Internal and external heat type low-temperature dry distillation system and process

Abstract

The invention discloses an internal and external simultaneous heating type low-temperature dry distillation system and process, which are suitable for 0-30mm set particle solid raw materials (the low-rank coal is 0-50mm) and can be applied to the fields of oil shale dry distillation, lignite upgrading and the like, and products comprise coke, semi-coke, tar and dry distillation gas. The core of the system is a horizontal rotary sleeve type dry distillation furnace, a drying bin and a dry distillation bin which are coaxial are arranged in the horizontal rotary sleeve type dry distillation furnace, and an annular space is formed by an outer cylinder and an inner bin. High-temperature hot flue gas in the annular space is subjected to radiation and conduction heat transfer, and hot slag is backmixed according to the proportion of 1 / 4-1 / 3 of materials in the bin, so that direct heat transfer is achieved; heat energy is utilized in a gradient mode, waste heat is subjected to gas-solid heat exchange, and fluid is mixed and recycled. According to the process, drying, destructive distillation and combustion are integrated in one furnace, energy output loss of a traditional process is avoided, generation of nitric oxide is inhibited through low-oxygen combustion, and moisture removed through drying can be recycled. The heat efficiency is high, integration is high, the operation and maintenance cost is low, and efficient resource utilization of low-quality solid raw materials is achieved.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature dry distillation technology of organic solid fuels, and relates to a low-temperature dry distillation process with internal and external heating, specifically to a dry distillation furnace system and process with internal and external heating. Background Technology

[0002] This invention belongs to the field of low-temperature dry distillation technology of organic solid fuels, and is aimed at the resource utilization of 0-30mm particulate solid raw materials (such as oil shale, lignite, coal gangue and solid organic waste), solving the technical problem of upgrading and converting low-quality solid fuels.

[0003] Existing low-temperature carbonization technology is mainly suitable for materials with a particle size of 12mm or larger and has formed a mature industrial system. However, the technology for processing particulate raw materials is still in the experimental stage and lacks large-scale application solutions. Its main drawbacks are as follows: First, the heat transfer efficiency is low. Existing technologies mostly use a single gas or solid heat carrier for heat transfer. The former has slow heat transfer, resulting in an excessively large reactor size, while the latter wastes the heat of high-temperature flue gas. In addition, traditional processes (such as the Fushun carbonization process) require the energy to be extracted outside the furnace for treatment and then fed back, resulting in serious energy loss. Second, the system integration is low. Drying, carbonization, combustion and other processes are dispersed across multiple pieces of equipment, resulting in large losses in material transportation and energy transfer, and high maintenance costs. Third, the resource and environmental economic efficiency is poor. The moisture removed during drying is mixed with hydrocarbon vapor, and the complex recycling process leads to water waste. The combustion process easily generates nitrogen oxides, requiring an additional denitrification section, which increases operating costs.

[0004] Therefore, developing a low-temperature dry distillation technology that is adaptable to specific particulate feedstocks, has high heat transfer efficiency, sufficient energy circulation, and a high degree of integration has become a key direction that urgently needs to be broken through in this field, and is of great significance for promoting the resource utilization of low-quality solid fuels. Summary of the Invention

[0005] To address these issues, this invention provides a method for modifying a six-beam composite cutterhead to solve the problems of limited adaptability, low heat transfer efficiency, severe energy loss, low system integration, and poor environmental and economic efficiency in existing low-temperature dry distillation technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an internal and external heating low-temperature dry distillation system, comprising a dry distillation furnace body, a heat carrier remixing device, a combustion unit, a waste heat recovery unit, and a product recovery unit; The main body of the pyrolysis furnace includes an outer cylinder and two independent inner chambers coaxially arranged inside the outer cylinder. Each inner chamber includes a drying chamber and a pyrolysis chamber. Annular spaces are formed between the drying chamber, the pyrolysis chamber, and the outer cylinder, and these annular spaces are used to accommodate the combustion reaction and the flow of the heat carrier. A heat carrier remixing device is located at the feed end of the inner chamber. This device returns the hot slag from the annular space to the drying chamber and the pyrolysis chamber, achieving solid heat carrier circulation. The combustion unit includes a burner and a hot air inlet located at the end face of the pyrolysis section. The combustion unit is used to burn the semi-coke produced by pyrolysis and the purified pyrolysis gas, generating high-temperature hot flue gas and hot slag. The waste heat recovery unit includes an air slag cooler and a gas mixer. The waste heat recovery unit connects the ash and slag and the flue gas outlet of the annular space, and is used to recover the waste heat from the ash and slag and the flue gas to prepare hot air for circulating combustion. The product recovery unit is sequentially equipped with a cyclone dust collector, a water washing tower, an intercooling tower, an electrostatic precipitator, and a gas blower along the hydrocarbon vapor discharge path. The product recovery unit is used to separate and recover tar, the dry distillation gas, and dust, and a portion of the dry distillation gas is reconnected to the combustion unit.

[0007] As a preferred embodiment of an internal and external co-heating low-temperature dry distillation system, the system is characterized in that the drying chamber and the dry distillation chamber have the same external dimensions and identical mechanical structure; the drying chamber and the dry distillation chamber rotate horizontally coaxially with the outer cylinder and are driven by the same drive device at the same speed; the inner walls of the drying chamber, the dry distillation chamber, and the outer cylinder are all equipped with lifting plates; the outer cylinder, the drying chamber, and the dry distillation chamber are all horizontally rotating structures, and the material running direction is determined by the angle and direction of the pusher plates embedded in the inner wall; the hot flue gas in the annular space moves in the opposite direction to the material in the inner chamber.

