JPH07136457A - Method for removing carbon dioxide in exhaust gas - Google Patents

Abstract

PURPOSE:To remove CO2 efficiently in a simple method by contacting the CO2 contained exhaust gas with highly active calcium oxide porous particles having a specified specific surface area and a specified particle size at temperature within a specified range. CONSTITUTION:Highly active calcium oxide porous particles are obtained which is characterized by the specific surface area of 5-60m<2>/g or more preferably 10-50m<2>/g, and the diameter 1-10mm, preferably 3-6mm. In order to come in contact with the porous particles, exhaust gas is passed through an apparatus composed of a cylindrical treatment tube which is filled with the particles. A net or glass wool is placed above and under the particles to hold them. A part of the column which is filled with the particles is heated by an appropriate means such as electric heating, infrared heating, and high-frequency heating to heat the particles at 400-700 deg.C preferably 500-650 deg.C. In this way, the CO2 in exhaust gas can be removed efficiently for a long period of time.

Description

Detailed Description of the Invention

[0001]

The present invention relates to industrial exhaust gas, automobiles,
The present invention relates to a method for efficiently removing carbon dioxide contained in exhaust gas such as exhaust gas from a ship. More specifically, the present invention relates to a method for rapidly removing carbon dioxide contained in exhaust gas with a high removal rate by using highly active calcium oxide porous particles produced by a special method.

[0002]

2. Description of the Related Art In recent years, global warming caused by carbon dioxide generated when burning fossil fuels such as oil and coal and incinerating various wastes has become a social problem as a source of destruction of the biological environment. .

Therefore, a method for removing carbon dioxide from exhaust gas has been studied, and a physical adsorption method using an adsorbent such as zeolite, a chemical absorption method using an amine-based absorbent solution, and a polymer membrane have been used so far. Many methods such as the membrane separation method used are known.

However, these methods have many problems to be put into practical use, such as low processing capacity, high cost of materials used, and large scale equipment, and they are still industrially not used. There is no known practical method.

On the other hand, it is known that when carbon dioxide-containing gas is brought into contact with heated calcium oxide, calcium carbonate is produced and carbon dioxide is consumed. Therefore,
It is also possible to contact the exhaust gas with calcium oxide to remove carbon dioxide therein, but conventional calcium oxide obtained so far has a small specific surface area, low absorption capacity, and contact with carbon dioxide. Since the removal rate in the case of making it fall rapidly falls in a short time, it is unsuitable as a carbon dioxide absorbent. It is also known that fine powder of calcium hydroxide is used as a raw material and is calcined under vacuum at a temperature of 300 to 390 ° C. to produce a calcium oxide powder having a large specific surface area of 110 to 133 m ² / g. ["Journal of the American Ceramic
Society (J. Am. Ceramic So
c. ) ", Vol. 64, No. 2, pp. 74-80],
The powder obtained by this method has a fine particle size of 1 to 10 μm, even though it has a higher activity than ordinary powders, and is therefore difficult to handle and is not practical.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a simple treatment for carbon dioxide contained in exhaust gas generated from factories and power plants and exhaust gas from engines of automobiles and ships,
Moreover, it was made for the purpose of providing a method for efficient removal.

[0007]

Means for Solving the Problems The present inventors have conducted various studies to develop a solid alkaline substance having high reactivity with carbon dioxide, and have previously conducted a specific surface area of at least 5 m ² / g and at least 1 mm. By firing a granulated body of calcium hydroxide or calcium carbonate having a particle size of
We have succeeded in obtaining a highly active calcium oxide porous body (Japanese Patent Application No. 4-345159), but using the highly active calcium oxide porous body thus obtained as an absorbent, under a specific condition It was found that the carbon dioxide contained in the exhaust gas can be efficiently removed by contacting with the exhaust gas, and the present invention has been completed based on this finding.

That is, according to the present invention, the carbon dioxide-containing exhaust gas is converted into highly active calcium oxide porous particles composed of calcium hydroxide granules having a specific surface area of 5 to 60 m ² / g and a particle diameter of 1 to 10 mm, and 400 to 700. The present invention provides a method for removing carbon dioxide in exhaust gas, which is characterized in that contact is performed at a temperature of ° C.

In the present invention, particles having a specific surface area of 5 to 60 m ² / g, which is much larger than that of ordinary calcium oxide powder, and 1 to 10 mm, which is much larger than the known high activity calcium oxide powder. Highly active calcium oxide porous particles having a diameter are used.

Such highly active calcium oxide porous particles are formed by, for example, granulating calcium hydroxide powder having a particle size of 300 μm or less into granules having a particle size of 1 to 10 mm, and heating the granulated body under atmospheric pressure to 390 to 390. Bake by raising the temperature between 480 ° C over at least 5 minutes, or by using a particle size of 300 μm
The following calcium hydroxide powder is granulated into granules having a particle size of 1 to 10 mm, and the granulated product is heated under normal pressure to give 390 to 480.
After raising the temperature between ℃ for at least 5 minutes, at an arbitrary temperature within the range of 480 to 950 ℃, C
It can be produced by firing for a time within a range in which the O ₂ reaction rate does not decrease to 40% or less.

