JP3482503B2 - Eddy current air classifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention also relates to a vortex type air classifier used for classifying raw materials of powder and granules such as cement, calcium carbonate and ceramics.

[0002]

2. Description of the Related Art In a conventional vortex type air classifier, a classification raw material is supplied from the upper side and enters a classification space while being dispersed by a dispersion plate. On the other hand, the air required for classification is fixed all around the classifier. It is sucked by the fan behind the classifier through the arranged guide vanes. At this time, the classified air starts a uniform vortex movement by the guide vanes, and is further accelerated by the rotor blade to a speed required for classification.

That is, when the space between the guide vanes and the rotor blade is defined as a classification space, the airflow there can be regarded as a two-dimensional vortex airflow. The particles supplied to the classification space start vortex motion together with this vortex flow, and are classified by the balance of centrifugal force and drag force acting on the particles at that time. As a result, particles smaller than the separated particle size determined by the balance between the two forces enter the rotor and are discharged and collected via the outlet duct.

On the other hand, large particles fall by gravity while being repeatedly classified in the classification space and discharged from the coarse powder discharge port. The separated particle size is controlled by the rotation speed of the rotor or the classified air flow rate, that is, the centrifugal force or drag force applied to the particles.

[0005]

A rotor outer periphery [0005], min classifier tangential velocity component and the particle velocity of the air velocity
Ideally, the tangential velocity components of the class are equal. However, in an actual classifier, the particle velocity with respect to air is low due to the inertia of the particles, and the velocity of the air is the same as the tangential velocity component of the rotor, so the following problems occur.

(1) A lot of rotor wear. This wear generally increases in proportion to the cube of the relative velocity of the rotor blade particles. (2) In order to classify particles with a predetermined separation particle size, the rotor must be rotated at a speed higher than the tangential component speed that should originally be imparted to the particles, which requires extra energy for the motor and also the rotor. Since the rotation speed of No. 1 increases, the pressure loss of the classifier also increases, and the fan that sucks in air requires extra energy.

In view of the above circumstances, it is an object of the present invention to reduce the delay of particle velocity with respect to air velocity.

[0008]

[Means for Solving the Problem] A tangential direction of a rotor outer peripheral portion
It is not easy to measure the tangential velocity component of particles at the same location with respect to the velocity component with an actual classifier. Therefore, theoretically, the orbits of the particles are calculated by a computer to determine how the width S of the classification chamber and the mounting angle θ _G of the guide vanes _G , that is, the angle of the guide vane inscribed circle with respect to the tangent line influences. Based on the investigation, based on that, the condition that the rotor peripheral velocity and the tangential velocity component at the same location of the particles are approximately equal was found by the following method.

FIG. 1 shows an airflow model of a cross section of a classifying unit for performing a two-dimensional particle orbital calculation for the vortex type air classifier. In this, R1 is the circumscribed circle B of the rotor blade B
C radius, R ₂ is radius of inscribed circle GC of guide vane G,
ω ₁ is the angular velocity of the rotor blade, and ω ₂ is the angular velocity of the airflow entering the classification space. The material to be classified shall be supplied at the radial position of 0.99R ₂ .

FIG. 2 is a conceptual diagram of classification based on the airflow model of FIG. The position of 0.99R _2, there initial velocity (V
_The particles supplied at _r0 , Vθ ₀ ) are accelerated or decelerated by the air flow in the classification space SP, and undergo a classification action.

Generally, as shown in FIG. 2, the rotor blade B
The outer peripheral portion BO of the rotor blade B plays a decisive role in the separation particle diameter, and the equilibrium particle diameter at each position in the classification space SP in the radial direction, that is, the particle diameter at which the centrifugal force and the drag force are balanced, is the outer peripheral portion B of the rotor blade B.
O is the smallest.

The equation of motion of a particle in a fluid which makes a rotational motion given by Lapple and Shephered is rewritten by adopting Schiller Naumann's equation as a drag coefficient acting on the particle. The following equations (1) and (2) It becomes like a formula.

M (dVr / dt) = m ・ Vθ ² / r (1-ρ _f Uθ ² / (ρp Uθ ² ) −3πμD _p κ (1 + 0.15Re _p 0.687) (U _r -V _r ) (1)

M (dVe / dt) = m · VθV _r / r−3πμD _p κ (1 + 0.15Re _p ^0.687 ) (Uθ-Vθ) (2)

In equations (1) and (2), when R1 and ω1 are used as the representative length and the representative angular velocity, respectively, each variable is made dimensionless as follows.

