JP2824816B2 - Drying method of wet powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a wet powder, for example, a slurry-like organic or inorganic powder mixed and dispersed in a dispersion medium, as a dry powder. The present invention also relates to a method of once attaching a wet powder to the drying medium particles and drying.

[0002]

2. Description of the Related Art Conventionally, as a method for drying a wet powder using dry medium particles, a wet powder is supplied into a drying container having a cylindrical bottom portion in which the dry medium particles are stored, and the dry medium is stored therein. A method in which the whole particles are fluidized by blowing hot air from the entire bottom surface of the cylindrical drying container, the stored drying medium particles are stirred by a stirring blade, and the dried powder is taken out together with the exhaust stream from the top of the drying container. It is known (JP-B-54-43747).

In this method, the supplied wet powder is uniformly adhered to the surface of the drying medium particles by fluidizing the drying medium particles by blowing hot air and stirring by a stirring blade, and is dried on the surfaces of the drying medium particles. The powder is separated and pulverized by collision between dry medium particles flowing by blowing hot air, and the powder is taken out together with an exhaust gas flow.

[0004] In addition, when the stirring is performed by the stirring blade together with the fluidization of the drying medium particles as in the above technique, the inner wall of the drying vessel and the drying medium particles are greatly worn, and a great amount of energy is required for the stirring. As an improved method,
A method is also known in which drying is performed only by fluidizing the entirety of the drying medium particles by blowing hot air from the entire cylindrical bottom of the drying container without performing stirring by a stirring blade (Japanese Utility Model Laid-Open No. 2-61401).

In the case of this method, since the agglomeration of the dry medium particles is likely to occur when the wet powder is supplied, the wet powder of the dry medium particles is attached and supplied in advance. That is, only fluidization of the dry medium particles by blowing hot air lacks the mixing force for uniformly dispersing and adhering the wet powder, so such a means is used. Further, in this method, the powder dried on the surface of the drying medium particles is separated and pulverized only by collision between the drying medium particles flowing by blowing hot air, and is taken out.

[0006]

However, in any of the above-mentioned conventional methods, there is a strong tendency that the particle size of the powder after drying is larger than the particle size of the powder before drying.
There is a problem that it is also difficult to adjust the particle size of the obtained powder. In particular, when the particle diameter of the dried powder increases, the use of the dried powder is restricted, and the value of the powder decreases. In addition, in either method, since the entire drying medium particles are fluidized by blowing hot air, it is necessary to operate using a large-capacity blower, which consumes a large amount of energy and increases the drying medium depending on the supply amount of the wet powder. Since the flow state of the particles changes, there is a problem that the operation control at the time of implementation is difficult.

Further, according to the method disclosed in Japanese Patent Publication No. 54-43747, as described in Japanese Utility Model Application Laid-Open No. 2-61401, the inner wall of the drying vessel and the particles of the drying medium are greatly worn, and a great deal of stirring is required. There is a problem that requires energy. Further, in the method disclosed in Japanese Utility Model Application Laid-Open No. 2-61401, a step of mixing the dry medium particles and the wet powder prior to the supply to the drying container is required to uniformly attach the wet powder to the dry medium particles. Therefore, there is a problem that the number of steps increases.

The present invention has been made in view of the above-mentioned conventional problems, and the particle size of the obtained dry powder (hereinafter referred to as “secondary particle size”) is to be as small as possible before drying. (Referred to as “primary particle size”), the adjustment of the secondary particle size is facilitated, the energy consumption is reduced, the equipment is prevented from being worn, and the number of steps is prevented from increasing.

[0009]

SUMMARY OF THE INVENTION The present invention reconsiders the role of stirring by a stirring blade and the role of fluidization of drying medium particles by blowing hot air, and makes the entire drying medium particles fluidized by blowing hot air. This is based on a completely different viewpoint from the conventional drying treatment using drying medium particles, in which the drying treatment is performed without causing the drying treatment.

That is, the means adopted in the present invention will be described with reference to FIG. 1. According to the present invention, a wet powder is supplied to a drying container 2 having an inverted conical bottom in which drying medium particles 1 are accommodated.
The drying medium particles 1 are stirred by the stirring blades 3 substantially buried in the stored drying medium particles 1, and the drying medium stored at a speed equal to or higher than the fluidization start speed of the drying medium particles 1 from the bottom center of the drying container 2. Hot air is blown at a blowing speed that does not fluidize at least the upper part of the particles 1,
The dry powder is taken out together with the exhaust gas flow from the upper part of the apparatus.

