Method for producing calcined clay

Abstract

To produce fired clay showing a color tone similar to that of cement without requiring the use of a reducing agent.SOLUTION: Supplying a clay raw material to a line, calcining the clay raw material in a stream of a gas having a low oxygen concentration, mixing a first calcined clay obtained after performing step (b) with a low-temperature first powder in an atmosphere of the gas having a low oxygen concentration, and primarily cooling the first calcined clay to a temperature of 600 °C or lower; The method includes a step (d) of further lowering the temperature of the second fired clay by secondary cooling in a gas or vacuum atmosphere having a temperature lower than that of the second fired clay and having an oxygen concentration higher than that of the gas constituting the atmosphere during the execution of the step (c), and a step (e) of recovering the cooled fired clay having a temperature lowered by the execution of the step (d).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing fired clay, and more particularly to a method for producing fired clay suitable for use as an admixture for cement. [Background technology]

[0002] In the existing cement industry, a process is carried out to produce cement clinker from limestone, the main raw material for cement. During this process, a decarbonation reaction occurs in the limestone, generating CO2. For this reason, the cement industry is considering a method to reduce CO2 emissions by producing blended cement, which is obtained by mixing a certain proportion of additives with cement, thereby reducing the proportion of cement clinker used.

[0003] In recent years, outside of Japan, the use of calcined clays (such as kaolin and bentonite) that exhibit pozzolanic activity, similar to coal ash, as admixtures (hereafter referred to as "calcined clay") has been gaining popularity, and standardization of such materials is also underway. However, in Japan, there are currently no standards for blended cements that use calcined clay. As a result, there is little knowledge about the manufacturing methods and quality of blended cements that use calcined clay, and new technologies need to be established in order to utilize calcined clay.

[0004] When calcined clay is used as a cement admixture, it is important to suppress its effect on the color of the cement.

[0005] Clay raw materials (clay minerals) contain iron (Fe). In the process of producing fired clay, the iron contained in the clay raw materials is oxidized to Fe2O3 during the firing / cooling process. Fe2O3 has a reddish color. Since cement has a grayish color, there is a concern that if fired clay, which has a reddish color, is mixed with cement, it may cause abnormalities in the color of the cement / concrete.

[0006] A conventional method for controlling the color tone of fired clay is disclosed in Patent Document 1 below. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2022 / 058206 Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Document 1 describes a method for controlling the color tone of fired clay raw materials by introducing a reducing agent such as oil or hydrogen from the outside, bringing the fired clay raw materials into contact with the reducing agent, and then cooling them in the air. However, the use of a reducing agent increases the production cost of fired clay.

[0009] In view of the above problems, the present invention aims to enable the production of fired clay that exhibits a color similar to that of cement by suppressing the oxidation of clay without the need for the use of a reducing agent. [Means for solving the problem]

[0010] The method for producing calcined clay according to the present invention is as follows: (a) feeding a clay feedstock into the line; (b) calcining the clay raw material in a stream of gas having a low oxygen concentration; The first fired clay, which is the clay raw material obtained after the step (b), is mixed with a first powder material having a temperature lower than that of the first fired clay in an atmosphere of a gas having a low oxygen concentration, and then cooled to a temperature of 600 ° C. or less. Step (c); The second fired clay, which is the first fired clay whose temperature has been reduced by the execution of the step (c), is cooled in a gas or vacuum atmosphere at a temperature lower than that of the second fired clay and having a higher oxygen concentration than the gas constituting the atmosphere during the execution of the step (c), to further reduce the temperature. Step (d); and (e) recovering the cooled fired clay, which is the second fired clay whose temperature has been reduced by carrying out the step (d).

[0011] In this specification, the term "clay raw material" refers to a substance whose main component is a clay mineral such as kaolinite or montmorillonite.

[0012] When clay raw material is fired at high temperatures exceeding 600°C, a gray-toned magnetite phase is produced. When this fired clay is cooled in an atmospheric environment, it transforms into a reddish hematite phase during the cooling process, resulting in the production of fired clay with a reddish color. The method using a reducing agent as described in Patent Document 1 is thought to be intended to forcibly reduce the component (Fe2O3) that exhibits hematite during the cooling process and transform it into a component (Fe3O4) that exhibits magnetite, thereby giving the product a gray color.

[0013] According to the method of the present invention, the development of a reddish hue in the cooled fired clay can be suppressed without using a reducing agent, resulting in a gray-based color. In this method, the clay raw material is calcined in an airflow of a gas atmosphere with a low oxygen concentration (appropriately referred to as an "oxygen-poor atmosphere"), and then cooled in the oxygen-poor atmosphere. In other words, the clay raw material is continuously placed in an oxygen-poor atmosphere from the calcination process to the cooling process. As a result, it is presumed that the transformation of the fired clay into a reddish hematite phase is suppressed during the cooling process, making it possible to maintain the cooled fired clay in a gray-based magnetite phase. This point will be described later with reference to the examples.

[0014] Furthermore, through intensive research by the present inventors, it has been found that after calcined clay is cooled to a predetermined temperature of 600°C or less in an oxygen-poor atmosphere, it can be cooled in an oxygen-containing atmosphere without causing a change to a reddish color tone.

[0015] Therefore, as in the above method, in step (c), a low-temperature powder (first powder) and calcined clay are mixed in an oxygen-poor atmosphere, followed by primary cooling to a predetermined temperature of 600°C or less, and then secondary cooling in an oxygen-containing atmosphere such as air or a vacuum atmosphere, thereby obtaining calcined clay in which the change to a reddish color tone is suppressed. The predetermined temperature is more preferably 500°C or less. In this specification, the high-temperature calcined clay obtained by carrying out the calcination step (b) is referred to as the "first calcined clay," and the first calcined clay after primary cooling in step (c) is referred to as the "second calcined clay," and the two are distinguished from each other.

[0016] The step (b) of calcining the clay raw material is preferably carried out in an air stream having an oxygen concentration of 2% or less without introducing a reducing agent from the outside. The oxygen concentration of the gas forming the air stream is more preferably 0% to 1%, and particularly preferably 0% to 0.5%.

[0017] More specifically, step (b) includes the steps of supplying the clay raw material to a firing facility (firing furnace) to which fuel is supplied, and transporting the fired clay raw material to a location where a cooling step is performed using the firing exhaust gas flow. While any of liquid, gaseous, and solid fuels can be used as the fuel, fuels that can be burned at as low an air ratio as possible are preferred in order to reduce the oxygen concentration of the firing exhaust gas. From this perspective, gaseous fuels such as LNG are particularly preferred. The use of gaseous fuels is also expected to facilitate the adjustment of the oxygen concentration of the firing atmosphere (the firing exhaust gas flow). Recycled fuels such as waste oil, refuse-derived fuel (RDF), and waste plastics can also be used as fuels.

[0018] There are no restrictions on the type of kiln as long as it has a facility and structure that can ensure the residence time (firing time) of the clay raw material. However, from the viewpoint of keeping the clay raw material within the flow of high-temperature firing exhaust gas for a certain period of time, a loop duct type kiln is preferably used.

[0019] Calcination of clay raw materials is intended to convert crystalline clay minerals into a highly reactive (highly active) amorphous state, in other words, to activate the clay minerals' pozzolanic properties, because the inactive calcined clay, when mixed with cement as a cement mix or concrete admixture, can lead to a decrease in the strength of the resulting blended cement and concrete produced from it.

[0020] There is a preferred range for the temperature (firing temperature) at which the clay raw material is calcined. If the firing temperature is too low, the clay raw material may not be sufficiently amorphized, resulting in a calcined clay with low activity. Conversely, if the firing temperature is too high, the transformation from the amorphous state to a crystalline mineral component (mullite state) may proceed, resulting in a calcined clay with low activity.

[0021] From this viewpoint, the firing temperature in step (b), i.e., the temperature of the air current in the oxygen-poor atmosphere in which the clay raw material is present, is preferably 550°C to 1,000°C, more preferably 600°C to 900°C, and particularly preferably 650°C to 850°C.

[0022] The execution time of step (b) is set depending on the firing temperature and the amount of recycled fuel used, but is preferably 0.5 to 10 seconds, more preferably 1 to 5 seconds. As the firing furnace, a mode in which fuel is burned with a burner, or a mode in which high-temperature hot air is blown, can be adopted. More specifically, step (b) may be a step in which the clay raw material is calcined in the short firing time exemplified above by transporting the clay raw material on a high-temperature gas flow (air current) to the facility in which the subsequent step (c) is executed. Note that the clay raw material to be calcined in step (b) is one in which the particle size of the particles constituting the clay raw material is equal to or smaller than the median diameter (D 50 ) is preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, and particularly preferably 5 μm to 20 μm.

[0023] The cooling step (c), like the calcination step (b), may be carried out in a gas atmosphere with an oxygen concentration of 2% or less without introducing a reducing agent from outside. Furthermore, this cooling step (c) is preferably a step of rapidly cooling the high-temperature calcined clay. Typically, it is preferable to cool the calcined clay at a cooling rate of 3°C / second or more.

[0024] As described above, in the cooling step (c), the fired clay (first fired clay), which is the clay raw material obtained after the calcination step (b), is cooled by mixing it with a low-temperature powder (first powder). The first powder used here can be one or more selected from the group consisting of cement, cement mixtures, concrete admixtures, auxiliary cementitious materials (SCM), ground clinker, raw concrete sludge, finely ground waste concrete, clinker dust, and blast furnace slag. Furthermore, a portion of the cooled fired clay recovered in step (e) can be mixed with the first fired clay as the first powder for cooling. In step (c), the ratio of the first powder to be mixed with the first fired clay is preferably 1% to 100%, more preferably 60% to 90%, of the amount of the first fired clay.

