Coal gangue near zero external combustion vertical roasting device and process

Abstract

The present application relates to a kind of coal gangue near zero external combustion vertical roasting device and process, its device includes vertical roasting furnace body, roasting furnace body is from top to bottom and is equipped with drying first section, drying second section, preheating section, roasting section, fast cooling section and slow cooling section;Air path system is material cooling, drying circulation, hot air circulation, flue gas circulation, waste heat output and wet air discharge respectively, and closed-circuit hot air circulation is formed.Cold air after material cooling system enters drying circulation, hot air circulation and roasting section.Drying circulation extracts 200-400 ℃ hot air from slow cooling section for drying;Hot air circulation extracts 400-700 ℃ hot flue gas from fast cooling section for preheating section;Waste heat output extracts 600-900 ℃ hot flue gas from roasting section for external supply;Flue gas circulation sends back roasting section and burns again with 200-500 ℃ volatile component-containing flue gas of drying second section and preheating section;Wet air is discharged after dust removal.The present application is synergized by six process sections and six air paths, realizes coal gangue roasting near zero external combustion and waste heat cascade utilization.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and thermal roasting equipment technology, and more specifically, to a near-zero external combustion vertical roasting device and process for coal gangue. Background Technology

[0002] Coal gangue is a major solid waste generated during coal mining and washing, with a massive accumulated stockpile. Long-term stockpiling not only occupies vast amounts of land and pollutes the surrounding environment, but also results in a serious waste of its contained fixed carbon and clay minerals. High-temperature roasting to decarbonize and activate coal gangue is an important way to utilize its resources, such as preparing building material raw materials, extracting valuable components, or producing lightweight aggregates.

[0003] Currently, the main equipment used for coal gangue roasting includes rotary kilns, tunnel kilns, and fluidized bed roasting furnaces, but they generally have the following shortcomings: a large amount of additional fuel is required to maintain the roasting temperature, resulting in high external combustion energy consumption; the recovery of waste heat from high-temperature flue gas is insufficient, leading to low system thermal efficiency; the temperature field and airflow distribution inside the furnace are difficult to precisely control, resulting in frequent under-burning or over-burning of materials, leading to large fluctuations in product quality; in addition, the flue gas emissions are large, resulting in a high pollution control load.

[0004] It is worth noting that existing vertical roasting furnaces mostly use intermediate furnace wall air ducts to introduce and distribute airflow. This involves setting fixed air ducts inside the furnace wall or in the interlayer to introduce cold or hot air into different areas of the furnace. While this structure achieves airflow to a certain extent, it has significant drawbacks: First, the cross-sectional area and opening positions of the intermediate furnace wall air ducts are fixed during the design phase, making it impossible to flexibly adjust them according to changes in material characteristics and roasting conditions during operation. This results in poor controllability of airflow distribution, making it difficult to effectively correct deviations when the airflow distribution inside the furnace deviates from the design conditions. Second, the air ducts are integrally constructed with the furnace wall, which is prone to deformation, burning, cracking, and even air leakage under long-term high-temperature operation. This not only causes airflow loss and increased energy consumption but also severely disrupts the uniformity of roasting temperature. Third, intermediate furnace wall air ducts typically only provide airflow in a single direction and at a single grade, making it difficult to implement differentiated and tiered airflow and temperature supply for different process stages, and even more difficult to achieve tiered utilization of high-temperature waste heat.

[0005] Although some roasting systems have been equipped with waste heat recovery devices, their air ducts are mostly open or semi-open designs, making it difficult to achieve self-sustaining roasting with almost no external fuel source, and also unable to perform cascaded closed-loop recycling of waste heat. Therefore, there is an urgent need to develop a vertical roasting equipment that can fully utilize the calorific value of coal gangue, achieve near-zero external combustion, cascaded waste heat recovery, and precise control of thermal parameters. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a vertical roasting device and process for coal gangue with near-zero external combustion that can make full use of the calorific value of coal gangue itself, achieve near-zero external combustion, and recover waste heat in stages.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: A near-zero external combustion vertical roasting device for coal gangue is constructed, comprising a vertical roasting furnace body, an air circulation system, and a multi-point monitoring and control system. The internal cavity of the vertical roasting furnace body, from top to bottom, includes a drying section, a drying section, a preheating section, a roasting section, a rapid cooling section, and a slow cooling section. The air circulation system includes a material cooling air circulation path, a drying circulation air circulation path, a hot air circulation air circulation path, a flue gas circulation air circulation path, a waste heat output air circulation path, and a humid air exhaust air circulation path. Each air circulation path is equipped with an independent on / off regulating valve. The material cooling air circulation path is used to introduce cold air into the rapid cooling section and the slow cooling section. The drying circulation air circulation path is used to extract 2% of the heat from the interface between the rapid cooling section and the slow cooling section. Hot air at 00-400℃ is sent to the drying section at the top of the furnace; the hot air circulation path is used to send hot flue gas at 400-700℃ extracted from the rapid cooling section to the preheating section; the waste heat output path is used to output high-temperature flue gas at 600-900℃ extracted from the roasting section area to the outside; the flue gas circulation path is used to send flue gas at 200-500℃ containing volatile heat extracted from the second drying section and the preheating section into the roasting section and the boundary area between the roasting section and the rapid cooling section; the humid air exhaust path is used to discharge the humid air from the first drying section and the second drying section after dust removal; the multi-point monitoring and control system is used to monitor and adjust the temperature field, pressure field and flow distribution inside the furnace.

