Method for controlling color of high-iron-content calcined clay

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 the following steps: 1) crushing, drying and grinding a clay raw material to prepare a micron-sized powdery raw material, adding a CaO powdery material, and uniformly mixing; 2) feeding the mixed material into a connecting pipeline between a first-stage cyclone cylinder and a second-stage cyclone cylinder; and the materials are dispersed in the high-temperature flue gas at the outlet of the second-stage cyclone cylinder through a material scattering device arranged at the position in the connecting pipeline. 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, heat consumption is greatly reduced, and when the content of iron in the clay is higher than 5%, the calcined clay can also be kept gray.

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-consuming and high-carbon dioxide emitter, has developed 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, in order to ensure the complete dehydroxylation reaction, the reaction temperature window is controlled at 750~850℃), 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: After the clay is preheated, calcined and activated, during the cooling stage at 650~300℃, if there is oxygen in the cooling medium, the iron-containing minerals in the calcined clay will exist in the form of hematite and remain red. Therefore, if you want to avoid the calcined clay being red, during the cooling stage at 650~300℃, the calcined clay cannot be directly exposed to oxygen, and can only be kept gray through indirect cooling or cooling with an inert gas that does not contain oxygen.

[0010] At present, the main technical directions include low-oxygen 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 this cooling stage. 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 with the high-temperature calcined clay, and cannot efficiently recover the waste heat of the high-temperature calcined clay in the form of convection heat exchange as the high-temperature combustion-supporting air in the decomposition furnace, 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 suspended calcination system, which largely offsets the advantages of the suspended 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

[0011] The purpose of the present invention is to provide a method for controlling the color of high-iron calcined clay in view of the problems existing in the prior art. The method is an efficient and simple clay suspension calcination technology, which has strong adaptability, that is, it can be applied to raw materials with an iron content of less than 5wt% in clay, and can be used for clay raw materials with an iron content of more than 5wt%, 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 present invention directly uses ambient air as a cooling medium, and directly contacts with the high-temperature calcined clay in a suspended state to achieve the purpose of controlling the color of the calcined clay to be controllable (i.e., keep gray and do not turn red). At the same time, since the air is in direct contact with the high-temperature calcined clay in a suspended state, the waste heat of the high-temperature calcined clay can be recovered to the maximum extent, and the high-temperature air after the waste heat is recovered enters the decomposition furnace as the combustion-supporting air for fuel combustion. Fundamentally realize the large-scale industrial application of high-iron clay, while controlling color, saving heat consumption, simplifying process design, and reducing construction investment.

[0012] In order to achieve one of the above invention objects, the technical solution of the present invention is as follows: A method for controlling the color of high-iron calcined clay, comprising the following main steps: adding a certain proportion of CaO powder material (CaO powder, limestone powder or powdered material that can provide CaO, or other powdered material that can generate CaO at high temperature) to clay powder raw materials, and mixing them evenly. After suspension preheating, suspension calcination, and suspension cooling, the calcined clay with controllable color is obtained. The added CaO will react with Fe2O3 in the clay in the high temperature stage of suspension calcination (850±50℃): 2CaO + Fe2O3=(CaO)2•Fe2O3. The Gibbs free energy of the reaction is: -8716.15 kcal / mol, which is significantly less than 0, indicating that the reaction is spontaneous at the high temperature stage and can generate stable dicalcium ferrite. The generation of dicalcium ferrite prevents the iron-containing minerals in the calcined clay from being oxidized and converted into magnetite in the suspension cooling stage, thereby fundamentally avoiding the possibility of the calcined clay turning into red.

[0013] The amount of CaO added depends on the iron content in the clay (as Fe2O3). For example, if the iron content in the clay is 10%, then the Fe2O3 content in 1 kg of clay powder is 100 g. Through the solid phase reaction 2CaO + Fe2O3=(CaO)2•Fe2O3, it can be known that the theoretical content of CaO powder material that needs to be added to 1 kg of clay powder is 100×(56×2 / 160)=70 g, where 56 is the molecular weight of CaO, 160 is the molecular weight of Fe2O3, and 2 represents the molar mass ratio of CaO to Fe2O3.

[0014] The present invention is applied to industrial production processes. To ensure that Fe2O3 is completely reacted with CaO, an appropriate excess (excess ratio is 1.05-1.15) is added based on the theoretical addition content. For example, 80 g of CaO powder material is added to 1 kg of clay powder material. CaO has a wide range of sources, is cheap and easy to obtain, and has a small amount of addition. It can be prepared into CaO powder by a separate grinding process, or ground together with clay raw materials to prepare powder material.

