An automatically adjustable autothermal pyrolysis process for a variety of biomass feedstocks

Abstract

The present application relates to biomass energy utilization technical field, particularly to a kind of automatically regulated self-heating pyrolysis process for multiple biomass raw materials, including drying after biomass is broken and sent into feed conveyor, then into low-temperature carbonization furnace for pyrolysis.Pyrolysis produces part of gas phase product by hot blast furnace combustion to produce hot flue gas, another part by spray tank recovery wood vinegar and produce non-condensable gas.Hot flue gas and part of circulating flue gas mixture heat low-temperature carbonization furnace, part of heat-exchanged flue gas is recycled back to hot blast furnace, another part is used for feed drying after denitration and air mixing.The present application sets first flow regulating valve and second flow regulating valve, respectively controls the distribution ratio of gas phase product and the circulation ratio of flue gas, can automatically regulate system heat balance according to raw material characteristics and working condition change, realizes stable self-heating operation under wide raw material adaptability, without external combustion.

Description

Technical Field

[0001] This invention relates to the field of biomass energy utilization technology, and in particular to an automatically adjustable self-heating pyrolysis process for various biomass raw materials. Background Technology

[0002] With the deepening of the goal of "carbon peaking and carbon neutrality", biomass, as an abundant renewable carbon-neutral resource, has attracted much attention for its high-value utilization technology. Biomass pyrolysis carbonization technology is widely used in the production of biochar, combustible gas, and wood vinegar, covering fields such as agricultural waste treatment, environmental protection material production, and energy recovery.

[0003] Existing biomass carbonization processes mostly employ direct heating, achieving heating through direct contact between flue gas and materials. This type of process suffers from the following technical bottlenecks: First, direct contact between flue gas and materials easily leads to product contamination and unstable carbonization quality; second, energy utilization efficiency is low, with a large amount of waste heat being emitted with the flue gas; third, raw material adaptability is poor, making it difficult to stably process different types and moisture contents of biomass raw materials on the same process equipment; fourth, system thermal balance relies on external supplementary combustion, making self-heating operation difficult; and fifth, the degree of automation is low, making it impossible to dynamically adjust process parameters according to raw material characteristics and changes in operating conditions.

[0004] In addition, as the core equipment of the carbonization process, the existing carbonization furnace has problems such as uneven material conveying, uneven heating, and poor sealing, which directly affect the stability of equipment operation and product quality. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention is proposed.

[0006] To solve the above technical problems, the present invention provides the following technical solution: an automatically adjustable self-heating pyrolysis process for various biomass raw materials, comprising a) crushing the biomass raw materials through a biomass crushing system and feeding them into a closed feed conveyor, using the exhaust gas after heat exchange to countercurrently dry the biomass in the conveyor, and then discharging the dried exhaust gas into the atmosphere after the dust collector removes impurities. b) The dried biomass enters a low-temperature carbonization furnace with indirect heat exchange and undergoes pyrolysis under anaerobic conditions to generate solid biochar and gaseous products. c) The gaseous products are pressurized by a booster fan and divided into two streams: the first stream of gaseous products is mixed with non-condensable gas from the spray tank and then sent to the hot air furnace for combustion; the second stream of gaseous products is sent to the spray tank and cooled to obtain wood vinegar and the non-condensable gas. d) The high-temperature flue gas generated by combustion in the hot blast stove is mixed with the exhaust gas of the first part of the circulating flue gas and then introduced into the heating jacket of the low-temperature carbonization furnace for indirect heat exchange after reaching the set temperature. e) The flue gas exhaust after heat exchange is drawn out by the induced draft fan and divided into two paths: the first part of the flue gas exhaust is circulated back to the hot air furnace, and the second part of the flue gas exhaust is denitrified and cooled by mixing air, and then used as the drying heat source in step a). In step c), the flow ratio of the first and second gaseous products is automatically adjusted by the first flow regulating valve, and in step e), the flow ratio of the first and second flue gas exhaust gases is automatically adjusted by the second flow regulating valve.

[0007] As a preferred embodiment of the automatically adjustable self-heating pyrolysis process for various biomass raw materials described in this invention, the pyrolysis reaction temperature is 250~350℃, the pyrolysis residence time is controlled at 15~40min by adjusting the chain speed of the low-temperature carbonization furnace, and the produced biochar has a calorific value ≥4000 kcal / kg and a solid dry basis yield of 40%~60%.

[0008] As a preferred embodiment of the automatically adjustable self-heating pyrolysis process for various biomass raw materials described in this invention, wherein: when the total ash content of the raw material is <20%, the feeding conveyor is a closed belt or scraper conveyor with a flue gas inlet at the tail end and a flue gas outlet at the beginning end, realizing countercurrent heat exchange between the flue gas and the material; the moisture content of the dried material is ≤10%. When the total ash content of the raw material is ≥20%, the feeding conveyor is a roller conveyor with a deashing screen plate, and other settings are the same.