[0008] As a preferred embodiment of an internal and external combined heating low-temperature dry distillation system, the amount of hot slag returned to the drying chamber by the heat carrier back mixing device is 1 / 4 to 1 / 3 of the total amount of material in the drying chamber, and the amount of hot slag returned to the dry distillation chamber is 1 / 4 to 1 / 3 of the total amount of material in the dry distillation chamber. The hot slag undergoes temperature changes without mass loss, and the amount of ash slag discharged from the dry distillation furnace corresponds to the amount of raw material fed into the furnace.

[0009] As a preferred embodiment of an internal and external co-heating low-temperature dry distillation system, the low-oxygen hot air provided by the combustion system is at a temperature of 260℃~280℃. The low-oxygen hot air is made by mixing 80℃ air after heat exchange in the air cooler, newly added air, and 350℃ flue gas discharged from the drying section.

[0010] As a preferred embodiment of an internal and external co-heating low-temperature dry distillation system, the dust recovered by the cyclone dust collector and the waste residue discharged by the air slag cooler are collected together in a waste residue bin; the water washing tower recovers 60% of the tar; the intercooling tower recovers 30% of the tar; the electrostatic precipitator recovers the remaining 10% of the tar; and the gas blower pressurizes the gas to obtain purified dry distillation gas. Part of the dry distillation gas is used for combustion in the dry distillation furnace, and the other part is used in a multi-product process.

[0011] This invention also provides an internal and external co-heating low-temperature dry distillation process, employing the aforementioned internal and external co-heating low-temperature dry distillation system, comprising the following steps: (1) Raw material pretreatment: The solid raw materials are crushed and screened to the preset particle size range and sent to the furnace front silo; (2) Drying process: The pretreated raw material enters the drying chamber and is mixed with the hot slag returned by the heat carrier back mixing device. Under the action of radiative heat transfer of hot flue gas and direct heat transfer of hot slag in the annular space, the temperature is raised and dehydrated to complete the drying process. (3) Drying process: The dried material enters the dry distillation chamber through the material sealing structure and mixes with the returned high-temperature hot slag. Under the dual heating of the hot flue gas and hot slag in the annular space, a low-temperature dry distillation reaction occurs, and the hydrocarbon vapor is discharged. (4) Combustion process: The semi-coke produced by dry distillation enters the annular space and comes into contact with the low-oxygen hot air after the waste heat is released and burns. The dry distillation gas is purified and sent to the burner for combustion. The hot flue gas and hot slag produced provide heat for the drying and dry distillation process. (5) Waste heat recovery: The ash residue after combustion is cooled by the air ash cooler. The air after heat exchange is mixed with the newly added air and part of the flue gas exported from the drying section to form the low oxygen hot air, which is recycled for combustion. (6) Product separation: The exported hydrocarbon vapor is treated by dust removal, cooling and electrostatic precipitation to recover the tar and purify the dry distillation gas respectively. The ash residue is collected as a product (coke) or discharged (shale ash, etc.).

[0012] As a preferred embodiment of the internal and external heating low-temperature dry distillation process, the particle size range of the solid raw material is 0-30 mm; when the raw material is low-rank coal such as lignite or low-quality coal, the particle size range is 0-50 mm.

[0013] As a preferred embodiment of the internal and external heating low-temperature dry distillation process, the raw material is heated to 300°C during the drying process to complete dehydration. The 180°C water vapor is removed, cooled, and condensed after dust removal to remove mechanical impurities and is used as industrial recycled water. During the dry distillation process, the raw material is heated to 500°C to complete the dry distillation reaction.

[0014] As a preferred embodiment of the internal and external combined heating low-temperature dry distillation process, the temperature within the annular space exhibits a distribution of initial heating followed by cooling along the direction from the dry distillation section to the drying section. The initial temperature at the end face of the dry distillation section is 500℃, the maximum temperature of the hot slag reaches 650℃, the temperature of the flue gas exiting the drying section is 350℃, the temperature of the hot slag discharge is 300℃, and the temperature difference between the hot and cold materials is maintained at 150℃~200℃. The heat transfer method of the drying chamber and the dry distillation chamber is a combination of internal and external heat. The internal heat is direct heat transfer from the hot slag, and the external heat is radiative heat transfer and heat conduction from the hot flue gas in the annular space. The heat contribution ratio of internal heat to external heat is 1:1~1:1.5.

[0015] As a preferred embodiment of an internal and external co-heating low-temperature dry distillation process, the material sealing structure includes a feed pipe connecting the drying chamber and the dry distillation chamber, and a backmixing material inlet mechanical structure at the feed end of the inner chamber; the feed pipe rotates synchronously with the inner chamber, and the pipe is filled with material during operation; the backmixing material inlet mechanical structure forms a material seal to prevent gas crossflow while picking up hot slag and feeding it into the inner chamber.

[0016] The beneficial effects of this invention are as follows: First, this invention specifically addresses the shortcomings of existing low-temperature carbonization technology, which is mainly suitable for lumpy materials and difficult to process granular raw materials on a large scale. It clarifies that the particle size range of the raw materials is 0-30mm, and for low-rank coals such as lignite and low-quality coal, due to their high volatile matter and the characteristics of further crushing during carbonization, the particle size range can be widened to 0-50mm. This invention can efficiently process a variety of low-quality solid raw materials such as oil shale, coal gangue, and solid organic waste, fully explore the resource utilization value of granular raw materials, and fill the relevant technological gaps.

