Clinker manufacturing method

Abstract

To provide a manufacturing method of clinker capable of obtaining clinker of a low chlorine grade at a low cost, while maintaining a utilization rate of a manufacturing facility in manufacturing a zinc oxide using iron steel dust as a raw material.SOLUTION: A manufacturing method of clinker includes: a reduction-roasting step S20 of reduction-roasting a roasting object including a reducer inner package pellet containing iron steel dust and a carbonaceous reducer, and a flux being an inorganic oxide, so as to separate and recover a crude zinc oxide from the roasting object and to discharge untreated clinker being a residue; and a fresh water cleaning step S30 of cleaning untreated clinker with fresh water. A melting point of the roasting object is set higher than a maximum temperature inside a reduction roasting furnace where the reduction roasting step S20 is performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing clinker from iron and steel dust. More specifically, the present invention relates to a method for producing clinker that is derived from iron and steel dust used as a raw material ore in the production of zinc oxide, has a low chlorine content, and can be preferably used as an iron source. [Background technology]

[0002] Conventionally, zinc oxide ore obtained by separating and removing impurities from zinc-containing raw materials such as crude zinc oxide has been widely used as a raw material for zinc ingots in zinc smelters. Crude zinc oxide can be obtained, for example, by subjecting steel dust generated from blast furnaces, electric furnaces, etc. in the steel industry to a reduction roasting treatment.

[0003] The reduction roasting process of steel dust is generally carried out in a reduction roasting rotary kiln (RRK). From this RRK, clinker, primarily composed of iron, is discharged as a residue after zinc recovery. This clinker is reused in electric furnaces and used as an iron source for cement. To be used as an iron source for cement, the chlorine content must be approximately 0.02% or less.

[0004] In the production of clinker (also referred to as "product clinker" in this specification) to be shipped as an iron source product, methods for increasing the chlorine removal rate include increasing the roasting temperature in the RRK or lengthening the residence time of the material to be roasted in the RRK. However, both of these methods involve the risk of excessive melting of the material to be roasted, resulting in adhesion of the molten material to the inner walls of the rotary kiln, thereby reducing the operating rate of the reducing roasting process. Furthermore, since the amount of fuel and reducing agent used increases, these methods are not desirable from the perspectives of energy conservation and CO2 emission reduction.

[0005] As another means for increasing the chlorine removal rate from iron-containing "clinker," for example, a clinker manufacturing method has been proposed in which clinker is classified into coarse clinker on the large particle size side and fine clinker on the small particle size side, and then the coarse clinker classified on the large particle size side is washed with water (see Patent Document 1).

[0006] However, implementing the manufacturing method disclosed in Patent Document 1 requires capital investment costs for large-scale crushing equipment for crushing reduced iron pellets, and an increase in operating costs due to the addition of a process. For this reason, it has been difficult to adopt such an expensive process in general industrial facilities that perform reduction roasting of steel dust, such as in the manufacturing process of zinc oxide ore. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-164385 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for producing clinker that can produce low-chlorine clinker at low cost while maintaining the operating rate of production equipment in the production of zinc oxide using steel dust as a raw material, etc. [Means for solving the problem]

[0009] The present inventors have found that the above-mentioned problems can be solved by adjusting the melting point of the material to be roasted in the reducing roasting step so that it can be maintained at or above the maximum temperature inside the reducing roasting furnace during the reducing roasting step, and have thus completed the present invention. More specifically, the present invention provides the following.

[0010] (1) A method for producing clinker, comprising: a reducing roasting step in which a material to be roasted, the material including reducing agent-loaded pellets containing steel dust and a carbonaceous reducing agent, and a flux that is an inorganic oxide, is subjected to reducing roasting to separate and recover crude zinc oxide from the material to be roasted, and untreated clinker that is a residue is discharged; and a freshwater washing step in which the untreated clinker is washed with freshwater, wherein the melting point of the material to be roasted is maintained at or above the maximum temperature in a reducing roasting furnace in which the reducing roasting step is carried out.

[0011] According to the clinker manufacturing method (1), in the production of zinc oxide ore using steel dust as a raw material through a reduction roasting process, it is possible to obtain low-chlorine iron-containing clinker at low cost while maintaining the operating rate of the manufacturing equipment.