T ^x = tω ₁ , r ^x = r / R ₁ , R ₂ ^x = R ₂ /
R ₁ , Vr ^x = Vr / (R ₁ ω ₁ ) Vθ ^x = Vθ / (R ₁ ω ₁ ), U _r ^x = U _r / (R ₁ ω ₁ ), Uθ ^x = Uθ / (R ₁ ω ₁ ), Ω ₂ ^x = ω ₂ / ω ₁ ,

Furthermore, since ρ _f / ρ _p ≈0, equation (1)
(2) can be rewritten as the following equations (3) and (4).

[0018] ^{(dVr X / dt x) =} (Vθ x) 2 / r x - (κ / P) (U r x -V r x) (1 + 0.15Re P 0.687) (3) (dVθ X / dt x = (Vθ ^x V _r ^x / r ^x − (κ / P) (Uθ ^x -Vθ ^x ) (1 + 0.15Re _p ^0.687 ) (4)

Here, k is a dynamic shape factor, and the inertia parameter P, the particle Reynolds number Re _p, etc. are as follows.

P = ρ _P D _P ² ω ₁ / (18μ) Re _p = Re _p0 {(V _r ^x -V _r ^x ) ² + (Uθ ^x -V θ ^x ) ² } ^0.5 Re _p0 = ρ _f D _P R ₁ ω ₁ / μ R ₁ ≦ r ≦ R ₂

That is, the motion of particles in the centrifugal field can be expressed by the inertia parameter P and the particle Reynolds number Rep. Further, when the airflow velocities Uθ and U _r are derived from the NAVIER-STOKES equation, they are as follows in the classifier assumed in this calculation.

Uθ = {J ₁ R ₁ ^{(1 + ct)} (r ^x ) ^{(1 + ct)} + R ₁ ³ (R ₂ ^x ) ² J ₂
/ r ^x } / (J ₃ R ₁ ω ₁ ) U _r = Ur (R ₂ ) ^x (R ₂ ^x / r ^x )

However, J ₁ = R ₁ ² ω ₁ {(R ₂ ^x ) ² ω ₂ ^x -1)} J ₂ = R ₁ ^ct ω ₁ {(R ₂ ^x ) ^ct -ω ₂ ^x } J ₃ = R ₁ ^{(2 + ct)} {(R ₂ ^x ) ^{(2 + ct)} -1} ct = R ₁ ² ω ₁ R ₂ ^x Ur _(R2) / (ν + ε _m )

For the two-dimensional particle orbital calculation in the classification space SP, the initial conditions (r _o , θ ₀ , V
r _o, giving Vθ _o), it was using the Runge-Kutta-Gill method. In that case, in order to obtain the separated particle size, it was decided to find the largest particle out of the particles inside the circumscribed circle BC of the rotor blade by a trial method.

The separated particle size obtained by this method is the measured value of 5
It has been confirmed that the diameter is almost the same as the 0% separation diameter.

An example of the result of the above calculation is shown in FIG. According to this figure, when the separated particle size exceeds 10 μm, the tangential velocity component ratio Vθ (R ₁ ) / Uθ (R
₁ ) is small, that is, the degree of particle delay with respect to the air flow is large. This phenomenon is more remarkable as the angular velocity ω ₂ is smaller.

Therefore, if the angular velocity ω ₂ is controlled according to the classification condition, this delay can be eliminated. The angular velocity ω ₂ can be controlled by the mounting angle θ _G of the guide vane G.

Then, the value of the angular velocity ω _{2 at which} the delay is almost eliminated is estimated from FIG. 3 as follows.

[0029]

[Equation 5]

Similarly, the influence of the particle density ρ _P and the width of the classification chamber, that is, the distance S between the rotor and the guide vane was investigated, and examples thereof are shown in FIGS. 4 and 5. Based on these, the limit value at which the delay of the particles with respect to the air flow hardly occurs is calculated as (R ₂ ω ₂ ) / (R ₁ ω ₁ ), and is as shown in FIG.

From this figure, the range of R ₂ ω _{2 in} which there is no delay with respect to the air flow of particles is expressed by the width S of the classification chamber and the density ρ _P of particles as follows.