The present invention employs a drying vessel 2 having an inverted conical bottom. That is, the lower part of the contained drying medium particles 1 can be fluidized, but the upper part can be heated by a hot air within a range not to be fluidized. Is different from the prior art in that the blowing is performed.

Among the above differences, the latter difference is a very important difference.

That is, the conventional technique is intended to peel and pulverize the dried powder adhered to the drying medium particles 1 by fluidizing the drying medium particles 1 by blowing hot air. In this case, the entire drying medium particles 1 are fluidized by blowing hot air to generate strong collisions between the drying medium particles 1. On the other hand, in the present invention, the entirety of the drying medium particles 1 is not fluidized by blowing hot air.

The reason why the blowing of the hot air in such a range ensures that the powder adhered and dried on the surface of the drying medium particles 1 is sufficiently separated and pulverized is that the stirring by the stirring blade 3 is also used in the present invention. by. That is, in the present invention, when the stirring by the stirring blade 3 is also used, a sufficient effect of peeling and pulverizing the dry powder can be obtained without blowing strong hot air for fluidizing the entire drying medium particles 1 as in the related art. It has a great feature in that it is found that it can be obtained.

When hot air is blown in as in the present invention, the entire dry medium particles 1 are fluidized. However, the lower part is in a state of being easily fluidized, and the screen 6 is not blocked, and the stirring by the stirring blade 3 is added thereto. Collision is obtained.

On the other hand, in the present invention, since the blowing speed of the hot air is lower than that of the prior art, the conveying force of the dried, peeled and pulverized powder is also weak. Therefore, only the powder having a relatively small particle diameter is selected. The powder having a relatively large particle diameter is rubbed by the drying medium particles 1 until the particle diameter becomes small without being immediately removed, so that the secondary particle diameter becomes close to the primary particle diameter. Further, since the blowing of the hot air does not strongly fluidize the entirety of the drying medium particles 1, the fluidization of the entire drying medium particles 1 does not hinder the stirring by the stirring blade 3.

In the present invention, the use of the drying container 2 having an inverted conical bottom portion facilitates the blowing of hot air in the above-mentioned range and facilitates the control of the secondary particle diameter. belongs to.

That is, when the hot air is blown from the center of the bottom of the inverted cone, the hot air is blown into the portion where the drying medium particles 1 are accumulated most deeply. Therefore, fluidization hardly occurs in the upper portion of the dry medium particles 1 even if the fluidization start speed is higher than the lower portion of the contained dry medium particles 1. In addition, the contained dry medium particles 1
Hot air will be supplied intensively to the center of the
Compared to the case where hot air is supplied from the entire surface of the conventional cylindrical bottom portion, the entirety of the stored drying medium particles 1 is less likely to float with hot air. Therefore, the speed of the hot air blown is
Even if it is faster at the lower part, the upper part of the contained drying medium particles 1 is hardly fluidized, and the speed adjustment range of the hot air is widened, so that the secondary particle diameter can be easily controlled by the adjustment.

The fluidization start speed of the drying medium particles 1 means a value obtained by the following equation (1).

[0020]

(Equation 1) Each symbol in the above equation 1 means the following value.

D: diameter of the drying medium particles ρ ₁ : density of the supply hot air ρ ₂ : density of the drying medium particles μ: viscosity of the supply hot air g: gravitational acceleration C in the expression 1 is expressed by the following expression 2 and expression 3 It is determined by Re. Here, u is the speed of the hot air.

[0022]

(Equation 2)

[0023]

(Equation 3) The phrase “at least the upper part of the contained dry medium particles 1 is not fluidized” means that at least the upper surface layer of the body layer of the dry medium particles 1 does not show the expansion phenomenon of the layer peculiar to the fluidized layer. Say.

The present invention will be further described with reference to FIG.

The wet powder to be dried in the present invention includes a slurry of an organic or inorganic powder. The dispersion medium of the slurry may be either water or an organic dispersion medium.