[0012] (2) The method for producing clinker according to (1), wherein the melting point of the material to be roasted is maintained at or above the maximum temperature by adjusting the composition and / or the amount of the flux added.

[0013] According to the clinker manufacturing method of (2), even if the composition and melting point of the steel dust vary, the effect of the invention of (1) can be stably realized, and low-chlorine iron-containing clinker can be obtained at low cost while maintaining the operating rate of the manufacturing equipment.

[0014] (3) The method for producing clinker according to (1) or (2), wherein the temperature of the untreated clinker is lowered to 800°C or less by air-cooling, and then the fresh water washing step is carried out.

[0015] The clinker manufacturing method (3) prevents the collapse of untreated clinker due to rapid cooling and suppresses the generation of dust due to Fe2O3, i.e., red rust, that accompanies the reoxidation of clinker. The clinker obtained in this way can be used not only as an iron source for cement but also as an iron source for steelmaking, which is highly suitable for use in a wide range of applications.

[0016] (4) The method for producing clinker according to any one of (1) to (3), wherein the chlorine content of the clinker after washing in the fresh water washing step is 0.02% or less.

[0017] By reducing the chlorine content of clinker to 0.02% or less using the clinker manufacturing method (4), it is possible to significantly expand the applications for reusing iron-containing clinker. For example, clinker that satisfies the standards for 0.035% or less chloride ions specified for "normal" or 0.020% or less chloride ions specified for "early-strength" and "ultra-early-strength" Portland cement as an iron source for cement applications can be obtained without requiring large-scale additional capital investment. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a clinker production method that can produce clinker with a low chlorine content at a lower cost while maintaining the operating rate of the production equipment in the production of zinc oxide ore using iron and steel dust as a raw material. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a flowchart showing an example of the overall process flow for producing zinc oxide ore, which is carried out in an embodiment including a clinker production method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The method for producing clinker of the present invention and the overall process for producing zinc oxide ore that is carried out in an embodiment including the method for producing clinker will be described below. However, the present invention is not limited to the following embodiments.

[0021] <Overall process of zinc oxide ore production> The "clinker" obtainable by the present invention is clinker mainly composed of iron components. This clinker is an industrial product that is produced as a by-product along with zinc oxide ore, which is the final product, in the entire process of zinc oxide ore production, the overall flow of which is shown in Figure 1, and is used as a source of iron for various purposes.

[0022] The overall process flow for producing zinc oxide ore is as shown in Figure 1. In this overall process, the steps for producing zinc oxide ore are sequentially performed: a pre-mixing step S10 for obtaining reducing agent-containing pellets containing steel dust and a carbonaceous reducing agent; a reduction roasting step S20 for feeding the reducing agent-containing pellets together with a high-melting-point flux into a reduction roasting treatment; a wet step S40 for removing halogen components by wet treatment from the crude zinc oxide separated and recovered from the steel dust in the reduction roasting step S20; and a dry-heating step S50 for dry-heating the crude zinc oxide cake obtained in the wet step S40 to obtain zinc oxide ore (zinc oxide cinder) as the final product.

[0023] The "clinker manufacturing method" of the present invention is a partial process, within the overall process flow of zinc oxide ore manufacturing shown in FIG. 1, that includes a reduction roasting step S20 and a freshwater washing step S30 for washing "untreated clinker" discharged from the reduction roasting step S20 as a residue after zinc component recovery, and is carried out in parallel with the above-mentioned zinc oxide ore manufacturing process.

[0024] <Clinker manufacturing method> As described above, the "clinker manufacturing method" of the present invention (hereinafter also simply referred to as "clinker manufacturing method") is a partial process that is carried out in parallel with the flow of producing zinc oxide ore within the overall process of producing zinc oxide ore. This "clinker manufacturing method" is a process that includes at least a reducing roasting step S20 and a fresh water washing step S30. By carrying out each of these steps under predetermined operating conditions unique to the present invention, this process makes it possible to obtain "product clinker" with a low chlorine content that can be shipped as an iron source product at a lower cost than conventional methods.