At this time, as the calcium hydroxide used as a raw material, commercially available calcium hydroxide (slaked lime) may be used as it is, or a hydrated product of commercially available calcium oxide (quick lime) may be used. When calcium is mixed, the activity of the obtained calcium oxide is lowered, so that it is preferable to use the one having the highest purity. This calcium hydroxide is used as a powder having an average particle size of 10 to 300 μm.

Next, for the granulation of the calcium hydroxide powder, water is added to the mixture and the mixture is kneaded, and a diameter of 1 is obtained by using a conventional granulator.
It is carried out by molding into a spherical shape having a diameter of 10 mm, preferably 3 mm to 6 mm, or a cylindrical granule having a diameter of 3 mm to 6 mm and a length of 3 mm to 6 mm. The amount of water added at this time is 5 to 25 based on the weight of calcium hydroxide.
A range of weight percent is suitable. At the time of this granulation, an organic binder may be added, if desired, in order to improve the shape retention. As the organic binder, a water-soluble polymer substance such as carboxymethyl cellulose (CMC) or polyvinyl alcohol is used. The amount of the organic binder added is appropriately in the range of 0.5 to 5% based on the weight of calcium hydroxide.

The granules thus obtained are then calcined using, for example, an electric furnace. The calcining conditions are, in the case of calcium hydroxide, a temperature in the range of 390 to 480 ° C. for at least 5 minutes. It is necessary to raise the temperature. When fired under other conditions, specific surface area of 5m ²
It is not possible to obtain a highly active substance having an activity of / g or more.

At this time, the rate of temperature rise is preferably in the range of 1 to 10 ° C./minute, and in the case of calcium hydroxide, 480.
In case of calcium carbonate and calcium carbonate, when the upper limit of 780 ° C. is reached, it is preferable to stop heating as soon as possible. When the pore distribution spectrum was measured, at this point,
A peak is recognized around 02 to 0.2 μm.

In the case of a large amount of treatment, it is necessary to further raise the temperature in order to complete the firing of the charged raw material, but in this case, the temperature does not exceed 950 ° C. and C
Care must be taken so that the O ₂ conversion does not fall below 40%. This is done, for example, by taking out a sample at regular time intervals and measuring the CO ₂ reaction rate for the sample.

This heating time is too long and the CO ₂ reaction rate is 4
When the state is reduced to 0% or less, once the highly active calcium oxide obtained is condensed, the activity begins to decrease and the time increases, and this tendency becomes remarkable.

[0017] The CO ₂ rate of reaction, a mixed gas of CO ₂ and N ₂ which are previously CO ₂ concentration in the sample is known, is contacted for 1 minute at 20 ° C., before and after contacting CO ₂
It is defined as the difference in concentration divided by the CO ₂ concentration before contact and multiplied by 100.

In the above firing, by adding a reducing agent such as calcium fluoride which decomposes at a low temperature,
The firing time can be shortened.

Further, by selecting the above-mentioned production conditions, it is possible to obtain calcium oxide whose activity is adjusted to a desired level.

In this way, the specific surface area is 5 to 60 m ^2.
/ G or more, preferably 10 to 50 m ² / g, a highly active calcium oxide porous body is obtained as a granular body having a diameter of 1 to 10 mm, preferably 3 to 6 mm.

This is a porous material having pores of 200 to 2000 angstrom, and its bulk specific gravity is 0.
It is about 7 to 0.8.

In order to bring the exhaust gas into contact with the highly active calcium oxide porous particles, the exhaust gas is passed through an apparatus constructed by filling the particles in a cylindrical processing tube and holding the upper and lower parts thereof with a mesh or glass wool. Let At this time, the filled portion of the particles is heated by an appropriate heating means such as electric heating, infrared irradiation, high-frequency heating, etc. to make the particles 400 to 70.
It is necessary to heat to a temperature of 0 ° C, preferably 500-650 ° C. If this temperature is lower than 400 ° C., the reaction between calcium oxide and carbon dioxide is insufficient and the carbon dioxide removal rate becomes low. The removal rate of this carbon dioxide is 40
The temperature rises between 0 and 600 ° C., begins to decrease when the temperature exceeds 600 ° C., and sharply decreases when the temperature exceeds 700 ° C.
This is because the calcium carbonate once generated is decarbonated,
It seems to release carbon dioxide again.

In order to suitably carry out the method of the present invention, 8 to 2 per minute per kilogram of the highly active calcium oxide porous body.
It is preferable to design so that the exhaust gas comes into contact with the mixture at a rate of 0 liter. If the contact amount is larger than this, the removal rate in the initial stage is high, but it rapidly decreases with time, and becomes about 1/3 or less of the initial value in about 2 hours. Further, if the contact amount is smaller than this, the removal rate is less decreased, but the processing speed becomes slower, which is impractical.

Next, in the method of the present invention, the amount of calcium oxide constituting the calcium oxide porous material to be used and the total amount of carbon dioxide present in the exhaust gas treated by the calcium oxide have a specific ratio. It is preferable to carry out under the conditions.