[0025] The method for mixing the first powder material with the first fired clay in an oxygen-poor atmosphere is not limited, but a method that provides excellent dispersibility is preferred.

[0026] In particular, in the calcination step (b), when the clay raw material is transported by the airflow of the calcination exhaust gas discharged from the calcination furnace, the calcination exhaust gas and the calcined clay are subsequently separated into solid-gas in a solid-gas separation facility. Therefore, by directly introducing the first powder material into this solid-gas separation facility or by introducing the first powder material into a pipe through which the airflow of the calcination exhaust gas flows toward the solid-gas separation facility, the probability of contact between the first powder material and the calcined clay in the solid-gas separation facility is increased, and high cooling performance is achieved.

[0027] More specifically, step (b) comprises: Step (b1) of charging the clay raw material into a firing furnace in which fuel is burned in an environment in which a combustion-supporting gas is supplied; and (b2) a step of transporting the clay raw material to a solid-gas separation facility by an airflow of the calcination exhaust gas discharged from the calcination furnace, The step (c) a step (c1) including at least one of a step of directly introducing the first powder material into the solid-gas separation facility and a step of introducing the first powder material into the solid-gas separation facility through a pipe through which the firing exhaust gas flows; The method may include a step (c2) of mixing the first powder material and the calcined clay in an atmosphere of gas with a low oxygen concentration containing the calcination exhaust gas in the solid-gas separation equipment.

[0028] In addition, when the first powder material is introduced into a pipe through which the combustion exhaust gas flow flows toward the solid-gas separation equipment, a mixer such as a static mixer may be provided in the pipe in order to further improve dispersibility.

[0029] The step (d) may include a step of mixing the second calcined clay discharged from the solid-gas separation equipment after the step (c2) with a gas stream containing air at a temperature lower than that of the second calcined clay.

[0030] As described above, the fired clay (second fired clay) after step (c) is cooled to a temperature of 600°C or less in an oxygen-poor atmosphere. Therefore, even if it is subsequently cooled in a gas containing air, the change to a reddish color tone is suppressed.

[0031] Furthermore, this gas containing atmospheric air is used to cool the second fired clay in step (d), and its temperature rises. Therefore, by using this heated gas as a combustion-supporting gas in the firing furnace, thermal efficiency can be improved. If the amount of this gas is large, a portion of it can be bypassed and used in other heat utilization equipment. Even though the heated gas is still low compared to the firing temperature in the firing furnace, if an excessive amount of air is introduced into the firing equipment, it may result in problems such as increased fuel consumption, worsening fuel efficiency, or a larger overall equipment size. To prevent such problems, it is preferable to introduce only the amount of heated gas necessary for fuel combustion into the firing furnace as a combustion-supporting gas, and the excess amount is bypassed and used in other heat utilization equipment.

[0032] The step (d) A step (d1) of cooling the second fired clay discharged from the solid-gas separation equipment by mixing it with a first cooling gas flow containing atmospheric air, which has a temperature lower than that of the second fired clay; A step (d2) of separating the mixture of the first cooling gas and the second calcined clay into solid and gas after the step (d1) is performed; The third fired clay, which is the second fired clay after cooling and discharged through the step (d2), is mixed with a second cooling gas flow containing atmospheric air, which is at a lower temperature than the third fired clay, and cooled (d3); After the step (d3), a step (d4) of solid-gas separating the mixture of the second cooling gas and the third calcined clay is included. the first cooling gas includes the second cooling gas after heating that has been discharged through the step (d4), The step (e) may be a step of recovering the cooled third fired clay discharged through the step (d4) as the cooled fired clay.

[0033] According to the above method, the fired clay (second fired clay) after primary cooling is cooled with a relatively high temperature first cooling gas, and then further cooled with a relatively low temperature second cooling gas. That is, the second fired clay is cooled in two stages, improving the cooling efficiency. However, the present invention does not exclude an embodiment in which the second fired clay is cooled in three or more stages.

[0034] When mixing the calcined clay (second calcined clay) into the low-temperature airflow, it is preferable to use discharge equipment with a sealing function, such as a double flap damper or rotary feeder, to prevent the airflow from flowing back toward the side where the calcined clay is being introduced. The same applies when mixing the first powder material into the airflow of the calcination exhaust gas that transports the first calcined clay.

[0035] In another embodiment, step (d) comprises: A step (d1) of cooling the second fired clay discharged from the solid-gas separation equipment by mixing it with a first cooling gas flow containing atmospheric air, which has a temperature lower than that of the second fired clay; A step (d2) of separating the mixture of the first cooling gas and the second calcined clay into solid and gas after the step (d1) is performed; The third fired clay, which is the second fired clay after cooling and discharged through the step (d2), is conveyed by an air flow while being raised and mixed with a second powder material having a lower temperature than the third fired clay. Step (d3); and a step (d4) of separating the gas and solid mixture into solids after the step (d3), The step (c) is a step of introducing a part of the mixture containing the cooled third fired clay discharged through the step (d4) into the solid-gas separation equipment while dropping it as the first powder material through a chute, The step (e) may be a step of recovering a portion of the mixture containing the cooled third calcined clay discharged through the step (d4) as the cooled calcined clay.

[0036] Here, the second powder material can be one or more selected from the group consisting of cement, cement mixtures, concrete admixtures, auxiliary cement materials (SCM), ground clinker, raw concrete sludge, fine waste concrete, clinker dust, and blast furnace slag, as described above.

[0037] According to the above method, the solids obtained after the solid-gas separation in step (d4) can be mixed with the high-temperature first fired clay while being dropped down the chute, so that the installation of a separate power source for transportation such as a belt conveyor is not necessarily required. In addition, when using this method, a dispersion plate may be provided at the end of the chute to further improve the dispersibility of the mixture.

[0038] In yet another embodiment, step (d) comprises: A step (d1) of feeding the second fired clay discharged from the solid-gas separation equipment into a long stirring equipment in which a gas containing air or a vacuum atmosphere at a temperature lower than that of the second fired clay is formed from an inlet; A step (d2) of conveying the second fired clay in the longitudinal direction while cooling it while stirring it in the stirring equipment; Step (d3) of discharging the cooled second fired clay from a discharge port located away from the inlet in the longitudinal direction; The step (e) may be a step of recovering the cooled second fired clay discharged through the step (d3) as the cooled fired clay.

[0039] According to the above method, the second fired clay is stirred in the stirring equipment, and the second fired clay is efficiently cooled in a low-temperature atmosphere. In addition, since physical stirring is performed in the equipment, the amount of gas required to cool the second fired clay can be reduced.

[0040] In case the temperature inside the mixing equipment rises, a cooling mechanism may be attached to the mixing equipment. For example, the mixing equipment may be equipped with a water sprinkler function so that it can be cooled with water. In this case, the water vapor generated inside the mixing equipment may be discharged from the mixing equipment and used for heat recovery.

[0041] As another example, a low-temperature fluid may be passed through the inside of stirring blades provided in the stirring equipment.

[0042] As yet another example, the stirring equipment may be cooled by periodically passing a low-temperature gas through the stirring equipment.

[0043] As another example, the second fired clay may be stirred while periodically passing a low-temperature gas through the stirring equipment.

[0044] That is, the step (d) includes a step (d4) of introducing a first cooling gas flow containing atmospheric air, which is lower in temperature than the second fired clay, into the stirring equipment from a first vent port longitudinally separated from the inlet, The step (d2) may be a step of conveying the second fired clay in the longitudinal direction while stirring the second fired clay introduced from the inlet and the airflow introduced from the first air outlet, which flows countercurrently to the second fired clay, in the stirring equipment.

[0045] In this case, a part of the gas heated in the stirring equipment may be used as the combustion-supporting gas. That is, the step (d) includes a step (d5) of discharging the first cooling gas, the temperature of which has been increased by the execution of the step (d2), through a second vent port provided in the stirring equipment at a position closer to the inlet than the first vent port in the longitudinal direction, A part of the gas discharged in the step (d5) may be used as the combustion-supporting gas.

[0046] Furthermore, the low-temperature powder material may be mixed in the stirring equipment. More specifically, the step (d) may include a step (d6) of feeding a part of the mixture containing the cooled third calcined clay, which has been discharged through the step (d3), into the stirring equipment from the same feeding port or another feeding port located near the feeding port in the longitudinal direction.

[0047] The calcination step (b) may be carried out after preheating the clay raw material by mixing the clay raw material with the exhaust gas flow discharged from the calcination furnace. That is, the method for producing calcined clay may include a step (a1) of mixing the clay raw material supplied in the step (a) with the exhaust gas flow discharged after the execution of the step (b) and preheating it.

[0048] In this case, the heat of the exhaust gas (preheated exhaust gas) after being used for preheating may be utilized in another heat exchanger, and the dust contained in the exhaust gas may then be mixed as the first powdered material with the first fired clay obtained after the calcination step (b).

[0049] That is, the method for producing fired clay further includes, after carrying out the step (a1), a step (f) of separating the solid and gas containing the preheated clay raw material; and a step (g) of cooling the preheated exhaust gas discharged after the step (f), The step (b) is a step of calcining the clay raw material discharged after the step (f), The first powder material may include dust contained in the preheated exhaust gas cooled by carrying out the step (g).

[0050] As mentioned above, the preheated exhaust gas discharged after step (f) is derived from the calcination exhaust gas discharged from the calcination furnace. The calcination exhaust gas contains moisture produced by dehydrating the clay raw material, and the moisture condensed by the heat exchange may corrode metal equipment or cause an abnormal noise known as water hammer. From this perspective, it is preferable to provide a drainage mechanism such as a drain to the mechanism for cooling the preheated exhaust gas, i.e., the heat exchange equipment.

[0051] When the oxygen concentration of the preheated exhaust gas is 2% or less, a part of the preheated exhaust gas may be used as a dust airflow, and the airflow may be mixed as is with the first fired clay.

