JPH08738B2 - Drying apparatus and method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drying device and method which can be suitably used for drying water-containing molded products such as ceramic molded products, clay molded products, and paper molded products.

Conventional Technology Conventionally, as a method for drying this type of water-containing material,
The following four methods are mainly adopted.

Place in a high humidity container with little air flow displacement or in a room for a long time to dry.

Freeze-dry.

Depending on the atmosphere in the drying chamber, a humidified or dehumidified air stream is fed into the drying chamber for drying.

Dry by microwave heating.

When the above-mentioned method is adopted, there is a drawback that it usually takes several days or a long period of one month or more for drying depending on the product. When adopting the method of (1), it is ideal in that the soft distortion can be solidified by freezing, and the distortion that occurs during drying can be minimized, but the drying cost is extremely high and the drying shrinkage is small, so ceramics However, there is a drawback in that the dry density is difficult to increase when drying such as. In addition, it is difficult to replenish the latent heat of vaporization required to evaporate the moisture in a molded product having a large volume. This method is widely adopted, and it operates by taking the control signal of the humidifier and dehumidifier from the sensor in the atmosphere of the dry room, but there is a problem in the accuracy of the sensor and the followability of the humidifier and dehumidifier. Therefore, it is necessary to see a certain range with respect to the set temperature, which makes precise drying difficult. The method (1) has a drawback that the microwave energy is nonuniformly applied to the material to be dried when the material to be dried has a complicated shape.

Of the above-mentioned conventional technologies, it is clear that the technology of 1 is the best if it can be controlled appropriately, but it is difficult to carry out accurate control as described below. That is, as shown by the chain line in FIG. 1, this type of water-containing molded product usually exhibits a dimensional shrinkage ratio of about 5% in the initial stage of drying, so that the molded product is apt to crack. Therefore, particularly in the initial stage of drying, it is necessary to enhance the detection accuracy of relative humidity and gradually lower the relative humidity from near 100% relative humidity to dry the molded product. However, according to the conventional method, the fluctuation range of relative humidity is 95% at room temperature and relative temperature.
Since it is 2% or more in the vicinity, precise relative humidity control of at least ± 1% is required and the initial drying (relative humidity 100
% ~ 90%) cannot be used.

As described above, since all the conventional methods have drawbacks, a wetting agent is added to the molded product, and further,
At present, the drying is performed by combining drying means such as the above, but there are various problems such as the process being complicated and the cost being high.

An object of the present invention is to solve the above problems, and to improve the conventional technique by positively utilizing the relationship between temperature and humidity, and the relative humidity of the air flow supplied to the drying chamber in the initial stage of drying ( (Hereinafter, abbreviated as RH) is precisely controlled to gradually lower it so that evaporation and dimensional shrinkage of water, which has been done rapidly in the past, are gradually and uniformly generated. The purpose is to obtain a dry molded product.

In order to achieve the above-mentioned object, the present invention positively utilizes the relationship between temperature and humidity as described above, and the relationship between temperature and humidity is as known from the moist air ix diagram. RH changes remarkably with temperature changes, for example, 30 ℃
RH when water is saturated with air (that is, RH 100%) 1 ℃
Is 94%, and if the temperature is further increased by 1 ° C, RH will be 89%. Therefore, if the air flow is gradually heated by a heating means that is highly controlled with respect to an air flow saturated with water or close to water saturation, it is possible to control the relative temperature to a high level, and the air to be dried placed in the air flow can be controlled. The object is to be able to dry very slowly, and the present invention aims to provide a method and apparatus for drying a water-containing molding using this principle.

That is, the present invention, the air flow to be supplied to the drying chamber, in advance at least relative humidity (maximum equilibrium humidity of the material to be dried) 90% or more is humidified to a value at which water in the material to be dried does not evaporate, Before the airflow enters the drying chamber or in the drying chamber, the relative humidity is gradually increased by heating the airflow by a controlled heating means based on a predetermined program pattern until at least the size of the material to be dried becomes substantially constant. To provide a drying method characterized by lowering After the size becomes constant, rapid drying can be performed by a usual drying means.

