Method for controlling color of calcined clay with high iron content

Abstract

The invention belongs to the technical field of thermal engineering of inorganic non-metallic materials, and particularly relates to a method for controlling the color of high-iron-content calcined clay. The method comprises a clay raw material suspension preheating system (1), a clay raw material suspension calcining section system (2) and a calcined clay suspension cooling system (3), wherein the clay raw material suspension preheating system (1) is connected with the clay raw material suspension calcining section system (2); and the clay raw material suspension calcining section system (2) is connected with the calcined clay suspension cooling system (3). By adopting the method, the atmosphere in the calcining and cooling stages does not need to be complexly controlled, and the technological process is simple. In the cooling stage, heat of high-temperature calcined clay can be efficiently recycled through ambient air, the recycled high-temperature air serves as combustion-supporting air for fuel combustion in the decomposing furnace, and heat consumption is greatly reduced; when the iron content of the clay is higher than 5%, the color of the calcined clay can be kept gray, and the magnetite product with high additional value can be obtained.

Description

Technical Field

[0001] The invention belongs to the field of thermal technology of inorganic non-metallic materials, and in particular relates to a method for controlling the color of calcined clay with high iron content. Background Art

[0002] In the context of the global advocacy of carbon emission reduction and carbon neutrality, the cement industry, as a high-energy consumer and high-carbon dioxide emitter, has seen a boom in technologies to reduce carbon dioxide emissions. Among them, the use of calcined clay as an auxiliary cementitious material for the production of low-carbon cement is one of the important carbon reduction technologies to reduce carbon dioxide emissions in the cement industry. The basic principle of this technology is as follows: After the clay is crushed, dried, and ground into a micron-sized powder material, it is calcined at a suitable temperature. During the calcination process, the kaolinite minerals in the clay undergo a dehydroxylation reaction (in the industrial production process, the reaction temperature window is controlled at 750~900℃), the crystal structure is destroyed, and an active kaolinite with an amorphous structure is generated. Therefore, the activated clay obtained after calcination (hereinafter referred to as calcined clay) can replace cement clinker in large quantities to produce low-carbon cement.

[0003] There are two main methods for the industrial production of calcined clay: rotary kiln calcination and suspension calcination. The product of rotary kiln calcination has low activity and high energy consumption. The main heat exchange mechanism of suspension calcination is convection heat exchange, which has high heat exchange efficiency and uniform and controllable temperature field. Therefore, suspension calcination technology has significant advantages in product activity and energy consumption when used to produce calcined clay.

[0004] The clay suspension calcination technology mainly includes three stages: "suspension preheating of clay raw materials, suspension calcination of clay raw materials, and suspension cooling of calcined clay". The three stages are described as follows.

[0005] The "clay raw material suspension preheating section" consists of multiple cyclones in series. The clay raw material, which has been pretreated to be micron-sized powder, is fed into the first cyclone of the preheating stage, and then preheated in a suspended state through multiple cyclones. The high-temperature flue gas for preheating the clay raw material in each cyclone comes from the decomposition furnace.

[0006] The "clay raw material suspension calcination section" is mainly composed of a decomposition furnace. After preheating, the clay powdered raw material entering the decomposition furnace is calcined in the high-temperature flue gas environment generated by the combustion of the fuel fed into the decomposition furnace, that is, a dehydroxylation reaction occurs and activity is generated. After the calcined clay leaves the decomposition furnace with the high-temperature flue gas, it passes through a cyclone for gas-solid separation, and the separated calcined clay enters the "suspension cooling section". The separated high-temperature flue gas enters the "clay raw material suspension preheating section" to preheat the clay powdered raw material. The high-temperature combustion-supporting 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 cyclones connected in series. The cooling medium in the cooling process uses ambient air. After the air cools the high-temperature calcined clay, the air itself is heated and then enters the decomposition furnace as the combustion air required for the fuel combustion in the decomposition furnace. After the clay is cooled, it is collected by the cooling cyclone and used as a product.

