JPH054001A - Method for supplying slurry to spray dryer - Google Patents

Abstract

PURPOSE:To uniformize the grain sizes the granulated powder of a spray dryer. CONSTITUTION:A pressure tank 3 is placed on the upper side of a drying column 11 of the spray dryer and a slurry is introduced therein by a pump 2. While the liquid level height of the slurry in the pressure tank 3 is kept constant, a pressurized gas is introduced into the pressure tank 3 to discharge the slurry by gravity downflow force and the gaseous pressure. Then, the slurry is supplied to the spray dryer without pulsating. The slurry can be supplied at a fixed rate. The closing of a nozzle, etc., is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying a slurry to a spray dryer, and more particularly to a method for supplying a slurry to a spray dryer by which a fixed amount of slurry can be supplied to the spray dryer.

[0002]

2. Description of the Related Art In many industrial fields such as fine ceramics, powder metallurgy, foods, medicines, etc., products made from powders are manufactured. Generally, the powder used to obtain a molded product (granular, pellet-shaped, or other structure) is a fine powder with a particle size of submicron to several microns, which is granulated into spheres of several tens of microns. Is widely used. The reason for using the granulated powder is that the fluidity and the filling property are improved, a homogeneous molded product is obtained, and it contributes to the improvement of physical properties and productivity. The particle size of the powder and the specific surface area of the powder have a correlation with the energy state of the surface of the powder, which affects the fluidity, cohesiveness, adsorptivity, repulsion, packing density, and the like. Therefore, it is desirable that even the granulated powder is a spherical powder having a single particle size and a sharp particle size distribution curve with no variation in particle size.

Now, the spray drying method (spray dryer) which is widely used in the granulation method will be described.
The spray dryer is a method in which a slurry in which raw material powders are dispersed in a solvent is supplied near the center of a rotating disk provided near the ceiling inside a drying container in a heating atmosphere. The supplied slurry is atomized due to the centrifugal force of the disk rotating at high speed, swirls in the drying container, receives the heat in the atmosphere, drops while being dried, and becomes a spherical powder. The mist of the slurry consists of minute droplets, which have the property of taking a minimum surface area and are necessarily spherical.

In order to obtain an ideal granulated powder close to a true sphere having a sharp particle size distribution as described above, the following conditions are required.

The slurry concentration is stable.
The dispersibility of the slurry is good and there is no aggregation. The surface state (specific surface area, etc.) of the primary particles is constant.
The viscosity of the slurry is constant. The operating conditions such as the device temperature, pressure and gas flow rate are stable. Slurry supply is stable without pulsation. If there are multiple nozzles, the amount of outflow from these nozzles must be the same. Etc.

Next, an outline of a conventional spray dryer will be described with reference to FIG. The slurry in the tank 1 for dispersing and mixing the slurry is sent to the buffer tank 3 by the slurry transfer pump 2. Then, the slurry is supplied to the nozzle 9 directly above the disk atomizer 7 through the forked pipe 5 and the slurry supply pipe 6 by the roller type service pump 4 for directly supplying the slurry into the drying tower. 8 is a drying tower. The granulated powder is taken out from the bottom of the drying tower 8. In addition, 10 is a return pipe.

[0007]

As a supply pump, a diaphragm pump, a roller pump, or the like is generally used because of a low head, a high-concentration slurry, a small flow rate, and the like. However, pulsation was unavoidable with these pumps, and stable granulated powder could not be obtained.

In the bifurcated pipe branching method, it is difficult to evenly divide the flow rate, and variations occur in the outflow amount from a plurality of nozzles.

In some cases, the injector effect sometimes occurs in the portion of the bifurcated branch pipe, and the flow direction of one of the supply pipes is reversed, which causes a blockage of the pipe.

In the conduit from the branch point to the tip of the nozzle, the amount of outflow from a plurality of nozzles varies due to a slight difference in loss head.

