Method for producing calcium oxide from limestone

Abstract

The application discloses a method for preparing calcium oxide by using limestone, which comprises the following steps: S1, small-particle limestone is mixed with calcium nitrate, and then is heated and calcined in a muffle furnace, and the calcium nitrate is heated and decomposed to prepare new calcium nitrate; S2, the temperature is increased to 800 DEG C again, and the calcination is continued until the small-particle limestone is completely converted into calcium oxide, the calcination is stopped, the temperature is reduced to room temperature, and the product calcium oxide is taken out; after the step S2, there are steps S3, S4 and S5 for preparing calcium nitrate; S3, the calcium nitrate in the step S1 is calcined and decomposed to obtain calcium oxide and nitrogen oxide gas, and the escaped nitrogen oxide gas is absorbed by water to prepare a nitric acid solution; S4, the small-particle limestone is soaked in the nitric acid solution in the step S3 to obtain calcium nitrate, and S5, the calcium nitrate in the step S4 is mixed with the small-particle limestone to prepare new calcium oxide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of limestone processing, in particular to a method for preparing calcium oxide from limestone. BACKGROUND

[0002] Calcium oxide (CaO) is a widely used inorganic material, which can be used as a filler for plastics, rubber and paint, as a raw material for the production of calcium carbide, calcium hydroxide, as a desulfurizer and denitrification agent for pollution control, and as a slagging agent for the metallurgical industry.

[0003] Calcium oxide is mainly prepared by calcining natural limestone (CaCO3), and when limestone is completely converted into calcium oxide, the weight loss rate is about 44%. Specifically, in a rotary kiln, a double-hearth kiln, a shaft kiln, etc., limestone is heated to 900-1200℃ using coal or natural gas combustion to obtain calcium oxide. This traditional method of producing calcium oxide has requirements for the particle size of the raw material limestone. Too small a particle size will increase the air resistance and heat transfer in the kiln, and too large a particle size will increase the time for limestone to decompose into calcium oxide, both of which will reduce the production capacity of the kiln. Therefore, patent [CN 107619203 A] uses 2-9 cm limestone, and the rotary kiln and double-hearth kiln require limestone particle size to be between 1.5-8 cm, while limestone smaller than 1.5 cm is waste slag, which is supplied to cement plants or used as bridge construction melon seeds, with a selling price of about 20 yuan per ton [Naihuo yu shuihai, 2017, 42(04): 13], which has very low economic value. Although limestone is a natural raw material, it is also a non-renewable resource. In order to fully exploit the economic value of limestone, it is necessary to develop a method that can convert small particle size limestone into calcium oxide.

[0004] Considering that the higher the calcination temperature of limestone, the more fuel consumed and the more carbon dioxide emissions produced, and the higher the requirement for furnace material, therefore, developing a low-temperature calcination technology for limestone is beneficial to improve the economy of the calcium oxide production process; for this purpose, the present application provides a method for preparing calcium oxide from limestone. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing calcium oxide from limestone to solve the problems raised in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution:

[0007] A method for preparing calcium oxide from limestone, comprising the following steps:

[0008] S1, after mixing small particle limestone with calcium nitrate, first perform temperature calcination in a muffle furnace, and the calcium nitrate is heated and decomposed to prepare new calcium nitrate;

[0009] S2, again heating to 800℃, and continue calcination until all the small particle limestone is converted into calcium oxide, stop calcination, and when the temperature drops to room temperature, remove the product calcium oxide;

[0010] There are steps S3, S4 and S5 after step S2 for preparing calcium nitrate;

[0011] S3, the step S1 of calcination and decomposition of calcium nitrate to obtain calcium oxide and nitrogen oxide gas, and absorbing the escaping nitrogen oxide gas with water to prepare a nitric acid solution;

[0012] S4, using the nitric acid solution in step S3 to soak the small particle limestone to obtain calcium nitrate,

[0013] S5, the step S4 of mixing calcium nitrate with small particle limestone to carry out a new round of calcium oxide preparation.

[0014] Further, the temperature in step S1 is 150℃-700℃, preferably 200℃-600℃.

[0015] Further, the calcination time in step S1 is 1 hour.

[0016] Further, the mass ratio of limestone to calcium nitrate in step S1 is 5%-60%, preferably 10%-50%.

[0017] Further, the particle size of the small particle limestone in step S1 is less than or equal to 1.5 cm.

[0018] Further, the calcination time in step S2 is 4-22 hours, preferably 5-20 hours.

[0019] Further, the nitrogen oxide gas in step S3 can also be recovered from the nitrogen oxide emission source of the lime kiln.

[0020] Further, the small particle limestone in steps S3 and S4 is unused, and the particle size is less than or equal to 1.5 cm.

[0021] Further, the molar ratio of nitrogen oxide gas to water in step S3 is 1:7-1:10.