[0008] However, the above-mentioned technology can only be applied to clay with low iron content (generally <5%). If it is greater than >5%, the calcined clay produced by the above scheme will be red. Although adding it to cement has no effect on product quality, it is easily mistaken for an inferior product by the market, so its acceptance is not high. This limits the application scenarios of suspended calcination technology (especially for clay with high iron content). This is also the technical bottleneck for the large-scale industrial application of suspended calcination technology.

[0009] The mechanism of the color change of high iron content calcined clay to red is as follows: During the process of heating and calcining the clay, the temperature is gradually raised to 850°C (industrial production ultimately needs to be heated to around 850°C to ensure that the clay dehydroxylation reaction is complete and produces sufficient activity). When the clay is heated to a temperature higher than 650°C, the hematite (Fe2O3, red) in the clay will undergo a reduction reaction and turn into magnetite (Fe3O4, gray). The clay continues to be heated to 850°C, and the iron-containing minerals in the clay still exist in the form of magnetite and remain gray.

[0010] When the clay is cooled to ambient temperature after calcination to form a product, the color changes as follows: (1) During the cooling process from 850°C to 650°C, the magnetite in the calcined clay can be stably present 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°C to 300°C, if there is an oxygen atmosphere in the cooling medium, the magnetite in the calcined clay will be oxidized to hematite again, 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 during the cooling process in stage (2), then when the calcined clay continues to cool from 300°C to ambient temperature, regardless of whether the cooling medium in this stage contains oxygen, the final color of the calcined clay will be red; if the iron-containing mineral in the calcined clay is still magnetite during the cooling process in stage (2), then when the calcined clay continues to cool from 300°C to ambient temperature, regardless of whether the cooling medium in this stage contains oxygen, the final color of the calcined clay will be gray.

[0011] To solve the technical problem that clay remains gray instead of turning red after suspension calcination. The main technical directions include reduction calcination, flue gas recirculation reduction cooling, indirect water cooling, indirect oil cooling and other technologies. These technologies are essentially to control the cooling atmosphere of the calcined clay in the cooling stage of 650~300℃, that is, to avoid the calcined clay from contacting with oxygen during the cooling stage, so that the magnetite in the calcined clay is not oxidized to hematite. However, these technologies all have complex atmosphere control and regulation (requiring alternating control of oxidation and reduction atmospheres), and cannot use air as a cooling medium to directly contact the high-temperature calcined clay, and efficiently recover the waste heat of the high-temperature calcined clay as high-temperature combustion-supporting air in the decomposition furnace in the form of convection heat exchange, which greatly affects the efficient, complete and stable combustion of the pulverized coal fed into the decomposition furnace. This leads to problems such as high energy consumption, complex operation, and difficulty in large-scale industrial application of the suspension calcination system, which largely offsets the advantages of the suspension calcination technology itself, such as high heat transfer efficiency, high waste heat recovery efficiency, low energy consumption, simple process flow, and large-scale industrial production. Summary of the invention

[0012] The purpose of the present invention is to provide a method for controlling the color of high-iron clay, which is an efficient and simple clay suspension calcination technology. The technology has strong adaptability, that is, it can be applied to raw materials with an iron content of less than 5% and clay raw materials with an iron content of more than 5%, and the purpose of keeping the color of the calcined clay gray can be achieved without complex control of the calcination atmosphere and the cooling atmosphere. The method fundamentally saves heat consumption, simplifies process design, reduces construction investment, and can be industrially applied.

[0013] In order to achieve at least one of the above invention purposes, the technical solution of the present invention is as follows: A method for controlling the color of calcined clay with high iron content comprises a clay raw material suspension preheating system, a clay raw material suspension calcining 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 calcining section system; and the clay raw material suspension calcining section system is connected to the calcined clay suspension cooling system.

