Cement clinker and method for producing cement

Abstract

A method for producing cement clinker, wherein a cement clinker powder raw material charged into a firing kiln 12 is fired by a kiln burner 10 using a thermal energy source containing ammonia, and the ammonia is heated before being introduced into the kiln burner 10.

Description

Cement clinker and method for manufacturing cement

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

[0002] The process of manufacturing cement mainly involves a raw material preparation process in which cement clinker raw materials such as limestone and clay are dried and crushed; a firing process in which the prepared cement clinker powder raw materials are fired in a firing device such as a firing kiln to produce cement clinker; and a finishing process in which gypsum and other materials are added to the manufactured cement clinker to make cement.

[0003] In the above firing process, the cement clinker powder raw material is generally pre-fired at approximately 900°C in a preheater section equipped with a calcination furnace, and then fully fired at approximately 1450°C in a firing kiln. In these calcination furnaces and firing kilns, carbon-containing thermal energy sources such as petroleum and coal are usually used as the heat source for the burners, and a large amount of CO is released during combustion. ２ There was a problem that CO was generated. ２ To reduce emissions, ２ It has been proposed to use gaseous fuels, which are produced in small quantities, as a source of thermal energy.

[0004] For example, methods using hydrogen as a gaseous fuel (see Patent Document 1) or ammonia (see Patent Document 2) have been proposed.

[0005] Japanese Patent Publication No. 2018-052746 Japanese Patent Publication No. 2019-137579

[0006] However, the hydrogen method is problematic because hydrogen is highly flammable and must be pre-mixed 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 problem is solved by pre-mixing with oxygen, but like hydrogen, 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.

[0008] The inventors of the present invention, CO ２ As a result of diligent research into effectively using ammonia, a relatively inexpensive fuel that does not produce waste, as a thermal energy source for kiln burners, we discovered that heating the ammonia before introducing it into the kiln burner improves its flammability, ensuring sufficient combustion 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 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], 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], characterized in that the heating of the ammonia is carried out using the exhaust gas of the cement clinker production equipment. [4] The method for producing cement clinker according to any one of [1] to [3], characterized in that hydrogen is mixed 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.

[0012] According to the method for producing cement clinker of the present invention, CO ２ This improves the flammability of ammonia, a relatively inexpensive fuel that does not produce waste, and allows for its effective use as a thermal energy source for kiln burners.

[0013] This figure shows an example of the steps in the method for producing cement clinker according to the present invention. This is a schematic diagram of the area around the kiln burner of the manufacturing equipment for carrying out figure shows an example of the steps in the method for producing cement according to the present 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 present invention's method for producing cement clinker, since ammonia is heated and introduced into the kiln burner, the flammability of the ammonia can be improved, compensating for the drawback of ammonia's low flammability and enabling effective firing of the cement clinker powder raw material. Furthermore, since ammonia is used as the thermal energy source for the kiln burner, CO2 is produced. ２ This can help reduce the amount of waste generated.

[0016] 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.

[0017] (Raw Material Preparation Process) The raw material preparation process is a process of preparing powdered raw materials by drying and pulverizing cement clinker raw materials (Step 1). Here, conventionally known general cement clinker raw materials such as limestone, clay, and silica can be used as cement clinker raw materials.

[0018] The raw material preparation process mainly involves blending, drying, and grinding. Blending is the process of mixing various cement clinker raw materials in predetermined proportions according to the purpose. Drying is the process of heating and drying the cement clinker raw materials, either individually or in a blended (mixed) state. Grinding is the process of grinding the dried cement clinker raw materials and may be performed simultaneously with the drying process. Drying can be performed before and / or simultaneously with the grinding process.

[0019] In the drying process of the raw material preparation stage, the thermal energy of the combustion gases generated in the calcination stage can be utilized.

