Cement firing method and firing device

Abstract

[Problem] To reduce the amount of heat that is used to produce cement clinker using calcium hydroxide as a starting material. [Solution] A cement firing device 1 comprises a preheater 2 that preheats a starting material R1 that includes calcium hydroxide using high-temperature air A2, A3, a cement kiln 3 that fires the starting material that has had the water removed therefrom by the preheating at the preheater 2, and a clinker cooler 4 that cools clinker C produced by the firing at the cement kiln 3. There may also be a heat exchanger 7 that uses exhaust gas G1 from the cement kiln 3 to raise the temperature of surrounding air A1 to produce the high-temperature air A2. There may also be a hot air furnace 6 that adds hot air to the exhaust gas A1 from the cement kiln 3. There may also be a gas shutoff device (double flap damper) 5 that supplies a starting material R2 into the cement kiln 3 without bringing the high-temperature air inside the preheater 2 and exhaust gas G4 from the cement kiln 3 into contact.

Description

Cement firing method and firing apparatus

[0001] The present invention relates to a method and an apparatus for firing cement clinker using calcium hydroxide as a raw material.

[0002] In general cement production, calcium carbonate (CaCO3) is used. However, in the case of a chemical plant using acetylene (C2H2), for example, calcium hydroxide (Ca(OH)2) is by-produced as a raw material for producing calcium carbide (CaC2) in order to produce acetylene, and cement may be produced using calcium hydroxide as a raw material.

[0003] The decarbonation reaction of calcium carbonate is CaCO3 → CaO + CO2 - 40 kcal / mol (850°C) ··· (1), while the dehydration reaction of calcium hydroxide is Ca(OH)2 → CaO + H2O - 26.1 kcal / mol (580°C) ··· (2). Therefore, when Ca(OH)2 is used as a raw material, the reaction temperature is lower and the heat absorption is less, so the heat used should be less.

[0004] However, actually, since carbon dioxide (CO2) generated by combustion exists in the system, carbonation occurs after the dehydration of Ca(OH)2 at 580°C to 850°C (the reverse reaction of the above (1)), and ultimately the decarbonation reaction also takes place (Ca(OH)2 → CaCO3 → CaO → CaCO3 → CaO). As a result, more heat is used when Ca(OH)2 is used as a raw material.

[0005] The present invention has been made in view of the problems in the above prior art, and an object thereof is to reduce the heat used in producing cement clinker using calcium hydroxide as a raw material.

[0006] To achieve the above object, the present invention is a cement firing method, characterized by contacting a raw material containing calcium hydroxide with high-temperature air for dehydration, firing the dehydrated raw material, and cooling the fired clinker.

[0007] According to the present invention, since the raw material containing calcium hydroxide is dehydrated by contacting it with high-temperature air, carbonation does not occur after dehydration, and the decarboxylation reaction is not performed, thus the amount of heat used can be kept low.

[0008] In the cement firing method described above, the temperature of the high-temperature air can be 580°C or higher and 1000°C or lower, and is preferably 800°C or higher.

[0009] Furthermore, the present invention is a cement firing apparatus characterized by comprising: a preheater for preheating raw materials containing calcium hydroxide with high-temperature air; a cement kiln for firing the raw materials dehydrated by the preheating in the preheater; and a clinker cooler for cooling the clinker fired in the cement kiln.

[0010] According to the present invention, since the raw material containing calcium hydroxide is dehydrated by contacting it with high-temperature air in the preheater, carbonation does not occur after dehydration, and the decarboxylation reaction is not performed, thus the amount of heat used can be kept low.

[0011] By providing a heat exchanger that uses the exhaust gas from the cement kiln to heat the surrounding air and produce high-temperature air, the exhaust gas from the cement kiln can be effectively utilized.

[0012] Furthermore, by providing a hot air furnace that adds hot air to the exhaust gas of the cement kiln, the insufficient heat content of the cement kiln's exhaust gas can be compensated for, and the raw materials can be heated efficiently.

[0013] Furthermore, by providing a gas shutoff device that supplies the raw materials into the cement kiln without bringing the high-temperature air in the preheater into contact with the exhaust gas from the cement kiln, it is possible to prevent the exhaust gas from the cement kiln from mixing into the preheater and to prevent carbonation of the raw materials after dewatering.

[0014] This is an overall configuration diagram showing one embodiment of a cement firing apparatus according to the present invention. This is an overall configuration diagram showing an example of a conventional cement firing apparatus.

[0015] Next, embodiments for carrying out the present invention will be described, but in order to facilitate understanding of the configuration and operation of the cement firing apparatus according to the present invention, a conventional cement firing apparatus will be described first.

[0016] Figure 2 shows an example of a conventional cement firing apparatus. This cement firing apparatus 11 uses a raw material R2 containing calcium carbonate and includes a preheater 2 for preheating the raw material R3, a calcination furnace 12 for calcining the preheated raw material R4, a cement kiln 3 for firing the calcined raw material R5, and a clinker cooler 4 for cooling the cement clinker C fired in the cement kiln 3. The exhaust gas A4 from the clinker cooler 4 is supplied to the calcination furnace 12 and used for burning fuel F in the calcination furnace 12.

[0017] In this cement firing apparatus 11, the raw material R3 is preheated and calcined to over 850°C before entering the cement kiln 3, and calcium oxide and carbon dioxide are produced by the decarboxylation of calcium carbonate, as shown in the following reaction equation (1).

