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: The method includes a step (a) of supplying a clay raw material to a line, a step (b) of calcining the clay raw material in a gas stream having a low oxygen concentration, a step (c) of mixing a calcined clay, which is the clay raw material obtained after performing the step (b), into the gas stream having a low oxygen concentration at a temperature lower than that of the calcined clay and cooling the calcined clay, a step (d) of cooling a first gas stream discharged after performing the step (c), and a step (e) of recovering a cooled calcined clay, which is the calcined clay after cooling obtained after performing the step (c). The step (c) is carried out in an air stream into which a part or all of the first air stream passed through the step (d) is merged.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing calcined clay, and more particularly to a method for producing calcined 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 tone 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 an air stream having a low oxygen concentration; Step (c) of mixing the fired clay, which is the clay raw material obtained after performing step (b), into an air stream having a lower temperature and a lower oxygen concentration than the fired clay and cooling it; a step (d) of cooling the first airflow discharged after the step (c) is performed; and (e) recovering the cooled calcined clay, which is the calcined clay obtained after the step (c), The step (c) is characterized in that it is performed in an air stream into which a part or all of the first air stream that has been subjected to the step (d) is joined.

[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 low-oxygen concentration atmosphere (appropriately referred to as an "oxygen-poor atmosphere"), and then cooled by mixing with an 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] 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%.

[0015] 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). Furthermore, recycled fuels such as waste oil, refuse-derived fuel (RDF), and waste plastics can also be used as fuels.

[0016] 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.

[0017] 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. This is because mixing low-activity calcined clay with cement as a cement admixture or concrete admixture can lead to a decrease in the strength of the resulting blended cement and concrete produced from it.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The cooling step (c), like the calcination step (b), may be carried out in an air stream 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, the calcined clay is preferably cooled at a cooling rate of 3°C / sec.

[0022] Here, 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.

[0023] As described above, the high-temperature calcined clay obtained after performing step (b) is cooled in step (c) in an oxygen-poor atmosphere at a temperature lower than that of the calcined clay. The cooled calcined clay is recovered in step (e) as cooled calcined clay.

[0024] In step (c), the oxygen-poor atmosphere used to cool the high-temperature fired clay is discharged as a first airflow, and after being cooled in step (d), part or all of it is reused in step (c).

[0025] Step (d) may include a step of performing heat exchange between a high-temperature first air stream and an air stream (second air stream) that is cooler than the first air stream. A known heat exchange facility can be used for the heat exchange. The first air stream, which is made up of the calcination exhaust gas or the like, contains moisture produced by dehydrating the clay raw material. 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 the heat exchange facility with a drainage mechanism, such as a drain.

[0026] Here, a part or all of the second airflow, which has been heated by heat exchange with the high-temperature first airflow, may be supplied to the firing furnace as a combustion-supporting gas. In this case, the second airflow may be an air flow.

[0027] Even when the firing furnace is configured to burn fuel in an environment where a combustion-supporting gas is supplied, the oxygen contained in the combustion-supporting gas is almost entirely utilized by the combustion of the fuel, and as a result, the exhaust gas (firing exhaust gas) discharged from the firing furnace exhibits a low oxygen concentration. In other words, in step (b), the clay raw material supplied to the firing furnace is transported by an air current in a high-temperature, oxygen-poor atmosphere.

[0028] In step (c), the low-oxygen-concentration airflow used to cool the high-temperature fired clay may correspond, for example, to the downstream airflow sent from an inert gas supply source. Here, the inert gas supply source may include an oxygen separation device that separates oxygen from air and a gas tank that stores the gas obtained by the oxygen separation device, the main component of which is nitrogen. In addition to nitrogen, rare gases and carbon dioxide can also be used as the main component of the inert gas, but in view of low production costs, nitrogen, which is present in an inexhaustible amount in the atmosphere, is particularly preferred.

[0029] When the calcination exhaust gas discharged from the calcination furnace, i.e., the exhaust gas stream discharged after carrying out the step (b), exhibits a low oxygen concentration suitable as a cooling gas, a portion of the gas can be contained in the low-oxygen-concentration air stream used in carrying out the step (c).

[0030] In detail, the method for producing the calcined clay comprises: 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 a portion of the third air flow discharged after the step (f) is performed. The step (c) may be performed in an air stream into which a part or all of the third air stream that has passed through the step (g) is joined.

[0031] As described above, when step (d) includes a step of exchanging heat between the first airflow and a second airflow having a lower temperature than the first airflow, step (g) may be a step of exchanging heat between a part of the third airflow and the second airflow. In this case, the low-temperature second airflow exchanges heat with the first airflow, which has been heated to a high temperature by being used to cool the high-temperature calcined clay, and also with a part of the third airflow corresponding to the downstream of the high-temperature calcination exhaust gas.

[0032] A portion of the third air flow whose temperature has been reduced by cooling may be merged with an inert gas supply line connected to an inert gas source. In this case, a blower (fan) for circulating the gas may be provided in the piping as appropriate. Alternatively, a portion of the third air flow whose temperature has been reduced by cooling may be directly supplied to the inert gas source. In this case, for the same reasons as described above, it is preferable to provide a drainage mechanism such as a drain in the inert gas source, similar to that of the heat exchanger.

[0033] The step (c) of cooling the calcined clay in an airflow with a low oxygen concentration may include a step of mixing a powdered material with a temperature lower than that of the calcined clay into the airflow, which powdered material may be one or more selected from the group consisting of cement, cement mixtures, concrete admixtures, supplementary cementitious materials (SCM), ground clinker, raw concrete sludge, finely ground waste concrete, clinker dust, blast furnace slag, and the cooled calcined clay recovered in the step (e).

