time is set according to the characteristics of the raw materials and the target product quality, and is usually 60-120 minutes. By adjusting the stepping cycle time, the total residence time of the material in each zone and the residence time ratio of each zone can be controlled. Since the length of each zone is fixed, the stepping operation keeps the residence time ratio of each zone constant, which is beneficial to product consistency.

[0051] Step 3: Control of process parameters in each zone.

[0052] Kiln car 9 sequentially passes through pre-drying zone 1, isothermal drying zone 2, slow-heating dehydroxylation zone 3, main pyrolysis zone 4, densification zone 5, and inerting cooling zone 6. The process parameter setting range and control targets for each zone are as follows: - Pre-drying zone 1: Temperature controlled at 140~170℃, oxygen concentration ≤10%, and pressure maintained at a slight positive pressure (+10~+30Pa) relative to adjacent zones. Moisture is uniformly removed by a high-flow-rate, low-velocity gas flow, avoiding the formation of localized high-speed scouring airflows.

[0053] - Isothermal Drying Zone 2: Temperature controlled at 180~210℃, heating rate ≤2℃ / min, oxygen concentration ≤8%, pressure maintained at a slight positive pressure (0~+15Pa). Maintain a constant temperature to ensure that the rate of moisture migration inside the logs is basically matched with the rate of evaporation outside.

[0054] - Slow-rise dehydroxylation zone 3: The temperature gradually increases from approximately 220℃ to 320℃, with a heating rate ≤1.5℃ / min. The oxygen concentration is controlled at 3%–6%, and the pressure is maintained at a slight negative pressure (-20 to -10 Pa). By limiting the heating rate and extending the residence time, the superposition of water vapor pressure and structural shrinkage is avoided, thereby significantly reducing the risk of cracking in thick-diameter logs.

[0055] - Main pyrolysis zone 4: Temperature controlled at 500±15℃, oxygen concentration ≤3%, reflux ratio 70%~85%, pressure maintained at negative pressure (-50~-30Pa). When oxygen concentration fluctuations are detected, the reflux ratio is increased and the fresh air intake is reduced for adjustment.

[0056] - Densification Zone 5: Temperature controlled at 680℃, oxygen concentration ≤2%, residence time approximately 2 hours, pressure maintained at a slight negative pressure (-30~-10Pa). High-temperature short-time treatment makes the surface texture of the carbon material uniform and increases its density.

[0057] - Inerting Cooling Zone 6: Maintain low oxygen level (≤5%), slowly cool down to below 180℃, and maintain a slightly positive pressure (+10~+20Pa). Ensure that the charcoal material does not come into direct contact with the outside air before the temperature drops to a safe range.

[0058] Step 4: Prioritize atmosphere control.

[0059] During operation, the central controller reads the temperature, oxygen concentration, and pressure feedback values ​​of each zone in real time and performs multi-variable collaborative control. Specifically, when the temperature and oxygen concentration in the main pyrolysis zone 4 simultaneously deviate from the set range (e.g., temperature below 480℃ and oxygen concentration above 5%), the controller implements an atmosphere-priority control strategy: first, it adjusts the recirculation ratio and exhaust volume to restore the oxygen concentration to the set range; after the oxygen concentration returns to the set range, it adjusts the output power of the heating module 11. Specifically, the controller increases the opening of the recirculation gas inlet, increases the recirculation ratio (e.g., from 75% to 85%), and simultaneously appropriately closes the exhaust valve group 12 to reduce the incorporation of fresh air, causing the oxygen concentration to drop rapidly. Once the oxygen concentration stabilizes at ≤3%, the power of the heating module 11 is adjusted according to the temperature deviation. This control logic avoids the risk of localized overheating or volatile deflagration that might result from simply increasing the heating power, prioritizing the stability of the low-oxygen environment.

[0060] For other zones, when both temperature and oxygen concentration deviate simultaneously, correction is prioritized through atmosphere regulation rather than directly increasing heating power. This flexible control method reduces energy consumption and improves operational stability.

[0061] Step 5: Discharge.

[0062] After carbonization, the charcoal is transported by kiln car 9 into the double-gate chamber 8 at the kiln tail. The discharge process is as follows: 1. The inner gate 17 is opened, and the kiln car 9 enters the sealed buffer chamber; 2. The inner gate 17 is closed, and the interlock control mechanism locks the inner gate 17; 3. Low-oxygen kiln gas or nitrogen is introduced into the buffer chamber through the atmosphere conditioning channel, so that the charcoal material is further cooled to below 150°C in a low-oxygen environment; 4. The outer gate 16 is opened, and the kiln car 9 is moved out of the tunnel kiln body; 5. The outer gate 16 closes, completing one discharge cycle.

[0063] Example 3 This embodiment is used to process large-diameter logs with a diameter of 12-18 cm and a moisture content of 40%-50%. Compared with Embodiment 2, the following parameters are mainly adjusted: - The step beat time has been extended to 105 minutes per step, with a total dwell time of approximately 96 hours.

