JPH10120448A - Production of slaked lime - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing dried slaked lime excellent in reactivity and having high specific surface area in high yield. SOLUTION: Mixing of quicklime (preferably quicklime whose surface is previously carbonated, e.g. quicklime carbonated by using a discharge gas of lime baking furnace) with slaking water (preferably an aqueous solution containing 0.01-10.0wt.% saccharide and/or 0.01-2.0wt.% surfactant) is carried out in a mixer 1 and then, the mixture is pulverized in a wet type pulverizer 2 and the resultant powder is transferred to a reactor 3 and subjected to slaking reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for industrially and advantageously producing dry slaked lime having a high specific surface area and excellent reactivity in a high yield, using quick lime as a raw material. The present invention relates to a method for industrially and advantageously producing dry slaked lime having a high specific surface area and excellent reactivity in a high yield using lightly calcined high-activity quick lime as a raw material.

[0002]

2. Description of the Related Art Conventionally, as a method of industrially producing dry slaked lime, there is a method of digesting in a pressurized container, and the like.
In most cases, a digestion method using normal pressure is employed, and in all of the digestion methods, low-activated quick lime that has been burned strongly and has a relatively slow digestion reaction is used as a raw material.

In this method of producing slaked lime by digestion under normal pressure, that is, normal pressure dry digestion, quick lime and digestive water are charged into a digester to cause a digestion reaction. As digestion water, about 60 parts by weight of water is used for 100 parts by weight of raw quicklime. When quicklime and digested water are put into a digester, they react rapidly and are mixed with stirring to form digested products. At this time, the temperature in the digester is 120 to 150 ° C. depending on the heat generated by the reaction.
However, the digested matter in the digester still contains a large amount of attached moisture and undigested matter. For this reason, it is then moved to a ripening machine and, under the retained high temperature, excess water evaporates and the attached moisture is adjusted.
The digestion of the undigested matter proceeds with the steam, but also undesired coarsening and aggregation of the particles occur. The relatively coarse digested matter discharged from the ripening machine is finally classified or pulverized into a dried slaked lime product.

[0004] In many cases, products are sorted out as products conforming to JIS special Nos. 1, 1 and 2, but in the above method,
The particle size of these calcined lime products is large due to the large particle size of the calcined lime that has been strongly baked, and due to the coarsening of the particles and the coagulation between the particles caused by the long-term retention of the digested material in a large amount of water vapor at high temperatures, 150μm even for JIS special name compliant products
It is a relatively coarse powder of the following order.

In the above-mentioned conventional production method, that is, a method of producing slaked lime by mixing and reacting strongly calcined low-activity quick lime and water, even the highest grade usually has an average particle diameter of 10%.
It is a relatively coarse and poorly reactive dried slaked lime having a specific surface area of about 10 μm and a specific surface area of about 10 to 15 m ² / g. Therefore, slaked lime produced by the conventional production method has poor reactivity, and is no longer applicable to dechlorination treatment of exhaust gas in a waste cleaning plant or advanced neutralization treatment of plant wastewater.

Lightly calcined quick lime has a smaller particle size and a larger pore volume than strongly calcined quick lime, and has properties suitable for producing fine slaked lime having a high specific surface area. . However, lightly calcined high-activity quick lime causes a radical reaction instantaneously upon mixing with water, which prevents a sufficient uniform mixing of quick lime and water, resulting in water shortage and a large amount of undigested matter. In the case where a large amount of water is used to reduce undigested substances, undigested substances are reduced, but slaked lime containing too much moisture is obtained. Not manufactured.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and is unsuitable in a method for producing a dried slaked lime having a high specific surface area and excellent reactivity in a high yield, particularly, in a conventional production method. It is intended to provide a method for producing dry slaked lime having a high specific surface area and excellent reactivity with a high yield using lightly calcined highly active quicklime as a raw material.

[0008]

Means for Solving the Problems The method of digesting quicklime is as follows:
It is broadly divided into wet digestion, in which a large amount of water is used, and dry digestion, in which a relatively small amount of water is added to produce powdered slaked lime.

