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, characterized in that hydrogen is mixed as a combustion aid for ammonia.

Description

Technical Field

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

Background Art

[0002] As the steps in manufacturing 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 rotary 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 heated to about 900°C in a preheater section equipped with a precalciner, and then fired at about 1450°C in a rotary kiln. In these precalciners and rotary 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 low CO2 generation amount 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 by mixing hydrogen with ammonia before introducing it into the kiln burner, the flammability of the ammonia is improved, and sufficient flammability can be ensured without the use of oxygen, thus completing 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 placed in a firing kiln with a kiln burner using a thermal energy source containing ammonia, characterized in that hydrogen is mixed as a combustion aid for the ammonia. [2] The method for producing cement clinker according to [1], characterized in that the mixing ratio of ammonia and hydrogen is 1:0.1 to 2.0 in terms of heat energy. [3] A method for producing cement, characterized by mixing gypsum with cement clinker produced by the cement clinker production method described in [1] or [2] above and then grinding it. [Effects of the Invention]

[0010] 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]

[0011] [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 figure shows an example of the steps in the cement manufacturing method of the present invention. [Modes for carrying out the invention]

[0012] The present invention relates to a method for producing cement clinker, which involves calcining a cement clinker powder raw material placed in a calcination kiln using a kiln burner with a thermal energy source containing ammonia, characterized in that hydrogen is mixed in as a combustion aid for ammonia.

[0013] In the present invention's method for producing cement clinker, hydrogen is mixed with ammonia as a combustion aid, thereby improving the flammability of ammonia and compensating for its low flammability, allowing for effective firing of the cement clinker powder raw material. Furthermore, since ammonia is used as the thermal energy source in the kiln burner, the amount of CO2 emitted can be reduced.

[0014] Here, Figure 1 shows an example of the steps in the method for producing cement clinker according to the present invention. The production method of the present invention typically includes a raw material preparation step and a firing step. Each step will be described in detail below.

[0015] (Raw material preparation process) The raw material preparation process is a process of drying and pulverizing cement clinker raw materials to prepare powder raw materials (Step 1). Here, as the cement clinker raw materials, conventionally known common cement clinker raw materials such as limestone, clay, and silica can be used.

[0016] In the raw material preparation process, mainly, blending treatment, drying treatment, and pulverizing treatment are performed. The blending treatment is a treatment of blending various cement clinker raw materials in a predetermined ratio according to the purpose. The drying treatment is a treatment of heating and drying the cement clinker raw materials for each raw material or in a blended (mixed) state. The pulverizing treatment is a treatment of pulverizing the dried cement clinker raw materials, and it may be performed simultaneously with the drying treatment. The drying treatment can be performed before and / or simultaneously with the pulverizing treatment.

[0017] In the drying treatment of the raw material preparation process, the thermal energy of the combustion gas generated in the firing process can be utilized.

[0018] (Firing process) The firing process includes a pre-firing process of pre-firing the cement clinker powder raw materials prepared in the above raw material preparation process in a pre-firing furnace, and a main firing process of main-firing the cement clinker powder raw materials pre-fired in the pre-firing process in a firing kiln (Step 2).

[0019] In the present invention, as the heat energy source of the kiln burner in the firing kiln, ammonia mixed with hydrogen as a combustion aid is used. Thereby, the combustibility of ammonia can be improved. Also, since ammonia and hydrogen do not generate CO2 by combustion, it is possible to reduce the amount of CO2 generated by firing. Also, since ammonia is less expensive than hydrogen, it is more cost-effective than using hydrogen alone.

[0020] As the mixing ratio of ammonia and hydrogen, in terms of heat quantity conversion, 1:0.1 to 2.0 is preferable, 1:0.3 to 1.5 is more preferable, and 1:0.5 to 1.2 is even more preferable.

[0021] In addition to ammonia and hydrogen, kiln burners can use carbon-containing fuels (excluding gaseous fuels) such as petroleum, coal (pulverized coal), and waste plastics as thermal energy sources, as well as gaseous fuels other than ammonia. Examples of gaseous fuels include methane, ethane, and propane. It is preferable not to use oxygen or oxygen-containing air.

[0022] 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 30-70%, and even more preferably 40-60%.

[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 located 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 provided at the outlet of the rotary kiln 12 to cool the fired cement clinker. In this invention, hydrogen is mixed before introducing ammonia into the kiln burner 10. The kiln burner 10 has, for example, a double-tube structure, with a carbon-containing fuel such as pulverized coal introduced into the center and ammonia and hydrogen introduced into the periphery.

[0024] Here, ammonia may be heated before mixing with hydrogen. The heating temperature of the 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 a temperature of 150°C or higher is preferable because it keeps the gas temperature in front of the kiln at about the same level as when using pulverized coal, and does not affect the clinker properties.

[0025] The preferred method for heating ammonia is to use 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. However, from the standpoint of equipment layout and ease of temperature control, the exhaust gas discharged from the clinker cooler is preferred. 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.

[0026] When heating ammonia, the amount of hydrogen added can be small. The preferred mixing ratio of ammonia to hydrogen, in terms of heat energy, is 1:0.1 to 1.5, more preferably 1:0.2 to 1.2, and even more preferably 1:0.3 to 1.0.

[0027] 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 2 is a diagram showing an example of the steps of the present invention's method for producing cement.

[0028] (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 process, 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]

[0029] The following are examples of the present invention, but the technical scope of the present invention is not limited thereto. Fluid simulations of gas temperature were performed in 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 supplemented with ammonia equivalent to 35% of the total heat energy source in terms of heat energy (Comparative Example 1), when pulverized coal was supplemented with ammonia equivalent to 35% of the total heat energy source in terms of heat energy and 35% of hydrogen (Example 1), and when pulverized coal was supplemented with ammonia equivalent to 60% of the total heat energy source in terms of heat energy and 20% of hydrogen (Example 2).

[0030] 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.

[0031] 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.

[0032] [Table 1]

[0033] [Table 2]

[0034] As shown in Table 2, in Example 1, when the composition was 30% pulverized coal (i.e., a 70% reduction in pulverized coal), 35% ammonia, and 35% hydrogen, 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 increased by only about 250°C, so it is considered that there will be no problems with the clinker properties. In Example 2, when the pulverized coal ratio and hydrogen ratio were reduced and the ammonia ratio was increased compared to Example 1, the temperature in front of the kiln and the maximum gas temperature were about the same as in Reference Example 1. Therefore, it is considered that there will be no problems with the clinker properties. In Comparative Example 1, the temperature in front of the kiln was lower, and there is a risk that problems will occur with the clinker properties. [Industrial applicability]

[0035] 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]

[0036] 10 Kiln Burners 12. Rotary Kiln (Firing Kiln) 14. Clinka Cooler

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 mixing hydrogen as a combustion aid for the ammonia.

2. The method for producing cement clinker according to claim 1, characterized in that the mixing ratio of ammonia and hydrogen is 1:0.1 to 2.0 in terms of heat energy.

3. A method for producing cement, characterized by mixing gypsum with cement clinker produced by the manufacturing method described in claim 1 or 2 and then grinding it.

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