[0032]

[Equation 6]

On the other hand, when the inflow angle of the air flow in the tangential direction at the radius R ₂ , that is, the mounting angle of the guide vane in the tangential direction is θ _G , the inward air flow velocity in the classification chamber, that is,
_Let U _r be the velocity component in the radial direction of the rotor blade circumscribing circle whose direction toward the center is negative,

Tan θ _G = -U _r / U θ = -U _r / R ₂ ω ₂

Therefore, if this is modified, the following equation is obtained.

[Equation 7]

Here, U _r is the air velocity low as described above.
In Taburedo circumcircle radial velocity component, the value of the component U _r is too small, the dispersion of the powder in the classifying space S deteriorates, resulting classification efficiency is greatly reduced. If the value of the component U _r is too large, the drag force exerted by air on the particles becomes large, and in order to carry out the predetermined classification, it is necessary to increase the rotation speed of the rotor and excessive energy is required. At the same time, turbulence of the air flow in the classification chamber is likely to occur.

Therefore, generally, the value of the component U _r is 2 to 6
It is selected according to the type of powder and the separated particle size within the range of about m / s. The particle density ρ _P is 10 for most powders.
It is between 00 and 8000 kg / m ³ and is set according to the type of powder to be classified. The distance between the guide vanes G and the rotor blades B, that is, the width S of the classification chamber is usually 10 to 150.
The value is set from mm, and a smaller value is set as the fine powder is classified.

The present inventor recognizes from the above research that the attachment angle θ _G of the guide vanes must be adjusted in order to achieve the object of the present invention, and the present invention is configured as follows. .

The rotor is provided with a plurality of rotor blades,
A vortex type air classifier having guide vanes provided outside the outer circumference of the rotor blade through a classifying chamber; the mounting angle of the guide vanes is the tangential velocity component of the classifier of the air speed at the outer circumference of the rotor. Vortex air classifier characterized in that the particle velocity classifier is adjusted to be equal to the tangential velocity component.

[0040]

[Function] Air is introduced into the classification chamber to form a vortex while the inflow angle is regulated by the guide vanes. When the grain fractions is turned converting said class room, a delay of the particle velocity is less for the air flow, the classifier <br/> tangential velocity component of the air velocity at the rotor outer peripheral portion and the classifier tangential particle velocity The direction velocity component becomes equal. Therefore, the classification efficiency is improved and the energy for driving the classifier can be saved.

[0041]

Embodiments of the present invention will be described with reference to FIGS. A conical hopper 2 is provided in the lower part of the cylindrical casing 1, and the lower part of the hopper 2 is communicated with the coarse powder discharge port 3.

A rotor 5 fixed to a rotating shaft 4 is arranged in the center of the casing 1. The rotor 5 has a diameter D and a height H.

A plurality of rotor blades 6 are attached to the outer peripheral portion of the rotor 5, and the attachment pitch p thereof is determined by the following equation (7) or equation (8) obtained by experiment. (See Japanese Patent Application No. 5-74670). p ≦ 1.04 × Dp (th) ^0.365 (7)

[0044]

[Equation 8]

Next, the particle density ρp =
Pitch p when classifying 2700 kg / m ³ limestone
Will be described. Rotor diameter D = 2.1m, rotor height H = 0.3
Air density ρ in air at m, temperature of 20 ° C, and 1 atm
_f = _1.20kg / m ^3, an air viscosity coefficient ^{μ = 1.81 × 10- 5 (Pa.s} ).

Under the above conditions, the theoretical separated particle size D _p (
Table 1 shows the mounting pitch p of the rotor blades required to achieve the above ( _th ). The value of this pitch P is the minimum separation particle size applied to the classifier from the above formula (7), for example, 3 μ.
It may be determined as a classifier applied to classification up to m.

[0047]

[Table 1]

Incidentally, Q indicates the classification air flow (m ³ / s), and Vt indicates the peripheral speed (m / s) at the tip of the rotor blade.

A classification chamber 7 is provided on the outer periphery of the rotor blade 6.
A guide vane 8 whose angle can be adjusted is provided via the. The mounting angle θ _G of the guide vane 8, that is, the inclination angle of the guide vane G with respect to the tangent line L will be described later.

Next, the determination of the width S of the classifying chamber 7 is extremely important. The steeper the velocity gradient of the tangential flow velocity distribution is, the stronger the shearing force due to the difference in velocity of the air flow acts on the agglomerates in this portion. Classification is promoted. However, if the width S is too narrow, the vortex will be disturbed. As a result, the particles do not reach a predetermined speed and normal classification cannot be performed.