[0008] According to the above scheme, the top of the vertical roasting furnace body is provided with a drying section extension section connected to the drying section above, and the bottom is provided with a cooling section extension section connected to the slow cooling section below. The drying section extension section and the cooling section extension section are used to optimize the airflow distribution in the furnace and stabilize the material residence time.

[0009] According to the above scheme, after the cold air is introduced through the material cooling air path, it is divided into two paths: one path is preheated by the rapid cooling section and then enters the hot air circulation air path or directly enters the roasting section; the other path is preheated by the slow cooling section and then enters the drying circulation air path for drying the material in the drying section.

[0010] According to the above scheme, the air intake of the drying circulating air path is set in the slow cooling section area; the air volume and air pressure are controlled by the switch regulating valve, and in conjunction with the air leakage sealing effect of the unloading system, the air volume and air temperature of the hot air drawn from the slow cooling section are adjusted, so as to adjust the air volume and air temperature of the drying circulating air introduced into the drying section at the top of the furnace.

[0011] According to the above scheme, the air pressure and air volume of the gas extracted from the high-temperature zone above and the low-temperature zone below the rapid cooling section are controlled by the switch regulating valve, so as to control the air volume and air temperature of the circulating hot air introduced into the preheating section.

[0012] According to the above scheme, the air pressure and air volume of the hot air circulation path in the preheating section and the flue gas circulation path below the calcination section are controlled by the switch regulating valve, so as to control the air volume and air temperature of the output waste heat.

[0013] According to the above scheme, the air intake of the flue gas circulation air path is set at the junction of the second drying section and the preheating section, and the exhaust port of the flue gas circulation air path is set at the junction of the roasting section and the rapid cooling section; the air pressure and air volume from the second drying section and the preheating section are controlled by switching the regulating valve, thereby controlling the air volume and air temperature of the flue gas circulation airflow.

[0014] According to the above scheme, the humid air exhaust air path forms a negative pressure at the fabric system. By controlling the air leakage effect of the fabric system and controlling the air pressure and air volume of the drying circulation air path by switching the regulating valve, the air volume and air temperature of the humid air exhaust are controlled.

[0015] According to the above scheme, the measuring points of the multi-point monitoring and control system are arranged in an unequal interval manner: the measuring points are arranged with a denser interval in the core reaction zone of the roasting and preheating sections, and with a sparser interval in the transition zone; the multi-point monitoring and control system also includes a reserved interface for connecting an external flue gas analyzer or adding additional sensors to monitor the flue gas composition.

[0016] This invention also provides a near-zero external combustion vertical roasting process for coal gangue, employing the aforementioned near-zero external combustion vertical roasting device, comprising the following steps: S1. Obtain the calorific value of the coal gangue fed into the furnace and determine its calorific value range; calorific value of 400-800 kcal / kg is the low calorific value range, calorific value of 800-1400 kcal / kg is the conventional calorific value range, and calorific value higher than 1400 kcal / kg is the high calorific value range. S2. If the range is determined to be low calorific value, adjust the opening of the regulating valves in each air path to make the external air supply volume of the waste heat output air path lower than the normal operating condition, prioritizing the retention of high-temperature flue gas heat in the furnace; at the same time, increase the volume of high-temperature hot air drawn from the rapid cooling section in the hot air circulation air path, and increase the circulation air volume of flue gas containing volatiles drawn from the second drying section and the preheating section in the flue gas circulation air path, so that all the circulating flue gas is guided into the roasting section to ensure that the volatiles are fully burned in the roasting section to compensate for the insufficient calorific value of the raw materials; in addition, appropriately increase the volume of hot air drawn from the slow cooling section in the drying circulation air path to enhance the drying effect and ensure timely preheating of the material after it enters the furnace; reduce the external air supply volume of waste heat to the minimum or shut it off. S3. If the value is determined to be within the normal calorific value range, adjust the regulating valves of each air path to make the hot air circulation volume and the flue gas circulation volume approximately equal. The combustion air volume and the drying circulation volume are automatically balanced according to the temperature of the calcination section and the drying section, maintaining the calcination section temperature at 950-1250℃, the preheating section temperature at 550-650℃, and the drying section temperature at 150-350℃. The waste heat output air path supplies high-temperature flue gas of 600-900℃ to the outside according to the set value to achieve a balance between heat supply and demand. S4. If the area is determined to be in the high calorific value range, adjust the regulating valves of each air path, increase the external air supply of the waste heat output air path, and promptly remove excess heat from the roasting section; at the same time, reduce the opening of the flue gas circulation air path, reduce the proportion of flue gas containing volatiles returning to the roasting section, and avoid overheating of the roasting section; and appropriately reduce the circulation air volume of the hot air circulation air path to reduce the heat supply to the preheating section; reduce the flue gas circulation air volume to 50% to 70% of the normal value. S5. During the adjustment process from T2 to T4, the temperature, pressure and flow data of the calcination section, preheating section and drying section are monitored in real time through a multi-point monitoring and control system. Based on the currently determined calorific value range, the corresponding air volume ratio and temperature range are maintained. The adjustment of each air path is achieved through independently set switch regulating valves, and at the same time, the air intake ratio of the fast cooling section and the slow cooling section is controlled until the system runs smoothly or stops.