In wet digestion, Ca (OH) ₂ is first formed by ionic bonding in a liquid phase, and crystals are formed when the solution becomes a supersaturated solution. The degree of crystal growth, that is, the size of the crystal is affected by the concentration of the liquid phase and the additives, but generally, fine slaked lime with less coagulation is produced as compared with the dry digestion.
On the other hand, in dry digestion, water rapidly turns into steam because the reaction occurs rapidly. Therefore, the digestion reaction is mostly steam digestion, the crystals become non-uniformly large, and the generated surface energy forms agglomerates to produce slaked lime of coarse particles. Moreover, the size of the slaked lime particles generated in the dry digestion is greatly affected by the particle size of the quicklime. The quicklime particles become larger as they are more strongly fired. In other words, the particles of slaked lime generated by digesting the calcined lime that has been strongly baked become large.

The digestion reaction in dry digestion proceeds in the following four stages.

1) absorption of water 2) formation of CaO.xH ₂ O 3) CaO.xH ₂ O → Ca (OH) ₂ + water vapor 4) coarsening of crystals and formation of aggregates In dry digestion, the above 4
The digestive processes of the stages are not clearly separated. Due to the transpiration of water due to the rapid digestion reaction, water does not evenly reach the quicklime,
Undigested and incompletely digested substances are present, resulting in a decrease in the yield and quality of slaked lime. This tendency is stronger in lightly calcined highly active quicklime and in quicklime having a small particle size. For this reason, in the conventional dry digestion, in order to prevent a decrease in yield and quality, low-activity relatively large particle size lime calcined with a relatively slow reaction strength is used as a raw material.

[0012] In the conventional dry digestion, the particles of calcined lime that are strongly burned are large, and the particles of slaked lime produced by the dry digestion are coarse. In dry digestion, in order to obtain fine particles of slaked lime, small calcined lime that has been lightly calcined must be used,
Due to the rapid reaction, the yield is extremely low, and the conventional production method is not industrially feasible.

[0013] In order to obtain fine slaked lime, lightly calcined quicklime must be used as a raw material, but the degree of calcining of industrially obtained quicklime is not uniform anyway. Therefore with the selection of quick lime, (1) uniformly to absorb water quicklime particles, the more uniform to produce an intermediate product (CaO · xH ₂ O), uniformly intermediate product from (3) (2) dehydration It is important to allow the reaction to take place.
Furthermore, it is advantageous if (4) it is possible to prevent coarsening of the digestion particles and formation of aggregates, that is, to prevent the generated slaked lime from being exposed to high temperatures and high steam.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, after mixing quicklime and digested water and then wet-milling, particularly, highly calcined lightly calcined quicklime is obtained. The raw lime is used as a raw material to form a coating on the surface of quick lime particles by carbonating the surface of quick lime in advance and / or adding carbohydrate to the digestion water to delay the digestion reaction, and to mix the quick lime and the digestion water sufficiently. After that, by wet pulverization, by causing a digestion reaction, and further by adding a surfactant to the digestion water, fine slaked lime of high specific surface area having a small particle size and a large pore volume, specifically, Is, for example, as compared with slaked lime obtained by a conventional method, the average particle size is 、, and the specific surface area is 2 to 2.
Finding that slaked lime which is three times more reactive can be obtained,
The present invention has been completed based on this finding.

That is, according to the present invention, in the method for producing dried slaked lime, first, quick lime (preferably quick lime having a surface which has been previously carbonated, for example, quick lime which has been carbonized using exhaust gas from a lime burning furnace) is digested. Water (preferably 0.01 to 10.0% by weight of carbohydrate and / or 0.0
Mixing in an aqueous solution containing 1 to 2.0% by weight of a surfactant) in a mixer (1), the mixture is then ground in a wet mill (2) and transferred to a reactor (3),
It is characterized by reacting.

[0016]

In the present invention, sufficient absorption of water by mixing is performed with quick lime having a relatively large particle size, preferably using quick lime having a carbonated surface, and converting an aqueous solution containing saccharides into digested water. The use delays the reaction to facilitate mixing, and the addition of a surfactant to the digested water allows the water to penetrate sufficiently uniformly between the quicklime particles.
If the mixture of quicklime and digestion water is wet-pulverized into a mixture of fine particles before quicklime causes an autolysis reaction, the quicklime is atomized before the reaction starts. The quicklime initiates or accelerates the autolysis reaction more uniformly due to the atomization.