Specifically, excess steam is sent into the air sent through the fan, and the water-containing air is cooled to a predetermined temperature to generate moisture-saturated air at a predetermined temperature. The temperature of the moisture-saturated air can be controlled to a constant temperature within ± 0.1 ° C by controlling the amount of cooling water and the amount of cooling air using a temperature sensor and a temperature controller, which is based on RH94%. RH accuracy of ± 0.5% will be obtained. The temperature of the moisture-saturated air is set to the same as or slightly higher than the temperature of the drying room (that is, the temperature of the material to be dried), but when it is low, the air is heated on the surface of the material to be dried and the relative temperature decreases. If it is too high, water will condense on the surface of the material to be dried (especially in the case of ceramics). Next, the moisture saturated air (air flow) is heated by a heater or the like before being supplied into the drying chamber or in the drying chamber. In the moisture-saturated air, the relative temperature of heating energy rises, and the temperature of 100% RH initially rises, so that the RH decreases corresponding to the heated temperature. This temperature rise width may be adjusted according to the drying characteristics of the material to be dried. For example, a honeycomb ceramic green body having an extremely thin wall thickness, and a material having a high moisture evaporation rate, has an extremely high temperature of moisture saturated air. It is desirable to gradually raise it. As a method of heating and heating the moisture-saturated air, there are a method of injecting while measuring the amount of steam in a steam radiator, a method of passing a controlled current to an electric heater, and the like, but a thyristor type voltage controller and a program controller are combined. The method of gradually increasing the voltage applied to the electric heater from 0% can most accurately reduce RH. That is, the thyristor changes the output voltage from 0% to 10%.
It can be set freely within the range of 0%, and its output curve can be set by the program controller.

The present invention also provides a drying device for carrying out the above-mentioned drying method, which comprises a blower for generating an air flow to be supplied into the drying chamber and an air flow fed from the blower. A humidifier for supplying excess steam to the cooler, a cooler for cooling the humidified airflow to obtain moisture-saturated air at a predetermined temperature, and a moisture-saturated airflow sent from the cooler immediately before flowing into the drying chamber. Alternatively, a heating device that heats according to a preset program pattern in the drying chamber to gradually reduce the relative velocity of the airflow is provided, and an electric heater with thyristor control is most preferably used as the heating device. Is used.

As described above, the drying apparatus of the present invention is characterized by gradually controlling the relative humidity while precisely controlling the water-saturated air having a predetermined temperature with the heating apparatus including the electric heater controlled by the thyristor. . For example, a gas flow (moisture-saturated air) with a predetermined flow rate of 100% RH is used as the heat output of this heating device at 20 ° C.
If the thyristor output voltage is set to 8%, the heater calorific value is 2
Since it is proportional to the power of From the known (ix) diagram, the initial dry atmosphere is RH 99% and temperature 30.2 ° C with respect to RH 100% and temperature 30 ° C.

As described above, when the heating device that controls the heater output by the thyristor is used, particularly high-precision heating control is possible, and as a result, it is possible to precisely control the relative humidity of the air flow supplied into the drying chamber. However, the heating device is not limited to the above, and any simple means capable of precisely controlling high RH heating can be adopted, and for example, a heat pump, an oil heater or the like may be used.

Examples Hereinafter, the present invention will be described in detail with reference to Examples shown in the drawings.

In FIG. 2 schematically showing a drying apparatus according to the present invention, 1 is a drying chamber, 2 is a fan for generating an airflow to be supplied to the drying chamber 1, and 3 is air supplied from the fan 2 from a steam source 3a. A humidifier 4 for blowing in excess steam cools the humidified air fed from the humidifier 3 into moisture-saturated air having a constant temperature, and a humidifier 5 feeds from the cooler 4 immediately before flowing into the drying chamber 1. A heating device that heats the supplied air,
6 is an electric heater provided in the heating device 5, 7 is a thyristor for controlling the voltage of the electric heater 6, and 8 is a program controller for controlling the thyristor 6 according to a preset program.

In the drying device, as shown in the figure, the air flow sent from the fan 2 is humidified by the excessive steam from the humidifier 3,
The water-containing air is cooled by a cooler 4 and made into a water saturated air having a constant temperature, and then heated by an electric heater 6 in a heating device 5 to be introduced into a drying chamber and placed in the drying chamber 1. The material to be dried 9 made of ceramics is dried. The above-mentioned honeycomb ceramic has a structure shown in FIG.