When the fluctuation of the slurry flow rate is large as described above, not only spherical powder is not generated, but only aggregates are generated, which causes a reduction in product yield. The production of agglomerates has a drawback in that a classification step must be inserted in a later step, and in the conventional method, the yield of the product was about 85%.

The device is complicated. Takes up a lot of space. The slurry supply pipe has an inner diameter of 6 mm and is thin and easily blocked. Equipment costs such as pumps and maintenance costs are high.

It is an object of the present invention to equalize the outflow amount from each nozzle even when a plurality of nozzles are provided without pulsation in a method of supplying slurry to a spray dryer.

Further, the object of the present invention is to shorten the slurry supply pipe, remove the factor of the variation in the outflow amount due to the loss head, and stably manufacture high-quality spherical powder. It is to provide a method for supplying a slurry to a spray dryer.

[0015]

According to a first aspect of the present invention, there is provided a method for supplying a slurry to a spray dryer, wherein a pressure tank is arranged above a drying tower of the spray dryer, and the slurry is supplied into the pressure tank so that a natural flow force is applied. It is characterized in that the slurry is caused to flow out from the pressure tank by applying a gas pressure to the liquid surface of the slurry in the pressure tank and to be supplied to the spray dryer.

A method of supplying slurry to a spray dryer according to a second aspect is the method of supplying slurry to a spray dryer according to the first aspect, wherein the slurry has a constant liquid level in the pressure tank. It is characterized in that the supply rate of the slurry is adjusted.

According to a third aspect of the present invention, there is provided a method of supplying slurry to a spray dryer according to the first or second aspect, wherein the slurry is introduced from a pressure tank to a plurality of nozzles, and each nozzle has an equal outflow amount. It is characterized in that the slurry is caused to flow out.

[0018]

In the method of supplying slurry to the spray dryer according to claim 1, since the slurry flows out of the pressure tank by the natural flow-down force and the gas pressure applied to the liquid surface of the slurry, the slurry does not pulsate in the spray dryer. Supplied. In this case, the slurry can be supplied to the spray dryer in a fixed amount by adjusting the gas pressure. Further, even when the slurry is made to flow out from a plurality of nozzles, the slurry can be evenly distributed and supplied to each nozzle.

In the method of supplying slurry to the spray dryer according to the second aspect, since the liquid level height of the slurry in the pressure tank is made constant, the natural downward force of the slurry from the pressure tank becomes constant. For this reason, it becomes easy to quantitatively supply the slurry to the spray dryer.

In the method of supplying slurry to the spray dryer according to the third aspect, the slurry is allowed to flow out uniformly from each nozzle, so that the slurry can be flowed out without causing blockage in each nozzle or a pipe communicating with the nozzle. it can.

[0021]

EXAMPLES Examples will be described below with reference to the drawings. FIG. 1 is a system diagram showing an embodiment. Mixing tank 1
The slurry mixed and dispersed in 1 is sent to the pressure tank 13 by the slurry transfer pump 12. Pressurized gas is introduced into the pressure tank 13 through a pipe 14 and a gas pressure control valve 15, so that the liquid surface of the slurry in the pressure tank 13 can be pressurized. Reference numeral 16 is a detector for detecting the liquid level in the pressure tank 13. The slurry pump speed controller 17 controls the rotation speed of the pump 12 so that the liquid level detected by the detector 16 becomes constant. Control. The slurry in the pressure tank 13 is a pinch valve 1
9 and the slurry supply pipe 18 to supply to the nozzle 9. 8 is a drying tower, and 7 is a disk atomizer.

The method of the present invention does not require the buffer tank and service pump (diaphragm pump, roller pump, etc.) used in conventional spray dryers. In the present invention, a pressure tank 13 is provided instead of the service pump, and the slurry supply amount is controlled by the pressure of nitrogen or air or other non-combustible gas supplied to the pressure tank 13. Slurry flow rate is pressure tank 1
Although it depends on the mounting position of No. 3, it is determined by Bernoulli's theorem from the head of the total of the natural fall and the supply gas pressure.

