A method of controlling the color of high iron content calcined clay
By using a multi-stage cyclone separator and a pipeline electromagnetic device to separate magnetite, the problem of red color during suspension calcination of high-iron-content clay was solved. This method achieves efficient and simple suspension calcination of clay, is highly adaptable, reduces energy consumption, simplifies process design, and is suitable for the industrial application of high-iron-content clay.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHENGDU DESIGN & RES INST OF BLDG MAT IND CO LTD
- Filing Date
- 2024-10-31
- Publication Date
- 2026-06-23
Smart Images
Figure CN119349984B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of inorganic non-metallic materials thermal technology, specifically a method for controlling the color of calcined clay with high iron content. Background Technology
[0002] Against the backdrop of a global push for carbon reduction and carbon neutrality, the cement industry, as a major energy consumer and emitter of carbon dioxide, is seeing rapid development in its carbon dioxide reduction technologies. One important carbon reduction technology is using calcined clay as an auxiliary cementitious material in the production of low-carbon cement. The basic principle of this technology is as follows: After crushing, drying, and grinding the clay into micron-sized powder, it is calcined at a suitable temperature. During calcination, the kaolinite minerals in the clay undergo a dehydroxylation reaction (in industrial production, the reaction temperature window is controlled between 750 and 900℃), destroying the crystal structure and generating active metakaolinite with an amorphous structure. Therefore, the activated clay obtained after calcination (hereinafter referred to as calcined clay) can largely replace cement clinker in the production of low-carbon cement.
[0003] There are two main methods for the industrial production of calcined clay: rotary kiln calcination and suspension calcination. Rotary kiln calcination produces clay with lower activity and higher energy consumption. Suspension calcination, on the other hand, primarily uses convection heat transfer, resulting in high heat transfer efficiency and a uniform and controllable temperature field. Therefore, suspension calcination technology offers significant advantages in terms of both product activity and energy consumption when used to produce calcined clay.
[0004] The clay suspension calcination technology mainly includes three stages: "clay raw material suspension preheating, clay raw material suspension calcination, and calcined clay suspension cooling". The three stages are described below.
[0005] The "clay raw material suspension preheating section" consists of multiple cyclones connected in series. Pre-treated clay raw materials, prepared into micron-sized powder, are fed into the first-stage cyclone of the preheating stage, and then preheated in a suspended state through multiple cyclones. The high-temperature flue gas used for preheating the clay raw materials in each cyclone stage originates from the decomposition furnace.
[0006] The "clay raw material suspension calcination section" mainly consists of a decomposition furnace. After preheating, the clay powder raw material enters the decomposition furnace and is calcined in the high-temperature flue gas environment generated by the combustion of fuel, undergoing a dehydroxylation reaction and becoming reactive. The calcined clay then exits the decomposition furnace with the high-temperature flue gas and undergoes gas-solid separation in a cyclone separator. The separated calcined clay enters the "suspension cooling section." The separated high-temperature flue gas then enters the "clay raw material suspension preheating section" to preheat the clay powder raw material. The high-temperature combustion air required for the fuel fed into the decomposition furnace comes from the downstream "calcined clay cooling section."
[0007] The "calcined clay cooling section" consists of multiple cyclone separators connected in series. Ambient air is used as the cooling medium during the cooling process. After cooling the high-temperature calcined clay, the air itself is heated and then enters the decomposition furnace as the combustion air required for fuel combustion. The cooled clay is collected by the cooling cyclone separators and treated as a product.
[0008] However, the aforementioned technology is only applicable to clays with low iron content (generally <5%). If the iron content is greater than or equal to 5%, the calcined clay produced using this method will be red. Although adding it to cement does not affect product quality, it is easily mistaken by the market as a substandard product, thus resulting in low acceptance. This limits the application scenarios of suspension calcination technology (especially for high-iron-content clays). This is also a technical bottleneck for the large-scale industrial application of suspension calcination technology.