[0034] According to this method, the high-temperature fired clay is mixed in a low-temperature, low-oxygen-concentration airflow while coming into contact with and colliding with the low-temperature powder material, so that the fired clay can be cooled more efficiently.

[0035] The method for mixing the powder into the airflow is not limited, but a method that provides excellent dispersibility is preferred. For example, when introducing the powder into a duct using a chute, it is preferable to provide a dispersion plate at the end of the chute. Furthermore, if mixing within the duct is insufficient, a mixer such as a static mixer may be provided within the duct.

[0036] More specifically, the step (c) of cooling the calcined clay in an air stream with a low oxygen concentration can employ several embodiments.

[0037] In a first aspect, The step (c) Step (c1) of primarily cooling the fired clay by mixing the fired clay obtained after the step (b) with a primary cooling airflow having a low oxygen concentration; The calcined clay after the primary cooling obtained after the step (c1) is mixed with a secondary cooling airflow having a low oxygen concentration and a temperature lower than the primary cooling airflow, thereby secondary cooling the calcined clay. The step (c1) is performed in the primary cooling airflow obtained by joining a part or all of the exhaust airflow discharged after the step (c2) is performed, The step (d) is a step of cooling the first air flow discharged after the execution of the step (c1), The step (c2) may be performed in the secondary cooling airflow obtained by joining a part or all of the first airflow that has passed through the step (d).

[0038] According to the above method, the high-temperature fired clay is cooled in two stages, improving the cooling efficiency. However, the present invention does not exclude an embodiment in which the fired clay is cooled in three or more stages.

[0039] After the calcined clay and the airflow for primary cooling are mixed, the calcined clay after primary cooling and the airflow (first airflow) whose temperature has increased due to use in primary cooling may be separated by a solid-gas separation device such as a cyclone. Similarly, after the calcined clay after primary cooling and the airflow for secondary cooling are mixed, the calcined clay after secondary cooling and the exhaust airflow whose temperature has increased due to use in secondary cooling may be separated by a solid-gas separation device such as a cyclone. The exhaust airflow whose temperature has increased after secondary cooling can be used as the airflow for primary cooling.

[0040] In this case, the step (c1) may include a step of mixing a powder material having a lower temperature than the fired clay obtained after the step (b) into the primary cooling airflow.

[0041] When mixing the fired clay into the primary cooling 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 into the side where the fired clay is being added. The same applies when mixing powdered materials into the primary cooling airflow.

[0042] In a second aspect, The step (c) Step (c1) of charging the fired clay into a long stirring equipment through an inlet; A step (c2) of introducing an airflow having a lower temperature and an oxygen concentration than the fired clay into the stirring equipment from a first air outlet longitudinally separated from the inlet; The 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 fired clay, are stirred in the stirring equipment while the fired clay is conveyed in the longitudinal direction (c3); A step (c4) of discharging the cooled fired clay from a discharge port located closer to the first vent port than the inlet in the longitudinal direction; The method may further include a step (c5) of discharging the first airflow through a second vent located closer to the input port than the first vent in the longitudinal direction.

[0043] According to the above method, the calcined clay can be efficiently cooled by stirring the low-temperature air in a countercurrent state in the stirring equipment. In this case, the low-temperature gas introduced into the stirring equipment has a low oxygen concentration, so the calcined clay is prevented from transforming into red hematite during the cooling process.

[0044] In this case, The step (c) includes a step (c6) of adding a powder material having a lower temperature than the calcined clay obtained after the execution of the step (b) to the stirring equipment from the same inlet or another inlet located near the inlet in the longitudinal direction, The step (c3) is a step of stirring the fired clay, the powder material, and the airflow flowing in from the first air port, The step (c4) may be a step of discharging the cooled mixture of the calcined clay and the powder material from the outlet.

[0045] After cooling the calcined clay in an oxygen-poor atmosphere, the cooled calcined clay may be discharged directly from the low-oxygen-concentration airflow and recovered in step (e).

[0046] On the other hand, as will be described later with reference to the examples, after the fired clay is cooled to a predetermined temperature of 600 ° C or less in an oxygen-poor atmosphere, even if it is cooled in an oxygen-containing atmosphere, it is possible to suppress the change to a reddish color tone.

[0047] That is, the step (c) is a step of lowering the temperature of the fired clay to a predetermined temperature of 600 ° C or less, After carrying out the step (c), a step (h) of further cooling the calcined clay in an airflow having a higher oxygen concentration than the airflow used in the step (c), The step (e) may be a step of recovering the cooled fired clay obtained after carrying out the step (h).

[0048] The predetermined temperature is preferably set to 500° C. or less.

[0049] In addition, step (e) can be a step of recovering the cooled fired clay using solid-gas separation equipment. Also, if the fired clay has been sufficiently cooled (for example, below 500°C), the cooled fired clay can be recovered using a bag filter. [Effects of the Invention]

[0050] 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]

[0051] [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. [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] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 12] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 13] 5 is an enlarged view of a part of the system shown in FIGS. 3 and 4. [Figure 14] 8 is a block diagram showing a part of a second embodiment of a system for carrying out a method for producing calcined clay according to the present invention, in accordance with FIG. 7.

[0023] FIG. [Figure 15] 15 is a diagram schematically illustrating a detailed configuration example of the stirring equipment 25 shown in FIG. 14. [Figure 16] 15 is a diagram schematically illustrating another detailed configuration example of the stirring equipment 25 shown in FIG. 14. [Figure 17] 8 is another block diagram showing a part of a second embodiment of a system for carrying out a method for producing calcined clay according to the present invention, in accordance with FIG. 7. FIG. [Figure 18] 1 is a diagram schematically illustrating the configuration of a first test facility used in verification. [Figure 19] 1 is a diagram schematically illustrating the configuration of a second test facility used in the verification. [Figure 20] 1 is a graph showing the results of verifying the relationship between the firing temperature and the activity of fired clay. [Figure 21] 1 is a graph showing the results of verifying the relationship between firing time and the activity of fired clay. [Figure 22] 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 23] 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 24] 1 is a graph showing the results of examining the relationship between the temperature at which cooling in a low-oxygen atmosphere is transitioned to cooling in an air atmosphere and the color tone of the fired clay. DETAILED DESCRIPTION OF THE INVENTION

[0052] 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.

