System and method for preparing metakaolin by high-efficiency decarburization, grading and activation of low-calorific-value coal gangue

Abstract

The invention provides a system and a method for preparing metakaolin through efficient decarburization, grading and activation of low-calorific-value coal gangue, and belongs to the technical field of coal gangue treatment. The system for preparing metakaolin by high-efficiency decarburization, grading and activation of low-heating-value coal gangue comprises a feeding subsystem and a discharging subsystem, wherein the feeding subsystem is suitable for providing low-heating-value coal gangue powder and pulverized coal; the combustion subsystem is suitable for receiving the low-heating-value coal gangue powder and the pulverized coal, the low-heating-value coal gangue powder and the pulverized coal are uniformly distributed in the combustion subsystem in a fluidized mode through gas fluidization circulation, and the adding amount of the pulverized coal is adjusted so that the low-heating-value coal gangue powder can be combusted in a self-sustaining mode; combustible components in the low-calorific-value coal gangue powder are converted into hot smoke, and non-combustible components are output as bottom slag; the recovery subsystem is suitable for recovering heat in the hot flue gas and separating the hot flue gas into dust-removed flue gas and fly ash; and the reforming subsystem is suitable for converting the kaolin component in the bottom slag and the fly ash into metakaolin by utilizing the heat of the bottom slag.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal gangue treatment, and particularly relates to a system and method for efficiently decarbonizing, classifying and activating low-calorie coal gangue to prepare metakaolin. Background Art

[0002] Coal gangue is the main by-product of the coal industry chain, with an annual discharge accounting for about 40% of the total industrial solid waste, and the annual new increment reaching 350 million tons. According to the calorific value characteristics, high-calorie coal gangue (calorific value ≥ 1500 kcal / kg) accounts for 10% of the total, and can be utilized for energy through direct combustion. For the remaining 90% of low-calorie coal gangue (calorific value < 1500 kcal / kg), due to technical and economic limitations, the comprehensive utilization rate is less than 30%. A large amount of piled-up low-calorie coal gangue not only occupies a large amount of land resources, but also releases harmful gases when it burns spontaneously, and heavy metals will be precipitated during weathering and being washed by rainwater, continuously threatening the regional ecological environment. In view of the current situation of low-calorie coal gangue with great harm and low utilization rate, in recent years, active exploration has been carried out on comprehensive utilization ways, focusing on building material resource utilization and exploring its potential value.

[0003] In the comprehensive utilization of coal gangue, building material resource utilization occupies an important position. Coal gangue contains clay minerals such as kaolinite and montmorillonite inside, and considerable application value can be released after treatment. When kaolinite (also known as kaolin, Al2Si2O5(OH)4) is calcined and activated at 650 - 950 °C, it will be transformed into amorphous high-activity metakaolin (Al2Si2O7). At this time, the specific surface area of metakaolin increases, and its pozzolanic activity improves. It can be used as a concrete admixture to improve impermeability, replace part of the cement clinker to reduce carbon, be compounded into refractory insulation materials, and is also an ideal gelling component for preparing high-performance geopolymers, showing good prospects in the development of solid waste-based building materials.

[0004] Currently, the mainstream process for preparing metakaolin from low-calorie coal gangue is as follows: First, it is crushed to 3 - 5 mm, and impurities and undissociated particles are screened out. Then, it is calcined in a rotary kiln at a high temperature of 1200 - 1300 °C to achieve the oxidation and removal of carbonaceous components, and the kaolin undergoes dehydration, lattice destruction and other reactions to be transformed into metakaolin. The calcined product is ground by a ball mill to improve its dispersibility and activity, and then different particle size products are separated by a classification device. Finally, it is dried to make the moisture content meet the standard and packaged. However, this industrial process has the following problems: The heating of materials depends on external heat sources such as natural gas and coal gasification gas. The rotary kiln needs to be maintained at a high temperature of 1200 - 1300 °C for 2 - 6 hours, resulting in extremely high energy consumption; The decarbonization and activation are concentrated in the same rotary kiln, making the system control complex, the equipment huge, and the heat transfer and mass distribution uneven during calcination, resulting in poor chemical stability and batch consistency of the product. Summary of the Invention

[0005] In view of the above technical problems, the present invention provides a system and method for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin, in order to at least partially solve the above technical problems. Thus, the specific technical solutions provided by the present invention are as follows.

[0006] As a first aspect of the present invention, there is provided a system for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin, comprising: a feeding subsystem adapted to provide low-calorie coal gangue powder and pulverized coal; a combustion subsystem adapted to receive the low-calorie coal gangue powder and pulverized coal, and through gas fluidization circulation, evenly fluidize and distribute the low-calorie coal gangue powder and pulverized coal in the combustion subsystem, adjust the addition amount of the pulverized coal so that the low-calorie coal gangue powder undergoes self-sustained combustion, convert the combustible components in the low-calorie coal gangue powder into hot flue gas, and output the incombustible components as bottom slag; a recovery subsystem adapted to recover the heat in the hot flue gas and separate the hot flue gas into dust-removed flue gas and fly ash; and a reforming subsystem adapted to utilize the heat of the bottom slag to convert the kaolin components in the bottom slag and fly ash into metakaolin.