[0022] Further, the mass ratio of the nitric acid solution to the small particle limestone in step S4 is 1:0.26-1:0.17.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] The present application solves the defects of traditional rotary kiln, double chamber kiln, shaft kiln and the like, which cannot use small particle size limestone as the production raw material of calcium oxide and have high working temperature, by heating the production raw material, i.e. small particle limestone with particle size less than or equal to 1.5 cm, together with calcium nitrate, so that the small particle limestone can be completely converted into calcium oxide at 800℃.

[0025] The present application greatly reduces the calcination time and improves the production efficiency by reasonable matching of the mass ratio of small particle limestone and calcium nitrate.

[0026] The present application can make the nitrogen oxide and carbon dioxide respectively escape from the calcination furnace by dividing the calcination temperature into two stages, so as to ensure the purity of the two kinds of gases, facilitate the water absorption of nitrogen oxide, reduce the emission of pollution gas and provide a good production environment.

[0027] The present application realizes the cyclic preparation of production raw material by preparing calcium nitrate by using water to absorb nitrogen oxide and soaking small particle limestone in nitric acid solution, reduces the production cost and improves the economic benefit; meanwhile, the nitrogen oxide can be recovered from the traditional lime kiln and other nitrogen oxide emission sources, which is very environmentally friendly and greatly reduces the emission of pollution gas. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The present application solves the defects of traditional rotary kiln, double chamber kiln, shaft kiln and the like, which cannot use small particle size limestone as the production raw material of calcium oxide and have high working temperature, by heating the production raw material, i.e. small particle limestone with particle size less than or equal to 1.5 cm, together with calcium nitrate, so that the small particle limestone can be completely converted into calcium oxide at 800℃.

[0029] Figure 2 The present application solves the defects of traditional rotary kiln, double chamber kiln, shaft kiln and the like, which cannot use small particle size limestone as the production raw material of calcium oxide and have high working temperature, by heating the production raw material, i.e. small particle limestone with particle size less than or equal to 1.5 cm, together with calcium nitrate, so that the small particle limestone can be completely converted into calcium oxide at 800℃.

[0030] Figure 3 The present application solves the defects of traditional rotary kiln, double chamber kiln, shaft kiln and the like, which cannot use small particle size limestone as the production raw material of calcium oxide and have high working temperature, by heating the production raw material, i.e. small particle limestone with particle size less than or equal to 1.5 cm, together with calcium nitrate, so that the small particle limestone can be completely converted into calcium oxide at 800℃. DETAILED DESCRIPTION

[0031] Example 1

[0032] First, the calcium nitrate and the limestone less than or equal to 1.5 cm are mixed according to the mass ratio of 10% and loaded into a crucible, then put into a muffle furnace, first calcined at 200℃ for 1 hour, then heated to 800℃ and kept for 20 hours, and then reduced to room temperature. After weighing, the weight loss rate of the limestone is calculated to be 44%.

[0033] Among them, the calcium nitrate is decomposed into calcium oxide and nitrogen oxide gas at 200℃, the escaped nitrogen oxide gas is absorbed by water to obtain a nitric acid solution, and then the limestone less than or equal to 1.5 cm is soaked in the nitric acid solution to obtain calcium nitrate; the obtained calcium nitrate can be mixed with the limestone less than or equal to 1.5 cm again to perform a new round of calcium oxide preparation process.

[0034] When the mass ratio and the first calcination temperature (referring to the first calcination temperature) change, the calcination time (the calcination time refers to the time for less than or equal to 1.5 centimeters of limestone to be completely converted into calcium oxide) also changes, as shown in the following table:

[0035] When the mass ratio is 10%:

[0036] Mass ratio First calcination temperature Calcination time Loss on ignition Example 2 10％ 300℃ 20 hours 44％ Example 3 10％ 400℃ 20 hours 44％ Example 4 10％ 500℃ 20 hours 44％ Example 5 10％ 600℃ 20 hours 44％

[0037] When the mass ratio is 20%:

[0038]

[0039]

[0040] When the mass ratio is 30%:

[0041]

[0042] When the mass ratio is 40%:

[0043]

[0044]

[0045] When the mass ratio is 50%:

[0046]

[0047] When the mass ratio is 60%:

[0048]

[0049]

[0050] When the mass ratio is 70%:

[0051]

[0052] As can be seen from Examples 1 to 35, the mass ratio of calcium nitrate to small particle limestone (small particle limestone refers to limestone less than or equal to 1.5 centimeters) affects the calcination time, and as the mass ratio gradually increases, the calcination time gradually decreases. Although the higher the proportion of calcium nitrate, the shorter the calcination time, it is not necessarily the shorter the combustion time the better, and sufficient reaction time needs to be given to calcium nitrate to ensure the labor amount of calcium nitrate.

[0053] Comparative Example 1

[0054] Calcium nitrate and limestone of 1.5 cm or less were mixed at a mass ratio of 30% and placed in a crucible. The crucible was then placed in a muffle furnace and calcined at 300°C for 1 hour. The temperature was then raised to 900°C and maintained for 4 hours. The mixture was then cooled to room temperature and weighed. The weight loss rate of the limestone was calculated to be 44%.