[0052] Step (e) can be a step of recovering the cooled fired clay using solid-gas separation equipment. If the clay has been sufficiently cooled (for example, below 300°C), the cooled fired clay can be recovered using a bag filter. [Effects of the Invention]

[0053] According to the present invention, it is possible to produce a highly active calcined clay that exhibits a color tone similar to that of cement without using a reducing agent. [Brief explanation of the drawings]

[0054] [Figure 1] 1 is a flowchart showing an example of the procedure for producing fired clay according to the present invention. [Figure 2] 1 is a conceptual block diagram showing a system for carrying out a method for producing fired clay according to the present invention. FIG. [Figure 3] 1 is a block diagram showing a first embodiment of a system for carrying out a method for producing fired clay according to the present invention. FIG. [Figure 4] 4 is a diagram illustrating the system shown in FIG. 3 with solid and gas flows noted. [Figure 5] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 6]5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 7] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 8] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 9] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 10] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 11] FIG. 1 is a block diagram schematically illustrating a second embodiment of a system for carrying out a method for producing calcined clay according to the present invention. [Figure 12] 12 is a diagram illustrating the system shown in FIG. 11 with solid and gas flows. [Figure 13] 13 is an enlarged view of a part of the system shown in FIGS. 11 and 12. [Figure 14] FIG. 10 is a block diagram schematically illustrating a third embodiment of a system for carrying out the method for producing fired clay according to the present invention. [Figure 15] 15 is a diagram illustrating the system shown in FIG. 14 with solid and gas flows noted. [Figure 16] 16 is an enlarged view of a part of the system shown in FIGS. 14 and 15. [Figure 17] 16 is an enlarged view of a part of the system shown in FIGS. 14 and 15. [Figure 18] 18 is a diagram schematically illustrating a detailed configuration example of the stirring equipment 35 shown in FIG. 17. [Figure 19] 10 is another enlarged view of a portion of a modified example of the third embodiment of the system for carrying out the method for producing calcined clay according to the present invention. [Figure 20] 1 is a diagram schematically illustrating the configuration of a first test facility used in verification. [Figure 21] 1 is a diagram schematically illustrating the configuration of a second test facility used in the verification. [Figure 22] 1 is a graph showing the results of verifying the relationship between the firing temperature and the activity of fired clay. [Figure 23]1 is a graph showing the results of verifying the relationship between firing time and the activity of fired clay. [Figure 24] 1 is a graph showing the results of verifying the relationship between the oxygen concentration in the firing atmosphere and the color tone of the fired clay. [Figure 25] 1 is a graph showing the results of verifying the relationship between the oxygen concentration in the cooling atmosphere and the color tone of the fired clay. [Figure 26] 1 is a graph showing the results of examining the relationship between the temperature at which cooling in an oxygen-poor atmosphere is transitioned to cooling in an air atmosphere and the color tone of the fired clay. DETAILED DESCRIPTION OF THE INVENTION

[0055] The present invention relates to a method for producing calcined clay, and more particularly to a method for producing calcined clay with high activity by calcining a clay raw material. Hereinafter, an embodiment of the method for producing calcined clay according to the present invention (hereinafter referred to as "this production method") will be described with reference to the drawings. The drawings are schematic illustrations, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily correspond.

[0056] [Overall Overview] 1 is a flowchart showing an example of the execution procedure of this manufacturing method. In the following description, the step numbers shown in FIG. 1 will be referred to as appropriate.

[0057] Figure 2 is a conceptual block diagram showing a system for carrying out this manufacturing method. In Figure 2, the flow of solids containing the clay raw material is shown by a straight line, the flow of gas used for combustion in the firing equipment is shown by a dashed line, and the flows of exhaust gas discharged from the firing equipment and gas used or used to cool the fired clay are shown by a two-dot chain line.

[0058] (Step S1) The clay raw material CR is supplied to the processing line. The clay raw material CR is a substance whose main component is a clay mineral such as kaolinite or montmorillonite, and is preferably crushed in advance. At the time of supplying the clay raw material CR to the processing line, the particle size of the particles constituting the clay raw material CR is determined by the median diameter (D 50 ) is preferably 5 μm to 100 μm, more preferably 5 μm to 50 μm, and particularly preferably 5 μm to 20 μm. The particle size of the clay raw material CR can be measured using a laser diffraction / scattering particle size distribution measuring device, for example, a Microtrac Bell MW3300EXII, using ethanol as a dispersion medium, and measuring after one minute of ultrasonic dispersion. 50 The value means the particle size at cumulative 50% in the volume-based particle size distribution.

[0059] Step S1 corresponds to the process (a).

[0060] (Step S2) The supplied clay raw material CR is preheated in the preheating equipment 41. Specifically, the clay raw material CR is preheated by being mixed with the relatively high-temperature exhaust gas GE discharged from the first cooling equipment 20, which has a solid-gas separation function. In this case, the preheating equipment 41 corresponds to a pipe through which the clay raw material CR and the exhaust gas GE are transported in a mixed state. As will be described later, this exhaust gas GE has an extremely low oxygen concentration, typically 2% or less. Hereinafter, an atmosphere with an oxygen concentration of 2% or less will be referred to as an "oxygen-poor atmosphere" as appropriate.

[0061] Step S2 corresponds to the step (a1).

[0062] (Step S3) The mixture of high-temperature exhaust gas GE and preheated clay raw material CR is sent to solid-gas separation equipment 43, where it is separated into solids and gas. The preheated clay raw material CR recovered from solid-gas separation equipment 43 is sent to firing equipment 10. In firing equipment 10, a high-temperature environment is formed by burning fuel VD in an environment where combustion-supporting gas GF is supplied, and exhaust gas GE generated by the combustion is discharged. The clay raw material CR is supplied to the high-temperature environment formed within firing equipment 10, and is transported by the airflow of exhaust gas GE.

[0063] In the calcination equipment 10, the fuel VD is combusted using the combustion-supporting gas GF to generate an exhaust gas GE having a low oxygen concentration. The oxygen concentration of the exhaust gas GE is preferably 2% or less, more preferably 0% to 1%, and particularly preferably 0% to 0.5%. The temperature of the exhaust gas GE generated in the calcination equipment 10 is preferably 550°C to 1,000°C, more preferably 600°C to 900°C, and particularly preferably 650°C to 850°C. In this embodiment, there is no need to introduce a reducing agent when performing combustion in the calcination equipment 10.

[0064] The clay raw material CR is calcined when it is present in the exhaust gas GE. More specifically, the clay raw material CR is calcined and converted into an amorphous state. The calcined clay CF (hereinafter referred to as "first calcined clay CF") produced by this calcination process is transported by the exhaust gas GE and sent to the first cooling facility 20.

[0065] The firing time of the clay raw material CR is set depending on the firing temperature, type of fuel, amount of fuel used, etc., but is preferably 0.5 to 10 seconds, and more preferably 1 to 5 seconds. The firing time here refers to the time during which the clay raw material CR is present in the airflow of the high-temperature exhaust gas GE. The firing time may also be the time from when the clay raw material CR is introduced into the firing equipment 10 until the mixture of the clay raw material CR and the high-temperature exhaust gas GE is separated into solid and gas by the solid-gas separation function of the first cooling equipment 20.

[0066] The exhaust gas GE discharged from the solid-gas separation equipment 43 is at a high temperature, and therefore may be heat exchanged in another exhaust heat utilization equipment 51. However, because the exhaust gas GE is a gas generated when the clay raw material CR is fired, moisture generated by dehydration of the clay raw material CR during the firing process may evaporate and mix with the exhaust gas GE, and condense as the exhaust gas GE is cooled in the heat exchanger in the exhaust heat utilization equipment 51. If liquid moisture exists in the piping route, it may corrode the equipment or cause an abnormal noise known as water hammer. From this perspective, the exhaust heat utilization equipment 51 may be provided with a drainage mechanism (not shown), such as a drain.

[0067] Step S3 corresponds to the step (b).

[0068] (Step S4) In the first cooling equipment 20, a powder material QD (hereinafter referred to as "first powder material QD") that is at a lower temperature than the first fired clay CF is mixed with the first fired clay CF. The first cooling equipment 20 has a solid-gas separation function, and the first fired clay CF, which has been transported on the airflow of the high-temperature exhaust gas GE, is mixed with the first powder material QD, thereby cooling the first fired clay CF by the first powder material QD. In this step S4, the first fired clay CF is cooled to a temperature of 600°C or less.

[0069] Thereafter, the mixture is separated into solid and gas by the first cooling equipment 20, and is discharged as a mixture of the first fired clay CF and the first powder material QD.

[0070] The first fired clay CF and the first powder QD are mixed in the atmosphere of the exhaust gas GE. That is, this atmosphere is an atmosphere with a low oxygen concentration (an oxygen-poor atmosphere) following the calcination process for the clay raw material CR. That is, in this step S4, the first fired clay CF is cooled to a temperature of 600 ° C or less in the oxygen-poor atmosphere.

[0071] Step S4 corresponds to the step (c). In this embodiment, when the first cooling equipment 20 cools the high-temperature first fired clay CF, it is not necessary to introduce a reducing agent.

[0072] (Step S5) The first fired clay CF (hereinafter referred to as "second fired clay CFA") cooled by executing step S4 is further cooled in the second cooling equipment 30. In other words, the first fired clay CF is cooled in multiple stages. That is, the first fired clay CF is primarily cooled by the first cooling equipment 20, and then secondarily cooled by the second cooling equipment 30.