[0017] Secondly, this invention adopts a dual heating mode of internal and external heating, combining the radiation and conduction heat transfer of high-temperature hot flue gas with the direct contact heat transfer of hot slag solid heat carrier, avoiding the thermal efficiency defects of single gas or solid heat carrier technology; at the same time, through the temperature gradient distribution of flue gas and hot slag in the annular space, the heat energy is utilized step by step from the dry distillation section to the drying section, and the temperature difference between hot and cold materials is stabilized at 150℃~200℃, ensuring sufficient heat transfer driving force. In addition, the waste heat of the system is recovered through gas-solid heat exchange, hot and cold fluid mixing and other processes, and the overall process thermal efficiency is significantly better than that of traditional dry distillation technology, significantly reducing energy consumption.

[0018] Third, the dry distillation furnace of this invention adopts a horizontal rotary sleeve structure, integrating the three main processes of drying, dry distillation, and combustion into a single reactor. Unlike traditional processes, it eliminates the need to export energy outside the furnace for processing and then return it, reducing additional losses in material and energy flow. The drying chamber and the dry distillation chamber have the same external dimensions and mechanical structure, and the accessories are interchangeable, reducing the difficulty and cost of equipment maintenance. At the same time, it simplifies the system process, reduces the number of independent equipment, and lowers the investment in engineering construction and the energy consumption of operation.

[0019] Fourth, the 180°C water vapor released during the drying process of this invention is independently exported and can be used as industrial recycled water after simple treatment, avoiding the complex treatment problems caused by mixing with hydrocarbon vapor and significantly saving water resources. The dry distillation products include a variety of high-value-added products such as coke, semi-coke, tar, and dry distillation gas. The purified dry distillation gas can be partially fed back to the combustion system, and the remainder can be used for power generation, gas boilers, and other multi-generation processes, realizing the full value transformation of low-quality solid raw materials and a complete resource utilization chain. The 260-280°C low-oxygen hot air is prepared by mixing flue gas with air, creating a high-temperature and low-oxygen combustion environment, effectively inhibiting the generation of nitrogen oxides, eliminating the need for a flue gas end-of-pipe denitrification section, and simplifying the environmental protection process. The final emission flue gas only needs to be desulfurized to meet the standards, with low pollutant emission concentrations that meet environmental protection requirements. At the same time, ash and dust are collected and treated centrally, with no secondary pollution, demonstrating outstanding environmental and economic benefits.

[0020] Fifth, this invention effectively blocks gas crossflow through the dual design of the material sealing guide pipe and the mechanical structure of the backmixing material inlet, ensuring a stable reaction environment in the drying chamber and the pyrolysis chamber; the hot slag, as a circulating heat carrier, only undergoes temperature changes without mass loss, and the backmixing amount is stable at 1 / 4 to 1 / 3 of the material in the chamber, which is easy to adjust to a steady-state operating state; the inner and outer cylinders and inner chamber of the pyrolysis furnace rotate horizontally synchronously, and the inner wall lifting plate drives the material to fully mix and exchange heat, avoiding material accumulation or entrainment, and ensuring continuous and stable operation of the process. Attached Figure Description

[0021] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0022] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0023] Figure 1 is a flow chart of an internal and external co-heating low-temperature dry distillation process provided in an embodiment of the present invention.

[0024] Figure 2 is a diagram showing the energy distribution inside a dry distillation furnace in an internally and externally heated low-temperature dry distillation process provided in an embodiment of the present invention. Detailed Implementation

[0025] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Referring to Figures 1 and 2, this embodiment of the invention provides an internal and external co-heating low-temperature dry distillation system, including a dry distillation furnace body, a heat carrier remixing device, a combustion unit, a waste heat recovery unit, and a product recovery unit. The dry distillation furnace body includes an outer cylinder and two independent inner chambers coaxially arranged inside the outer cylinder. The inner chambers include a drying chamber and a dry distillation chamber. Annular spaces are formed between the drying chamber, the dry distillation chamber, and the outer cylinder, and these annular spaces are used to accommodate the combustion reaction and the flow of the heat carrier. The heat carrier remixing device is located at the feed end of the inner chamber. The heat carrier remixing device returns the hot slag in the annular space to the drying chamber and the dry distillation chamber, realizing solid heat carrier circulation. The combustion unit includes... The system includes a burner and a hot air inlet located at the end of the dry distillation section. The combustion unit is used to burn the semi-coke produced by dry distillation and the purified dry distillation gas to generate high-temperature hot flue gas and hot slag. The waste heat recovery unit includes an air slag cooler and a gas mixer. The waste heat recovery unit is connected to the ash and flue gas outlet of the annular space. The waste heat recovery unit is used to recover the waste heat of the ash and flue gas to prepare hot air for circulating combustion. The product recovery unit is arranged along the hydrocarbon vapor outlet path with a cyclone dust collector, a water washing tower, an intercooling tower, an electrostatic precipitator, and a gas blower. The product recovery unit is used to separate and recover tar, the dry distillation gas, and dust. A portion of the dry distillation gas is reconnected to the combustion unit.

[0027] Specifically, the system integrates the three main processes of drying, pyrolysis, and combustion into a single rotary sleeve reactor, avoiding energy losses from external processing in traditional processes and significantly improving thermal efficiency. The annular space serves as a key channel, providing a site for the combustion reaction and enabling the orderly flow of hot flue gas and hot slag, thus laying the structural foundation for the "internal and external heat transfer" mode. The heat carrier remixing device overcomes the limitations of single heat carrier heat transfer, achieving direct heat transfer of the solid heat carrier through hot slag circulation. This forms a composite system with the radiation and conduction heat transfer of hot flue gas, maximizing the extraction of high-order thermal energy released by combustion and solving the problem of low thermal efficiency of single gas or solid heat carriers. The high-temperature heat carrier generated by the combustion unit supplies the drying and pyrolysis reactions, while the waste heat recovery unit converts the waste heat energy from ash, slag, and flue gas into hot air for circulating combustion. The pyrolysis gas separated by the product recovery unit is fed back into the combustion system, forming a self-sufficient energy cycle and reducing external energy consumption. The product recovery unit, taking into account the characteristics of different components in hydrocarbon vapor, recovers dust, tar, and dry distillation gas respectively through dust removal, gradient cooling, and electric field collection, thereby realizing the transformation of low-quality raw materials into high-value-added products.