[0014] Furthermore, the clay raw material suspension preheating system is composed of multiple cyclones connected in series; the number of cyclones is set according to the amount of heat required by the clay raw material in the drying and grinding pretreatment preparation stage, and can generally be designed to be two to six stages, preferably four stages of cyclones connected in series, that is, including a first stage cyclone, a second stage cyclone, a third stage cyclone and a fourth stage cyclone. The multiple stages of cyclones connected in series can also be combined in multiple columns in parallel according to the production scale.

[0015] Furthermore, the clay raw material suspension calcination section system includes a decomposition furnace, a cyclone, an electromagnetic device, a small bin and a conveying device; the calcined clay suspension cooling system enters the decomposition furnace together with the fuel; the decomposition furnace and the cyclone are connected through a pipeline, and an electromagnetic device is arranged on the corresponding pipeline; the electromagnetic device is connected to the small bin through its discharge port, and a conveying device is arranged under the small bin.

[0016] Furthermore, the calcined clay suspension cooling system is composed of multiple stages of cyclones connected in series, which can generally be designed to be two to six stages, preferably four stages of cyclones connected in series, namely including a first stage cyclone, a second stage cyclone, a third stage cyclone and a fourth stage cyclone; it can also be set to multiple series in parallel according to the scale of the production line.

[0017] Furthermore, the above method for controlling the color of high iron content calcined clay comprises the following specific steps: The clay raw material is prepared into micron-sized powdered raw material through processes such as crushing, drying, and grinding; then it is fed into the connecting pipe between the first-stage cyclone and the second-stage cyclone in the clay raw material suspension preheating system where multiple cyclones are connected in series; the powdered raw material is then dispersed into the high-temperature flue gas at the outlet of the second-stage cyclone through a spreading device arranged in the connecting pipe, and convection heat exchange occurs. The waste heat in the high-temperature flue gas is used to preheat the clay powdered raw material; the high-temperature flue gas carries the clay powdered raw material into the first-stage cyclone, and after gas-solid separation in the first-stage cyclone, the high-temperature flue gas is discharged, and the clay powdered raw material after the first preheating is collected, and then successively enters the downstream cyclones of each stage, and achieves the purpose of preheating the clay powdered raw material through convection heat exchange with the high-temperature flue gas at the outlet of each stage of the cyclone; The preheated clay powdered raw material from the fourth stage cyclone in the clay raw material suspension preheating system enters the decomposition furnace, where a dehydroxylation reaction occurs to produce active calcined clay. In the traditional process, when the powdered clay raw material is calcined in the decomposition furnace (calcination temperature>650℃, generally to ensure continuous and stable combustion of fuel, industrial control is around 750~900℃), the iron-containing minerals in the clay will change from hematite (red) to magnetite (gray) when the temperature is above 650℃. As we all know, magnetite is magnetic. When the powdered clay raw material is calcined in the decomposition furnace, when the high-temperature flue gas carries the calcined powdered clay through the pipeline electromagnetic device, the electromagnetic device will separate the magnetic magnetite from the clay raw material through the electromagnetic field; since the clay raw material is a micron-sized powdered raw material and is in a suspended state, the electromagnetic separation efficiency will reach more than 95%. The selected magnetite enters the storage bin through the discharge port of the electromagnetic device and is then transported to the downstream storage area through the conveying device. The magnetite selected from the calcined clay fundamentally avoids the problem of the calcined clay turning red during the cooling process. On the other hand, the magnetite collected by the electromagnetic device can also be sold as a high value-added product.

[0018] The calcined clay after electromagnetic separation enters the cyclone in the clay raw material suspension calcination section system. After 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; Furthermore, the calcined clay suspension cooling system is divided into two sections. The first section is composed of two cyclones connected in series, which are used 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 is composed of two cyclones connected in series, which are used to cool the medium and low temperature sections 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 and finally becomes a product.

[0019] Furthermore, after the air in the second cooling section of the calcined clay suspension cooling system completes the task of cooling the calcined clay, it can be used as low-temperature waste heat air in the pretreatment process of preparing the clay raw material into powdery raw material, namely, the drying and grinding process.