[0055] Comparative Example 2

[0056] Calcium nitrate and limestone of 1.5 cm or less were mixed at a mass ratio of 30% and placed in a crucible. The crucible was then placed in a muffle furnace and calcined at 300°C for 1 hour. The temperature was then raised to 700°C and maintained for 13 hours. The mixture was then cooled to room temperature and weighed. The weight loss rate of the limestone was calculated to be 21%.

[0057] As can be seen from Comparative Examples 1 and 2, when the mass ratio remains constant, the calcination time will be prolonged when the temperature is below 800℃. However, when the temperature rises above 800℃, the calcination time can still be shortened rapidly even when the mass ratio is low. Therefore, when the temperature exceeds 900℃, calcium oxide is produced more by high temperature, which reduces the role of calcium nitrate. Thus, calcium nitrate can only play its role when the temperature rises to 800℃, and the calcination time can also be reduced.

[0058] Comparative Example 3:

[0059] Limestone of 1.5 cm or less was placed in a crucible, then placed in a muffle furnace, heated to 800°C and held for 16 hours. After cooling to room temperature, it was weighed and the weight loss rate of the limestone was calculated to be 25%.

[0060] Comparative Example 4:

[0061] Limestone of 1.5 cm or less is placed in a crucible, then placed in a muffle furnace, heated to 800°C and held for 5 hours, then cooled to room temperature. After weighing, the weight loss rate of the limestone is calculated to be 10%.

[0062] Comparative Example 5:

[0063] Limestone of 1.5 cm or less was placed in a crucible, then placed in a muffle furnace, heated to 900°C and held for 5 hours, then cooled to room temperature. After weighing, the weight loss rate of the limestone was calculated to be 44%.

[0064] Comparative Example 6:

[0065] Limestone of 1.5 cm or less was placed in a crucible, then placed in a muffle furnace, heated to 800°C and held for 25 hours, then cooled to room temperature. After weighing, the weight loss rate of the limestone was calculated to be 44%.

[0066] Please see Figure 3As can be seen from Comparative Examples 3, 4 and 6, it takes 25 hours for small limestone particles to be completely converted into calcium oxide after calcination at a constant temperature of 800℃, which is too long.

[0067] Please see Figure 2 As shown in Comparative Example 5, when the calcination temperature exceeds 800℃ and reaches 900℃, limestone of 1.5 cm or less can be completely converted into calcium oxide in 5 hours. When the calcination temperature is 900℃, more heating fuel will be consumed, the carbon dioxide emissions will be large, which will affect the environment, and the requirements for furnace materials will also be high.

[0068] In summary, using limestone of 1.5 cm or less and calcium nitrate mixed at a mass ratio of 60% and heated, limestone can be completely converted into calcium oxide at 800℃ in 5 hours. This also ensures the reaction time of calcium nitrate, while using less fuel, controlling carbon dioxide emissions, and having lower requirements for furnace materials. Nitrogen oxide can also be reused to produce new calcium nitrate, reducing economic costs. Therefore, it is more environmentally friendly and generates higher economic benefits.

Claims

1. A method for preparing calcium oxide using limestone, characterized in that: Includes the following steps: S1. Select small-particle limestone and mix it with calcium nitrate and calcine it at a higher temperature. The calcium nitrate is decomposed by heating and used to produce new calcium nitrate. The particle size of the small-particle limestone is less than or equal to 1.5 cm. S2. Raise the temperature to 800℃ again and continue calcining until all the small limestone particles are converted into calcium oxide. Stop calcining, wait for the temperature to drop to room temperature, and take out the product calcium oxide. Step S2 is followed by steps S3, S4 and S5, which are used to prepare calcium nitrate; S3. In step S1, calcium nitrate is calcined and decomposed to obtain calcium oxide and nitrogen oxide gas, and the escaped nitrogen oxide gas is absorbed by water to prepare nitric acid solution. S4. Soak small-particle limestone in the nitric acid solution from step S3 to obtain calcium nitrate. S5. In step S4, calcium nitrate is mixed with small-particle limestone to prepare calcium oxide in a new round.

2. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: The temperature in step S1 is 150℃-700℃.

3. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: The calcination time in step S1 is 1 hour.

4. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: In step S1, the mass ratio of calcium nitrate to limestone is 5%-60%.

5. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: The calcination time in step S2 is 4 to 22 hours.

6. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: In step S3, the nitrogen oxide gas is recovered from the nitrogen oxide emission source of the lime kiln.

7. The method for preparing calcium oxide from limestone according to claim 1, characterized in that: In step S3, the molar ratio of nitrogen oxide gas to water is 1:7 to 1:

10.

8. The method for preparing calcium oxide using limestone according to claim 1, characterized in that: In step S4, the mass ratio of nitric acid solution to small-particle limestone is 1:0.26-1:0.17.

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