JPH01180285A - Classifying method - Google Patents

Abstract

PURPOSE:To improve a classification efficiency of powder and to improve the yield of fine powder by adding an amt. of classification additive controlled basing on a degree of classification of a powdery body measured immediately before classification to the powdery body, then performing the classification of the powdery body. CONSTITUTION:A feed for classification mixed in a mixing apparatus 1 is classified in a classifying apparatus 2 having a high performance, providing a final product by collecting fine powder in a collector 4, and circulating coarse powder after repulverizing it in a pulverizer 3 through the classifying system, wherein a part of the feed for the classification is sampled just before the classifying apparatus 2 and transported to a dispersion degree measuring device 10. Data of classification yield and particle size distribution measured on fine powder and coarse powder obtd. after a practical classification in the classifying apparatus 2 are inputted into the dispersion degree measuring device 10, and signals are outputted to a solenoid valve 5 for controlling the amt. of a classification additive together with the data concerning the degree of dispersion measured in the measuring device 10. Thus, the amt. of the classification additive is controlled so as to provide an optimum amt.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a classification method for separating powder into coarse powder and fine powder based on a predetermined particle size, and particularly relates to a classification method for dry classification.

[Prior Art] The process of dividing a powder having a predetermined particle size distribution into several parts with more uniform particle sizes is generally called classification. As a classification method that is often used industrially, there is a method that separates powder having a relatively wide particle size distribution into fine powder and coarse powder based on a certain particle size.

Such classification is used, for example, when obtaining a hydraulic material such as cement from vitreous blast furnace slag such as granulated blast furnace slag. In other words, since cement using such slag has the disadvantage that hydration hardening, especially in the initial material, is slow, this slag is ground to a predetermined plane specific surface area using a ball mill, etc., and then classified to form a fine powder. is used as a cement material to improve its hydration hardening properties (Japanese Unexamined Patent Publication No. 61-141647).

[Problems to be Solved by the Invention] However, such glassy blast furnace slag tends to form agglomerated particles during or after crushing, and also tends to form agglomerated particles after classification, so the collection efficiency of fine powder is low. The problem is that it is extremely low.

By the way, when producing a hydraulic material from such glassy blast furnace slag, the slag is crushed by adding alcohol as a crushing aid, and then the crushed material is classified to have a plain specific surface area of 6,000 to 6,000. 12000cIj
A method for obtaining a slag powder of 1.2 g/g has been proposed (Japanese Unexamined Patent Publication No. 61-270240). The grinding aid used in this technique is
It is added to improve grinding efficiency. By adding this grinding aid, it is possible to suppress the generation of aggregated particles in the grinding process and increase the amount of fine powder present, and as a result, the classification efficiency in the subsequent classification process is improved to some extent. In other words, such grinding aids are added only to improve the overall grinding efficiency, and the grinding aids themselves may change over time during the grinding process, so they are not suitable for particularly fine particles. Particle agglomeration cannot be prevented effectively enough. In addition, as described later,
Even in this technique, the yield of fine powder is insufficient, as dense agglomerated particles may be formed due to the mechanical force during crushing.

The above-mentioned problems exist not only when classifying vitreous blast furnace slag after crushing, but they are problems that generally occur when trying to obtain fine powder by classification, and even worse. Classification efficiency will be significantly reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a classification method with high classification efficiency and particularly high fine powder yield.

[Means for Solving the Problem] The classification method according to the present invention is a classification method in which a classification aid is added to powder and then the powder is classified, and the dispersion degree of the powder immediately before classification is The method is characterized in that the amount of the classification aid added is controlled based on the value of the degree of dispersion. In this case, alcohols or amines can be used as classification aids. The degree of dispersion of the powder to be classified can be measured by sampling immediately before classification.

Further, it is preferable that the classification is performed using a dry air classifier. Furthermore, vitreous blast furnace slag can be used as the powder to be classified, and in this case, it is preferable that the fine powder side after classification has a plain specific surface area of 6000 cta2/g or more.

[Function] In this invention, when adding a classification aid to the powder to improve the classification efficiency, the degree of dispersion of the powder immediately before classification is measured, and the dispersion degree of the powder is measured based on the value. Control the amount of classification aid added. The classification aid has the effect of neutralizing the reaction sites present in the powder, thereby suppressing the agglomeration of powder particles and dispersing the already formed agglomerated particles. The amount added can be determined by measuring the degree of dispersion of the powder immediately before classification. Therefore, by controlling the amount of the classification aid added based on the degree of dispersion of the powder as described above, the classification efficiency can be significantly increased, and in particular, the yield of fine powder can be extremely increased.