[0020] Furthermore, in order to reliably control the color of the calcined clay, it is necessary to pay attention to controlling the intensity of the magnetic field device, which should be above 8000 Gs, so as to ensure that the magnetite separation efficiency reaches above 95%.

[0021] Furthermore, the calcination temperature is 850°C ± 50°C to ensure that the iron-containing minerals in the clay are completely transformed into magnetite with magnetic properties. However, it cannot exceed 900°C. When it is greater than 900°C, there is a risk of overburning the kaolinite in the clay, causing the generated metakaolinite to recrystallize into mullite, which affects the activity of the product.

[0022] Furthermore, the fuel in the decomposition furnace is fossil fuel or biomass alternative fuel; the high-temperature combustion-supporting air for fuel combustion comes from the downstream cooling system.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (I) With the present invention, when the iron content in the clay is greater than 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 only through the pipeline electromagnetic device to ensure that the clay is gray. The installation position of the pipeline electromagnetic device is located on the decomposition furnace connecting pipeline. At this time, the temperature of the clay powder raw material is greater than 650°C, and the iron-containing minerals in the clay will exist in the form of magnetic magnetite rather than non-magnetic hematite. The entire process flow is simple. In the cooling stage, the heat of the high-temperature calcined clay can be efficiently recovered through the ambient air. The recovered high-temperature air is used as the combustion-supporting air for the fuel combustion in the decomposition furnace, and the heat consumption is greatly reduced.

[0024] (II) According to the present invention, in the clay raw material suspension preheating system, an electromagnetic device (pipeline) is installed on the connection pipe of the decomposition furnace, and the magnetite in the calcined clay can be separated by the electromagnetic field. On the one hand, the calcined clay remains gray, and on the other hand, the separated magnetite can be sold as a high value-added by-product.

[0025] (III) In the present invention, regardless of whether the iron content of the clay raw material is greater than 5%, the cooling medium of the cooling system is ambient air. The ambient air is in direct contact with the high-temperature calcined clay, generating convection heat exchange, thereby cooling the clay and heating the ambient air itself. The ambient air then enters the decomposition furnace as combustion-supporting air for the fuel, without indirectly cooling the high-temperature calcined clay. This fundamentally ensures that the waste heat is recovered to the greatest extent in the form of ambient air, which is beneficial for the fuel in the decomposition furnace to directly utilize high-temperature air for efficient and stable combustion, thereby generating the effect of energy saving and consumption reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structures of various systems in a method for controlling the color of high-iron-content calcined clay according to the present invention; Figure 2 It is a structural schematic diagram of the suspension preheating system; Reference numerals: 1—clay raw material suspension preheating system, 2—clay raw material suspension cooling system, 3—calcined clay suspension cooling system; 4—electromagnetic device, 5—small warehouse, 6—conveying device; C1, C2, C3, C4, and C5 respectively represent the first-stage cyclone, the second-stage cyclone, the third-stage cyclone, the fourth-stage cyclone, and the fifth-stage cyclone in the clay raw material suspension preheating system; CC1, CC2, CC3, and CC4 respectively represent the first-stage cyclone, the second-stage cyclone, the third-stage cyclone, and the fourth-stage cyclone in the calcined clay suspension cooling system; the cyclones at each level are connected through connecting pipes. DETAILED DESCRIPTION

[0027] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0028] Any feature disclosed in this specification (including claims and abstract), unless otherwise stated, may be replaced by other alternative features that are equivalent or have similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0029] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0030] In this application, % not specifically mentioned here means the percentage by mass, and any specific steps or conditions not specified here can be carried out according to the conventional steps or conditions described in the literature in this field. All the raw materials used are commercially available raw materials.

[0031] Embodiment 1: A method for controlling the color of calcined clay with high iron content, comprising a clay raw material suspension preheating system 1, a clay raw material suspension calcining 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 calcining section system 2; the clay raw material suspension calcining section system 2 is connected to the calcined clay suspension cooling system 3.