[0025] In the "clinker manufacturing method," the furnace temperature of the RRK or the like in which the reducing roasting step S20 is performed is sufficiently increased to maintain a desirable recovery rate of zinc components, while at the same time, the composition of the roasted material is adjusted so that its melting point is equal to or higher than the furnace temperature in order to suppress melting of the material. This prevents the molten material from adhering to the inner wall of the RRK. Furthermore, the "untreated clinker" discharged from the RRK is converted into porous clinker with numerous fine voids, thereby enhancing the cleaning effect in the subsequent freshwater cleaning step S30.

[0026] [Pre-mixing process] In the "overall process for producing zinc oxide ore," prior to the reduction roasting step S20, raw ore containing zinc, such as steel dust, is mixed with powder mainly composed of a carbonaceous reducing agent, such as recycled carbon, and granulated to form reducing agent-containing pellets.

[0027] The mixing and granulation of the reducing agent-containing pellets, or so-called pelletizing, can be carried out using a commonly used pelletizing device. For example, using a rotary pan pelletizer or a twin-screw variable speed pin granulator, a Dow pelletizer, steel dust and recycled carbon are continuously fed to form a predetermined pellet composition, and pelletized while adding mist-like moisture, to obtain reducing agent-containing pellets to be fed into the reduction roasting step S20.

[0028] The pre-mixing step S10 is not an essential step in the "clinker manufacturing method" of the present invention. For example, the "clinker manufacturing method" can also be carried out in a mode in which reducing agent-containing pellets that have been processed and molded to an appropriate size in advance in another factory or the like are directly introduced into the reducing roasting step S20 without going through the pre-mixing step S10.

[0029] (reducing agent-containing pellets) The size of the reducing agent-containing pellets used in the "clinker manufacturing method" is preferably about 1 mm or more and 20 mm or less, and more preferably about 5 mm or more and 10 mm or less. By making the size of the reducing agent-containing pellets about 1 mm or more, carryover during insertion into the rotary kiln can be suppressed. Furthermore, by making the size about 20 mm or less, deterioration of the zinc recovery rate can be avoided, and chlorine can be efficiently removed in the freshwater washing step S30 performed in the flow of the "clinker manufacturing method".

[0030] (carbonaceous reducing agent) As the carbonaceous reducing agent, PC carbon, recycled carbon, etc., which can be pelletized in powder or slurry form, can be appropriately selected and used. Among them, recycled carbon is preferably used from the viewpoints of promoting resource recycling and reducing costs.

[0031] Recycled carbon contains not only carbon but also hydrogen as a combustible component. Therefore, the proportion of unburned combustible components is relatively small compared to reducing agents with a high carbon content. Therefore, by selecting recycled carbon as a carbonaceous reducing agent, it is possible to generate more fine voids within the pellets during roasting in the reduction roasting step S20. Therefore, selecting recycled carbon as a carbonaceous reducing agent is advantageous in terms of giving the "untreated clinker" discharged from the reduction roasting step S20 a more porous shape that enhances the cleaning effect in the freshwater cleaning step S30.

[0032] [Reduction roasting process] The reducing roasting step S20 is a step in which the material to be roasted, which includes the reducing agent-containing pellets and the flux, is charged into a reducing roasting furnace such as a reducing roasting rotary kiln (RRK) and subjected to a reducing roasting treatment.

[0033] The reduction roasting step S20 is a step in the "overall process for producing zinc oxide ore" that plays a role in separating and recovering zinc components from the roasted material. At the same time, in the "clinker production method", it is also a step in which "untreated clinker" is obtained, which is the residue after the zinc components have been separated and recovered and is mainly composed of iron.

[0034] In the reducing roasting step S20, the material to be roasted fed into the RRK may further include untreated steel dust and coke that have not been subjected to a pelletizing process, in addition to the reducing agent-containing pellets and flux.

[0035] In the reduction roasting step S20, in order to efficiently reduce and volatilize metallic zinc from the material to be roasted, the maximum temperature inside the furnace of the RRK reaches approximately 1050°C or higher and 1200°C or lower. The reduced and volatilized metallic zinc is reoxidized in the furnace to become powdered zinc oxide, which is recovered as crude zinc oxide. At the same time, chlorine is also removed by chlorination with metallic zinc, etc., and any chlorine that is not removed remains in the "untreated clinker," which is the residue after zinc recovery.