The fine lime which has absorbed water sufficiently uniformly forms an intermediate product (CaO.xH ₂ O) more uniformly, and the intermediate product causes a more uniform dehydration exothermic reaction, thereby simultaneously removing excess water. Evaporate outside the system. For this reason, the digested matter produced is not exposed to a large amount of steam, and undesired coarsening of particles and formation of aggregates due to the effect of high-temperature steam are unlikely to occur, and fine slaked lime can be obtained in high yield. Can be. The digestion reaction can also be controlled by adjusting the degree of wet grinding. Furthermore, the surfactant contained in the digestion water can suppress the generation of surface energy peculiar to dry digestion, and can prevent aggregation between slaked lime particles.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment, lightly calcined quicklime is used as a raw material. As the calcined lime that is lightly calcined, for example, calcined lime obtained by calcining limestone at 1100 ° C or less, particularly about 800 to 1000 ° C can be used. Slightly calcined quicklime readily reacts with water, delaying the reaction upon use. For example, the reaction of quicklime can be delayed by previously carbonating the surface of quicklime and using an aqueous solution containing 0.01 to 10.0% by weight of carbohydrate as digestion water. By using carbonated quicklime as a raw material and using an aqueous solution containing a saccharide as digestion water, a better delay effect is produced. In general, when carbonated quicklime is used, the amount of carbohydrate used may be small, and may be about 以下 or less of the case where normal quicklime is used.

In the method for producing dried slaked lime according to the present invention, the particle size of quicklime in the mixture of quicklime and digested water is usually 1%.
The wet pulverization is performed so as to be 50 μm or less, and more preferably the wet pulverization is performed to about 75 μm or less. The smaller the particle size of the raw quicklime is, the more preferable, but from the viewpoint of surface carbonation and ease of mixing or a reaction delay effect, the particle size of the raw quicklime is usually preferably about 5.0 mm or less, more preferably. That is, the particles are sized so as to be 0.5 to 3.0 mm. For example, if calcined lime sized to 0.5 to 3.0 mm is allowed to enter the exhaust gas (CO ₂ concentration: 20%) of a lime burning furnace (rotary kiln) for ₂ to 5 minutes, the surface is easily carbonated and only water is used. Digestion reaction is 5 when mixed with digestive water
It is easily delayed for about 10 minutes.

Carbonation of the quicklime surface forms a thick calcium carbonate surface coating in the highly active areas,
In the low activity part, a thin calcium carbonate surface film is formed, and even if it is industrially calcined lime with non-uniform activity, the reaction is delayed more uniformly and sufficient mixing time to absorb water into quick lime. Can be obtained.

When water passes through the calcium carbonate coating and reaches the inner layer of quicklime, a quick digestion reaction of quicklime and water occurs. As the coating forms and the digestion reaction is further delayed, water will penetrate better between the quicklime particles.
In a preferred embodiment, the digestion kinetics is slowed by adding carbohydrates to the digestion water. Carbohydrates are monosaccharides,
There are disaccharides and polysaccharides, and sucrose, a disaccharide, is preferred. In the present invention, molasses by-produced in sugar production is more preferably used in terms of price. If the concentration of carbohydrate contained in the digested water is less than 0.01% by weight, the effect is insufficient.
If the content exceeds 0.0% by weight, the amount of water adhering to the coating may increase, or may cause agglomeration of particles.

The surfactant further promotes the penetration of water between the quicklime particles. By using an aqueous solution containing 0.01 to 2.0% by weight of a surfactant as digestion water, mixing of quicklime and digestion water is facilitated, and penetration of water and carbohydrate between quicklime particles is improved. In addition, the dispersion of the wet crushed fine lime can be improved, and the reaction can be made more uniform. Although any surfactant can be used, anionic, nonionic and amphoteric surfactants are preferred. Preferable examples include polyoxyethylene alkyl ethers, salts of highly condensed melamine sulfonic acid formalin, and dialkyl sulfosuccinates.