[0015] The method specifically comprises the following steps: 1) After the clay raw material is crushed, dried and ground into a micron-sized powdered raw material, a CaO powdered material is added according to the iron content in the clay and mixed evenly to obtain a mixed powdered raw material; 2) The mixed powdered raw material in step 1) is fed into the connecting pipe between the first-stage cyclone and the second-stage cyclone in the suspension preheating system; and dispersed into the high-temperature flue gas at the outlet of the second-stage cyclone through the spreading device provided at that location in the connecting pipe, so that 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 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 powdered raw material after the first preheating is collected, and then successively enters the downstream cyclones of each stage, and performs convection heat exchange with the high-temperature flue gas at the outlet of each stage of the cyclone, so as to achieve the purpose of preheating the powdered raw material; 3) The preheated powdered raw materials from the last stage cyclone in the suspension preheating system enter the decomposition furnace. In the high temperature environment of the decomposition furnace, on the one hand, a dehydroxylation reaction occurs to produce active calcined clay. On the other hand, in the high temperature environment, the added CaO powder reacts with the Fe2O3 in the clay in a solid phase: 2CaO + Fe2O3=(CaO)2•Fe2O3. The Gibbs free energy of the reaction is -8716.15 kcal / mol, which is significantly less than 0. It is spontaneous in the high temperature stage and generates stable dicalcium ferrite. The generation of dicalcium ferrite prevents the iron-containing minerals in the calcined clay from being oxidized and converted into magnetite during the suspension cooling stage, thereby fundamentally avoiding the possibility of the calcined clay turning into red.

[0016] 4) The calcined clay 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.

[0017] Furthermore, the CaO powder material is CaO powder, limestone powder or a powder that can provide CaO, or other powder materials that can generate CaO at high temperature. First, CaO powder is selected because the reaction between CaO and Fe2O3 is a slightly endothermic reaction, and the energy required is very small, about 7kcal / mol. If limestone powder is added, although the color of the calcined clay can also be controlled, the limestone powder mainly contains CaCO3, which first needs a large amount of endothermic decomposition to generate CaO (about 42.5kcal / mol), and then reacts with Fe2O3 to generate (CaO)2•Fe2O3. This will significantly increase fuel consumption, thereby increasing heat consumption.

[0018] Furthermore, in order to reliably control the color of calcined clay, it is necessary to pay attention to controlling the amount of CaO-containing materials added, and the amount added is 1.05~1.15 times the theoretical amount added. Because when the amount added is less than 1.05, the clay color pass rate cannot be fully guaranteed. Red will appear in the product. When the amount added is greater than 1.15, the color pass rate is high, but the addition of CaO requires additional energy consumption and increases heat consumption.

[0019] The theoretical addition amount of CaO powder material depends on the iron content in the clay. That is, it is determined by the stoichiometric ratio (2:1) of CaO and Fe2O3 to generate 2CaO•Fe2O3. In the industrial production process, the actual addition amount should be 1.05~1.1 times the theoretical addition amount. Taking the added CaO powder material as CaO powder as an example, assuming that the CaO content in the CaO powder is 90%, the addition amount of CaO powder under different iron content conditions in the clay is shown in the following table.

[0020]

[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 a downstream cooling system.

[0023] Furthermore, the temperature in the decomposition furnace is controlled at 850℃±50℃. Below this temperature, the solid phase reaction 2CaO + Fe2O3=(CaO)2•Fe2O3 has a low reaction rate and poor color control effect. Above this temperature, although the reaction is sufficient, there is a risk of overburning of kaolinite in the clay, resulting in the recrystallization of the generated metakaolinite to form mullite, which affects the activity of the product.

[0024] The purpose of the present invention also includes protecting a device for controlling the color of high-iron calcined clay, which is used in the method for controlling the color of high-iron clay as mentioned above, wherein the device 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; the clay raw material suspension calcination section system is connected to the calcined clay suspension cooling system; the clay raw material suspension preheating system is composed of four-stage cyclones connected in series; the cyclones connected in series can be combined in multiple columns in parallel according to the production scale; the clay raw material suspension calcination section system includes a decomposition furnace and a fifth-stage cyclone.

[0025] Furthermore, the four-stage cyclone barrels are respectively a first-stage cyclone barrel, a second-stage cyclone barrel, a third-stage cyclone barrel and a fourth-stage cyclone barrel.