[0009] As a preferred embodiment of the automatically adjustable self-heating pyrolysis process for various biomass raw materials described in this invention, the hot air furnace adopts a low flow resistance burner and a low nitrogen combustion design; the denitrification adopts a catalytic oxidation denitrification tower; the second part of the flue gas exhaust gas is mixed with the cold air blown in by the mixing fan after denitrification, and then enters the feeding conveyor.

[0010] As a preferred embodiment of the automatically adjustable self-heating pyrolysis process for various biomass raw materials described in this invention, the spray tank is provided with a spray water ring at the top, a liquid-sealed storage area at the bottom with a drain outlet, and an exhaust outlet in the upper middle part; the non-condensable gas is led out through the exhaust outlet and mixed with the first gas phase product.

[0011] A low-temperature carbonization furnace for an automatically adjustable self-heating pyrolysis process for various biomass raw materials, as described above, includes a flue gas outer casing, and at least two layers of chain conveyors arranged in parallel vertically are provided inside the flue gas outer casing, including an upper chain conveyor and a lower chain conveyor, and the number of chain conveyor layers can be further increased according to the processing capacity requirements. The top of the flue gas outer casing is provided with a feed inlet and a feed lock valve, and the bottom is provided with a discharge outlet and a discharge lock valve. The side wall is provided with multiple flue gas inlets and flue gas outlets. The upper chain conveyor and the lower chain conveyor both include a drive sprocket, a driven sprocket, a chain wound around the sprocket, and scrapers fixed at intervals on the chain. The chain is installed in conjunction with the chain guide rail.

[0012] As a preferred embodiment of the low-temperature carbonization furnace of the present invention, wherein: the feeding end of the upper chain conveyor is provided with a material distribution plate with an adjustable tilt angle, which is used to evenly distribute the material across the entire width of the chain. The outer wall of the scraper is provided with a toothed material turner, the teeth of which are arranged perpendicular to the direction of scraper movement and are used to turn the material layer.

[0013] As a preferred embodiment of the low-temperature carbonization furnace described in this invention, the flue gas outer casing contains multiple independent flue gas channels forming around the upper and lower chain conveyors. Each channel is connected to the corresponding flue gas inlet and outlet, thereby achieving segmented temperature control along the material conveying direction.

[0014] As a preferred embodiment of the low-temperature carbonization furnace of the present invention, the inner wall of the flue gas outer box is provided with a heat-insulating lining, and the feed lock valve and the discharge lock valve are star-shaped discharge valves with a contact-type self-lubricating sealing structure. The drive sprocket is independently driven by a variable frequency motor, and the chain speed is adjustable.

[0015] As a preferred embodiment of the low-temperature carbonization furnace of the present invention, the scraper has a length of 500~1200mm, a height of 100~200mm, and a spacing of 300~1000mm between adjacent scrapers; the driven sprocket is provided with a tension adjustment mechanism to maintain the tension of the chain.

[0016] The beneficial effects of this invention are as follows: By setting a first flow regulating valve and a second flow regulating valve, the distribution ratio of gaseous products and the circulation ratio of flue gas and exhaust gas are controlled respectively. This allows for automatic adjustment of the system's thermal balance based on raw material characteristics and operating conditions, achieving stable self-heating operation with wide raw material adaptability, eliminating the need for external combustion. The invention employs an indirect heat exchange method, where the high-temperature flue gas generated from the combustion of pyrolysis gaseous products heats the materials through a heating jacket, ensuring the purity of the biomass pyrolysis products by preventing direct contact between the flue gas and materials. Simultaneously, the flue gas energy is utilized in a tiered manner: high-temperature flue gas is used for carbonization heating, while low-temperature flue gas and exhaust gas are used for raw material drying and as a heat carrier in the reflux hot air furnace, maximizing energy efficiency. Waste heat recovery significantly improves energy efficiency; the low-temperature carbonization furnace adopts a multi-layer chain plate structure, combined with a material distribution plate to achieve uniform material distribution, and a comb-tooth turning device to forcefully turn the material layer, effectively solving the problems of material accumulation and uneven heating; the chain guide rail prevents chain deviation, and the scraper cleans residual material, ensuring long-term continuous and stable operation of the equipment; the design of multi-layer independent flue gas channels enables segmented temperature control along the material conveying direction, which can accurately match the temperature requirements of different stages such as drying, preheating, carbonization, and cooling in the biomass pyrolysis process, further optimizing the carbonization quality; the use of a double-sealed inlet and outlet air lock valve effectively maintains a low-oxygen environment in the carbonization chamber, ensuring the normal progress of the pyrolysis reaction. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the self-heating pyrolysis process in this invention; Figure 2 This is a schematic diagram of the overall structure of the low-temperature carbonization furnace in this invention; Figure 3 This is a schematic diagram of the middle structure of the flue gas outer casing in this invention.