[0073] As will be described later with reference to the examples, when calcined clay is cooled to a temperature of 600°C or less in an oxygen-poor atmosphere, the transformation to reddish hematite is suppressed, and the clay exhibits a grayish color tone, even when subsequently cooled in an oxygen-containing atmosphere. Therefore, cooling using atmospheric air is possible in the second cooling equipment 30. In this case, a portion of the air used for cooling and heated can be used as a combustion-supporting gas GF in the calcination equipment 10 or can be used as heat in other heat exchange equipment.

[0074] As another example, step S5 can be a process in which the second calcined clay CFA is cooled by stirring it in a gas such as the atmosphere or in a low-temperature vacuum atmosphere using equipment with a stirring function as the second cooling equipment 30.

[0075] In this embodiment, there is no need to introduce a reducing agent when the second calcined clay CFA is cooled in the second cooling equipment 30.

[0076] Step S5 corresponds to step (d).

[0077] (Step S6) The second fired clay CFA (hereinafter referred to as "third fired clay CFC") after being cooled in the second cooling facility 30 is recovered as cooled fired clay. This cooled fired clay is inhibited from transforming into reddish hematite and has a grayish color tone, making it suitable for use as an admixture for cement.

[0078] Step S6 corresponds to step (e).

[0079] In this manufacturing method, step S2 can be omitted. In this case, the system 1 shown in Fig. 2 may not include the preheating equipment 41 and the solid-gas separation equipment 43, and the clay raw material CR may be directly supplied to the firing equipment 10.

[0080] The details of the embodiment of the manufacturing method will be described below with reference to the drawings.

[0081] [First embodiment] A first embodiment of the present manufacturing method will be described with reference to the drawings. Note that the content described above in the "Overall Overview" section will be appropriately simplified or omitted to avoid duplication.

[0082] Figures 3 and 4 are conceptual block diagrams that schematically show a system for carrying out the manufacturing method of this embodiment. Figure 3 is a drawing in which symbols corresponding to those in Figure 2 are used, and Figure 4 is a drawing in which the flows of solids and gases are also shown in the system shown in Figure 3. Figures 5 to 10 correspond to enlarged views of parts of the systems shown in Figures 3 and 4.

[0083] As shown in Fig. 5, typically, the clay raw material CR is supplied to the line from a feeder 61 (step S1). In the example of Fig. 5, the clay raw material CR is supplied to a pipe 42 and transported to a pipe 41D side.

[0084] The pipe 41D forms a flow path for transporting a mixture of high-temperature exhaust gas GE and clay raw material CR. That is, the clay raw material CR is preheated by the airflow (exhaust flow) of high-temperature exhaust gas GE while being transported through the pipe 41D (step S2). In this case, the pipe 41D forms the preheating equipment 41.

[0085] In this embodiment, the high-temperature exhaust gas GE is discharged toward the pipe 41D through a pipe 71a connected to a cyclone 21H, which is one element of the first cooling equipment 20 described later.

[0086] The mixture of high-temperature exhaust gas GE and clay raw material CR transported through pipe 41D is introduced into cyclone 43H, which is an example of solid-gas separation equipment 43, and separated into solids and gas. High-temperature exhaust gas GEA (preheated exhaust gas GEA) is discharged from pipe 72a connected to cyclone 43H. The preheated exhaust gas GEA may be discharged as outside air, but because it is at a high temperature of 200°C to 400°C, it may also be introduced into exhaust heat utilization equipment 51 as shown in FIG. 9. Examples of the exhaust heat utilization equipment 51 include waste heat power generation and other heat utilization equipment.

[0087] As shown in Figure 9, after the heat of the preheated exhaust gas GEA is utilized in the exhaust heat utilization equipment 51, the temperature of the preheated exhaust gas GEA (hereinafter referred to as "exhaust gas GEB") decreases, and the temperature of the dust DE contained in the exhaust gas GEB also decreases. Therefore, this dust DE can also be utilized for cooling the first fired clay CF. This point will be described later.

[0088] As shown in FIGS. 5 and 6, preheated clay raw material CR is discharged from pipe 72b connected to cyclone 43H and transported toward firing equipment 10. In the example shown in FIG. 6, firing equipment 10 includes a firing furnace 11 and a burner 12. Fuel VD and combustion-supporting gas GF are introduced into firing furnace 11 from a fuel supply source 62. In firing furnace 11, fuel VD is combusted by burner 12 in an atmosphere of combustion-supporting gas GF to generate high-temperature exhaust gas GE. As described above, the oxygen concentration of this exhaust gas GE is preferably 2% or less, more preferably 0% to 1%, and particularly preferably 0% to 0.5%. Furthermore, as described above, the temperature of this exhaust gas GE is preferably 550°C to 1,000°C, more preferably 600°C to 900°C, and particularly preferably 650°C to 850°C. As described above, in the case of the method of this embodiment, it is not necessary to use a reducing agent when generating this exhaust gas GE.

[0089] The clay raw material CR is calcined (fired) in the high-temperature, low-oxygen atmosphere of the exhaust gas GE (step S3). During this firing process, the crystalline structure of the clay raw material CR is broken down, becoming amorphous and increasing its activity. The fired clay raw material CR, known as the first fired clay CF, is transported to the first cooling facility 20 by the high-temperature, low-oxygen atmosphere of the exhaust gas GE.

[0090] The firing time of the clay raw material CR is set to a time sufficient to convert the clay raw material CR into a first fired clay CF, which exhibits high activity. As described above, in this embodiment, the clay raw material CR is fired by placing the clay raw material CR in an atmosphere of high-temperature exhaust gas GE. More specifically, this is achieved by transporting the clay raw material CR using the airflow formed by this exhaust gas GE. To ensure the time required for the clay raw material CR to be placed in this airflow, it is preferable to connect a loop duct 14 to the exhaust outlet of the firing furnace 11. Compared to a linear duct, the use of the loop duct 14 can ensure the required residence time for the exhaust gas GE from the firing furnace 11 to reach the first cooling equipment 20 while suppressing the expansion of the equipment's occupied area.

[0091] The time for which the clay raw material CR is retained in the airflow formed by the exhaust gas GE depends on the temperature of the exhaust gas GE, etc., but is preferably 0.5 to 10 seconds, more preferably 1 to 5 seconds. By ensuring that the time for which the clay raw material CR is retained in the airflow of the high-temperature exhaust gas GE falls within the above range, it is possible to achieve the effect of completely burning off foreign matter (mostly organic matter) such as biomass contained in the clay raw material CR.

[0092] The fired clay (first fired clay CF) that has been transported by the airflow of high-temperature exhaust gas GE is introduced into a cyclone 21H, which is an element of the first cooling equipment 20, together with the airflow of exhaust gas GE, as shown in Figure 6.

[0093] 6, a first powder material QD having a temperature lower than that of the first fired clay CF is introduced into the cyclone 21H. At this time, the first powder material QD may be introduced directly into the cyclone 21H through a pipe 85a, or may be introduced into the loop duct 14 through a pipe 85b.

[0094] As described above, the first calcined clay CF is transported to the cyclone 21H by the airflow of the exhaust gas GE, which has a low oxygen concentration. Then, in the cyclone 21H or in a stage preceding it, the first powder material QD, which is at a lower temperature than the first calcined clay CF, is mixed. As a result, the first calcined clay CF is cooled by contact with the low-temperature first powder material QD in an oxygen-poor atmosphere. In particular, in the cyclone 21H, the first powder material QD and the first calcined clay CF are vigorously mixed, allowing the first calcined clay CF to be rapidly cooled (step S4).

[0095] The first calcined clay CF is mixed with the low-temperature first powder material QD in the cyclone 21H, where it is cooled to a temperature of 600°C or less and then discharged. That is, the first calcined clay CF discharged from the cyclone 21H is in a primarily cooled state and corresponds to the second calcined clay CFA described above. This second calcined clay CFA is sent to the second cooling facility 30 via pipe 71b (see FIG. 7). Meanwhile, the high-temperature exhaust gas GE separated into solid and gas in the cyclone 21H is discharged toward pipe 41D via pipe 71a, as described above.

[0096] In the example shown in FIG. 7, the second cooling equipment 30 includes a cyclone 31C and a cyclone 32C.

[0097] The cyclone 32C is connected to a pipe 74a, and the gas (first cooling gas GAB) obtained by solid-gas separation by the cyclone 32C flows through the pipe 74a. This first cooling gas GAB is a gas with a lower temperature than the second fired clay CFA discharged through the pipe 71b after being primarily cooled by the cyclone 21H. The second fired clay CFA merges with the flow of the first cooling gas GAB flowing through the pipe 74a. In order to prevent the flow of the first cooling gas GAB from flowing back toward the pipe 71b, as shown in FIG. 6, a discharge device 21F with a sealing function, such as a double flap damper or a rotary feeder, is preferably provided on the discharge outlet side of the cyclone 21H.

[0098] The second fired clay CFA is cooled by being mixed with the flow of the first cooling gas GAB flowing through the pipe 74a. This step corresponds to step (d1).

[0099] The mixture of the second calcined clay CFA and the first cooling gas GAB flowing through the pipe 74a is introduced into the cyclone 31C and subjected to solid-gas separation. This step corresponds to step (d2).

[0100] The cyclone 31C discharges gaseous GAC, which has been heated by the first cooling gas GAB due to its use in cooling the second fired clay CFA. As will be described later, the first cooling gas GAB is a gas derived from the atmosphere and therefore contains oxygen. Therefore, a portion of the gaseous GAC can be introduced into the calcination furnace 11 as a combustion-supporting gas GF. Alternatively, a portion of the gaseous GAC may be bypassed and introduced into another heat utilization facility. Here, the proportion of the gaseous GAC that is bypassed and not used as the combustion-supporting gas GF is 0% to 70%, preferably 20% to 65%, and more preferably 40% to 60%.