[0009] The mechanism by which calcined clay with high iron content turns red is as follows:
[0010] During the process of heating and calcining clay, the temperature is gradually increased to 850℃ (industrial production ultimately requires heating to around 850℃ to ensure complete dehydroxylation reaction and sufficient activity). When the clay is heated to a temperature higher than 650℃, the hematite (Fe2O3, red) in the clay undergoes a reduction reaction and transforms into magnetite (Fe3O4, gray). If the clay is further heated to 850℃, the iron-containing minerals in the clay still exist in the form of magnetite, remaining gray.
[0011] The color changes during the cooling process of clay to ambient temperature after calcination are as follows: (1) During the cooling process from 850℃ to 650℃, the magnetite in the calcined clay remains stable regardless of whether the cooling medium contains an oxygen atmosphere, and the color of the calcined clay is gray; (2) During the cooling process from 650℃ to 300℃, if there is an oxygen atmosphere in the cooling medium, the magnetite in the calcined clay will be oxidized again to hematite, and the color of the calcined clay will turn red. If there is no oxygen atmosphere in the cooling medium, the magnetite remains stable, and the color of the calcined clay remains gray. (3) If the iron in the calcined clay has been oxidized to hematite in the cooling process of (2), the final color of the calcined clay will be red regardless of whether the cooling medium in this section contains oxygen when the calcined clay continues to cool from 300°C to ambient temperature. If the iron mineral in the calcined clay is still magnetite in the cooling process of (2), the final color of the calcined clay will be gray regardless of whether the cooling medium in this section contains oxygen when the calcined clay continues to cool from 300°C to ambient temperature.
[0012] To address the technical challenge of maintaining the gray color of clay after suspension calcination instead of turning it red, key technological directions include reduction calcination, flue gas recirculation reduction cooling, indirect water cooling, and indirect oil cooling. These technologies essentially control the cooling atmosphere during the 650–300°C cooling phase of calcined clay, preventing contact between the clay and oxygen to avoid oxidizing magnetite to hematite. However, these technologies suffer from complex atmosphere control and regulation (requiring alternating control of oxidizing and reducing atmospheres), and the inability to directly contact the high-temperature calcined clay with air as a cooling medium for efficient recovery of waste heat from the calcined clay via convective heat transfer, significantly impacting the efficient, complete, and stable combustion of pulverized coal fed into the decomposition furnace. This results in high energy consumption, complex operation, and difficulty in large-scale industrial application of suspension calcination systems, largely negating the inherent advantages of suspension calcination technology, such as high heat transfer efficiency, high waste heat recovery efficiency, low energy consumption, simple process flow, and suitability for large-scale industrial production. Summary of the Invention
[0013] The purpose of this invention is to provide a method for controlling the color of high-iron-content clay. This method is a highly efficient and simple clay suspension calcination technology. This technology is highly adaptable, applicable to both raw materials with an iron content below 5% and those with an iron content above 5%. Furthermore, it achieves the goal of maintaining the gray color of calcined clay without requiring complex control of the calcination and cooling atmospheres. This fundamentally saves heat consumption, simplifies process design, reduces construction investment, and allows for industrial application.
[0014] In order to achieve at least one of the above-mentioned objectives, the technical solution of the present invention is as follows:
[0015] A method for controlling the color of calcined clay with high iron content includes a clay raw material suspension preheating system, a clay raw material suspension calcination section system, and a calcined clay suspension cooling system; wherein the clay raw material suspension preheating system is connected to the clay raw material suspension calcination section system; and the clay raw material suspension calcination section system is connected to the calcined clay suspension cooling system.
[0016] Furthermore, the clay raw material suspension preheating system consists of multiple cyclone separators connected in series. The number of cyclone separator stages is set according to the amount of heat required by the clay raw material during the drying and grinding pretreatment stage, and can generally be designed as two to six stages, preferably four stages connected in series, including a first-stage cyclone separator, a second-stage cyclone separator, a third-stage cyclone separator, and a fourth-stage cyclone separator. The multi-stage cyclone separators connected in series can also be combined in parallel in multiple rows according to the production scale.