[0017] The near-zero external combustion vertical roasting device and process for coal gangue of the present invention have the following beneficial effects: 1. By constructing a closed-loop hot air circulation system comprising six subsystems—material cooling, drying circulation, hot air circulation, flue gas circulation, waste heat output, and humid air emission—the sensible heat recovered from the cooling section and the waste heat from the roasting flue gas are applied in stages to drying, preheating, and roasting. Combined with the stable combustion of the fixed carbon in the coal gangue, self-sustaining roasting can be maintained without external fuel or with only a small amount of supplementation, truly achieving "near-zero external combustion" and significantly reducing operating costs.

[0018] 2. The cooling section adopts a graded design of fast cooling section and slow cooling section, which not only realizes the efficient recovery of waste heat of high temperature materials, but also provides hot air of different grades to hot air circulation and drying circulation respectively. The utilization of waste heat is more scientific and reasonable, and avoids the downgraded use of high-quality heat energy.

[0019] 3. The flue gas recirculation air path returns the low-temperature flue gas containing volatiles to the calcination section for re-combustion, which not only makes full use of the residual calorific value of the volatiles in the flue gas, but also effectively reduces the heat loss of the flue gas. At the same time, it helps to reduce the flue gas treatment load of the equipment and ensures that the concentration of combustible gases such as CO in the flue gas meets the standards.

[0020] 4. Compared with the traditional intermediate furnace wall air duct structure, the present invention adopts an independent external air duct system. Each air duct is equipped with an independent switch regulating valve, which can flexibly adjust the air volume, air temperature and air intake ratio of each section according to the actual working conditions, greatly improving the degree of adjustment. At the same time, it avoids the risk of air leakage due to high temperature deformation of the furnace wall air duct, making the system more reliable and enabling the independent output of high temperature waste heat, thus broadening the ways of heat energy utilization.

[0021] 5. The extension section, pipe inlet, and observation window of the furnace body further improve the uniformity of airflow distribution, the convenience of equipment maintenance, and the degree of process visualization, thereby enhancing the engineering adaptability and operational reliability of the device. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic diagram of the near-zero external combustion vertical roasting device for coal gangue of the present invention. Detailed Implementation

[0023] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1 As shown, the near-zero external combustion vertical roasting device for coal gangue of the present invention includes a vertical roasting furnace body, an air duct system, and a multi-point monitoring and control system.

[0025] The internal cavity of the vertical roasting furnace is divided into six process sections from top to bottom: drying section one, drying section two, preheating section, roasting section, rapid cooling section, and slow cooling section. An extension section connecting to the drying section one is located at the top of the furnace, and an extension section connecting to the slow cooling section is located at the bottom, to optimize airflow distribution and stabilize material residence time.

[0026] The air circulation system comprises six subsystems: material cooling, drying circulation, hot air circulation, flue gas circulation, waste heat output, and humid air exhaust, forming a closed-loop hot air circulation system. The cooling section is divided into a rapid cooling section and a slow cooling section. The cooling air, introduced through the material cooling air path, is divided into two paths: one path undergoes intense heat exchange with the high-temperature material in the rapid cooling section, preheating it to high-temperature hot air before merging into the hot air circulation branch or directly entering the roasting section; the other path undergoes preheating in the slow cooling section to medium-low temperature hot air before entering the drying circulation for material drying in the drying section. The drying circulation air path independently extracts 200-400℃ hot air from the interface between the rapid and slow cooling sections, controlling the airflow and pressure via a switching valve, and then introduces it into the drying section at the top of the furnace. The hot air circulation loop extracts 400-700℃ hot flue gas from the rapid cooling section inside the furnace and returns it to the furnace as a heat source for the preheating section, thus avoiding additional heat input to the preheating section. The waste heat output duct extracts high-temperature flue gas (600-900℃) from the area above the roasting section of the furnace and outputs it for use in waste heat boiler power generation or steam production. The flue gas recirculation duct extracts hot flue gas containing volatiles (200-500℃) from the second drying section and preheating section of the furnace and recirculates it into the roasting section and high-temperature cooling section for combustion, fully utilizing the calorific value of the volatiles and avoiding excessive combustible gas emissions. The humid air exhaust duct directly discharges the humid air from the first and second drying sections after dust removal, without the need for desulfurization and denitrification treatment, and creates negative pressure at the material distribution system to prevent dust overflow.