[0101] The cyclone 31C discharges the second fired clay CFA (hereinafter referred to as "second fired clay CFB") after being cooled by the first cooling gas GAB. This second fired clay CFB is further cooled by merging with a gas (second cooling gas GAA) that is lower in temperature than the first cooling gas GAB introduced from the atmospheric air introduction source 63 and flowing through the piping 84. This step corresponds to step (d3). Note that the piping 84 may be provided with an induced draft fan 81 as appropriate.

[0102] The mixture of the second calcined clay CFB and the second cooling gas GAA is introduced into the cyclone 32C and subjected to solid-gas separation. This step corresponds to step (d4).

[0103] The cyclone 32C discharges the gas GAB, which has been heated by the second cooling gas GAA due to its use in cooling the second fired clay CFB. This gas GAB flows through the pipe 74a as the first cooling gas GAB and is used to cool the second fired clay CFA.

[0104] The cooled second calcined clay CFB discharged from the cyclone 32C through the pipe 74b corresponds to the "third calcined clay CFC" described above. Because the temperature of the third calcined clay CFC has dropped sufficiently, it can be recovered as cooled calcined clay (step S6). The temperature of the third calcined clay CFC obtained through step S6 is preferably 500°C or less, more preferably 400°C or less, and particularly preferably 300°C or less. If the temperature of the third calcined clay CFC is approximately 300°C or less, solid-gas separation can also be performed using a bag filter instead of the cyclone 32C. In this case, the third calcined clay CFC separated by the bag filter is recovered as cooled calcined clay, and the gas separated by the bag filter is combined with the second calcined clay CFA discharged through the pipe 71b as the first cooling gas GAB.

[0105] As shown in Figure 8, a portion of the third fired clay CFC may be transported through a pipe 75 and introduced into the first cooling equipment 20 as the first powder material QD. As an example, as shown in Figure 8, a pipe 75 branching from a pipe 74b connected to the cyclone 32C is provided, and the third fired clay CFC can be introduced into the cyclone 21H constituting the first cooling equipment 20 through pipes 85a and 85b using the power of the transport equipment 64 consisting of a fan, belt conveyor, screw conveyor, bucket conveyor, flight conveyor, etc. As a result, as described above, in the cyclone 21H, the high-temperature first fired clay CF and the low-temperature first powder material QD are vigorously mixed to cool the first fired clay CF, and then sent to the second cooling equipment 30 as the second fired clay CFB.

[0106] Here, as shown in Fig. 8, a second powder material MD having a lower temperature than the first calcined clay CF may be supplied from a feeder 65 and introduced into the first cooling equipment 20 as the first powder material QD. Fig. 8 illustrates an embodiment in which a mixture of the second powder material MD and the third calcined clay CFC is mixed with the first calcined clay CF in the first cooling equipment 20 as the first powder material QD, but the first powder material QD may also consist of only the second powder material MD without containing the third calcined clay CFC. The second powder material MD may be one or more selected from the group consisting of cement, cement mixtures, concrete admixtures, auxiliary cementitious materials (SCM), ground clinker, raw concrete sludge, finely ground waste concrete, clinker dust, and blast furnace slag.

[0107] As described above, the exhaust gas GEA discharged from the solid-gas separation equipment 43 (hereinafter referred to as "preheated exhaust gas GEA") is at a high temperature (see FIGS. 3 to 5). For this reason, as shown in FIG. 9, the preheated exhaust gas GEA flowing through a pipe 72a connected to the solid-gas separation equipment 43 may be supplied as a heat source to the exhaust heat utilization equipment 51. In this manner, the step of cooling the preheated exhaust gas GEA by heat exchange typically corresponds to step (g). The preheated exhaust gas GEA (hereinafter referred to as "exhaust gas GEB") cooled by heat exchange in the exhaust heat utilization equipment 51 may be discharged directly to the outside of the system.

[0108] Incidentally, the preheated exhaust gas GEA contains dust resulting from the firing of the clay raw material CR, and as the preheated exhaust gas GEA is cooled as it passes through the exhaust heat utilization equipment 51, the temperature of the dust DE contained in the exhaust gas GEB also drops. If the dust DE is at a lower temperature than the first fired clay CF, it may be mixed with the first fired clay CF in the first cooling equipment 20 together with the second powder material MD via the piping 86. In other words, in this case, the dust DE contained in the cooled preheated exhaust gas GEA (exhaust gas GEB) constitutes part of the first powder material QD.

[0109] As described above, the oxygen concentration of the exhaust gas GE discharged from the calcination equipment 10 is preferably 2% or less, more preferably 0% to 1%, and particularly preferably 0% to 0.5%. In this case, the oxygen concentrations of the preheated exhaust gas GEA discharged from the solid-gas separation equipment 43 and the exhaust gas GEB, which is the gas after cooling, are also preferably 2% or less, more preferably 0% to 1%, and particularly preferably 0% to 0.5%.

[0110] When the oxygen concentration of the exhaust gas GEB is 2% or less, even if this exhaust gas GEB is introduced into the first cooling equipment 20, the cooling atmosphere for the first fired clay CF can continue to be in an oxygen-poor state. Therefore, when the oxygen concentration of the exhaust gas GEB is 2% or less, a portion of the exhaust gas GEB can be used as an airflow for transporting the dust DE to the first cooling equipment 20. In detail, as shown in FIG. 9, a valve for adjusting the flow rate is provided in the piping 86 as appropriate, and a portion of the exhaust gas GEB flowing through the piping 87 may be branched via the piping 86 and merged with the piping 75 through which the third fired clay CFC transported for cooling flows (see also FIG. 10). In this case, a check valve or the like may be provided in the piping as appropriate to prevent the airflow of the exhaust gas GEB from flowing back toward the feeder 65 for the second powder material MD or the cyclone 32C, which is the supply source of the third fired clay CFC.

[0111] The exhaust gas GE is a gas generated when the clay raw material CR is fired. Therefore, moisture generated by dehydration of the clay raw material CR during the firing process vaporizes and is mixed into the exhaust gas GE and the preheated exhaust gas GEA. Here, when the heat of the preheated exhaust gas GEA is utilized in the waste heat utilization equipment 51, condensation may occur as the preheated exhaust gas GEA is cooled through the heat exchanger. The presence of liquid moisture in the piping route may corrode the equipment or cause an abnormal noise known as water hammer. From this perspective, the heat exchanger installed in the waste heat utilization equipment 51 may be provided with a drainage mechanism (not shown), such as a drain.

[0112] The exhaust gas GE discharged from the firing furnace 11 has a low oxygen concentration (preferably 2% or less), and the clay raw material CR is fired while present in the atmosphere of this exhaust gas GE. During this firing, reducing gases such as carbon monoxide may be generated. However, the concentration of the reducing gas generated during this firing is at most 1% or less, and is typically an extremely low concentration such as 5,000 ppm or less or 1,000 ppm or less. Therefore, the reducing gas generated during the firing of the clay raw material CR is not in an amount sufficient to have a reducing effect on the clay raw material CR. Furthermore, because the concentration of the reducing gas is thus extremely low, there is no need to install equipment to treat the reducing gas contained in the exhaust gas GE.

[0113] In this embodiment, the second fired clay CFB is cooled in the second cooling equipment 30 using cooling gas (GAA, GAB) introduced from the air introduction source 63. However, the cooling gas used in the second cooling equipment 30 is not limited to air, but also includes gas with an oxygen concentration higher than the oxygen concentration of the atmosphere when the clay raw material CR is calcined. The same applies to the following embodiments.

[0114] [Second embodiment] The second embodiment of the manufacturing method will be described mainly in terms of the differences from the first embodiment.

[0115] This embodiment is different from the first embodiment in the configuration of the second cooling equipment 30. Fig. 11 is a conceptual block diagram showing a part of the system 1 of this embodiment in accordance with Fig. 3. Similarly, Fig. 12 is a conceptual block diagram showing a part of the system 1 of this embodiment in accordance with Fig. 4. Fig. 13 corresponds to an enlarged view of a part of the system shown in Figs. 11 and 12.

[0116] As shown in FIG. 13, in this embodiment, similarly to the first embodiment, the second cooling unit 30 includes a cyclone 31C and a cyclone 32C.

[0117] As in the first embodiment, the first fired clay CF is mixed with the low-temperature first powder material QD in the cyclone 21H, where it is cooled to a temperature of 600°C or less, and then discharged as the second fired clay CFA. This second fired clay CFA is further cooled by joining the low-temperature gas (first cooling gas GA1) introduced from the air introduction source 63. This cooling step corresponds to step (d1).

[0118] The second calcined clay CFA transported by the air current of the first cooling gas GA1 is stirred in the cyclone 31C and separated into solid and gas. This step corresponds to step (d2).

[0119] The second calcined clay CFA (hereinafter referred to as "second calcined clay CFB") is discharged from the cyclone 31C after being cooled by the first cooling gas GAB.

[0120] Furthermore, the cyclone 31C discharges gas GB, which has been heated by being used to cool the second fired clay CFA. The first cooling gas GA1 is a gas derived from the atmosphere and therefore contains oxygen. Therefore, a portion of the gas GB can be introduced into the firing furnace 11 as a combustion-supporting gas GF (see FIGS. 6 and 12). Also, a portion of the gas GB may be bypassed and introduced into another heat utilization facility. Here, the proportion of the gas GB that is bypassed and not used as the combustion-supporting gas GF is 0% to 70%, preferably 20% to 65%, and more preferably 40% to 60%.

[0121] The second fired clay CFB discharged from the cyclone 31C is transported by the transport gas GA2 through the pipe 76 toward the cyclone 32C. This gas GA2 can be, for example, a gas containing oxygen introduced from the air introduction source 63. Note that this gas GA2 is preferably at a lower temperature than the second fired clay CFB.

[0122] In this embodiment, the cyclone 32C is located vertically above the cyclone 31C and the cyclone 21H.

