Coal-based solid waste comprehensive treatment process and system containing volatile matter

Abstract

The present application relates to a kind of coal-based solid waste comprehensive treatment process and system containing volatile matter, belong to coal-based solid waste resource utilization technical field.The process aims to solve the problems of existing technology when processing coal-based solid waste containing volatile matter, such as material easy to be cemented, low thermal utilization efficiency and unstable product quality.Process technical scheme includes drying section, anaerobic pyrolysis section, preheating section, decarburization section and rapid cooling section, slow cooling section, final cooling section executed in sequence;Anaerobic pyrolysis section uses circulating pyrolysis gas as heat carrier to exchange heat with dried material to precipitate volatile matter, and the pyrolysis gas discharged from the anaerobic pyrolysis section is partly returned to circulation after dust removal, and the other part is output as fuel.The process and system are mainly used to realize efficient and stable treatment of coal gangue and other coal-based solid waste containing volatile matter and produce cement admixture or ceramsite products.

Description

Technical Field

[0001] This invention relates to the field of coal-based solid waste resource utilization technology. More specifically, this invention relates to a comprehensive treatment process and system for coal-based solid waste containing volatile matter. Background Technology

[0002] Coal mining processes generate large amounts of coal-based solid waste containing volatile matter, such as coal gangue, coal slime, and sludge. These materials contain a certain amount of volatile matter and fixed carbon, and thus have a certain calorific value.

[0003] Coal gangue, the largest byproduct of coal mining and utilization, is a mineral with low carbon content and high ash content, accounting for approximately 20% of raw coal production. To improve coal quality and applications, coal gangue is separated during coal preparation after raw coal mining and disposed of as solid waste. Coal gangue with a calorific value ≤400 kcal / kg is used for self-heating brick firing, while gangue with a calorific value ≥1800 kcal / kg is used for co-firing or direct power generation, and the technologies for these two types of gangue are relatively mature. However, there is no mature technology for decarbonizing coal gangue with a calorific value of 400-1800 kcal / kg. While publicly available technologies provide direction for decarbonizing coal gangue with a calorific value of 400-1800 kcal / kg, they still suffer from the uncontrollable issues of process temperature, product quality, and production status inherent in traditional combustion decarbonization methods.

[0004] For example, Chinese Patent Publication No. CN117419555A discloses a decarbonization device and process for coal gangue. This process relies on the sintering machine and belt roasting machine processes used in the metallurgical industry. A trolley arranged sequentially on upper and lower elliptical tracks serves as the carrier for the coal gangue. The coal gangue passes through a preheating section, an ignition section, a combustion decarbonization section, and a cooling section along the trolley to complete the entire decarbonization process. At the tail end of the machine, the trolley reverses to unload the material. In the ignition section, the coal gangue is ignited by top-down exhaust air. In the combustion decarbonization section, it is further combusted and decarbonized by hot air from the cooling section. This process enables large-scale processing of coal gangue and achieves energy recovery through the reuse of hot air in the cooling section. However, this process suffers from problems such as caking and low heat utilization. At an ignition temperature of 1150±20℃, the coal gangue bed rapidly releases volatiles and combusts, releasing heat. A combustion zone forms in the upper part of the bed due to the high temperature of the ignition flue gas, causing liquefaction, adhesion, and eventually caking. The rapid release and downward movement of volatiles from the coal gangue at high temperatures causes rapid heating and caking of the surface layer in the middle and lower parts of the bed. This rapid heating of the surface layer of the coal gangue particles also prevents effective decarburization inside, affecting product quality. The coal gangue entering the cooling section clumps into large pieces, resulting in poor cooling efficiency due to the low cooling surface area. This necessitates the use of large amounts of cooling air and extended cooling sections, leading to high costs and low waste heat utilization. Furthermore, the decarburization airflow from top to bottom, with the high-temperature area downwind, requires the use of a bottom layer of material or large amounts of cold air for cooling to protect the equipment, resulting in energy waste.

[0005] Therefore, in view of the shortcomings of existing coal gangue and other coal-based solid waste treatment technologies, there is an urgent need for an efficient and feasible method to decarbonize coal gangue and other calorific value solid wastes and transform them into cement admixtures, ceramsite and other products, so as to realize the comprehensive utilization of coal gangue. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0007] Another objective of this invention is to provide a comprehensive treatment process for coal-based solid waste containing volatiles. This process, which combines anaerobic pyrolysis with pyrolysis gas as a carrier with a circulating hot air system, effectively prevents caking and overburning of materials during the pyrolysis and decarbonization process. It achieves efficient and stable resource utilization treatment of medium and low calorific value coal-based solid waste and significantly improves energy utilization efficiency and product quality.

[0008] To achieve these objectives and other advantages according to the present invention, a comprehensive treatment process for coal-based solid waste containing volatile matter is provided, comprising process steps performed in the following order:

[0009] Drying section: Uses hot air to dry materials;

[0010] Oxygen-free pyrolysis section: In an oxygen-free environment, circulating pyrolysis gas is used to exchange heat with the dried material, causing the volatiles in the material to be released.

[0011] Preheating section: In an oxygen-containing environment, the material after oxygen-free pyrolysis is heated and its temperature is increased using the first circulating hot air;

[0012] Decarbonization section: In an oxygen-containing environment, the preheated material is decarbonized using the second circulating hot air.

[0013] Cooling section: includes a rapid cooling section, a slow cooling section, and a final cooling section. The rapid cooling section cools the material discharged from the decarburization section to 580℃-650℃ at a cooling rate of 40℃ / min-105℃ / min. The slow cooling section cools the material discharged from the rapid cooling section to 350℃-450℃ at a cooling rate of 10℃ / min-40℃ / min. The final cooling section cools the material discharged from the slow cooling section to ≤120℃.

[0014] The first circulating hot air discharged and cooled from the preheating section and the second circulating hot air discharged and cooled from the decarbonization section are combined and then heated in the rapid cooling section before being divided into two paths. One path leads to the inlet of the preheating section to participate in the circulation and form the first circulating hot air, and the other path leads to the inlet of the decarbonization section to participate in the circulation and form the second circulating hot air. The circulating pyrolysis gas discharged from the oxygen-free pyrolysis section is dusted, and part of it is reheated and returned to the inlet of the oxygen-free pyrolysis section to participate in the circulation, while the other part is output as fuel.

[0015] The final cooling section uses ambient temperature air to cool the material discharged from the slow cooling section. Part of the air discharged from the final cooling section is sent to the slow cooling section to cool the material discharged from the rapid cooling section. Part of the air discharged from the slow cooling section is sent to the preheating section and the decarburization section as oxygen supplement gas for the preheating section and the decarburization section.

[0016] Preferably, a calcination section is further provided between the decarburization section and the cooling section; the calcination section includes:

[0017] Roasting stage 1: Roasting circulating hot air at 800℃-1000℃ is used to heat the material discharged from the decarburization stage, promoting the decarburization and consolidation of the material;

[0018] Second roasting stage: Receives material from first roasting stage;

[0019] The roasting circulating hot air discharged from the first roasting stage is cooled to 450℃-550℃ and then introduced into the second roasting stage. After exchanging heat with the material in the second roasting stage, the temperature is raised. The heated roasting circulating hot air is then reheated to 800℃-1000℃ by the pyrolysis gas output as fuel, so that it can continue to be returned to the first roasting stage for recycling.

[0020] In addition to some of the air discharged from the slow cooling section going to the preheating section and the decarburization section, some of the air also goes to the first roasting section as oxygen supplement gas for the first roasting section.

[0021] Preferably, the drying section includes a primary drying section and a secondary drying section performed sequentially, as follows:

[0022] Primary drying section: The material is dried using first hot air, which originates from the air discharged from the final cooling section and / or the air discharged from the slow cooling section, and is adjusted to a temperature of 120℃-200℃.

[0023] Secondary drying section: The material discharged from the primary drying section is dried using a second hot air source. The second hot air is derived from the second circulating hot air discharged from the decarburization section before cooling, and / or the roasting circulating hot air discharged from the roasting section before cooling. The temperature of the second hot air is adjusted to be 200℃-260℃.

[0024] Preferably, the second circulating hot air discharged from the decarbonization section before cooling, and / or the roasting circulating hot air discharged from the roasting section before cooling, are passed to the secondary drying section after exchanging heat with the dust-removed circulating pyrolysis gas, serving as the second hot air; simultaneously, the circulating pyrolysis gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the reheated circulating pyrolysis gas is divided into a first circulating pyrolysis gas and a second circulating pyrolysis gas, the first circulating pyrolysis gas being adjusted and cooled to 270℃-500℃;

[0025] The oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage I and an oxygen-free pyrolysis stage II, which are performed sequentially. In the oxygen-free pyrolysis stage I, a first circulating pyrolysis gas is used to exchange heat with the material discharged from the secondary drying stage. After heat exchange, the first circulating pyrolysis gas is cooled down and discharged from the oxygen-free pyrolysis stage I. In the oxygen-free pyrolysis stage II, a second circulating pyrolysis gas is used to exchange heat with the material discharged from the oxygen-free pyrolysis stage I. After heat exchange, the second circulating pyrolysis gas is cooled down and discharged from the oxygen-free pyrolysis stage II.

[0026] The first circulating pyrolysis gas discharged from the first stage of oxygen-free pyrolysis and the second circulating pyrolysis gas discharged from the second stage of oxygen-free pyrolysis are combined to form a combined gas. After gravity dust removal, part of the combined gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the other part is divided into a first part and a second part. The first part leads to the gas boiler, and the second part leads to the inlet of the first stage of roasting.

[0027] Preferably, the first circulating pyrolysis gas is cooled to 270℃-500℃ in the following specific manner:

[0028] Apart from the first part leading to the gas boiler and the second part leading to the inlet of the roasting section, the remaining part of the combined gas is divided into a third part and a fourth part. The third part is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air. The fourth part serves as a cooling source for the first circulating pyrolysis gas and is mixed with the first circulating pyrolysis gas. By adjusting the mixing ratio of the fourth part with the first circulating pyrolysis gas, the temperature of the first circulating pyrolysis gas is reduced to 270℃-500℃.

[0029] Preferably, the calorific value of the coal-based solid waste containing volatile matter ranges from 200 kcal / kg to 1800 kcal / kg, and before entering the drying section, the material undergoes pulverization and pelletizing treatment to form green pellets with a particle size of 5 mm to 25 mm.

[0030] This invention also provides a treatment system for implementing a comprehensive treatment process for coal-based solid waste containing volatile matter, comprising a drying section, an anaerobic pyrolysis section, a preheating section, a decarbonization section, a rapid cooling section, a slow cooling section, and a final cooling section connected sequentially along the material processing direction; the system further includes a cooling fan, a slow cooling fan, a decarbonization circulating fan, a roasting circulating fan, a dust removal device, a pyrolysis gas circulating fan, a pyrolysis gas heating device, a gas boiler, and a circulating gas cooling device; the system is configured to establish a circulating hot air loop and a circulating pyrolysis gas loop;

[0031] The circulating hot air circuit is configured as follows: the air outlet of the rapid cooling section is divided into two paths, which are respectively connected to the air inlet of the preheating section and the air inlet of the decarbonization section; the hot air outlet of the preheating section and the hot air outlet of the decarbonization section are merged and then connected to the air inlet of the rapid cooling section; the decarbonization circulating fan is provided on the flow path from the merged end of the air outlets of the preheating section and the decarbonization section to the air inlet of the rapid cooling section.

[0032] The circulating pyrolysis gas circuit is configured as follows: the outlet of the oxygen-free pyrolysis section is fluidly connected to the inlet of the dust removal device, the outlet of the dust removal device is fluidly connected to the inlet of the pyrolysis gas heating device, and the outlet of the pyrolysis gas heating device is fluidly connected to the inlet of the oxygen-free pyrolysis section; and a pyrolysis gas circulating fan is provided in the flow path from the outlet of the dust removal device to the inlet of the pyrolysis gas heating device.

[0033] The flow path between the outlet of the pyrolysis gas circulating fan and the inlet of the pyrolysis gas heating device is further configured with a branch for outputting a portion of the circulating pyrolysis gas as fuel, and the branch is connected to the gas inlet of the gas boiler.