That is, when the total number of moles of carbon dioxide in the exhaust gas supplied during the entire treatment time is K and the number of moles of calcium oxide filled is L, the molar ratio R = K / L of both is 0.5 or less. By controlling the flow rate of exhaust gas, the amount of calcium oxide, and the treatment time so that the above, the removal rate of 90% or more can be maintained. For example, the exhaust gas of an automobile contains 0.7 to 15% of carbon dioxide, but according to the method of the present invention, carbon dioxide can be removed from this exhaust gas at a removal rate of 90% or more. .

Further, according to the method of the present invention, in the exhaust gas,
When acidic substances such as halogens, nitrogen oxides and sulfur oxides are contained, these can be removed at the same time.

[0027]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The CO ₂ reaction rate and specific surface area in each example are obtained as follows.

(1) CO ₂ reaction rate;
mm, 600 mm long cylindrical reactor, temperature 2
A mixture of CO ₂ gas and N ₂ gas was passed through the mixture at 0 ° C. at a rate of 100 ml / min, and the CO ₂ concentration in the mixture before and after contacting with the sample was measured by the JIS R6124 combustion capacity method. It was calculated according to the following formula.

[0029]

[Equation 1]

(2) Specific surface area: 0.5 g of each sample was measured by a BET common point method using a monosoap specific surface area measuring device (manufactured by Yuasa Ionics), and the obtained measured value was doubled. The surface area per gram was calculated.

Reference Example Calcium hydroxide powder having a particle size of 75 to 150 μm (manufactured by Suzuki Kogyo Co., Ltd., industrial slaked lime, purity 95.9%) and 25 parts of water.
% By weight, and granulated into granules having a diameter of 3 mm and a length of 3 to 4 mm using a disk pelleter [manufactured by Fuji Paudal Co., Ltd.], and the granules were placed in an electric furnace to raise the temperature to 10 It was heated to 700 ° C at ° C / min, then the temperature was raised to 900 ° C and calcined for 1 hour. Thus, a white porous body containing CaO as a main component and having a specific surface area of 9.0 m ² / g, a CO ₂ reaction rate of 94.0% and a bulk specific gravity of 0.7 was obtained.

Example 1 5 g of the highly active calcium oxide porous body obtained in the reference example was filled over approximately 50 mm in the central portion of a cylindrical quartz tube having an inner diameter of 20 mm, an outer diameter of 24 mm and a length of 600 mm, and the both sides had a thickness. A 15 mm quartz glass wool layer was provided and fixed to obtain a reaction tube.

Next, this reaction tube was charged into a horizontal electric furnace, and exhaust gas with a CO ₂ content of 10% was passed through one end of the porous body 1.
It was supplied at a rate of 20 g / min and the CO ₂ removal rate at 200 to 800 ° C. was measured. The results are shown in Table 1.

[0034]

[Table 1]

Example 2 In the same manner as in Example 1, the porous body obtained in Reference Example was
(A) 2.5g or (B) 10g filling, and Example 1
Similarly, each CO at a temperature of 600 ° C ₂Excluding
The change in the removal rate with time was examined. The results are shown in Table 2.

[0036]

[Table 2]

Example 3 As in Example 1, 5 g of the porous body was used, the temperature was kept at 600 ° C., and the exhaust gas supply rate was set to 15 ml per minute of the porous body (C) or 25 ml (D). , And the time-dependent change in the CO ₂ removal rate of each of them was examined. The results are shown in Table 3.

[0038]

[Table 3]

Example 4 In Example 1, by fixing the temperature to 600 ° C. and changing the amount of the porous body and the exhaust gas supply rate, the amount of calcium oxide in the porous body, K mol, and the carbon dioxide in the exhaust gas. The ratio R = K / L with respect to the total supply amount L mol of R was varied within the range of 0.1 to 1.0, and the respective CO ₂ removal rates were determined. The results are shown in Table 4.

[0040]

[Table 4]

[0041]

EFFECTS OF THE INVENTION According to the method of the present invention, carbon dioxide in exhaust gas can be efficiently removed over a long period of time and halogen, nitrogen oxides and sulfur oxides can also be removed by a dry contact method which is easy to handle. It can be suitably used for purification of combustion gas from factories and power plants and exhaust gas from engines of automobiles and ships.

Claims (3)

[Claims] 1. The specific surface area of the carbon dioxide-containing exhaust gas is 5 to 5.
Removal of carbon dioxide in exhaust gas, which is characterized in that highly active calcium oxide porous particles composed of a calcined product of calcium hydroxide granules having a particle diameter of 1 to 10 mm and a particle size of 60 m ² / g are contacted at a temperature of 400 to 700 ° C. Method. 2. The method according to claim 1, wherein the exhaust gas containing carbon dioxide is contacted at a rate of 8 to 20 liters per minute per 1 kilogram of highly active calcium oxide porous particles. 3. The ratio R = K / L of the molar amount L of calcium oxide in the highly active calcium oxide porous particles and the molar amount K of carbon dioxide contained in the exhaust gas during the entire treatment time is 0.5 or less. The method according to claim 1 or 2, wherein the amount of exhaust gas supplied, the amount of highly active calcium oxide porous particles and the contact time are controlled so as to achieve the above.