The wet powder is stored in a raw material tank 4 and supplied to a drying vessel 2 by a pump 5.
Although the wet powder is supplied to the drying container 2 by the pump 5 in the illustrated example, the supply may be performed by a screw conveyor (not shown) or the like without using the pump 5. The selection may be made according to the properties of the wet powder to be dried.

The supply of the wet powder to the drying container 2 may be a continuous supply at a predetermined flow rate in accordance with the drying capacity of the drying container 2 or may be performed after the predetermined amount of the wet powder previously supplied is completely dried. Batch supply for supplying a predetermined amount of wet powder again may be employed.

The drying container 2 has an inverted conical bottom, and is heated by a heating device 7 such as a steam heater or an electric heater through a permeable screen 6 provided at the center of the bottom. Hot air is blown by the blower 8. In the drying container 2, the drying medium particles 1 are accommodated on a screen 6, and a stirring blade 3 which is almost buried in the drying medium particles and rotated by a motor 9 is provided.

As described above, the wet powder is supplied to the dry container 2
In order to easily prevent the agglomeration of the dry medium particles 1 caused by the supply and to make it easier for the wet powder to uniformly adhere to the entire dry medium particles 1, As described above, it is preferable that the height is within the range of the deposition height of the drying medium particles 1, and particularly near the center of the deposition height of the drying medium particles 1.

The diameter of the drying medium particles 1 is preferably as close to a spherical shape as possible.
It is preferably 0 mm. If the diameter is too small, the entire drying medium particle 1 is likely to be fluidized by blowing hot air,
Conversely, if it is too large, the stirring by the stirring blade 3 becomes difficult.

The material of the drying medium particles 1 is selected depending on the properties of the wet powder to be dried, the temperature of the hot air to be blown, and the like. For example, ceramics such as alumina, silica and mullite, and polypropylene, polyethylene and polyamide A synthetic resin or the like can be used.

The amount of the drying medium particles 1 to be charged into the drying container 2 depends on the size of the drying container 2 and the like, but may be an amount just enough to fill the inverted conical portion at the bottom of the drying container 2. preferable. If the amount of the drying medium particles 1 is too small, the drying efficiency is poor and the entire drying medium particles 1 are easily fluidized. Conversely, if the amount of the drying medium particles 1 is too large, stirring by the stirring blade 3 becomes difficult.

The hot air is blown into the drying vessel 2 at a blowing speed that is higher than the fluidization start speed of the drying medium particles 1 and the upper portion of the contained drying medium particles 1 is not fluidized as described above. There is a need. If the blowing speed is too low, the drying efficiency deteriorates. On the other hand, if the blowing speed is too high, the entire drying medium particles 1 are fluidized, and powder having a large particle diameter is easily discharged.

If the diameter of the screen 6 serving as the hot air blowing port in the drying vessel 2 is too small, it is difficult to blow a sufficient amount of hot air. Conversely, if it is too large, the entire drying medium particles 1 tend to fluidize. It is preferable to determine these so as to harmonize them. Also, from the harmony point of the input amount of the drying medium particles 1 and the diameter of the screen 6 and the like, the vertex angle of the inverted conical portion at the bottom of the drying container 2 is 20 to
Preferably it is 100 degrees.

In the illustrated drying container 2, two stirring blades 3 are provided for each stage in two stages. However, if the drying container 2 is located at a position substantially buried in the contained drying medium particles 1, the stirring blades 3 are provided.
Are not limited to these. Also,
The stirring blade 3 does not need to be completely buried in the drying medium particles 1, and may be partially exposed as long as the main part is buried in the drying medium particles 1.

The stirring blade 3 is rotated by a motor 9 to stir the drying medium particles 1.
The rotation is preferably 0 to 100 rotations. If the number of rotations is too large, the drying medium particles 1 and the inner wall of the drying container 2 are easily damaged, and the energy required for the rotation increases. Conversely, if the number of rotations is too low, the agglomeration of the drying medium particles 1 tends to occur during the supply of the wet powder, and the drying efficiency tends to decrease. The rotation of the stirring blade 3 is normally performed in a fixed direction, but can be reversed at regular intervals.

The screen 6 may be a mesh having a mesh size enough to hold the drying medium particles 1, and the mesh size is selected according to the diameter of the drying medium particles 1 to be used. It is. The falling off of the dry powder from the screen 6 is prevented by the supply of hot air.