[0019] Attached reference numerals: 1. Biomass crushing system; 2. Feed conveyor; 3. Low-temperature carbonization furnace; 4. Discharge conveyor; 5. Booster fan; 6. Hot air furnace; 7. Combustion fan; 8. Exhaust fan; 9. Denitrification tower; 10. Mixing fan; 11. Dust collector; 12. Spray tank; 13. First flow control valve; 14. Second flow control valve; 301. Flue gas outer casing; 302. Upper chain conveyor; 303. Lower chain conveyor; 304. Feed inlet; 305. Feed airlock valve; 306. Discharge outlet; 307. Discharge airlock valve; 308. Flue gas inlet; 309. Flue gas outlet; 310. Drive sprocket; 311. Driven sprocket; 312. Chain; 313. Scraper; 314. Chain guide rail; 315. Fabric distribution plate; 316. Comb tooth turning device; 317. Insulation lining. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments. Example 1

[0023] Reference Figure 1 and Figure 2 This is the first embodiment of the present invention, which provides an automatically adjustable self-heating pyrolysis process for various biomass raw materials.

[0024] Specifically, a) after the biomass raw material is crushed by the biomass crushing system 1, it is fed into the closed feed conveyor 2. The exhaust gas after heat exchange is used to countercurrently dry the biomass in the conveying process. After drying, the exhaust gas is discharged into the atmosphere after being cleaned by the dust collector 11. b) The dried biomass enters the low-temperature carbonization furnace 3 with indirect heat exchange, and undergoes pyrolysis under low oxygen conditions with an oxygen content of <1% to generate solid biochar and gaseous products. c) The gaseous products are pressurized by the booster fan 5 and divided into two streams: the first stream of gaseous products is mixed with non-condensable gas from the spray tank 12 and then sent to the hot air furnace 6 for combustion; the second stream of gaseous products is sent to the spray tank 12 and cooled to obtain wood vinegar and non-condensable gas. d) The high-temperature flue gas generated by combustion in the hot blast stove 6 is mixed with the exhaust gas of the first part of the circulating flue gas and then introduced into the heating jacket of the low-temperature carbonization furnace 3 for indirect heat exchange after reaching the set temperature. e) The flue gas exhaust after heat exchange is drawn out by the induced draft fan 8 and divided into two paths: the first part of the flue gas exhaust is circulated back to the hot air furnace 6, and the second part of the flue gas exhaust is denitrified and cooled by mixing air, and then used as the drying heat source in step a). In step c), the flow ratio of the first and second gaseous products is automatically adjusted by the first flow regulating valve 13, and in step e), the flow ratio of the first and second flue gas exhaust gases is automatically adjusted by the second flow regulating valve 14.

[0025] In this embodiment, corn stalks are selected as the biomass raw material. They are shredded and crushed in one process by the biomass crushing system 1, and the length of the crushed material is controlled within 10cm. The crushed material enters the closed scraper feed conveyor 2, which has a flue gas inlet at the tail end and a flue gas outlet at the beginning end, so as to realize the countercurrent contact between the flue gas and the material.

[0026] The second portion of flue gas from the subsequent processing section has already undergone denitrification treatment in the denitrification tower 9 and is mixed with cold air blown in by the mixing fan 10 to cool it to 150-180°C. This flue gas enters from the flue gas inlet at the tail end of the feed conveyor 2, forming a counter-current heat exchange with the biomass crushed material being conveyed forward. The residual heat in the flue gas heats and dries the wet material, and the moisture is discharged from the flue gas outlet at the beginning of the feed conveyor 2 with the airflow. After the solid particles entrained in the gas are removed by the bag filter 11, the clean gas is discharged into the atmosphere. After drying, the moisture content of the material entering the low-temperature carbonization furnace 3 is reduced to below 10%.

[0027] The dried biomass crushed material enters the low-temperature carbonization furnace 3 through the feed inlet 304. The low-temperature carbonization furnace 3 is an indirect heat exchange type moving bed carbonization device specifically designed for this invention, which is equipped with an upper chain conveyor 302 and a lower chain conveyor 303. The material first falls into the feed end of the upper chain conveyor 302, and is evenly spread across the entire width of the chain by the distribution plate 315, and then moves to the right with the chain. During the movement, the comb-tooth turning device 316 set above the chain continuously rotates, and its comb teeth insert into the material layer and continuously turn it over, exposing the bottom layer of material and ensuring that the material is heated evenly. When the upper chain conveyor 302 conveys to the right end, the material falls into the lower chain conveyor 303 by gravity, and then moves to the left in the opposite direction for secondary heating.

[0028] The entire pyrolysis process is carried out under low oxygen conditions (oxygen content <1%). As a preferred embodiment, the pyrolysis temperature is controlled in the range of 280~320℃, and the pyrolysis residence time is controlled in the range of 15~20min by adjusting the drive chain speed of the active sprocket 310. It should be noted that biomass pyrolysis can be achieved in a wide temperature range of 250~350℃.