[0123] 13, the airflow containing the second fired clay CFB flowing through the pipe 76 is joined with the low-temperature second powder material MD from the feeder 65. As a result, the second fired clay CFB is cooled by contact with the second powder material MD and is guided to the cyclone 32C. This step corresponds to step (d3).

[0124] In the cyclone 32C, the mixture of the second fired clay CFB and the low-temperature second powder material MD and the transport gas GA2 used to transport this mixture are separated into solid and gas. By vigorously stirring the second fired clay CFB and the low-temperature second powder material MD in the cyclone 32C, the cooling of the second fired clay CFB further progresses. This step corresponds to step (d4).

[0125] The cooled second fired clay CFB discharged from the cyclone 32C through the pipe 74b is hereinafter referred to as the "third fired clay CFC." Because the temperature of this third fired clay CFC has dropped sufficiently, it can be recovered as cooled fired clay. This recovery step corresponds to step (e). In practice, the third fired clay CFC is recovered in the form of a mixture of the third fired clay CFC and the second powder material MD.

[0126] Because this mixture has a low temperature, it can be introduced as the first powder material QD into the first cooling equipment 20. As described above, in this embodiment, the cyclone 32C is located vertically above the cyclone 21H included in the first cooling equipment 20, and therefore the mixture can be introduced into the first cooling equipment 20 while being dropped from the cyclone 32C through a chute. In other words, part or all of the pipes 85a and 85b can be configured as chutes.

[0127] The same method as in the first embodiment can be adopted for the position at which the first powder material QD is introduced into the first cooling device 20. That is, the first powder material QD may be introduced directly into the cyclone 21H through the pipe 85a, or may be introduced into the loop duct 14 through the pipe 85b.

[0128] According to this configuration, compared to the first embodiment, it is possible to introduce the first powder material QD containing the third fired clay CFC into the first cooling equipment 20 without using the power of the conveying equipment 64 consisting of a belt conveyor or the like.

[0129] The gas GQ discharged by solid-gas separation in the cyclone 32C is discharged to the outside of the system via an induced draft fan as appropriate, as shown in FIG.

[0130] In the case where the second fired clay CFB is sufficiently cooled by the transport gas GA2 and the low-temperature second powder material MD while flowing through the pipe 76, a bag filter can be used instead of the cyclone 32C.

[0131] In this embodiment, as in the first embodiment, the dust DE contained in the preheated exhaust gas GEA may be mixed with the second powder material MD. In this case, the mixture of the dust DE, the second powder material MD, and the second calcined clay CFB is transported to the cyclone 32C through the pipe 76 and subjected to solid-gas separation. Then, a portion of the mixture of the dust DE, the second powder material MD, and the second calcined clay CFB discharged from the cyclone 32C is introduced into the first cooling equipment 20 as the first powder material QD.

[0132] The other configurations are the same as those of the system 1 of the first embodiment, and therefore the description thereof will be omitted.

[0133] [Third embodiment] The third embodiment of the manufacturing method will be described mainly in terms of the differences from the first embodiment.

[0134] This embodiment is different from the first embodiment in the configuration of the second cooling equipment 30. Fig. 14 is a conceptual block diagram showing a part of the system 1 of this embodiment in accordance with Fig. 3. Fig. 15 is a conceptual block diagram showing a part of the system 1 of this embodiment in accordance with Fig. 4. Figs. 16 and 17 correspond to enlarged views of a part of the system shown in Figs. 14 and 15.

[0135] In the system 1 of this embodiment, the second cooling equipment 30 has an agitation equipment 35. FIG.

[0136] As shown in FIGS. 16 and 17, the agitation equipment 35 has an elongated shape and has an inlet 35a, an outlet 35b, a first vent 35c, and a second vent 35d.

[0137] As in the first embodiment, the first fired clay CF is mixed with the low-temperature first powder QD in the cyclone 21H to cool it to a temperature of 600°C or less, and then discharged as the second fired clay CFA through the pipe 71b. In this embodiment, this second fired clay CFA is introduced into the mixing equipment 35 through the inlet 35a.

[0138] The first vent 35c is provided at a position away from the feed port 35a in the longitudinal direction, and a low-temperature gas (first cooling gas GA) flowing from the air introduction source 63 via the piping 78 is introduced into the stirring equipment 35 via the first vent 35c. This step corresponds to step (d4).

[0139] In the agitation equipment 35, the relatively high-temperature second fired clay CFA and the relatively low-temperature first cooling gas GA are agitated and mixed. More specifically, as shown in Fig. 18, the agitation equipment 35 has a cylindrical body 91, and a support shaft 92 and a plurality of paddles 93 arranged in the cylindrical body 91. The plurality of paddles 93 are configured to be rotatable along a plane transverse to the longitudinal direction of the cylindrical body 91 while connected to the support shaft 92.

[0140] The outlet 35b is located closer to the first vent 35c than the inlet 35a in the longitudinal direction. That is, the second calcined clay CFA is mixed with the countercurrent flow of the first cooling gas GA, stirred, and cooled before being guided to the outlet 35b. The second calcined clay CFA cooled in the mixing equipment 35 is discharged from the outlet 35b through the pipe 77. This cooled second calcined clay CFA corresponds to the "third calcined clay CFC" described above in the first and second embodiments. Because the temperature of this third calcined clay CFC has been sufficiently reduced, it can be recovered as cooled calcined clay.

[0141] Furthermore, as described above in the first embodiment, a portion of the third fired clay CFC may be transported through piping 75 using the power of the transport equipment 64 and introduced into the first cooling equipment 20 as the first powder material QD.

[0142] The second vent 35d is located closer to the inlet 35a in the longitudinal direction than the first vent 35c. In the agitation equipment 35, the first cooling gas GA is heated by contact with the relatively high-temperature second fired clay CFA, and then discharged into the pipe 79 through the second vent 35d (gas GB). The first cooling gas GA is a gas derived from the atmosphere and therefore contains oxygen. Therefore, the gas GB discharged through the second vent 35d also contains oxygen, and therefore a portion of it can be introduced into the calcination furnace 11 as a combustion-supporting gas GF (see Figures 15 and 16). Alternatively, a portion of the gas GB may be bypassed and introduced into another heat-utilization facility.

[0143] In the system 1 of this embodiment, the second calcined clay CFA can be cooled while physical stirring is performed in the stirring equipment 35 using a paddle 93 or the like. Therefore, the flow rate of the first cooling gas GA in this embodiment can be reduced compared to the flow rate of the cooling gas GAA used to cool the second calcined clay CFA in the first embodiment and the flow rate of the cooling gases GA1 and GA2 used to cool the second calcined clay CFA in the second embodiment. Therefore, all of the gas GB discharged through the second vent 35d may be used as the combustion-supporting gas GF. Furthermore, the gas GB discharged from the stirring equipment 35 in the system 1 of this embodiment tends to be hotter than the gas GAC discharged from the cyclone 31C in the system 1 of the first embodiment (see FIG. 7) or the gas GB discharged from the cyclone 31C in the system 1 of the second embodiment (see FIG. 13). Therefore, by using at least a part of the gas GB discharged from the stirring equipment 35 as the combustion-supporting gas GF, an effect is achieved in that a higher temperature combustion-supporting gas GF can be supplied to the firing furnace 11.

[0144] The structure of the stirring equipment 35 described above with reference to Fig. 18 is merely one example. As the stirring equipment 35, in addition to the paddle type shown in Fig. 18, a pug mill, a stirrer having two or more shafts, etc. can be used as appropriate.

[0145] In the system 1 of this embodiment, the following modifications can be adopted.

[0146] <1> In the above description, the second calcined clay CFA is cooled using a countercurrent flow of low-temperature first cooling gas GA in the agitation equipment 35. However, the present invention does not exclude an embodiment in which the second calcined clay CFA is cooled in the agitation equipment 35 using a parallel flow of low-temperature first cooling gas GA. In addition, from the viewpoint of enhancing the cooling effect on the second calcined clay CFA, for example, a water sprinkling process may be performed in parallel in the agitation equipment 35. In this case, a drainage mechanism such as a drain may be attached to the agitation equipment 35 to drain water vapor and condensed water generated by the water sprinkling.

[0147] <2> The second calcined clay CFA may be cooled without passing a flow of the first cooling gas GA through the agitation equipment 35. For example, a low-temperature first cooling gas GA may be introduced into the agitation equipment 35 through the first vent 35c to create a low-temperature atmosphere inside the agitation equipment 35, and then the second calcined clay CFA introduced through the inlet 35a may be agitated in the agitation equipment 35 with the first vent 35c and the second vent 35d closed.

[0148] In this case, since the temperature of the atmosphere in the agitation equipment 35 increases as the cooling process of the second fired clay CFA continues, a process of lowering the temperature of the atmosphere in the agitation equipment 35 may be performed periodically.

[0149] For example, the first vent port 35c and the second vent port 35d may be opened periodically to allow a low-temperature first cooling gas GA to flow through. As another example, the agitator 35 may be provided with a water sprinkling function, and the inside of the agitator 35 may be cooled by sprinkling water. In this case, the agitator 35 may be provided with a vent port for discharging water vapor, and the water vapor discharged from this vent port may be supplied to another heat-utilization facility.

[0150] Furthermore, the paddle 93 may be configured to be cooled by a refrigerant using internal convection cooling or impingement cooling technology. In this way, the paddle 93 operates to stir the inside of the stirring equipment 35, thereby suppressing the rate at which the ambient temperature inside the stirring equipment 35 rises.

[0151] <3> A pressure reducing fan may be installed in the pipe 79 connected to the second ventilation port 35d, and the second fired clay CFA may be cooled in a state where the inside of the mixing equipment 35 is in a reduced pressure or vacuum environment.