[0028] In one possible embodiment, the drying chamber and the pyrolysis chamber have the same external dimensions and identical mechanical structure. The drying chamber and the pyrolysis chamber rotate horizontally coaxially with the outer cylinder, driven by the same drive device at the same speed. The inner walls of the drying chamber, the pyrolysis chamber, and the outer cylinder are all equipped with lifting plates. The outer cylinder, the drying chamber, and the pyrolysis chamber are all horizontally rotating structures. The material running direction is determined by the angle and direction of the pusher plates embedded in the inner wall. The hot flue gas in the annular space moves in the opposite direction to the material in the inner chamber.

[0029] Specifically, the drying chamber and the distillation chamber are the same size and have the same structure, enabling interchangeable parts, reducing the difficulty and cost of maintenance, reducing the pressure of spare parts reserves, and adapting to the needs of large-scale industrial production.

[0030] The synchronized rotation of the same drive unit ensures coordinated movement between the inner and outer cylinders, preventing material conveying blockages or uneven back-mixing of the heat carrier, ensuring continuous and stable process operation, and avoiding a decrease in heat and mass transfer efficiency due to speed differences. The lifting plates, through their rotational motion, fully lift and tumble the material, breaking down the heat transfer boundary layer on the material surface, allowing for uniform contact between the material and the heat carrier and hot flue gas, thus solving the problem of uneven heat exchange caused by the accumulation and entrainment of particulate materials. The angle of the pusher plates controls the material's direction of movement, precisely adjusting the residence time of the material within the chamber, ensuring sufficient drying and distillation reactions, and preventing excessively fast or slow material flow rates due to slope. The counter-current movement of hot flue gas and material increases the temperature difference between the hot and cold fluids, extending the heat exchange time. Compared to co-current heat exchange, this significantly improves thermal energy utilization, allowing the heat from the hot flue gas and hot slag to be fully transferred to the material, reducing heat waste.

[0031] In one possible embodiment, the amount of hot slag returned to the drying chamber by the heat carrier remixing device is 1 / 4 to 1 / 3 of the total amount of material in the drying chamber, and the amount of hot slag returned to the pyrolysis chamber is 1 / 4 to 1 / 3 of the total amount of material in the pyrolysis chamber. The hot slag undergoes temperature change without mass loss, and the amount of ash slag discharged from the pyrolysis furnace corresponds to the amount of raw material fed into the furnace.

[0032] Specifically, the amount of hot slag remixed is controlled between 1 / 4 and 1 / 3. This ratio ensures that the hot slag provides sufficient direct heat transfer to meet the material's rapid heating requirements, while preventing excessive hot slag from increasing equipment load or causing excessively long material residence time, thus achieving a balance between high efficiency and energy saving. As a circulating heat carrier, the hot slag does not participate in chemical reactions such as drying or distillation; it only transfers heat between the annular space and the inner chamber. Only temperature changes occur when it enters and exits the system, with no chemical consumption or physical loss, ensuring a stable total amount of heat carrier. The circulating hot slag always circulates within the system, and the discharged ash is only the ash contained in the raw material itself, excluding the circulating hot slag. This ensures the full conversion of effective components in the raw material while maintaining a dynamic balance of heat carrier within the system, avoiding heat carrier accumulation or shortage.

[0033] In one possible embodiment, the low-oxygen hot air provided by the combustion system is at a temperature of 260°C to 280°C, and the low-oxygen hot air is made by mixing 80°C air after heat exchange in the air cooler, additional air, and 350°C flue gas discharged from the drying section.

[0034] Specifically, the 80°C air after heat exchange in the air-cooled ash cooler carries the residual heat from the ash slag, while the 350°C flue gas from the drying section carries underutilized heat energy. These two components mix with the newly added air, recovering the waste heat energy within the system and diluting the oxygen concentration. Temperature control between 260°C and 280°C balances combustion efficiency and environmental requirements. This temperature range ensures complete combustion of semi-coke and dry distillation gas, providing sufficient heat for drying and dry distillation. Simultaneously, the low-oxygen environment inhibits nitrogen oxide formation, avoiding the NOx exceedance problem caused by traditional high-temperature oxygen-enriched combustion, and eliminating the need for a terminal denitrification section.

[0035] In one possible embodiment, the dust recovered by the cyclone dust collector and the waste residue discharged by the air slag cooler are collected together in a waste residue bin. The water washing tower recovers 60% of the tar, the intercooling tower recovers 30% of the tar, the electrostatic precipitator recovers the remaining 10% of the tar, and the gas blower pressurizes the gas to obtain the purified dry distillation gas. Part of the dry distillation gas is used for combustion in the dry distillation furnace, and the other part is used in a multi-product process.

