JPH01123601A - Spray drying method - Google Patents

Abstract

PURPOSE:To increase the yield of dried powder without changing the exhaustion performance by sucking the atmospheric gas upward at a specified velocity from the end of an exhaust duct, and spray-drying ceramic particles when the particles, etc., are granulated. CONSTITUTION:The air heated to high temp. by a heater 5 is spirally blown into a drying chamber 1 through a hot air blowing nozzle 3. Meanwhile, the slurry in a slurry tank 6 is sent under pressure by a pump 7, sprayed into the drying chamber 1 from the upper rotary disk 8, granulated by the surface tension, dried rapidly by high-temp. hot air, and dropped downward. In this case, the atmospheric gas is sucked upward at the velocity lower than the free falling velocity of the dried powder having mean particle diameter x' from the exhaust duct 9 having a hood 10 at the bottom to dry the powder, and hence the suction of the powder into the exhaust duct 9 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spray drying method used for granulating ceramic particles.

(Prior Art) Spray drying equipment has been used for a long time to granulate ceramic particles and the like. This device sprays the raw material slurry with hot air into the drying chamber, instantly granulating it and dropping it into the collection pot at the bottom of the chamber. In order to maintain a constant temperature, high-temperature hot air is constantly blown in, so it is necessary to exhaust the air. Conventionally, an exhaust duct was inserted into the center of the drying chamber to exhaust the air. In reality, the amount of powdered powder was nearly 20% of the total. Particularly in the case of fine ceramics, this amount is discarded as having no commercial value, so there has been a strong demand for increasing the yield into the collection pot.

(Problems to be Solved by the Invention) The present invention solves the conventional problems as described above, and provides a spray drying method that can increase the yield of dry powder in a drying chamber without changing the exhaust performance. It was completed with the purpose of

(Means for Solving the Problems) The present invention provides a spray drying method for obtaining dry powder by spraying a slurry inside a drying chamber into which hot air is blown.
From the end of the air duct inserted into the drying chamber,
The method is characterized in that spray drying is performed while atmospheric gas is sucked upward at a speed lower than the final free fall velocity V of a dry powder having a particle size of x (x is the average particle size).

The present invention will be explained in more detail below with reference to FIG. 1, in which (1) is a drying chamber, (2) is a collection pot provided at the bottom thereof, and (3) is a hot air blowing duct. In addition, (4) is an intake blower, and (5) is a heater, and the air heated to a high temperature by this heater (5) is blown into the drying chamber mouth through the hot air blowing duct (3) in a spiral shape. It will be done. On the other hand, the slurry in the slurry tank (6) is pumped by the pump (7) and sprayed from the upper rotating circle [(81) into the drying chamber +11, where it becomes spherical due to surface tension and is rapidly dried by high-temperature hot air. It falls downward.

(9) is an exhaust duct inserted into the drying chamber (11) for exhausting the atmospheric gas to the outside, and a hood Ql with an open bottom is attached to the end of the duct to remove the atmosphere inside the chamber. The structure is such that the gas rises inside the hood Ql as shown by the arrow and then flows into the exhaust duct (9).The inner diameter of this hood α1 is determined by the speed V of the airflow rising inside it, which will be explained next. Powder free fall velocity V
is set to be smaller than. That is, the particle size ds,
Specific gravity T! ! , the final velocity V when a particle with a drag coefficient Cs falls freely in air with a specific gravity ra is v= (4gds (rs-ra) /3Csra)
Represented by “”. Since the particle size of the dry powder is widely distributed as shown in Figure 2, the final free fall velocity V varies greatly depending on the particle size, but in the present invention, the final free fall velocity V of the dry powder with a particle size of T is The velocity of the rising air (■) is set to be smaller than V. However, T is the average particle size of the dry powder. In this way, the free fall terminal velocity V
If the atmospheric gas is sucked upward at a speed V lower than that, the particles will still try to fall during suction, and the amount of dry powder sucked into the exhaust duct (9) will be significantly reduced. Note that (11) is a dust collector for collecting dry powder sucked into the exhaust duct (9), and (12) is a dust collection pot.

In the above explanation, the hood 01 was provided at the end of the exhaust duct (9) to reduce the suction speed V in this part. The suction speed V may be adjusted by forming .

(Example) Spray drying was performed by spraying a slurry of A 1 gos while blowing hot air at 200° C. into a drying chamber with an inner diameter of 4 m. The particle size distribution of the dry powder in this case is as shown in Figures 2 and 3.In the conventional method, which sucked atmospheric gas at a rate of 0.5 m''/sec from an exhaust duct with a diameter of 300 m, the suction speed was was approximately 7°1 m/s, and in this case, as shown in Figure 3, the proportion of dry powder collected in the collection pot of the drying chamber was approximately 80%, and the remainder was collected in the dust collector (11). On the other hand, a hood with an inner diameter of 2.4 mm was placed at the end of the exhaust duct so that the suction speed V was lower than the free fall final velocity of 0.13 + 1/sec for particles with an average particle diameter of ds 74 μ-. Set up V
-0,11■1 second, the ratio of dry powder collected in the collection pot of the drying chamber is more than 90%, as shown in Figure 2, and the dry powder sucked into the exhaust duct is 1/2 that of the conventional one. I was able to make it 2.

(Effects of the Invention) As is clear from the above description, the present invention is capable of improving the recovery ratio of dry powder in the drying chamber without affecting the exhaust performance or drying performance in the drying chamber. The effect is particularly great when the particles recovered in the dust collector cannot be used as commercial products, such as fine ceramic particles.

Therefore, the present invention greatly contributes to the development of industry as a spray drying method that eliminates the problems of the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view explaining the present invention in detail, and FIG.
The figure is a graph showing the particle size distribution of the dry powder obtained by the method of the example, and FIG. 3 is a graph showing the particle size distribution of the dry powder obtained by the conventional method (1): Drying chamber.

Claims (1)

[Claims] In a spray drying method in which a dry powder is obtained by spraying a slurry inside a drying chamber into which hot air is blown, particle size is
A spray drying method characterized by carrying out spray drying while sucking atmospheric gas upward at a speed lower than the final free fall velocity v of a dry powder of x@ (@x@ is the average particle diameter).