[0053] [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.

[0054] 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.

[0055] (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.

[0056] Step S1 corresponds to the process (a).

[0057] (Step S2) The supplied clay raw material CR is preheated in preheating equipment 41. Specifically, the clay raw material CR is preheated by being mixed with high-temperature exhaust gas GE discharged from solid-gas separation equipment 45. In this case, preheating equipment 41 corresponds to a pipe through which the clay raw material CR and 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.

[0058] Step S2 corresponds to the step (a1).

[0059] (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.

[0060] 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.

[0061] The clay raw material CR is calcined by being 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 produced by this calcination process is transported by the exhaust gas GE and sent to the solid-gas separation equipment 45.

[0062] 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 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 high-temperature exhaust gas GE is solid-gas separated by the solid-gas separation equipment 45.

[0063] Step S3 corresponds to the step (b).

[0064] (Step S4) The mixture of high-temperature exhaust gas GE and calcined clay CF is separated into solid and gas by solid-gas separation equipment 45. The exhaust gas GE recovered from solid-gas separation equipment 45 is sent to preheating equipment 41 and used to preheat the clay raw material CR as described above in step S2. The calcined clay CF recovered from solid-gas separation equipment 45 is sent to cooling equipment 20 and cooled.

[0065] The cooling equipment 20 is a facility that has the function of cooling high-temperature calcined clay CF using low-temperature inert gas GI. More specifically, the calcined clay CF is cooled by mixing the high-temperature calcined clay CF into the airflow of low-temperature inert gas GI. In other words, the piping that mixes and transports the high-temperature calcined clay CF and the airflow of low-temperature inert gas GI is one component of the cooling equipment 20. Also, as will be described later, the stirring equipment for improving the mixed state of the high-temperature calcined clay CF and the low-temperature inert gas GI is also one component of the cooling equipment 20. Furthermore, the solid-gas separation equipment for separating the calcined clay and the inert gas from the mixed state can also be said to be equipment that forms a mixed state just before separation, and is therefore one component of the cooling equipment 20. In this embodiment, it is not necessary to introduce a reducing agent when cooling the high-temperature calcined clay CF in the cooling equipment 20.

[0066] Step S4 corresponds to the step (c).

[0067] (Step S5) The inert gas GI used for cooling in the cooling equipment 20 is sent to the heat exchange equipment 51 in a heated state. In Fig. 2, in order to indicate that it is a heated inert gas, it is written as "inert gas GIA" using a different symbol from the inert gas GI. The airflow of this inert gas GIA corresponds to the "first airflow."

[0068] The first airflow containing the inert gas GIA is cooled in the heat exchanger 51. In the example of Fig. 2, the inert gas GIA is cooled by heat exchange with an airflow of low temperature air GA. In the example of Fig. 2, the airflow of air GA corresponds to the "second airflow."

[0069] In Figure 2, in order to indicate that the inert gas GIA is the inert gas after it has been cooled, a different symbol is used, denoted as "inert gas GIC." The inert gas GIC is mixed with the low-temperature inert gas GI supplied from the inert gas supply equipment 30, and is then used again in the cooling equipment 20 as a cooling gas for the calcined clay CF.

[0070] Furthermore, as shown in FIG. 2, a portion of the exhaust gas GE may also be cooled in the heat exchange equipment 51 to become an inert gas GIE, which is mixed with the low-temperature inert gas GI supplied from the inert gas supply equipment 30, and then used again in the cooling equipment 20 as a cooling gas for the fired clay CF.

[0071] In the example of FIG. 2, the air GA, which has been heated by heat exchange with the high-temperature inert gas GIA, is introduced into the firing equipment 10 as a preheated combustion-supporting gas GF.

[0072] Step S5 corresponds to step (d).

[0073] (Step S6) As described above, in the cooling equipment 20, the high-temperature calcined clay CF is cooled by an airflow of inert gas GI, which has a low oxygen concentration. After this cooling process, the calcined clay (cooled calcined clay) CFC is recovered. The cooled calcined clay CFC is inhibited from transforming into a reddish hematite phase and has a gray-based color tone, making it suitable for use as an admixture for cement.

[0074] Step S6 corresponds to step (e).

[0075] 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. In this case, the exhaust gas GE from the solid-gas separation equipment 45 may be discharged to the outside air, and a portion of the exhaust gas GE may be cooled by the heat exchange equipment 51 and mixed with the inert gas GI as the inert gas GIE.

[0076] The details of the embodiment of the manufacturing method will be described below with reference to the drawings.

[0077] [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.

[0078] 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 13 correspond to enlarged views of parts of the systems shown in Figures 3 and 4.

[0079] 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.

[0080] 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.

[0081] In this embodiment, the high-temperature exhaust gas GE is discharged through a pipe 71a connected to a cyclone 45H, which is an example of the solid-gas separation equipment 45, toward a pipe 41D.