Specifically, the honeycomb-shaped ceramics 9 that is the material to be dried
The FIC 10 is set so that the flow velocity in the hole 9a of the fan is a predetermined speed, for example, 2 Nm / sec, and the fan 2 is set through the inverter 11.
Is being supplied to supply the air stream at 25 ° C. to the supply path 12. on the other hand,
In the humidifier 3, steam of 10 kg / cm ² and 200 ° C. is regulated by the automatic pressure regulating valve (PCV) 13 to 3 kg / cm ^2, and excessive steam is blown into the above airflow through the orifice 14 in the supply passage 12. . Next, this water-containing air is introduced from the supply path 12 into the cooler 4 composed of a cooling cylinder. In the cooler 4, the temperature of the outlet A is set to a predetermined temperature, for example, 30 by an automatic temperature controller (TIC) 15.
The cooling water is set so that the temperature is set to ℃ and the cooling water supplied into the cooling cylinder is controlled.

The temperature of the automatic temperature controller 15 is set to be several degrees higher than the outside air temperature, which causes a decrease in RH when the humidified and temperature-controlled air is heated in the process of reaching the heater 5,
On the contrary, when it is low, RH100 is retained. In this way, the airflow that was cooled by the cooling cylinder and became the moisture-saturated air having a predetermined temperature of 30 ° C. at the outlet portion A was then introduced into the heating device 5 provided with the electric heater 6 and was generated in the cooling cylinder. The mist is collected by the demister 17 provided in the cooling cylinder and discharged to the lower seal pot 18. In the heating device 5, first, the mist generated in the supply path 12 from the cooler 4 is collected by the demister 19, and the demisted water-saturated air is heated by the electric heater 6. The electric heater 6 has its voltage controlled by a thyristor 7 whose output is controlled by a program controller 8 and gradually heats and rises from a voltage output of 0% to gradually and gradually lower the RH of the water saturated with air. . In this way, by gradually heating with the heater 6, the air flow supplied into the drying chamber 1 is at least a honeycomb ceramics which is a material to be dried according to a program pattern defined by the program controller 7 from a state of 100% RH. Until the water shrinkage rate is almost constant
RH is gradually decreased.

As mentioned above, the RH of the air flow supplied to the drying chamber 1 is 100%
→ 98% → 96%, gradually decreasing over time, the first
As indicated by the solid line in the figure, the dimension uniformly decreases in proportion to the increase in the moisture evaporation rate, and as indicated by the solid line in FIG. Gradually a gentle curve is drawn until it reaches a certain level, and no significant change occurs in the initial stage of drying as in the conventional case.

<< Experimental Example >> A molded article of honeycomb-shaped ceramics containing titanium oxide was dried by the drying apparatus of the above-mentioned Example.

When the flow rate of the air flow in the honeycomb holes was set to 3 Nm / sec and the temperature of point A of the cooler 3 was set to 25 ° C, the temperature of point B immediately before being heated by the heater 5 was 24 ° C. .
(However, the outside air temperature is 20 ° C) The thyristor 6 controlling the heater 5 was adjusted to raise the temperature to 24.2 ° C. The RH of the air flow at this time is calculated to be 99% from the moist air ix diagram. The RH 99% air stream was introduced into the drying chamber. When two honeycomb-shaped molded products were placed in the drying chamber and the weight was measured after 5 hours, there was almost no change. Then, the temperature of the air flow is from 24.2 ℃ to 50
The voltage of the heater 6 was linearly program-controlled so that the temperature became 0 ° C., and the voltage was raised over 24 hours. The honeycomb-shaped ceramics dried by the air flow had neither cracks nor distortions on the outside and inside. The loss on drying was 22%.

<< Comparative Example 1 >> Two identical honeycomb ceramics used in the above experimental example were placed in a gas circulation dryer for one day and night, and were dried by rotating only a circulation fan without heating. After drying, the honeycomb-shaped ceramics had both morning glory-like cracks on both end faces, and many cracks were also seen on the outer surface.