[0032] Furthermore, the clay raw material suspension preheating system 1 is composed of multiple cyclones connected in series; the number of cyclones is set according to the amount of heat required by the clay raw material in the drying and grinding pretreatment preparation stage, and can generally be designed to be two to six stages. In this embodiment, four cyclones are preferably connected in series, that is, including a first-stage cyclone, a second-stage cyclone, a third-stage cyclone and a fourth-stage cyclone. The multiple cyclones connected in series can also be combined in multiple columns in parallel according to the production scale.

[0033] Furthermore, the clay raw material suspension calcination section system includes a decomposition furnace, a cyclone, an electromagnetic device 4, a small bin 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 are connected through a pipeline, and the electromagnetic device 4 is arranged on the corresponding pipeline; the electromagnetic device 4 is connected to the small bin 5 through its discharge port, and a conveying device 6 is arranged below the small bin 5.

[0034] Furthermore, the calcined clay suspension cooling system is composed of multiple stages of cyclones connected in series, which can generally be designed to be two to six stages. In this embodiment, four stages of cyclones are preferably connected in series, namely, a first stage cyclone, a second stage cyclone, a third stage cyclone and a fourth stage cyclone; it can also be set to multiple series in parallel according to the scale of the production line.

[0035] Furthermore, the above method for controlling the color of high iron content calcined clay comprises the following specific steps: The clay raw material is prepared into micron-sized powdered raw material through processes such as crushing, drying, and grinding; then it is fed into the connecting pipe between the first-stage cyclone and the second-stage cyclone of the multi-stage cyclone series in the clay raw material suspension preheating system; the powdered raw material is then dispersed in the high-temperature flue gas at the outlet of the second-stage cyclone through the spreading device arranged in the connecting pipe, and convection heat exchange occurs. The waste heat in the high-temperature flue gas is used to preheat the clay powdered raw material; the high-temperature flue gas carries the clay powdered raw material into the first-stage cyclone, and after gas-solid separation in the first-stage cyclone, the high-temperature flue gas is discharged, and the clay powdered raw material after the first preheating is collected, and then successively enters the downstream cyclones of each level, and achieves the purpose of preheating the clay powdered raw material through convection heat exchange with the high-temperature flue gas at the outlet of each level of cyclone.

[0036] The preheated clay powdered raw material from the fourth stage cyclone in the clay raw material suspension preheating system enters the decomposition furnace, where a dehydroxylation reaction occurs to produce active calcined clay. In the traditional process, when the powdered clay raw material is calcined in the decomposition furnace (calcination temperature>650℃, generally to ensure continuous and stable combustion of fuel, industrial control is around 750~900℃), the iron-containing minerals in the clay will change from hematite (red) to magnetite (gray) when the temperature is above 650℃. As we all know, magnetite is magnetic. When the powdered clay raw material is calcined in the decomposition furnace, when the high-temperature flue gas carries the calcined powdered clay through the pipeline electromagnetic device, the electromagnetic device will separate the magnetic magnetite from the clay raw material through the electromagnetic field; since the clay raw material is a micron-sized powdered raw material and is in a suspended state, the electromagnetic separation efficiency will reach more than 95% (proven by experiments, the magnetic field of the electromagnetic device>8000Gs). The selected magnetite enters the storage bin through the discharge port of the electromagnetic device and is then transported to the downstream storage area through the conveying device. The magnetite selected from the calcined clay fundamentally avoids the problem of the calcined clay turning red during the cooling process. On the other hand, the magnetite collected by the electromagnetic device can also be sold as a high value-added product.

[0037] The calcined clay after electromagnetic separation enters the cyclone in the clay raw material suspension calcination section system. After 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.

[0038] Furthermore, the calcined clay suspension cooling system is divided into two sections. The first section is composed of two cyclones connected in series, which are used 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 is composed of two cyclones connected in series, which are used to cool the medium and low temperature sections 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 and finally becomes a product.