[0034] The air inlet of the cooling fan is connected to the outside, the air outlet of the cooling fan is connected to the air inlet of the final cooling section, the air outlet of the final cooling section is connected to the air inlet of the slow cooling section through the slow cooling fan, and the air outlet of the slow cooling section is connected to the air outlet of the rapid cooling section, so as to supplement the oxygen consumed in the decarbonization process of the preheating section and the decarbonization section.

[0035] The cooling end of the circulating gas cooling device is connected to the flow path between the air outlet and the merging end of the preheating section, and the flow path between the air outlet and the merging end of the decarbonization section.

[0036] Preferably, a roasting device is also provided between the decarbonization section and the rapid cooling section; the roasting device includes a first roasting device and a second roasting device; the material inlet of the first roasting device is connected to the material outlet of the decarbonization section, the material outlet of the first roasting device is connected to the material inlet of the second roasting device, and the material outlet of the second roasting device is connected to the material inlet of the rapid cooling section.

[0037] The system is also equipped with a roasting circulating air circuit, which is configured in the following way: the air inlet of the first roasting stage device is in fluid communication with the air outlet of the second roasting stage device; the air outlet of the first roasting stage device is in communication with the air inlet of the second roasting stage device; and the roasting circulating fan is provided on the flow path connecting the air outlet of the first roasting stage device and the air inlet of the second roasting stage device.

[0038] The outlet of the pyrolysis gas circulating fan is connected to the combustion device of the first roasting stage device, and the combustion device organizes combustion to supply heat to the first roasting stage as fuel; the air outlet of the slow cooling stage is connected to the hot air inlet of the first roasting stage device to supply oxygen for roasting; the flow path of the first roasting stage device and the roasting circulating fan is connected to the cooling end of the circulating gas cooling device.

[0039] Preferably, the drying section includes a primary drying section and a secondary drying section connected in sequence, with the material outlet of the primary drying section connected to the material inlet of the secondary drying section; the system further includes:

[0040] A primary drying fan, the outlet of which is connected to the air inlet of the primary drying section, and the inlet of which is connected to the air outlet of the slow cooling section and the air outlet of the final cooling section, respectively, for conveying low-temperature hot air from the slow cooling section and the final cooling section to the primary drying section.

[0041] A secondary drying fan, wherein the inlet of the secondary drying fan is connected to the air outlet of the pyrolysis gas heating device, and the outlet of the secondary drying fan is in fluid communication with the hot air inlet of the secondary drying section;

[0042] The flow path between the air outlet of the decarbonization section and the cooling end connection point of the circulating gas cooling device, and the flow path between the first roasting unit and the cooling end connection point of the circulating gas cooling device, are both connected to the air inlet of the pyrolysis gas heating device, so that the excess waste gas from the air outlets of the decarbonization section and the first roasting unit is cooled by the pyrolysis gas heating device and used as the drying gas for the secondary drying fan.

[0043] Preferably, the oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage 1 device and an oxygen-free pyrolysis stage 2 device; the material outlet of the oxygen-free pyrolysis stage 1 device is connected to the material inlet of the oxygen-free pyrolysis stage 2 device.

[0044] The outlet of the pyrolysis gas heating device is connected to the pyrolysis gas inlet of the first stage oxygen-free pyrolysis device and the pyrolysis gas inlet of the second stage oxygen-free pyrolysis device through a flow path.

[0045] The pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device and the pyrolysis gas outlet of the oxygen-free pyrolysis stage 2 device are combined and then connected to the inlet of the dust removal device.

[0046] The system is also equipped with a pyrolysis gas return pipeline. One end of the pyrolysis gas return pipeline is connected to the flow path at the pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device, and the other end is connected to the flow path before the pyrolysis gas inlet of the oxygen-free pyrolysis stage 1 device. It is used to return part of the pyrolysis gas from the oxygen-free pyrolysis stage 1 device to its inlet in order to adjust the inlet temperature of the oxygen-free pyrolysis stage 1 device.

[0047] The present invention has at least the following beneficial effects:

[0048] First, it effectively prevents material caking and surface overburning: by separating the "oxygen-free pyrolysis" and "preheating and decarbonization" into stages, and carrying out pyrolysis in an oxygen-free environment, the pyrolysis and combustion processes of the material are separated, avoiding the violent combustion of volatiles when they come into contact with oxygen at high temperatures. This prevents the material surface from liquefying, sticking, and caking due to a rapid increase in temperature, and ensures the full progress of the internal decarbonization reaction of the material.

[0049] Secondly, it improves energy utilization efficiency: The multi-stage circulating hot air and pyrolysis gas circulation system enables the cascade recovery and reuse of heat within the system, significantly reducing external energy consumption. In particular, the hot air recovered in the cooling section is used for preheating and decarbonization, and pyrolysis gas can be obtained independently during the pyrolysis process. This gas can be purified, collected, stored, and transported as fuel, or it can be directly used to generate steam for power generation, thus improving the overall energy utilization rate.

[0050] Third, it achieves precise control of process temperature: by separating the oxygen-free pyrolysis section and the oxygen-containing decarbonization section, and by independently regulating the circulating air system, the temperature of each stage is highly controllable, avoiding the temperature runaway problem caused by the combustion of volatiles in traditional processes, and improving the stability of product quality.

[0051] Fourth, it is applicable to a wider range of calorific value materials: This process is particularly suitable for coal-based solid waste with a calorific value between 200-1800 kCal / kg, filling the gap in decarbonization technology for solid wastes such as medium and low calorific value coal gangue, and expanding the scope of application for resource utilization of coal-based solid waste.

[0052] Fifth, improve product quality and yield: Through multi-stage cooling methods such as slow cooling and rapid cooling, the thermal stress cracking of materials during the cooling process is reduced, the pulverization rate is lowered, and the strength and physical properties of finished products are improved. It is suitable for the production of high-quality building materials such as ceramsite and cement admixtures.

[0053] Sixth, unlike the open air system of traditional processing processes, this invention uses a closed-loop circulating air system. The low thermal conductivity of the material results in slow heating, and the heat transfer and diffusion time is longer than the decarbonization reaction time. This invention, taking into account the characteristics of the material, uses circulating air as a heat carrier, and replenishes fresh air through the circulating system to provide the oxygen required for the reaction. While pursuing a high heating rate, it reduces the air volume entering and leaving the system, thereby reducing process energy consumption.

[0054] Seventh, unlike traditional processing techniques, this invention separates the roasting stage (i.e., roasting stage two) into an independent process and uses a circulating air system to bring the heat back to the roasting stage (i.e., roasting stage one) for self-circulating roasting.

[0055] Eighth, unlike the "series air" design of rotary kiln processing and other static roasting processes, which results in excess airflow during the material decarburization process and causes heat to be carried away by the air system, the air system of each process in this invention is relatively independent and can be individually controlled to meet the material processing requirements. By controlling the airflow and temperature, the heat released during the material oxidation process is used to heat the material itself, achieving self-heating roasting and reducing external heat and grade.

[0056] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0057] Figure 1 This is a process flow diagram of a comprehensive treatment process for coal-based solid waste containing volatiles, according to one of the technical solutions of the present invention. Detailed Implementation

[0058] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0059] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0060] like Figure 1 As shown, the present invention provides a comprehensive treatment process for coal-based solid waste containing volatile matter, used to treat coal-based solid waste materials containing volatile matter, comprising process steps executed in the following order:

[0061] Drying section: Uses hot air to dry materials;

[0062] Oxygen-free pyrolysis section: In an oxygen-free environment, circulating pyrolysis gas is used to exchange heat with the dried material, causing the volatiles in the material to be released.

[0063] Preheating section: In an oxygen-containing environment, the material after oxygen-free pyrolysis is heated and its temperature is increased using the first circulating hot air;

[0064] Decarbonization section: In an oxygen-containing environment, the preheated material is decarbonized using the second circulating hot air.

[0065] Cooling section: includes a rapid cooling section, a slow cooling section, and a final cooling section. The rapid cooling section cools the material discharged from the decarburization section to 580℃-650℃ at a cooling rate of 40℃ / min-105℃ / min. The slow cooling section cools the material discharged from the rapid cooling section to 350℃-450℃ at a cooling rate of 10℃ / min-40℃ / min. The final cooling section finally cools the material discharged from the slow cooling section to ≤120℃.

[0066] The first circulating hot air discharged and cooled from the preheating section and the second circulating hot air discharged and cooled from the decarbonization section are combined and then heated in the rapid cooling section before being divided into two paths. One path leads to the inlet of the preheating section to participate in the circulation and form the first circulating hot air, and the other path leads to the inlet of the decarbonization section to participate in the circulation and form the second circulating hot air. The circulating pyrolysis gas discharged from the oxygen-free pyrolysis section is dusted, and part of it is reheated and returned to the inlet of the oxygen-free pyrolysis section to participate in the circulation, while the other part is output as fuel.

[0067] The final cooling section uses ambient temperature air to cool the material discharged from the slow cooling section. Part of the air discharged from the final cooling section is sent to the slow cooling section to cool the material discharged from the rapid cooling section. Part of the air discharged from the slow cooling section is sent to the preheating section and the decarburization section as oxygen supplement gas for the preheating section and the decarburization section.

[0068] In the above technical solution, the comprehensive treatment process for coal-based solid waste containing volatile matter is used to treat coal-based solid waste materials with a calorific value range of 200 kCal / kg-1800 kCal / kg. The materials can be common coal-based solid waste containing volatile matter such as coal gangue and coal slime, or mixtures of solid waste such as red mud and tailings containing coal (carbon). These raw materials all come from solid waste accumulations generated during coal mining and coal processing.

[0069] A belt dryer can be used as the drying equipment in the drying section. The temperature of the drying hot air introduced into the drying section inlet can be 120-260℃. The material after crushing and pelletizing is dried for 20-30 minutes to remove most of the moisture from the material.

[0070] The oxygen-free pyrolysis section can be equipped with a closed-loop pyrolysis furnace. The temperature of the circulating pyrolysis gas introduced into the oxygen-free pyrolysis section can be 450-600℃. The circulating pyrolysis gas at 450-600℃ processes the material from the drying section for 12-20 minutes, directly exchanging heat with the material to release the volatiles in the material. Nitrogen can be used as the base carrier gas for the circulating pyrolysis gas. During the oxygen-free pyrolysis process, an oxygen-free environment can be achieved by continuously introducing inert gas. After dust removal, a portion of the circulating pyrolysis gas exiting the oxygen-free pyrolysis section is reheated to the required temperature and returned to the oxygen-free pyrolysis section inlet for reuse, while the other portion can be used as fuel to supply a gas-fired boiler.

[0071] The preheating stage can use a box-type preheater as the preheating equipment, and the decarbonization stage can use a continuous decarbonization reactor as the decarbonization equipment. Both are commercially available industrial equipment. The temperature of the first circulating hot air introduced into the preheating stage inlet can be 750-1000℃. The first circulating hot air treats the material from the anaerobic pyrolysis stage for 8-12 minutes to preheat the material. The temperature of the second circulating hot air introduced into the decarbonization stage inlet can also be 750-1000℃. The second circulating hot air treats the material from the preheating stage for 5-10 minutes to promote the decarbonization reaction of the material.

[0072] The rapid cooling section can use a fluidized bed cooler as the rapid cooling equipment. The rapid cooling section introduces first circulating hot air (cooled) from the preheating section outlet and second circulating hot air (cooled) from the decarburization section outlet as cooling media to rapidly cool the material from the decarburization section. The temperature of the first circulating hot air entering the rapid cooling section can be controlled at 450-500℃, and the temperature of the second circulating hot air entering the rapid cooling section can be controlled at 600-650℃. By adjusting the mixing ratio and flow rate of the two hot airs, the material is rapidly cooled from a high temperature to 580-650℃. The cooling rate of the material in the rapid cooling section is 40℃ / min-105℃ / min, ensuring that the cooling rate meets the requirements of subsequent processes while avoiding cracking of the material due to excessively rapid cooling. In this process, the mixture of the first and second circulating hot air is reheated to 750-1000°C by the material in the rapid cooling section. Then, the mixture of the first and second circulating hot air exiting the rapid cooling section is introduced into the inlet of the preheating section and the inlet of the decarburization section, respectively, forming a cycle.