[Example] When classifying powder by number, in order to achieve highly accurate classification, it is necessary to disperse the powder supplied to the classifier down to the polar particles. The powder after pulverization includes agglomerated particles with a relatively coarse structure that are naturally agglomerated, and agglomerated particles that are mechanically densely agglomerated during pulverization, and these need to be dispersed. Generally, high-performance classifiers often have a built-in powder dispersion mechanism, and the former of the agglomerated particles can be sufficiently dispersed by this dispersion mechanism. However, in the latter case, it is difficult to disperse using such a dispersion mechanism.

In order to solve these problems, the present inventors proposed a classification method in which an agent that promotes the dispersion of the powder (hereinafter referred to as a classification aid) is added to the powder before classification, and then classified. (Patent application No. 62-241454). This classification aid suppresses the formation of aggregated particles after classification, and makes it easier to disperse or disperse the aggregated particles that have already been formed before classification, thereby increasing the classification efficiency. In this case, it is preferable to use a classification aid composed of molecules with large polarity (dipole moment), such as alcohols or amines. Immediately, by adsorbing highly polar molecules to the surface of the powder particles, the particle surface can be electrically neutralized, and the outside of the young absorbing layer can be made negative polar. Therefore, it is possible to facilitate the dispersion of already formed aggregated particles, and it is also possible to suppress reagglomeration.

However, simply adding a classification aid may cause the following disadvantages.

(1) The optimum amount of the classification aid to be added varies depending on the type and properties of the raw material to be classified, as well as the type and addition method of the classification aid.

(2) Basically, the optimum amount of dispersion aid to be added is the amount that allows single molecules to be adsorbed on the particle surface, but it is difficult to make it adsorb uniformly, and if it is added in an extremely excessive amount, crosslinking may occur. There is a possibility that the particles may be agglomerated instead.

(3) When the classification conditions are changed, the yield and quality (particle size distribution, etc.) of fine powder/coarse powder will change, and especially when coarse powder is recycled, the amount of auxiliary agent will also change. Managing the amount of additive added becomes complicated.

(4) In the grinding process before classification, a grinding aid having the same composition as the classification aid may be added, and in this case as well, the control of the amount of the classification aid added becomes complicated.

Inconveniences such as E can be overcome by quickly and highly accurately determining the classifiability of the powder to be classified and adding an appropriate amount of classification aid. As a result of various studies carried out by the inventors of the present application, the classification property is represented by the degree of dispersion, which is one of the characteristics of powder, and by measuring this degree of dispersion in advance, the optimum amount of the classification aid to be added can be determined. I discovered that it can be done. This invention was made based on such knowledge.

This invention will be specifically explained below.

As the classification aid used in this invention, the above-mentioned patent application
As shown in No. 2-241454, it is preferable to use a liquid with low viscosity because it must be quickly adsorbed or bonded to the powder surface. In this way, a liquid with low viscosity can be quickly and uniformly added to powder by means such as spraying. - When it is desired to add the classification aid to a uniform layer, the aid may be sprayed onto the powder and then mixed using an appropriate mixing device. As such a classification aid, alcohols or amines are preferred as described above. These are generally highly polar;
Since the viscosity is low, the above conditions are met. These can be used after being diluted with water, etc., if necessary.

Next, the mechanism by which the classification aid suppresses agglomeration of powder particles will be explained, taking as an example the case where vitreous blast furnace slag is used as the powder.

Glassy blast furnace slag does not have a clear crystal structure, but like calcium silicate, it has a strong covalent bond of 5t.
The structure is based on -0 bonds and Ca-0 bonds with strong ionic bonding properties. To crush this glassy blast furnace slag into powder, a crushing device such as a rotary mill is used.
-Proceeds selectively at the 0 bond. In this case, electrically unsaturated Ca2÷ or 02- remains on the surface of the slag particles after pulverization, and since the electron density of the pulverized particles varies microscopically, there is a difference between these particles. Electrical bonding occurs between unsaturated electrons, and reaggregation is likely to occur in this part.

When molecules with large polarity (dipole moment) such as alcohols are added to the pulverized particles of glassy blast furnace slag thus formed, electrically unsaturated portions (hereinafter referred to as Polar molecules such as alcohol chemically adsorb onto the reaction site (referred to as the reaction site) and neutralize the unsaturated electron valence of the reaction site. Thereby, reagglomeration of the pulverized particles can be suppressed.

By the way, as mentioned above, in the vitreous blast furnace slag after pulverization, there are agglomerated particles formed by mechanically densely aggregating fine powder particles (primary particles) and secondary particles during pulverizing. Agglomerated particles are the main cause of reducing classification efficiency. Classification aids have the function of making these aggregated particles easier to disperse, or have the function of actively dispersing them7, so they are applied to airflow classification type classification equipment that has a large dispersion effect on aggregated particles. By doing so, a large dispersion effect can be obtained, and the classification efficiency can be extremely increased.