[0017] Furthermore, the clay raw material suspension calcination section system includes a decomposition furnace, a cyclone separator, an electromagnetic device, a silo, and a conveying device; the calcined clay suspension cooling system enters the decomposition furnace along with the fuel; the decomposition furnace and the cyclone separator are connected by a pipeline, and an electromagnetic device is installed on the corresponding pipeline; the electromagnetic device is connected to the silo through its discharge port, and a conveying device is installed below the silo.
[0018] Furthermore, the calcined clay suspension cooling system consists of multiple cyclone separators connected in series, which can generally be designed as two to six stages, preferably four stages connected in series, including a first-stage cyclone separator, a second-stage cyclone separator, a third-stage cyclone separator, and a fourth-stage cyclone separator; it can also be configured as multiple series connected in parallel depending on the scale of the production line.
[0019] Furthermore, the method for controlling the color of calcined clay with high iron content described above includes the following specific steps:
[0020] Clay raw materials are prepared into micron-sized powder through crushing, drying, and grinding processes. This powder is then fed into the connecting pipe between the first and second stage cyclones in a multi-stage cyclone suspension preheating system. The powder is dispersed into the high-temperature flue gas at the outlet of the second stage cyclone via a spreading device within the connecting pipe, resulting in convective heat exchange. The residual heat in the high-temperature flue gas is used to preheat the clay powder. The high-temperature flue gas carries the clay powder into the first stage cyclone. After gas-solid separation in the first stage cyclone, the high-temperature flue gas is discharged, and the preheated clay powder is collected. It then sequentially enters each downstream cyclone stage, where it exchanges heat with the high-temperature flue gas at the outlet of each stage through convection, thus achieving the purpose of preheating the clay powder.
[0021] The preheated clay powder from the fourth-stage cyclone in the clay raw material suspension preheating system enters the decomposition furnace, where a dehydroxylation reaction occurs, producing active calcined clay. In traditional processes, after the powdered clay raw material is calcined in the decomposition furnace (calcination temperature > 650℃, generally controlled at around 750~900℃ in industrial applications to ensure continuous and stable fuel combustion), the iron-containing minerals in the clay will transform from hematite (red) to magnetite (gray) at temperatures above 650℃. As is well known, magnetite is magnetic. When the powdered clay raw material is calcined in the decomposition furnace, and the high-temperature flue gas carries the calcined powdered clay through a pipeline electromagnetic device, the electromagnetic device separates the magnetic magnetite from the clay raw material using an electromagnetic field. Because the clay raw material is a micron-sized powder in suspension, the electromagnetic separation efficiency will reach over 95%. The selected magnetite is collected in a storage bin through the discharge port of an electromagnetic device, and then transported to the downstream storage area via a conveyor. Magnetite selected from calcined clay fundamentally avoids the problem of the clay turning red during cooling. Furthermore, the magnetite collected by the electromagnetic device can be sold as a high-value-added product.
[0022] After being separated by electromagnetic means, the calcined clay enters the cyclone in the clay raw material suspension calcination section system. Through gas-solid separation, the calcined clay enters the calcined clay suspension cooling system to complete waste heat recovery; the high-temperature flue gas enters the clay raw material suspension preheating system to preheat the clay powder raw material.
[0023] Furthermore, the calcined clay suspension cooling system is divided into two sections. The first section consists of two cyclones connected in series to cool the high-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is the same as the amount of air required for fuel combustion in the decomposition furnace. The second section consists of two cyclones connected in series to cool the medium- and low-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is adjusted according to the cooling temperature required for the final product. The calcined clay is finally collected after gas-solid separation in the last stage cyclone and becomes the final product.
[0024] Furthermore, after the air in the second cooling section of the calcined clay suspension cooling system completes its task of cooling the calcined clay, it can be used as low-temperature waste heat air for the pretreatment process when the clay raw material is prepared into powdered raw material, namely the drying and grinding process.
[0025] Furthermore, in order to reliably control the color of calcined clay, it is necessary to pay attention to controlling the strength of the magnetic field device. The strength of the magnetic field device should be above 8000 Gs, so as to ensure that the magnetite separation efficiency reaches more than 95%.