[0064] - Isothermal drying zone 2: The temperature is controlled at a constant 190℃, the heating rate is limited to ≤1.5℃ / min, and the residence time is extended to more than 20 hours.

[0065] - Slow-heating dehydroxylation zone 3: The temperature range is adjusted to 220~340℃, the heating rate is reduced to ≤1℃ / min, the residence time is extended to 22 hours, and the oxygen concentration is controlled at 3%~5%.

[0066] - Main pyrolysis zone 4: Reflux ratio increased to 85%, oxygen concentration controlled at ≤2%.

[0067] - The pressure gradient is adjusted to a more gradual distribution: pre-drying zone 1+15Pa, isothermal drying zone 2+5Pa, slow heating dehydroxylation zone 3-10Pa, main pyrolysis zone 4-30Pa, densification zone 5-15Pa, and inerting cooling zone 6+10Pa.

[0068] After continuous operation, the cracking rate of large-diameter logs was reduced from 8% to 15% in traditional continuous kilns to below 1%, proving the significant effect of slow-heating dehydroxylation zone 3 and heating rate control on crack prevention.

[0069] Example 4 This embodiment increases production capacity while ensuring product quality (end face integrity rate ≥95%). The kiln car 9-step cycle time is shortened to 60 minutes / step, and the total dwell time is approximately 50 hours. The following enhancement measures are adopted: The average recirculation rate of the entire kiln has been increased to 80%, reducing the amount of fresh air introduced.

[0070] Strengthen micro-pressure differential control: form a pressure differential that varies along the length of the kiln: pre-drying zone 1+30Pa, isothermal drying zone 2+15Pa, slow heating dehydroxylation zone 3-10Pa, main pyrolysis zone 4-50Pa, densification zone 5-20Pa, inerting cooling zone 6+20Pa.

[0071] The temperature in densification zone 5 was increased to 700℃, and the residence time was shortened to 1.5 hours.

[0072] Control logic optimization: When the temperature and oxygen concentration in the main pyrolysis zone 4 deviate simultaneously, the reflux ratio is preferentially increased to 90%.

[0073] Results: The integrity rate of the carbon material end face remained above 96%, and the unit energy consumption was reduced by about 12%.

[0074] Example 5 This embodiment describes in detail the specific implementation of the detection and control system.

[0075] The central controller adopts a programmable logic controller (PLC) with a built-in multivariable collaborative control algorithm. The controller is connected to the following actuators: the heating module 11 of each zone, the frequency converter of the circulating fan, the electric actuator of the inlet and outlet valve group 12, the flow regulating valve of the return air inlet, the drive mechanism of the double gate of the kiln head and kiln tail, and the stepper drive mechanism.

[0076] The controller has six preset temperature setpoints T_set(i), oxygen concentration setpoints O_set(i), pressure setpoints P_set(i), and allowable deviation ranges (ΔT, ΔO, ΔP), where i=1~6 correspond to the pre-drying zone 1 to the inerting cooling zone 6, respectively.

[0077] During operation, the controller reads the feedback values ​​from each temperature sensor 13, oxygen concentration sensor 14, and pressure sensor 15 in real time and executes the following control logic: Temperature control: A PID algorithm is used to calculate the output power of the heating module 11 to maintain the temperature within ±5℃ of the set value. However, when the oxygen concentration deviates from the set range, the integral term of the temperature PID is frozen, and atmosphere regulation is prioritized.

[0078] Oxygen concentration control: This is achieved by adjusting the opening of the flow regulating valve at the reflux gas inlet and the opening of the inlet / outlet valve assembly 12. If the oxygen concentration is higher than the set upper limit, the reflux ratio is increased and the exhaust volume is decreased; if the oxygen concentration is lower than the set lower limit, the reflux ratio is decreased and the exhaust volume is increased. Oxygen concentration control has a higher priority than temperature control.

[0079] Pressure differential control: Based on the feedback values ​​from the pressure sensors 15 of each zone, the opening degree of the intake and exhaust valve groups 12 of each zone is independently adjusted to maintain the pressure difference between adjacent zones near the set gradient value. The pressure adjustment cycle is 1 to 5 minutes to avoid coupling oscillation with oxygen concentration adjustment.

[0080] Dual-chamber interlocking control: The outer gate 16 and inner gate 17 of the kiln head dual-chamber 7 are interlocked to ensure they cannot open simultaneously. When the outer gate 16 is open, the inner gate 17 is locked closed; after the outer gate 16 is closed, the atmosphere conditioning channel begins to be purged, and the inner gate 17 can only be opened after the oxygen concentration in the sealed buffer chamber drops to the set value. The kiln tail dual-chamber 8 uses similar logic.

[0081] Stepper drive control: The controller outputs pulse signals at regular intervals to drive the stepper drive mechanism to advance the kiln car 9 by one pitch. The stepper cycle time can be set through the human-machine interface according to process requirements.