[0039] Embodiment 2: On the basis of Example 1, a clay raw material with an iron content of 10% and a mass flow rate of 200t / h is prepared into a micron-sized powdered raw material through crushing, drying, grinding and other processes, and then fed into the connecting pipe between the suspension preheating system C2 and C1. The powdered raw material is immediately dispersed in the high-temperature flue gas at the outlet of C2 in the connecting pipe through the spreading device, and convection heat exchange occurs. The waste heat in the high-temperature flue gas is used to preheat the clay powdered raw material. The high-temperature flue gas carries the clay powdered raw material into the first-stage cyclone C1. After gas-solid separation in the C1 cyclone, the high-temperature flue gas is discharged. The clay powdered raw material after the first preheating is collected, and then enters the downstream cyclones at each level one by one, and the high-temperature flue gas at the outlet of each level of the cyclone is convectively exchanged to achieve the purpose of preheating the clay powdered raw material.

[0040] The preheated clay powdery raw material out of C4 enters the decomposition furnace, where a dehydroxylation reaction occurs to produce active calcined clay. As mentioned above, after the powdered clay raw material is calcined in the decomposition furnace (the calcination temperature is controlled at 850°C), the iron-containing minerals in the clay will be transformed from hematite (red) to magnetite (gray) when the temperature is above 650°C. As we all know, 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 through the electromagnetic field (according to the iron content of 10% in the clay, the magnetic field strength of the electromagnetic device is set to 10000Gs). Since the clay raw material is a micron-sized powdery raw material and is in a suspended state, the electromagnetic separation efficiency will reach more than 95%. The selected magnetite enters the storage silo 5 through the discharge port of the electromagnetic device for collection, and then is transported to the downstream storage area through the conveying device 6. On the one hand, the magnetite selected from the calcined clay fundamentally avoids the problem that the calcined clay may appear red during the cooling process. On the one hand, magnetite collected by electromagnetic device can also be sold as high value-added products. The calcined clay after electromagnetic separation enters C5, and after gas-solid separation, the calcined clay enters the cooling system to complete waste heat recovery. The high-temperature flue gas enters the preheating system to preheat the clay powder raw materials. 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.

[0041] The suspension cooling system is divided into two sections, such as Figure 1As shown, the first section is composed of two cyclones CC1 and CC2 connected in series, which are used to cool the high temperature section of the calcined clay, and the cooling medium is ambient air. The amount of air used is the amount of air required for fuel combustion in the decomposition furnace. The second section is composed of two cyclones CC3 and CC4 connected in series, which are used to cool the medium and low temperature sections of the calcined clay, and the cooling medium is ambient air. The amount of air used is adjusted according to the cooling temperature required by the final product. After the air in the second cooling section completes the task of cooling the calcined clay, it can be used as low-temperature waste heat air in the pretreatment process when the clay raw material is prepared into a powdered raw material, that is, the drying and grinding process. The calcined clay is finally collected as a product after CC4 gas-solid separation, and the product color finally remains gray.

[0042] experiment: On the basis of Example 1 and Example 2, the requirements of different iron contents (in terms of Fe2O3 mass percentage) in the clay on the magnetic field strength of the electromagnetic device were tested. After experiments, in order to ensure that the magnetite separation efficiency reaches more than 95% and the final product remains gray, the magnetic field strength of the electromagnetic device needs to be set accordingly according to the iron content in the clay. The specific setting conditions are shown in the following table.

[0043]

[0044] After experimenting and setting according to the above table, the product color finally remained gray.

[0045] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0046] This background section is provided to generally present the context of the invention, and the work of the presently 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 explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A method for controlling the color of high iron content calcined clay, characterized in that The invention comprises 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).

2. The method for controlling the color of high iron content calcined clay according to claim 1, characterized in that: The clay raw material suspension preheating system (1) is composed of multiple cyclones connected in series; the number of cyclones is set according to the amount of heat required for the clay raw material in the drying and grinding pretreatment preparation stage; the multiple cyclones connected in series can also be combined in multiple rows in parallel according to the production scale.