[0026] Furthermore, the calcined clay suspension cooling system (3) is composed of multiple cyclones connected in series, and can also be configured as multiple series in parallel according to the scale of the production line.

[0027] Furthermore, the multi-stage cyclone in the calcined clay suspension cooling system is 2-4 stages.

[0028] 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.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The technology of the present invention does not require complex control of the atmosphere during the calcination and cooling stages, and the process flow is simple. During the cooling stage, the heat of the high-temperature calcined clay can be efficiently recovered through the ambient air, and the recovered high-temperature air is used as the combustion air for the fuel combustion in the decomposition furnace. The heat consumption is greatly reduced. 2. By using the technology of the present invention, when the iron content of the clay is higher than 5wt%, the color of the calcined clay can also remain gray. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of each unit in a method for controlling the color of high-iron content calcined clay according to the present invention; Reference numerals: 1—clay raw material suspension preheating unit, 2—clay raw material suspension calcination section system, 3—calcined clay suspension cooling unit; 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 unit; 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 unit; the cyclones at each level are connected through connecting pipes. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] The features and performance of the present invention are further described in detail below in conjunction with the embodiments. The methods, steps or devices not described in the embodiments are all prior art.

[0034] Embodiment 1: A device for controlling the color of high-iron calcined clay, 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.

[0035] Furthermore, the clay raw material suspension preheating system 1 is composed of four-stage cyclones (first-stage cyclone, second-stage cyclone, third-stage cyclone and fourth-stage cyclone) connected in series, and the multi-stage cyclones connected in series can also be combined in multiple rows in parallel according to the production scale.

[0036] Furthermore, the clay raw material suspension calcination section system includes a decomposition furnace, a fifth-stage 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 is connected to the fifth-stage cyclone 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.

[0037] 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.

[0038] 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 four-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.

[0039] 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.

[0040] 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; 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.

[0041] Embodiment 2: A method for controlling the color of calcined clay with high iron content, a device for controlling the color of calcined clay with high iron content in Example 1 (such as Figure 1 shown).

[0042] The clay raw material (iron content is 10wt%) with a feeding rate of 100t / h is crushed, dried, ground and prepared into micron-sized powdered raw materials, and then evenly mixed with micron-sized CaO powder (according to the solid phase reaction 2CaO + Fe2O3=(CaO)2•Fe2O3, the theoretical addition amount of CaO powder can be calculated to be 7t / h. Considering the industrial production situation, it can be appropriately excessive to 8t / h. CaO powder can be mixed and ground with clay raw materials or ground separately), and then fed into the connecting pipe between the second-stage cyclone and the first-stage cyclone (C2~C1) of the suspension preheating system. The powdered raw materials are then dispersed in the high-temperature flue gas at the outlet of the second-stage cyclone 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 materials. The high-temperature flue gas carries the powdered raw materials into the first-stage cyclone C1. After gas-solid separation in the first-stage cyclone C1, the high-temperature flue gas is discharged. The powdered raw materials after the first preheating are collected and then enter 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 powdered raw materials is achieved.

[0043] The preheated powdered raw materials from the fourth-stage cyclone C4 enter the decomposition furnace. In the high-temperature environment of the decomposition furnace (the controlled temperature is 850℃), on the one hand, dehydroxylation reaction occurs to produce active calcined clay. On the other hand, in the high-temperature environment, the added CaO powder reacts with Fe2O3 in the clay in a solid phase: 2CaO + Fe2O3=(CaO)2•Fe2O3. The Gibbs free energy of this reaction is -8716.15kcal / mol, which is significantly less than 0. It is spontaneous at high temperature and can generate stable dicalcium ferrite. The generation of dicalcium ferrite prevents the iron-containing minerals in the calcined clay from being oxidized and converted into magnetite during the suspension cooling stage, which fundamentally avoids the possibility of the calcined clay turning into red.

[0044] The calcined clay enters the fifth-stage cyclone 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.

