Cement clinker and method for manufacturing cement

Abstract

To provide a method for manufacturing cement clinker using ammonia as the thermal energy source for a kiln burner, which improves the flammability of ammonia and ensures sufficient flammability without pre-mixing with oxygen. [Solution] A method for producing cement clinker, comprising firing cement clinker powder raw material placed in a firing kiln 12 with a kiln burner 10 using a thermal energy source containing ammonia, wherein the ammonia is heated before being introduced into the kiln burner 10.

Description

Technical Field

[0001] The present invention relates to a method for producing cement clinker and cement.

Background Art

[0002] As the steps in producing cement, mainly, there are a raw material preparation step of drying and pulverizing cement clinker raw materials such as limestone and clay, a firing step of firing the prepared cement clinker powder raw material in a firing device such as a firing kiln to produce cement clinker, and a finishing step of adding gypsum or the like to the produced cement clinker to make cement.

[0003] In the above firing step, generally, the cement clinker powder raw material is calcined at about 900°C in a preheater section equipped with a precalciner, and then is main-fired at about 1450°C in a firing kiln. In these precalciners and firing kilns, usually, a carbon-containing heat energy source such as petroleum or coal is used as the heat source of the burner, and there has been a problem that a large amount of CO2 is generated during combustion. Therefore, in order to reduce the amount of CO2 generated, it has been proposed to use a gas fuel with a small amount of CO2 generated as the heat energy source.

[0004] For example, as a gas fuel, a method of using hydrogen (see Patent Document 1) or a method of using ammonia (see Patent Document 2) has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the hydrogen method is problematic because hydrogen is highly flammable, requiring pre-mixing with air (oxygen). This pre-mixing of hydrogen and oxygen carries the risk of flashback, thus increasing the burden of ensuring safety. Similarly, the ammonia method, unlike hydrogen, has low flammability, which generally leads to low gas temperatures at the kiln outlet and problems with clinker properties. This is solved by pre-mixing with oxygen, but similarly, pre-mixing with oxygen carries the risk of flashback, increasing the burden of ensuring safety.

[0007] The object of the present invention is to provide a method for producing cement clinker using ammonia as the thermal energy of a kiln burner, which improves the flammability of ammonia and ensures sufficient flammability without pre-mixing with oxygen. [Means for solving the problem]

[0008] The inventors of this invention diligently studied how to effectively use ammonia, a relatively inexpensive fuel that does not produce CO2, as a thermal energy source for kiln burners. As a result, they discovered that heating ammonia before introducing it into the kiln burner improves its flammability, ensuring sufficient flammability without the use of oxygen, and thus completed the present invention.

[0009] In other words, the present invention is as follows: [1] A method for producing cement clinker, comprising firing a cement clinker powder raw material introduced into a firing kiln with a kiln burner using a thermal energy source containing ammonia, characterized in that the ammonia is heated before the introduction of the kiln burner.

[0010] [2] The method for producing cement clinker according to [1] above, characterized in that ammonia is heated to 150°C or higher before introducing the kiln burner. [3] The method for producing cement clinker according to [1] or [2] above, characterized in that the ammonia is heated using exhaust gas from a cement clinker production facility. [4] A method for producing cement clinker according to any one of [1] to [3] above, characterized by mixing hydrogen with the heated ammonia.

[0011] [5] A method for producing cement, characterized by mixing gypsum with cement clinker produced by any of the manufacturing methods described in [1] to [4] above and then grinding it. [Effects of the Invention]

[0012] According to the present invention's method for producing cement clinker, the flammability of ammonia, which is relatively inexpensive as a fuel that does not generate CO2, can be improved, and ammonia can be effectively used as a thermal energy source for a kiln burner. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows an example of the steps in the method for producing cement clinker according to the present invention. [Figure 2] This is a schematic diagram of the area around the kiln burner of a manufacturing facility for carrying out the cement clinker manufacturing method of the present invention. [Figure 3] This is a schematic diagram of the area around the kiln burner of a manufacturing facility for carrying out the cement clinker manufacturing method of the present invention. [Figure 4] This figure shows an example of the steps in the cement manufacturing method of the present invention. [Modes for carrying out the invention]

[0014] The present invention relates to a method for producing cement clinker, which involves firing cement clinker powder raw material placed in a firing kiln using a kiln burner with a thermal energy source containing ammonia, characterized in that the ammonia is heated before being introduced into the kiln burner.