On the other hand, the degree of dispersion of the powder in order to determine the optimum amount of the above-mentioned dispersion aid is measured, for example, as follows.

Pour 10g of powder sample into a hopper with a funnel diameter of 15m1,
From a predetermined height (e.g. 400 w+m)
Let it fall freely into a saucer at 0a+s. In this case, the degree of dispersion can be expressed by the formula shown below.

Dispersity - ((sample input amount - m accumulated in the saucer) / sample input amount) This is expressed as the degree of scattering of particles, and the larger the degree of dispersion, the fewer aggregated particles, and the better the classification performance.

In other words, the higher the degree of dispersion, the higher the yield of fine powder after classification. Therefore, by adding the classification aid in an amount that maximizes the degree of dispersion of the powder, the fine powder yield, that is, the classification efficiency can be improved. Note that such a measurement of the degree of dispersion is carried out immediately before classification, taking into consideration changes in the powder over time.

When such a principle is applied to actual classification, equipment as shown in FIG. 1 is used, for example. In the figure, solid lines indicate the flow of powder, and broken lines indicate the flow of signals. A re-pulverized powder crushed by a crushing device 3 described later is added to a crushed raw material that has been crushed into powder by a crusher such as a ball mill or a roller mill vibrating mill to obtain a classified raw material, and a classification aid is added to this classified raw material.

Thereafter, this raw material powder is uniformly mixed in a mixing device 1.

The mixed classified raw materials are classified by a high-performance classifier 2.

After classification, the fine powder is collected by the collecting device 4 to become a product, and the coarse powder is re-pulverized by the aforementioned crushing device 3 and circulated within the system.

A portion of the dispersed raw material is sampled just before the classifier 2 and guided to the dispersity measuring device 10. The classification yield and quality (particle size distribution) data measured on the fine powder and coarse powder after they have been actually classified by the classifier 2 are input to the dispersity measurement device 10, and the dispersity data measured here is inputted. At the same time, a signal is output to the solenoid valve 5 that adjusts the amount of the classification aid supplied, and the classification aid is controlled to be in the optimum amount.

This dispersion measuring device 10 will be explained in more detail with reference to FIG. 2. In the apparatus 10, the sampled sample is divided into two routes, one route is directly measured for dispersion by the dispersity measuring device 12, and the other is added with a classification aid of, for example, 0.01% by weight, and is routed to the mixer 11. After mixing, the degree of dispersion is measured by a degree of dispersion measurement device 13. These data signals are then input to the data processing control unit 14 and output to the solenoid valve 5 together with the aforementioned classification yield and quality data. In this case, the classification aid usually has an optimum amount of addition, and the dispersity peaks at that amount.
The control unit 14 outputs a signal to decrease the amount of classification aid added when the amount is larger than , and outputs a signal to increase the amount of classification aid added in the opposite case.
Set. By doing so, the amount of the classification aid added can always be optimally controlled, and the aforementioned problems caused by changes in the properties of the classified raw material, recirculation of coarse powder, etc. can be solved.

Next, a test example in which the method of the present invention was actually implemented will be specifically explained.

First, prior to this test, the influence of the classification aid on the fine powder yield and degree of dispersion after classification was tested. After drying and deironating the vitreous blast furnace slag having the chemical composition shown in Table 1, 50 kg of the slag was placed in a ball mill with an internal volume of 385 mm and pulverized until the plain specific surface area became 4000 d/g.

Table 1 (unit: % weight) Next, 0.05, 0.10, 0.15, 0.20 and 0.25% by weight of classification aids were added by spraying to 2 kg of the pulverized slag powder. A high-speed fluid mixer (manufactured by Nisshin Engineering, capacity 4.2
), the stirring speed was 3000 rpm) for 5 minutes, and the powder was subjected to a dispersity test and a dispersity test. Here, diethylene glycol and triethanolamine were used as classification aids. Further, as a comparative example, slag powder without the addition of a classification aid, which had been treated in the same manner using a mixer, was subjected to a dispersity test and a classification test.

The dispersity test was conducted as described above.

The classification test was conducted using a forced vortex centrifugal classifier (Nissin Engineering Turbo Classifier TC-15 model). At this time, the classification point was set to 5 μm, the raw material supply rate was 5.7 kg/hour, and the rotor rotation speed was 391 Or
pm and air volume were set to 1.4 m3/min. Figure 3 is a graph showing the relationship between the addition rate of the classification aid on the horizontal axis and the fine powder yield after classification on the vertical axis, and shows the results of the classification test. be. The circles in Figure tJ3 indicate the case where diethylene glycol was used as a classification aid, and the triangle marks indicate the case where triethanolamine was used. As is clear from this graph, the fine powder yield improves with the addition of the classification aid, but there is an optimum amount for each classification aid, and exceeding that amount may actually reduce the fine powder yield. Recognize. The optimum amount of diethylene glycol and triethanolamine used here was 0.1% by weight.