[0036] Specifically, centralized collection of dust and slag simplifies solid waste treatment processes, avoids secondary pollution caused by dispersed dust emissions, and allows the centralized slag to be utilized as building materials, achieving both solid waste reduction and resource recovery. Tar staged recovery utilizes the condensation characteristics of tar at different temperatures. When 450℃ hydrocarbon vapor is cooled to 60℃ in a water washing tower, most of the tar condenses and precipitates due to the temperature decrease (60%). Further cooling to 40℃ causes the remaining tar to continue condensing (30%). Finally, trace amounts of tar droplets are captured by an electric field, achieving efficient tar recovery with a total recovery rate approaching 100%. Partial recirculation of distilled coal gas and partial cogeneration balance energy recycling and economic benefits. Recirculated coal gas supplements the system's heat source, reducing external fuel consumption and improving energy efficiency. Cogeneration expands energy output pathways by converting distilled coal gas into electricity and heat, enhancing the overall economic efficiency of the process.

[0037] Referring to Figures 1 and 2, this embodiment of the invention provides an internal and external co-heating low-temperature dry distillation process, employing the aforementioned internal and external co-heating low-temperature dry distillation system, including the following steps: (1) Raw material pretreatment: The solid raw materials are crushed and screened to the preset particle size range and sent to the furnace front silo; (2) Drying process: The pretreated raw material enters the drying chamber and is mixed with the hot slag returned by the heat carrier back mixing device. Under the action of radiative heat transfer of hot flue gas and direct heat transfer of hot slag in the annular space, the temperature is raised and dehydrated to complete the drying process. (3) Drying process: The dried material enters the dry distillation chamber through the material sealing structure and mixes with the returned high-temperature hot slag. Under the dual heating of the hot flue gas and hot slag in the annular space, a low-temperature dry distillation reaction occurs, and the hydrocarbon vapor is discharged. (4) Combustion process: The semi-coke produced by dry distillation enters the annular space and comes into contact with the low-oxygen hot air after the waste heat is released and burns. The dry distillation gas is purified and sent to the burner for combustion. The hot flue gas and hot slag produced provide heat for the drying and dry distillation process. (5) Waste heat recovery: The ash residue after combustion is cooled by the air ash cooler. The air after heat exchange is mixed with the newly added air and part of the flue gas exported from the drying section to form the low oxygen hot air, which is recycled for combustion. (6) Product separation: The exported hydrocarbon vapor is treated by dust removal, cooling and electrostatic precipitation to recover the tar and purify the dry distillation gas respectively. The ash residue is collected as a product (coke) or discharged (shale ash, etc.).

[0038] Specifically, the overall process follows a flow of raw materials, reaction, energy supply, waste heat recovery, and product separation, achieving gradient energy utilization and resource recycling, reducing energy consumption and pollutant emissions. Raw material pretreatment, by controlling particle size, lays the foundation for subsequent efficient heat transfer, addressing the pain point of low heat transfer efficiency in particulate materials; the drying process removes moisture from the raw materials, preventing moisture from affecting the efficiency of the dry distillation reaction and the quality of the products; the dry distillation process, under the combined heat transfer effect, precipitates volatiles to generate the target product; the combustion process converts the dry distillation residue (semi-coke) and products (dry distillation gas) into a heat source, achieving energy self-sufficiency; waste heat recovery reuses waste heat energy, reducing the need for external energy supplementation; product separation achieves graded recovery of each component, increasing resource added value and forming a flow of raw materials, energy, and products.

[0039] In one possible embodiment, the particle size range of the solid raw material is 0–30 mm; when the raw material is low-rank coal such as lignite or low-quality coal, the particle size range is 0–50 mm.

[0040] Specifically, controlling the particle size within 0–30 mm ensures efficient heat transfer. Cold-state and hot-state small-scale tests have demonstrated that this particle size range allows for sufficient contact between the material and the heat carrier and flue gas, resulting in a short heat transfer path and reasonable time. This avoids the problem of excessively large particles leading to an oversized reactor and increased operational difficulty, or excessively small particles causing material to be carried away by the flue gas. Allowing the particle size of low-rank coal to be relaxed to 0–50 mm is suitable for its inherent characteristics. Low-rank coal has high volatile matter (typically above 20%, some reaching 40%), and during drying and carbonization, it loses moisture and organic matter, forming a porous structure, which reduces its mechanical strength and thermal stability. It also undergoes further breakage and wear during rotational collisions. Reducing the particle size still meets the requirements for heat transfer and reaction, eliminating the need for additional crushing and reducing pretreatment costs.

[0041] In one possible embodiment, during the drying process, the raw material is heated to 300°C to complete dehydration, and the 180°C water vapor is removed by dust removal, cooling and condensation to remove mechanical impurities and is used as industrial recycled water; during the dry distillation process, the raw material is heated to 500°C to complete the dry distillation reaction.

[0042] Specifically, setting the drying temperature to 300℃ balances dehydration effectiveness with energy conservation. This temperature effectively removes free water and some bound water from the raw materials without causing premature precipitation of volatiles, thus avoiding energy waste and product contamination. It also ensures that the moisture content of the dried material meets the requirements for the dry distillation reaction. Setting the dry distillation temperature to 500℃ is optimal for low-temperature dry distillation. This temperature allows for the complete extraction of volatiles such as tar and gas, ensuring product yield and quality, while avoiding tar cracking and quality degradation due to excessively high temperatures. It also reduces the high-temperature resistance requirements of the equipment and lowers operating energy consumption. The independent extraction and reuse of 180℃ steam avoids mixing with hydrocarbon vapors, simplifying the water treatment process. After simple dust removal, condensation, and impurity removal, the steam can be used as industrial recycled water to supplement the water needs of equipment such as water scrubbing towers, achieving water resource recycling and reducing external water replenishment.