[0015] In the method for producing cement clinker of the present invention, ammonia is heated and introduced into the kiln burner, so that the flammability of ammonia can be improved, compensating for the disadvantages of ammonia with low flammability and effectively firing the cement clinker powder raw material. Further, since ammonia is used as the heat energy source used in the kiln burner, it is possible to reduce the amount of CO2 generated.

[0016] Here, FIG. 1 is a diagram showing an example of the steps of the method for producing cement clinker of the present invention. The production method of the present invention generally has a raw material preparation step and a firing step. Hereinafter, each step will be specifically described.

[0017] (Raw material preparation step) The raw material preparation step is a step of drying and pulverizing the cement clinker raw material to prepare a powder raw material (step 1). Here, as the cement clinker raw material, conventionally known general cement clinker raw materials such as limestone, clay, and silica can be used.

[0018] In the raw material preparation step, mainly, blending treatment, drying treatment, and pulverizing treatment are performed. The blending treatment is a treatment of blending various cement clinker raw materials at a predetermined ratio according to the purpose. The drying treatment is a treatment of heating and drying the cement clinker raw material for each raw material or in a blended (mixed) state. The pulverizing treatment is a treatment of pulverizing the dried cement clinker raw material, and it may be performed simultaneously with the drying treatment. The drying treatment can be performed before and / or simultaneously with the pulverizing treatment.

[0019] In the drying treatment of the raw material preparation step, the thermal energy of the combustion gas generated in the firing step can be utilized.

[0020] (Firing step) The firing step includes a pre-firing step of pre-firing the cement clinker powder raw material prepared in the above raw material preparation step in a pre-firing furnace, and a main firing step of main-firing the cement clinker powder raw material pre-fired in the pre-firing step in a firing kiln (step 2).

[0021] In this invention, heated ammonia is used as the thermal energy source for the kiln burner in the firing kiln. This improves the flammability of ammonia. Furthermore, since ammonia does not produce CO2 when burned, the amount of CO2 emitted during firing can be reduced. In addition, ammonia is cheaper than hydrogen, making it more cost-effective than using hydrogen.

[0022] Here, it is preferable to heat the ammonia before introducing the kiln burner using the exhaust gas from the cement clinker manufacturing equipment. Examples of exhaust gas from the cement clinker manufacturing equipment include exhaust gas from the clinker cooler and exhaust gas discharged from the top of the preheater section including the calcination furnace, but exhaust gas discharged from the clinker cooler is preferred in terms of equipment layout and ease of temperature control. The exhaust gas discharged from the clinker cooler is hotter when extracted from a point closer to the calcination kiln and cooler when extracted from a point further away from the calcination kiln, and the extraction point can be set as appropriate. This makes it possible to efficiently utilize the waste heat.

[0023] Here, Figure 2 is a schematic diagram of the area around the kiln burner of a manufacturing facility that implements the cement clinker manufacturing method of the present invention. As shown in Figure 2, the kiln burner 10 is installed on the outlet side of the rotary kiln (firing kiln) 12 and fires the raw materials being transported within the rotary kiln 12. A clinker cooler 14 is also installed at the outlet of the rotary kiln 12 to cool the fired cement clinker. The exhaust gas discharged from the exhaust passage 16 extending from the clinker cooler 14 heats ammonia, and the heated ammonia is used as the thermal energy source for the kiln burner 10.

[0024] The heating temperature for ammonia is preferably 150°C or higher, more preferably 200°C or higher, even more preferably 250°C or higher, and particularly preferably 300°C or higher. There is no particular upper limit, but for example, it is around 350°C. Heating the ammonia to 150°C or higher is preferable because it keeps the gas temperature in front of the kiln at a similar level to when using pulverized coal, and does not affect the properties of the clinker.

[0025] In addition to ammonia, carbon-containing fuels (excluding gaseous fuels) such as petroleum, coal (pulverized coal), and waste plastics can be used as thermal energy sources for the kiln burner. For example, as shown in Figure 2, the kiln burner 10 preferably has a double-tube structure, with carbon-containing fuel such as pulverized coal introduced into the center and heated ammonia introduced into the periphery.

[0026] In addition to ammonia, other gaseous fuels can be used. Examples of gaseous fuels include hydrogen, methane, ethane, and propane, with hydrogen being preferred due to its reduced CO2 emissions and flammability. Hydrogen acts as a combustion enhancer for ammonia. For example, as shown in Figure 3, heated ammonia and hydrogen can be mixed. Furthermore, to ensure higher safety, it is preferable not to use oxygen or oxygen-containing air.