[0152] <4> As shown in Fig. 19, a part of the third fired clay CFC may be introduced into the mixing equipment 35 through the inlet 35a or through another inlet provided near the inlet 35a via the pipe 75a branching off from the pipe 75. Note that Fig. 19 shows a case where the first cooling gas GA flows through the mixing equipment 35, but this can also be applied to the above-mentioned modified example.

[0153] <5> The above-mentioned modifications can be combined with each other. [Example]

[0154] Specific test examples will be shown below to explain the present invention in more detail, but the present invention is not limited to the embodiments of these test examples.

[0155] [Explanation of the test sample] Kaolin clay was used as the test sample for clay-based CR. The chemical composition of the kaolin clay used is shown in Table 1. The chemical composition was measured by X-ray fluorescence analysis using a calibration curve method (clay) with an X-ray fluorescence analyzer (Rigaku Corporation, ZSX Primus II).

[0156] [Table 1]

[0157] The mineral composition obtained by qualitative analysis of the kaolin clay used as the test sample is shown in Table 2. In Table 2, minerals whose presence was confirmed based on the results of XRD analysis are marked with a "○". Furthermore, according to the results of TG analysis, the main component of the kaolin clay used as the sample was halloysite, with an estimated purity of 68%.

[0158] [Table 2]

[0159] In the tests described below, the test samples used were kaolin clay that had been dried at 105°C and then crushed beforehand. The particle size distribution after crushing is shown in Table 3. The particle size distribution shown in Table 3 was measured using a laser diffraction particle size distribution analyzer (MT3300EX II manufactured by Microtrack Bell).

[0160] [Table 3]

[0161] [Test equipment explanation] In the test, two types of equipment shown in Figures 20 and 21 were used.

[0162] The first test facility 100 shown in Fig. 20 includes a flash calciner 101 equipped with a burner 102, a feeder 103 that supplies the clay raw material CR, and a cyclone 104 and a bag filter 105 as solid-gas separation equipment. The flash calciner 101 simulates the firing facility 10 shown in Fig. 3, and the clay raw material CR is fired by the exhaust gas GE, which has been heated to a high temperature by being combusted by the burner 102 while a combustion-supporting gas GF is supplied, to produce a first fired clay CF.

[0163] The second test equipment 110 shown in FIG. 21 includes a storage chamber 113, a tubular electric furnace 114, an air pump 111, and an N2 gas source 112. The oxygen concentration of the mixed gas A3 can be adjusted by controlling a valve 117 while detecting the flow rate of air A1 supplied from the air pump 111 and the flow rate of nitrogen gas A2 supplied from the N2 gas source 112 using flow meters (111a, 112a). With the mixed gas A3 introduced into the storage chamber 113, the clay raw material CR stored in a container 118 is placed in the storage chamber 113, more specifically, in the heating region 113A, whereby the clay raw material CR is fired. That is, in the second test equipment 110, the storage chamber 113 and the tubular electric furnace 114 simulate the firing equipment 10 shown in FIG. 3.

[0164] In the following description, when the term "calcined clay" is simply used, it refers to the calcined clay raw material CR before the cooling process (corresponding to the "first calcined clay CF" in the above embodiment), and the calcined clay raw material CR after the cooling process has been carried out (corresponding to the "second calcined clay CFA," "second calcined clay CFB," and "third calcined clay CFC" in the above embodiment).

[0165] When firing the clay raw material CR using the second testing facility 110, the fired clay raw material CR (first fired clay CF) can be moved to a non-heating area 113B located outside the tubular electric furnace 114 in the storage chamber 113, thereby allowing cooling within the atmosphere of the storage chamber 113. Furthermore, the first fired clay CF can be discharged from the storage chamber 113, allowing atmospheric cooling.

[0166] As described above, the second test equipment 110 allows for more detailed setting of the oxygen concentration in the firing atmosphere and cooling conditions compared to the first test equipment 100. On the other hand, the second test equipment 110 requires a relatively longer firing time compared to the first test equipment 100, because firing is performed in a static field rather than by airflow. In this test, when firing the clay raw material CR using the second test equipment 110, the firing time was set to 30 minutes.

[0167] It was previously confirmed that there was no difference in activity (quality) between the fired clay obtained by firing the clay raw material CR for 30 minutes using the second test equipment 110 and the fired clay obtained by firing the clay raw material CR for 1.5 seconds using the first test equipment 100.

[0168] (Verification 1: Relationship between firing temperature and activity) The clay raw material CR was fired using the first test facility 100, and the relationship between the firing temperature and the activity of the resulting fired clay CF was examined. The levels and results are shown in Table 4 and Figure 22. Activity evaluation was performed using the R3 hydration exotherm method specified in ASTM C 1897 to evaluate pozzolanic activity. Table 5 shows the qualitative mineral composition results of the fired clay obtained after firing at each level. In Table 5, XRD analysis results indicate that the presence of a mineral was confirmed with an "O," that a trace amount was confirmed with a "△," and that no presence was confirmed at all with an "X."

[0169] [Table 4]

[0170] [Table 5]

[0171] The results of Verification 1 confirmed that samples #3 to #6, which were fired at temperatures between 550°C and 1,000°C, exhibited high activity. Meanwhile, samples #2, fired at temperatures below 400°C, contained residual clay minerals, resulting in a relatively low activity of the fired clay. Furthermore, samples #7 and #8, fired at temperatures above 1,100°C, exhibited relatively low activity compared to samples #3 to #6. This is presumably due to the formation of mullite minerals that do not exhibit pozzolanic activity.

[0172] (Verification 2: Relationship between firing time and activity) Using the first test equipment 100, the clay raw material CR was fired at a fixed firing temperature of 850°C, and the relationship between the firing time and the activity of the resulting fired clay CF was examined. The levels and results are shown in Table 6 and Figure 23. Note that the firing temperature for level #5 in verification 1 was 850°C.

[0173] [Table 6]

[0174] According to the results of Verification 2, when the firing time exceeded 10 seconds, the activity of the obtained first fired clay CF began to decrease, and in the case of Level #13, where the firing time was set to 20 seconds, the activity of the first fired clay CF decreased further. According to the results of this verification, it can be said that it is preferable to set the firing time to about 10 seconds or less. However, at this time, it is unclear why the activity of the fired clay CF decreased when the firing time was too long.

[0175] (Verification 3: Relationship between oxygen concentration in firing atmosphere and color tone) Using the second test facility 110, the clay raw material CR was fired under different oxygen concentrations in the firing atmosphere, and the oxygen concentration and the color tone of the resulting fired clay CF were examined. In this test 3, the oxygen concentration during cooling was fixed at 0% (nitrogen atmosphere). The levels and results are shown in Table 7 and Figure 24. For comparison, Table 7 also lists the color tone results for OPC (ordinary Portland cement).

[0176] [Table 7]

[0177] The color tone of the fired clay was measured using a spectrophotometer SE6000 manufactured by Nippon Denshoku Industries Co., Ltd., to measure the L value, a value, and b value. For the measurement, a standard white board was used as the reference, and then 5 g of each fired clay CF sample obtained at each level was placed in a glass cell, filled with the sample using a tapping device, and then the measurement was carried out. The color tone of the OPC was measured in the same way.

[0178] L * a * b * Color space is a method of expressing color tone by using positive and negative values. As mentioned above, the problem with fired clay is that it turns reddish due to the oxidation of iron, and this is thought to be mainly due to an increase in the a value as well as an increase in the b value.

[0179] Therefore, by adjusting the firing and cooling atmospheres, if "a value: reduced, b value: reduced" is observed, it can be determined that the appearance of reddish tinge has been suppressed in terms of color tone. Furthermore, it can be said that the appearance of reddish tinge has been suppressed by shifting the color tones of the fired clay CF in the direction of approaching the color tone of OPC.

[0180] The results in Table 7 and Figure 24 confirm that lowering the oxygen concentration during firing tends to reduce the a-value and b-value of the fired clay. The change in each color value is more pronounced when the oxygen concentration during firing is 2% or less. These results show that when firing clay raw material CR, the oxygen concentration of the firing atmosphere should preferably be 2% or less, and more preferably 0.5% or less.

[0181] (Verification 4: Relationship between oxygen concentration and color tone during cooling) Using the second test facility 110, the clay raw material CR was fired at a firing temperature of 850°C and an oxygen concentration of the firing atmosphere of 0% (nitrogen atmosphere), and then the color tone of the fired clay obtained by varying the oxygen concentration of the cooling atmosphere was examined. The fired clay was cooled in the non-heated area 113B in the storage chamber 113, as described above with reference to Figure 21. The levels and results are shown in Table 8 and Figure 25.

[0182] [Table 8]

[0183] According to the results in Table 8 and Figure 25, when the oxygen concentration of the atmosphere during firing is fixed at a low concentration, lowering the oxygen concentration of the cooling atmosphere further reduces the a-value and b-value of the fired clay. The change in each color value is more pronounced when the oxygen concentration of the atmosphere during cooling is 2% or less. In addition, Levels #14 and #21 had a color tone that could be judged to have completely suppressed the appearance of redness.

[0184] (Verification 5: Relationship between temperature and color tone at the start of air cooling) Using the second test facility 110, the clay raw material CR was fired at a firing temperature of 850°C and an oxygen concentration of 0.5% in the firing atmosphere. The fired clay was then subjected to primary cooling in the unheated area 113B of the storage chamber 113. The fired clay was then removed from the storage chamber 113 and subjected to secondary cooling in the atmosphere. Specifically, step S4 was simulated by cooling the fired clay in the unheated area 113B of the storage chamber 113, and step S5 was simulated by cooling the fired clay in the atmosphere. The relationship between the start temperature of secondary cooling, i.e., the temperature at the start of atmospheric cooling, and the color tone of the resulting fired clay was examined. The levels and results are shown in Table 8 and Figure 26.

