JPH063049A - Automatically drying method for material to be dried - Google Patents

Abstract

PURPOSE:To always enable drying optimally regardless of material and shape by measuring a water content of a material to be dried such as wood continuously to control temperature, humidity and the volume of air according to a drying schedule as indicated by an optimum water content change curve. CONSTITUTION:A water content measuring sensor 12 is mounted on wood 10 housed properly in a drying furnace and the water content of the wood 10 is measured continuously with a water content meter 14 from a measurement signal thereof. A dry-bulb temperature sensor 15 and a wet-bulb temperature sensor 16 are arranged in the furnace and signals thereof are outputted to a dry-bulb temperature controller 20 and a wet-bulb temperature controller 22. Optimum temperature and moisture conditions by a drying schedule are inputted with a feeder 26 and a signal is sent to the adjusting meters 20 and 22 via converters 28 and 30 to set the optimum drying schedule indicated by a dry-bulb/wet-bulb temperature change curve. Then, a heater solenoid value 32 and a damper motor 34 are controlled based on measured values of dry-bulb and wet-bulb temperature and a difference between the dry-bulb and wet-bulb temperatures corresponding to the optimum drying schedule.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic drying method for materials to be dried, such as wood or the like, which can be used with a moisture content meter.

[0002]

2. Description of the Related Art Many drying methods such as drying of wood have been carried out in the industrial world, and many attempts have been made to improve the production cost and energy saving even today. Hereinafter, drying of wood will be described as an example.

Conventionally, for controlling the drying method of wood, an on-off type automatic temperature controller is simply used, and the water content change abruptly while monitoring the transition of the water content of the temperature set value ( In order to prevent (decrease) from occurring, a so-called manual setting method is used to control each time, a method of empirically inputting a time-dependent drying schedule in advance and controlling with a time schedule, and a weight change due to drying with a load cell One of the methods has been used in which the optimum temperature and humidity conditions are continuously set so that signalization is performed and excessive weight changes do not occur.

Of these three methods, most of them are presently used, the methods are expensive, and there are very few practical examples. The method is suitable for a certain stable material to be dried due to the problem of deviation from the substance, but it is not suitable for drying wood with different conditions each time, and in the end it requires a considerable safety factor for operation. It has the drawback of greatly increasing the cost of drying.

Also, in any of the above-mentioned methods, the control of the drying is performed regardless of the change value of the water content with the progress of drying, and the drying schedule proposed from the drying theory for the water content is used. It has the drawback that it is not completely guaranteed. In reality, it is set while estimating it each time as time passes, or it is set afterwards by continuously measuring the change in weight of the sample material.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic drying method according to the actual condition of drying, in which the drying always proceeds under optimum drying conditions regardless of the material and the form which change each time. Is to provide a method.

[0007]

Here, the present inventors
We have found that it is possible to realize a fully automatic control system with the function of changing the conditions of the optimum drying schedule momentarily based on the signal by directly and continuously measuring the change in water content of the material to be dried such as wood. . Moreover, the present inventors have completed the present invention, knowing that the control device for this purpose has a function that is cheaper than the conventional product and has a convenience that anyone can easily operate.

Furthermore, the present inventors preset the optimum dry-bulb temperature and wet-bulb temperature conditions with respect to changes in water content as described above, and compared the set values with the actual dry-bulb temperature and wet-bulb temperature. However, by controlling the exhaust valve and the steam valve so that the difference becomes zero, it became possible to perform a simple and accurate dry operation.

Therefore, the gist of the present invention is that the optimum moisture content change curve that defines the stage of measuring the initial moisture content of the material to be dried and the drying process up to the measured initial moisture content and the final target moisture content. And the step of determining the dry-bulb temperature, the drying gradient, the material and the morphology, starting the drying, measuring the water content at every moment, and measuring the difference between the measured water content and the optimum water content change curve. The step of performing at least one condition change of the temperature, humidity and air volume of the dry atmosphere in response to the degree of the difference and sequentially repeating it along the optimum moisture content change curve, and reaching the target moisture content This is an automatic drying method for the material to be dried, which comprises the steps of confirming and ending the drying operation.

Thus, according to the present invention, regarding the atmosphere control for maintaining the drying along the optimum moisture content change curve, that is, the drying schedule control of the wood drying, the drying is performed by directly following the moisture content change of the material to be dried. A system for controlling sphere temperature and wet bulb temperature has been realized, and this new system is a water content automatic measuring device that is a sensor unit and a converter that converts the signal into a control signal for optimum dry bulb temperature and wet bulb temperature. And temperature
Consists of a humidity controller, the operating part of which operates the fan,
It consists of a mechanism that controls the opening and closing of the heater valve and damper,
By converting the signal from the water content automatic measuring device into an operation signal of the optimum dry-bulb temperature and the wet-bulb temperature and comparing them with those at the present time, at least one of the optimum temperature / humidity / air volume with respect to the water content at that time is calculated. It has a function to automatically change the conditions, and the system itself is simpler than the conventional one, so it can be said that it is a practical system.

