JPS58217521A - Drying of powder - Google Patents

Abstract

PURPOSE:To dry powders at reduced equipment and energy costs, by controlling the drying conditions so that the air velocity of a blower is heightened during the initial drying stage and lowered after the particles reach a predetermined temperature, and continuing the drying. CONSTITUTION:A dryer consists of a humidity controller 1, a blower 2, a heater 3, a drying kettle 10, a high-speed motor 13 and a low-speed motor 14. The humidity-controlled air delivered from the blower 2 is heated in the heater 3 to a predetermined temperature and sent to the drying kettle 10. Part of this air is recirculated and returned to the blower 2 and the rest is discharged from the system. Moist powders are thrown by batches of a definite amount into the drying kettle 10 from a moist powder tank 9 placed above the kettle 10. During the initial drying stage, the air velocity of the blower 2 is heightened so as to fluidize the powders. After the powders reach a predetermined temperature, the air velocity of the blower 2 is lowered to cease the powders from fluidizing without transferring them from the kettle to elsewhere, continuing the drying and after reaching a predetermined moisture, the powders are transferred to a dry powder tank 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for drying granular materials, particularly plastic chips, in particular polyester chips.

Raw material chips used for polyester melt spinning and melt film forming must have a moisture content of approximately It is necessary to suppress the concentration to 50 ppm or less, and drying of the chip is required as a pre-process.

In addition, when drying undried chips, the temperature, humidity, air flow, and residence time of the hot air must be adjusted to prevent the chips from fusing together and from decreasing the viscosity of the chips, which increases with exposure to high temperatures. There is a strong desire to strictly control conditions and at the same time to reduce equipment costs and energy costs required for the drying process.

Dryers for polyester chips are commonly used, such as dryers and fluidized bed dryers.

Figure 1 shows the flow sheet for a tower dryer.

1 is a humidifier, 2 is a blower, 3 is a heater, and 4 is a drying pot. A supply valve 6 for the powder and granular material 5 is attached to the upper part of the drying pot, and a discharge valve 7 is attached to the lower part.

A stirring blade 8 is rotatably mounted inside the drying pot by a motor.

The tower dryer shown in Figure 1 is designed to maintain a constant residence time in the drying pot by balancing the input amount of undried powder and the amount of dried chips discharged.

A portion of the hot air introduced into the drying oven is circulated, the remainder is added to the humidifier, and the newly added amount is released outside the system.

The speed of the hot air is kept low, so that the powder and granules inside the drying pot do not flow, and the first-in, first-out system is maintained. The stirring blades are attached so as to uniformly stir the particles in the same horizontal layer so as not to break the stack of powder and granules. The single type tower dryer shown in FIG. 1 has the following drawbacks.

That is, since the wind speed inside the drying pot is low, the electric power of the blower is small, but it takes time to raise the temperature of the powder and granules.

The amount of drying per hour is small. In addition, in order to keep the residence time in the drying pot constant, it is necessary to balance the amount of powder and granules in the drying pot so that it is not full and the amount of input and the amount of discharged are equal.

When starting the dryer, it is impossible to keep the residence time constant until a certain amount of powder is filled in the drying pot, and it is impossible to keep the residence time constant until the dryer is filled with a certain amount of powder and granules. It is necessary to dispose of it as a body.

Furthermore, if the drying capacity is to be changed depending on the amount used, the moisture content and viscosity of the dry powder can be adjusted by storing the dry powder and operating the dryer intermittently or by changing the residence time in the drying pot. In order to compensate for quality changes such as

Although it is necessary to adjust the temperature and wind speed of the hot air.

The tolerance range for quality changes is small, and therefore the range over which the drying equipment capacity can be changed is also small.

Figures 2 and 6 are flowsheets of a fluidized bed dryer.

The fluidized bed dryer shown in Figure 2 is a batch type.

The residence time of the powder in the drying pot can be kept constant.

This dryer divides the drying pot into two parts in series.

The upper drying pot 10 is placed in a fluid state to shorten the heating time of the powder and granules, and the lower drying pot 11 is kept in a stationary state after the temperature has been raised, and the residence time of the powder and granules in each pot is set to 1:2. In order to avoid this, there is one bed of 10 drying pots at the top.