[0007] As a second aspect of the present invention, there is provided a method for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin, using the system for preparing metakaolin, comprising: respectively pulverizing and sieving the low-calorie coal gangue and coal in the feeding subsystem to obtain low-calorie coal gangue powder and pulverized coal; transporting the low-calorie coal gangue powder and pulverized coal to the combustion subsystem with the powder-feeding air as the carrier, and transporting primary air into the combustion subsystem, through gas fluidization circulation, evenly fluidize and distribute the low-calorie coal gangue powder and pulverized coal in the combustion subsystem, adjust the addition amount of the pulverized coal so that the low-calorie coal gangue powder undergoes self-sustained combustion, convert the combustible components in the low-calorie coal gangue powder into hot flue gas, and output the incombustible components as bottom slag; transporting the hot flue gas to the recovery subsystem for gas-solid separation, and respectively outputting the dust-removed flue gas and fly ash; transporting the fly ash and bottom slag to the reforming subsystem, and utilizing the heat of the bottom slag to convert the kaolin components in the bottom slag and fly ash into metakaolin.

[0008] In the embodiments of the present invention, the combustion subsystem promotes the uniform fluidized distribution of low-calorie coal gangue powder and pulverized coal through gas fluidization circulation, adjusts the addition amount of pulverized coal to achieve the self-sustained combustion of low-calorie coal gangue powder, avoids the large consumption of external heat sources, significantly reduces energy consumption, and realizes the energy-saving goal while efficiently completing the conversion of combustible components into hot flue gas. The recovery subsystem can effectively recover the heat in the hot flue gas, separate it into dedusted flue gas and fly ash, which not only reduces energy waste, but also the recovered products such as fly ash can enter the subsequent process for further utilization, improving the overall utilization rate of low-calorie coal gangue resources. The reforming subsystem utilizes the bottom slag heat generated by the combustion subsystem to convert the kaolin components in the bottom slag and fly ash. This reasonable utilization of heat makes the kaolin conversion process more stable, is conducive to producing metakaolin with stable quality and high activity, and improves the quality and market competitiveness of the product. Each subsystem has a clear division of labor and close cooperation. The feeding subsystem provides raw materials, the combustion subsystem completes combustion and preliminary separation of products, the recovery subsystem recovers heat and resources, and the reforming subsystem realizes the final conversion. The entire system and method for preparing metakaolin form an efficient and collaborative production process, greatly improving production efficiency and production stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the system principle for efficiently decarbonizing, classifying and activating low-calorie coal gangue to prepare metakaolin in the embodiments of the present invention;

[0010] Figure 2 It is a schematic diagram of the structure of the combustion subsystem in the embodiments of the present invention;

[0011] Figure 3 It is a schematic diagram of the structure of the reforming subsystem in the embodiments of the present invention;

[0012] Figure 4 It is a flowchart of the method for efficiently decarbonizing, classifying and activating low-calorie coal gangue to prepare metakaolin in the embodiments of the present invention.

[0013] Description of the reference numerals:

[0014] 100 - feeding subsystem; 101 - fuel input end; 102 - crushing and screening module; 103 - magnetic separation and drying module; 104 - desulfurization and mixing module; 105 - low-calorie coal gangue powder silo; 106 - pulverized coal silo; 107 - bed material silo; 108 - first pneumatic conveying module; 109 - second pneumatic conveying module; 110 - screw feeder;

[0015] 200 - Combustion subsystem; 201 - Feeding port for low - calorific - value coal gangue powder; 202 - Feeding port for pulverized coal; 203 - Feeding port for bed material; 204 - Riser; 205 - Cyclone separator; 206 - Loop seal; 207 - Air distribution plate; 208 - Air chamber; 209 - Primary air module; 210 - Return air module; 211 - Ignition module; 212 - Flue gas outlet; 213 - Slag discharge pipe; 214 - Insulated slag bin; 215 - Screw slag discharger;

[0016] 300 - Recovery subsystem; 301 - Flue gas inlet; 302 - Heat exchange module; 303 - Dust removal module; 304 - Heat energy recovery module; 305 - Pollutant removal module; 306 - Ash discharge pipe; 307 - Insulated ash bin; 308 - Ash transportation module;

[0017] 400 - Reforming subsystem; 401 - Bottom slag inlet; 402 - Fly ash inlet; 403 - Vertical activation furnace; 404 - Stirring module; 405 - Screw discharge machine; 406 - Screening module; 407 - Metakaolin silo. Detailed implementation manners

[0018] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the following further elaborates on the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0019] In the scope disclosed in the present invention, the endpoints and any values of the scope are not limited to the exact scope or value. These scopes or values should be understood to include values close to these scopes or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0020] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0021] The terms used herein are merely for describing specific embodiments and are not intended to limit the present invention. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0022] Throughout the accompanying drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in the understanding of the present invention, conventional structures or configurations will be omitted. Also, the shapes, sizes, and positional relationships of the components in the drawings do not reflect the actual sizes, proportions, and actual positional relationships. Additionally, in the present invention, any reference signs between parentheses should not be construed as limiting the present invention.

