JP2010180086A - Method for producing slaked lime - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing slaked lime which is one lime having a high specific surface area (≥40 m<SP>2</SP>/g) and consequent high reactivity and, in addition, having a larger pore volume (≥0.3 mL/g) and therefore exhibiting high performance of removing acid gases, especially sulfur oxides from tail gas. <P>SOLUTION: The raw material used is (1) quicklime obtained by firing limestone or (2) quicklime obtained by firing slaked lime is used. This raw material is slaked by adding thereto slaking water containing 1-10 pts.wt. (in total in the case where two or more additives are used), per 100 pts.wt. calcium oxide to be slaked, at least one additive selected from (1) the group consisting of ethylene glycol, diethylene glycol, propylene glycol, glycerol, and triethanolamine or from (2) the group consisting of citric acid and a saccharide in addition to the members of group (1). The slaking is performed under conditions in which the slaking water of an initial water temperature in the range of 10-50°C is added in an amount of 4-8 pts.wt., per pt.wt. calcium oxide and the temperature during the slaking becomes 60°C or higher. The obtained slurry is filtered under pressure and the filter cake is dried to obtain a slaked lime product. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing highly active slaked lime that has a large specific surface area and pore volume, and therefore has a high ability to absorb acidic gases, particularly sulfur oxides.

In order to remove acidic gases (hydrogen chloride and sulfur oxides) in the gas discharged from the garbage incinerator, a process of blowing slaked lime is performed. In general, slaked lime is produced by a digestion method in which digested water is reacted with quick lime. There are two types of digestion methods: dry and wet.

The dry digestion method is a method for drying the produced hydrous slaked lime using digested water slightly exceeding the theoretical hydration amount with respect to quick lime, and can obtain slaked lime having a relatively large specific surface area. The pores have a distribution centering on small pores having a diameter of about 4 nm, and the reaction with the acidic gas is mainly performed on the surface of slaked lime.

In contrast, the wet digestion method is known to give larger pores. Slaked lime having large pores is particularly suitable for removing sulfur oxides, which have a slower reaction rate than hydrogen chloride, because the acid gas is likely to diffuse inside the secondary particles when used to remove the acid gas. The applicant has developed a method for producing highly reactive calcium hydroxide that makes use of such characteristics of the wet digestion method, and has previously proposed (Patent Document 1).

The production method is as follows: 2 to 10 parts by weight of digested water is added to 1 part by weight of calcium oxide (hereinafter sometimes referred to as “quick lime”), and the formed slurry is filtered under pressure to give a cake having a water content of 50% or less. The cake is dried by hot gas using a dryer having a crushing function, and powdered calcium hydroxide (hereinafter sometimes referred to as “slaked lime”) is recovered by solid-gas separation. In a preferred embodiment, a specific amount of one or two selected from citric acid and its water-soluble salt, tartaric acid and its water-soluble salt, sodium carbonate and calcium carbonate, and sorbitol is added for digestion. Among the obtained slaked lime, in the example that gave the best results, the specific surface area was 37 m ² / g, the pore volume was 0.28 mL / g, and when it was used to remove the acid gas in the exhaust gas of the garbage incinerator, The removal rates were HCl: 98.3% and SO ₂ : 88%.

It has been experienced that slaked lime produced by this method has a large variation in performance for removing acidic gas in exhaust gas, while some of the performance reaches the high results as described above. A list of specific surface area, pore volume, HCl and SO ₂ removal rates for Examples 1 to 6 of Patent Document 1 is as follows.

Example Specific surface area (m ² / g) Pore volume (mL / g) HCl removal rate (%) SO ₂ removal rate (%)
1 25.8 0.15 96.7 70.3
2 37.1 0.23 98.2 86.8
3 35.8 0.28 98.3 88.0
4 33.5 0.21 97.6 84.5
5 34.3 0.19 98.0 83.3
6 26.2 0.15 96.3 71.8

From this data, it can be seen that slaked lime having a large specific surface area and a large pore volume is necessary.

Thereafter, a method for producing porous slaked lime having a specific surface area of 30 m ² / g or more and a pore volume of 20 to 1000 mm (2 to 100 nm) in diameter of 0.30 mL / g or more was proposed (patent document). 2). The manufacturing method is 1.5 to 5 times the theoretical amount necessary for digestion with respect to 1 part by weight of quick lime, based on quick lime, with a specific water-soluble organic compound such as oxycarboxylic acid added to quick lime. Is used to obtain a low hydrous slaked lime having a moisture content of 5 to 33% by mass, and water is added to obtain a highly hydrous slaked lime having a moisture content of 35 to 55% by mass. Add more than 3.2 times the amount of digestion water and digest with stirring to make high water content slaked lime with a moisture content of 35-55% by mass, and dry the high water content slaked lime obtained in any step Made up of. The acid gas removal performance of slaked lime produced by this method is not disclosed.
JP 2002-114543 A JP-A-2005-350343

The inventors of the present invention previously proposed (Patent Document 1) In the above-described method for producing slaked lime, a high specific surface area is intended to realize a method with less variation in acid gas removal performance of the obtained slaked lime. At the same time, he continued his research seeking a method for producing a large pore volume and a high ability to absorb acid gas, especially sulfur oxides. As a result, it has been found that this intention can be achieved by adjusting the conditions of digestion, that is, the temperature of water used for digestion and the temperature during digestion. In addition, it was confirmed that the additive to be added to the digested water should be appropriately selected, and that quick lime used as a raw material preferably has a certain degree of activity.