[0026] Furthermore, the calcination temperature is 850℃±50℃ to ensure that the iron-containing minerals in the clay are completely transformed into magnetic magnetite. However, it cannot exceed 900℃. When the temperature is above 900℃, there is a risk of over-burning of the kaolinite in the clay, which will cause the metakaolinite to recrystallize into mullite, affecting the product's activity.
[0027] Furthermore, the fuel in the decomposition furnace is either fossil fuel or biomass alternative fuel; the high-temperature combustion air for fuel combustion comes from the downstream cooling system.
[0028] Compared with existing technologies, the advantages of this invention are:
[0029] (I) Using this invention, when the iron content in the clay is >5%, the entire process does not require complex control of the atmosphere during the calcination and cooling stages. The separation of magnetite in the clay is achieved solely through a pipeline electromagnetic device, ensuring the clay remains gray. The pipeline electromagnetic device is installed on the connecting pipeline to the decomposition furnace. At this point, the temperature of the clay powder raw material is >650℃, and the iron-containing minerals in the clay will exist as magnetic magnetite, rather than as non-magnetic hematite. The entire process is simple. During the cooling stage, the heat from the high-temperature calcination of the clay can be efficiently recovered through ambient air. The recovered high-temperature air serves as combustion air for fuel combustion in the decomposition furnace, significantly reducing heat consumption.
[0030] (ii) The invention utilizes an electromagnetic device installed on the decomposition furnace connecting pipe in the clay raw material suspension preheating system, which allows for the separation of magnetite from calcined clay via an electromagnetic field. This ensures the calcined clay remains gray in color, while the separated magnetite can be sold as a high-value-added byproduct.
[0031] (iii) In this invention, regardless of whether the iron content of the clay raw material is >5%, the cooling medium of the cooling system is ambient air. The ambient air comes into direct contact with the high-temperature calcined clay, generating convective heat transfer. The clay is cooled, and the ambient air itself is heated. It then enters the decomposition furnace as combustion air for fuel, without the need for indirect cooling of the high-temperature calcined clay. This fundamentally ensures maximum waste heat recovery in the form of ambient air, which is beneficial for the fuel in the decomposition furnace to directly utilize the high-temperature air for efficient and stable combustion, thereby producing energy-saving and consumption-reducing effects. Attached Figure Description
[0032] Figure 1 This is a schematic diagram of the structure of each system in the method for controlling the color of calcined clay with high iron content according to the present invention;
[0033] Figure 2 This is a schematic diagram of the suspension preheating system;
[0034] Figure reference numerals: 1—Clay raw material suspension preheating system; 2—Clay raw material suspension cooling system; 3—Calcinated clay suspension cooling system; 4—Electromagnetic device; 5—Small silo; 6—Conveying device; 7—Decomposition furnace;
[0035] C1, C2, C3, C4, and C5 represent the first, second, third, fourth, and fifth stage cyclones in the clay raw material suspension preheating system, respectively; CC1, CC2, CC3, and CC4 represent the first, second, third, and fourth stage cyclones in the calcined clay suspension cooling system, respectively; all stages of the cyclones are connected by connecting pipes. Detailed Implementation
[0036] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.
[0037] Any feature disclosed in this specification (including the claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.
[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0039] In this application, unless otherwise specified, % refers to the percentage content by mass. For procedures or conditions not specifically described, the procedures or conditions described in the literature in this field can be followed. All raw materials used are commercially available.
[0040] Example 1:
[0041] A method for controlling the color of calcined clay with high iron content includes a clay raw material suspension preheating system 1, a clay raw material suspension calcination section system 2, and a calcined clay suspension cooling system 3; wherein the clay raw material suspension preheating system 1 is connected to the clay raw material suspension calcination section system 2; and the clay raw material suspension calcination section system 2 is connected to the calcined clay suspension cooling system 3.