[0023] Similarly, in order to streamline the present invention and assist in understanding one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. Descriptions with reference terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0024] Furthermore, terms such as "first", "second", etc. are used only for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0025] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0026] When preparing metakaolin from coal gangue by traditional processes, the decarbonization and activation of coal gangue are concentrated in the same rotary kiln, resulting in complex system control, large equipment, and uneven heat transfer and mass distribution during calcination, leading to problems such as poor chemical stability of the product and poor batch consistency. Based on this, the present invention provides a system and method for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin. By adopting a design that couples a combustion subsystem with a reforming subsystem, the decarbonization process of low-calorie coal gangue and the activation process of the product are effectively separated, thereby producing metakaolin with stable quality and high activity.

[0027] Figure 1 It is a schematic diagram of the system principle for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin in the embodiments of the present invention.

[0028] As a first aspect of the present invention, a system for efficiently decarbonizing, classifying, and activating low-calorie coal gangue to prepare metakaolin is provided. As shown in Figure 1 , it includes: a feeding subsystem 100, suitable for providing low-calorie coal gangue powder and pulverized coal; a combustion subsystem 200, suitable for receiving the coal gangue powder and pulverized coal, enabling the low-calorie coal gangue powder and pulverized coal to be evenly fluidized and distributed in the combustion subsystem 200 through gas fluidization circulation, adjusting the addition amount of the pulverized coal to cause the low-calorie coal gangue powder to undergo self-sustained combustion, converting the combustible components in the low-calorie coal gangue powder into hot flue gas, and outputting the incombustible components as bottom slag; a recovery subsystem 300, suitable for recovering the heat in the hot flue gas and separating the hot flue gas into dust-removed flue gas and fly ash; and a reforming subsystem 400, suitable for using the heat of the bottom slag to convert the kaolin components in the bottom slag and fly ash into metakaolin.

[0029] In an embodiment of the present invention, the combustion subsystem 200 promotes the uniform fluidization and distribution of the low-calorie coal gangue powder and pulverized coal through gas fluidization circulation, adjusts the addition amount of the pulverized coal to achieve self-sustained combustion of the low-calorie coal gangue powder, avoids a large amount of consumption of external heat sources, significantly reduces energy consumption, and achieves the energy-saving goal while efficiently completing the conversion of combustible components into hot flue gas. The recovery subsystem 300 can effectively recover the heat in the hot flue gas and separate it into dust-removed flue gas and fly ash, not only reducing energy waste, but also enabling the recycled products such as fly ash to enter the subsequent process for continued utilization, improving the overall utilization rate of low-calorie coal gangue resources. The reforming subsystem 400 uses the heat of the bottom slag generated by the combustion subsystem to convert the kaolin components in the bottom slag and fly ash. This reasonable utilization method of heat makes the kaolin conversion process more stable, is conducive to producing metakaolin with stable quality and high activity, and improves the quality and market competitiveness of the product. Each subsystem has a clear division of labor and close cooperation. The feeding subsystem 100 provides raw materials, the combustion subsystem 200 completes combustion and preliminary separation of products, the recovery subsystem 300 recovers heat and resources, and the reforming subsystem 400 realizes the final conversion. The entire system and method for preparing metakaolin form an efficient and collaborative production process, greatly improving production efficiency and production stability.

[0030] According to an embodiment of the present invention, the feeding subsystem 100 includes a fuel input end 101, a crushing and screening module 102, a magnetic separation and drying module 103, a desulfurization and mixing module 104, a low-calorie coal gangue powder silo 105, a pulverized coal silo 106, a bed material silo 107, a first pneumatic conveying module 108, a second pneumatic conveying module 109, and a screw feeder 110.

[0031] According to an embodiment of the present invention, the crushing and screening module 102 is applicable to crush and screen the low calorific value coal gangue or coal input from the fuel input end 101 to obtain the first low calorific value coal gangue powder or the first pulverized coal. Among them, the particle size of the first low calorific value coal gangue powder or the first pulverized coal is ≤ 0.2 mm.

[0032] According to an embodiment of the present invention, the magnetic separation and drying module 103 is applicable to remove iron impurities in the first low calorific value coal gangue powder or the first pulverized coal and perform drying to obtain the second low calorific value coal gangue powder or the second pulverized coal. Among them, removing iron impurities is to reduce slagging during subsequent combustion and improve the whiteness and activity of metakaolin; drying is to remove moisture so that the water content of the second low calorific value coal gangue powder or the second pulverized coal is reduced to ≤ 2%.

[0033] According to an embodiment of the present invention, the desulfurization mixing module 104 is applicable to mix limestone powder with the second low calorific value coal gangue powder or the second pulverized coal to obtain the low calorific value coal gangue powder or pulverized coal. Among them, mixing limestone powder can improve the desulfurization efficiency during subsequent combustion, and the Ca / S molar ratio during mixing is 1.5 - 2.5. The particle size of the limestone powder is ≤ 0.2 mm, which can be obtained by purchase or by crushing limestone through the crushing and screening module 102.