[0073] The slow cooling section can be a horizontal slow cooling furnace, which receives the rapidly cooled material. The final cooling section can be a rotary cooler, serving as the final stage of the cooling process, receiving the material from the slow cooling section. During the slow cooling process, some recovered hot air from the final cooling section can be introduced as cooling air. The temperature of this recovered hot air can be controlled at 180-220℃ and is transported to the inlet of the slow cooling section by a slow cooling fan to gently exchange heat with the material, slowly cooling the material temperature from 580-650℃ to 300-450℃. The cooling rate of the material in the slow cooling section can be 10℃ / min-40℃ / min. The air heated in the slow cooling section can reach a temperature of 400-450℃. Part of this air is introduced into the preheating and decarbonization sections as oxygen supply gas to supplement the oxygen required for the two-step reaction. In actual use, it is preferable to introduce this part of the air into the rapid cooling section, where it is heated and then sent to the preheating and / or decarbonization sections along with the outlet air of the rapid cooling section. Part of the air can be transported to the inlet of the drying section as drying gas to assist in the dehydration of the material.

[0074] During the final cooling process, ambient temperature air (typically 20-30℃) is introduced as the cooling medium via a cooling fan. This ambient temperature air is then transported by the cooling fan to the inlet of the final cooling section, where it fully contacts and exchanges heat with the 300-450℃ material exiting the slow cooling section, ultimately cooling the material to below 120℃. The air heated by the material in the final cooling section can reach a temperature of 180-220℃. This air is then divided into two paths via pipelines: one path, as described above, is transported to the slow cooling section via a slow cooling fan, serving as the cooling air for that section; the other path is transported to the drying section.

[0075] Throughout the cooling section, the temperature of the material and the temperature of the hot air in each section can be monitored in real time by temperature sensors. At the same time, the flow rate of hot air and cooling air in each section can be adjusted by air volume regulating valves. The air volume regulating valves are butterfly valves commonly used in industry, which are installed on the air supply ducts of each section to ensure that the cooling process is stable and controllable.

[0076] The technical advantages of this solution are mainly reflected in the following aspects: First, existing technologies use a single oxygen-containing hot air system to simultaneously complete pyrolysis and combustion, while this solution separates oxygen-free pyrolysis from oxygen-containing preheating and decarbonization steps, and uses circulating pyrolysis gas as the heat carrier for oxygen-free pyrolysis. This avoids over-burning and caking of the material surface caused by the combustion of volatiles during the pyrolysis stage, solving the problems of material caking and insufficient internal decarbonization in existing technologies. Second, existing technologies use an open-circuit hot air system with low waste heat recovery efficiency. This solution designs a multi-stage circulating hot air system to recover heat from the cooling step. The air is used for preheating and decarbonization, and part of the pyrolysis gas is recycled and part is exported as fuel, which significantly improves energy utilization efficiency and overcomes the serious energy waste of existing technologies. Third, existing technologies have a narrow adaptability to the calorific value of materials and low temperature control accuracy. This technology, through the temperature gradient design of the oxygen-free pyrolysis section and the independent control of the circulating air system, can process coal-based solid waste of 200-1800 kcal / kg, with small temperature fluctuations in each step and significantly improved product quality stability. Fourth, existing technologies with a single cooling section cannot balance the cooling rate and material integrity. High-temperature materials are prone to cracking due to thermal stress when directly exposed to cold air, resulting in a high product pulverization rate. This technical solution divides the cooling process into three stages: rapid cooling, slow cooling, and final cooling. Through gradient cooling, it avoids cracking of materials due to excessive temperature differences, solving the problem of poor product integrity in existing technologies. Fifth, existing technologies directly discharge waste heat during the cooling process, resulting in significant energy waste. This technical solution utilizes multi-stage waste heat recovery: the rapid cooling stage uses preheated and decarbonized circulating hot air for cooling, and the heated hot air is returned to the original cycle; the slow cooling stage utilizes the hot air recovered from the final cooling stage, and the heated air is returned to the original cycle. The air is used for oxygen supply and drying; the air heated in the final cooling section is used for slow cooling and drying, realizing the cascade utilization of waste heat, which improves the waste heat recovery efficiency compared with the existing technology and overcomes the energy waste of the existing technology; sixth, the existing technology only uses room temperature cold air as the cooling medium, which cannot flexibly adjust the cooling intensity according to the material temperature. This technical solution selects circulating hot air, recovered hot air and room temperature air as cooling media according to the material temperature characteristics of each cooling section. The cooling intensity is flexibly controlled by the air volume regulating valve, which can adapt to the cooling needs of materials with different initial temperatures and broaden the applicability of the process.

[0077] In another technical solution, a roasting section is further provided between the decarburization section and the cooling section; the roasting section includes:

[0078] Roasting stage 1: Roasting circulating hot air at 800℃-1000℃ is used to heat the material discharged from the decarburization stage, promoting the decarburization and consolidation of the material;

[0079] Second roasting stage: Receives material from first roasting stage;

[0080] The roasting circulating hot air discharged from the first roasting stage is cooled to 450℃-550℃ and then introduced into the second roasting stage. After exchanging heat with the material in the second roasting stage, the temperature is raised. The heated roasting circulating hot air is then reheated to 800℃-1000℃ by the pyrolysis gas output as fuel, so that it can continue to be returned to the first roasting stage for recycling.

[0081] A portion of the air discharged from the slow cooling section goes to the preheating and decarburization sections, while another portion goes to the first roasting section as supplementary oxygen gas.

[0082] In the above technical solution, a roasting section is added between the decarburization section and the cooling section. The roasting section includes a first roasting section and a second roasting section. The first roasting section can be a high-temperature resistant belt roasting furnace. The temperature of the roasting circulating air entering the inlet of the first roasting section is 800-1000℃. The roasting circulating air at 800-1000℃ directly contacts and heats the material from the decarburization section, causing the mineral components in the material to undergo a solidification reaction. The residence time of the material in the first roasting section can be set according to the material's solidification requirements, such as 10-20 minutes, to ensure that the material is fully solidified and does not over-burn.

[0083] The second roasting stage can use a belt roaster with the same structure as the first roasting stage, receiving materials from the first stage. The roasting circulating hot air discharged from the hot air outlet of the first stage can be cooled to 450-550℃ via a tubular heat exchanger or other cooling device. The cooled roasting circulating hot air is then introduced into the inlet of the second roasting stage, where it exchanges heat with the materials from the first stage, causing its temperature to rise. The heat exchange time between the cooled roasting circulating hot air and the materials in the second roasting stage can be 5 minutes. Simultaneously, the circulating pyrolysis gas, which can be used as fuel, is output from the anaerobic pyrolysis step and introduced into the combustion device of the first roasting stage. Through organized combustion, it supplies heat to the first stage. After combustion, the pyrolysis gas reheats the roasting circulating hot air to 800-1000℃ and returns it to the inlet of the first roasting stage to participate in the circulation. The roasting circulating hot air is driven by a roasting circulating fan.

[0084] This technical solution adds a two-stage roasting step, which has the following technical effects: First, the material is fully solidified by high-temperature hot air at 800-1000℃, solving the problem of low product strength in the existing technology; Second, the existing hot air system is an open circuit, and the high-temperature hot air is directly discharged after use, resulting in low energy utilization. This technical solution designs a roasting circulating hot air loop, which cools the high-temperature hot air discharged from the first roasting stage and uses it for heat exchange in the second roasting stage. Then, it is heated by circulating pyrolysis gas and circulated back to the first roasting stage, realizing the recycling of hot air. At the same time, the pyrolysis gas generated by oxygen-free pyrolysis is used as fuel to replace external fuel, which reduces external energy consumption compared with the existing technology and overcomes the serious energy waste of the existing technology.

[0085] In another technical solution, the drying section includes a primary drying section and a secondary drying section performed sequentially, as follows:

[0086] Primary drying section: The material is dried using first hot air, which originates from the air discharged from the final cooling section and / or the air discharged from the slow cooling section, and is adjusted to a temperature of 120℃-200℃.

[0087] Secondary drying section: The second hot air originates from the second circulating hot air discharged from the decarburization section before cooling, and / or the roasting circulating hot air discharged from the roasting section before cooling, and is adjusted so that the temperature of the second hot air is 200℃-260℃.

[0088] In the above technical solution, the primary drying section of the drying step can be a mesh belt dryer. The primary drying section is used to receive raw pellets with a particle size of 5-25mm after powdering and pelletizing. The first hot air used in the primary drying section originates from the relatively low-temperature hot air discharged from the final cooling section (e.g., 130-210℃) and / or the relatively high-temperature hot air discharged from the slow cooling section (e.g., 350-400℃). The temperature of the first hot air can be controlled at 120℃-200℃ by adjusting the mixing ratio of the hot air discharged from the final cooling section and / or the hot air discharged from the slow cooling section. If the initial moisture content of the material is high (e.g., exceeding 12%), the temperature can be set to 160℃-200℃ to accelerate dehydration; if the initial moisture content of the material is low (e.g., 8%-10%), it can be set to 120℃-140℃ to avoid material bursting. The primary drying time can be controlled within 15-20 minutes. Since the temperature of the first hot air is lower than the material volatilization temperature (usually above 200℃), the exhaust gas generated after primary drying can be directly discharged without additional treatment, reducing subsequent environmental protection costs.

[0089] The secondary drying section also uses a mesh belt dryer, which receives the material after primary drying. The second hot air used for secondary drying originates from the second circulating hot air (approximately 500–900°C) discharged from the decarburization section before cooling, and / or the roasting circulating hot air (approximately 500–900°C) discharged from the roasting section before cooling. That is, a portion of the second circulating hot air discharged from the decarburization section before cooling is directed to the secondary drying section, and a portion of the roasting circulating hot air discharged from the roasting section before cooling is directed to the secondary drying section. Valves are installed on the pipes leading to the secondary drying section, and the temperature or source of the second hot air can be adjusted by regulating the valve opening or closing. The temperature of the second hot air is 200–260°C. During the actual process, the temperature of the second hot air can be adjusted according to the moisture content of the material when it enters the secondary drying stage. If the moisture content of the material is still high after the primary drying stage (e.g., 7%-8%), the temperature can be set to 240℃-260℃; if the moisture content has dropped to 5%-6%, it can be set to 200℃-220℃. The secondary drying time can be controlled within 5-12 minutes to ensure that the final moisture content of the material drops below 2%, meeting the moisture requirements of the material for subsequent anaerobic pyrolysis.

[0090] The technical advantages of this solution are reflected in the following aspects: First, existing technologies use a single drying stage. High-temperature hot air can easily cause materials to burst due to excessive dehydration, while low-temperature hot air results in low drying efficiency. This solution, however, employs a two-stage drying process. The first stage uses low-temperature waste heat air (120℃-200℃) to prevent material bursting, while the second stage uses medium-temperature waste heat air (200℃-260℃) to improve drying efficiency, solving the problem of balancing drying efficiency and material integrity in existing technologies. Second, existing technologies often directly use highly polluting waste gas for drying, requiring additional investment in desulfurization and denitrification equipment. Existing technologies often involve high costs for treating waste gas. This technical solution addresses this by using low-temperature air from the final cooling section for the primary drying stage, allowing for direct discharge of the waste gas. The secondary drying stage utilizes cooled, low-pollution flue gas, requiring only simple dust removal before discharge. This significantly reduces waste gas treatment costs compared to existing technologies, overcoming the high environmental costs associated with them. Thirdly, existing drying technologies often rely on external heat sources or a single waste heat source, resulting in low energy utilization. This technical solution utilizes waste heat from different stages within the system (final cooling stage, slow cooling stage, and decarbonization / calcination stage) for both drying stages, achieving cascaded utilization of waste heat and reducing external energy consumption compared to existing technologies.

[0091] In another technical solution, the second circulating hot air discharged from the decarbonization section before cooling, and / or the roasting circulating hot air discharged from the roasting section before cooling, are passed to the secondary drying section after exchanging heat with the dust-removed circulating pyrolysis gas, serving as the second hot air; at the same time, the circulating pyrolysis gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the reheated circulating pyrolysis gas is divided into a first circulating pyrolysis gas and a second circulating pyrolysis gas, and the first circulating pyrolysis gas is adjusted and cooled to 270℃-500℃;

[0092] The oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage I and an oxygen-free pyrolysis stage II, which are performed sequentially. In the oxygen-free pyrolysis stage I, a first circulating pyrolysis gas is used to exchange heat with the material discharged from the secondary drying stage. After heat exchange, the first circulating pyrolysis gas is cooled down and discharged from the oxygen-free pyrolysis stage I. In the oxygen-free pyrolysis stage II, a second circulating pyrolysis gas is used to exchange heat with the material discharged from the oxygen-free pyrolysis stage I. After heat exchange, the second circulating pyrolysis gas is cooled down and discharged from the oxygen-free pyrolysis stage II.