[0043] In one possible embodiment, the temperature within the annular space exhibits a distribution of initial increase followed by decrease along the direction from the pyrolysis section to the drying section. The initial temperature at the end face of the pyrolysis section is 500°C, the maximum temperature of the hot slag reaches 650°C, the temperature of the flue gas exiting the drying section is 350°C, the temperature of the hot slag discharge is 300°C, and the temperature difference between the hot and cold materials is maintained at 150°C to 200°C. The heat transfer method of the drying chamber and the pyrolysis chamber is a combination of internal and external heat. The internal heat is direct heat transfer from the hot slag, and the external heat is radiative heat transfer and heat conduction from the hot flue gas in the annular space. The heat contribution ratio of internal heat to external heat is 1:1 to 1:1.5.

[0044] Specifically, the temperature distribution in the annular space, which first heats up and then cools down, utilizes a thermal energy gradient. The dry distillation section requires higher heat to ensure the release of volatiles, and the combustion of semi-coke and dry distillation gas releases heat, raising the temperature to 650℃. Moving towards the drying section, hot flue gas and hot slag transfer heat to the drying chamber, with no additional combustion heat release, and the temperature gradually decreases. This achieves a step-by-step utilization of higher-order thermal energy to lower-order thermal energy, avoiding concentrated energy loss. Maintaining a temperature difference between hot and cold materials at 150℃~200℃ ensures sufficient driving force for heat transfer, guaranteeing rapid and efficient heat transfer to the materials, meeting the heating requirements of the drying and dry distillation processes, and preventing slow heat transfer rates and prolonged reaction cycles due to excessively small temperature differences. The combination of internal and external heat and the setting of the contribution ratio complement the defects of single heat transfer. Internal heat (direct heat transfer from hot slag) has a fast rate and high efficiency, while external heat (radiation and conduction of hot flue gas) has a wide coverage and stable temperature. The two are set in a ratio of 1:1 to 1:1.5, which can not only quickly increase the material temperature, but also ensure temperature uniformity, thus solving the problems of low thermal efficiency and uneven heat transfer of single heat transfer methods.

[0045] In one possible embodiment, the material sealing structure includes a feed pipe connecting the drying chamber and the pyrolysis chamber, and a backmixing material inlet mechanical structure at the feed end of the inner chamber; the feed pipe rotates synchronously with the inner chamber, and the pipe is filled with material during operation; the backmixing material inlet mechanical structure forms a material seal to prevent gas crossflow while picking up hot slag and feeding it into the inner chamber.

[0046] Specifically, the material sealing structure prevents gas cross-flow. The water vapor generated in the drying chamber has different properties from the hydrocarbon vapor in the distillation chamber. If they cross-flow, it will lead to product contamination problems such as water content in the tar and decreased purity of the coal gas, and will also cause energy loss. The feed pipe is filled with material to form a static material column seal, while the mechanical structure at the backmix inlet forms a dynamic material seal through the accumulation of hot slag. This double seal effectively isolates the flue gas in the annular space from the gas in the inner chamber. The synchronous rotation of the feed pipe and the inner chamber avoids bridging and blockage during material transportation, while maintaining the continuity and sealing of the material column, ensuring uninterrupted sealing, and guaranteeing independent reaction environments in the drying chamber and distillation chamber, thereby ensuring product purity and process stability.

[0047] The working principle of this invention is as follows: First, the core structural support principle: The main body of the dry distillation furnace adopts a horizontal rotary sleeve structure. The outer cylinder, along with the coaxially arranged drying chamber and dry distillation chamber, forms an annular space, constituting an integrated "one furnace, two chambers" reaction system. The drying chamber and dry distillation chamber are identical in size and structure, driven by the same drive equipment to rotate synchronously horizontally without any slope angle. The material flow direction is controlled by the angle of the inner wall pusher plate, ensuring that the material remains uniformly within the chamber and completes the reaction. The annular space serves as a combustion reaction and heat carrier flow channel, forming an "outer" and "inner" heat transfer interface with the inner chamber, providing a structural basis for dual heating. Simultaneously, the feed pipe connecting the two chambers rotates synchronously with the inner chamber. During operation, the pipe is filled with material, forming a material seal. The mechanical structure of the backmixing material inlet at the inner chamber's feed end forms a material seal while simultaneously lifting the hot slag. This dual material seal design prevents gas crossflow, ensuring independent reaction atmospheres in the drying chamber (water vapor environment) and the dry distillation chamber (hydrocarbon vapor environment), avoiding product contamination and energy loss.

[0048] Second, the principle of combined internal and external heat transfer: This invention breaks through the limitations of single heat carrier heat transfer and adopts a combined heat transfer mode of "external heat radiation and conduction, and internal heat direct contact" to maximize the utilization of the high-order heat energy released by combustion: External heat transfer: In the annular space, the combustion of semi-coke and dry distillation gas produces high-temperature hot flue gas and hot slag at 650°C. The hot flue gas passes through the outer walls of the drying chamber and dry distillation chamber, transferring heat to the materials inside the chamber through heat radiation (accounting for the majority of external heat, about 70-80%) and heat conduction (accounting for 20-30% of external heat); Internal heat transfer: Through the heat carrier remixing device, the hot slag in the annular space is mixed with the heat carrier at a ratio of 1 / 4 to 1 / 3 of the total amount of materials in the chamber. The materials are fed back to the drying chamber (300℃ hot slag) and the carbonization chamber (650℃ hot slag) respectively. During the rotation, the hot slag and the materials are fully mixed and turned by the lifting plates, achieving direct contact heat transfer in the form of solid heat carrier. The heat transfer rate is much higher than that of single gas heat transfer. Heat transfer synergy effect: the internal and external heat transfer forms a multi-mode heat transfer system of "radiation, conduction and convection". Moreover, the hot flue gas, hot slag and the materials in the inner chamber move in opposite directions in the annular space. The temperature difference between the hot and cold materials is stable at 150℃~200℃, ensuring sufficient heat transfer driving force, greatly improving heat transfer efficiency, and avoiding the problems of excessive reactor size or energy waste caused by a single heat transfer method.