[0082] The mixture of high-temperature exhaust gas GE and clay raw material CR transported through pipe 41D is introduced into cyclone 43H, an example of solid-gas separation equipment 43, where it is separated into solids and gas. High-temperature exhaust gas GE is discharged from pipe 72a connected to cyclone 43H. This exhaust gas GE is either discharged as outside air via induced draft fan 81 or sent to an exhaust gas treatment mechanism (not shown). In particular, this exhaust gas GE has a high temperature of 200°C to 400°C, so it can also be used for applications such as waste heat power generation. Furthermore, a portion of the exhaust gas GE may be sent to cooling equipment 20 or to inert gas supply equipment 30. This point will be described later.

[0083] Meanwhile, preheated clay raw material CR is discharged from pipe 72b connected to cyclone 43H and transported toward calcination equipment 10 (see FIG. 6). In the example shown in FIG. 6, calcination equipment 10 includes a calcination furnace 11 and a burner 12. Fuel VD and combustion-supporting gas GF are introduced into calcination furnace 11 from a fuel supply source 62. In calcination 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.

[0084] The clay raw material CR is calcined (fired) in the high-temperature, low-oxygen atmosphere of the exhaust gas GE (step S3). During this calcination process, the crystalline structure of the clay raw material CR is broken down, becoming amorphous and increasing its activity. The calcined clay CF, which is the clay raw material CR, is transported to the solid-gas separation equipment 45 by the high-temperature, low-oxygen atmosphere of the exhaust gas GE.

[0085] The firing time of the clay raw material CR is set to a time sufficient to convert the clay raw material CR into a highly active fired clay CF. 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 the solid-gas separation equipment 45 while suppressing the expansion of the equipment's occupied area.

[0086] 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.

[0087] The fired clay CF, which has been transported by the airflow of high-temperature exhaust gas GE and fired, is introduced into a cyclone 45H, an example of solid-gas separation equipment 45, together with the airflow of exhaust gas GE, as shown in FIG. 6. The cyclone 45H separates the high-temperature exhaust gas GE from the fired clay CF. As described above, the exhaust gas GE is discharged through pipe 71a toward pipe 41D. The fired clay CF is sent to cooling equipment 20 via pipe 71b (see FIG. 7).

[0088] In the example shown in FIG. 7, the cooling equipment 20 includes a cyclone 21C and a cyclone 22C.

[0089] Cyclone 22C is connected to pipe 74a, and the inert gas GIA obtained by solid-gas separation by cyclone 22C flows through pipe 74a. The high-temperature fired clay CF, which has been separated into solids and gases by cyclone 45H and discharged through pipe 71b, merges with the flow of inert gas GIA, which is at a lower temperature than the fired clay CF and flows through pipe 74a. In order to prevent the flow of inert gas GIA from flowing back toward pipe 71b, as shown in Figure 6, a discharge device 45F with a sealing function, such as a double flap damper or rotary feeder, is preferably provided on the discharge outlet side of cyclone 45H.

[0090] The high-temperature fired clay CF is primarily cooled by merging with the gas flow of inert gas GIA (gas flow for primary cooling) flowing through the pipe 74a (step S4). This step corresponds to step (c1).

[0091] The mixture of the calcined clay CF and the inert gas GIA flowing through the pipe 74a is introduced into the cyclone 21C for solid-gas separation. The inert gas GIA, which has been heated by being used for primary cooling, is discharged from the cyclone 21C and sent to the heat exchanger 51. The calcined clay CFB is also discharged from the cyclone 21C after primary cooling. This calcined clay CFB is then merged with the inert gas GI flow (secondary cooling flow) discharged from the inert gas supply equipment 30, which is at a lower temperature than the inert gas GIA, for secondary cooling (step S4). This step corresponds to step (c2).

[0092] The mixture of the calcined clay CFB and the inert gas GI is introduced into the cyclone 22C and subjected to solid-gas separation. The inert gas GI, which has been heated by being used for secondary cooling, is discharged from the cyclone 22C and flows through piping 74a. The inert gas GI discharged from the cyclone 22C is a gas heated by the low-temperature inert gas GI cooling the calcined clay CFB, which has already been primarily cooled and whose temperature has dropped to a certain extent. Therefore, the temperature after heating is lower than that of the high-temperature calcined clay CF discharged through piping 71b. Therefore, as described above, the inert gas GI discharged from the cyclone 22C can be mixed with the high-temperature calcined clay CF discharged through piping 71b to perform primary cooling of the calcined clay CF.

[0093] Furthermore, the calcined clay (cooled calcined clay) CFC discharged from the cyclone 22C through pipe 74b after secondary cooling has sufficiently dropped in temperature, so it can be recovered as is (step S6). The temperature of the cooled calcined clay CFC obtained through step S6 is preferably 600°C or less, more preferably 500°C or less. Note that if the temperature of the cooled calcined clay CFC after secondary cooling by mixing the primarily cooled calcined clay CFB with low-temperature inert gas GI is sufficiently low, typically about 300°C or less, solid-gas separation can also be performed using a bag filter instead of the cyclone 22C. In this case, the cooled calcined clay CFC separated by the bag filter is recovered, and the gas separated by the bag filter is combined with the high-temperature calcined clay CF discharged through pipe 71b as the inert gas GIA for primary cooling.

[0094] As shown in Figure 8, a portion of the cooled fired clay (CFC) after secondary cooling may be merged with the inert gas (GIA) discharged from the cyclone 22C. This allows the high-temperature fired clay (CF) and the low-temperature cooled fired clay (CFC) to be mixed together via the pipe 71b, improving the cooling performance of the fired clay (CF). As an example, as shown in Figure 8, a pipe 75 branching from the pipe 74b connected to the cyclone 22C can be provided, and the cooled fired clay (CFC) can be merged with the pipe through which the inert gas (GIA) discharged from the cyclone 22C flows, using the power of the conveying equipment 64, such as a fan or a belt conveyor.