[0093] The first circulating pyrolysis gas discharged from the first stage of oxygen-free pyrolysis and the second circulating pyrolysis gas discharged from the second stage of oxygen-free pyrolysis are combined to form a combined gas. After gravity dust removal, part of the combined gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the other part is divided into a first part and a second part. The first part leads to the gas boiler, and the second part leads to the inlet of the first stage of roasting.

[0094] The specific method for adjusting and cooling the first circulating pyrolysis gas to 270℃-500℃ is as follows:

[0095] Apart from the first part leading to the gas boiler and the second part leading to the inlet of the roasting section, the remaining part of the combined gas is divided into a third part and a fourth part. The third part is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air. The fourth part serves as a cooling source for the first circulating pyrolysis gas and is mixed with the first circulating pyrolysis gas. By adjusting the mixing ratio of the fourth part with the first circulating pyrolysis gas, the temperature of the first circulating pyrolysis gas is reduced to 270℃-500℃.

[0096] In the above technical solution, the oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage I and an oxygen-free pyrolysis stage II, which are carried out sequentially. Both the oxygen-free pyrolysis stage I and the oxygen-free pyrolysis stage II can be selected from horizontal oxygen-free pyrolysis furnaces. The oxygen-free pyrolysis stage I is used to receive the material after secondary drying.

[0097] After dust removal, the circulating pyrolysis gas is divided into two paths: one for fuel output and the other for recirculation. The fuel output portion is further divided into a first part and a second part. The first part leads to the gas boiler, and the second part leads to the combustion device in the first roasting stage. A portion of the second part is used as fuel output. The recirculating portion is divided into a third part and a fourth part. The third part is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air to form heated circulating pyrolysis gas. This reheated circulating pyrolysis gas is then divided into a first circulating pyrolysis gas and a second circulating pyrolysis gas. The first circulating pyrolysis gas is introduced into the inlet of the first oxygen-free pyrolysis stage, and the second circulating pyrolysis gas is introduced into the inlet of the second oxygen-free pyrolysis stage. Simultaneously, the fourth part serves as a cooling source and mixes with the first circulating pyrolysis gas. By adjusting the mixing ratio of the fourth part and the first circulating pyrolysis gas, the temperature of the first circulating pyrolysis gas can be controlled between 270-500℃.

[0098] The first circulating pyrolysis gas directly exchanges heat with the material to achieve heat transfer. The residence time of the material in the first stage of oxygen-free pyrolysis can be set to 8-15 minutes. During this process, the material temperature gradually increases, and some low-boiling-point volatiles are released. At the same time, the pyrolysis gas itself decreases in temperature due to heat exchange, laying the foundation for subsequent reflux temperature control. The second stage of oxygen-free pyrolysis receives the material discharged from the first stage and continues to perform oxygen-free pyrolysis on the material. The residence time of the material in the second stage of oxygen-free pyrolysis can be set to 4-6 minutes. Through heat exchange with the high-temperature second circulating pyrolysis gas, the temperature of the material further increases to 520℃-600℃, and the remaining high-boiling-point volatiles are released. At this time, the temperature of the pyrolysis gas itself decreases, and it then merges with the cooled pyrolysis gas discharged from the first stage of oxygen-free pyrolysis, and together they enter the subsequent dust removal stage.

[0099] Throughout the oxygen-free pyrolysis process, the oxygen-free environment is maintained by circulating pyrolysis gas. First, an inert gas (such as nitrogen or flue gas) is continuously introduced to replace the air in the equipment. During operation, the generated pyrolysis gas replaces the inert gas introduced during startup. During normal production, the gas environment in the oxygen-free pyrolysis section is pyrolysis gas. Simultaneously, an oxygen content sensor (commercially available electrochemical oxygen content sensors) is installed on the equipment to monitor the oxygen content in real time, ensuring that the oxygen content in the system is ≤0.5%, thus preventing the dangers posed by the combustion of pyrolysis gas.

[0100] The technical advantages of this solution are reflected in the following aspects: First, existing technologies do not have an independent oxygen-free pyrolysis process, while this solution divides oxygen-free pyrolysis into two stages. A first-stage circulating pyrolysis gas at 270℃-500℃ achieves gentle heating and initial volatilization of the material, followed by a second-stage circulating pyrolysis gas at 550℃-650℃ for deep volatilization, avoiding surface overheating and caking caused by a single high temperature. Second, the temperature of the pyrolysis gas in existing technologies cannot be flexibly controlled; it can only be achieved by adjusting the power of the heating device, resulting in a slow response. This solution utilizes the low-temperature pyrolysis gas discharged from the first stage of oxygen-free pyrolysis to mix with the main pyrolysis gas, rapidly controlling the inlet temperature of the first stage, shortening the control response time compared to existing technologies. Third, existing technologies have large temperature gradients during pyrolysis (e.g., directly from 200℃ to 600℃), easily leading to internal cracks in the material. This solution, through two-stage pyrolysis and temperature gradient design, reduces the internal temperature difference of the material, lowering the crack initiation rate.

[0101] In another technical solution, the calorific value of the coal-based solid waste containing volatile matter ranges from 200 to 1800 kcal / kg, and before the drying step, the material is subjected to pulverization and pelletizing treatment to form green pellets with a particle size of 5-25 mm.

[0102] In the above technical solution, the calorific value of the coal-based solid waste containing volatile matter processed by this process can be selected from 200-1800 kCal / kg. In practical applications, the selection can be flexibly made according to the source of the material. For example, when processing coal gangue associated with coal mining, materials with a calorific value of 500-800 kCal / kg can be selected; when processing coal slime produced by coal washing plants, materials with a calorific value of 1200-1500 kCal / kg can be selected. These materials all come from solid waste generated in industrial processes such as coal mining and coal washing, or are mixtures of solid waste such as red mud and tailings with coal (carbon), without the need to purchase special raw materials. Before the material enters the drying step, it needs to be pulverized. Ball mills and vertical mills can be used to grind the lumpy material. After grinding, the particle size of the material must meet the requirement that the proportion of -200 mesh is not less than 50%.

[0103] After grinding, the material enters the pelletizing process, which can be achieved using a disc pelletizer. During pelletizing, an appropriate amount of water needs to be added to the ground material (the amount of water should be controlled at 10%-15% of the material mass) to ensure the shapeability of the green pellets. During the pelletizing process, the particle size of the green pellets is controlled between 5-25mm by adjusting the rotation speed and tilt angle of the disc pelletizer. After pelletizing, the green pellets need to be screened, using a vibrating screen to remove fragments smaller than 5mm and large pieces larger than 25mm. The qualified green pellets after screening are conveyed to the primary drying unit, while the fragments and large pieces are returned to the ball mill for regrinding and pelletizing to improve material utilization.

[0104] Existing technologies cannot effectively treat low- to medium-calorific-value coal-based solid waste with a calorific value of 200-1800 kcal / kg. Low-calorific-value materials are prone to incomplete treatment due to insufficient heat, while high-calorific-value materials are prone to combustion caking due to excessive heat. This technical solution, however, specifies the calorific value range of materials as 200-1800 kcal / kg. Through parameter adaptation in subsequent steps (such as adjustment of pyrolysis temperature and residence time), it can stably treat various types of coal-based solid waste within this range, broadening the scope of application of the process and solving the problem of strict limitations on material calorific value in existing technologies.

[0105] This invention also provides a treatment system for a comprehensive treatment process of coal-based solid waste containing volatile matter, comprising a drying section, an anaerobic pyrolysis section, a preheating section, a decarbonization section, a rapid cooling section, a slow cooling section, and a final cooling section connected sequentially along the material processing direction; the system further includes a cooling fan, a slow cooling fan, a decarbonization circulating fan, a roasting circulating fan, a dust removal device, a pyrolysis gas circulating fan, a pyrolysis gas heating device, a gas boiler, and a circulating gas cooling device; the system is configured to establish a circulating hot air loop and a circulating pyrolysis gas loop;

[0106] The circulating hot air circuit is configured as follows: the air outlet of the rapid cooling section is divided into two paths, which are respectively connected to the air inlet of the preheating section and the air inlet of the decarbonization section; the hot air outlet of the preheating section and the hot air outlet of the decarbonization section are merged and then connected to the air inlet of the rapid cooling section; the decarbonization circulating fan is provided on the flow path from the merged end of the air outlets of the preheating section and the decarbonization section to the air inlet of the rapid cooling section.

[0107] The circulating pyrolysis gas circuit is configured as follows: the outlet of the oxygen-free pyrolysis section is fluidly connected to the inlet of the dust removal device, the outlet of the dust removal device is fluidly connected to the inlet of the pyrolysis gas heating device, and the outlet of the pyrolysis gas heating device is fluidly connected to the inlet of the oxygen-free pyrolysis section; and a pyrolysis gas circulating fan is provided in the flow path from the outlet of the dust removal device to the inlet of the pyrolysis gas heating device.

[0108] The flow path between the outlet of the pyrolysis gas circulating fan and the inlet of the pyrolysis gas heating device is further configured with a branch for outputting a portion of the circulating pyrolysis gas as fuel, and the branch is connected to the gas inlet of the gas boiler.

[0109] The air inlet of the cooling fan is connected to the outside, the air outlet of the cooling fan is connected to the air inlet of the final cooling section, the air outlet of the final cooling section is connected to the air inlet of the slow cooling section through the slow cooling fan, and the air outlet of the slow cooling section is connected to the air outlet of the rapid cooling section, so as to supplement the oxygen consumed in the decarbonization process of the preheating section and the decarbonization section.

[0110] The cooling end of the circulating gas cooling device is connected to the flow path between the air outlet and the merging end of the preheating section, and the flow path between the air outlet and the merging end of the decarbonization section.

[0111] In the above technical solution, the drying section can be a mesh belt dryer, the oxygen-free pyrolysis section can be a horizontal oxygen-free pyrolysis furnace, the preheating section can be a box-type preheater, the decarbonization section can be a continuous decarbonization reactor, the rapid cooling section can be a fluidized bed cooler, the slow cooling section can be a horizontal slow cooling furnace, and the final cooling section can be a rotary cooler. These devices are all commercially available industrial-grade equipment. These devices are connected sequentially along the material processing direction, that is, the material outlet of the drying section is connected to the material inlet of the oxygen-free pyrolysis section, the material outlet of the oxygen-free pyrolysis section is connected to the material inlet of the preheating section, the material outlet of the preheating section is connected to the material inlet of the decarbonization section, the material outlet of the decarbonization section is connected to the material inlet of the rapid cooling section, the material outlet of the rapid cooling section is connected to the material inlet of the slow cooling section, and the material outlet of the slow cooling section is connected to the material inlet of the final cooling section, forming a continuous material processing flow path.

[0112] The construction of the circulating hot air loop requires precise connection of pipes and equipment. The hot air outlet of the rapid cooling section is divided into two branches through the main pipe, which are respectively connected to the hot air inlet of the preheating section and the hot air inlet of the decarbonization section through flange sealing. The hot air outlets of the preheating section and the decarbonization section are each connected to a main return air duct through pipes. The main return air duct is connected to the hot air inlet of the rapid cooling section. At the same time, a decarbonization circulating fan (a high-temperature resistant centrifugal fan can be selected) is installed on the main return air duct. The fan provides power to make the hot air circulate between the rapid cooling section and the preheating section, which is the first circulating hot air. The hot air circulates between the rapid cooling section and the decarbonization section, which forms the second circulating hot air.