[0082] The aforementioned control system enables precise and coordinated control of temperature, oxygen concentration, and pressure difference in each zone under continuous operation conditions, ensuring stable overall operation of the tunnel kiln system and strong resistance to disturbances.

[0083] Comparative Example To verify the technical effects of the "slow-heating dehydroxylation zone 3" and the "pressure difference controlled along the material running direction" in this invention, the following comparative examples are set up.

[0084] The comparative example uses a conventional continuous tunnel kiln. The kiln body is divided along the material flow direction into only a drying zone (150–250℃), a pyrolysis zone (450–550℃), and a cooling zone (natural cooling), without a separate slow-heating dehydroxylation zone 3. This tunnel kiln lacks separate inlet and outlet valve groups 12 and a return gas inlet; the kiln pressure is only regulated by the main exhaust fan, failing to create a directional micro-pressure gradient along the kiln's length. Only a single curtain is installed at the kiln head and tail, without a double-chamber structure. During operation, a temperature-priority control strategy is employed: when the temperature deviates from the set range, the heating power is adjusted first.

[0085] Logs of the same specifications as in Example 1 (8-12 cm in diameter, 35% moisture content) were used for continuous carbonization at the same rate (85 minutes / step). The results are as follows: 1. About 2 hours after entering the pyrolysis zone, it was observed that about 8% of the logs showed obvious cracks on the end face, with some cracks extending into the interior of the charcoal material, resulting in product scrap.

[0086] 2. The oxygen concentration in the pyrolysis zone fluctuates significantly, changing periodically between 3% and 10%, and about 15% of the carbon material surface shows a gray or white oxide layer.

[0087] 3. When exiting the kiln, due to the absence of a double gate chamber 8 at the kiln tail, the high-temperature charcoal material is in direct contact with the air, and about 5% of the charcoal material undergoes localized combustion or severe surface oxidation.

[0088] 4. The integrity rate of the end face of the finished charcoal material is only about 75%, resulting in poor quality consistency.

[0089] The comparison shows that the present invention, by setting a slow-heating dehydroxylation zone 3, allows the logs to complete the release of internal stress before entering the main pyrolysis zone 4. At the same time, by forming a controlled pressure difference between the partitioned air intake and exhaust valve group 12 and the return air inlet, the backflow of external air is effectively suppressed. Combined with the atmosphere priority control logic, the cracking rate is significantly reduced and the integrity of the charcoal end face and batch consistency are improved.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-section zoned tunnel kiln, characterized in that, include: The tunnel kiln body comprises, along the material running direction, a pre-drying zone, an isothermal drying zone, a slow-heating dehydroxylation zone, a main pyrolysis zone, a densification zone, and an inertization cooling zone. The kiln car is used to transport raw materials sequentially through the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone.

2. The multi-segment zoned tunnel kiln according to claim 1, characterized in that, It also includes the track; The kiln car is positioned on the track.

3. The multi-segment zoned tunnel kiln according to claim 1, characterized in that, It also includes a detection system; The detection system is configured to detect the temperature and oxygen concentration of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone.

4. The multi-segment zoned tunnel kiln according to claim 1, characterized in that, It also has a double gate chamber; The double gate chambers are located at one or both ends of the tunnel kiln body to isolate the interior and exterior atmospheres of the tunnel kiln body during feeding or discharging.

5. The multi-segment zoned tunnel kiln according to claim 1, characterized in that, It also includes a circulating fan system; The circulating fan system is configured to circulate gas within the tunnel kiln body.

6. The multi-segment zoned tunnel kiln according to claim 1, characterized in that, The pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone are all equipped with exhaust valve groups and reflux gas inlets.

7. A continuous carbonization method, characterized in that, The kiln cars carrying logs pass sequentially through the pre-drying zone, isothermal drying zone, slow-heating dehydroxylation zone, main pyrolysis zone, densification zone, and inerting cooling zone. The temperature and oxygen concentration of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone are adjusted within a set range; Adjusting the opening degree of the exhaust valve group of the pre-drying zone, the isothermal drying zone, the slow-heating dehydroxylation zone, the main pyrolysis zone, the densification zone, and the inerting cooling zone, along with the reflux ratio of the reflux gas inlet, so that a controlled pressure difference is formed in the tunnel kiln body along the material running direction.

8. The continuous carbonization method according to claim 7, characterized in that, The kiln cars adopt a step-by-step operation mode. After completing one process cycle, multiple kiln cars move forward as a whole by a set pitch, so that the dwell time ratio in each zone remains constant.

9. The continuous carbonization method according to claim 7, characterized in that, When the temperature and oxygen concentration in the main pyrolysis zone deviate from the set range at the same time, the reflux ratio and exhaust volume are first adjusted to restore the oxygen concentration to the set range. After the oxygen concentration is restored to the set range, the output power of the heating module is then adjusted.

10. The continuous carbonization method according to claim 7, characterized in that, After carbonization, the carbon material is carried into the double gate chamber at the kiln tail by the kiln car, and after atmosphere conditioning and cooling, it is moved out of the tunnel kiln body.

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