[0034] According to an embodiment of the present invention, the low calorific value coal gangue powder is stored in the low calorific value coal gangue powder silo 105 and is transported to the combustion subsystem 200 through the first pneumatic conveying module 108. The pulverized coal is stored in the pulverized coal silo 106 and is transported to the combustion subsystem 200 through the second pneumatic conveying module 109.

[0035] According to an embodiment of the present invention, the bed material silo 107 is used to store the bed material required for fluidization and circulation, and continuously transports it to the combustion subsystem 200 through the screw feeder 110 to maintain the bed material balance of the combustion subsystem 200. Among them, the bed material can be selected as quartz sand with a particle size of 1 - 2 mm, and at the same time, 1 - 2 mm boiler bottom slag or 1 - 2 mm low calorific value coal gangue particles screened out by the crushing and screening module 102 is admixed.

[0036] Figure 2 It is a schematic structural diagram of the combustion subsystem in the embodiment of the present invention.

[0037] According to an embodiment of the present invention, as Figure 2 shown, the combustion subsystem 200 includes a low calorific value coal gangue powder feed port 201, a pulverized coal feed port 202, a bed material feed port 203, a riser 204, a cyclone separator 205, a return feeder 206, a distributor plate 207, an air chamber 208, a primary air module 209, a return air module 210, an ignition module 211, a flue gas outlet 212, a slag discharge pipe 213, an adiabatic slag bin 214, and a screw slag discharger 215.

[0038] According to an embodiment of the present invention, low calorific value coal gangue powder enters the riser 204 through the low calorific value coal gangue feed port 201, pulverized coal enters the riser 204 through the pulverized coal feed port 202, and bed material enters the riser 204 through the bed material feed port 203. Among them, the low calorific value coal gangue powder feed port 201, the pulverized coal feed port 202, and the bed material feed port 203 are all located in the middle and lower part of the riser 204.

[0039] According to an embodiment of the present invention, the riser 204 is suitable for receiving low calorific value coal gangue powder and pulverized coal, and making the low calorific value coal gangue powder and pulverized coal evenly fluidized and distributed in the combustion subsystem through gas fluidization circulation, adjusting the addition amount of pulverized coal so that the low calorific value coal gangue powder undergoes self-sustained combustion, converting the combustible components in the low calorific value coal gangue powder into hot flue gas, and outputting the incombustible components as bottom slag.

[0040] According to an embodiment of the present invention, the top of the cyclone separator 205 is connected to the top of the riser 204. The cyclone separator 205 is suitable for making the relatively coarser particles of low calorific value coal gangue powder move towards the bottom of the cyclone separator 205 under the action of centrifugal force and inertial force, and outputting the hot flue gas generated by self-sustained combustion through the flue gas outlet 212 located at the top of the cyclone separator 205.

[0041] According to an embodiment of the present invention, the inlet of the return feeder 206 is connected to the bottom of the cyclone separator 205, and the outlet of the return feeder 206 is connected to the middle and lower part of the riser 204. The return feeder 206 is suitable for receiving relatively coarser particles of low calorific value coal gangue powder and transporting them into the riser 204 for secondary self-sustained combustion.

[0042] According to an embodiment of the present invention, the bottom of the cyclone separator 205 is conical, and the return air module 210 is located at the bottom of the return feeder 206 to increase the wind force in the return feeder 206 and transport the relatively coarser particles of low calorific value coal gangue powder separated by the cyclone separator 205 to the riser 204.

[0043] According to an embodiment of the present invention, a wind distribution plate 207 is provided at the bottom of the riser 204, which is connected to the air chamber 208. The air chamber 208 is connected to the primary air module 209. The primary air enters the air chamber 208 through the primary air module 209, and then the air is transported into the riser 204 by the wind distribution plate 207. The low calorific value coal gangue powder is mixed with the primary air and evenly fluidized and distributed in the riser 204 to achieve uniform heat and mass transfer. During the cold start stage of the riser 204, bed material is filled at the wind distribution plate 207 to construct an initial fluidized bed layer using the characteristics of high density and high temperature resistance. In view of the fuel characteristics of low calorific value coal gangue, the wind distribution plate 207 can adopt wear-resistant bell-shaped air caps to enhance the fluidization uniformity by increasing the air cap aperture and the flow velocity of the small holes.

[0044] According to an embodiment of the present invention, the ignition module 211 is located in the middle part of the riser 204. During the ignition stage, the ignition module 211 operates in coordination with the primary air module 209. The primary air enters the air chamber 208 through the primary air module 209 and is then evenly fed into the riser 204 through the air distribution plate 207. At this time, the temperature is rapidly increased to the ignition point of pulverized coal (400 - 500 °C) in a stepwise manner. During the temperature increase process, a stable combustion condition is gradually established by intermittently feeding pulverized coal. At the same time, the temperature at the bottom of the riser 204 is strictly controlled to stably maintain at 850 - 950 °C, and it is ensured that the axial temperature difference in the riser 204 is less than 10 °C, so as to ensure uniform temperature distribution in the riser 204 and effectively avoid local coking. After entering the fuel switching stage, it is necessary to coordinately control the fuel supply amount and the air volume to achieve a smooth transition of the combustion mode. During this period, the feeding amount of low-calorie coal gangue powder and the primary air volume are dynamically adjusted, and the proportion of pulverized coal in the fuel is gradually reduced until the self-sustaining combustion of low-calorie coal gangue powder is finally achieved.

