JP3662158B2 - Method for producing slaked lime - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing fine slaked lime useful for uses such as drinking water treatment, wastewater treatment, exhaust gas treatment, castings and wire-forming lubricants.
[0002]
[Prior art]
Slaked lime is widely used as a water treatment process, removal of harmful gases, castings and wire-forming lubricants, and the like. In these applications, it is known that the efficiency and effect can be enhanced by using slaked lime having a smaller particle diameter. For example, in the exhaust gas desulfurization process using slaked lime slurry, generally, purification capacity and efficiency become higher as finer slaked lime. Therefore, a method for producing slaked lime composed of finer particles is required. For example, German Patent No. DE2714858 discloses a method for obtaining a slaked lime slurry composed of slaked lime particles having a median diameter of 1 μm or less from a cyclone while circulating the slaked lime slurry through a digestion reaction tank-pump-in-line mixer-cyclone-digestion reaction tank. However, this method has a complicated process and requires a long time.
[0003]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for easily and efficiently producing slurry-like or paste-like slaked lime composed of fine slaked lime particles of, for example, 1 μm or less.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention configures a method for producing slaked lime including the following two steps. That is, step (a): a quick lime having a purity of 95% by weight or more, an activity (t60) of 100 seconds or less, and a size of 35 mm or less, and water having a temperature of 80 to 95 ° C. and a water ratio of 1.2 to 1.8 ( Water / quick lime (weight ratio)), shearing and / or kneading under pressure and mixing to digest quick lime; and step (b): water is further added to the paste-like slaked lime obtained in step (a). In addition, it is a step of making the digestion reaction substantially complete while stirring. Furthermore, (c) process: The process of adjusting the slaked lime obtained at the (b) process to the slaked lime slurry of a desired density | concentration, and removing a coarse particle can also be included.
[0005]
The main factors that influence the quality of slaked lime in the digestion process include the following.
(1) Reactivity of quicklime with water (2) Particle size distribution of quicklime (3) Quantity and quality of water used (4) Water temperature (5) Digestion method (6) Agitation during digestion
The reactivity of quicklime with water (activity (t60)) test was performed by adding 150 g of quicklime of a predetermined size to 600 mL of water at 20 ° C, and using a calorimeter and a stopwatch at 60 ° C during the digestion. Measure the time to reach. This test has been standardized with AWWA B202 and ASTM C110.
[0007]
Generally, the digestion mechanism consists of a stage in which a digestive phase is quickly generated on the surface of the quicklime mass in a short period of 2 to 3 minutes, and a quicklime mass in 10 to 30 minutes until the quicklime mass bursts with heat generated by digestion. It can be divided into two stages in which a digestive phase is gradually generated inside. This mechanism is difficult to control and it is difficult to produce a uniform reaction. In general, it is known that as the digestion rate increases, the supersaturation degree of calcium hydroxide increases, a large amount of nucleation occurs, and finally finer slaked lime can be generated. Therefore, in order to prevent the digestion rate from becoming slow, a mechanism for removing the slaked lime layer formed on the quicklime surface layer is considered necessary. For this purpose, it is not sufficient to simply increase the conventional digestive agitation. A mechanism for applying special stress to effectively grind the quicklime particles is required, and fine slaked lime particles are produced. It was confirmed that it was most important to give high temperature and strong grinding during the rapid digestion phase formation on the surface of This is not believed by the inventor to be bound by the above theory or any other specific theory, but is believed by the fact that fine slaked lime particles are produced as a result.
[0008]
Therefore, in the present invention, the water ratio, which is the value of water / quick lime (weight ratio), is low, that is, the kneaded lime particles are strongly kneaded in a high concentration state, the agglomeration of the paste obtained thereby is dispersed, and By stirring so as to complete the slaked lime, the proportion of fine particles was higher than in the past.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, when quicklime is digested, its volume increases 2.5 times or more, and if it is placed in a narrow space, it can be pressurized by utilizing the property of generating an expansion force reaching about 5000 t / m ² . If the initial digestion reaction is carried out using a pressurized digester that can knead while advancing the contents of an extruder, kneader, etc., quick lime and digested water can be used while being sheared and / or kneaded in a sealed pressure vessel. Thus, a large pressure and shearing force and / or kneading force for pulverizing and refining the quicklime particles can be constantly obtained. Considering the temperature and pressure rising during digestion in an enclosed narrow space such as in an extrusion kneader, it is concluded that the quicklime particles were digested under high temperature and pressure. Therefore, in the step of digesting high purity and high activity quicklime and hot water at a low water ratio, according to the digestion method of the present invention using an extruder or a kneader at an initial stage and then using a stirrer, it has been conventionally performed. Fine particles, for example, slaked lime having a particle size of 1 μm or less, are obtained much more than conventional digestion methods.