Figure 4 is a graph showing the relationship between the addition rate of the classification aid on the horizontal axis and the degree of dispersion of the powder on the vertical axis, and shows the results of the dispersion test. It is something. Note that the circles and triangles in FIG. 4 are the same as in FIG. 3. According to this, the degree of dispersion showed the same tendency as the fine powder yield shown in FIG. 3, and the optimum addition amount was also 0.1% by weight for both diethylene glycol and triethanolamine.

That is, by measuring the degree of dispersion of the powder just before classification,
It was found that the yield of fine powder after classification can be determined.

Next, vitreous blast furnace slag having the same composition as the slag used above was classified using the apparatus shown in FIG. The raw material is ground using a ball mill with a plain specific surface area of approximately 4000c+a.
This was done until the concentration reached 2/g. Note that no grinding aid was added during this grinding.

Diethylene glycol was used as a classification aid.

The mixer used was of the same high-speed flow type as described above. A forced vortex centrifugal classifier (Turbo Classifier TC-40, manufactured by Nisshin Engineering) was used as the classifier, and the classified fine powder was collected in two stages: a cyclone and a bag filter. The plain specific surface area of the classified coarse powder is approximately 4 by ball milling.
The powder was re-pulverized to 000 es2/g and circulated within the system. To measure the degree of dispersion, as described above, 10 g of the sampling sample was placed in a hopper with a funnel diameter of 15 m +++, and the sample was placed at a height of 400 mm with a diameter of 80 mm.
This was done by letting the liquid fall freely into a saucer and measuring the amount collected in the saucer.゛For the powder after classification obtained in this way, the fine powder yield was measured, and the fine powder after classification was further measured.
From the particle size distribution of coarse powder (laser diffraction type Microtrac particle size analyzer), 50% separation particle size (DP5o), classification accuracy (25% particle size/75% particle size, D p 25/D
P 75) and the Newtonian efficiency (ηN) at 50% separated particle size were determined. In addition, as Comparative Example 1, 0.10% by weight of a classification aid was added to the pulverized raw material (excluding re-ground powder), and as Comparative Example 2, no classification aid was added at all. Measurements were made. The results are shown in Table 2.

As can be seen from this table, this test example has a higher fine powder yield and higher classification efficiency than the comparative example. Thereby, the effect of this invention could be confirmed.

Although the case of vitreous blast furnace slag has been described above, the present invention can be similarly applied to other powders.

[Effects of the Invention] According to the present invention, the degree of dispersion of the powder before classification can be measured and the amount of the classification aid can be appropriately controlled based on the measured value, so that the classification efficiency, especially the fine powder yield can be improved. can be made higher. In addition, even if the type and properties of the classified raw materials change or the type of classification aid changes, the addition amount of the classification aid can be quickly adjusted to the optimum amount, making it easier to manage the addition amount of the classification aid. .

Furthermore, excessive addition of the classification aid can be prevented. Furthermore, whether the classification device is of the type that circulates coarse powder or the type that circulates coarse powder, the amount of the classification aid can be made to correspond immediately to changes in the amount of circulating coarse powder. Furthermore, even when a grinding aid is added during the grinding process, the classification aid can be managed all at once, including the remaining amount of the grinding aid.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing a classification method according to an embodiment of the present invention, Fig. 2 is a configuration diagram of a dispersity measuring device used in this classification method, and Fig. 3 shows the amount of classification aid added and the fine powder yield. FIG. 4 is a graph showing the relationship between the amount of the classification aid added and the degree of dispersion. 1; Mixing device; 2; Classifying device; 3; Grinding device; 4; Collection device; 5; Classification aid solenoid valve; 10; Dispersity measurement device. Applicant's representative Patent attorney Takehiko Suzue Motion aid 9 Shika) (Electronic manufacturing -) Figure 3 Ai Shima J11 No. A5 power υt (l Sea) No. 4@

Claims (6)

[Claims] (1) A classification method in which a classification aid is added to a powder and then the powder is classified, the degree of dispersion of the powder is measured immediately before classification, and the degree of dispersion of the powder is measured based on the value of the degree of dispersion. A classification method characterized by controlling the amount of agent added. (2) The classification method according to claim 1, wherein the classification aid is an alcohol or an amine. (3) The classification method according to claim 1 or 2, wherein the degree of dispersion is measured by sampling the powder immediately before classification. (4) The classification method according to any one of claims 1 to 3, wherein the classification is performed using a dry air classifier. (5) The classification method according to any one of claims 1 to 5, wherein the powder is vitreous blast furnace slag. (6) The classification method according to claim 5, wherein the fine powder side of the classified vitreous blast furnace slag has a plane specific surface area of 6000 cm^2/g or more.