[0045] The suspension cooling system is divided into two sections, such as Figure 1 As shown in the figure, the first section is composed of the first stage cyclone CC1 of the calcined clay suspension cooling system and the second stage cyclone CC2 of the calcined clay suspension cooling system, which are connected in series 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. In this embodiment, the required amount of air is about 68000m 3 / h. The second stage is composed of two cyclones in series, namely, the third stage cyclone CC3 of the calcined clay suspension cooling system and the fourth stage cyclone CC4 of the calcined clay suspension cooling system, which are used to cool the calcined clay at medium and low temperatures, and the cooling medium is ambient air. The amount of air used is adjusted according to the cooling temperature required by the final product. In this embodiment, when the temperature of the calcined clay is cooled to below 100°C, the required amount of air is about 94,000m 3 / h. After the air in the second cooling section cools the calcined clay, it can be used as low-temperature waste heat air for the pretreatment process of preparing the clay raw materials into powdered raw materials, namely, drying and grinding. The calcined clay is finally collected as a product after gas-solid separation in the fourth-stage cyclone CC4 of the suspension cooling system. The product color is gray.

[0046] experiment: The theoretical addition amount of CaO powder depends on the iron content in the clay, that is, it is determined by the stoichiometric ratio (2:1) of CaO and Fe2O3 to form 2CaO•Fe2O3.

[0047] On the basis of Example 1 and Example 2, the iron content in different clays was investigated. To make the product appear gray in color, the amount of CaO powder added was as shown in the following table.

[0048]

[0049] Adjust according to the above addition amount and the product color will be gray.

[0050] 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.

[0051] 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 following steps are involved: 1) After the clay raw material is crushed, dried and ground into a micron-sized powdered raw material, a CaO powdered material is added according to the iron content in the clay and mixed evenly to obtain a mixed powdered raw material; 2) feeding the mixed powdered raw material in step 1) into the connecting pipe between the first-stage cyclone and the second-stage cyclone in the suspension preheating system; and dispersing the mixed powdered raw material into the high-temperature flue gas at the outlet of the second-stage cyclone through a spreading device provided at that location in the connecting pipe, so that 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 powdered raw materials into the first-stage cyclone. After gas-solid separation in the first-stage cyclone, the high-temperature flue gas is discharged. The powdered raw materials after the first preheating are collected and then enter 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 powdered raw materials is achieved. 3) The preheated powdered raw materials from the last stage cyclone in the suspension preheating system enter the decomposition furnace. In the high temperature environment of the decomposition furnace, on the one hand, a dehydroxylation reaction occurs to produce active calcined clay. On the other hand, in the high temperature environment, the added CaO powder reacts with Fe2O3 in the clay to produce stable dicalcium ferrite. The formation of dicalcium ferrite prevents the iron-containing minerals in the calcined clay from being oxidized and converted into magnetite during the suspension cooling stage. 4) The calcined clay 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.

2. The method for controlling the color of high iron content calcined clay according to claim 1, characterized in that: The CaO powdery material is CaO powder and limestone powder or a powdery material that can provide CaO, or other powdery materials that can generate CaO at high temperature.

3. The method for controlling the color of high iron content calcined clay according to claim 1 or 2, characterized in that: The amount of CaO powder material added is 1.05 to 1.15 times the theoretical amount based on the mass of CaO.

4. The method for controlling the color of high iron content calcined clay according to claim 3, characterized in that: The fuel in the decomposition furnace is fossil fuel or biomass alternative fuel; the high-temperature combustion air for fuel combustion comes from the downstream cooling system.

5. The method for controlling the color of high iron content calcined clay according to claim 4, characterized in that: The temperature in the decomposition furnace is controlled at 850℃±50℃.

6. A device for controlling the color of high-iron calcined clay, used in the method for controlling the color of high-iron clay as claimed in claim 1, 4 or 5, characterized in that: The device 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 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); the clay raw material suspension preheating system (1) is composed of cyclones connected in series, with the number of series stages being 2 to 6; the cyclones connected in series can be combined in multiple rows in parallel according to the production scale; the clay raw material suspension calcining section system (2) comprises a decomposition furnace and a cyclone; the calcined clay suspension cooling system (3) enters the decomposition furnace together with the fuel; the decomposition furnace and the cyclone are connected through a pipeline.

7. The device for controlling the color of high iron content calcined clay as claimed in claim 6, characterized in that: The cyclone in the clay raw material suspension preheating system (1) is a four-stage cyclone, and the four-stage cyclone comprises a first-stage cyclone, a second-stage cyclone, a third-stage cyclone and a fourth-stage cyclone.

8. The device for controlling the color of high iron content calcined clay according to claim 6 or 7, 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.

9. The device for controlling the color of high iron content calcined clay as claimed in claim 8, characterized in that: The multi-stage cyclone in the calcined clay suspension cooling system (3) is 2-6 stages.

10. The device for controlling the color of high iron content calcined clay according to claim 6 or 8, characterized in that: 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.

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