JPH04131168A - Dry classifier - Google Patents

Abstract

PURPOSE:To permit particles to be classified into more ultra-fine particles than attained by the conventional dry classifier by a method wherein, in a dry classifier for classifying the particles while carrying the same by a gaseous stream, the gaseous stream consists of the gas lower in viscosity than the air at normal temp. CONSTITUTION:In a dry classifier A for classifying particles while carrying the same by a gaseous stream, the gaseous stream consists of the gas lower in viscosity than the air at ordinary temp. In addition to cooled air, there are used as the aforesaid gas at least one kind of the gases or vapors selected from hydrogen, nitrogen, methane, ethane, propane, normal butane, normal pentane, normal hexane, normal heptane, normal octane, ethylene, propylene, carbon tetrachloride and chlorofluorocarbon. When the dew point of the aforesaid gas is not higher than its normal temp., it is a low temp. gas lower in viscosity than the normal temp. air. As a result, this method permits the particles to be classified inexpensively into more ultra-fine particles than attained by the conventional dry classifier.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 2. The present invention relates to a dry classifier for powder, and more particularly to a dry classifier that classifies particles while being conveyed by an air current.

[Conventional technology]

Generally, the extreme particle size dt of a dry classifier, such as a centrifugal classifier
h is expressed by the following formula.

Here, u and d are the circumferential velocity of the sorting surface, μ is the gas viscosity, and r
is the radius from the central axis to the sorting surface, ur is the linear velocity of the gas flowing into the sorting surface in the radial direction, ρS is the density of the powder, and ρ is the density of the gas.

There is an extremely high demand for reducing the ultimate particle diameter dth that can be classified by a dry classifier. The ud was increased, the radius r was increased, and the linear velocity ur was decreased.

The gas used was room temperature air.

[Invention or problem to be solved]

However, in the above conventional dry classifier, (1)
Increasing the circumferential speed ud and radius r of the sorting surface in the formula requires a large amount of equipment costs, and there is also a limit to the equipment, and as the linear speed ur decreases, the accuracy of classification tends to decrease. There is a problem in that it is no longer possible to reduce the ultimate particle size dth by this method unless the chance of abnormal coarse particles, so-called "kite", being mixed into the fine powder region is increased.

Therefore, in order to solve the problems of the above-mentioned conventional technology,
An object of the present invention is to provide a dry classifier that can classify particles into even smaller ultraparticle diameters dth that could not be achieved with conventional dry classifiers without incurring a large amount of expense.

[Means to solve the problem]

In order to achieve the above object, the characteristic structure of the dry classifier according to the present invention is that, in the dry classifier described in the above [Industrial Application Field], the conveying air stream is made of a gas having a lower viscosity than normal temperature air. It is in.

The above gases include hydrogen, nitrogen, methane, ethane, propane,
It is convenient to use one or more gases or vapors selected from normal butane, normal pentane, normal hexane, normal heptane, normal octane, ethylene, propylene, carbon tetrachloride, chlorofluorocarbon, and the like.

Also, when handling these gases under atmospheric pressure, liquid vapors above the boiling point or room temperature, such as n-butane, n-pentane, n-hexane, n-octane, carbon tetrachloride, and fluorocarbons, should be handled at relatively low temperatures. However, there is an advantage that no steam condensation occurs.

Even if the dew point of the gas is below room temperature, it may be a low temperature gas that has a lower viscosity than room temperature air.

[Action/Effect]

Next, the functions and effects of the dry classifier according to the present invention will be explained.

Since the dry classifier of the present invention has the above configuration, by introducing a gas having a lower viscosity than air at room temperature into the classification chamber, it is possible to limit the classification, as is clear from equation (1) above. It is possible to reliably reduce the outer particle size. In other words,
When a gas with a lower viscosity than air at room temperature is used as an air stream, the resistance of falling particles in the air stream becomes smaller, making it easier for the particles to fall, and the diameter of the particles discharged and collected with the air stream becomes even smaller.

Moreover, since conventional techniques can be applied to convey low viscosity gases, the cost required to introduce them can be reduced.