[0029] After the pyrolysis reaction is completed, the solid product, namely biochar, falls from the left end of the lower chain conveyor 303 into the discharge port 306, is discharged through the discharge air lock valve 307, and enters the discharge conveyor 4 with a cooling water jacket for indirect cooling. The cooled biochar is collected as the finished product. Testing shows that the biochar produced in this embodiment has a calorific value ≥4000 kcal / kg, and a solid dry basis yield between 40% and 60%.

[0030] The high-temperature gaseous products generated by the pyrolysis reaction are discharged from the top of the low-temperature carbonization furnace 3, pressurized by the booster fan 5, and then transported through pipelines to the first flow regulating valve 13. The first flow regulating valve 13 automatically distributes the gaseous products into two streams: the first stream is sent to the hot blast furnace 6 via pipeline, and the second stream is sent to the spray tank 12 via pipeline. The distribution ratio of the two streams is automatically adjusted according to the system's heat balance requirements.

[0031] The second stream of gaseous products enters the spray tank 12 from the lower part of the tank and comes into countercurrent contact with the cooling water sprayed from the top spray ring. The condensable components in the gaseous products are absorbed and condensed by the cooling water, forming wood vinegar in the liquid storage area at the bottom of the tank, which is periodically discharged and collected through the bottom drain port. The non-condensable gaseous components are led out from the exhaust port at the upper part of the spray tank 12, and merge with the first stream of gaseous products through a pipeline, and are jointly sent into the hot blast furnace 6.

[0032] The first stream of gaseous products, mixed with non-condensable gases, enters the hot blast stove 6. Simultaneously, the combustion blower 7 blows air into the stove, causing the gas to burn completely and produce high-temperature flue gas. The start-up / emergency natural gas pipeline for this process is only used for emergency combustion during the initial ignition and heating phases of the system or in case of abnormal operating conditions. During normal self-heating operation, this pipeline is closed, and no external combustion is required. The hot blast stove 6 employs a low-flow-resistance burner design and a low-NOx combustion design to adapt to the combustion conditions of large fluctuations in the composition and unstable calorific value of biomass pyrolysis gas.

[0033] The high-temperature flue gas generated by combustion mixes with the first portion of flue gas returning from the low-temperature carbonization furnace 3, which is controlled by the second flow regulating valve 14, at the outlet of the hot blast stove 6, and the temperature is adjusted to the set temperature. The heated mixed flue gas, after temperature adjustment, enters the heating jacket of the low-temperature carbonization furnace 3 through the flue gas inlet 308.

[0034] The flue gas outer casing 301 forms multiple independent flue gas channels surrounding the upper chain conveyor 302 and the lower chain conveyor 303. The hot-mixed flue gas flows within each channel, indirectly exchanging heat with the material in the carbonization chamber through the metal wall plates, transferring heat to the material to maintain the pyrolysis reaction. After heat exchange, the flue gas temperature drops to approximately 350°C, becoming exhaust gas, which is discharged through the flue gas outlet 309 and drawn out by the induced draft fan 8.

[0035] The exhaust gas from the outlet of the induced draft fan 8 is transported through pipeline to the second flow regulating valve 14. This valve automatically divides the exhaust gas into two streams: the first stream circulates back to the hot air furnace 6 via pipeline, mixing with the high-temperature flue gas to regulate the hot air temperature; the second stream is sent to the denitrification tower 9 via pipeline, where nitrogen oxides are removed from the flue gas using catalytic oxidation. The denitrified flue gas is mixed with the cold air blown in by the mixing fan 10 and cooled to 150~180℃, then used as a drying heat source and fed into the tail end flue gas inlet of the feed conveyor 2, completing the entire heat and mass circulation.

[0036] Throughout the entire operation of this embodiment, the system dynamically maintains thermal balance based on the characteristics of raw materials and changes in operating conditions through the automatic adjustment of the first flow regulating valve 13 and the second flow regulating valve 14, without the need for external fuel replenishment, thus achieving self-heating stable operation. Example 2

[0037] Reference Figure 1 and Figure 2 This is the second embodiment of the present invention, which is implemented based on the previous embodiment.

[0038] Specifically, in a preferred embodiment of the present invention, the temperature of the pyrolysis reaction is controlled within the range of 280~320℃, and the pyrolysis residence time is controlled by adjusting the chain speed of the low-temperature carbonization furnace 3 to maintain the reaction time within 15~40 min; the calorific value of the produced biochar is ≥4000 kcal / kg, and the solid dry basis yield is 40%~60%. The pyrolysis reaction can be achieved in a relatively wide range of 250~350℃, with only slight differences in product characteristics.