[0010]
An extrusion kneader or the like serves as a reaction field in the initial digestion. In the digester, quick lime and water are confined in a narrow space, digested while being crushed under a strong shearing force and / or kneading force, and gradually move forward. Strong shearing and / or kneading at a low water ratio, i.e. high concentration, grinds and breaks up the quicklime particles and promotes the initial digestion reaction. The digestive phase of the surface layer of quicklime particles is quickly removed, crushed, and the unreacted portion inside is exposed to water to cause a uniform reaction.
[0011]
After the initial digestion, more water is added to the resulting slaked lime paste and stirred. For example, the slaked lime paste and water are mixed using a high-speed agitator to make the digestion reaction substantially complete while dispersing the agglomerates. The slaked lime particles can be further ground by stirring to disperse the agglomeration.
[0012]
In the step (a), high purity and highly active quicklime is digested at a low water ratio while being sheared and / or kneaded under pressure. High purity and high activity quicklime has a purity of 95% or more, an activity t60 of 100 seconds or less, and a water ratio of 1.2 to 1.8. The temperature of water is 80-95 ° C. As a digester, a pressure type device such as an extrusion kneader is used for digestion for 1 to 2 minutes.
[0013]
In the step (b), water is further added to the slaked lime paste obtained in the step (a), and the digestion reaction is substantially completed while stirring. For example, slaked lime paste is put in a high-speed stirring device and dispersed in hot water for 10 to 20 minutes. At this time, the water ratio is preferably 1.75 to 12.0, and the water temperature is preferably 60 ° C. or higher. At this time, the peripheral speed of the stirring blade is preferably 2 m / s or more.
[0014]
In step (c), the slaked lime slurry obtained in step (b) is diluted to a desired concentration to remove coarse particles. For removing the coarse particles, a pulverizing / milling device such as a ball mill or a classification device such as a sieve can be used.
[0015]
【The invention's effect】
According to the present invention, for example, a slaked lime slurry or paste made of fine particles having a particle size of about 1 μm or less can be easily and efficiently produced. By using this slaked lime in a water treatment process, removal of harmful gases, castings, wire-forming lubricants, and the like, higher efficiency and effects than before can be obtained.
[0016]
【Example】
Hereinafter, the Example of the manufacturing method of the slaked lime which consists of microparticles | fine-particles based on this invention is described.
[0017]
(Example)
Quick lime (special lime of JIS industrial lime, purity 95% or more, particle size 5-35 mm, t60 = 30 seconds) 200 g is extruded and kneaded with water 275 g (water ratio 1.375) at a temperature of 85 ° C. (manufactured by Takeuchi Seisakusho). , NES-KO-KNEADER). The residence time of the slaked lime paste in the apparatus was about 1.5 minutes, and the rotation speed of the rotary blade of the apparatus was 80 rpm. The obtained paste was transferred to a high-speed stirrer (manufactured by Shinto Kagaku, BL600), diluted with 950 g of water at 60 ° C. to a water ratio of 6.125, and stirred at a peripheral speed of 2 m / s for 10 minutes. Subsequently, slaked lime slurry from which coarse particles were removed with a sieve having an opening of 150 μm was used as a sample No. It was set to 1. The proportion of coarse particles remaining on the sieve having an opening of 150 μm was about 5% by weight. FIG. 1 is an observation photograph by a scanning electron microscope, and it was shown that the obtained slaked lime particles were substantially all having a particle size of 1 μm or less.
[0018]
(Comparative example)
Digestion was performed using an open-type kneader (manufactured by Maruto Seisakusho, C138A) that does not receive pressure due to expansion due to digestion. Except for the initial digester, the same procedure as in Example 1 was repeated to obtain the sample No. 2 was obtained. FIG. A large number of large slaked lime particles having a particle diameter of 1 μm or more were observed in the observation photograph taken by scanning electron microscope 2.
[Brief description of the drawings]
FIG. 1 is a photomicrograph of slaked lime produced by an example of a method for producing slaked lime according to the present invention.
FIG. 2 is a photomicrograph of slaked lime produced by a conventional method for producing slaked lime.

Claims (2)

The manufacturing method of the slaked lime characterized by including the following two processes.
(A) Step: A quick lime having a purity of 95% by weight or more, an activity (t60) of 100 seconds or less, and a size of 35 mm or less, and water having a temperature of 80 to 95 ° C. and a water ratio of 1.2 to 1.8 (water / Quick lime (weight ratio)) and digesting quick lime by mixing while shearing and / or kneading under pressure.
(B) Step: A step of further adding water to the paste-like slaked lime obtained in the step (a) to substantially complete the digestion reaction while stirring. Furthermore, the manufacturing method of the slaked lime of Claim 1 including the process of adjusting the slaked lime obtained at the (c) process: (b) process to the slaked lime slurry of a desired density | concentration, and removing a coarse particle.

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