[0027] The multi-point monitoring and control system includes multiple thermometers, pressure sensors, vortex flow meters, and differential pressure gauges arranged at predetermined intervals along the furnace height to monitor and regulate the temperature, pressure, and flow distribution within the furnace in real time. The measuring points are arranged with denser intervals in the core reaction zones of the roasting and preheating sections, and with sparser intervals in transitional areas such as the drying and cooling sections, to accurately capture the location of the reaction zone. The multi-point monitoring and control system also has reserved interfaces for connecting external flue gas analyzers or adding additional sensors to monitor CO, CO2, and NO in the flue gas online. x It contains components such as SO2. Multiple insertion ports are located at predetermined positions along the height of the furnace body for installing thermometers or pressure sensors, thereby obtaining complete temperature and pressure field information from the drying section to the cooling section.

[0028] In addition, the roasting section is equipped with an ignition device, which is interlocked with the air circulation system. This device only assists in ignition during the initial cold start-up phase and automatically shuts off once the furnace temperature reaches the ignition point of the coal gangue and a stable thermal cycle is established. The roasting process then relies on the circulating hot air and the combustion of the material's own fixed carbon to sustain roasting. High-temperature resistant glass-covered observation windows are also installed at corresponding heights in the preheating and roasting sections of the furnace body to visually observe the roasting status, movement, and presence of agglomeration in the material layer.

[0029] The process consists of six stages arranged from top to bottom: drying stage 1 → drying stage 2 → preheating stage → calcination stage → rapid cooling stage → slow cooling stage. A closed-loop hot air circulation system is formed by six subsystems: material cooling, drying circulation, hot air circulation, flue gas circulation, waste heat output, and humid air exhaust. The core of the coordinated control is "heat cascade recovery and grade-matched utilization," recovering heat of different grades from the cooling stage and precisely supplying it to different process stages.

[0030] After being introduced through the material cooling air path, the cold air is divided into two paths: The first path, the high-temperature loop, enters the rapid cooling section to exchange heat with the high-temperature material, preheating it to 550-650℃. It then enters the hot air circulation branch and is supplied back to the roasting section as a heat source for both the preheating and roasting sections. The hot air circulation loop draws 400-700℃ hot flue gas from the rapid cooling section and sends it back to the preheating section, stabilizing the preheating section temperature at 550-650℃. The second path, the medium-temperature loop, enters the slow cooling section and is preheated to approximately 300℃ before entering the drying circulation, flowing into the drying section at the top of the furnace for material drying. The drying circulation air path draws 200-400℃ hot air from the interface between the rapid and slow cooling sections. The ratio of hot air drawn from the two sections is independently controlled by a switching regulating valve, ensuring that the air temperature entering the drying section is stable at 250-350℃.

[0031] The flue gas recirculation path draws hot flue gas containing volatiles at approximately 350°C from the second drying section and the preheating section, and sends it into the calcination section for secondary combustion. This fully utilizes the calorific value of the volatiles and effectively reduces the concentration of combustible gases in the exhaust. The air intake is located at the interface between the second drying section and the preheating section, and the exhaust port is located at the interface between the calcination section and the rapid cooling section.

[0032] The waste heat output air duct extracts approximately 780°C high-temperature flue gas from the area above the calcination section and outputs it externally. This gas can be used for production heat in the plant area or recovered by the waste heat boiler to generate steam. By controlling the air pressure and air volume of the hot air circulation loop in the preheating section and the hot flue gas circulation loop below the calcination section through the on / off regulating valve, the air volume and temperature of the output waste heat can be controlled.

[0033] The humid air exhaust duct removes dust from the first and second drying stages of the humid air and discharges it directly without desulfurization and denitrification treatment. It also creates negative pressure at the fabric system to prevent dust from escaping.

[0034] A multi-point monitoring and control system is equipped with thermometers, pressure sensors, vortex flow meters, and differential pressure gauges arranged at predetermined intervals along the furnace height to monitor and regulate the temperature, pressure, and flow distribution within the furnace in real time. Measuring points are spaced more closely in the core reaction zones of the roasting and preheating sections, and more sparsely in the transition areas. Each air path is equipped with an independent on / off regulating valve, allowing for flexible adjustment of airflow, temperature, and intake ratio according to actual operating conditions. An ignition device is installed inside the roasting section, interlocked with the air circulation system. Ignition is only used for auxiliary ignition during the initial cold start-up phase; after normal operation, self-sustaining roasting is maintained by circulating hot air and the combustion of fixed carbon within the material itself.