[0039] The pyrolysis reaction temperature is controlled between 280 and 320°C. This temperature range falls within the category of low-temperature pyrolysis, and its function is to suppress excessive release of volatiles from biomass, thereby increasing the yield of solid biochar. When the pyrolysis temperature exceeds 400°C, cellulose and hemicellulose in the biomass decompose rapidly, leading to a significant decrease in char yield. The low-temperature conditions of 280–320°C allow the pyrolysis reaction to proceed gently, retaining more fixed carbon while reducing the generation of tar and gases.

[0040] The pyrolysis residence time is controlled between 15 and 40 minutes by adjusting the chain speed driven by the drive sprocket 310 of the low-temperature carbonization furnace 3. A faster chain speed results in a shorter residence time, and vice versa. In actual operation, operators can adjust the chain speed via a variable frequency motor according to the type of raw material and the target product quality requirements, ensuring sufficient and uniform pyrolysis time for the material within the furnace. Within the above temperature and time range, the biochar produced has a stable calorific value of ≥4000 kcal / kg, and the solid dry basis yield remains between 40% and 60%, providing high-quality raw materials for subsequent dry powder gasification or direct combustion.

[0041] Preferably, when the total ash content of the raw material is <20%, the feeding conveyor 2 is a closed belt or scraper conveyor with a flue gas inlet at the tail end and a flue gas outlet at the beginning end to achieve countercurrent heat exchange between the flue gas and the material; the moisture content of the dried material is ≤10%. When the total ash content of the raw material is ≥20%, the feeding conveyor 2 is a roller conveyor with a deashing screen plate, and other settings are the same.

[0042] Among them, the selection of the feeding conveyor 2 is designed according to the ash content of the raw materials, in order to match the characteristics of different raw materials, optimize the drying effect and improve the subsequent carbonization conditions.

[0043] For low-ash raw materials with a total ash content of <20% (such as corn stalks, wood chips, rice husks, etc.), a closed belt or scraper conveyor is used. These raw materials have less impurity content, and the main requirements are efficient drying and closed conveying. The structure of this conveyor has multiple functions. The arrangement of the flue gas inlet at the tail end and the flue gas outlet at the beginning end realizes the countercurrent contact between the flue gas and the material. The high-temperature flue gas and the low-temperature wet material meet at the inlet end, resulting in a large driving force for heat and mass transfer and a significant improvement in drying efficiency. The temperature of the flue gas gradually decreases along the conveying direction, while the temperature of the material gradually increases, which can avoid surface coking caused by rapid heating. Closed conveying can prevent the leakage of odors and dust generated during the drying process and improve the working environment. After being dried by this conveyor, the moisture content of the material entering the low-temperature carbonization furnace (3) can be reduced to ≤10%. Low moisture content is crucial for the carbonization process. On the one hand, it can reduce the heat consumption required for moisture vaporization and reduce the system heat load. On the other hand, it can prevent water vapor from reacting with high-temperature carbon to form water gas, avoid the decrease in biochar yield and the destruction of pore structure, thereby ensuring the quality of the final product.

[0044] For high-ash raw materials with a total ash content ≥20% (such as some forestry materials and municipal solid waste-derived fuels), a roller conveyor with a deashing screen is used. High-ash raw materials often contain impurities such as mud, sand, and stones. If these materials are directly fed into the carbonization furnace, it will not only reduce the quality of biochar but also accelerate equipment wear. During the conveying process, the roller conveyor rotates the cylinder, causing the material to tumble. The screen structure can actively remove smaller ash particles and impurities, allowing them to be separated and discharged during the drying stage.

[0045] By using a roller conveyor, two advantages are achieved: first, the amount of ash entering the carbonization furnace is reduced, thus improving the purity of the biochar product; second, the risk of wear and tear on subsequent equipment due to impurities is reduced, extending the equipment's service life. Simultaneously, the roller conveyor retains the flue gas inlet and outlet structure, enabling the same counter-current heat exchange drying function as the low-ash solution, ensuring that the material's moisture content reaches ≤10%.

[0046] Through the aforementioned differentiated design, this process can automatically match the optimal feeding and conveying method based on the ash content of the raw materials: low-ash raw materials are conveyed using efficient closed conveying to ensure drying effect and environmental hygiene; high-ash raw materials undergo pre-ash removal treatment during drying, improving product quality and protecting equipment. This design significantly enhances the process's adaptability to different raw materials, expands the range of raw material sources, and provides technical support for the large-scale treatment of biomass waste.

[0047] The hot blast stove 6 adopts a low flow resistance burner and a low nitrogen combustion design; the denitrification adopts a catalytic oxidation denitrification tower 9; the second part of the flue gas exhaust gas is mixed with the cold air blown in by the mixing fan 10 after denitrification, and then enters the feeding conveyor 2.