On the contrary, if the width S of the classification chamber is too wide, a uniform vortex cannot be formed, and the agglomerated particles will leave the classification chamber 7 without being dispersed in the primary particles. The effect gets worse.

Then, various experiments were conducted to determine an appropriate value of the width S of the classifying chamber 7, and the following formula was obtained. However, the coefficient K is 5 to 20 (m ^1/2 ). S = K√p

It is also important to determine the circumferential thickness T of the rotor blade 6. The ratio T / p between the thickness T and the pitch p is 0.
35 or less, and the opening area M of the rotor 5 is formed to be 65% or more.

According to experiments, when the thickness T of the rotor blade 6 in the circumferential direction exceeds the above range, the width S of the classification chamber 7 and the mounting pitch P of the rotor blade 6 are within the above range. In some cases, the vortex flow near the rotor blade 6 is disturbed, and the coarse powder portion having a size equal to or larger than the separated particle diameter is often jumped in, so that sharp fine powder classification cannot be performed.

On the contrary, when the opening area is less than the above range,
Although the thickness T becomes abnormally thin and there are problems in strength and construction, it is desirable that the thickness T be as thin as possible without causing the above problems.

The ratio T / p between the thickness T and the pitch p is 0.
It is desirable that the thickness T is 35 or less, but from the viewpoint of the current technical strength, it is known that when the fine fine powder classification, for example, 3 μm cutting is performed, the thickness T is T / P of 0.1. Next, the inclination angle θ _G of the guide vane 8 with respect to the tangent line L is obtained from the above equation (5). In this case, when the separated particle size is 10 μm or less, the mounting angle of the guide vane 8 can be appropriately determined. In particular, when the separation particle size is 10 μm or more, as shown in FIG. 3, unless the mounting angle of the guide vanes 8 is appropriate, a delay occurs with respect to the air velocity, and wear of the rotor blades and excessive energy consumption occur. Therefore, the tilt angle θ _G is obtained from the above equation (5), and the tilt angle θ _G is set to 15 degrees, for example.

The opening area M of the rotor is preferably 65% or more because the pressure loss in the classifier is reduced if the opening area M is as large as possible in terms of structure, mechanical strength and fine powder classification.

Next, the operation of the embodiment will be described. The classified air is sent from the classified air supply passage 11 to the classification chamber 7 through the guide vane 8 to form a vortex in the classification chamber 7 and the rotating shaft 4 is rotated to rotate the rotor blade 6 to form a forced vortex. .

Then, the vortex is swirled in the classification chamber 7, passes between the rotor blades 6 and is discharged from the product discharge port 12 to the outside of the machine. In this state, when the material to be classified Y, for example, calcium carbonate, is introduced from the raw material inlet 13,
The material to be classified Y collides with the dispersion plate 14 and falls into the classification chamber 7 while scattering in the outer peripheral direction.

During this time, the particles of the material to be classified swirl in the classification chamber according to the balance between the centrifugal force and the drag force while being accelerated by the vortex flow. At this time, the particles are classified by the shearing force of the eddy current and the collision friction between the particles, and particles having a size smaller than the separated particle size determined by the state of swirl reach the outer periphery of the rotor blade.

At this time, since the particle velocity with respect to the air flow in the outer peripheral portion of the rotor has almost no delay, the tangential velocity component of the air velocity of the classifier is equal to the tangential velocity component of the classifier of the particle velocity . . In this classification chamber, the particles are classified by the counteracting action of the centrifugal force and the drag force of air. The classified fine powder Y ₂ , for example, a particle size of 5 μm or less, passes through the rising air stream and passes through the rotor 5, and the product discharge port 1
While flowing into No. 2, it enters an air filter (not shown) and is collected.

The coarse powder Y ₁ drops in the hopper 2 while swirling in the casing _{1, and} is discharged from the coarse powder discharge port 3.

The embodiment of the present invention is not limited to the above, and for example, the product outlet of the vortex type air classifier is provided below the classifier instead of above the classifier,
Also, it can be applied to various rotor classifiers, such as providing a raw material inlet at the center of the upper part of the classifier, providing a product discharge port downward, and introducing the raw material inlet together with classification air on the side or below the classifier. It is a thing.