[0049] Third, the principle of energy gradient utilization and process energy supply: This invention achieves efficient energy utilization through a process design of "combustion heat generation, gradient heating, waste heat recovery, and cycle energy supply". Heat generation: The semi-coke produced by dry distillation enters the annular space and slowly combusts in contact with preheated low-oxygen hot air. Simultaneously, purified dry distillation gas is fed into the burner and mixes with the low-oxygen hot air for combustion. Together, they generate high-temperature flue gas and hot slag at 650°C, providing the primary heat source for the drying and dry distillation processes. Gradient heating: The high-temperature flue gas and hot slag first provide heat for the dry distillation reaction in the annular space section corresponding to the dry distillation chamber (initial temperature of the dry distillation section is 500°C). After the temperature drops by 200°C, they enter the annular space section corresponding to the drying chamber to provide heat for the drying reaction. Finally, the flue gas is discharged at 350°C and the hot slag at 300°C. This achieves the gradient utilization of high-order thermal energy to low-order thermal energy, avoiding concentrated energy loss; waste heat recovery and recycling: the 300℃ hot slag is cooled to 180℃~200℃ by an air slag cooler, and the air after heat exchange is heated to 80℃. It is sent to a gas mixer together with the newly added air and part of the 350℃ flue gas exported from the drying section to prepare low-oxygen hot air at 260℃~280℃, which is circulated to supply the combustion system, forming a process of "combustion, heat generation, heat exchange, and circulating energy supply", which greatly reduces the demand for external energy supplementation; at the same time, the low-oxygen combustion environment inhibits the generation of nitrogen oxides, eliminating the need for the end-of-pipe denitrification section and simplifying the environmental protection process.

[0050] Fourth, the principle of process flow synergy: Raw material pretreatment and drying: Solid raw materials are crushed and screened to 0-30mm (0-50mm for low-rank coal), and enter the drying chamber through a closed conveyor. They are mixed with 300℃ back-mixed hot slag. Under the synergistic effect of the external heat of the hot flue gas and the internal heat of the hot slag in the annular space, the temperature is gradually raised to 300℃. The 180℃ water vapor is independently discharged and, after dust removal, condensation, and impurity removal, is used as industrial recycled water to achieve water resource recycling; Dry distillation reaction: The dried material enters the dry distillation chamber through the material sealing guide pipe and is mixed with 650℃ high-temperature hot slag. Under double heating, the temperature is raised to 500℃, and a low-temperature dry distillation reaction occurs, precipitating volatiles such as tar and gas, forming hydrocarbon vapor at about 450℃, which is directed out. The remaining semi-coke and ash residue mixture is discharged into the annular space; Product separation and recovery: The exported hydrocarbon vapor is first passed through a cyclone dust collector to remove dust (collected together with the ash and slag discharged from the slag cooler), and then sequentially passed through a water washing tower (60℃, recovering 60% of tar), an intercooling tower (40℃, recovering 30% of tar), and an electrostatic precipitator (recovering the remaining 10% of tar) to achieve efficient and graded recovery of tar; part of the purified dry distillation gas is fed back to the combustion system, and the other part is used for power generation, boiler heating and other multi-product processes to complete the transformation of low-quality raw materials into high-value-added products.

[0051] Fifth, the principle of stable heat carrier circulation: The hot slag, as a circulating solid heat carrier, only flows between the annular space and the drying and pyrolysis chambers, without participating in chemical reactions. Only temperature changes occur before and after entering and leaving the chambers (no mass loss). The hot slag generated by the combustion of the semi-coke discharged from the pyrolysis chamber in the annular space is partially returned to the pyrolysis chamber and partially flows back to the drying section and returned to the drying chamber. The total circulation volume maintains a dynamic balance, and the amount of ash discharged corresponds only to the ash content of the raw material entering the furnace, ensuring stable heat transfer efficiency and controllable process.

[0052] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A low-temperature dry distillation system with internal and external heating, characterized in that, The system includes a dry distillation furnace body, a heat carrier remixing device, a combustion unit, a waste heat recovery unit, and a product recovery unit. The dry distillation furnace body includes an outer cylinder and two independent inner chambers coaxially arranged inside the outer cylinder. Each inner chamber includes a drying chamber and a dry distillation chamber. Annular spaces are formed between the drying chamber, the dry distillation chamber, and the outer cylinder, and these annular spaces are used to accommodate the combustion reaction and the flow of the heat carrier. The heat carrier remixing device is located at the feed end of the inner chamber and returns the hot slag from the annular space to the drying chamber and the dry distillation chamber, achieving solid heat carrier circulation. The combustion unit includes a burner and a heat exchanger located at the end face of the dry distillation section. An air inlet is provided. The combustion unit is used to burn the semi-coke produced by dry distillation and the purified dry distillation gas to generate high-temperature hot flue gas and hot slag. The waste heat recovery unit includes an air slag cooler and a gas mixer. The waste heat recovery unit is connected to the ash and flue gas outlet of the annular space. The waste heat recovery unit is used to recover the waste heat of the ash and flue gas to prepare hot air for circulating combustion. The product recovery unit is arranged along the hydrocarbon vapor outlet path with a cyclone dust collector, a water washing tower, an intercooling tower, an electrostatic precipitator, and a gas blower. The product recovery unit is used to separate and recover tar, the dry distillation gas, and dust. A portion of the dry distillation gas is reconnected to the combustion unit.