[0035] After 72 hours of continuous operation testing, the system was found to be able to sustain roasting entirely through the combustion of fixed carbon in the coal gangue and the circulation of hot air. Through the above-mentioned coordinated control, near-zero external combustion, cascade utilization of waste heat, and precise control of thermal parameters were achieved in the coal gangue roasting process.

[0036] This invention also provides a near-zero external combustion vertical roasting process for coal gangue. During the process operation, based on the calorific value range of the coal gangue raw material entering the roasting section, the external air supply volume of the material cooling air path, the circulating air volume supplied to the preheating section by the hot air circulation air path, the circulating air volume returned to the roasting section by the flue gas circulation air path, and the hot air volume extracted from the slow cooling section by the drying circulation air path are all adjusted in a coordinated manner. Specifically, the process includes the following steps: S1. Obtain the calorific value of the coal gangue fed into the furnace and determine its calorific value range; S2. If the calorific value is determined to be in the low calorific value range, such as 400-800 kcal / kg, adjust the opening of the regulating valves in each air path to make the external air supply volume of the waste heat output air path lower than the normal operating condition, prioritizing the retention of high-temperature flue gas heat in the furnace; at the same time, increase the volume of high-temperature hot air drawn from the rapid cooling section in the hot air circulation air path, and increase the circulation air volume of flue gas containing volatiles drawn from the second drying section and the preheating section in the flue gas circulation air path, so that all the circulating flue gas is conducted into the roasting section to ensure that the volatiles are fully burned in the roasting section to compensate for the insufficient calorific value of the raw materials; in addition, appropriately increase the volume of hot air drawn from the slow cooling section in the drying circulation air path to enhance the drying effect and ensure timely preheating of the material after it enters the furnace; reduce the external air supply volume of waste heat to the minimum or shut it off. S3. If the calorific value is determined to be within the normal range, such as 800-1400 kcal / kg, adjust the regulating valves of each air path to make the hot air circulation volume and the flue gas circulation volume approximately equal. The combustion air volume and the drying circulation volume are automatically balanced according to the temperature of the roasting section and the drying section, maintaining the roasting section temperature at 950-1250℃, the preheating section temperature at 550-650℃, and the drying section temperature at 150-350℃. The waste heat output air path supplies high-temperature flue gas of 600-900℃ to the outside according to the set value to achieve a balance between heat supply and demand. S4. If the calorific value is determined to be in the high-calorific-value range (e.g., calorific value higher than 1400 kcal / kg), adjust the regulating valves of each air path to increase the external air supply volume of the waste heat output air path and promptly remove excess heat from the roasting section; simultaneously reduce the opening of the flue gas circulation air path to decrease the proportion of flue gas containing volatiles returning to the roasting section and prevent the roasting section from overheating; and appropriately reduce the circulation volume of the hot air circulation air path to reduce the heat supply to the preheating section; reduce the flue gas circulation air volume to 50%–70% of the normal value. S5. During the adjustment process from T2 to T4, the temperature, pressure and flow data of the calcination section, preheating section and drying section are monitored in real time through a multi-point monitoring and control system. Based on the currently determined calorific value range, the corresponding air volume ratio and temperature range are maintained. The adjustment of each air path is achieved through independently set switch regulating valves, and at the same time, the air intake ratio of the fast cooling section and the slow cooling section is controlled until the system runs smoothly or stops.

[0037] Example 1 The near-zero external combustion vertical roasting device for coal gangue described in this invention is used to process coal gangue with a calorific value of 800~1400kcal / kg in a certain mining area.

[0038] After being crushed and screened to a suitable particle size, the material is fed into the furnace by the top feeding device. Cold air is introduced through the material cooling air path, with one path entering the rapid cooling section, where it is preheated to approximately 550-650°C after heat exchange with the high-temperature material. It then enters the hot air circulation branch and is fed back to the roasting section as a heat source for both the preheating and roasting sections. The other path enters the slow cooling section, where it is preheated to approximately 300°C before entering the drying circulation and being introduced into the top drying section for material drying. The drying circulation air path is independently controlled by a switch regulating valve to determine the ratio of hot air drawn from the rapid cooling and slow cooling sections, ensuring that the air temperature entering the drying section remains stable at 250-350°C.