[0095] Furthermore, as shown in FIG. 9, a powder material MD at a lower temperature than the calcined clay CF may be supplied from a feeder 65 and mixed with the inert gas GIA discharged from the cyclone 22C. This allows the high-temperature calcined clay CF and the low-temperature powder material MD, which are joined via piping 71b, to be mixed, thereby improving the cooling performance of the calcined clay CF. While FIG. 9 illustrates a configuration in which cooled calcined clay CFC is mixed with the calcined clay CF along with the powder material MD, only the powder material MD may be mixed with the calcined clay CF without the cooled calcined clay CFC. Examples of the powder material MD include cement, ground clinker, raw concrete sludge, finely ground waste concrete, clinker dust, and blast furnace slag. When cooled calcined clay CFC is mixed with the calcined clay CF, the cooled calcined clay CFC can also be considered a type of powder material to be mixed.

[0096] The method for mixing the powder material MD with the inert gas GIA discharged from the cyclone 22C is not limited, but a feeding method with excellent dispersibility is preferred. When feeding the powder material MD from the feeder 65 through a chute (not shown) toward a pipe through which the inert gas GIA discharged from the cyclone 22C flows, it is preferable to provide a dispersion plate at the end of the chute. Furthermore, if the powder material MD is not mixed sufficiently in the pipe, a mixer such as a static mixer may be provided in the pipe.

[0097] As shown in FIG. 7, the heated inert gas GIA discharged from the cyclone 21C is sent to the heat exchanger 51. In the example shown in FIG. 7, the heat exchanger 51 is composed of a heat exchanger 51E, and heat exchange is performed between the low-temperature air GA discharged from the air supply source 63 and the heated inert gas GIA. This heat exchange reduces the temperature of the inert gas GIA (inert gas GIC). This inert gas GIC is merged with the flow of inert gas GI discharged from the inert gas supply equipment 30 and can be used as a secondary cooling gas. In addition, the air GA heated by the heat exchange is introduced into the calciner 11 as a combustion-supporting gas GF (see FIG. 6).

[0098] 7 and 10, an induced draft fan 81 may be provided on the path of the pipe 84 through which the inert gas GI discharged from the inert gas supply facility 30 flows. As a result, the inert gas GIC, whose temperature has been reduced through the heat exchanger 51E, merges with the inert gas GI discharged from the inert gas supply facility 30, and then flows toward the cyclone 22C.

[0099] 4, 5, and 10, a portion of the high-temperature exhaust gas GE (third airflow) discharged from the cyclone 43H may be guided to a heat exchanger 51E. In this case, in the heat exchanger 51E, the high-temperature exhaust gas GE is subjected to heat exchange with low-temperature air GA, thereby lowering its temperature. As described above, the exhaust gas GE has a low oxygen concentration, and therefore can be directly combined as an inert gas GID with the inert gas GI discharged from the inert gas supply facility 30. In this case, too, an induced draft fan 82 may be provided on the piping path through which the exhaust gas GE flows toward the heat exchanger 51E, or on the piping path through which the exhaust gas GE passes through the heat exchanger 51E and is combined with the inert gas GI discharged from the inert gas supply facility 30.

[0100] As described above, the exhaust gas GE is a gas generated when the clay raw material CR is fired. Therefore, moisture contained in the clay raw material CR evaporates during the firing process and is mixed into the exhaust gas GE. This may cause condensation when the exhaust gas GE is cooled in the heat exchanger 51E. If liquid moisture is present in the piping, it may corrode the equipment or cause an abnormal noise called water hammer. From this perspective, the heat exchange equipment 51 may be provided with a drainage mechanism (not shown), such as a drain.

[0101] 11, a portion of the inert gas GID may be discharged to the outside air or to a processing system outside the system 1 via a pipe 76. In this case, by providing an appropriate control valve 83 or the like in the pipe, the amount of the inert gas GID to be merged with the inert gas GI discharged from the inert gas supply equipment 30 may be adjusted.

[0102] FIG. 12 is a conceptual block diagram showing a detailed configuration example of the inert gas supply system 30. In the example shown in FIG. 12, the inert gas supply system 30 includes an air supply source 66, a compressor 67, an oxygen separator 68, and a gas tank 69. The compressor 67 compresses atmospheric air GA supplied from the air supply source 66 and sends it to the oxygen separator 68. The oxygen separator 68 separates oxygen from the high-pressure air sent out from the compressor 67 using a known method such as cryogenic separation, adsorption separation, or membrane separation to produce an inert gas GI containing nitrogen as its main component. The inert gas GI sent out from the oxygen separator 68 is temporarily stored in the gas tank 69 and sent to a pipe 84 with its flow rate adjusted.

[0103] As shown in Figures 3, 4, and 13, a portion of the high-temperature exhaust gas GE discharged from the cyclone 43H may be introduced into the inert gas supply facility 30. In this case, for example, as shown in Figure 13, a portion of the high-temperature exhaust gas GE discharged from the cyclone 43H may be sent to an inert gas replenishment facility 80 having storage and predetermined pre-treatment functions, and then merged with air GA and sent to the oxygen separation device 68. As another example, the high-temperature exhaust gas GE may be sent directly from the inert gas replenishment facility 80 to a pipe 84 with its flow rate adjusted. In this case, a drainage mechanism (not shown), such as a drain, may be attached to the inert gas supply facility 30, similar to the heat exchange facility 51.

[0104] As will be described later with reference to the examples, once the calcined clay CF has been cooled to a predetermined temperature of 600°C or less, it is possible to suppress the color change to a reddish color even when cooled in an oxygen-containing atmosphere. Therefore, if the cooled calcined clay CFC discharged through the cyclone 22C is at or below the predetermined temperature and it is desired to further lower the temperature, it can be cooled using low-temperature air or the like.