[0185] [Table 9]

[0186] It was confirmed that the a-value and b-value of the fired clay tend to decrease by lowering the temperature at which the clay is exposed to the atmosphere. This result suggests that by first cooling the fired clay to a predetermined temperature or below in an atmosphere with a low oxygen concentration, the appearance of redness due to reoxidation can be suppressed even if the clay is subsequently cooled in an atmosphere containing oxygen. From these verification results, it is confirmed that if the fired clay CF is cooled in an atmosphere with a low oxygen concentration to a temperature of 600 ° C or less, preferably 500 ° C or less, at which the changes in the a-value and b-value become small, it can then be cooled in an atmosphere containing oxygen such as air. [Explanation of symbols]

[0187] 1: System 10: Firing equipment 11: Kiln 12: Burner 14: Loop duct 20:First cooling equipment 21F: Discharge equipment with sealing function 21H: Cyclone 30:Second cooling equipment 31C: Cyclone 32C: Cyclone 35: Mixing equipment 35a: Inlet 35b: Outlet 35c: First ventilation hole 35d: Second vent 41: Preheating equipment 41D, 42: Piping 43: Solid-gas separation equipment 43H: Cyclone 51: Waste heat utilization equipment 61: Feeder 62 :Fuel supply source 63: Atmospheric introduction source 64:Transportation equipment 65: Feeder 71a, 71b, 72a, 72b, 74a, 74b, 75, 75a: Piping 76, 77, 78, 79: Piping 81: Attractive Fan 84, 85a, 85b, 86, 87: Piping 91: Cylinder 92: Support shaft 93: Paddle 100: First test facility 101: Flash Calsaina 102: Burner 103: Feeder 104: Cyclone 105: Bag filter 110: Second Test Facility 111: Air pump 112: N2 gas source 113: Containment room 113A: Heating area 113B: Non-heating area 114: Tubular electric furnace 117: Valve 118: Container A1: Air A2: Nitrogen gas A3: Mixed gas CF: First fired clay CFA,CFB: Second fired clay CFC: Third fired clay CR: Clay raw material DE: Dust GA, GA1: First cooling gas GA2: Gas GAA: Secondary cooling gas GAB: Primary cooling gas GAC, GB: Gas GE: Exhaust gas GEA: Preheated exhaust gas GEB: Cooled preheated exhaust gas GF: Combustion-supporting gas GQ: Gas MD:Second powder material QD: First powder material VD: fuel

Claims

1. (a) feeding a clay raw material into the line; (b) calcining the clay raw material in a stream of gas having a low oxygen concentration; The first fired clay, which is the clay raw material obtained after the step (b), is mixed with a first powder material having a temperature lower than that of the first fired clay in an atmosphere of a gas having a low oxygen concentration, and primary cooling is performed to reduce the temperature to 600 ° C. or less. Step (c); The second fired clay, which is the first fired clay whose temperature has been reduced by the execution of the step (c), is cooled in a gas or vacuum atmosphere at a temperature lower than that of the second fired clay and having a higher oxygen concentration than the gas constituting the atmosphere during the execution of the step (c), to further reduce the temperature. Step (d); A method for producing calcined clay, characterized by having a step (e) of recovering cooled calcined clay, which is the second calcined clay whose temperature has been reduced by carrying out the step (d).

2. The method for producing calcined clay according to claim 1, characterized in that the step (b) is carried out in an air stream having an oxygen concentration of 2% or less without introducing a reducing agent from the outside.

3. The step (b) Step (b1) of charging the clay raw material into a firing furnace in which fuel is burned in an environment in which a combustion-supporting gas is supplied; and a step (b2) of transporting the clay raw material to a solid-gas separation facility by an airflow of the calcination exhaust gas discharged from the calcination furnace, The step (c) a step (c1) including at least one of a step of directly introducing the first powder material into the solid-gas separation facility and a step of introducing the first powder material into the solid-gas separation facility through a pipe through which the firing exhaust gas flows; The method for producing fired clay according to claim 2, further comprising the step (c2) of mixing the first powder material and the fired clay in an atmosphere of a gas having a low oxygen concentration containing the fired exhaust gas in the solid-gas separation equipment.

4. The step (d) is characterized in that the second calcined clay discharged from the solid-gas separation equipment after the execution of the step (c2) is mixed with a gas flow containing atmospheric air at a temperature lower than that of the second calcined clay. A method for producing calcined clay according to claim 3, characterized in that it includes a step of mixing.

5. The step (d) A step (d1) of cooling the second calcined clay discharged from the solid-gas separation equipment by mixing it with a first cooling gas flow containing atmospheric air, which has a temperature lower than that of the second calcined clay; A step (d2) of separating the mixture of the first cooling gas and the second calcined clay into solid and gas after the step (d1); The third fired clay, which is the second fired clay after cooling and discharged through the step (d2), is mixed with a second cooling gas flow containing atmospheric air, which is lower in temperature than the third fired clay, to cool it. (d3) After the step (d3), a step (d4) of solid-gas separating the mixture of the second cooling gas and the third calcined clay is included. The first cooling gas includes the second cooling gas after being heated and discharged through the step (d4), The method for producing calcined clay according to claim 4, characterized in that the step (e) is a step of recovering the cooled third calcined clay discharged through the step (d4) as the cooled calcined clay.

6. The step (d) A step (d1) of cooling the second calcined clay discharged from the solid-gas separation equipment by mixing it with a first cooling gas flow containing atmospheric air, which has a temperature lower than that of the second calcined clay; A step (d2) of separating the mixture of the first cooling gas and the second calcined clay into solid and gas after the step (d1); The third fired clay, which is the second fired clay after cooling and discharged through the step (d2), is conveyed by an air flow while being raised and mixed with a second powder material having a lower temperature than the third fired clay. Step (d3); and a step (d4) of separating the gas and solid mixture into solid and gas after the step (d3), The step (c) is a step of introducing a part of the mixture containing the cooled third fired clay discharged through the step (d4) into the solid-gas separation equipment while dropping it as the first powder material through a chute, The step (e) is a step of recovering a portion of the mixture containing the cooled third calcined clay discharged through the step (d4) as the cooled calcined clay. A method for producing calcined clay according to claim 4, characterized in that

7. The method for producing fired clay according to claim 6, characterized in that the second powder material comprises at least one selected from the group consisting of cement, cement admixtures, concrete admixtures, supplementary cement materials (SCM), ground clinker, raw concrete sludge, waste concrete fines, clinker dust, and blast furnace slag.

8. The step (d) The second fired clay discharged from the solid-gas separation equipment is introduced into a long stirring equipment in which a gas containing air or a vacuum atmosphere at a temperature lower than that of the second fired clay is formed through an inlet (d1); A step (d2) of conveying the second fired clay in the longitudinal direction while cooling it while stirring it in the stirring equipment; Step (d3) of discharging the cooled second fired clay from a discharge outlet located away from the inlet in the longitudinal direction; The step (e) is a step of recovering the cooled second fired clay discharged through the step (d3) as the cooled fired clay. A method for producing fired clay according to claim 3.

9. The step (d) includes a step (d4) of introducing a first cooling gas flow containing atmospheric air into the stirring equipment from a first vent port longitudinally spaced from the inlet, the first cooling gas flow having a temperature lower than that of the second fired clay, The step (d2) is a step of conveying the second fired clay in the longitudinal direction while stirring the second fired clay introduced from the inlet and the airflow introduced from the first air outlet, which is in a countercurrent state with respect to the second fired clay, in the stirring equipment. The method for producing fired clay according to claim 8, characterized in that

10. The step (d) includes a step (d5) of discharging the first cooling gas, the temperature of which has been increased by the execution of the step (d2), through a second vent port provided in the stirring equipment at a position closer to the inlet than the first vent port in the longitudinal direction, The method for producing calcined clay according to claim 9, characterized in that a part of the gas discharged in the step (d5) is used as the combustion-supporting gas.

11. The step (d) is performed through the same inlet or another inlet located near the inlet in the longitudinal direction. A step (d6) of introducing a portion of the mixture containing the cooled third calcined clay discharged through the step (d3) into the stirring equipment. The method for producing calcined clay according to claim 8, characterized in that it includes the step (d6).

12. The method for producing calcined clay according to claim 2, characterized in that it includes a step (a1) of mixing the clay raw material supplied in the step (a) with the exhaust gas flow discharged after the execution of the step (b) and preheating it.

13. After carrying out the step (a1), a step (f) of separating the preheated clay raw material into a solid and a gas; and a step (g) of cooling the preheated exhaust gas discharged after the step (f), The step (b) is a step of calcining the clay raw material discharged after the step (f), The method for producing calcined clay according to claim 12, characterized in that the first powder material includes dust contained in the preheated exhaust gas cooled by performing the step (g).

14. The preheated exhaust gas has an oxygen concentration of 2% or less, 14. The method for producing calcined clay according to claim 13, wherein the step (c) includes a step of mixing the preheated exhaust gas containing the dust with the first calcined clay.

15. The first powder material is cement, cement mixture, concrete admixture, supplementary cement material (SCM), ground clinker, raw concrete sludge, fine waste concrete, clinker dust, blast furnace slag, and the cooled fired clay recovered in the step (e). The method for producing fired clay according to any one of claims 1 to 14, characterized in that it comprises one or more selected from the group consisting of cement, cement mixture, concrete admixture, supplementary cement material (SCM), ground clinker, raw concrete sludge, fine waste concrete, clinker dust, blast furnace slag, and the cooled fired clay recovered in the step (e).

16. The step (b) is a step of calcining the clay raw material in an air flow at a temperature range of 550 ° C to 1,000 ° C for a time period of 0.5 seconds to 10 seconds. A method for producing calcined clay according to any one of claims 1 to 14.

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