[0042] Furthermore, the clay raw material suspension preheating system 1 is composed of multiple cyclone separators connected in series. The number of cyclone separator stages is set according to the amount of heat required by the clay raw material during the drying and grinding pretreatment preparation stage, and can generally be designed as two to six stages. In this embodiment, four cyclone separators are preferably connected in series, including a first-stage cyclone separator, a second-stage cyclone separator, a third-stage cyclone separator, and a fourth-stage cyclone separator. The multi-stage cyclone separators connected in series can also be combined in parallel in multiple rows according to the production scale.
[0043] Furthermore, the clay raw material suspension calcination section system includes a decomposition furnace, a cyclone separator, an electromagnetic device 4, a small silo 5, and a conveying device 6; the calcined clay suspension cooling system enters the decomposition furnace together with the fuel; the decomposition furnace and the cyclone separator are connected by a pipeline, and the electromagnetic device 4 is installed on the corresponding pipeline; the electromagnetic device 4 is connected to the small silo 5 through its discharge port, and the conveying device 6 is installed below the small silo 5.
[0044] Furthermore, the calcined clay suspension cooling system is composed of multiple cyclone separators connected in series, which can generally be designed as two to six stages. In this embodiment, four cyclone separators are preferably connected in series, namely, a first-stage cyclone separator, a second-stage cyclone separator, a third-stage cyclone separator, and a fourth-stage cyclone separator; multiple series and parallel connections can also be configured according to the scale of the production line.
[0045] Furthermore, the method for controlling the color of calcined clay with high iron content described above includes the following specific steps:
[0046] Clay raw materials are prepared into micron-sized powder through crushing, drying, and grinding processes. This powder is then fed into the connecting pipe between the first and second stage cyclones in a multi-stage cyclone suspension preheating system. The powder is dispersed into the high-temperature flue gas at the outlet of the second stage cyclone via a spreading device within the connecting pipe, resulting in convective heat exchange. The residual heat in the high-temperature flue gas is used to preheat the clay powder. The high-temperature flue gas carries the clay powder into the first stage cyclone. After gas-solid separation in the first stage cyclone, the high-temperature flue gas is discharged, and the preheated clay powder is collected. It then sequentially enters each downstream cyclone stage, where it exchanges heat with the high-temperature flue gas at the outlet of each stage through convection, thus achieving the purpose of preheating the clay powder.
[0047] The preheated clay powder from the fourth-stage cyclone in the clay raw material suspension preheating system enters the decomposition furnace, where a dehydroxylation reaction occurs, producing active calcined clay. In traditional processes, after the powdered clay raw material is calcined in the decomposition furnace (calcination temperature > 650℃, generally controlled at around 750~900℃ in industrial applications to ensure continuous and stable fuel combustion), the iron-containing minerals in the clay will transform from hematite (red) to magnetite (gray) at temperatures above 650℃. As is well known, magnetite is magnetic. When the powdered clay raw material is calcined in the decomposition furnace, and the high-temperature flue gas carries the calcined powdered clay through a pipeline electromagnetic device, the electromagnetic device separates the magnetic magnetite from the clay raw material using an electromagnetic field. Because the clay raw material is a micron-sized powder in suspension, the electromagnetic separation efficiency will reach over 95% (proven by experiments, the electromagnetic device's magnetic field is > 8000 Gs). The selected magnetite is collected in a storage bin through the discharge port of an electromagnetic device, and then transported to the downstream storage area via a conveyor. Magnetite selected from calcined clay fundamentally avoids the problem of the clay turning red during cooling. Furthermore, the magnetite collected by the electromagnetic device can be sold as a high-value-added product.
[0048] After being separated by electromagnetic means, the calcined clay enters the cyclone in the clay raw material suspension calcination section system. Through gas-solid separation, the calcined clay enters the cooling system to complete waste heat recovery; the high-temperature flue gas enters the clay raw material suspension preheating system to preheat the clay powder raw material.
[0049] Furthermore, the calcined clay suspension cooling system is divided into two sections. The first section consists of two cyclones connected in series to cool the high-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is the same as the amount of air required for fuel combustion in the decomposition furnace. The second section consists of two cyclones connected in series to cool the medium- and low-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is adjusted according to the cooling temperature required for the final product. The calcined clay is finally collected after gas-solid separation in the last stage cyclone and becomes the final product.