The gas may be hydrogen, nitrogen, methane, ethane, propane,
When the gas or vapor is one or more selected from normal octane, normal butane, normal pentane, normal hexane, normal heptane, ethylene, propylene, carbon tetrachloride, fluorine, etc., the viscosity is lower than that of air at room temperature. The gas can be reliably introduced into the classification chamber, and the cost of the gas itself is not high, so favorable results can be obtained.

In addition, when handling these gases under atmospheric pressure, liquid vapors with boiling points above room temperature, such as n-butane, n-pentane, n-hexane, n-octane, carbon tetrachloride, and fluorocarbons, must be heated to a relatively low temperature. It has the advantage that vapor condensation does not occur even when handled at high temperatures. These vapors are generally preferred because of their low viscosity.

Furthermore, if the dew point of the gas is below room temperature, the viscosity will be lower than that at room temperature by cooling, so by using a general-purpose gas cooling device, a gas with low viscosity can be easily obtained, thereby ensuring reliable It is possible to reduce the ultimate particle size that can be classified. Moreover, according to this method, air can be cooled and used, and the extreme particle size can be made much smaller than when room temperature air is used.

As described above, according to the present invention, it is possible to classify even smaller extreme particle sizes that could not be achieved with conventional dry classifiers, without requiring particularly large equipment or incurring large costs. We were able to provide a dry classifier.

〔Example〕

The sorting cylinder (3) has a large number of slit-shaped holes (7) formed in the vertical direction on its conical circumferential surface, and has a conical lower part. It has a hanging structure so that it can freely rotate around a shaft (9) via a bearing (8) disposed in the shaft. This slit-shaped hole (7) passes through the airflow to the machine side (1) and then to the sorting tube (3).
It is communicated so that it passes through the inside of the tank and is discharged to the upper discharge port (4). Furthermore, the airflow is sent from this outlet (4) to the solid-gas separator (12), and whether only gas or airflow introduction path (
11) to be recycled and used.

However, instead of the slit-shaped hole (7) provided on the conical circumferential surface of the sorting cylinder (3), holes of various shapes can be considered, and the slit shape does not necessarily have to be as shown in the figure.

The shape of the sorting tube (3) does not necessarily have to be a downward conical shape, but may be cylindrical. Alternatively, the holes (7) may be inflow passages formed at intervals between a plurality of rotating sorting blades arranged substantially radially.

Further, the inlet port (2) is configured to merge with a particle introduction path (10) through which raw material particles to be classified are introduced via the powder feeder (13) and an air flow introduction path (11) through which air flow is introduced. The air flow introduction path (11) is equipped with a low-viscosity gas generator (5) that heats a liquid with a boiling point or above room temperature to turn it into vapor, or in the case of a gas with a dew point or below room temperature,
A gas cooling device is provided to cool this gas and generate a low-temperature air flow.

Next, the operation of the centrifugal classifier will be explained.

Air cooled by the gas cooling device (5) is introduced from the air flow introduction path (11) through the introduction port (2) to the machine side (1), and raw material particles are introduced from the particle introduction path (10).

At the same time, when the shaft (9) is rotated to rotate the sorting tube (3), the cooling air introduced into the machine side (1) swirls, and this swirling airflow creates a centrifugal force field inside the machine side (1). As it forms, raw material particles are thrown away.

The airflow then passes through the slit hole (7) of the sorting tube (3) and is discharged from the upper outlet (4). Coarse particles contained in the airflow introduced into the machine side (1) are removed from the lower outlet (6).
), the fine particles are discharged together with the air stream through the slit hole (7) through the upper outlet (4) and are thus accurately classified.

In this case, since the air introduced into the machine side (1) is cooled, the gas viscosity μ in equation (1) above becomes smaller, and therefore the particle size to be classified is much smaller than that with a conventional centrifugal classifier. A finer result was obtained.

For example, when air at -73°C is used, the viscosity decreases to about 70% compared to air at 27°C. can be reduced to about 85%.

In addition, when using steam with a dew point or room temperature or higher as the air stream, it is not possible to lower the viscosity by cooling, or the vapors such as normal hexane mentioned above have a very low viscosity compared to air even at room temperature or higher. For example, 400% normal octane vapor (viscosity 7.3μ) is used as a low viscosity gas.
Using Pa-5), it was possible to reduce the critical particle size to be classified to about 64% of the critical particle size classified by the current centrifugal classifier.