[0039] The hot air circulation loop extracts 400-700℃ hot flue gas from the rapid cooling section and returns it to the preheating section as a heat source. The air pressure and volume in the high-temperature zone above and low-temperature zone below the rapid cooling section are controlled by regulating valves to stabilize the preheating section temperature at 550-650℃. The waste heat output duct extracts approximately 780℃ high-temperature flue gas from the area above the calcination section and outputs it externally, providing heat for plant production. The flue gas circulation duct extracts approximately 350℃ hot flue gas containing volatiles from the second drying section and the preheating section and sends it to the calcination section for secondary combustion, fully utilizing the calorific value of the volatiles and effectively reducing the concentration of combustible gases in the exhaust. The humid air exhaust duct directly discharges the humid air from the first and second drying sections after dust removal, eliminating the need for desulfurization and denitrification treatment, and creates negative pressure at the material distribution system to prevent dust overflow.

[0040] The temperature of the roasting section is monitored in real time by a multi-point monitoring and control system, which also adjusts the valves in each air path to maintain a stable temperature between 850 and 950°C. An ignition device is installed inside the roasting section. This device is interlocked with the air circulation system and only assists in ignition during the initial cold start-up. Once the furnace temperature reaches the ignition point of the coal gangue and a stable thermal cycle is established, it automatically shuts off, switching to self-sustaining roasting through the combustion of circulating hot air and the fixed carbon within the material itself. High-temperature resistant glass-covered observation windows are installed at corresponding heights in the preheating and roasting sections of the furnace body to facilitate visual observation of the roasting status of the material layers.

[0041] After 72 hours of continuous operation testing, once the system is running normally, it relies entirely on the combustion of fixed carbon from the coal gangue and circulating hot air to maintain self-sustaining roasting, reducing external fuel consumption by approximately 95% compared to traditional rotary kilns. Testing of the roasted products showed that the loss on ignition decreased from 18%–22% upon entering the kiln to below 3%, and the activity index reached over 85%, meeting the requirements for use as active building materials. The CO concentration in the flue gas decreased to below 1000 ppm, lower than the relevant national standard limits.

[0042] Example 2 The apparatus of this invention is used to process coal gangue with a calorific value of 600-800 kcal / kg. Given the low calorific value of the raw material, this embodiment appropriately increases the airflow entering the drying cycle from the slow cooling section, introducing more hot air (approximately 280°C) after cooling the material into the drying section to enhance the drying effect. Simultaneously, the amount of hot air extracted from the rapid cooling section in the hot air circulation loop is appropriately reduced, concentrating more heat in the roasting section to ensure that the low-calorific-value material receives sufficient roasting heat. The hot air temperature in the rapid cooling section, approximately 620°C-720°C, is then fed back to the roasting section.

[0043] The temperature in the calcination section is monitored in real time by a multi-point monitoring and control system, which adjusts the opening of valves in each air path to maintain a stable temperature between 820 and 920°C. The temperature in the preheating section is controlled between 500 and 600°C, and the temperature in the drying section is controlled between 200 and 300°C. The monitoring points of the multi-point monitoring and control system are arranged at relatively close intervals in the core reaction zones of the calcination and preheating sections, and at wider intervals in the transition zones, to accurately capture the location of the reaction zone and make timely adjustments. The multi-point monitoring and control system also has a reserved interface for connecting to an external flue gas analyzer to monitor CO, CO2, and NO in the flue gas online. x And SO2 and other components, the circulating air volume of the flue gas circulation path is adjusted according to the feedback of flue gas composition.

[0044] The waste heat output duct extracts high-temperature flue gas of approximately 820°C from the roasting section. After being recovered by the supporting waste heat boiler, it generates saturated steam at 0.8MPa, which is used for production and daily life in the plant area. The waste heat recovery efficiency reaches 68%. The flue gas recirculation duct extracts low-temperature flue gas containing volatiles at approximately 350°C from the drying section and preheating section and recirculates it into the roasting section for secondary combustion. This significantly reduces the CO concentration in the exhaust gas from 3000ppm before the modification to below 800ppm, ensuring that the emissions of combustible gases fully meet the standards.

[0045] After 72 hours of continuous operation testing, the system was able to maintain self-sustaining roasting entirely by relying on the combustion of fixed carbon in the coal gangue and the circulation of hot air. The product qualification rate reached 94.5%, which is about 10 percentage points higher than that of the traditional vertical furnace. The comprehensive energy consumption per unit product was reduced by about 55% compared with the traditional rotary kiln, which fully verified the good adaptability of the device of the present invention to low-calorific-value coal gangue and its significant energy-saving advantages.

