Methods for producing cement clinker and cement

Abstract

This method for producing cement clinker which comprises firing a raw powder material for cement clinker introduced into a firing kiln 12, with a kiln burner 10 using a heat energy source including ammonia, characterized by mixing hydrogen as a combustion promoter for the ammonia.

Description

Method for producing cement clinker and cement

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

[0002] As 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 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 a large amount of CO ２ is generated during combustion. Therefore, in order to reduce the amount of CO ２ generated, it has been proposed to use a gas fuel with a low CO ２ 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.

[0005] JP-A-2018-052746 JP-A-2019-137579

[0006] However, in the method using hydrogen, since the combustibility of hydrogen is too high, it must be premixed with air (oxygen), and the premixing of hydrogen and oxygen has a risk of flashback, so the burden for ensuring safety increases. Also, in the method using ammonia, since the combustibility is low, contrary to hydrogen, the gas temperature in front of the kiln (exit of the rotary kiln) becomes low, and it is generally known that problems occur in the clinker properties. Although this problem is solved by premixing with oxygen, similarly, the premixing of oxygen has a risk of flashback, and the burden for ensuring safety increases.

[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 mixing hydrogen with ammonia before introducing it into the kiln burner improves the flammability of ammonia, ensuring sufficient flammability 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 introduced into 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 in that gypsum is added to the cement clinker produced by the method for producing cement clinker according to [1] or [2] and then pulverized.

[0010] 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.

[0011] 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 used to carry out the method for producing cement clinker according to the present invention. This figure shows an example of the steps in the method for producing cement according to the present 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, CO2 is produced. ２ This can help reduce the amount of waste generated.

[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 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.

[0016] 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.

[0017] 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.

[0018] (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).

[0019] In this invention, ammonia mixed with hydrogen as a combustion aid is used as the thermal energy source for the kiln burner in the firing kiln. This improves the flammability of ammonia. Furthermore, ammonia and hydrogen are combusted 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 alone.

[0020] The mixing ratio of ammonia to hydrogen is preferably 1:0.1 to 2.0 in terms of heat energy, more preferably 1:0.3 to 1.5, and even more preferably 1:0.5 to 1.2.

[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 provided on the outlet side of the rotary kiln (firing kiln) 12 and fires the raw materials being transported in 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 the present invention, hydrogen is mixed before introducing ammonia into the kiln burner 10. The kiln burner 10 has, for example, a double-tube structure, in which a carbon-containing fuel such as pulverized coal is introduced into the center, and ammonia and hydrogen are 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 about 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 properties of the clinker.

[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-described 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 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.

[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, where only pulverized coal was used as the thermal energy source (Reference Example 1), where pulverized coal was supplemented with ammonia equivalent to 35% of the total thermal energy source in terms of heat energy (Comparative Example 1), where pulverized coal was supplemented with ammonia equivalent to 35% of the total thermal energy source in terms of heat energy and 35% of hydrogen (Example 1), and where pulverized coal was supplemented with ammonia equivalent to 60% of the total thermal 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 adopted because water evaporation is also being simulated.

[0031] 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.

[0032]

[0033]

[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 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.

[0035] The present invention's method for producing cement clinker is industrially useful because it is a useful method for producing cement clinker.

[0036] 10 Kiln burner 12 Rotary kiln (firing kiln) 14 Clinker 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, characterized in that hydrogen is mixed 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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