This example shows a drying pot with two beds at the bottom.

9 and 12 are undried powder tanks, respectively.

The dry powder tank is shown.

This dryer has a fluidized bed in the upper drying pot.

The heat transfer of the hot air to the powder and granule material is fast, and the temperature required for drying the powder and granule material can be obtained in a short time, and viscosity reduction in the drying process can be prevented accordingly, and at the same time, the drying capacity of the dryer can be increased. Also, after the powder reaches the set temperature, the amount of time required for the moisture inside the powder to move out of the powder by diffusion and dry.

Since the drying material remains in the lower non-fluidized bed for a certain period of time, the power required for the blower in the lower drying pot can be kept low, contributing to energy savings. Furthermore, there is no generation of inferior quality waste particles at the start, which is a drawback of the tower dryer shown in FIG. 1 mentioned above.

Changes in drying capacity can be easily covered by adjusting the number of batches.

However, this dryer has the following drawbacks.

That is, the ratio of flow time to non-flow time has an appropriate value depending on the moisture content of the undried granular material.

In the dryer shown in FIG. 2, the ratio of the number of fluidized beds to non-fluidized beds is determined and cannot be changed. In addition, there are two parts of the drying pot.
Divided into two at the bottom, each with a blower.

Equipment costs are high due to the need for a heater and possibly a separate humidifier.

Generally, equipment costs are compared in proportion to drying capacity; however, there are fixed parts that are not proportional to capacity, such as instrumentation (not shown), such as opening and closing of temperature control device valves, blower on/off control, and sequence control systems. The smaller the capacity, the higher the equipment cost per drying capacity, including the drying pot, piping, etc.

The fluidized bed dryer shown in FIG. 6 has a lower drying pot 11 shown in FIG.
This is an example of a composite type in which the tower dryer shown in FIG. 1 is replaced.

This dryer, like the one shown in Fig. 2, speeds up the temperature rise of the powder and granule material in the initial stage of drying, and after the temperature rise of the powder and granule material is completed, the hot air speed is low, so it is possible to save power for the blower.

It has drawbacks such as the inability to maintain a constant residence time, the generation of chips of inferior quality at the start, and the high equipment cost because it is divided into two pots.

An object of the present invention is to provide a method for drying powder and granular materials that eliminates the above-mentioned drawbacks, and has the following secondary structure.

In other words, in a powder dryer consisting of a humidifier, an air blower, a heater, and a drying pot, the air speed of the blower is increased at the beginning of drying to fluidize the powder and bring it to a predetermined temperature. After reaching the drying pot, the air speed of the blower is reduced to substantially stop the flow of the powder and granules, and drying is continued until the powder reaches a predetermined moisture content. This method of drying powder and granules is characterized in that the powder and granules are transferred from the drying pot after reaching the drying pot.

Furthermore, in the drying process, after substantially stopping the flow of the powder, it is preferable to momentarily increase the wind speed of the blower one or more times to flow the powder and stir the powder.

The present invention will be described in detail with reference to the following two drawings.

FIG. 4 is a flowchart of a dryer applied to the drying method of the present invention.

The dryer shown in Figure 4 has a humidity controller 1. Air blowing 2. Heater 3t Drying pot 10. Two electric motors driving the blower, namely a high speed electric motor 13 and a low speed electric motor 14, are also configured. Humidity-controlled air blown from the blower 2 is heated to a predetermined temperature by the heater 3 and sent to the drying oven 1°, part of which is recycled and returned to the blower 2, and the remainder is exhausted outside the system. be done.

A predetermined amount of the undried granular material is fed into each patch from the undried granular material tank 9 located at the upper part of the drying pot 10.

Dry powder and granules that have not yet been dried are placed in the drying pot 10.
The powder is transferred to a dry powder/granular material tank 12 provided at the bottom of the container. - Figure 5 is a graph showing the relationship between drying time (horizontal axis), powder temperature and wind speed (vertical axis). In the figure, A shows the hot air inlet set temperature, 1 port shows the powder temperature, and C shows the wind speed over time.