<< Comparative Example 2 >> One honeycomb ceramic, which is the same as that used in the above experimental example, is placed vertically in a 200 □ × 1000 L box made of hard vinyl chloride, and the bottom is covered with a breathable metal net and a lid is attached. And allowed to stand at room temperature. When checked one week later, there was almost no loss on drying, and there was no change in appearance. Then, 10 mm on the top of the outer cylinder
The sample was left for another week with the round hole in the sample. The honeycomb became hard near the upper end surface, but many cracks were formed on the end surface and large cracks were formed on the outer periphery of the upper half. Then, a 10 mm round hole was also drilled on the lower surface of the outer box and left for 2 weeks. The loss on drying was 0%, but many cracks were generated on both the upper and lower edges.

The device according to the present invention is not limited to the above embodiment,
As shown in FIG. 5, a circulation fan 21 is installed and a drying chamber 1 '
The airflow to be supplied may be circulated, and the use of this circulation system has an advantage that the energy required for heating in the heating device 5 can be greatly saved.

Effects of the Invention As is clear from the above description, according to the method and apparatus of the present invention, the relative humidity of the air flow supplied into the drying chamber is substantially 90% or more, preferably from 100% according to a predetermined program pattern, Since the shrinkage rate of the material to be dried is gradually decreased until it reaches a substantially constant level, rapid evaporation of water in the initial stage of drying and dimensional deformation due to evaporation are suppressed, and extremely gentle evaporation of water and dimensional deformation occur. Can be prevented and high quality products can be provided. In particular, since the wall thickness is thin, the water content evaporates quickly and dry cracks easily occur. For example, it can be suitably used when drying the honeycomb ceramics.

In addition, the relative humidity of the air flow is controlled by utilizing a relationship between temperature and humidity (i.e., i-X diagram of moist air), and after heating as moisture saturated air at a predetermined temperature, a heating device capable of precise control, for example, a program controller, By heating with an electric heater that is controlled in combination with a thyristor, it has various advantages such that the relative humidity of the airflow can be decreased step by step from substantially 100%. .

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the water evaporation rate and the size of a dried product, FIG. 2 is a schematic configuration diagram of a drying device according to the present invention, and FIG. 3 is a cross-sectional view of a honeycomb-shaped ceramic which is an object to be dried. , Fig. 4 is a diagram showing the relationship between the size of dried product and time,
FIG. 5 is a schematic view showing another embodiment. 1 ... Drying room, 2 ... Fan, 3 ... Humidifier, 4 ... Cooler, 5 ... Heating device, 6 ... Heater, 7 ... Thyristor, 8 ... Program controller.

Claims (9)

[Claims] 1. An airflow supplied to the drying chamber is humidified in advance to a value at which relative humidity of 90% or more does not substantially evaporate the moisture in the material to be dried, and before the airflow flows into the drying chamber. Drying characterized by gradually lowering the relative humidity based on a predetermined program pattern by heating an air flow by a controlled heating means in a drying chamber until at least the moisture contraction rate of the material to be dried becomes substantially constant. Method. 2. The drying method according to claim 1, wherein the relative humidity of the air flow supplied into the drying chamber is substantially 10%.
The drying method is characterized by being 0%. 3. The drying method according to claim 1, wherein the material to be dried placed in the drying chamber is ceramics. 4. The drying method according to claim 1, wherein the material to be dried placed in the drying chamber is honeycomb ceramics. 5. A blower for generating an air flow to be supplied into the drying chamber, a humidifier for supplying excessive steam to the air flow sent from the blower, and a moisture-containing air sent from the humidifier. A cooler that cools to a moisture-saturated air of a predetermined temperature,
A heating device for heating the moisture-saturated airflow sent from the cooler immediately before flowing into the drying chamber or in a drying chamber according to a preset program pattern to gradually reduce the relative velocity of the airflow. And drying equipment. 6. A drying device according to claim 5, wherein an electric heater with thyristor control is used as the heating device. 7. A drying apparatus according to claim 6, wherein the thyristor is combined with a program controller and an output curve of the thyristor is set by the program controller. 8. The drying apparatus according to claim 5, wherein the material to be dried placed in the drying chamber is ceramics. 9. The drying device according to claim 5, wherein the material to be dried placed in the drying chamber is honeycomb ceramics.