The hot air supplied to the drying container 2 dries the wet powder adhering to the surface of the drying medium particles 1, and is dried together with the powder separated and pulverized from the drying medium particles 1 from the top of the drying container 2. Taken out.

The exhaust stream taken out from the upper part of the drying vessel 2 is accompanied by dry powder, and the accompanying powder is
For example, it is collected by a collection device 10 such as a bag filter and deposited in a storage tank 11.

[0040]

【Example】

Example 1 The upper part is a cylindrical shape having an inner diameter of 1 m and a height of 1 m, and the lower part has an apex angle of 60.
A stainless steel mesh screen 6 having a diameter of 40 cm was attached to the bottom of a stainless steel container having an inverted conical shape, to obtain a drying container 2. In addition, as shown in FIG. 1, two agitating blades 3 made of stainless steel having both ends bent upward are provided in the inverted conical portion at the bottom of the drying container 2.

As the drying medium particles 1, spherical alumina having a diameter of 6 mm (density: 3900 kg / m ³ ) was used.
150 kg of this was charged into the drying container 2. By the introduction of the drying medium particles 1, the stirring blades 3 are buried in the drying medium particles 1 except for both ends bent above the upper blade.

After the drying medium particles 1 are charged, hot air heated to 130 ° C. is passed through the screen 6 to 3000 m ³ / hr.
I blew it.

The fluidization start speed calculated from the above formula 1 is 3.3 m / sec. In this embodiment, the blowing speed of the hot air is determined based on the flow rate of the hot air and the sectional area of the drying container 2 at the screen 6. .65 m / sec, which exceeded the fluidization start speed, but no fluidization was observed above the dry medium particles 1.

Further, the wet powder was continuously supplied to the drying vessel 2 at a flow rate of 100 kg / hr while rotating the stirring blade 3 at 30 rpm. The rotation of the stirring blade 3 has an output of 1.5
It went through the reduction gear with the motor of KW.

The wet powder is a cobalt hydroxide slurry having a primary particle diameter of about 1 μm, composed of 10 parts by weight of solid content and 90 parts by weight of water. Supplied.

Hot air is taken out from the upper surface of the drying vessel 2 and
When the accompanying powder was collected using a bag filter as the collecting device 10, a powder of cobalt hydroxide having a water content of 0.3% by weight was obtained at a rate of 10 kg / hr. When the particle size of the obtained powder was measured with a Microtrac particle size analyzer (manufactured by Nikkiso Co., Ltd.), the average particle size was about 1.6 μm.
Met.

Example 2 The same equipment as in Example 1 was used, except that the object to be dried was a cobalt hydroxide slurry having a primary particle diameter of about 1 μm, comprising 20 parts by weight of solids and 80 parts by weight of water. Is Example 1
A drying treatment was performed in the same manner as described above.

As a result, a powder of cobalt hydroxide having a water content of 0.4% by weight was obtained at a rate of 20 kg / hr, and the average particle size was about 2.5 μm.

[0049]

The present invention is as described above, and has the following effects.

(1) A powder having a secondary particle diameter close to the primary particle diameter and having high utility value can be obtained, and the secondary particle diameter can be easily controlled.

(2) Since it is not necessary to blow strong hot air for fluidizing the entirety of the drying medium particles 1, the energy required for blowing hot air is small.

(3) The drying container 2 and the drying medium particles 1 are not damaged and their life is long.

(4) Energy required for stirring by the stirring blade 3 is small.

(5) Control during continuous operation of supplying a wet powder continuously is easy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drying medium particle 2 Drying container 3 Stirring blade 4 Raw material tank 5 Pump 6 Screen 7 Heating device 8 Blower 9 Motor 10 Collection device 11 Storage tank

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F26B 3/088

Claims (1)

(57) [Claims] The wet powder is supplied to a drying container having an inverted conical bottom in which the drying medium particles are stored, and the drying medium particles are stirred by a stirring blade substantially buried in the stored drying medium particles. From the bottom center of the drying container, hot air is blown at a blowing speed that is higher than the fluidization start speed of the drying medium particles and at least the upper portion of the contained drying medium particles is not blown. A method for drying a wet powder, comprising removing a body.