Undried powder and granules may be introduced into the drying oven before, after, or at the same time as the high-speed hot air blowing. However, considering the stability of the temperature of the hot air and the drying oven, and the saving of energy, it is preferable to feed the hot air at a high speed. Immediately after is best. The introduced powder and granules continue to rise in temperature while being fluidized by high-speed air supply, and asymptotically approach the hot air inlet set temperature A. Then, after the temperature of the granular material reaches a predetermined temperature, the hot air is switched to low speed, the flow of the granular material is stopped, and the flow is continued.

After the moisture content of the powder reaches a predetermined moisture content and drying is completed, the dry powder is transferred to the lower dry powder tank.

What is meant by the flow of powder and granular material due to high-speed air supply?

This is the range in which the powder and granules in the pot are stirred as a whole.

The flow causes agitation of the powder and granules, preventing uneven drying and eliminating the need for a stirrer.

This improves heat transfer from hot air to powder.

In the present invention, the hot air is switched to a low speed after the temperature of the powder reaches a predetermined temperature.

This predetermined temperature means that stirring of the chips is stopped by stopping the flow, and the temperature is increased or decreased.

Even if stirring is stopped, uneven drying will not be a problem, and even if the temperature rise rate decreases from there, the drying rate will not decrease significantly compared to the hot air inlet set temperature, and in fact, the hot air inlet set temperature , the temperature difference from the input chip temperature is 70 to 9
It is preferable to reach the 0% range, but it may be 90% or more.

This predetermined temperature can also be determined by measuring the time taken to reach the predetermined temperature, which can be obtained through experience.

It is difficult to measure the moisture content of powder or granular material online, and this may be representative of the time it takes to reach the predetermined moisture content, which can be obtained from experience.

In the drying method of the present invention, the powder and granular materials are loaded and discharged in a patch manner, with the drying pot being emptied each time, but in the case of repeating this process for drying.

High-speed air supply and low-speed air supply may be repeated without stopping the blower.

The method of switching the hot air speed is such that high speed allows the powder to flow, and low speed is for the purpose of reducing energy costs, and is suitable for drying the powder without flowing. The hot air may be reduced to a sufficient extent, and implementation means may include variable speed inverter drive of the electric motor, switching by two or more blowers, or mechanical switching by a reduced transmission.

However, when considering energy savings, conversion losses are unavoidable with inverter systems and mechanical speed reduction systems, and if you still have two blowers, equipment costs including switching valves will increase, and polarity conversion motors (pole change ) Alternatively, it is advantageous to attach motors with different polarities in series to one blower.

In the embodiment shown in FIG. 4, the blower switches between high-speed air supply and low-speed air supply using a polarity conversion motor, with a two-pole motor used for high-speed air supply and a four-pole motor used for low-speed air supply.

For this reason, the air speed is halved, the air pressure is reduced to 1/4, and the electric power of the motor is reduced to approximately 1/8.

Significant power savings were achieved.

Figure 6 shows the drying time (horizontal axis), the temperature of the powder and the wind speed (
It is a graph showing the relationship with the vertical axis). The embodiment shown in Figure 6 can supplement the stirring function due to flow that is lost during low-speed air supply, and there is no need to install a special stirrer, and the time of pulsed high-speed air supply is the same as the time of low-speed air supply. It is extremely small in comparison and maintains the same power saving effect.

It can prevent uneven drying.

FIG. 7 is a graph showing the state of temperature rise of powder and granular material due to differences in hot air velocity, where a indicates high velocity and b indicates low velocity.

The state of temperature increase in powder and granular material due to differences in hot air speed is 1. When the hot air inlet temperature is kept constant to maintain quality, when the air velocity is increased and the powder and granular material is made to flow, the temperature of the powder and granular material increases due to so-called high-speed forced convection. Improves heat transfer to the surface.

This process is accelerated by the synergistic effect with the stirring of the powder and granule by the flow, and the heating of the powder and granule necessary for drying is completed in a short time.