2. The internal and external co-heating low-temperature dry distillation system according to claim 1, characterized in that, The drying chamber and the pyrolysis chamber have the same external dimensions and identical mechanical structure. The drying chamber and the pyrolysis chamber rotate horizontally coaxially with the outer cylinder and are driven by the same drive device at the same speed. The inner walls of the drying chamber, the pyrolysis chamber, and the outer cylinder are all equipped with lifting plates. The outer cylinder, the drying chamber, and the pyrolysis chamber are all horizontally rotating structures. The direction of material movement is determined by the angle and direction of the pusher plates embedded in the inner wall. The hot flue gas in the annular space moves in the opposite direction to the material in the inner chamber.

3. The internal and external co-heating low-temperature dry distillation system according to claim 1, characterized in that, The amount of hot slag returned to the drying chamber by the heat carrier remixing device is 1 / 4 to 1 / 3 of the total amount of material in the drying chamber, and the amount of hot slag returned to the dry distillation chamber is 1 / 4 to 1 / 3 of the total amount of material in the dry distillation chamber. The hot slag undergoes temperature change without mass loss, and the amount of ash slag discharged from the dry distillation furnace corresponds to the amount of raw material fed into the furnace.

4. The internal and external co-heating low-temperature dry distillation system according to claim 1, characterized in that, The combustion system provides low-oxygen hot air at a temperature of 260°C to 280°C. The low-oxygen hot air is made by mixing 80°C air after heat exchange in the air cooler, newly added air, and 350°C flue gas from the drying section.

5. The internal and external co-heating low-temperature dry distillation system according to claim 4, characterized in that, The dust recovered by the cyclone dust collector and the waste residue discharged by the air slag cooler are collected together in the waste residue bin. The water washing tower recovers 60% of the tar, the intercooling tower recovers 30% of the tar, the electrostatic precipitator recovers the remaining 10% of the tar, and the gas blower pressurizes the gas to obtain purified dry distillation gas. Part of the dry distillation gas is used for combustion in the dry distillation furnace, and the other part is used in the multi-product process.

6. A low-temperature dry distillation process with internal and external heating, employing the low-temperature dry distillation system with internal and external heating as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Raw material pretreatment: The solid raw materials are crushed and screened to the preset particle size range and sent to the furnace front silo; (2) Drying process: The pretreated raw material enters the drying chamber and is mixed with the hot slag returned by the heat carrier back mixing device. Under the action of radiative heat transfer of hot flue gas and direct heat transfer of hot slag in the annular space, the temperature is raised and dehydrated to complete the drying process. (3) Drying process: The dried material enters the dry distillation chamber through the material sealing structure and mixes with the returned high-temperature hot slag. Under the dual heating of the hot flue gas and hot slag in the annular space, a low-temperature dry distillation reaction occurs, and the hydrocarbon vapor is discharged. (4) Combustion process: The semi-coke produced by dry distillation enters the annular space and comes into contact with the low-oxygen hot air after the waste heat is released and burns. The dry distillation gas is purified and sent to the burner for combustion. The hot flue gas and hot slag produced provide heat for the drying and dry distillation process. (5) Waste heat recovery: The ash residue after combustion is cooled by an air ash cooler. The air after heat exchange is mixed with the newly added air and part of the flue gas exported from the drying section to form the low-oxygen hot air, which is recycled for combustion. (6) Product separation: The exported hydrocarbon vapor is treated by dust removal, cooling and electrostatic precipitation to recover the tar and purify the dry distillation gas respectively. The ash residue is collected as a product or discharged.

7. The low-temperature dry distillation process with internal and external heating according to claim 6, characterized in that, The particle size range of the solid raw material is 0-30 mm; when the raw material is low-rank coal such as lignite or low-quality coal, the particle size range is 0-50 mm.

8. The low-temperature dry distillation process with internal and external heating according to claim 6, characterized in that, During the drying process, the raw material is heated to 300°C to complete dehydration. The 180°C water vapor that is removed is cooled and condensed after dust removal to remove mechanical impurities and is used as industrial recycled water. During the dry distillation process, the raw material is heated to 500°C to complete the dry distillation reaction.

9. The low-temperature dry distillation process with internal and external heating according to claim 6, characterized in that, The temperature within the annular space exhibits a distribution of initial increase followed by decrease along the direction from the pyrolysis section to the drying section. The initial temperature at the end face of the pyrolysis section is 500℃, the maximum temperature of the hot slag reaches 650℃, the temperature of the flue gas exiting the drying section is 350℃, the temperature of the hot slag discharge is 300℃, and the temperature difference between the hot and cold materials is maintained at 150℃~200℃. The heat transfer method of the drying chamber and the pyrolysis chamber is a combination of internal and external heat. The internal heat is direct heat transfer from the hot slag, and the external heat is radiative heat transfer and heat conduction from the hot flue gas in the annular space. The heat contribution ratio of internal heat to external heat is 1:1~1:1.

5.

10. The low-temperature dry distillation process with internal and external heating according to claim 6, characterized in that, The material sealing structure includes a feed pipe connecting the drying chamber and the pyrolysis chamber, and a backmixing material inlet mechanical structure at the feed end of the inner chamber; the feed pipe rotates synchronously with the inner chamber, and the pipe is filled with material during operation; the backmixing material inlet mechanical structure forms a material seal to prevent gas crossflow while picking up hot slag and sending it into the inner chamber.

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