It is known that quick lime obtained by baking slaked lime as a raw material may be used as a raw material for obtaining highly reactive slaked lime. It was found that this raw material is also useful in the production of slaked lime having a large pore volume with a high specific surface area.

The object of the present invention is to utilize the knowledge obtained by the above-described inventors and the like to secure a large pore volume in slaked lime having a wide specific surface area and high reactivity, and therefore, acid gas in exhaust gas, particularly sulfur oxide. An object of the present invention is to provide a method for producing slaked lime with high removal performance.

In the method for producing highly reactive slaked lime having a high specific surface area and a large pore volume according to the present invention, the first aspect using quick lime obtained by firing limestone as a raw material, and obtained by firing slaked lime. And a second embodiment using quicklime.

In the first aspect, calcium oxide obtained by firing limestone is used as a raw material, and an additive selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, glycerin and triethanolamine is used as digestion water. 1 to 2 parts or more of water in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of calcium oxide to be digested (in the case of two or more kinds), the initial water temperature is 10 to 50 parts. Add 4 to 8 parts by weight with respect to 1 part by weight of calcium oxide in the range of ° C. Digestion is performed under the condition that the temperature during digestion is 60 ° C or higher, and the resulting slurry is filtered under pressure and then dried. This is a method for producing highly reactive slaked lime having a specific surface area of 40 m ² / g or more and a pore volume of 0.3 mL / g or more.

In the second aspect, calcium oxide obtained by baking slaked lime is used as a raw material, and citric acid and saccharides are added to ethylene glycol, diethylene glycol, propylene glycol, glycerin and triethanolamine as digestion water. Water containing one or more additives selected from the above group in a range of 1 to 10 parts by weight (in the case of two or more, in a total amount) with respect to 100 parts by weight of calcium oxide to be digested Add 4 to 8 parts by weight with respect to 1 part by weight of calcium oxide at an initial water temperature of 10 to 50 ° C., digestion is performed under the condition that the temperature during digestion is 60 ° C. or higher, and the resulting slurry is added. A method for producing highly reactive slaked lime having a specific surface area of 40 m ² / g or more and a pore volume of 0.3 mL / g or more, comprising pressure filtration followed by drying.

According to the production method of the present invention, when producing the slaked quicklime obtained by calcining limestone as a raw material, beyond easily specific surface area of 30 m ^{2 /} g, and a large one to reach 50 to 60 m ^{2 /} g, And the highly reactive slaked lime whose pore volume is 0.3 mL / g or more is obtained. If the acid gas in the exhaust gas is removed using this slaked lime, removal rates of 97 to 99% for HCl and 80% for SO ₂ can be achieved.

Moreover, according to the production method of the present invention, if slaked lime is produced using quick lime obtained by firing slaked lime, the specific surface area easily exceeds 40 m ² / g, and is a wide one of 60 m ² / g or more, and A highly reactive slaked lime having a pore volume exceeding 0.3 mL / g is obtained. If acid gas in the exhaust gas is removed using this slaked lime, a removal rate of up to 99% for HCl and 90% or more for SO ₂ can be achieved.

In the case of producing slaked lime according to the present invention using quick lime obtained by firing limestone as a raw material, the calcium oxide obtained by firing quick lime as a raw material has an activity t ₆₀ value of 60 seconds according to EN459-02. The following are preferred. Thereby, more preferable slaked lime can be obtained in terms of specific surface area and pore volume.

When producing slaked lime according to the present invention using quick lime obtained by calcining slaked lime, calcium oxide obtained by calcining slaked lime as a raw material has a specific surface area of 3 m ² / g or more. It is preferable to do. Thereby, high-performance slaked lime can be obtained in terms of specific surface area and pore volume. More preferably, it is 3 m ² / g or more.

In any case, as described above, 5 to 8 parts by weight of digestion water having an initial water temperature in the range of 10 to 50 ° C is added to 1 part by weight of calcium oxide, and the temperature during digestion is 60 ° C or more. Digest under certain conditions. When the initial water temperature is a low temperature of less than 10 ° C., there arises a problem that undigested matter remains, the specific surface area is not sufficiently wide, or slaked lime having a small pore volume may be formed. This is considered to be one factor causing the variation in product performance. On the other hand, when it becomes high temperature exceeding 50 degreeC, the viscosity of the slaked lime slurry during digestion will increase, and operation with a real apparatus will become difficult.