[0113] In the construction of the circulating pyrolysis gas loop, the pyrolysis gas outlet of the oxygen-free pyrolysis section is connected to the inlet of a dust removal device (a gravity dust collector can be selected) via a pipeline. The outlet of the dust removal device is connected to the inlet of a pyrolysis gas heating device (a gas-fired heater can be selected, which is commercially available) via a pipeline. The outlet of the pyrolysis gas heating device is connected to the pyrolysis gas return port of the oxygen-free pyrolysis section via a pipeline. A pyrolysis gas circulating fan (a centrifugal fan can be selected) is installed on the pipeline from the outlet of the dust removal device to the inlet of the pyrolysis gas heating device to drive the pyrolysis gas circulation. At the same time, a branch line is led out from the pipeline between the outlet of the dust removal device and the inlet of the pyrolysis gas heating device. This branch line is connected to the gas inlet of a gas-fired boiler via a pipeline to output a portion of the pyrolysis gas as fuel. In a preferred embodiment, the pyrolysis gas heating device adopts an indirect heating method, such as a tubular heat exchanger or a regenerative heat exchanger, using high-temperature waste gas from the decarbonization section and the roasting section as a heat source to indirectly heat the circulating pyrolysis gas. This measure ensures that no oxygen is introduced during the heating process, strictly maintains the inert atmosphere of the circulating pyrolysis gas, and meets the process requirements of the oxygen-free pyrolysis section.

[0114] The system also requires a slow-cooling fan and a cooling fan. The inlet of the slow-cooling fan (a centrifugal fan can be selected) is connected to the hot air outlet of the final cooling section via a pipe, and the outlet of the slow-cooling fan is connected to the cooling air inlet of the slow cooling section via a pipe. The hot air outlet of the slow cooling section merges with the main hot air outlet pipe of the rapid cooling section via a pipe, and together with the hot air discharged from the slow cooling section, enters the preheating section and decarbonization section respectively to replenish oxygen for the preheating section and decarbonization section. The outlet of the cooling fan (a centrifugal fan can be selected) is connected to the cooling air inlet of the final cooling section via a pipe, and is used to transport room temperature air to the final cooling section to provide a cooling medium for the final cooling of materials.

[0115] The cooling end of the circulating air cooling device is connected to the flow path between the air outlet and the merging end of the preheating section and the flow path between the air outlet and the merging end of the decarbonization section, respectively, so as to cool the hot air coming out of the hot air outlet of the preheating section and the decarbonization section.

[0116] During the entire system operation, the air volume and airflow direction can be controlled by valves (such as butterfly valves and gate valves, which are available on the market) installed on each pipeline. Temperature sensors (such as thermocouple sensors) and pressure sensors (such as pressure gauges) are used to monitor the temperature and pressure in each device in real time to ensure stable system operation.

[0117] This technical solution constructs a circulating hot air loop, allowing the heat recovered in the rapid cooling section to be used for preheating and decarbonization through hot air circulation, reducing heat loss and lowering external heat source consumption compared to existing technologies. Simultaneously, the design of supplementing oxygen with hot air in the slow cooling section avoids temperature fluctuations caused by directly introducing cold air, improving system operational stability. Furthermore, existing technologies do not separate and utilize pyrolysis gas separately, instead burning it directly during volatilization, resulting in energy waste and environmental pollution. This technical solution constructs a circulating pyrolysis gas loop, allowing the pyrolysis gas to be circulated for oxygen-free pyrolysis after dust removal and heating, with only the excess portion output as fuel. This improves the utilization rate of pyrolysis gas and reduces pollutant emissions, overcoming the shortcomings of the extensive pyrolysis gas treatment in existing technologies. Finally, by clearly defining the connection methods and loop construction of each device, this technical solution achieves synergy between material conveying and airflow circulation, making the overall system operation more efficient and more adaptable to different operating conditions.

[0118] In another technical solution, a roasting device is also provided between the decarbonization section and the rapid cooling section; the roasting device includes a first roasting device and a second roasting device; the material inlet of the first roasting device is connected to the material outlet of the decarbonization section, the material outlet of the first roasting device is connected to the material inlet of the second roasting device, and the material outlet of the second roasting device is connected to the material inlet of the rapid cooling section.

[0119] The system is also equipped with a roasting circulating air circuit, which is configured in the following way: the air inlet of the first roasting stage device is in fluid communication with the air outlet of the second roasting stage device; the air outlet of the first roasting stage device is in communication with the air inlet of the second roasting stage device; and the roasting circulating fan is provided on the flow path connecting the air outlet of the first roasting stage device and the air inlet of the second roasting stage device.

[0120] The outlet of the pyrolysis gas circulating fan is connected to the combustion device of the first roasting stage device, and the combustion device organizes combustion to supply heat to the first roasting stage as fuel; the air outlet of the slow cooling stage is connected to the hot air inlet of the first roasting stage and / or the second roasting stage to supply oxygen for roasting; the flow path of the first roasting stage device and the roasting circulating fan is connected to the cooling end of the circulating gas cooling device.

[0121] In the above technical solution, the roasting device added between the decarburization section and the rapid cooling section can be either a belt-type high-temperature roasting furnace or a roasting stage two device. The material inlet of the roasting stage one device is sealed to the material outlet of the decarburization section to ensure that the decarburized material can smoothly enter the roasting stage one device; the material outlet of the roasting stage one device is connected to the material inlet of the roasting stage two device, and the material outlet of the roasting stage two device is connected to the material inlet of the rapid cooling section, forming a continuous material flow path of decarburization-roasting-cooling, avoiding excessive heat dissipation or contamination of the material during the transfer process.

[0122] The construction of the roasting circulating air circuit relies on pipelines and fans. The hot air inlet of the first roasting unit is sealed to the hot air outlet of the second roasting unit through the main hot air pipeline. The hot air outlet of the first roasting unit is connected to the hot air inlet of the second roasting unit through a pipeline. At the same time, a roasting circulating fan is installed on the pipeline from the hot air outlet of the first roasting unit to the hot air inlet of the second roasting unit. This fan can be a high-temperature resistant centrifugal fan, which is a common equipment on the market and can provide stable power for hot air circulation.

[0123] Furthermore, the outlet of the dust removal device needs to be connected to the hot air inlet pipe of the combustion device of the first roasting stage via a branch pipe, so that part of the pyrolysis gas after dust removal can be introduced into the first roasting stage as fuel, and combusted by the combustion device to supply heat to the first roasting stage. Specifically, the combustion device of the first roasting stage is preferably a burner. Specifically, part of the pyrolysis gas from the pyrolysis gas circulation fan, together with the oxygen-supplementing air from the slow cooling section, is combusted by the burner to produce high-temperature flue gas. The roasting circulation air (i.e., the gas from the second roasting stage that has been pre-heated) flows through the heat exchange tube bundle in the hot air furnace, and is indirectly heated to 800-1000°C by the high-temperature flue gas before being sent into the first roasting stage to uniformly heat the material. This indirect heating method avoids direct contact between the flame and the material, ensuring the uniformity, stability and controllability of the roasting temperature, and preventing over-burning of the material.

[0124] The hot air outlet of the slow cooling section is connected to the hot air inlet pipe of the first roasting unit through another branch pipe to supplement the oxygen required for the roasting process and ensure that the roasting reaction is fully carried out.

[0125] The flow path of the roasting section device connected to the roasting circulating fan is connected to the cooling end of the circulating gas cooling device to cool the roasting circulating hot air coming out of the roasting section hot air outlet.

[0126] During system operation, the hot air temperature in the first-stage roasting unit needs to be maintained at 800-1000℃, which can be controlled by adjusting the supply of circulating pyrolysis gas as fuel. Before being transported to the second-stage roasting unit via pipeline, the high-temperature hot air discharged from the first-stage roasting unit is cooled to 450-550℃ by a circulating gas cooling device before entering the second-stage roasting unit to exchange heat with the material. The heated hot air is then reheated to 800-1000℃ by the pyrolysis gas and returned to the first-stage roasting unit for reuse, driven by the roasting circulating fan. Simultaneously, thermocouple temperature sensors can be installed on the hot air pipelines of the first and second-stage roasting units to monitor the hot air temperature in real time. If the temperature is lower than the set value, the supply of pyrolysis gas can be increased; if the temperature is higher than the set value, the supply of pyrolysis gas can be reduced or the replenishment of hot air in the slow cooling section can be appropriately increased to ensure that the roasting temperature remains stable within the process requirements, providing a suitable temperature environment for material solidification.

[0127] The technical advantages of this solution are as follows: First, existing technologies lack a calcination and curing process, resulting in low material strength after decarburization, which fails to meet the strength requirements of high-strength ceramsite and other high-quality building materials. This solution adds a calcination device (including a first and second calcination stage), using 800-1150℃ high-temperature hot air to fully solidify the material. Testing shows that the compressive strength of the product using this calcination device is significantly improved compared to existing technologies, meeting the standards for high-specification building materials and solving the core problem of low product strength in existing technologies. Second, existing technologies lack a calcination circulation air loop, and the high-temperature hot air is directly discharged after use, resulting in low energy efficiency. Furthermore, it requires continuous heating with external fuel. This technical solution designs a roasting circulation air circuit, which cools the high-temperature hot air discharged from the first roasting stage and uses it for heat exchange in the second roasting stage. It is then heated and recycled through pyrolysis gas. At the same time, it uses the pyrolysis gas generated by oxygen-free pyrolysis as fuel to replace external fuel, which reduces external energy consumption compared with existing technologies and overcomes the serious energy waste of existing technologies. Thirdly, existing technologies cannot accurately supplement oxygen in the roasting process, which can easily lead to insufficient roasting due to insufficient oxygen or heat loss due to excessive oxygen. This technical solution supplements oxygen to the roasting stage through hot air in the slow cooling stage, ensuring a stable and efficient roasting reaction.

[0128] In another technical solution, the drying section includes a primary drying section and a secondary drying section connected in sequence, wherein the material outlet of the primary drying section is connected to the material inlet of the secondary drying section; the system further includes:

[0129] A primary drying fan, the outlet of which is connected to the air inlet of the primary drying section, and the inlet of which is connected to the air outlet of the slow cooling section and the air outlet of the final cooling section, respectively, for conveying low-temperature hot air from the slow cooling section and the final cooling section to the primary drying section.

[0130] A secondary drying fan, wherein the inlet of the secondary drying fan is connected to the air outlet of the pyrolysis gas heating device, and the outlet of the secondary drying fan is in fluid communication with the hot air inlet of the secondary drying section;

[0131] In the above technical solution, both the primary drying section and the secondary drying section can be selected from mesh belt dryers. During assembly, the material outlet of the primary drying section is sealed to the material inlet of the secondary drying section through a conveyor belt, ensuring that the material after primary drying can continuously enter the secondary drying section and reducing heat loss during the transfer process. The entire drying section is assembled after the material pelletizing equipment and before the oxygen-free pyrolysis section, forming a continuous material processing link of "pelletizing - primary drying - secondary drying - oxygen-free pyrolysis".

[0132] Centrifugal fans can be used for the primary drying stage, which are common ventilation equipment on the market. Their outlets are connected to the hot air inlet flange of the primary drying section via hot air ducts. The inlet is connected to the hot air outlets of the slow cooling section and the final cooling section via two branch pipes, respectively. Airflow regulating valves can be installed on the branch pipes to control the ratio of hot air from the slow cooling and final cooling sections. In actual operation, the primary drying fan mixes the 400-450℃ hot air discharged from the slow cooling section with the 180-220℃ hot air discharged from the final cooling section in a specific ratio, stabilizing the temperature of the hot air entering the primary drying section at 120-200℃. This meets the primary drying stage's requirement for low-temperature hot air and simultaneously recovers and utilizes waste heat from the slow cooling and final cooling stages, eliminating the need for an external heat source.

[0133] Centrifugal fans can also be used for the secondary drying fan. Their inlet is connected to the flue gas outlet of the pyrolysis gas heating device via a pipe, and their outlet is connected to the hot air inlet flange of the secondary drying section via a hot air duct. The flue gas inlet of the pyrolysis gas heating device needs to be connected to the hot air outlets of the first-stage roasting unit and the decarburization unit via pipes. Excess waste gas at 600-1000℃ discharged from the first-stage roasting unit and part of the waste gas discharged from the decarburization unit enter the pyrolysis gas heating device, where it exchanges heat with the pyrolysis gas, reducing its temperature to 200-260℃. This cooled air then enters the secondary drying section as hot air for the secondary drying, driven by the secondary drying fan, to further dehydrate the material after the first-stage drying. During this process, a temperature sensor can be installed on the flue gas outlet pipe of the pyrolysis gas heating device to monitor the hot air temperature entering the secondary drying section in real time. If the temperature is too high, the airflow can be reduced; if the temperature is too low, the proportion of excess waste gas diverted from the first-stage roasting unit can be reduced to ensure that the hot air temperature meets the process requirements of the secondary drying. Meanwhile, the exhaust outlet of the secondary drying section can be connected to a bag filter (available on the market) to collect and treat the dust generated during the drying process, thus preventing direct dust emissions and environmental pollution.