[Another example]

In the above examples, cooling air was used as the air flow, or instead of hydrogen, nitrogen, methane, ethane, propane, n-butane, n-pentane, n-hexane,
Low viscosity gases such as normal heptane, normal octane, ethylene, propylene, carbon tetrachloride, and chlorofluorocarbons may be used alone or in combination.

It is preferable to use these gases after cooling them through the gas cooling device (5) because a low-viscosity airflow can be obtained.

Further, although the above embodiments show a centrifugal classifier having an internal rotation mechanism, the present invention is not limited to this, and a centrifugal classifier without an internal rotation mechanism, for example, a free swirl A classifier known as a type classifier, such as the classifier shown in Figures 1 and 2 of Japanese Patent Publication No. 31-6939, may be used, or a classifier such as the classifier shown in Figures 1 and 2 of Japanese Patent Publication No. 31-6939, or Japanese Patent Publication No. 32-275
The classifier shown in FIGS. 1 to 5 of Publication No. 1 may also be used.

Alternatively, it may be a so-called inertial classifier as shown in FIGS. 1 to 7 of Japanese Utility Model Publication No. 44-21415, which utilizes adhesion airflow (utilizes the Coander effect).

When particles are conveyed by airflow using a substance that is a liquid at room temperature but easily becomes a gas when heated, it can be carried out using the apparatus shown in FIGS. 2 to 4.

That is, in the case shown in FIG. 2, the liquefied low-viscosity gas is guided from the liquefied stock solution tank (20) of the low-viscosity gas containing powder to one end of the heating tube (22) by the pump (21).
The powder and low-viscosity gas are ejected from the other end to a centrifugal classifier (A) for classification. Then, the classifier (
Coarse powder is collected from the lower discharge port of A), and fine powder is sucked from the upper part and collected using a bag filter or the like. The low viscosity gas used should be collected and reused as appropriate.

In the device shown in FIG. 3, the liquefied low-viscosity gas is guided from the liquefied stock solution tank (20) of low-viscosity gas containing powder to one end of the heating tube (22) by a pump (21), similar to the device shown in FIG. This is a system in which powder and low-viscosity gas are ejected from the other end of the heating tube (22) to a classifier (A) that utilizes the Coander effect.

The one in Fig. 4 is an apparatus configuration in which the gas is low viscosity or liquid at room temperature, and the liquefied gas stored in the tank (23) is turned into gas through the heating pipe (22), and the powder feeder is connected to the liquefied gas stored in the tank (23). The powders from (13) are combined and then inserted into the above-mentioned various classifiers (A) for classification.

In addition, the dry classifier according to the present invention can also be applied as a device for the purpose of dust collection, in which case, for example, the device side (1)
What is necessary is to provide an opening in the side wall.

In addition, various auxiliary devices for increasing the classification effect may be provided, such as equipment that applies shock waves to the particles being transported by the airflow to prevent the transported particles themselves from agglomerating.

It should be noted that the present invention is not limited to the structure shown in the accompanying drawings by adding reference numerals in the claims for convenient comparison with the drawings.

[Brief explanation of drawings]

FIG. 1 is a conceptual vertical cross-sectional diagram showing one embodiment of the dry classifier according to the present invention, FIG. A conceptual diagram of the layout,
FIG. 4 is a conceptual layout diagram showing still another embodiment of the present invention. (A)・・・Classifier

Claims (1)

[Claims] 1. Dry classifier that classifies particles while transporting them with air current (
The dry classifier according to A), wherein the air flow is made of a gas having a lower viscosity than air at room temperature. 2. The gas is one or more selected from hydrogen, nitrogen, methane, ethane, propane, normal butane, normal pentane, normal hexane, normal heptane, normal octane, ethylene, propylene, carbon tetrachloride, and fluorocarbons. The dry classifier according to claim 1, which is a gas or steam. 3. The dry classifier according to claim 1 or 2, wherein when the dew point of the gas is below room temperature, it is a low temperature gas having a lower viscosity than room temperature air.