[0020] (Casturing process) The calcination process includes a calcination step in which the cement clinker powder raw material prepared in the raw material preparation step is calcined in a calcination furnace, and a final calcination step in which the cement clinker powder raw material calcined in the calcination step is final calcined in a calcination 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, ammonia burns to produce CO2. ２ Since it does not generate CO2, ２ This allows for a reduction in the amount of waste generated. Furthermore, since ammonia is cheaper than hydrogen, it is 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, FIG. 2 is a schematic view of the vicinity of the kiln burner of the manufacturing equipment for implementing the method for manufacturing cement clinker of the present invention. As shown in FIG. 2, the kiln burner 10 is provided on the outlet side of the rotary kiln (firing kiln) 12 and fires the raw materials transferred in the rotary kiln 12. Further, a clinker cooler 14 is provided at the outlet of the rotary kiln 12 to cool the fired cement clinker. Ammonia is heated by the exhaust gas discharged from the exhaust passage 16 extending from this clinker cooler 14, and the heated ammonia is used as the heat energy source of the kiln burner 10.

[0024] As the heating temperature of ammonia, it is preferably 150°C or higher, more preferably 200°C or higher, still more preferably 250°C or higher, and particularly preferably 300°C or higher. The upper limit is not particularly limited, but for example, it is about 350°C. When the heating temperature of ammonia is 150°C or higher, the pre-kiln gas temperature is maintained at about the same level as when using pulverized coal, which is preferable because it does not affect the properties of the clinker.

[0025] As the heat energy source of the kiln burner, in addition to ammonia, carbon-containing fuels (excluding gas fuels) such as petroleum, coal (pulverized coal), and waste plastics can be used. For example, as shown in FIG. 2, the kiln burner 10 has a double-tube structure, and it is preferable that a carbon-containing fuel such as pulverized coal is introduced into the central part and the heated ammonia is introduced into the peripheral part.

[0026] In addition to ammonia, gas fuels other than ammonia can also possible. Examples of the gas fuel include hydrogen, methane, ethane, and propane. From the viewpoints of reducing the generation of CO and flammability, hydrogen is preferable. Hydrogen serves as an auxiliary fuel for ammonia. For example, as shown in FIG. 3, the heated ammonia and hydrogen can be mixed. From the viewpoint of ensuring higher safety, it is preferable not to use oxygen or air containing oxygen. ２ Here, FIG. 3 is a schematic view of the vicinity of the kiln burner of the manufacturing equipment for implementing the method for manufacturing cement clinker of the present invention. As shown in FIG. 3, the kiln burner 10 is provided on the outlet side of the rotary kiln (firing kiln) 12 and fires the raw materials transferred in the rotary kiln 12. Further, a clinker cooler 14 is provided at the outlet of the rotary kiln 12 to cool the fired cement clinker. Ammonia is heated by the exhaust gas discharged from the exhaust passage 16 extending from this clinker cooler 14, and the heated ammonia is used as the heat energy source of the kiln burner 10.

[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-described method and 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 crushed 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.

[0031] Examples of the present invention are shown below, 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, where only pulverized coal was used as the thermal energy source (Reference Example 1), where pulverized coal was mixed with ammonia equivalent to 35% of the total thermal energy source in terms of unheated heat (Comparative Example 1), where pulverized coal was mixed with ammonia equivalent to 35% of the total thermal energy source in terms of heat when heated to 300°C (Example 1), and where pulverized coal was mixed with hydrogen equivalent to 10% of the total thermal energy source in terms of heat and ammonia equivalent to 80% of the total thermal energy source in terms of heat when 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 adopted because water evaporation is also being simulated.

[0033] The 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]

[0035]

[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 combustion state was improved by adding 10% hydrogen, so the amount of pulverized coal could be reduced and the amount of ammonia used could be increased. However, in Comparative Example 1, the temperature in front of the kiln was lower, which may cause problems with the clinker properties.

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

[0038] 10 Kiln burner 12 Rotary kiln (firing kiln) 14 Clinker cooler 16 Exhaust passage

Claims

1. A method for producing cement clinker, comprising firing 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.

2. The 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 heating of the ammonia is carried out using the exhaust gas of a cement clinker production facility.

4. The method for producing cement clinker according to claim 1, characterized by mixing hydrogen 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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