[0027] When ammonia and hydrogen are used in a mixture, the mixing ratio of ammonia to hydrogen is preferably 1:0.1 to 1.5 in terms of heat energy, more preferably 1:0.2 to 1.2, and even more preferably 1:0.3 to 1.0.

[0028] Furthermore, the amount of ammonia used in the kiln burner is preferably 20% or more of the total thermal energy source of the kiln burner in terms of heat energy, more preferably 30-85%, and even more preferably 40-80%.

[0029] Furthermore, the present invention's method for producing cement is characterized by having a finishing step of mixing gypsum with the cement clinker produced by the above manufacturing method and then grinding it. Here, Figure 4 is a diagram showing an example of the steps of the present invention's method for producing cement.

[0030] (Finishing process) In the finishing process, the cement clinker prepared in steps 1 and 2 is mixed with at least gypsum and ground to produce cement (step 3). In this step, other materials such as blast furnace slag or fly ash may be added to the cement clinker or cement mixed with gypsum as needed. [Examples]

[0031] The following are examples of the present invention, but the technical scope of the present invention is not limited thereto. Fluid simulations of the gas temperature inside the furnace were performed for the following cases in a firing kiln: when only pulverized coal was used as the heat energy source (Reference Example 1); when pulverized coal was mixed with ammonia equivalent to 35% of the total heat energy source in terms of unheated heat (Comparative Example 1); when pulverized coal was mixed with ammonia equivalent to 35% of the total heat energy source in terms of heat heated to 300°C (Example 1); and when pulverized coal was mixed with hydrogen equivalent to 10% of the total heat energy source in terms of heat and ammonia equivalent to 80% of the total heat energy source in terms of heat heated to 300°C (Example 2).

[0032] The calorific values ​​of each heat energy source are 6840 kcal / kg for pulverized coal, 4030 kcal / Nm3 for ammonia, and 3000 kcal / Nm3 for hydrogen. High calorific values ​​were chosen because water evaporation is also being simulated.

[0033] These fluid simulation conditions are shown in Table 1, and the results are shown in Table 2. In this fluid simulation, the kiln structure was defined as two-dimensional axisymmetric, and solutions were obtained by applying turbulence, radiation, and combustion models. This fluid simulation was performed using Ansys Fluent 2021, a general-purpose fluid simulation software from Ansys. The kiln front gas temperature difference is the temperature difference relative to the kiln front gas temperature when 100% pulverized coal is used. The kiln front gas temperature is the temperature at point A in Figure 2. The maximum gas temperature is the highest gas temperature inside the kiln.

[0034] [Table 1]

[0035] [Table 2]

[0036] As shown in Table 2, in Example 1, the maximum gas temperature was about the same as that of 100% pulverized coal (Reference Example 1), and the temperature difference in front of the kiln was only about 100°C lower, so it is considered that there would be no problems with the clinker properties. In Example 2, the addition of 10% hydrogen improved the combustion state, allowing for a reduction in the amount of pulverized coal and an increase in the amount of ammonia used. However, in Comparative Example 1, the temperature in front of the kiln was lower, which may cause problems with the clinker properties. [Industrial applicability]

[0037] The present invention's method for producing cement clinker is industrially useful because it is a useful method for producing cement clinker. [Explanation of Symbols]

[0038] 10 Kiln Burners 12. Rotary Kiln (Firing Kiln) 14. Clinka Cooler 16 Exhaust passage

Claims

1. A method for producing cement clinker, comprising firing cement clinker powder raw material placed in a firing kiln with a kiln burner using a thermal energy source containing ammonia, A method for producing cement clinker, characterized by heating ammonia before introducing the kiln burner.

2. A method for producing cement clinker according to claim 1, characterized in that ammonia is heated to 150°C or higher before introducing the kiln burner.

3. The method for producing cement clinker according to claim 1, characterized in that the ammonia is heated using the exhaust gas of a cement clinker production facility.

4. A method for producing cement clinker according to claim 1, characterized in that hydrogen is mixed with the heated ammonia.

5. A method for producing cement, characterized by mixing gypsum with cement clinker produced by the manufacturing method described in any one of claims 1 to 4 and then grinding it.

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