[0036] As described above, the "clinker manufacturing method" of the present invention requires that the melting point of the material to be roasted input into the reducing roasting step S20 be controlled to be equal to or higher than the maximum temperature inside the reducing roasting furnace where the reducing roasting step S20 is performed. Strictly speaking, this maximum temperature differs for each industrial facility in which the "clinker manufacturing method" is performed and for each actual operation. However, as described above, in the overall process of producing zinc oxide ore, the maximum temperature inside the RRK where the reducing roasting step S20 is performed is usually between about 1050°C and 1200°C. Therefore, by setting the melting point of the material to be roasted to be equal to or higher than this maximum temperature, the "clinker manufacturing method" of the present invention can be implemented in the overall process of producing general crude zinc oxide, and its effects can be enjoyed.

[0037] Specifically, the melting point of the material to be roasted that is input into the reducing roasting step S20 can be controlled so that the melting point according to the average composition of the material to be roasted is equal to or higher than the above-mentioned predetermined temperature. As a specific means for adjusting the melting point, the melting point of the material to be roasted can be adjusted by adding an appropriate amount of a high-melting-point inorganic oxide as a flux. When the "clinker manufacturing method" is carried out within the overall process of general zinc oxide ore manufacturing, the high-melting-point flux can be added in an appropriate ratio so that the melting point of the material to be roasted is equal to or higher than the above-mentioned maximum temperature (the maximum temperature in the RRK where the reducing roasting step S20 is carried out).

[0038] In the "clinker manufacturing method," the high-melting-point inorganic oxide used as a flux is preferably lime (CaO). By adding an appropriate amount of limestone or the like containing or generating lime (CaO) as a flux to the roasting material, the melting point of the roasting material can be maintained at or above the maximum temperature (the maximum temperature in the RRK where the reducing roasting step S20 is performed). In the production of zinc oxide ore, limestone (CaCO3) is widely used as a flux to be added as a lime (CaO) source because of its low cost.

[0039] Another practical control method for quickly controlling the melting point of the roasted material during the operation of the zinc oxide ore production process is to determine the amount of lime (CaO) added as flux so that the lime (CaO) to silica (SiO2) content ratio (CaO / SiO2) (weight ratio) in the roasted material is between 1.8 and 2.5, provided that the maximum temperature in a reducing roasting furnace such as an RRK that performs the reducing roasting step S20 is between 1050°C and 1200°C, and the composition of the steel dust used is within the general range shown in Table 1 below. This method prevents clinker from melting and produces porous clinker by adjusting the amount of flux added so that the CaO / SiO2 ratio is 1.8 or higher. On the other hand, if the value of the ratio (CaO / SiO2) is greater than 2.5, the cost of the flux will be excessively high, so this ratio is preferably 2.5 or less. The silica (SiO2) content in the material to be roasted can be measured by X-ray fluorescence analysis. When the above method is carried out to determine the amount of flux to be added, the amount of flux to be added as a lime (CaO) source can be appropriately adjusted according to the measured value of the silica content in the material to be roasted by X-ray fluorescence analysis so that the content ratio (CaO / SiO2) (weight ratio) of lime (CaO) to silica (SiO2) in the material to be roasted falls within the above-mentioned appropriate ratio range.

[0040] [Table 1]

[0041] In the "clinker manufacturing method," the melting point of the material to be roasted fed into the reduction roasting step S20 is adjusted to be higher than the maximum temperature inside the furnace in the RRK, which limits melting in the furnace and causes many fine voids to form inside the material to be roasted (clinker) due to the volatilization of zinc or carbon. These voids promote the penetration of water into the clinker in the subsequent freshwater washing step S30, contributing to improving the removal rate of chlorine contained in the clinker.

[0042] On the other hand, to increase the efficiency of chlorine removal in the RRK where the reducing roasting step S20 is performed, it is preferable to lengthen the residence time of the roasted material in the kiln as much as possible. Therefore, the rotation speed of the RRK during operation is preferably set to 0.9 rpm or more and 1.1 rpm or less for a typical rotary kiln with an inner diameter of approximately 3.5 m, for example. If the rotation speed is lower than 0.9 rpm, the movement of the roasted material in the RRK becomes small, increasing the risk of adhesion to the kiln inner wall. Furthermore, if the rotation speed exceeds 1.1 rpm, the movement of the roasted material in the kiln becomes too vigorous, which increases the risk of a sudden increase in carryover.