As a result, the drying time can be shortened, the drying capacity can be increased, and at the same time, the heat radiation loss, which is approximately proportional to the product of the surface area of the drying pot and the drying time, can be reduced.

The rate at which the temperature of the granular material is increased by the fluidized bed is faster than that of a so-called paddle dryer, which attempts to raise the temperature by contact between the wall of the drying pot and the stirring blade.

FIG. 8 is a graph showing changes in the moisture content of powder and granular material due to differences in hot air speed, where a is high speed and b is low speed.

C is the equilibrium moisture content of the powder.

What are the characteristics of the hot air velocity and the moisture content of powder and granules over time?

As shown in Figure 8, the moisture content eventually approaches the equilibrium moisture content C determined by the temperature of the hot air in the atmosphere and the physical properties of the powder, but at the end of drying, that is, in the lapse rate drying region, the hot air velocity changes. There was no significant difference in the moisture content (the hot air velocity was changed at two points in Figure 8). Therefore, the extension of drying time that must be extended due to the lower hot air velocity is not significant.

Special polyester (polyethylene tere phthalate)
The effect on drying was negligible.

FIG. 9 is a graph showing the relationship between hot air speed and blower power.

The relationship between the hot air speed and the blower power is approximately proportional to the fifth power of the wind speed, and in the case of the polarity conversion motor shown in the embodiment, since the wind speed was halved, the power was reduced to 1/8, resulting in a significant reduction in power. Electricity costs were reduced.

υ, the effects of the above two inventions were summarized as follows.

(A) Because the drying pot, humidifier, blower, and heater were all combined into one, the equipment cost was reduced by about 60 units compared to the fluidized bed dryer shown in Figure 2, which has the same capacity.

(B) In the same fluidized bed dryer, the power cost was reduced by 50% or less by halving the speed of the hot air after the powder reached a predetermined temperature.

(C) The residence time of the powder and granules in the drying pot can always be kept constant regardless of changes in production volume, and not only can there be no scraps with poor quality at the start, but also the dry powder can have a stable quality. Granules were obtained.

(D) It is possible to easily change the drying time independently of the temperature increase time for the moisture content of undried granular material, which is expected to decrease in the future.

[Brief explanation of the drawing]

Figure 1 shows the flow sheet of a tower dryer. Figures 2 and 6 are flow sheets of a fluidized bed dryer. FIG. 4 shows a flow sheet of a dryer to which the present invention is applied. FIG. 5 is a graph showing the relationship between drying time, powder temperature and wind speed. FIG. 6 is a graph showing the relationship between the drying time, powder temperature, and wind speed, which shows a drying method in which air is sent at high speed in a pulsed manner when air is sent at low speed. Figures 7 and 8
The figure is a graph showing the temperature increase state of powder and granular material and the change in moisture content due to differences in hot air velocity. FIG. 9 is a graph showing the relationship between hot air speed and blower power. 1: Humidity controller 2: Air blower: Heater 4, 10, 11: Drying pot 9: Undried powder/granular material tank 12: Dry powder/granular material tank Patent applicant Azuma Shi Co., Ltd. Figure 3 ＼ 5 figure

Claims (2)

[Claims] (1) In a powder dryer consisting of a humidifier, an air blower, a heater, and a drying pot, the air speed of the blower is increased at the beginning of drying to make the powder flow. After the granular material reaches a predetermined temperature, the air speed of the blower is lowered without transferring the granular material from the drying pot. The flow of the powder material is substantially stopped and drying is continued. A method for drying powder and granules, which comprises transferring the powder and granules to the drying pot after the powder has reached a predetermined moisture content. (2) In a powder dryer consisting of a humidifier, an air blower, a heater, and a drying pot, the air speed of the blower is increased at the beginning of drying to fluidize the powder and granule until the powder reaches a predetermined level. After reaching the temperature, reduce the air speed of the blower without transferring the powder or granules from the drying pot. The flow of the granular material is substantially stopped, and then the air speed of the blower is momentarily increased one or more times to cause the granular material to flow. A method for drying powder and granules, which comprises continuing drying and transferring the powder and granules from the drying pot after the powder reaches a predetermined moisture content.