The presence of a surfactant is important in order for the process of digestion of quicklime to proceed more smoothly. Surfactants not only improve the penetration of water into quicklime particles when mixing quicklime and digestion water, but also improve the penetration of carbohydrates and water into quicklime, as well as efficiently perform wet pulverization. Even after the pulverization, there is an effect of promptly permeating water to promote and stabilize a uniform digestion reaction. The surfactant is
(1) Improve the mixing of quicklime and digestive water, (2) promote the penetration of water between quicklime particles, (3) improve the efficiency of wet grinding, (4) quicklime in a mixture with digestive water It has the effect of improving the dispersion of particles, (5) suppressing the generation of surface energy peculiar to dry digestion, and preventing aggregation between slaked lime particles.

Although two or more surfactants can be used in combination, one surfactant is usually sufficient. If the concentration of the surfactant contained in the digested water is less than 0.01% by weight, the above effect is insufficient, and if it exceeds 2.0% by weight, the effect is not significantly changed.

However, the method of surface carbonation of quicklime, carbohydrate, surfactant or quicklime is not limited to the above examples as long as the effect of the present invention is not exceeded.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of the steps in one embodiment of the manufacturing method according to the present invention.

The present invention is preferably implemented as follows. First, 0.01 to 10.0% by weight, more preferably 0.1 to 5.0% by weight of saccharide, and 0.01 to 2.0% by weight, more preferably 0.05 to 0.5% by weight. % Of the aqueous solution to which the surfactant has been added is used as digestion water. The digested water and surface-carbonated quicklime (hereinafter, simply carbonated quicklime) are mixed in the mixer (1). The digestion water amount is preferably 45 to 80 parts by weight, more preferably 55 to 65 parts by weight, based on 100 parts by weight of the raw quicklime.

The mixture sufficiently mixed in the mixer (1) is transferred to a wet pulverizer (2) and wet-pulverized to a particle size of 150 μm or less, preferably 75 μm or less to increase the reactivity. Move to (3). In the reactor (3), a digestion reaction is caused by atomization of quick lime, and the temperature is gradually increased to be transferred to the ripening machine (4). Further, in the ripening machine (4), the amount of adhering water is adjusted and cooled, and then discharged. Exhausted digests are completely converted into slaked lime product tanks (6)
Is stored in.

[0029]

The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

Example 1 An aqueous solution containing molasses having a concentration of 0.2% by weight and polyoxyethylene nonylphenyl ether having a concentration of 0.05% by weight was used as digestion water, and 100 parts by weight of carbonated lime having a particle size of 3.0 mm or less was used. And 58 parts by weight of digested water are mixed in a mixer (1) for 5 minutes, and then wet-pulverized by a wet-type pulverizer (2) to form solids having a particle size of 150 μm or less, and then in a reactor (3). For 4 minutes in the ripening machine (4) for 8 minutes to obtain dried slaked lime, which was subjected to dry classification and a product having a particle size of less than 150 μm was obtained. The yield was a numerical value calculated by dividing the product weight by the quicklime weight, and the specific surface area was measured by a BET specific surface area meter. As a result, as shown in Table 1, the yield was 1.31 and the specific surface area was 38.6 m ² / g.

Example 2 Using an aqueous solution containing molasses at a concentration of 1.0% by weight and polyoxyethylene nonylphenyl ether at a concentration of 0.05% by weight as digestion water, quicklime 10 having a particle size of 3.0 mm or less was used.
0 parts by weight and 61 parts by weight of digested water were mixed for 3 minutes in the mixer (1). The subsequent operations were performed in exactly the same manner as in Example 1 to obtain a product. As shown in Table 1, the result was a yield of 1.32 and a specific surface area of 35.5 m ² / g.

Example 3 A product was obtained in exactly the same manner as in Example 1 except that an aqueous solution containing only 0.05% by weight of polyoxyethylene nonylphenyl ether was used as digestion water. Table 1 shows the results
As shown in Table ² , the yield was 1.31 and the specific surface area was 33.9 m ^2.
/ G.