The slurry supply pipe 18 is made sufficiently large (for example, 12 to 25 mmφ) with respect to the diameter of the nozzle 9 (for example, 6 mmφ). By doing so, the discharge coefficient of the nozzle becomes much larger than the line loss. As a result,
Even if the pipe 18 is blocked to some extent, the change in the flow rate due to the line loss can be almost ignored.

The slurry is supplied to the pressure tank 13 by the slurry transfer pump 12. Pressure tank 1
The pressure tank 13 is controlled by controlling the speed of the slurry pump based on a signal from a liquid level detector 16 (for example, an ultrasonic type or an electrostatic capacitance type non-contact type) provided in FIG.
Keep the liquid level inside constant. The slurry transfer pump 12 is controlled only by speed control, not ON / OFF control. This is to avoid sedimentation, separation, or drying in the pipe for transferring the slurry to the pressure tank 13.

As a means for accurately grasping the outflow amount from the nozzle 9, there is a method in which the weight of the pressure tank 13 is detected by a load cell and the weight loss per unit time is calculated to detect the slurry flow rate. In the invention, the slurry flow rate can be accurately controlled without using such a strict method.

Further, a pinch valve 19 or an orifice plate may be provided at the outlet of the pressure tank 13 so that the flow rate of each nozzle is strictly balanced.

An embodiment of the operation of the apparatus shown in FIG. 1 will be described. In this embodiment, the diameter of the drying tower 8 is 2500 mm, the slurry concentration is 30 to 70%, the inner diameter of the slurry supply pipe 18 is 16 mm, and the inner diameter of the nozzle 9 is 6 mm. When the secondary pressure of the gas pressure control valve 15 was set to 100 to 500 mmH ₂ O in order to set the slurry supply amount to 75 liters per hour, the slurry could always be stably supplied at a constant flow rate without pulsation. . As a result, the obtained granulated powder could be a good quality spherical powder having an average particle size of 70 μm and a sharp particle size distribution curve.

The obtained product contained almost no agglomerates, only a transient loss at the start and end of the operation of the apparatus, and the yield reached 99%.

[0029]

As described above, according to the method of the present invention, the slurry can be supplied to the spray dryer without pulsation. Further, according to the present invention, the slurry can be supplied to the spray dryer in a fixed amount. According to the method of the present invention, it is possible to generate spherical particles having a uniform particle size with a spray dryer.

Particularly, according to the method for supplying slurry to the spray dryer according to the second aspect, it becomes easy to supply the slurry accurately and quantitatively.

In the method for supplying slurry to the spray dryer according to the third aspect, the slurry in the pressure tank is evenly discharged from a plurality of nozzles, the nozzles and the slurry pipe are prevented from being blocked, and the granulated powder is discharged. Can be manufactured efficiently.

[Brief description of drawings]

FIG. 1 is a system diagram illustrating an example method.

FIG. 2 is a system diagram illustrating a conventional method.

[Explanation of symbols]

8 drying tower 9 nozzles 11 mixing tank 12 Slurry pump 13 Pressure tank 14 Disk atomizer 15 Gas pressure control valve 16 Liquid level detector 17 Slurry pump speed controller 18 Slurry supply pipe 19 pinch valve

Claims (3)

[Claims] 1. A pressure tank is arranged above a drying tower of a spray dryer, and slurry is supplied into the pressure tank,
A method for supplying slurry to a spray dryer, characterized in that the slurry is caused to flow out from the pressure tank by applying a natural flow force and a gas pressure to the liquid surface of the slurry in the pressure tank, and to supply the slurry to the spray dryer. . 2. The method of supplying slurry to a spray dryer according to claim 1, wherein the supply rate of the slurry into the pressure tank is adjusted so that the liquid level of the slurry in the pressure tank becomes constant. Method for supplying slurry to spray dryer. 3. The spray dryer according to claim 1 or 2, wherein the slurry is introduced from a pressure tank to a plurality of nozzles, and the slurry is caused to flow out from each nozzle at an equal outflow rate. To supply slurry to the.