[0105] As described above, 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 by being 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.

[0106] [Second embodiment] The second embodiment of the manufacturing method will be described mainly in terms of the differences from the first embodiment.

[0107] This embodiment is different from the first embodiment in the configuration of the cooling equipment 20. Fig. 14 is a conceptual block diagram that schematically shows a part of the system 1 of this embodiment, following Fig. 7. However, in Fig. 14, unlike Fig. 7, the air supply source 63 and the inert gas supply equipment 30 are omitted due to space limitations.

[0108] In the system 1 of this embodiment, the cooling equipment 20 has an agitation equipment 25. FIG.

[0109] As shown in FIGS. 14 and 15, the agitation equipment 25 has an elongated shape and has an inlet 25a, an outlet 25b, a first vent 25c, and a second vent 25d.

[0110] The high-temperature fired clay CF discharged through the pipe 71b is introduced into the stirring equipment 25 through the introduction port 25a.

[0111] The first vent port 25c is provided at a position away from the inlet 25a in the longitudinal direction. A current of low-temperature inert gas GI delivered from the inert gas supply equipment 30 flows into the agitation equipment 25 through the first vent port 25c.

[0112] In the stirring equipment 25, high-temperature fired clay CF and low-temperature inert gas GI are mixed in a stirred state. More specifically, the stirring equipment 25 has a cylindrical body 91, and a support shaft 92 and multiple paddles 93 arranged inside the cylindrical body 91. The multiple 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.

[0113] The discharge port 25b is located closer to the first vent port 25c in the longitudinal direction than the inlet 25a. That is, the fired clay CF is mixed with the countercurrent flow of inert gas GI, stirred, and cooled before being led to the discharge port 25b. The fired clay CF is then discharged as cooled fired clay CFC from the discharge port 25b through the pipe 77 and recovered.

[0114] The second vent 25d is located closer to the inlet 25a than the first vent 25c in the longitudinal direction. In the stirring equipment 25, the low-temperature inert gas GI is heated by contact with the high-temperature fired clay CF, and then discharged through the second vent 25d as high-temperature inert gas GIA. This inert gas GIA is transported to the heat exchange equipment 51 via piping 79 and cooled in the heat exchange equipment 51. After being cooled by the heat exchange equipment 51, this inert gas GIA is merged with the low-temperature inert gas GI and used again as a cooling gas for the fired clay CF, which is the same as in the first embodiment.

[0115] In the case of the system 1 of this embodiment, the low-temperature inert gas GI comes into contact with the high-temperature fired clay CF more frequently than in the system 1 of the first embodiment. Therefore, the flow rate of the inert gas GI can be reduced compared to the system 1 in which the high-temperature fired clay CF is cooled during the process of transporting it with the airflow of the low-temperature inert gas GI. Therefore, the heated inert gas GIA transported to the heat exchange equipment 51 becomes a high-temperature gas at a relatively low flow rate, and the heat exchange efficiency in the heat exchange equipment 51 can be improved.

[0116] As will be described later with reference to the examples, after the calcined clay CF is cooled to a predetermined temperature of 600 ° C or less, it is possible to suppress the change to a reddish color tone even if it is cooled in an oxygen-containing atmosphere. From this perspective, for example, as shown in Figure 16, as the agitation equipment 25, two agitation equipments 25A and 25B are provided in series, and the agitation equipment 25A uses low-temperature inert gas GI to primarily cool the high-temperature calcined clay CF to a predetermined temperature of 600 ° C or less, and then the agitation equipment 25B uses low-temperature air GA to perform secondary cooling.

[0117] In this case, more specifically, the primarily cooled fired clay CFB is sent from the agitator 25A through a pipe 95 into the agitator 25B. Low-temperature air flows into the agitator 25B through a pipe 96. The primarily cooled fired clay CFB is cooled by being agitated and mixed with a countercurrent low-temperature air flow in the agitator 25B, and is recovered as cooled fired clay CFC through a pipe 77. The heated air GAA discharged from the agitator 25B and flowing through a pipe 97 may be used, for example, as a combustion-supporting gas GF for the calciner 11.

[0118] Although Figure 16 illustrates a case where different stirring equipment 25A and stirring equipment 25B are connected via piping 95, it is also possible to form an area with the same function as stirring equipment 25A and an area with the same function as stirring equipment 25B within a single stirring equipment 25 by dividing the inside of the single stirring equipment 25 using a partition member or the like.

[0119] Also, in this embodiment, as in the system 1 of the first embodiment described above with reference to FIG. 9, a powder material MD having a lower temperature than the calcined clay CF may be supplied from the feeder 65 and mixed with the calcined clay CF (see FIG. 17). In the system 1 shown in FIG. 17, the low-temperature powder material MD is introduced into the agitation equipment 25 together with the high-temperature calcined clay CF from an inlet 25a provided in the agitation equipment 25. In the agitation equipment 25, the high-temperature calcined clay CF is cooled by contact with the low-temperature powder material MD while being agitated with a low-temperature inert gas GI in a counterflow state, and the cooled calcined clay CFC is recovered through the outlet 25b. In this configuration, strictly speaking, the mixture of the cooled calcined clay CFC and the powder material MD discharged through the outlet 25b is recovered.

[0120] Furthermore, in this embodiment, as shown in Fig. 17, a part of the cooled fired clay CFC may be mixed with the fired clay CF. In this case, similar to the system of the first embodiment described above with reference to Fig. 8, a pipe 75 branching from a pipe 77 connected to the outlet 25b of the mixing equipment 25 is provided, and the cooled fired clay CFC can be introduced to the inlet 25a of the mixing equipment 25 using the power of a conveying equipment 64 consisting of a fan, a belt conveyor, or the like.