[0134] The technical benefits of this solution are mainly reflected in three aspects: First, by using segmented drying and precise temperature control, the drying efficiency and material integrity are effectively balanced. The first-stage drying uses low-temperature waste heat air at 120-200℃ to prevent the material from bursting due to excessive dehydration. The second-stage drying uses medium-temperature hot air at 200-260℃ to ensure that the final moisture content of the material is stably reduced to 2%-5%, meeting the process requirements of subsequent oxygen-free pyrolysis. Second, it achieves the tiered recovery and utilization of waste heat within the system. The first-stage drying recovers the low-temperature waste heat from the slow cooling and final cooling stages, and the second-stage drying recovers the medium-temperature waste heat after heat exchange in the roasting stage. This eliminates the need to rely on external heat sources and reduces the energy consumption of the entire process. Third, it reduces the cost of waste gas treatment. The hot air used in the first-stage drying comes from low-pollution slow cooling and final cooling waste heat air, and the waste gas can be directly discharged without complex treatment. The hot air used in the second-stage drying is low-pollution flue gas that has been cooled by heat exchange, and only simple dust removal is required to meet emission standards, significantly reducing the investment in environmental protection treatment.

[0135] In another technical solution, the oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage 1 device and an oxygen-free pyrolysis stage 2 device; the material outlet of the oxygen-free pyrolysis stage 1 device is connected to the material inlet of the oxygen-free pyrolysis stage 2 device.

[0136] The outlet of the pyrolysis gas heating device is connected to the pyrolysis gas inlet of the first stage oxygen-free pyrolysis device and the pyrolysis gas inlet of the second stage oxygen-free pyrolysis device through a flow path.

[0137] The pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device and the pyrolysis gas outlet of the oxygen-free pyrolysis stage 2 device are combined and then connected to the inlet of the dust removal device.

[0138] The system is also equipped with a pyrolysis gas return pipeline. One end of the pyrolysis gas return pipeline is connected to the flow path at the pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device, and the other end is connected to the flow path before the pyrolysis gas inlet of the oxygen-free pyrolysis stage 1 device. It is used to return part of the pyrolysis gas from the oxygen-free pyrolysis stage 1 device to its inlet in order to adjust the inlet temperature of the oxygen-free pyrolysis stage 1 device.

[0139] In the above technical solution, the oxygen-free pyrolysis section includes a horizontal oxygen-free pyrolysis furnace for the first oxygen-free pyrolysis stage and a horizontal oxygen-free pyrolysis furnace with the same structure as the first oxygen-free pyrolysis stage for the second oxygen-free pyrolysis stage. Both are commercially available industrial-grade oxygen-free reaction equipment. During assembly, the material outlet of the first oxygen-free pyrolysis stage is connected to the material inlet of the second oxygen-free pyrolysis stage via a high-temperature resistant sealed conveyor belt to ensure continuous material transfer in an oxygen-free environment and prevent air from entering and disrupting the oxygen-free atmosphere. The entire oxygen-free pyrolysis section is assembled after the secondary drying stage and before the preheating stage, forming a continuous material processing flow of "secondary drying - first oxygen-free pyrolysis stage - second oxygen-free pyrolysis stage - preheating".

[0140] The outlet of the pyrolysis gas heating device needs to be connected to the pyrolysis gas inlet of the first-stage oxygen-free pyrolysis unit and the pyrolysis gas inlet of the second-stage oxygen-free pyrolysis unit via two branch pipes, respectively, with flange seals. Flow regulating valves can be installed on the branch pipes to control the amount of pyrolysis gas entering the two stages of pyrolysis. The pyrolysis gas outlets of the first-stage and second-stage oxygen-free pyrolysis units can be merged and connected to the same main pipe, which is then connected to the inlet of the dust removal device to ensure that the pyrolysis gas discharged from both stages can be centrally treated for dust removal. If it is necessary to monitor the composition and temperature of the pyrolysis gas from the two stages separately, the pyrolysis gas outlets of the two stages can also be connected to the inlet of the dust removal device via independent pipes to meet different process monitoring needs.

[0141] The pyrolysis gas return pipeline can be made of high-temperature resistant stainless steel. One end is connected to the pipeline at the pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 unit, specifically located between the oxygen-free pyrolysis stage 1 unit and the pyrolysis gas junction point (or between the oxygen-free pyrolysis stage 1 unit and the dust removal device inlet). The other end is connected to the main pipeline before the pyrolysis gas inlet of the oxygen-free pyrolysis stage 1 unit, specifically located between the pyrolysis gas heating device outlet and the pyrolysis gas inlet of the oxygen-free pyrolysis stage 1 unit. An electric flow regulating valve and a check valve can be installed on the pipeline. The electric flow regulating valve is used to control the amount of refluxed pyrolysis gas, and the check valve is used to prevent the high-temperature pyrolysis gas in the main pipeline from flowing back into the return pipeline. In actual operation, when the inlet pyrolysis gas temperature of the first stage of oxygen-free pyrolysis is higher than 500℃, the opening of the electric flow regulating valve can be increased to increase the return flow of the low-temperature pyrolysis gas at the outlet of the first stage of oxygen-free pyrolysis, thereby reducing the inlet pyrolysis gas temperature through mixing. When the inlet temperature is lower than 270℃, the valve opening can be reduced to decrease the return flow, ensuring that the pyrolysis gas temperature of the first stage of oxygen-free pyrolysis is stable at 270-500℃ and the pyrolysis gas temperature of the second stage of oxygen-free pyrolysis is stable at 550-650℃, thus meeting the temperature requirements of different stages of pyrolysis.

[0142] The technical benefits of this solution are mainly reflected in three aspects: First, through the segmented oxygen-free pyrolysis design, a gradient release of volatiles from the material is achieved. The medium-temperature environment of the first stage of oxygen-free pyrolysis promotes the release of low-boiling-point volatiles, while the high-temperature environment of the second stage promotes the full release of high-boiling-point volatiles, thus improving the extraction efficiency of volatiles and providing better conditions for the subsequent utilization of pyrolysis gas. Second, through precise control of the pyrolysis gas reflux pipeline, the inlet temperature of the first stage of oxygen-free pyrolysis is flexibly adjusted, avoiding local overheating, cracking, or caking of the material due to excessively high pyrolysis temperature, and ensuring the structural integrity of the material during the pyrolysis process. Third, through clear pipeline connections and valve control, the stable operation of the pyrolysis gas circulation system is ensured. The pyrolysis gas discharged from the two stages of pyrolysis is centrally dust-removed and recycled, reducing the waste of pyrolysis gas and also reducing the environmental pressure that may be caused by direct emission of pyrolysis gas, thereby improving the economy and environmental friendliness of the entire process.

[0143] The technical effects of the present invention will be illustrated below through specific embodiments and comparative examples.

[0144] <Process Framework>

[0145] This invention discloses a comprehensive treatment process for coal-based solid waste containing volatile components, comprising a drying section, an anaerobic pyrolysis section, a preheating section, a decarbonization section, a roasting section (optional), and a cooling section connected sequentially. Each section is further subdivided into multiple sub-sections: the drying section is divided into a primary drying section and a secondary drying section; the anaerobic pyrolysis section is divided into an anaerobic pyrolysis stage one and an anaerobic pyrolysis stage two; the roasting section is divided into roasting stage one and roasting stage two; and the cooling section is divided into a rapid cooling section, a slow cooling section, and a final cooling section. The process air system includes a pyrolysis gas circulation system, a decarbonization circulation air system, a roasting circulation air system, and a cooling air system, which achieve airflow circulation and parameter control through pipelines, valves, and fans to ensure stable process conditions in each section.

[0146] <Detection Indicators>

[0147] In the embodiments and comparative examples of this invention, the methods for detecting the performance indicators of the finished product are as follows:

[0148] 1. Residual carbon

[0149] Reference standard: GB / T 212-2021 "Industrial Analysis Methods for Coal"

[0150] Method Summary: The moisture (Mad), ash (Aad), and volatile matter (Vad) of the sample are determined through industrial analysis. The content of fixed carbon (i.e., residual carbon, Fad) is calculated using the formula Fad = 100 - Mad - Aad - Vad, and all values ​​are percentages.

[0151] 2. Cylinder compressive strength

[0152] Reference standard: GB / T 17431.2-2010 "Lightweight aggregates and their test methods - Part 2: Test methods for lightweight aggregates"

[0153] Method Summary: Naturally graded ceramsite samples are loaded into a pressure vessel of specified dimensions, ensuring a smooth surface. The pressure vessel is then placed on a pressure testing machine, and a pressure of 300 N / m² is applied. 2 -500N / m 2 The pressure is increased at a constant rate until the piston is pressed into the ground to a depth of 20 mm. The pressure value at this point is recorded, and the compressive strength is calculated using a formula, with the unit being megapascals (MPa).

[0154] 3. Water absorption rate

[0155] Reference standard: GB / T 17431.2-2010 "Lightweight aggregates and their test methods - Part 2: Test methods for lightweight aggregates"

[0156] Method Summary: The sample was dried to constant weight at 105±5℃ and its mass (G1) was recorded. The sample was then immersed in water at 20±5℃ and allowed to stand for 1 hour. The sample was removed, and the surface water was wiped off with a damp towel. The mass after water absorption was immediately recorded (G2). The water absorption rate was calculated using the formula (G2 - G1) / G1 × 100%.

[0157] 4. Powdering rate

[0158] Method Summary: Randomly weigh approximately 500g of finished ceramsite (M1), accurate to 0.1g. Place the sample on a standard vibrating sieve with a 5.0mm aperture, turn on the sieve, and vibrate for 10 minutes. After vibration, carefully collect all the fine powder material that has passed through the 5.0mm sieve and weigh it (M2), accurate to 0.1g. The pulverization rate (η) is calculated using the following formula: η = (M2 / M1) × 100%.

[0159] <Example 1>

[0160] This embodiment processes pure coal gangue, which has the following composition: fixed carbon 6.13%, volatile matter 10.24%, moisture 4.8%, ash 78.83%, and calorific value 592 kCal / kg.

[0161] The processing technology for the above-mentioned pure coal gangue includes the following steps:

[0162] (1) The raw material is crushed to -200 mesh ≥50%, and pellets are made using a disc pelletizer. The green pellets have a particle size of 8-25mm and an average moisture content of 11.8%.

[0163] (2) The green pellets enter the first drying section. The first hot air comes from the final cooling section. The inlet temperature is set to 180℃ and the drying time is 20min.

[0164] (3) The moisture content of the pellets exiting the primary drying section is 2%~5%, and they enter the secondary drying section. The inlet hot air (i.e., the second hot air) temperature of the secondary drying section is set to 250℃, and the drying time is 10min.

[0165] (4) The inlet hot air temperature of the first stage of oxygen-free pyrolysis is set at 500℃ and the pyrolysis time is 12min; the inlet hot air temperature of the second stage of oxygen-free pyrolysis is 600℃ and the pyrolysis time is 6min.

[0166] (5) The inlet hot air temperature of the preheating section is 750-800℃, which will increase the average temperature of the green balls to 700-800℃. The preheating time is 12min.

[0167] (6) The inlet hot air temperature of the decarbonization section is 750-800℃, which raises the material temperature to 1030℃ and the decarbonization time is 8min;

[0168] (7) In the roasting section, the circulating hot air is heated to about 1150°C by pyrolysis gas combustion. The material is heated to 1150°C to complete the solidification. The roasting time is 15 minutes and the roasting time is 5 minutes.

[0169] (8) The rapid cooling section uses 550℃ circulating hot air to cool the material to 600℃ in 8 minutes, with a cooling rate of 68.75℃ / min;

[0170] (9) The slow cooling section uses hot air at about 200°C to slowly cool the material to 400°C for 16 minutes, with a cooling rate of 12.5°C / min.

[0171] (10) The final cooling section cools the material to below 120°C for 8 minutes.

[0172] Total processing time: 120 minutes. Finished product properties: average residual carbon content 0.29%, maximum compressive strength 15.5 MPa, average water absorption 3.1%, pulverization rate 0.52%.

[0173] <Example 2>

[0174] This embodiment processes pure coal gangue with a high calorific value, and its composition is as follows: fixed carbon 10.47%, volatile matter 9.82%, moisture 0.86%, ash 82.56%, and calorific value 758 kCal / kg.