[0043] [Freshwater washing process] The freshwater washing step S30 is a step in which the untreated clinker discharged from the reducing roasting step S20 is washed with freshwater. Washing of the untreated clinker with freshwater can be carried out by any method in which the clinker comes into contact with freshwater, such as spraying freshwater onto the clinker while it is being transported on a transporting device such as a belt conveyor or pan conveyor, immersing the transporting device itself in freshwater, or immersing the clinker after transport in a freshwater tank. In this way, the freshwater washing step S30 is a step that can be satisfactorily carried out without the need to install any additional dedicated equipment for washing.

[0044] As described above, in the "clinker manufacturing method," many voids are formed in the "untreated clinker" discharged from the reducing roasting step S20. By washing the porous clinker with many voids in this way with fresh water, it is possible to remove chlorine from the clinker with an extremely high removal rate.

[0045] It is preferable to wash untreated clinker with fresh water after the temperature of the clinker has been reduced to below 800°C by air cooling, rather than immediately after it has been discharged from the RRK. This prevents the porous clinker, which has a temperature of around 1000°C, from rapidly decreasing in temperature, preventing the clinker from cracking or breaking and becoming powdery, which is prone to re-oxidation.

[0046] As a means for subjecting "untreated clinker" to the air-cooling treatment of the above-mentioned aspect, for example, the "untreated clinker" discharged from the RRK can be transported by conveyor or the like without immediately bringing it into contact with washing water, and after it has been piled up in a predetermined storage area, washed, thereby lowering the temperature of the clinker to 800°C or less. In this way, the "clinker manufacturing method" can enjoy the effect of suppressing the reoxidation of clinker without the need to install any special additional equipment dedicated to air-cooling.

[0047] [Chlorine removal rate measurement process] It is more preferable that the "clinker manufacturing method" further includes a chlorine removal rate measurement process (not shown) for measuring the chlorine removal rate in the reducing roasting process S20 and the freshwater washing process S30. By providing the chlorine removal rate measurement process downstream of the freshwater washing process S30 and continuously or at appropriate intervals, the chlorine removal rate of the "product clinker" can be controlled with higher accuracy. Note that, in this specification, the "chlorine removal rate from steel dust" refers to the ratio of the total amount of chlorine removed by volatilization in the RRK and the amount of chlorine removed in the freshwater washing process to the amount of chlorine contained in the reducing agent-containing pellets and steel dust fed to the reducing roasting process S20. This "chlorine removal rate from steel dust" can be calculated from the chlorine content in the raw steel dust and the chlorine content in the iron-containing clinker produced from the RRK measured using an X-ray fluorescence analyzer.

[0048] <Other processes involved in the overall process of zinc oxide ore manufacturing> [Wet process] The wet process S40 is a process in which water-soluble impurities are removed from the crude zinc oxide dust recovered in the reduction roasting process by wet treatment to obtain a crude zinc oxide cake.

[0049] [Drying and heating process] The dry heating step S50 is a step of obtaining zinc oxide ore (zinc oxide cinder) by calcining the crude zinc oxide cake and subjecting it to a dry heat treatment. The calcination treatment is carried out in a dry heat rotary kiln (DRK). [Example]

[0050] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0051] The following test was carried out to confirm the effect of improving the chlorine removal rate by the "clinker manufacturing method" of the present invention.

[0052] The test was conducted by subjecting a sample of roasted material consisting of a mixture of carbonaceous reducing agent-containing pellets, additional carbonaceous reducing agent (recycled carbon), and flux, as shown below, to a reduction roasting treatment under the following conditions using an electric muffle furnace that simulates the reaction in a reduction roasting kiln. The clinker obtained by this reduction roasting treatment was then subjected to the following freshwater washing treatment. The reduction roasting treatment was carried out by placing 40 g of the sample of roasted material in a quartz crucible and reducing roasting it for 3 hours in an electric muffle furnace at a temperature of 1100°C. The freshwater washing treatment was carried out by immersing the clinker obtained by the reduction roasting treatment in freshwater for 1 hour.

[0053] (Test pellets containing carbonaceous reducing agent) Steel dust and a carbonaceous reducing agent were mixed and granulated in a Dow pelletizer to produce carbonaceous reducing agent-containing pellets with particle sizes of 5.0 to 10.0 mm. These were used as carbonaceous reducing agent-containing pellets for testing. The blending ratio of steel dust to carbonaceous reducing agent was adjusted so that the carbon content in the pellets was 8.0%, with the amount of carbonaceous reducing agent added relative to the total amount of steel dust. The steel dust used had a composition within the ranges shown in Table 1 above. Recycled carbon was used as the carbonaceous reducing agent.