[0050] Example 2:
[0051] Based on Example 1, clay raw material with an iron content of 10% and a mass flow rate of 200 t / h was prepared into micron-sized powder through crushing, drying, and grinding processes, and then fed into the connecting pipe between C2 and C1 of the suspension preheating system. The powdered raw material was immediately dispersed in the high-temperature flue gas at the outlet of C2 through a spreading device, resulting in convective heat transfer. The residual heat in the high-temperature flue gas was used to preheat the clay powdered raw material. The high-temperature flue gas carried the clay powdered raw material into the first-stage cyclone separator C1. After gas-solid separation in the C1 cyclone separator, the high-temperature flue gas was discharged, and the clay powdered raw material after the first preheating was collected. Subsequently, it entered the downstream cyclone separators of each stage, where it exchanged heat with the high-temperature flue gas at the outlet of each cyclone separator through convection, thus achieving the purpose of preheating the clay powdered raw material.
[0052] The preheated clay powder raw material from C4 enters the decomposition furnace, where a dehydroxylation reaction occurs, producing active calcined clay. As mentioned earlier, after the powdered clay raw material is calcined in the decomposition furnace (calcination temperature controlled at 850℃), the iron-containing minerals in the clay will transform from hematite (red) to magnetite (gray) at temperatures above 650℃. As is well known, magnetite is magnetic. When the high-temperature flue gas carries the calcined powdered clay through the pipeline electromagnetic device 4, the electromagnetic device 4 separates the magnetic magnetite from the clay raw material using an electromagnetic field (based on an iron content of 10% in the clay, the magnetic field strength of the electromagnetic device is set to 10000 Gs). Since the clay raw material is a micron-sized powder and is in a suspended state, the electromagnetic separation efficiency will reach over 95%. The selected magnetite is collected in the storage bin 5 through the discharge port of the electromagnetic device and then transported to the downstream storage area via the conveying device 6. The magnetite selected from the calcined clay fundamentally avoids the problem of the calcined clay turning red during the cooling process. On the one hand, the magnetite collected by the electromagnetic device can be sold as a high-value-added product. The calcined clay, after electromagnetic separation, enters C5, where it undergoes gas-solid separation and then enters a cooling system for waste heat recovery. The high-temperature flue gas then enters a preheating system to preheat the powdered clay raw material. The fuel in the decomposition furnace can be fossil fuel or biomass alternative fuel. The high-temperature combustion air for fuel combustion comes from the downstream cooling system.
[0053] The suspension cooling system is divided into two sections, such as... Figure 1 As shown, the first section consists of two cyclones, CC1 and CC2, connected in series, for high-temperature cooling of the calcined clay, using ambient air as the cooling medium. The amount of air used is the same as the amount required for fuel combustion in the decomposition furnace. The second section consists of two cyclones, CC3 and CC4, connected in series, for medium- and low-temperature cooling of the calcined clay, again using ambient air as the cooling medium. The amount of air used is adjusted according to the cooling temperature required for the final product. After cooling the calcined clay, the air in the second cooling section serves as low-temperature waste heat air, which can be used in the pretreatment process of preparing the clay raw material into powder, namely, drying and grinding. The calcined clay is finally collected as the product after gas-solid separation in CC4, and the final product color remains gray.
[0054] experiment:
[0055] Based on Examples 1 and 2, the magnetic field strength requirements of the electromagnetic device were tested for different iron contents (as a percentage of Fe2O3 by mass) in the clay. Experiments showed that to ensure a magnetite separation efficiency of over 95% and maintain the final product's gray color, the magnetic field strength of the electromagnetic device needed to be set according to the iron content in the clay, as shown in the table below.
[0056]
[0057] Experiments showed that, when the settings were configured according to the table above, the product color remained gray.
[0058] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.
[0059] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.