[0175] The processing technology for the above-mentioned pure coal gangue includes the following steps:

[0176] (1) The raw material is crushed to -200 mesh ≥50%, and pellets are made using a disc pelletizer. The green pellets have a particle size of 8-25 mm and an average moisture content of 13%.

[0177] (2) The green pellets enter the primary drying section. The hot air in the primary drying section comes from the final cooling section. The inlet temperature is set at 180℃ and the drying time is 15min.

[0178] (3) The moisture content of the pellets exiting the primary drying section is 2%–5%, and they enter the secondary drying section for further drying. The hot air in the secondary drying section comes from the preheating, decarburization, and calcination circulating air system. The inlet hot air temperature is set at 250℃, and the drying time is 7.5 min.

[0179] (4) The heat required for pyrolysis in the anaerobic pyrolysis section comes from indirect heat exchange with the exhaust gas from the preheating, decarbonization, and roasting sections. The inlet hot air temperature of the first anaerobic pyrolysis section is 450℃, and the pyrolysis time is 9 min; the inlet hot air temperature of the second anaerobic pyrolysis section is 550℃, and the pyrolysis time is 4.5 min.

[0180] (5) The inlet hot air temperature of the preheating section is set at 750-800℃, which increases the average temperature of the green pellets from 500-600℃ to 700-800℃; the heat required for the preheating section comes from the circulating air system of the preheating section, decarburization section and rapid cooling section, and the preheating time is 9 minutes.

[0181] (6) The inlet hot air temperature of the decarbonization section is set at 750-800℃. By controlling the hot air volume entering the decarbonization section, the material is heated by the heat released from decarbonization oxidation, so that its temperature generally rises to 1050℃ and the decarbonization time is 6 minutes.

[0182] (7) The roasting section is divided into roasting section one and roasting section two. The circulating hot air is heated to 950-1100℃ in roasting section two, and the temperature is raised to about 1150℃ by the combustion of the pyrolysis gas generated in the anaerobic pyrolysis process. The material is heated to 1150℃ by the heat released by the hot air and oxidation process, and the solidification is completed. The roasting time is 11.25min, and the roasting time of roasting section two is 3.75min;

[0183] (8) The rapid cooling section uses 550℃ circulating hot air to cool the material. The material is cooled to 600℃ and then enters the slow cooling section. The rapid cooling time is 6 minutes and the cooling rate is 91.67℃ / min.

[0184] (9) The slow cooling section uses hot air at about 200℃ to slowly cool the material temperature to 400℃, with a slow cooling time of 12min and a cooling rate of 16.67℃ / min;

[0185] (10) The final cooling section cools the material to below 120 degrees Celsius to complete the entire process. The final cooling time is 6 minutes.

[0186] Total processing time: 90 minutes. Finished product properties: average residual carbon content 0.77%, maximum compressive strength 15.1 MPa, average water absorption 3.6%, and pulverization rate 0.49%.

[0187] <Example 3>

[0188] This embodiment processes a mixture of coal gangue and red mud. The coal gangue composition is as follows: fixed carbon 6.13%, volatile matter 10.24%, moisture 4.8%, ash content 78.83%, and calorific value 592 kCal / kg. The main components of the red mud are: SiO2 15.64%, Al2O3 43.71%, and Fe2O3 23.23%. The coal gangue and red mud are mixed at a mass ratio of 9:1.

[0189] The processing technology includes the following steps:

[0190] (1) The coal gangue and red mud are crushed to -200 mesh ≥50% and mixed evenly according to the mass ratio of coal gangue to red mud of 9:1;

[0191] (2) The mixture is pelletized using a disc pelletizer, with a green pellet diameter of 8-25 mm and an average moisture content of 11.5%.

[0192] (3) The green pellets enter the primary drying section. The hot air in the primary drying section comes from the final cooling section. The inlet temperature is set at 180℃ and the drying time is 20min.

[0193] (4) The moisture content of the pellets exiting the primary drying section is 2%–5%, and they enter the secondary drying section for further drying. The hot air in the secondary drying section comes from the preheating, decarburization, and calcination circulating air system. The inlet hot air temperature is set at 250℃, and the drying time is 10 minutes.

[0194] (5) The heat required for pyrolysis in the anaerobic pyrolysis section comes from indirect heat exchange with the exhaust gas from the preheating, decarbonization, and roasting sections. The inlet hot air temperature of the first anaerobic pyrolysis section is 500℃, and the pyrolysis time is 12min; the inlet hot air temperature of the second anaerobic pyrolysis section is 600℃, and the pyrolysis time is 6min.

[0195] (6) The inlet hot air temperature of the preheating section is set at 800℃, which increases the average temperature of the green pellets from 500-600℃ to 700-750℃; the heat required for the preheating section comes from the circulating air system of the preheating section, decarburization section and rapid cooling section, and the preheating time is 12min.

[0196] (7) The inlet hot air temperature of the decarbonization section is set at 800℃. By controlling the hot air volume entering the decarbonization section, the material decarbonization oxidation release heat heats itself, causing its temperature to rise to 1000℃. The decarbonization time is 8 minutes.

[0197] (8) The roasting section is divided into roasting section one and roasting section two. The circulating hot air is heated to 950-1100℃ in roasting section two, and the temperature is raised to about 1150℃ by the combustion of the pyrolysis gas generated in the anaerobic pyrolysis process. The material is heated to 1150℃ by the heat released by the hot air and oxidation process, and the solidification is completed. The roasting time is 15 minutes, and the roasting time in section two is 5 minutes.

[0198] (9) The rapid cooling section uses 550℃ circulating hot air to cool the material. The material is cooled to 600℃ and then enters the slow cooling section. The rapid cooling time is 8 minutes and the cooling rate is 68.75℃ / min. (10) The slow cooling section uses hot air at about 200℃ to slowly cool the material temperature to 400℃. The slow cooling time is 16 minutes and the cooling rate is 12.5℃ / min. (11) The final cooling section cools the material to below 120 degrees Celsius to complete the entire process. The final cooling time is 8 minutes.

[0199] Total processing time: 120 minutes. Finished product properties: average residual carbon content 0.26%, maximum compressive strength 16.3 MPa, average water absorption 3.0%, pulverization rate 0.42%.

[0200] <Example 4>

[0201] This embodiment aims to produce water-retaining ceramsite by processing pure coal gangue. Its industrial analysis composition is the same as that of Example 1 (fixed carbon 6.13%, volatile matter 10.24%, moisture 4.8%, ash 78.83%, calorific value 592 kCal / kg).

[0202] The processing technology includes the following steps:

[0203] (1) The raw material is crushed to -200 mesh ≥50%, and pellets are made using a disc pelletizer. The green pellets have a particle size of 8-25mm and an average moisture content of 12%. (2) The green pellets enter the primary drying section. The hot air in the primary drying section comes from the final cooling section. The inlet temperature is set at 180℃, and the drying time is 20min. (3) The pellets exiting the primary drying section have a moisture content of 2%-5%, and they enter the secondary drying section for drying. The hot air in the secondary drying section comes from the preheating, decarbonization, and roasting circulating air system. The inlet hot air temperature is set at 250℃, and the drying time is 10min. (4) The heat required for pyrolysis in the anaerobic pyrolysis section comes from the indirect heat exchange of the exhaust gas from the preheating, decarbonization, and roasting sections. The inlet hot air temperature of the first stage of anaerobic pyrolysis is 500℃, and the pyrolysis time is 12min; the inlet hot air temperature of the second stage of anaerobic pyrolysis is 600℃, and the pyrolysis time is 6min; (5) the inlet hot air temperature of the preheating section is set at 750~800℃, which increases the average temperature of the green pellets from 500~600℃ to 700~800℃; the heat required for the preheating section comes from the circulating air system of the preheating section, decarbonization section and rapid cooling section, and the preheating time is 12min; (6) the inlet hot air temperature of the decarbonization section is set at 750~800℃, and the heat is generated by controlling the hot air volume entering the decarbonization section and using the exothermic reaction of the material decarbonization oxidation to heat the material. (7) The decarbonized material directly enters the rapid cooling section and uses 550℃ circulating hot air to cool the material. The material is cooled to 500℃ and enters the slow cooling section. The rapid cooling time is 12 minutes and the cooling rate is 44.17℃ / min. (8) The slow cooling section uses hot air of about 200℃ to rapidly cool the material temperature to 400℃. The slow cooling time is 6 minutes and the cooling rate is 16.67℃ / min. (9) The final cooling section cools the material to below 120 degrees Celsius to complete the entire process. The final cooling time is 6 minutes.

[0204] Total processing time: 92 minutes. Finished product properties: average residual carbon content 0.93%, maximum compressive strength 8.5 MPa, average water absorption 20.1%, pulverization rate 0.32%.

[0205] <Comparative Example 1>

[0206] The process flow and steps of Example 1 were adopted, but the raw material was changed to high volatile coal gangue, with the following composition: fixed carbon 7.06%, volatile matter 15.72%, moisture 3.24%, ash 73.97%, and calorific value 1249.28 kCal / kg.

[0207] Compared to Example 1, the average residual carbon content of the finished product in Comparative Example 1 increased from 0.29% to 0.41%; the maximum compressive strength of the cylinder decreased from 15.5 MPa to 13.9 MPa; the average water absorption rate increased from 3.1% to 3.6%; and the pulverization rate of the process materials increased from 0.52% to 0.86%. Meanwhile, the pyrolysis gas generated in the oxygen-free pyrolysis section increased by 49%, and the material temperatures during preheating, decarburization, and calcination increased by 50°C, 35°C, and 29°C, respectively.

[0208] <Comparative Example 2>

[0209] This comparative example uses the process flow and steps of Example 1, only changing the inlet hot air temperature of the first stage of oxygen-free pyrolysis to 350℃ and the inlet hot air temperature of the second stage of oxygen-free pyrolysis to 550℃. After decarburization and roasting, the average residual carbon content of the finished product of the raw material pellets increased from 0.29% to 1.16%, the maximum cylinder compressive strength decreased from 15.5MPa to 12.6MPa, the average water absorption rate decreased from 3.1% to 3.0%, and the material pulverization rate increased from 0.52% to 0.92%. At the same time, the pyrolysis gas generated in the oxygen-free pyrolysis stage decreased by 13.6%. The main reason is that the pyrolysis temperature of the first stage of oxygen-free pyrolysis is too low, and the material is not effectively pyrolyzed, resulting in an incomplete oxygen-free pyrolysis process. Some volatiles enter the preheating stage, react with oxygen in the circulating gas, and cause the material temperature to rise rapidly. A liquid phase forms on the material surface, which hinders the decarburization process.

[0210] <Comparative Example 3>

[0211] This comparative example uses the process flow and steps of Example 1, only changing the closed-loop circulation system of the oxygen-free pyrolysis section to an open system. The hot air comes from the slow cooling section and its temperature is guaranteed to be ≥380℃. After decarburization roasting, the average residual carbon content of the raw material pellets increased from 0.29% to 2.21%, the maximum compressive strength decreased from 15.5MPa to 10.1MPa, the average water absorption rate increased from 3.1% to 7.9%, the material pulverization rate increased from 0.52% to 1.4%, and uncontrollable temperature, liquefaction and adhesion of the finished product surface occurred. The main reason is that during the volatile matter release process in this section, the material reacts with oxygen in the hot air, releasing heat and rapidly increasing the surface temperature, thus affecting the decarburization process inside the material.

[0212] In Comparative Example 3, due to the use of an open system, oxygen and volatiles undergo a violent exothermic reaction in the anaerobic pyrolysis section, causing the material surface to heat up rapidly and liquefy, hindering the internal decarburization process, thus significantly increasing the residual carbon value. Simultaneously, surface liquefaction and increased temperature gradient lead to uneven material structure and increased internal stress, further exacerbating pulverization, thus increasing the pulverization rate accordingly.

[0213] <Comparative Example 4>

[0214] This comparative example uses the process flow and steps of Example 1, only changing the hot air in the preheating and decarburizing sections from a circulating system to an open system, sourced from the rapid cooling section. The hot air in the calcination section is also changed from a circulating system to an open system, again sourced from the rapid cooling section. After ensuring the process temperatures for preheating, decarburizing, and calcination, the average residual carbon content of the product increased from 0.29% to 0.71%; the maximum cylinder compressive strength decreased from 15.5 MPa to 10.9 MPa; the average water absorption rate increased from 3.1% to 3.9%; and the process material pulverization rate increased from 0.52% to 0.96%. Simultaneously, burners are required to meet the process temperatures in the preheating, decarburizing, and calcination hot air sections, increasing fuel consumption by 4.1 times, and the hot air temperature is lower, resulting in lower recovery grade.