[0048] The hot air furnace 6 employs a low-flow-resistance burner and a low-NOx combustion design. The low-flow-resistance burner features a smooth gas flow path and low pressure drop, adapting to conditions of large fluctuations in biomass pyrolysis gas composition and unstable calorific value, ensuring stable combustion. The low-NOx combustion design reduces peak flame temperature through technologies such as staged air distribution or internal flue gas recirculation, reducing NOx generation at the source. In conjunction with this, a catalytic oxidation denitrification tower 9 is used to deeply denitrify the exhaust gas from the second section of the flue gas, further reducing NOx emission concentrations. The denitrified flue gas is mixed with cold air blown in by the mixing fan 10, and after the temperature is controlled to 150-180℃, it enters the feed conveyor 2 as a drying heat source.

[0049] This process enables the cascade utilization of waste heat from flue gas, using the low-temperature flue gas that would otherwise be discharged into the atmosphere for drying, thus saving external energy; at the same time, it avoids damage to conveyor seals or ignition of materials by mixing air and cooling.

[0050] Preferably, the spray tank 12 has a spray water ring at the top, a liquid-sealed storage area at the bottom with a drain port, and an exhaust port in the upper middle part; non-condensable gas is led out through the exhaust port and mixed with the first gas phase product.

[0051] The spray tank 12 has a spray water ring at the top, a liquid-sealed storage area at the bottom with a drain port, and an exhaust port in the upper middle part. The spray water ring allows cooling water to be sprayed evenly and come into full contact with the rising gaseous products. The temperature difference is used to condense the condensable components, which fall into the bottom storage area to form wood vinegar.

[0052] The liquid seal design prevents non-condensable gases from leaking from the bottom, ensuring a sealed gas path. The wood vinegar liquid accumulated in the storage area can be periodically discharged and collected from the drain port. The exhaust port in the upper middle part is used to draw out the non-condensable gas components, which are mixed with the first gaseous product through a pipeline and then sent to the hot blast stove 6 for combustion and utilization. Example 3

[0053] Reference Figures 1-3 This is the third embodiment of the present invention, which provides a low-temperature carbonization furnace.

[0054] It should be noted that this embodiment uses a double-layer chain plate machine as an example to illustrate the present invention, but the present invention is not limited to a double-layer structure. Depending on the processing capacity requirements, the number of layers of the chain plate machine can be expanded to three, four or more layers, and its structural principle is the same as that of the double-layer structure.

[0055] Specifically, it includes a flue gas outer casing 301, which is equipped with at least two layers of chain conveyors arranged in parallel, including an upper chain conveyor 302 and a lower chain conveyor 303, and the number of chain conveyor layers can be further increased according to the processing capacity requirements. The flue gas outer casing 301 has a feed inlet 304 and a feed air lock valve 305 at the top, a discharge outlet 306 and a discharge air lock valve 307 at the bottom, and multiple flue gas inlets 308 and flue gas outlets 309 on the side walls. The upper chain conveyor 302 and the lower chain conveyor 303 both include a drive sprocket 310, a driven sprocket 311, a chain 312 wound on the sprocket, and scrapers 313 fixed at intervals on the chain. The chain 312 is installed on the chain guide rail 314, and the scrapers 313 can clean the residual material on the chain plate.

[0056] The flue gas outer casing 301 is an integral pressure-bearing shell structure, welded from heat-resistant steel plates. Inside the flue gas outer casing 301, an upper chain conveyor 302 and a lower chain conveyor 303 are arranged in parallel, stacked vertically to form a double-layer conveying structure. The top of the flue gas outer casing 301 is equipped with a feed inlet 304 and a feed airlock valve 305, while the bottom is equipped with a discharge outlet 306 and a discharge airlock valve 307. Multiple flue gas inlets 308 and flue gas outlets 309 are evenly arranged along the length of the side walls.

[0057] The upper chain conveyor 302 and the lower chain conveyor 303 have basically the same structure, both including a drive sprocket 310, a driven sprocket 311, a chain 312 wound around the sprocket, and scrapers 313 fixed at intervals on the chain. The chain 312 is fitted onto a chain guide rail 314, which has a groove structure and is arranged along both sides of the chain conveyor. The chain 312 is embedded in the grooves of the guide rail on both sides.

[0058] The function of this structure is to limit the left and right swing trajectory of the chain 312, preventing deviation due to chain wear or uneven tension after long-term operation, and ensuring the smooth operation of the chain conveyor. When the drive sprocket 310 rotates, the chain 312 drives the scraper 313 to move horizontally along the guide rail 314, and the scraper 313 pushes the material forward to achieve continuous material conveying.

[0059] Preferably, the upper chain conveyor 302 has an adjustable tilt angle material distribution plate 315 at the feeding end, which is used to evenly distribute the material across the entire width of the chain. The outer wall of the scraper 313 is provided with a toothed material turner 316. The teeth of the toothed material turner 316 are arranged perpendicular to the direction of scraper movement and are used to turn the material layer.