Comparative Example 1 During the digestion step, the wet pulverization was omitted. That is, 0.2
An aqueous solution containing molasses at a concentration of 0.05% by weight and polyoxyethylene nonyl phenyl ether at a concentration of 0.05% by weight was used as digestion water, and carbonated lime 100 having a particle size of 3.0 mm or less was used.
Parts by weight and 61 parts by weight of digested water were mixed in the mixer (1) for about 18 minutes until the temperature of the mixture reached 70 ° C., and then without passing through the wet pulverizer (2) and the reactor (3), It was directly transferred to the ripening machine (4) and allowed to stay there for 8 minutes to obtain dried slaked lime, which was subjected to dry classification and a product having a particle size of less than 150 μm was obtained. As a result, as shown in Table 1, the yield was 0.98 and the specific surface area was 25.8 m ² / g.

Comparative Example 2 An experiment was performed based on a conventional manufacturing method. That is, the particle size is 3.0 m.
After mixing and reacting 100 parts by weight of quicklime having a particle size of m or less and 65 parts by weight of digested water in a reactor, the mixture is aged in an aging machine to obtain dry slaked lime, which is dry-classified to obtain a product having a particle size of less than 150 μm. The results were as shown in Table 1, and the yield was 0.9.
7, specific surface area was 10.7 m ² / g.

[0035]

Table 1 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Quicklime particles (mm) 0 to 30 to 30 to 30 to 30 to 3 Activity (ml) ^{* 1} Before carbonation 163 161 165 160 31 78-8377- hydrated lime product after carbonation 1.31 1.32 1.31 0.98 0.97 Specific product surface area (m ² / g) 38.6 35.5 33.9 25 0.8 10.7 Particle size (μm) ^{* 2} +150 0.7 0.9 1.0 24.0 23.4 75 to 150 3.3 5.8 6.3 3.3 18.9 45 to 75 1. 3 1.3 1.4 0.7 13.4 -45 94.7 92.0 91.3 72.0 44.3 * 1: For the activity, 25 g of quicklime was poured into 1 liter of water at 40 ° C. While stirring with a stirrer, titrate with 4N-HCl.
After 4 minutes, it was indicated by the titer of 4N-HCl.

* 2: The particle size is expressed as a weight percentage by a water sieve.

[0037]

As described above in detail, according to the method of the present invention, dry slaked lime having a high specific surface area and excellent reactivity can be stably produced in a high yield in an industrially advantageous manner. The highly reactive dried slaked lime obtained by the present invention is extremely suitable for dechlorination of exhaust gas in a waste cleaning plant, and is also advantageously used in highly neutralizing treatment of factory wastewater.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of steps in an embodiment of a manufacturing method according to the present invention.

[Explanation of symbols]

 1. Mixer 2. Wet pulverizer 3. Reactor 4. Aging machine 5. Dust collector 6. Product tank

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kaichi Fujiyoshi 47 Gifu Pref., Kasamatsu-cho, Hatori-gun 47 Gifu Prefectural Industrial Technology Center

Claims (6)

[Claims] 1. First, mixing quicklime and digested water is performed.
Then, the mixture is wet-pulverized and subjected to a digestion reaction, thereby producing a dry slaked lime. 2. The method for producing dry slaked lime according to claim 1, wherein the mixing of quicklime and digested water is performed in a mixer (1), and the mixture is ground in a wet mill (2), and then the reactor (3) A method for producing dried slaked lime, which is transferred to and reacted. 3. The method for producing dry slaked lime according to claim 1, wherein the surface of quicklime is carbonated in advance. 4. The method for producing dry slaked lime according to claim 3, wherein the surface of the quick lime has been carbonated in advance using exhaust gas from a lime burning furnace. 5. The digested water is an aqueous solution containing 0.01 to 10.0% by weight of carbohydrate.
The method for producing dry slaked lime according to any one of the above. 6. The digested water is an aqueous solution containing 0.01 to 2.0% by weight of a surfactant.
The method for producing dried slaked lime according to any one of claims 1 to 5.