[0215] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of the comprehensive treatment process for coal-based solid waste containing volatile matter according to this invention will be readily apparent to those skilled in the art.

[0216] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A comprehensive treatment process for coal-based solid waste containing volatile matter, used to treat coal-based solid waste materials containing volatile matter, characterized in that, This includes process segments executed in the following order: Drying section: Uses hot air to dry materials; Oxygen-free pyrolysis section: In an oxygen-free environment, circulating pyrolysis gas is used to exchange heat with the dried material, causing the volatiles in the material to be released. Preheating section: In an oxygen-containing environment, the material after oxygen-free pyrolysis is heated and its temperature is increased using the first circulating hot air; Decarbonization section: In an oxygen-containing environment, the preheated material is decarbonized using the second circulating hot air. Cooling section: includes a rapid cooling section, a slow cooling section, and a final cooling section. The rapid cooling section cools the material discharged from the decarburization section to 580℃-650℃ at a cooling rate of 40℃ / min-105℃ / min. The slow cooling section cools the material discharged from the rapid cooling section to 350℃-450℃ at a cooling rate of 10℃ / min-40℃ / min. The final cooling section cools the material discharged from the slow cooling section to ≤120℃. The first circulating hot air discharged and cooled from the preheating section and the second circulating hot air discharged and cooled from the decarbonization section are combined and then heated in the rapid cooling section before being divided into two paths. One path leads to the inlet of the preheating section to participate in the circulation and form the first circulating hot air, and the other path leads to the inlet of the decarbonization section to participate in the circulation and form the second circulating hot air. The circulating pyrolysis gas discharged from the oxygen-free pyrolysis section is dusted, and part of it is reheated and returned to the inlet of the oxygen-free pyrolysis section to participate in the circulation, while the other part is output as fuel. The final cooling section uses ambient temperature air to cool the material discharged from the slow cooling section. Part of the air discharged from the final cooling section is sent to the slow cooling section to cool the material discharged from the rapid cooling section. Part of the air discharged from the slow cooling section is sent to the preheating section and the decarburization section as oxygen supplement gas for the preheating section and the decarburization section. A calcination section is further provided between the decarburization section and the cooling section; the calcination section includes: Roasting stage 1: Roasting circulating hot air at 800℃-1000℃ is used to heat the material discharged from the decarburization stage, promoting the decarburization and consolidation of the material; Second roasting stage: Receives material from first roasting stage; The roasting circulating hot air discharged from the first roasting stage is cooled to 450℃-550℃ and then introduced into the second roasting stage. After exchanging heat with the material in the second roasting stage, the temperature is raised. The heated roasting circulating hot air is then reheated to 800℃-1000℃ by the pyrolysis gas output as fuel, so that it can continue to be returned to the first roasting stage for recycling. In addition to some of the air discharged from the slow cooling section going to the preheating section and the decarburization section, some of the air also goes to the first roasting section as oxygen supplement gas for the first roasting section. The drying section includes a primary drying section and a secondary drying section performed sequentially, as detailed below: Primary drying section: The material is dried using first hot air, which originates from the air discharged from the final cooling section and / or the air discharged from the slow cooling section, and is adjusted to a temperature of 120℃-200℃. Secondary drying section: The material discharged from the primary drying section is dried using a second hot air. The second hot air originates from the second circulating hot air discharged from the decarburization section before cooling, and / or the roasting circulating hot air discharged from the roasting section before cooling. The temperature of the second hot air is adjusted to be 200℃-260℃. The oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage I and an oxygen-free pyrolysis stage II, which are performed sequentially.

2. The comprehensive treatment process for coal-based solid waste containing volatile matter as described in claim 1, characterized in that, The second circulating hot air discharged from the decarbonization section and before cooling, and / or the roasting circulating hot air discharged from the roasting section and before cooling, after exchanging heat with the dust-removed circulating pyrolysis gas, are sent to the secondary drying section as the second hot air; at the same time, the circulating pyrolysis gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the reheated circulating pyrolysis gas is divided into the first circulating pyrolysis gas and the second circulating pyrolysis gas, and the first circulating pyrolysis gas is adjusted and cooled to 270℃-500℃; In the first stage of oxygen-free pyrolysis, the first circulating pyrolysis gas is used to exchange heat with the material discharged from the second stage drying section. After heat exchange, the first circulating pyrolysis gas is cooled down and discharged from the first stage of oxygen-free pyrolysis. In the second stage of oxygen-free pyrolysis, the second circulating pyrolysis gas is used to exchange heat with the material discharged from the first stage of oxygen-free pyrolysis. The second circulating pyrolysis gas cools down and is discharged from the second stage of oxygen-free pyrolysis. The first circulating pyrolysis gas discharged from the first stage of oxygen-free pyrolysis and the second circulating pyrolysis gas discharged from the second stage of oxygen-free pyrolysis are combined to form a combined gas. After gravity dust removal, part of the combined gas is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air, and the other part is divided into a first part and a second part. The first part leads to the gas boiler, and the second part leads to the inlet of the first stage of roasting.

3. The comprehensive treatment process for coal-based solid waste containing volatile matter as described in claim 2, characterized in that, The specific method for adjusting and cooling the first circulating pyrolysis gas to 270℃-500℃ is as follows: Apart from the first part leading to the gas boiler and the second part leading to the inlet of the roasting section, the remaining part of the combined gas is divided into a third part and a fourth part. The third part is reheated to 550℃-650℃ by the second circulating hot air and / or the roasting circulating hot air. The fourth part serves as a cooling source for the first circulating pyrolysis gas and is mixed with the first circulating pyrolysis gas. By adjusting the mixing ratio of the fourth part with the first circulating pyrolysis gas, the temperature of the first circulating pyrolysis gas is reduced to 270℃-500℃.

4. The comprehensive treatment process for coal-based solid waste containing volatile matter as described in claim 1, characterized in that, The calorific value of the coal-based solid waste containing volatile matter ranges from 200 kcal / kg to 1800 kcal / kg, and before entering the drying section, the material undergoes pulverization and pelletizing to form green pellets with a particle size of 5 mm to 25 mm.

5. A treatment system employing the comprehensive treatment process for coal-based solid waste containing volatile matter as described in claim 1, characterized in that, The system comprises, in sequence along the material handling direction, a drying section, an oxygen-free pyrolysis section, a preheating section, a decarbonization section, a rapid cooling section, a slow cooling section, and a final cooling section; the system also includes a cooling fan, a slow cooling fan, a decarbonization circulating fan, a roasting circulating fan, a dust removal device, a pyrolysis gas circulating fan, a pyrolysis gas heating device, a gas boiler, and a circulating gas cooling device; the system is configured to establish a circulating hot air loop and a circulating pyrolysis gas loop; The circulating hot air circuit is configured as follows: the air outlet of the rapid cooling section is divided into two paths, which are respectively connected to the air inlet of the preheating section and the air inlet of the decarbonization section; the hot air outlet of the preheating section and the hot air outlet of the decarbonization section are merged and then connected to the air inlet of the rapid cooling section; the decarbonization circulating fan is provided on the flow path from the merged end of the air outlets of the preheating section and the decarbonization section to the air inlet of the rapid cooling section. The circulating pyrolysis gas circuit is configured as follows: the outlet of the oxygen-free pyrolysis section is fluidly connected to the inlet of the dust removal device, the outlet of the dust removal device is fluidly connected to the inlet of the pyrolysis gas heating device, and the outlet of the pyrolysis gas heating device is fluidly connected to the inlet of the oxygen-free pyrolysis section; and a pyrolysis gas circulating fan is provided in the flow path from the outlet of the dust removal device to the inlet of the pyrolysis gas heating device. The flow path between the outlet of the pyrolysis gas circulating fan and the inlet of the pyrolysis gas heating device is further configured with a branch for outputting a portion of the circulating pyrolysis gas as fuel, and the branch is connected to the gas inlet of the gas boiler. The air inlet of the cooling fan is connected to the outside, the air outlet of the cooling fan is connected to the air inlet of the final cooling section, the air outlet of the final cooling section is connected to the air inlet of the slow cooling section through the slow cooling fan, and the air outlet of the slow cooling section is connected to the air outlet of the rapid cooling section, so as to supplement the oxygen consumed in the decarbonization process of the preheating section and the decarbonization section. The cooling end of the circulating gas cooling device is connected to the flow path between the air outlet and the merging end of the preheating section, and the flow path between the air outlet and the merging end of the decarbonization section.

6. The treatment system for the comprehensive treatment process of coal-based solid waste containing volatile matter as described in claim 5, characterized in that, A roasting device is also provided between the decarbonization section and the rapid cooling section; the roasting device includes a first roasting device and a second roasting device; the material inlet of the first roasting device is connected to the material outlet of the decarbonization section, the material outlet of the first roasting device is connected to the material inlet of the second roasting device, and the material outlet of the second roasting device is connected to the material inlet of the rapid cooling section. The system is also equipped with a roasting circulating air circuit, which is configured in the following way: the air inlet of the first roasting stage device is in fluid communication with the air outlet of the second roasting stage device; the air outlet of the first roasting stage device is in communication with the air inlet of the second roasting stage device; and the roasting circulating fan is installed on the flow path connecting the air outlet of the first roasting stage device and the air inlet of the second roasting stage device. The outlet of the pyrolysis gas circulating fan is connected to the combustion device of the first roasting stage device, and the combustion device organizes combustion to supply heat to the first roasting stage as fuel; the air outlet of the slow cooling stage is connected to the hot air inlet of the first roasting stage device to supply oxygen for roasting; the flow path of the first roasting stage device and the roasting circulating fan is connected to the cooling end of the circulating gas cooling device.

7. The treatment system for the comprehensive treatment process of coal-based solid waste containing volatile matter as described in claim 6, characterized in that, The drying section includes a primary drying section and a secondary drying section connected in sequence, with the material outlet of the primary drying section connected to the material inlet of the secondary drying section; the system also includes: A primary drying fan, the outlet of which is connected to the air inlet of the primary drying section, and the inlet of which is connected to the air outlet of the slow cooling section and the air outlet of the final cooling section, respectively, for conveying low-temperature hot air from the slow cooling section and the final cooling section to the primary drying section. A secondary drying fan, wherein the inlet of the secondary drying fan is connected to the air outlet of the pyrolysis gas heating device, and the outlet of the secondary drying fan is in fluid communication with the hot air inlet of the secondary drying section; The flow path between the air outlet of the decarbonization section and the cooling end connection point of the circulating gas cooling device, and the flow path between the first roasting unit and the cooling end connection point of the circulating gas cooling device, are both connected to the air inlet of the pyrolysis gas heating device, so that the excess waste gas from the air outlets of the decarbonization section and the first roasting unit is cooled by the pyrolysis gas heating device and used as the drying gas for the secondary drying fan.

8. The treatment system for the comprehensive treatment process of coal-based solid waste containing volatile matter as described in claim 7, characterized in that, The oxygen-free pyrolysis section includes an oxygen-free pyrolysis stage 1 device and an oxygen-free pyrolysis stage 2 device; the material outlet of the oxygen-free pyrolysis stage 1 device is connected to the material inlet of the oxygen-free pyrolysis stage 2 device. The outlet of the pyrolysis gas heating device is connected to the pyrolysis gas inlet of the first stage oxygen-free pyrolysis device and the pyrolysis gas inlet of the second stage oxygen-free pyrolysis device through a flow path. The pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device and the pyrolysis gas outlet of the oxygen-free pyrolysis stage 2 device are combined and then connected to the inlet of the dust removal device. The system is also equipped with a pyrolysis gas return pipeline. One end of the pyrolysis gas return pipeline is connected to the flow path at the pyrolysis gas outlet of the oxygen-free pyrolysis stage 1 device, and the other end is connected to the flow path before the pyrolysis gas inlet of the oxygen-free pyrolysis stage 1 device. It is used to return part of the pyrolysis gas from the oxygen-free pyrolysis stage 1 device to its inlet in order to adjust the inlet temperature of the oxygen-free pyrolysis stage 1 device.

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