[0060] The upper chain conveyor 302 is equipped with an adjustable-angle feeding plate 315 at its feed end. The feeding plate 315 is hinged to a bracket directly below the feed inlet 304, and its tilt angle can be adjusted within the range of 15° to 45° using adjusting bolts.

[0061] When the material falls from the feed inlet 304, it first lands on the distribution plate 315. After being guided by the plate surface, it is evenly distributed across the entire width of the chain plate, preventing the material from accumulating in strips or cones in the middle of the chain plate. Even distribution ensures a consistent material layer thickness on the chain plate, resulting in uniform heating conditions during subsequent heating and preventing incomplete pyrolysis due to excessively thick localized material layers. Simultaneously, a uniform material layer also facilitates even force distribution during the turning of the comb-tooth turning device 316, reducing the risk of equipment jamming.

[0062] A toothed material turner 316 is provided on the outer wall of the scraper 313, with the teeth of the turner 316 arranged perpendicular to the direction of scraper movement. The turner 316 moves with the scraper 313. When the scraper pushes the material forward, the teeth insert into the material layer and loosen and turn the material, causing the bottom layer material to turn to the surface layer, and the surface layer material to be buried in the bottom layer. By forcibly breaking the caking and bridging phenomena that may form in the material during the heating process, the turner 316 allows the material in all parts of the material layer to have the opportunity to contact the heated chain plate, while increasing the contact area between the material and the heat radiation in the furnace, significantly improving the uniformity of heat exchange.

[0063] The flue gas outer casing 301 forms multiple independent flue gas channels around the upper chain conveyor 302 and the lower chain conveyor 303. Each channel is connected to the corresponding flue gas inlet 308 and flue gas outlet 309, realizing segmented temperature control along the material conveying direction.

[0064] The flue gas outer casing 301 is divided into multiple independent spaces by partitions, including the upper chain conveyor channel, the upper chain conveyor internal cavity channel, the middle gap channel between the two chain conveyors, the lower chain conveyor internal cavity channel, and the lower chain conveyor channel.

[0065] Each channel is connected to its corresponding flue gas inlet 308 and flue gas outlet 309, forming an independent flue gas circuit. Operators can independently control the flue gas flow and temperature in each channel by adjusting the valve opening of each flue gas inlet 308 according to the needs of the material at different pyrolysis stages.

[0066] The inner wall of the flue gas outer casing 301 is provided with a heat-insulating lining 317. The feed lock valve 305 and the discharge lock valve 307 are star-shaped discharge valves with a contact-type self-lubricating sealing structure. The drive sprocket 310 is independently driven by a variable frequency motor, and the chain speed is adjustable.

[0067] The 317 insulation lining uses high-temperature resistant aluminum silicate fiberboard insulation material to reduce heat loss from the equipment's interior to the outside through the metal casing, lowering the external wall temperature and improving the operating environment. It also enhances the efficiency of heat transfer to materials. This reduction in heat loss lowers the system's demand for heat from the hot air furnace, further strengthening the energy-saving effect of the self-heating process.

[0068] Both the feed airlock valve 305 and the discharge airlock valve 307 are star-shaped discharge valves, employing a contact-type self-lubricating sealing structure. The valve plate is made of polytetrafluoroethylene or graphitized carbon fiber composite material, which fits tightly against the inner wall of the valve body to form a double sealing surface. During the rotation of the valve plate, the sealing material forms a transfer film under friction, achieving self-lubrication, reducing drive power while ensuring long-term leak-free operation.

[0069] Preferably, the scraper 313 has a length of 500~1200 mm, a height of 100~200 mm, and a spacing of 300~1000 mm between adjacent scrapers; the driven sprocket 311 is provided with a tension adjustment mechanism to maintain the tension of the chain 312.

[0070] The driven sprocket 311 is equipped with a tension adjustment mechanism, which usually adopts a screw-type or spring-type tensioning structure. The tension of the chain 312 is changed by adjusting the position of the driven sprocket 311.

[0071] By compensating for the plastic elongation of the chain during long-term operation, the chain and sprocket are properly meshed, preventing tooth skipping, jamming, or chain slippage caused by chain slack, thus ensuring long-term continuous and stable operation of the equipment.