3. The method for controlling the color of high iron content calcined clay according to claim 1, characterized in that: The clay raw material suspension calcination section system (2) comprises a decomposition furnace, a cyclone, an electromagnetic device (4), a small bin (5) and a conveying device (6); the calcined clay from the suspension cooling system (3) enters the decomposition furnace together with the fuel; the decomposition furnace and the cyclone are connected through a pipeline, and the electromagnetic device (4) is arranged on the corresponding pipeline; the electromagnetic device (4) is connected to the small bin (5) through its discharge port, and the conveying device (6) is arranged below the small bin (5).

4. The method for controlling the color of high iron content calcined clay as claimed in claim 2, characterized in that: The multi-stage cyclone in the clay raw material suspension preheating system (1) is 2-4 stages.

5. The method for controlling the color of high iron content calcined clay as claimed in claim 3, characterized in that: The calcined clay suspension cooling system (3) is composed of multiple stages of cyclones connected in series, and can also be configured as multiple series in parallel according to the scale of the production line.

6. The method for controlling the color of high iron content calcined clay according to claim 5, characterized in that: The multi-stage cyclone in the calcined clay suspension cooling system (3) is 2-4 stages.

7. The method for controlling the color of high iron content calcined clay as claimed in any one of claims 1 to 6, characterized in that The following steps are involved: The clay raw material is crushed, dried and ground into a micron-sized powdered raw material; then the powdered raw material is fed into a connecting pipe between a first-stage cyclone and a second-stage cyclone in a clay raw material suspension preheating system (1); the powdered raw material is dispersed in the high-temperature flue gas at the outlet of the second-stage cyclone through a spreading device provided in the connecting pipe, and convection heat exchange occurs, and the waste heat in the high-temperature flue gas is used to preheat the clay powdered raw material; The high-temperature flue gas carries the clay powder raw material into the first-stage cyclone. After the gas-solid separation in the first-stage cyclone, the high-temperature flue gas is discharged. The clay powder raw material after the first preheating is collected and then enters the downstream cyclones of each level one by one. Through convection heat exchange with the high-temperature flue gas at the outlet of each level of cyclone, the purpose of preheating the clay powder raw material is achieved. The preheated clay powdery raw material from 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 powdery clay raw material is calcined in the decomposition furnace, when the high-temperature flue gas carries the calcined powdery clay through the pipeline electromagnetic device (4), the electromagnetic device (4) separates the magnetic magnetite from the clay raw material through the electromagnetic field; the selected magnetite enters the storage bin (5) through the discharge port of the electromagnetic device (4) for collection, and is then transported to the downstream storage area through the conveying device (6); the calcined clay after electromagnetic separation enters the cyclone in the clay raw material suspension calcination section system (2), where it enters the calcined clay suspension cooling system to complete waste heat recovery through gas-solid separation; the high-temperature flue gas enters the clay raw material suspension preheating system to preheat the clay powdery raw material; The calcined clay suspension cooling system (3) is divided into two sections. The first section is composed of two cyclones connected in series, which are used to cool the high temperature section of the calcined clay. The cooling medium is ambient air. The amount of air used is the amount of air required for fuel combustion in the decomposition furnace. The second section is composed of two cyclones connected in series, which are used to cool the medium and low temperature sections of the calcined clay. The cooling medium is ambient air. 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.

8. The method for controlling the color of high iron content calcined clay according to claim 7, characterized in that: After the air in the second cooling section of the calcined clay suspension cooling system (3) has completed the task of cooling the calcined clay, it can be used as low-temperature waste heat air in the pretreatment process of preparing the clay raw material into powdery raw material, that is, the drying and grinding process.

9. The method for controlling the color of high iron content calcined clay according to claim 7, characterized in that: The intensity of the magnetic field device is above 8000Gs, and the temperature is 850℃±50℃.

10. The method for controlling the color of high iron content calcined clay according to claim 7, characterized in that: The fuel in the decomposition furnace (7) is fossil fuel or biomass alternative fuel; the high-temperature combustion-supporting air for the fuel combustion comes from the downstream cooling system.

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