Claims
1. A method for controlling the color of calcined clay with high iron content, characterized in that... It includes a clay raw material suspension preheating system (1), a clay raw material suspension calcination section system (2), and a calcined clay suspension cooling system (3); wherein the clay raw material suspension preheating system (1) is connected to the clay raw material suspension calcination section system (2); and the clay raw material suspension calcination section system (2) is connected to the calcined clay suspension cooling system (3). The clay raw material suspension calcination section system (2) includes a decomposition furnace, a cyclone separator, an electromagnetic device (4), a small bin (5), and a conveying device (6); high-temperature combustion air from the calcined clay suspension cooling system (3) enters the decomposition furnace along with fuel; the decomposition furnace and the cyclone separator are connected by a pipe, and an electromagnetic device (4) is installed on the corresponding pipe; the electromagnetic device (4) is connected to the small bin (5) through its discharge port, and a conveying device (6) is installed below the small bin (5); the method includes the following steps: The clay raw material is prepared into micron-sized clay powder through crushing, drying and grinding processes; then it is fed into the connecting pipe between the first and second stage cyclones in the clay raw material suspension preheating system (1) with multiple cyclones connected in series; the clay powder is dispersed into the high-temperature flue gas at the outlet of the second stage cyclone through the spreading device set in the connecting pipe, and convective heat exchange occurs. The residual heat in the high-temperature flue gas is used to preheat the clay powder; the high-temperature flue gas carries the clay powder into the first stage cyclone. After gas-solid separation in the first stage cyclone, the high-temperature flue gas is discharged. The clay powder after the first preheating is collected and then enters the downstream cyclones one after another. It exchanges heat with the high-temperature flue gas at the outlet of each stage cyclone through convection to achieve the purpose of preheating the clay powder. The clay raw material suspension preheating system (1) has four stages of multi-stage cyclones. The clay powder raw material preheated by the fourth stage cyclone in the clay raw material suspension preheating system (1) enters the decomposition furnace (7), where a dehydroxylation reaction occurs to produce active calcined clay. After the clay powder raw material is calcined in the decomposition furnace, the high-temperature flue gas carries the calcined clay powder raw material through the pipeline electromagnetic device (4). The electromagnetic device (4) separates the magnetic magnetite from the clay powder raw material through the electromagnetic field. The selected magnetite enters the small bin (5) through the discharge port of the electromagnetic device (4) and is then transported to the downstream storage area through the conveying device (6). The calcined clay separated by electromagnetic separation enters the cyclone in the clay raw material suspension calcination section system (2). Through gas-solid separation, the calcined clay enters the calcined clay suspension cooling system to complete the waste heat recovery. The high-temperature flue gas enters the clay raw material suspension preheating system to preheat the clay powder raw material. The calcined clay suspension cooling system (3) is divided into two sections. The first section consists of two cyclones connected in series to cool the high-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is the amount of air required for fuel combustion in the decomposition furnace. The second section consists of two cyclones connected in series to cool the medium and low-temperature section of the calcined clay. The cooling medium is ambient air, and the amount of air used is adjusted according to the cooling temperature required by the final product. The calcined clay is finally collected after gas-solid separation through the last stage cyclone. The electromagnetic device (4) has a strength of over 8000 Gs and a temperature of 850℃±50℃.
2. The method for controlling the color of calcined clay with high iron content as described in claim 1, characterized in that: The number of cyclone stages is set according to the amount of heat required by the clay raw materials in the drying, grinding and pretreatment preparation stage; multi-stage cyclones connected in series are combined in parallel according to the production scale.
3. The method for controlling the color of calcined clay with high iron content as described in claim 1, characterized in that: The calcined clay suspension cooling system (3) consists of four cyclone separators connected in series, and is configured as multiple series in parallel depending on the scale of the production line.
4. The method for controlling the color of calcined clay with high iron content as described in claim 1, characterized in that: After the air in the second cooling section of the calcined clay suspension cooling system (3) completes the task of cooling the calcined clay, it is used as low-temperature waste heat air for the drying and grinding processes when the clay raw material is prepared into clay powder.
5. The method for controlling the color of calcined clay with high iron content as described in claim 1, characterized in that: The fuel in the decomposition furnace (7) is fossil fuel or biomass alternative fuel.