[0054] (Test flux) Limestone was used as the flux for testing, and the amount added was appropriately adjusted so that the CaO / SiO2 ratio of the roasted material samples was 2.3 for Examples 1 to 3 and 1.7 for Comparative Example 1.

[0055] (Additional carbonaceous reductants for testing) The additional carbonaceous reducing agent was adjusted so that the carbon content, including the inner content, was 18.0% of the total amount of steel dust. (Measurement of chlorine removal rate) The test was carried out four times, and the chlorine content of the raw steel dust, the "untreated clinker" after reduction roasting, and the clinker after freshwater washing was measured using an X-ray fluorescence analyzer. The results are shown in Table 2.

[0056] [Table 2]

[0057] The test results of Examples 1 to 3 shown in Table 2 confirm that the "clinker manufacturing method" of the present invention can reduce the chlorine content in clinker to 0.02% or less. Such low-chlorine clinker can also be suitably used as an iron source for cement applications. In Examples 1 to 3, fine irregularities were observed on the surface of the "untreated clinker after reduction roasting treatment," confirming that it had a porous shape.

[0058] On the other hand, the test results of Comparative Example 1 confirmed that if the melting point of the material to be roasted was not maintained above the maximum temperature inside the reducing roasting furnace in which the reducing roasting step was carried out, a sufficient cleaning effect could not be obtained in the freshwater washing step, and the chlorine content in the clinker could not be reduced to 0.02% or less. Also, in Comparative Example 1, a smooth surface where metal had melted and then solidified was observed on the surface of the "untreated clinker after reducing roasting treatment," and it was confirmed that the surface in particular was not sufficiently porous.

[0059] From the above, it can be seen that the "clinker manufacturing method" of the present invention is a manufacturing method that can obtain low-chlorine clinker at low cost in the production of zinc oxide using steel dust as a raw material, etc. [Explanation of symbols]

[0060] S10 Pre-mixing process S20 Reduction roasting process S30 Freshwater washing process S40 Wet process S50 Drying and heating process

Claims

1. a reducing roasting step in which a roasting target including a reducing agent-containing pellet containing steel dust and a carbonaceous reducing agent and a flux which is an inorganic oxide is reduced and roasted in a reducing roasting furnace, thereby separating and recovering crude zinc oxide from the roasting target, and discharging untreated clinker which is a residue; and a fresh water washing step of washing the untreated clinker with fresh water, The steel dust is The zinc (Zn) content is in the range of 20 to 30% by weight of the total amount of steel dust, The lead (Pb) content is in the range of 0.5 to 3.0 wt % in the total amount of steel dust, The iron (Fe) content is in the range of 20 to 30% by weight of the total amount of the steel dust, The chromium (Cr) content is in the range of 0.1 to 1.0 wt% in the total amount of the steel dust, The fluorine (F) content is in the range of 0 to 1.0% by weight based on the total amount of the steel dust, The cadmium (Cd) content is in the range of 0 to 0.1% by weight in the total amount of steel dust, The content of chlorine (Cl) is in the range of 3 to 5 wt % of the total amount of the steel dust, The content of silicon oxide (SiO 2 ) is in the range of 1 to 5% by weight of the total amount of the steel dust, In the reducing roasting step, the roasted object is reduced and roasted using a reducing roasting furnace having a maximum internal temperature in the range of 1050° C. or more and 1200° C. or less, In the reduction roasting process, lime (CaO) is used as a flux, and lime (CaO) and silica (SiO ２ ) content ratio (CaO / SiO ２ The amount of the flux to be added is determined so that the melting point of the roasted material is maintained at or above the maximum temperature of the reducing roasting furnace by adding the flux. A method for producing clinker.

2. The temperature of the untreated clinker is reduced to 800°C or less by air cooling, and then the fresh water washing step is carried out. A method for producing the clinker according to claim 1.

3. The chlorine content of the clinker after washing in the fresh water washing step is 0.02% or less. A method for producing clinker according to claim 1 or 2.

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