[0045] According to an embodiment of the present invention, in the riser 204, the low-calorie coal gangue powder completes the removal of combustible components within 1 - 10 s. At the same time, some kaolin components in the low-calorie coal gangue powder are transformed into metakaolin through dehydration phase change. The relatively coarser low-calorie coal gangue powder (> 0.1 mm) is captured by the cyclone separator 205 and returned to the riser 204 for secondary self-sustaining combustion through the combined action of the return feeder 206 and the return air module 210; the relatively finer low-calorie coal gangue powder (≤ 0.1 mm) enters the recovery subsystem 300 with the hot flue gas through the flue gas outlet 212 to achieve fly ash collection, heat energy collection, and removal of flue gas pollutants (NO x , SO2, SO3, and dust). Due to the insufficient calcination time of the low-calorie coal gangue powder in the combustion subsystem 200, only some kaolin components are transformed into metakaolin, and the bottom slag (including bed material, untransformed kaolin components, and metakaolin components) at 850 - 950 °C at the bottom of the riser 204 has significant sensible heat recovery value. The bottom slag is transported to the adiabatic slag bin 214 for temporary storage through the slag discharge pipe 213 located at the bottom of the riser 204, and then transported to the reforming subsystem 400 through the screw slag discharger 215 for activation of the remaining kaolin components.

[0046] In the traditional process of calcining kaolin in a rotary kiln, kaolin enters the kiln body from the kiln tail. With the inclination and slow rotation of the kiln body, complex movements occur inside the kiln, including tumbling along the circumferential direction and moving axially from the high end to the low end. The calcination temperature of the rotary kiln is 1200 - 1300 °C, close to the flow temperature (FT) of kaolin. During the operation of the rotary kiln, ring formation and caking may occur between kaolin particles and between kaolin and the inner wall of the kiln, resulting in uneven heat and mass transfer during the kaolin calcination process. Ring formation and caking will change the movement state of kaolin inside the kiln, increasing the rotational resistance of the kiln body. When the kiln body operates to overcome these additional resistances, the rotational speed will be affected and become unstable. Moreover, the flow of kaolin is blocked at the sites of ring formation and caking, while the kaolin in other areas will flow relatively faster, leading to uneven discharge. Severe ring formation and caking may even block part of the kiln body cross-section, preventing the normal passage of materials and causing discharge interruption or severe unevenness. To overcome the problems of poor chemical stability and batch consistency of the products in the traditional process, the present invention provides a system for efficiently decarbonizing, classifying, and activating low-calorific-value coal gangue to prepare metakaolin.

[0047] Specifically, in the circulating fluidized bed of the combustion subsystem 200, the low-calorific-value coal gangue powder is driven by a high-speed air flow to form a dispersed suspended flow state. It successively passes through the dense phase zone at the bottom of the riser 204, the intermediate transition zone, and the dilute phase zone at the top, completing rapid heat transfer and chemical reactions. When the low-calorific-value coal gangue powder enters the bottom dense phase zone, the rapid flow of the air flow and particle collisions break the low-calorific-value coal gangue powder into smaller particles; when rising to the transition zone, the particles are more evenly mixed with the air flow; finally, a pneumatic conveying state is formed in the top dilute phase zone to transport the material to the cyclone separator 205 for gas-solid separation. The entire movement process only takes 1 - 10 seconds, and the low-calorific-value coal gangue quickly completes the dehydration and decarbonization reactions. Part of the remaining ash (mainly composed of kaolin) is activated and transformed into highly active metakaolin under uniform heating. The particles are always in a flowing state, with uniform heat and mass transfer. The entire device stably maintains a working temperature of 850 - 950 °C, avoiding both the uneven heat transfer and coking risks of the traditional rotary kiln and achieving a stable thermodynamic environment through self-sustained combustion. The frequent collisions between the air flow and particles improve the heat transfer efficiency, and the dispersed flow state maximizes the reaction contact surface, realizing the continuous and efficient reaction of low-calorific-value coal gangue from decarbonization combustion to mineral transformation and solving the problem of uneven heat and mass transfer in the preparation of metakaolin by the traditional rotary kiln.

[0048] According to an embodiment of the present invention, as Figure 1 shown, the recovery subsystem 300 includes a flue gas inlet 301, a heat exchange module 302, a dust removal module 303, a heat energy recovery module 304, a pollutant removal module 305, an ash discharge pipe 306, an adiabatic ash bin 307, and an ash conveying module 308.