[0046] Comparative Example 1 A conventional rotary kiln is used for roasting coal gangue. The rotary kiln has dimensions of Φ3.2m × 50m, a cylinder inclination of 3.5%~4%, and an adjustable rotation speed of 0.5~4 r / min. The material, after being crushed and screened to a suitable particle size, is added from the kiln tail and slowly moves towards the kiln head as the cylinder rotates. Heating is achieved by a coal burner at the kiln head, with hot flue gas flowing counter-currently to the material from the kiln head to the kiln tail. The kiln temperature gradually increases from approximately 700℃ at the kiln tail to approximately 1050℃ at the kiln head, creating a temperature gradient. The material residence time in the kiln is approximately 60~90 minutes, with at least 25 minutes in the high-temperature section. The roasting temperature is controlled between 950~1100℃, with a temperature fluctuation range of ±50℃. The roasted material is discharged from the kiln head, and the high-temperature flue gas is partially discharged and partially returned for material preheating after being filtered by a cyclone dust collector. During continuous system operation, the kiln head burner continuously replenishes coal, with a fuel consumption of approximately 150-200 kg / h. Based on a processing capacity of 150 kg / h, the calcination heat consumption is approximately 1250 kcal / kg. With a four-stage cyclone preheater, the system thermal efficiency is approximately 75%, and the flue gas waste heat recovery rate is only 15%-20%. Testing revealed that the loss on ignition of the roasted product is approximately 5%-8%, the product activity index fluctuates significantly, and the pass rate is approximately 85%-90%. The CO concentration in the exhaust gas is approximately 2000-3000 ppm, requiring a flue gas desulfurization and denitrification device to meet emission standards.

[0047] Comparative Example 2 The coal gangue is roasted using a traditional vertical roasting furnace with a central furnace wall and air duct structure. The furnace body is vertical, and its internal cavity is roughly divided into a preheating zone, a roasting zone, and a cooling zone from top to bottom, with a total height of 8-12 meters. Fixed air ducts are installed inside the furnace wall to introduce cold or hot air into each area of ​​the furnace chamber through the wall's interlayer. The material is added from the top of the furnace and moves slowly downwards under gravity, passing through each zone before being discharged from the bottom. The decarburization and sintering temperature is controlled at 700-850℃. The heat required for roasting is mainly provided by the combustion of the fixed carbon in the coal gangue itself; if the temperature is insufficient, a small amount of external fuel needs to be added in the middle of the furnace.

[0048] The comparative model has the following problems: the cross-sectional area and opening position of the intermediate furnace wall air duct are fixed in the design stage, and cannot be flexibly adjusted according to changes in material characteristics and roasting conditions during operation, resulting in poor controllability of air volume distribution; it is difficult to control the uniformity of furnace temperature during continuous production, with temperature differences of 80~120℃ on the same cross section. The air duct and furnace wall are built as a single unit, and under long-term high-temperature operation, the wall is prone to deformation, burn-out, cracking, and air leakage, requiring shutdown for maintenance every 6~12 months. The decarburization effect of the product is not uniform, with the loss on ignition fluctuating between 3% and 10%, and the product activity index fluctuating greatly, failing to meet the stable use requirements of active composite building materials. Due to the open or semi-open design of the air duct, the waste heat of high-temperature flue gas is not recovered and utilized in a tiered manner, the system thermal efficiency is only 40%~55%, and it is difficult to achieve self-sustaining roasting with almost no external fuel source.

[0049] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A near-zero external combustion vertical roasting device for coal gangue, characterized in that, The system includes a vertical roasting furnace body, an air circulation system, and a multi-point monitoring and control system. The internal cavity of the vertical roasting furnace body, from top to bottom, includes a drying section, a drying section, a preheating section, a roasting section, a rapid cooling section, and a slow cooling section. The air circulation system includes a material cooling air circulation path, a drying circulation air circulation path, a hot air circulation air circulation path, a flue gas circulation air circulation path, a waste heat output air circulation path, and a humid air exhaust air circulation path. Each air circulation path is equipped with an independent on / off regulating valve. The material cooling air circulation path is used to introduce cold air into the rapid cooling section and the slow cooling section. The drying circulation air circulation path is used to send hot air at 200-400°C extracted from the interface between the rapid cooling section and the slow cooling section to the drying section at the top of the furnace. The hot air circulation duct is used to send the 400-700°C hot flue gas extracted from the rapid cooling section to the preheating section; the waste heat output duct is used to output the 600-900°C high-temperature flue gas extracted from the calcination section area to the outside; the flue gas circulation duct is used to send the 200-500°C flue gas containing volatile heat extracted from the second drying section and the preheating section into the calcination section and the boundary area between the calcination section and the rapid cooling section. The humid air exhaust duct is used to remove dust from the humid air from the first and second drying stages before discharging it; the multi-point monitoring and control system is used to monitor and adjust the temperature field, pressure field, and flow distribution inside the furnace.

2. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The top of the vertical roasting furnace is provided with a drying section extension that connects to the drying section above, and the bottom is provided with a cooling section extension that connects to the slow cooling section below. The drying section extension and the cooling section extension are used to optimize the airflow distribution inside the furnace and stabilize the material residence time.

3. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, After being introduced into the material cooling air path, the cold air is divided into two paths: one path is preheated by the rapid cooling section and then enters the hot air circulation air path or directly enters the roasting section; the other path is preheated by the slow cooling section and then enters the drying circulation air path for drying the material in the drying section.

4. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The air intake of the drying circulating air path is located in the slow cooling section area; the air volume and air pressure are controlled by the switch regulating valve, and in conjunction with the air leakage sealing effect of the unloading system, the air volume and air temperature of the hot air drawn in from the slow cooling section are adjusted, so as to adjust the air volume and air temperature of the drying circulating air introduced into the drying section at the top of the furnace.

5. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The air pressure and air volume of the gas drawn from the high-temperature zone above and the low-temperature zone below the rapid cooling section are controlled by the switch regulating valve, so as to control the air volume and air temperature of the circulating hot air introduced into the preheating section.

6. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The air pressure and air volume of the hot air circulation path in the preheating section and the flue gas circulation path below the calcination section are controlled by the switch regulating valve, so as to control the air volume and air temperature of the output waste heat.

7. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The air intake of the flue gas circulation air path is located at the junction of the second drying section and the preheating section, and the exhaust port of the flue gas circulation air path is located at the junction of the roasting section and the rapid cooling section; the air pressure and air volume from the second drying section and the preheating section are controlled by switching the regulating valve, thereby controlling the air volume and air temperature of the flue gas circulation airflow.

8. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The humid air exhaust path creates negative pressure at the fabric system. By controlling the air leakage effect of the fabric system and controlling the air pressure and air volume of the drying circulation path through the switch regulating valve, the air volume and air temperature of the humid air exhaust are controlled.

9. The near-zero external combustion vertical roasting device for coal gangue according to claim 1, characterized in that, The multi-point monitoring and control system employs an unequal spacing arrangement for its monitoring points: denser spacing is used in the core reaction zones of the roasting and preheating sections, while sparser spacing is used in the transition zone. The multi-point monitoring and control system also includes a reserved interface for connecting an external flue gas analyzer or adding additional sensors to monitor flue gas composition.

10. A near-zero external combustion vertical roasting process for coal gangue, characterized in that, The near-zero external combustion vertical roasting device for coal gangue as described in claim 1 includes the following steps: S1. Obtain the calorific value of the coal gangue fed into the furnace and determine its calorific value range; calorific value of 400-800 kcal / kg is the low calorific value range, calorific value of 800-1400 kcal / kg is the conventional calorific value range, and calorific value higher than 1400 kcal / kg is the high calorific value range. S2. If the range is determined to be low calorific value, adjust the opening of the regulating valves in each air path to make the external air supply volume of the waste heat output air path lower than the normal operating condition, prioritizing the retention of high-temperature flue gas heat in the furnace; at the same time, increase the volume of high-temperature hot air drawn from the rapid cooling section in the hot air circulation air path, and increase the circulation air volume of flue gas containing volatiles drawn from the second drying section and the preheating section in the flue gas circulation air path, so that all the circulating flue gas is conducted into the roasting section, ensuring that the volatiles are fully burned in the roasting section to compensate for the insufficient calorific value of the raw materials; in addition, appropriately increase the volume of hot air drawn from the slow cooling section in the drying circulation air path to enhance the drying effect and ensure timely preheating of the material after it enters the furnace; reduce the external air supply volume of waste heat to the minimum or shut it off. S3. If the value is determined to be within the normal calorific value range, adjust the regulating valves of each air path to make the hot air circulation volume and the flue gas circulation volume approximately equal. The combustion air volume and the drying circulation volume are automatically balanced according to the temperature of the calcination section and the drying section, maintaining the calcination section temperature at 950-1250℃, the preheating section temperature at 550-650℃, and the drying section temperature at 150-350℃. The waste heat output air path supplies high-temperature flue gas of 600-900℃ to the outside according to the set value to achieve a balance between heat supply and demand. S4. If the area is determined to be in the high calorific value range, adjust the regulating valves of each air path, increase the external air supply of the waste heat output air path, and promptly remove excess heat from the roasting section; at the same time, reduce the opening of the flue gas circulation air path, reduce the proportion of flue gas containing volatiles returning to the roasting section, and avoid overheating of the roasting section; and appropriately reduce the circulation air volume of the hot air circulation air path to reduce the heat supply to the preheating section; reduce the flue gas circulation air volume to 50% to 70% of the normal value. S5. During the adjustment process from T2 to T4, the temperature, pressure and flow data of the calcination section, preheating section and drying section are monitored in real time through a multi-point monitoring and control system. Based on the currently determined calorific value range, the corresponding air volume ratio and temperature range are maintained. The adjustment of each air path is achieved through independently set switch regulating valves, and at the same time, the air intake ratio of the fast cooling section and the slow cooling section is controlled until the system runs smoothly or stops.

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