[0018] CaCO3 → CaO + CO2 - 40 kcal / mol (850°C) ... (1) Figure 1 shows one embodiment of the cement firing apparatus according to the present invention. This cement firing apparatus 1, like the cement firing apparatus 11, is equipped with a preheater 2, a cement kiln 3, and a clinker cooler 4. The preheater 2 preheats and dehydrates the cement raw material R1 containing calcium hydroxide, the dehydrated raw material R2 is fired in the cement kiln 3, and the fired cement clinker C is cooled in the clinker cooler 4. The cement firing apparatus 1 does not have a calcination furnace 12, which is provided in the cement firing apparatus 11.

[0019] The cement firing apparatus 1 includes a double flap damper (gas shutoff device) 5 at the outlet chute of the lowest cyclone 2B of the preheater 2, a hot air furnace 6 that supplies hot air to the exhaust gas G1 of the cement kiln 3 at approximately 1000°C, and a heat exchanger 7 that raises the surrounding air A1 to approximately 900°C with the exhaust gas G2 after the hot air supply and supplies it as high-temperature air A2 to the lowest cyclone 2B.

[0020] In this cement firing apparatus 1, the raw material R1 supplied to the preheater 2 is preheated and dehydrated by high-temperature air A2 of about 900°C from the heat exchanger 7 and exhaust gas (high-temperature air) A3 of about 800°C from the clinker cooler 4, and is supplied to the cement kiln 3 from the double flap damper 5 at about 580°C (raw material R2).

[0021] Before entering cement kiln 3, the raw material R is preheated to approximately 580°C and dehydrated, which produces calcium oxide and water as shown in the following reaction equation (2).

[0022] Ca(OH)2 → CaO + H2O - 26.1 kcal / mol (580°C) ... (2) Reaction equation (2) has a lower reaction temperature and less heat absorption compared to reaction equation (1), resulting in less heat being used.

[0023] Here, since the exhaust gas G1 from cement kiln 3 contains a large amount of carbon dioxide, if the exhaust gas G is brought directly into preheater 2, calcium carbonate is produced from calcium oxide and carbon dioxide at 580°C to 850°C, as shown in the following reaction equation (3).

[0024] CaO + CO2 → CaCO3 + 40 kcal / mol ... (3) When calcium carbonate is produced by reaction equation (3), decarboxylation as shown in reaction equation (1) is required, which necessitates an endothermic reaction to generate CaO again, thus increasing the amount of heat used. Therefore, a double flap damper 5 is provided to prevent the exhaust gas G4 from the cement kiln 3 (exhaust gas that flows directly from the cement kiln 3 through the double flap damper 5 to the lowest stage cyclone 2B) from mixing with the preheater 2, thereby preventing the reaction according to reaction equation (3) in the preheater 2 and reducing the amount of heat used. The exhaust gas G1 from the cement kiln 3, after heat exchange in the heat exchanger 7, is discharged as exhaust gas G3 directly from the outlet gas duct of the preheater 2 without passing through the preheater 2.

[0025] Furthermore, the raw material R2 discharged from the double flap damper 5 and supplied to the cement kiln 3 is supplied to the cement kiln 3, which has a high CO2 concentration. However, since the temperature rises to about 1000°C immediately after supplying to the cement kiln 3, there is no need to consider decarboxylation after dewatering, and an increase in the amount of heat used can be avoided.

[0026] Next, the simulation results of the present invention will be described. The simulation results of the amount of heat used in the cement firing apparatus 1 described above were used as an example, and a standard operating example using the cement firing apparatus 11 was used as a comparative example to compare the two. The results are shown in Table 1. In the same table, the heat energy unit "kcal / kg-cli" indicates the amount of heat required to fire 1 kg of cement clinker in the cement firing apparatus.

[0027]

[0028] As shown in the table, in the example, the calcination furnace heat intensity of 429 kcal / kg-cli in the comparative example is unnecessary, and only the heat intensity of 209 kcal / kg-cli for the hot blast furnace 6 is required. Since the cement kiln heat intensity is the same in both the example and the comparative example, it can be seen that the amount of heat used is significantly reduced in the example.

[0029] The present invention is not limited to the embodiments described above, and can be implemented by partially modifying the configuration or partially adding other configurations within the scope of its gist. Furthermore, the illustrated embodiments are merely illustrative and are not intended to limit the technical scope of the present invention.

[0030] 1. Cement firing apparatus 2. Preheater 3. Cement kiln 4. Clinker cooler 5. Double flap damper 6. Hot air furnace 7. Heat exchanger

Claims

1. A cement firing method characterized by dehydrating a raw material containing calcium hydroxide by contacting it with high-temperature air, firing the dehydrated raw material, and cooling the fired clinker.

2. The cement firing method according to claim 1, characterized in that the temperature of the high-temperature air is 580°C or higher and 1000°C or lower.

3. A cement firing apparatus characterized by comprising: a preheater for preheating raw materials containing calcium hydroxide with high-temperature air; a cement kiln for firing the raw materials dehydrated by the preheating in the preheater; and a clinker cooler for cooling the clinker fired in the cement kiln.

4. The cement firing apparatus according to claim 3, further comprising a heat exchanger that heats the surrounding air with the exhaust gas from the cement kiln to produce the high-temperature air.

5. The cement firing apparatus according to claim 3 or 4, characterized in that it is equipped with a hot air furnace that adds hot air to the exhaust gas of the cement kiln.

6. The cement firing apparatus according to claim 3 or 4, further comprising a gas shutoff device for supplying the raw materials into the cement kiln without bringing the high-temperature air in the preheater into contact with the exhaust gas of the cement kiln.

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