[0049] According to an embodiment of the present invention, the heat exchange module 302 receives hot flue gas from the combustion subsystem 200 through the flue gas inlet 301 and recovers the heat in the hot flue gas. The recovered heat is used to heat air, which is then transported into the riser 204 through the first pneumatic conveying module 108, the second pneumatic conveying module 109, and the primary air module 209. Among them, the first pneumatic conveying module 108 and the second pneumatic conveying module 109 respectively convey the powder feeding air for low calorific value coal gangue powder and pulverized coal, and the primary air module 209 conveys the fluidizing air of the combustion subsystem 200. Specifically, the high-temperature hot flue gas (about 800 °C) enters the heat exchange module 302 from the flue gas outlet 212 through the flue gas inlet 301 and is cooled step by step to 260 - 280 °C. At the same time, the powder feeding air and the primary air are respectively preheated to 150 - 250 °C and 250 - 350 °C, realizing waste heat recovery.

[0050] According to an embodiment of the present invention, the dust removal module 303 is suitable for recovering the hot flue gas output by the heat exchange module 302 and separating the hot flue gas into dust removal flue gas and fly ash. The fly ash (about 260 °C) is temporarily stored in the adiabatic ash bin 307 through the ash discharge pipe 306 and is directionally transported to the reforming subsystem 400 through the ash conveying module 308. The dust removal flue gas (about 230 °C) is processed by the heat energy recovery module 304 (the heat can be used for fuel drying in the magnetic separation drying module 103) and the pollutant removal module 305, and is discharged at a safe temperature of 80 - 90 °C (higher than the acid dew point temperature of 75 °C), meeting the ultra-low emission standards: NO x <50mg / m 3 ;SO2 < 35mg / m 3 ;dust concentration < 5mg / m 3 。

[0051] Figure 3 It is a schematic structural diagram of the reforming subsystem in the embodiment of the present invention.

[0052] According to an embodiment of the present invention, as Figure 3 shown, the reforming subsystem 400 includes a bottom slag inlet 401, a fly ash inlet 402, a vertical activation furnace 403, a stirring module 404, a screw discharger 405, a screening module 406, and a metakaolin silo 407.

[0053] According to an embodiment of the present invention, bottom ash and fly ash from the spiral slag discharger 215 and the ash conveying module 308 enter the vertical activation furnace 403 through the bottom ash inlet 401 and the fly ash inlet 402 respectively. The heat of the bottom ash is used to convert the kaolin component in the bottom ash and fly ash into metakaolin. The motor drives the stirring shaft to rotate counterclockwise to drive the axial movement of the material. At the same time, two groups of screws on the shaft rotate radially in clockwise and counterclockwise directions respectively, realizing double mixing in the axial and radial directions, enabling efficient conduction of the sensible heat of the bottom ash and promoting chemical reactions. After the conversion is completed, the products (bed material, metakaolin) move steadily downward through the spiral discharger 405 with a residence time of 0.5 - 2 hours, and the gradient separation of the bed material (particle size ≥ 0.5 mm) and metakaolin (particle size ≤ 0.1 mm) is completed through the screening device 406. The metakaolin is stored in the metakaolin silo 407 after cooling.

[0054] Compared with the traditional rotary kiln process that requires continuous treatment at a high temperature of 1200 - 1300 °C for 2 - 6 hours, the energy consumption and treatment duration are significantly reduced. The device combines adiabatic design with the utilization of the sensible heat of the bottom ash to optimize the process while ensuring the conversion rate of metakaolin. The generated metakaolin can replace 30 - 50% of the cement clinker and become an ideal cementitious component for high-performance concrete, refractory materials (refractoriness ≥ 1650 °C), or high-performance geopolymers.

[0055] The vertical activation furnace 403 is an adiabatic fixed bed, which, in cooperation with the stirring module 404 driven by the motor, realizes full mixing of the bottom ash and fly ash. The vertical activation furnace 403 can maintain a temperature of 650 - 750 °C. This temperature range can not only ensure the mineral phase reconstruction of kaolin but also avoid the crystallization of metakaolin into inert crystalline products such as mullite and cristobalite due to excessive temperature, losing its hydration activity. The sensible heat of the bottom ash is fully utilized to realize the transformation of kaolin into metakaolin. The reaction mechanism is as follows: Kaolin (Al2Si2O5(OH)4) loses the bound water in the mineral, and calcium and other cations reoccupy the voids, destroying the long chains of silicon-oxygen tetrahedrons and aluminum-oxygen triangles. A large number of active silica and alumina are generated at the free ends of the fracture points, forming a thermodynamically metastable glass phase, producing an amorphous, high specific surface area, and highly active artificial pozzolanic material, metakaolin (Al2Si2O7). Its chemical reaction formula is shown in Equation (1).

[0056] 。

[0057] Figure 4 It is a process flow chart for the efficient decarbonization and classification activation of low-calorie coal gangue to prepare metakaolin in the embodiment of the present invention.

[0058] As the second aspect of the present invention, a method for preparing metakaolin from low-calorie coal gangue is provided. Using the above system for preparing metakaolin, as Figure 4 shown, it includes steps S1 - S4.