[0064]

Since the present invention is constructed as described above, there is almost no delay in the particle velocity with respect to the air flow. Therefore, the classifier tangential velocity component and a classifier tangential component are equal becomes ideal classification state of the particle velocity of the air velocity at the rotor outer peripheral portion. Therefore, the wear of the rotor is reduced as compared with the conventional example, the cost required for maintenance and the number of operation stoppages are reduced, and the deterioration of the classification accuracy due to the wear of the rotor can be alleviated. In addition, since it is not necessary to rotate the rotor at an extra speed, and the pressure loss of the classifier is also low, the pressure loss of the classifier is small, and as a result, the motor load of the rotor shaft and the load of the fan motor that sucks air are reduced. Both can be reduced, energy can be saved, and productivity can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an airflow model in a cross section of a classifying chamber of a classifier.

FIG. 2 is a diagram showing a classification model based on the airflow model of FIG.

FIG. 3 is a diagram showing an influence of an inlet air velocity.

FIG. 4 is a diagram showing the influence of particle density.

FIG. 5 is a diagram showing the influence of the width S of the classification chamber.

FIG. 6 is a diagram showing a relationship between particles and an air flow.

FIG. 7 is a partial sectional front view showing an embodiment of the present invention.

8 is a sectional view taken along line VIII-VIII of FIG.

[Explanation of symbols]

5 rotor 6 rotor blade 7 classification chamber 8 guide vane P rotor blade mounting pitch D _p ( _th ) theoretical separation particle size μ air viscosity coefficient ρ _p particle density H rotor height Q classification Air volume V _t Peripheral speed of rotor blade tip S Width of classification chamber θ _G Guide vane mounting angle

Claims (7)

(57) [Claims] 1. A vortex type air classifier in which a plurality of rotor blades are provided on a rotor, and guide vanes are provided on the outer periphery of the rotor blades through a classifying chamber; A vortex air classifier, wherein the tangential velocity component of the air velocity of the classifier and the tangential velocity component of the particle velocity of the classifier are adjusted to be equal at the outer peripheral portion. 2. A vortex type air classifier in which a plurality of rotor blades are provided on a rotor, and guide vanes are provided on the outer periphery of the rotor blades through a classifying chamber; and the mounting angle θ _{G of the} guide vanes is Determined by the following equation in relation to the air velocity radial velocity component U _{r of} the rotor blade circumscribing circle, the radius R ₁ of the rotor blade circumscribing circle, the angular velocity ω _{1 of the} rotor blade, the particle density ρ _p , and the width S of the classification chamber. A vortex type air classifier characterized by being used. [Equation 1] 3. A rotor blade circumscribing circle radial direction velocity component U _{r of the} air velocity is 2 to 8 m / s, and a particle density ρ _p is 100.
0-8000 kg / m ³ , width S of the classification chamber is 10-150
The vortex type air classifier according to claim 2, wherein 4. A swirl type air classifier in which a rotor is provided with a plurality of rotor blades, and guide vanes are provided outside a circumference of the rotor blades through a classifying chamber; and a mounting angle θ _{G of the} guide vanes is Determined by the following equation in relation to the air velocity radial velocity component U _{r of} the rotor blade circumscribing circle, the radius R ₁ of the rotor blade circumscribing circle, the angular velocity ω _{1 of the} rotor blade, the particle density ρ _p , and the width S of the classification chamber. The pitch p of the rotor blades is equal to the separation particle size Dp (t
A vortex type air classifier characterized by being determined by the following equation in relation to h). [Equation 2] P ≦ 1.04 × Dp (th) ^0.365 5. A vortex air classifier in which a rotor is provided with a plurality of rotor blades, and guide vanes are provided outside the outer circumference of the rotor blades through a classification chamber; and the mounting angle θ _{G of the} guide vanes is Determined by the following equation in relation to the air velocity radial velocity component U _{r of} the rotor blade circumscribing circle, the radius R ₁ of the rotor blade circumscribing circle, the angular velocity ω _{1 of the} rotor blade, the particle density ρ _p , and the width S of the classification chamber. Swirl-type air characterized in that the pitch P of the rotor blades is determined by the following equation from the relationship among the viscosity coefficient μ of air, the height H of the rotor, the air volume Q for classification, and the peripheral speed Vt of the tip of the rotor blades. Classifier. [Equation 3] [Equation 4] 6. The width S of the classifying chamber is obtained by the following equation in relation to the pitch p and the coefficient K:
Or the vortex type air classifier according to 5. S = K√p 7. The vortex type air classifier according to claim 6, wherein K is 5 to 20.