[0072] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An automatically adjustable self-heating pyrolysis process for various biomass raw materials, characterized in that: include: a) After the biomass raw material is crushed by the biomass crushing system (1), it is fed into the closed feed conveyor (2). The exhaust gas after heat exchange is used to dry the biomass in the conveying process in a countercurrent manner. After drying, the exhaust gas is discharged into the atmosphere after being cleaned by the dust collector (11). b) The dried biomass enters the low-temperature carbonization furnace (3) with indirect heat exchange. Under low oxygen conditions, when the oxygen content is <1%, a pyrolysis reaction is carried out to generate solid biochar and gaseous products. c) The gaseous products are pressurized by the booster fan (5) and divided into two paths: the first path of gaseous products is mixed with non-condensable gas from the spray tank (12) and sent to the hot air furnace (6) for combustion; the second path of gaseous products is sent to the spray tank (12) and cooled to obtain wood vinegar and the non-condensable gas. d) The high-temperature flue gas generated by combustion in the hot blast stove (6) is mixed with the exhaust gas of the first part of the circulating flue gas and then introduced into the heating jacket of the low-temperature carbonization furnace (3) for indirect heat exchange after reaching the set temperature. e) The exhaust gas after heat exchange is drawn out by the induced draft fan (8) and divided into two paths: the first part of the exhaust gas is circulated back to the hot air furnace (6), and the second part of the exhaust gas is denitrified and cooled by mixing air, and then used as the drying heat source in step a). In step c), the flow ratio of the first and second gas phase products is automatically adjusted by the first flow regulating valve (13), and in step e), the flow ratio of the first and second part flue gas is automatically adjusted by the second flow regulating valve (14).

2. The automatically adjustable self-heating pyrolysis process for various biomass raw materials as described in claim 1, characterized in that: The temperature of the pyrolysis reaction is 250~350℃, and the pyrolysis residence time is controlled at 15~40min by adjusting the chain speed of the low-temperature carbonization furnace (3); the calorific value of the produced biochar is ≥4000 kcal / kg, and the solid dry basis yield is 40%~60%.

3. The automatically adjustable self-heating pyrolysis process for various biomass raw materials as described in claim 1, characterized in that: When the total ash content of the raw material is <20%, the feeding conveyor (2) is a closed belt or scraper conveyor with a flue gas inlet at the tail end and a flue gas outlet at the beginning end to achieve countercurrent heat exchange between the flue gas and the material; the moisture content of the dried material is ≤10%; when the total ash content of the raw material is ≥20%, the feeding conveyor (2) is a roller conveyor with a deashing screen plate, and the other settings are the same.

4. The automatically adjustable self-heating pyrolysis process for various biomass raw materials as described in claim 1, characterized in that: The hot blast stove (6) adopts a low flow resistance burner and a low nitrogen combustion design; the denitrification adopts a catalytic oxidation denitrification tower (9); the second part of the flue gas exhaust gas is mixed with the cold air blown in by the mixing fan (10) after denitrification, and then enters the feeding conveyor (2).

5. The automatically adjustable self-heating pyrolysis process for various biomass raw materials as described in claim 1, characterized in that: The spray tank (12) is provided with a spray water ring at the top, a liquid-sealed storage area at the bottom and a drain outlet at the bottom, and an exhaust outlet at the middle and upper part; the non-condensable gas is led out through the exhaust outlet and mixed with the first gas phase product.

6. A low-temperature carbonization furnace applied to the pyrolysis process as described in any one of claims 1 to 5, characterized in that: It includes a flue gas outer casing (301), and at least two layers of chain conveyors arranged in parallel, including an upper chain conveyor (302) and a lower chain conveyor (303), and the number of chain conveyor layers can be further increased according to the processing capacity. The flue gas outer casing (301) is provided with a feed inlet (304) and a feed air lock valve (305) at the top, a discharge outlet (306) and a discharge air lock valve (307) at the bottom, and multiple flue gas inlets (308) and flue gas outlets (309) on the side wall; the upper chain plate machine (302) and the lower chain plate machine (303) both include a drive sprocket (310), a driven sprocket (311), a chain (312) wound on the sprocket, and scrapers (313) fixed at intervals on the chain, and the chain (312) is installed on the chain guide rail (314).

7. The low-temperature carbonization furnace as described in claim 6, characterized in that: The upper chain conveyor (302) is equipped with an adjustable tilting angle feeding plate (315) at the feeding end, which is used to evenly distribute the material across the entire width of the chain. The outer wall of the scraper (313) is provided with a toothed material turner (316), the teeth of which are arranged perpendicular to the direction of scraper movement and are used to turn the material layer.

8. The low-temperature carbonization furnace as described in claim 7, characterized in that: The flue gas outer casing (301) forms multiple independent flue gas channels around the upper chain plate machine (302) and the lower chain plate machine (303). Each channel is connected to the corresponding flue gas inlet (308) and flue gas outlet (309) to realize segmented temperature control along the material conveying direction.

9. The low-temperature carbonization furnace as described in claim 8, characterized in that: The inner wall of the flue gas outer casing (301) is provided with a heat-insulating lining (317), and the feed lock valve (305) and the discharge lock valve (307) are star-shaped discharge valves with a contact-type self-lubricating sealing structure. The drive sprocket (310) is independently driven by a variable frequency motor, and the chain speed is adjustable.

10. The low-temperature carbonization furnace as described in claim 9, characterized in that: The scraper (313) has a length of 500~1200mm, a height of 100~200mm, and a spacing of 300~1000mm between adjacent scrapers; the driven sprocket (311) is provided with a tension adjustment mechanism to maintain the tension of the chain (312).

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