[0059] Step S1: Pretreat low calorific value coal gangue and coal in the feeding subsystem 100 respectively to obtain low calorific value coal gangue powder and pulverized coal.

[0060] Step S2: Convey the low calorific value coal gangue powder and pulverized coal to the combustion subsystem 200 with the powder feeding air as the carrier, and convey primary air into the combustion subsystem. Through gas fluidization circulation, the low calorific value coal gangue powder and pulverized coal are evenly fluidized and distributed in the combustion subsystem. By adjusting the addition amount of pulverized coal, the low calorific value coal gangue powder undergoes self-sustained combustion to convert the combustible components in the low calorific value coal gangue powder into hot flue gas, and the incombustible components are output as bottom slag.

[0061] Step S3: Convey the hot flue gas to the recovery subsystem 300 for gas-solid separation, and output dedusted flue gas and fly ash respectively.

[0062] Step S4: Convey the fly ash and bottom slag to the reforming subsystem 400, and use the heat of the bottom slag to convert the kaolin components in the bottom slag and fly ash into metakaolin.

[0063] In the embodiment of the present invention, the method for efficiently decarbonizing, classifying and activating low calorific value coal gangue to prepare metakaolin provided by the present invention pretreats low calorific value coal gangue and coal in the feeding subsystem 100 respectively, laying a good foundation for subsequent reactions; with the cooperation of powder feeding air and primary air, in the combustion subsystem 200, the low calorific value coal gangue powder and pulverized coal are evenly distributed through gas fluidization circulation and self-sustained combustion is achieved, which is energy-saving and has stable combustion; the recovery subsystem 300 conducts gas-solid separation on the hot flue gas, and recovers fly ash to maximize resource utilization; the reforming subsystem 400 uses the heat of the bottom slag to convert the kaolin components, producing high-quality metakaolin; each subsystem cooperates closely to form a complete and efficient process, with good synergy, greatly improving production efficiency and product quality, and being conducive to large-scale and high-quality production of metakaolin.

[0064] According to the embodiment of the present invention, the pretreatment of low calorific value coal gangue and coal includes: respectively pulverizing, sieving, removing iron impurities and drying low calorific value coal gangue and coal, and blending limestone powder to obtain low calorific value coal gangue powder and pulverized coal. Among them, the calorific value of the low calorific value coal gangue is 800 - 1500 kcl / kg; the particle size of the low calorific value coal gangue powder ≤ 0.2mm, and the particle size of the pulverized coal ≤ 0.2mm.

[0065] According to the embodiment of the present invention, the flow rate of the powder feeding air is 10 - 20m / s, and the temperature range of the powder feeding air is 150 - 250°C. The flow rate of the primary air is 4 - 6m / s, and the temperature range of the primary air is 250 - 350°C. The powder feeding air volume is 5 - 15% of the total volume of the powder feeding air and the primary air.

[0066] According to an embodiment of the present invention, the temperature range of the combustion subsystem is 850 - 950 °C; the self-sustained combustion time of the low calorific value coal gangue powder in the combustion subsystem is 1 - 10 s.

[0067] According to an embodiment of the present invention, the temperature range of the reforming subsystem is 650 - 750 °C; the conversion time of the bottom slag and fly ash in the reforming subsystem is 0.5 - 2 h.

[0068] In an embodiment of the present invention, the circulating fluidized bed self-sustained combustion technology is adopted to achieve self-sustained combustion at a low temperature (850 - 950 °C). Through the coordinated control of the fluidization velocity (4 - 6 m / s) and the excess air coefficient (1.1 - 1.3), the waste heat of the flue gas is recovered and reused, promoting the rapid and uniform heat and mass transfer and decarbonization reaction of the low calorific value coal gangue (800 - 1500 kcal / kg) within 1 - 10 s. Compared with the traditional rotary kiln process, the calcination temperature is reduced by 250 - 450 °C, the comprehensive energy consumption of the system is reduced, the product homogeneity is significantly improved, and the solid waste consumption rate is also increased. In terms of sensible heat-driven activation, the vertical activation furnace uses the sensible heat of the high-temperature bottom slag to drive the phase reconstruction of kaolin, generating high-activity products with a high proportion of amorphous phase, specific surface area, and pozzolanic activity index. The system for preparing metakaolin adopts a combustion subsystem coupled with a reforming subsystem, successfully realizing the separation of decarbonization of low calorific value coal gangue and product activation, and having the advantages of modularization, simple control, uniform heat and mass transfer, short calcination cycle, and high chemical stability and batch consistency of the product.

[0069] The above specific embodiments have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A system for efficiently decarbonizing, classifying and activating low calorific value coal gangue to prepare metakaolin, characterized in that, Comprising: A feeding subsystem, suitable for providing low calorific value coal gangue powder and pulverized coal; A combustion subsystem, suitable for receiving the low calorific value coal gangue powder and pulverized coal, enabling the low calorific value coal gangue powder and pulverized coal to be evenly fluidized and distributed in the combustion subsystem through gas fluidization circulation, adjusting the addition amount of the pulverized coal to cause self-sustained combustion of the low calorific value coal gangue powder, so as to convert the combustible components in the low calorific value coal gangue powder into hot flue gas, and outputting the incombustible components as bottom slag; A recovery subsystem, suitable for recovering the heat in the hot flue gas and separating the hot flue gas into dedusted flue gas and fly ash; And A reforming subsystem, suitable for converting the kaolin components in the bottom slag and the fly ash into metakaolin by using the heat of the bottom slag.