[0121] 17 shows a case where the inlet 25a for feeding high-temperature fired clay CF into the mixing equipment 25 also serves as an inlet for feeding low-temperature powder material MD into the mixing equipment 25 and an inlet for feeding cooled fired clay CFC into the mixing equipment 25. However, in the mixing equipment 25, the inlet for feeding low-temperature powder material MD and the inlet for feeding cooled fired clay CFC may each be provided in a location separate from the inlet 25a for feeding high-temperature fired clay CF. However, even in this case, each inlet is positioned near the inlet 25a for feeding high-temperature fired clay CF in the longitudinal direction of the mixing equipment 25.

[0122] The structure of the stirring equipment 25 described above with reference to Fig. 15 is merely one example. As the stirring equipment 25, in addition to the paddle type shown in Fig. 15, a pug mill, a stirrer having two or more shafts, etc. can be used as appropriate.

[0123] In the above explanation, the calcined clay CF is cooled using a countercurrent flow of low-temperature inert gas GI in the agitation equipment 25, but the present invention does not exclude an embodiment in which the calcined clay CF is cooled in the agitation equipment 25 using a parallel flow of low-temperature inert gas GI. In addition, from the viewpoint of enhancing the cooling effect on the calcined clay CF, for example, a water sprinkling treatment may be carried out in parallel in the agitation equipment 25. In this case, a drainage mechanism such as a drain may be attached to the agitation equipment 25 to drain the water vapor and condensed water generated by the water sprinkling. [Example]

[0124] 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.

[0125] [Description 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).

[0126] [Table 1]

[0127] 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%.

[0128] [Table 2]

[0129] 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).

[0130] [Table 3]

[0131] [Test equipment explanation] In the test, two types of equipment shown in Figures 18 and 19 were used.

[0132] The first test facility 100 shown in Fig. 18 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 fired clay CF.

[0133] The second test facility 110 shown in FIG. 19 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 facility 110, the storage chamber 113 and the tubular electric furnace 114 simulate the firing facility 10 shown in FIG. 3.

[0134] When firing the clay raw material CR using the second testing facility 110, the fired clay raw material CR (fired clay CF) can be moved to a non-heating area 113B of the storage chamber 113 located outside the tubular electric furnace 114, thereby allowing cooling within the atmosphere of the storage chamber 113. Furthermore, the fired clay CF can be discharged from the storage chamber 113, allowing atmospheric cooling.

[0135] 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.

[0136] It was previously confirmed that there was no difference in activity (quality) between the fired clay CF obtained by firing the clay raw material CR for 30 minutes using the second test equipment 110 and the fired clay CF obtained by firing the clay raw material CR for 1.5 seconds using the first test equipment 100.

[0137] (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 20. 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."

[0138] [Table 4]

[0139] [Table 5]

[0140] 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.

[0141] (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 verified. The levels and results are shown in Table 6 and Figure 21. Note that the firing temperature for level #5 in verification 1 was 850°C.

[0142] [Table 6]

[0143] According to the results of verification 2, when the firing time exceeds 10 seconds, the activity of the obtained fired clay CF begins to decrease, and in the case of level #13, where the firing time was set to 20 seconds, the activity of the 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.

[0144] (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 22. For comparison, Table 7 also lists the color tone results for OPC (ordinary Portland cement).

[0145] [Table 7]

[0146] The color tone of the fired clay CF 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.

[0147] 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 CF is that it turns reddish due to the oxidation of iron, which is thought to be mainly due to an increase in the a value as well as an increase in the b value.

[0148] 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.

[0149] The results in Table 7 and Figure 22 confirm that lowering the oxygen concentration during firing tends to reduce the a-value and b-value of fired clay CF. The change in each color value is more pronounced when the oxygen concentration during firing is 2% or less. From these results, it can be seen that when firing clay raw material CR, the oxygen concentration of the firing atmosphere is preferably 2% or less, and more preferably 0.5% or less.

[0150] (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 CF obtained by varying the oxygen concentration of the cooling atmosphere was examined. The fired clay CF was cooled in the non-heated area 113B in the storage chamber 113, as described above with reference to Figure 19. The levels and results are shown in Table 8 and Figure 23.

[0151] [Table 8]

[0152] According to the results of Table 8 and Figure 23, when the oxygen concentration of the atmosphere during firing is fixed at a low concentration, by lowering the oxygen concentration of the cooling atmosphere, the a value and b value of the fired clay CF tend to decrease further. The change in each color value is more pronounced when the oxygen concentration of the atmosphere during cooling is 2% or less. In addition, the color tone of levels #14 and #21 was such that it could be determined that the appearance of redness was completely suppressed.

[0153] (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 in the firing atmosphere of 0.5%, and then the fired clay CF was subjected to primary cooling in the non-heated area 113B of the storage chamber 113. The fired clay CF was then removed from the storage chamber 113 and subjected to secondary cooling in the atmosphere. The relationship between the starting temperature of the secondary cooling, i.e., the temperature at the start of atmospheric cooling, and the color tone of the resulting fired clay CF was examined. The levels and results are shown in Table 8 and Figure 23.