If the amount of digested water is not 4 parts by weight or more, the viscosity of the slaked lime slurry is too high and production becomes difficult, and if it exceeds 8 parts by weight, there is a concern that the productivity will decrease due to the excessive amount of digested water. .

The test methods employed in the following examples are as follows.
[Measurement of activity “t ₆₀ ”]
In accordance with EN459-02, 600 g of water at 20 ° C. is put into a 1 L capacity Dewar bottle and stirred at 300 rpm, and 150 g of quicklime sample is put into it to cause a hydration reaction. The water temperature is measured and the time elapsed until reaching 60 ° C. is measured.
[Specific surface area measurement]
BET method [Measurement of pore volume]
BJH method [measurement of acid gas removal rate]
A 0.5 g sample of slaked lime is placed in the reaction tube and heated to 200 ° C. Separately, a mixed gas containing HCl: 6000 ppm and SO ₂ : 1000 ppm in N ₂ and adding water vapor to make RH 30% was prepared, which was also heated to 200 ° C., and the inside of the reaction tube at a space velocity of 300 mL / min. Let the slaked lime absorb the acid gas. The HCl gas that has not been absorbed by the slaked lime is recovered with a cold trap, and the SO ₂ gas is recovered with hydrogen peroxide. The amount of acid gas recovered is measured by titration with NaOH, and the acid gas removal rate is determined by calculating what percentage of the gas that has passed through the reaction tube has been absorbed.

[Raw material calcium oxide]
With -10mm particle size by limestone was calcined crushed activity t ₆₀ was prepared two different calcium oxide. In addition, two types of calcium oxide obtained by baking slaked lime were prepared. The value of each activity t ₆₀ is as follows.

Calcium oxide Origin Activity t ₆₀
Raw material 1 Limestone 31 seconds Raw material 2 Limestone 99 seconds Raw material 3 Slaked lime 9 seconds Raw material 4 Slaked lime 53 seconds

Digestion was performed on the raw material calcium oxide under the conditions shown in Table 1 to produce slaked lime.

^＊１ ジエチレングリコール
^＊２ トリエタノールアミン
^＊３ 酸化カルシウム１００重量部に対する重量部
^＊４ 酸化カルシウム１重量部に対する重量部
比較例１は消化水が添加剤を含まない場合、比較例２は水和温度が低い場合であって、前掲特許文献１の技術の一実施例に相当する。比較例３は添加剤の種類が適切でない場合、比較例４は原料生石灰の活性度が低い場合であり、比較例５は従来技術による場合である。 Table 1

^{* 1} Diethylene glycol
^{* 2} Triethanolamine
^{* 3} parts by weight per 100 parts by weight of calcium oxide
^{* 4} parts by weight relative to 1 part by weight of calcium oxide Comparative Example 1 is a case where the digestion water does not contain an additive, and Comparative Example 2 is a case where the hydration temperature is low, which corresponds to an example of the technique of the aforementioned Patent Document 1. To do. The comparative example 3 is a case where the kind of additive is not appropriate, the comparative example 4 is a case where the activity of raw quicklime is low, and the comparative example 5 is a case based on a prior art.

About the slaked lime manufactured on the conditions shown in Table 1, the specific surface area and the pore volume were measured. Furthermore, the removal rate when acid gas was removed using them was measured. The results are shown in Table 2.

Table 2

Claims (4)

Calcium oxide obtained by calcining limestone is used as a raw material, and one or two additives selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, glycerin and triethanolamine are used as digestion water. Water containing 1 to 10 parts by weight of the above with respect to 100 parts by weight of calcium oxide to be digested (in the case of two or more kinds) is oxidized in an initial water temperature range of 10 to 50 ° C. 4-8 parts by weight with respect to 1 part by weight of calcium, digestion is performed under the condition that the temperature during digestion is 60 ° C. or higher, and the resulting slurry is filtered under pressure and then dried, 40 m ² / G or more specific surface area and the manufacturing method of highly reactive slaked lime which has 0.3 mL / g or more pore volume. As a raw material, as calcium oxide obtained by firing limestone process of claim 1 carried out using those values of activity t ₆₀ due EN459-02 is less than 60 seconds. Calcium oxide obtained by calcining slaked lime is used as a raw material. Addition selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, glycerin and triethanolamine plus citric acid and saccharides as digestion water Water containing 1 or 2 or more of agents in a range of 1 to 10 parts by weight (in the case of two or more, in a total amount) with respect to 100 parts by weight of calcium oxide to be digested, the initial water temperature is 10 to 10 parts by weight. Add 4 to 8 parts by weight with respect to 1 part by weight of calcium oxide in the range of 50 ° C., digestion is performed under the condition that the temperature during digestion is 60 ° C. or more, and the resulting slurry is filtered under pressure and then dried. A process for producing highly reactive slaked lime having a specific surface area of 40 m ² / g or more and a pore volume of 0.3 mL / g or more. The manufacturing method of Claim 3 implemented using what has a specific surface area of 3 m < ² > / g or more as calcium oxide obtained by baking slaked lime used as a raw material.