2. The system for preparing metakaolin according to claim 1, wherein, The combustion subsystem includes: A riser, suitable for receiving the low calorific value coal gangue powder and pulverized coal, enabling the low calorific value coal gangue powder and pulverized coal to be evenly fluidized and distributed in the combustion subsystem through gas fluidization circulation, and adjusting the addition amount of the pulverized coal to cause self-sustained combustion of the low calorific value coal gangue powder; A cyclone separator, the top of the cyclone separator is connected to the top of the riser, the cyclone separator is suitable for making the relatively coarser particles of the low calorific value coal gangue powder move towards the bottom of the cyclone separator under the action of centrifugal force and inertial force, and outputting the hot flue gas generated by the self-sustained combustion; and A return feeder, the inlet of the return feeder is connected to the bottom of the cyclone separator, the outlet of the return feeder is connected to the middle and lower part of the riser, the return feeder is suitable for receiving the relatively coarser particles of the low calorific value coal gangue powder and transporting it into the riser for secondary self-sustained combustion.

3. The system for preparing metakaolin according to claim 1, characterized in that, The recovery subsystem includes: A heat exchange module, suitable for receiving the hot flue gas and recovering the heat in the hot flue gas; and A dust removal module, suitable for recovering the hot flue gas output by the heat exchange module and separating the hot flue gas into dedusted flue gas and fly ash.

4. The system for preparing metakaolin according to claim 1, characterized in that, The reforming subsystem includes: A vertical activation furnace, suitable for converting the kaolin components in the bottom slag and the fly ash from the recovery subsystem into metakaolin by using the heat of the bottom slag from the combustion subsystem.

5. The system for preparing metakaolin according to claim 1, wherein The feeding subsystem includes: A crushing and screening module, suitable for crushing and screening the input low calorific value coal gangue or coal to obtain first low calorific value coal gangue powder or first pulverized coal; A magnetic separation and drying module, suitable for removing iron impurities in the first low calorific value coal gangue powder or first pulverized coal and drying it to obtain second low calorific value coal gangue powder or second pulverized coal; and A desulfurization and mixing module, suitable for mixing limestone powder with the second low calorific value coal gangue powder or second pulverized coal to obtain low calorific value coal gangue powder or pulverized coal.

6. A method for efficiently decarbonizing, classifying and activating low-calorie coal gangue to prepare metakaolin, which uses the system for preparing metakaolin as described in any one of claims 1-5, and is characterized in that, Comprising: Pre-treating low calorific value coal gangue and coal in the feeding subsystem respectively to obtain low calorific value coal gangue powder and pulverized coal; Convey the low calorific value coal gangue powder and pulverized coal to the combustion subsystem by using the powder feeding air as the carrier, and convey primary air into the combustion subsystem. Through gas fluidization circulation, make the low calorific value coal gangue powder and pulverized coal evenly fluidized and distributed in the combustion subsystem. By adjusting the addition amount of the pulverized coal, make the low calorific value coal gangue powder undergo self-sustained combustion, so as to convert the combustible components in the low calorific value coal gangue powder into hot flue gas, and output the incombustible components as bottom slag; Convey the hot flue gas to the recovery subsystem for gas-solid separation, and output dust-removed flue gas and fly ash respectively; Convey the fly ash and the bottom slag to the reforming subsystem, and use the heat of the bottom slag to convert the kaolin components in the bottom slag and the fly ash into metakaolin.

7. The method according to claim 6, characterized in that, The pretreatment includes: Crush, screen, remove iron impurities, dry the low calorific value coal gangue and coal respectively, and blend limestone powder to obtain low calorific value coal gangue powder and pulverized coal; Among them, the calorific value of the low calorific value coal gangue is 800 - 1500 kcl / kg; The particle size of the low calorific value coal gangue powder ≤ 0.2mm, and the particle size of the pulverized coal ≤ 0.2mm.

8. The method according to claim 6, wherein The flow rate of the powder feeding air is 10 - 20m / s, and the temperature range of the powder feeding air is 150 - 250°C; The flow rate of the primary air is 4 - 6m / s, and the temperature range of the primary air is 250 - 350°C; The powder feeding air volume is 5 - 15% of the total volume of the powder feeding air and the primary air.

9. The method according to claim 6, wherein The temperature range of the combustion subsystem is 850 - 950°C; The self-sustained combustion time of the low calorific value coal gangue powder in the combustion subsystem is 1 - 10s.

10. The method according to claim 6, wherein The temperature range of the reforming subsystem is 650 - 750°C; The conversion time of the bottom slag and the fly ash in the reforming subsystem is 0.5 - 2h.

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