[0154] [Table 9]

[0155] It was confirmed that the a-value and b-value of the fired clay CF 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 CF 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]

[0156] 1: System 10: Firing equipment 11: Firing furnace 12: Burner 14: Loop duct 20: Cooling equipment 21C, 22: Cyclone 25, 25A, 25B: Mixing equipment 25a: Inlet 25b: Discharge port 25c: First ventilation hole 25d: Second vent 30: Inert gas supply equipment 41: Preheating equipment 41D, 42: Piping 43: Solid-gas separation equipment 43H: Cyclone 45: Solid-gas separation equipment 45F: Discharge equipment with sealing function 45H: Cyclone 51:Heat exchange equipment 51E: Heat exchanger 61: Feeder 62 :Fuel supply source 63: Air supply source 64:Transportation equipment 65: Feeder 66: Air supply source 67: Compressor 68: Oxygen separation device 69: Gas tank 71a, 71b, 72a, 72b, 74a, 74b, 75, 76, 77, 79: Piping 80: Inert gas replenishment equipment 81, 82: Induction fan 83: Control valve 84: Piping 91: Cylinder 92: Support shaft 93: Paddle 95,96: Piping 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: Calcined clay CFB: Calcined clay CFC: Cooled fired clay CR: Clay raw material GA, GAA: Air GE: Exhaust gas GF: Combustion-supporting gas GI, GIA, GIC, GID, GIE: Inert gas MD: Powder VD: fuel

Claims

1. (a) feeding a clay raw material into the line; (b) calcining the clay raw material in an air stream having a low oxygen concentration; Step (c) of mixing the fired clay, which is the clay raw material obtained after performing step (b), into an air stream having a lower temperature and a lower oxygen concentration than the fired clay and cooling it; a step (d) of cooling the first airflow discharged after the step (c) is performed; and (e) recovering the cooled calcined clay, which is the calcined clay obtained after the step (c), A method for producing calcined clay, characterized in that the step (c) is carried out in an air stream into which part or all of the first air stream that has undergone the step (d) is joined.

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

3. The method for producing calcined clay according to claim 2, characterized in that the step (c) includes a step of mixing a powder material having a lower temperature than the calcined clay obtained after performing the step (b) into the air flow.

4. The method for producing calcined clay according to claim 1, 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.

5. The step (d) includes a step of performing heat exchange between the first airflow and a second airflow having a lower temperature than the first airflow, 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 (b2) transporting the clay raw material by a high-temperature, low-oxygen-concentration airflow discharged from the firing furnace; 5. The method for producing calcined clay according to claim 4, wherein part or all of the second airflow heated by the execution of step (d) is supplied to the calcination furnace as the combustion-supporting gas.

6. After carrying out the step (a1), a step (f) of separating the preheated clay raw material into a solid and a gas; and (g) cooling a portion of the third air flow discharged after the step (f) is performed, The method for producing calcined clay according to claim 5, characterized in that the step (c) is carried out in an airflow into which part or all of the third airflow that has passed through the step (g) is joined.

7. The step (d) includes a step of performing heat exchange between the first airflow and a second airflow having a lower temperature than the first airflow, 7. The method for producing calcined clay according to claim 6, wherein the step (g) includes a step of performing heat exchange between a portion of the third airflow and the second airflow.

8. The method for producing calcined clay according to claim 2, characterized in that step (b) is a step of calcining the clay raw material in an air flow at a temperature ranging from 550 ° C to 1,000 ° C for a time period ranging from 0.5 seconds to 10 seconds.

9. 2. The method for producing calcined clay according to claim 1, wherein the step (e) is a step of recovering the cooled calcined clay discharged from the low-oxygen-concentration airflow.

10. The step (c) is a step of lowering the temperature of the calcined clay to a predetermined temperature of 600 ° C or less, After carrying out the step (c), a step (h) of further cooling the calcined clay in an airflow having a higher oxygen concentration than the airflow used in the step (c), 2. The method for producing calcined clay according to claim 1, wherein the step (e) is a step of recovering the cooled calcined clay obtained after carrying out the step (h).

11. The step (c) Step (c1) of primarily cooling the fired clay by mixing the fired clay obtained after the step (b) with a primary cooling airflow having a low oxygen concentration; The calcined clay after the primary cooling obtained after the step (c1) is mixed with a secondary cooling airflow having a low oxygen concentration and a temperature lower than the primary cooling airflow, thereby secondary cooling the calcined clay. The step (c1) is performed in the primary cooling airflow obtained by joining a part or all of the exhaust airflow discharged after the step (c2) is performed, The step (d) is a step of cooling the first air flow discharged after the execution of the step (c1), The step (c2) is carried out in the secondary cooling airflow formed by merging part or all of the first airflow that has passed through the step (d). A method for producing fired clay according to claim 1.

12. 12. The method for producing calcined clay according to claim 11, wherein the step (c1) includes a step of mixing a powder material having a lower temperature than the calcined clay obtained after performing the step (b) into the primary cooling airflow.

13. The step (c) Step (c1) of charging the fired clay into a long stirring equipment through an inlet; A step (c2) of introducing an airflow having a lower oxygen concentration and a lower temperature than the fired clay into the stirring equipment from a first air outlet longitudinally separated from the inlet; The 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 fired clay, are stirred in the stirring equipment while the fired clay is conveyed in the longitudinal direction (c3); A step (c4) of discharging the cooled fired clay from a discharge outlet located closer to the first vent than the inlet in the longitudinal direction; and (c5) discharging the first air flow through a second vent located closer to the inlet than the first vent in the longitudinal direction. A method for producing fired clay according to claim 1.

14. The step (c) includes a step (c6) of adding a powder material having a lower temperature than the calcined clay obtained after the execution of the step (b) to the stirring equipment from the same inlet or another inlet located near the inlet in the longitudinal direction, The step (c3) is a step of stirring the fired clay, the powder material, and the airflow flowing in from the first air port, The method for producing fired clay according to claim 13, characterized in that the step (c4) is a step of discharging the cooled mixture of the fired clay and the powder material from the discharge outlet.

15. The powder material is at least one selected from the group consisting of cement, ground clinker, raw concrete sludge, fine waste concrete, clinker dust, blast furnace slag, and the cooled fired clay recovered in step (e). A method for producing fired clay according to claim 3, claim 12, or claim 14.

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