Originally, the drying schedule, which should be directly controlled by the water content, had no means for comparison / evaluation, so that the temperature / humidity controller was artificially operated each time based on the experience of the operator. By defining it in relation to the dry-bulb temperature and the wet-bulb temperature, we have made it possible to easily set and control the drying schedule. In addition, in relation to this, by collecting a large amount of drying data and obtaining an empirical formula, there is an advantage that it is possible to more accurately follow the drying schedule without requiring complicated calculation. .

In this respect, in the conventional automatic control system based on the change in weight, several monitor materials are selected, the change in weight is measured by a special heat-resistant load cell, and the signal is controlled by a large-scale system which is processed by a computer. It is not easy and convenient because it requires a high degree of knowledge to operate it. Moreover, since it is monitored with small sample materials, there is a risk that the difference from the actual situation will be greatly different.

[0013]

Next, the operation of the present invention will be described more specifically. The present invention comprises each of the following first to fourth steps, and the steps are as follows.

First step: This is a step of determining the water content (initial water content) of the material to be dried at the present time when starting the drying operation. Although there are many possible definitions of the water content, it is usually calculated by the following formula. Definition of water content

[0015]

[Equation 1]

G _A: Total dry weight, G _B : Moisture weight, G _C :
Material weight (G _A, the constant temperature value for 24 hours total dry at 100 ° C. The tester) Second stage: initial water content and the dry bulb temperature and a final target moisture content, drying gradient, in consideration of the material and forms This is the stage of obtaining the optimum moisture content change curve, that is, the drying schedule.
According to the present invention, the drying schedule obtained at that time is read and displayed as the dry-bulb temperature and the wet-bulb temperature by an empirical formula obtained in advance for each material to be dried. Therefore, the drying schedule can be set only by inputting the respective temperatures into the program in advance.

An example of a functional expression showing the relationship between the water content and the dry-bulb temperature (wet-bulb temperature) found in the optimum water content curve is as an empirical expression in the case of the material to be dried shown in FIG. Can be shown as. 1) Dry-bulb temperature curve y = -0.5x + (A + 20) y: Dry-bulb temperature, x: Moisture content, A: Constant (A is the initial dry-bulb temperature, 65 in the case of Fig. 3 described later) 2) Wet-bulb temperature curve

[0018]

[Equation 2]

Y: wet-bulb temperature, x: water content, A: constant (the same dry-bulb initial temperature as above, 65 in the case of FIG. 3) As described above, in the present invention, the drying schedule is the dry-bulb. It is a table of optimum drying conditions in which moisture content and temperature / humidity conditions are correlated in consideration of temperature, drying gradient, tree species (material) and morphology. It is a guideline for setting dry conditions.

That is, the factors for determining the wood drying schedule are the dry-bulb temperature, the drying gradient, the species such as the tree species, the thickness and the size, the initial water content and the finished water content, and these elements are always used when selecting the drying schedule. Is selected and selected. For example, the difference between the initial water content and the finished water content is divided by the required drying time to calculate the average water content reduction rate, which is then corrected by taking into consideration the dry-bulb temperature, the tree species,
Depending on the material thickness, the rate of decrease in water content per hour should not exceed 1% of the total water content, and the decrease rate should be increased during the first half of the drying period, while the decrease rate should be increased during the latter half of the finishing period. The water content decrease curve is obtained so that the finished water content can be obtained within a predetermined period by reducing the total amount. Furthermore, in this case, the measurement of the water content at the center of thickness, 1/2 point, 1/4 point, etc., taking into account the measurement points determined by the tree species and morphology, for example, grain wood, board wood, and conquering wood. Determine the point. Preferably, the average value of the water content measured at these several measurement points or the optimum condition point is selected to determine the optimum water content change curve.

As described above, the optimum water content change curve is
It is determined in consideration of morphology such as material thickness and size, initial moisture content and finished moisture content, but in the present invention, the dry-bulb temperature required to obtain such an optimum moisture content curve. Since the wet-bulb temperature and the wet-bulb temperature are specified, it is sufficient to determine the drying condition after the start of drying by setting and controlling only the dry-bulb temperature and the wet-bulb temperature among these factors. The order of inputting the drying schedule to the control system is to set the dry-bulb temperature and the wet-bulb temperature corresponding to each moisture content of the drying schedule calculated from the shape, the drying gradient, etc. to each signal converter as described above. Start with These settings are made by a driving tool for input.

Such control can be easily and easily achieved by a control system in which a moisture content continuous measuring instrument, its signal converter, and a dry bulb and wet bulb temperature controller are integrated. The point of the drying operation is to use any means according to the set schedule described above, and the most preferable method is to set the conditions directly by the water content as described above.

This is because the establishment of the schedule is based on the condition setting corresponding to the water content, and in the present invention, the dry-bulb temperature and the wet-bulb temperature are replaced for simplicity of the operation. Since a certain strong correlation is found in the water content, it is understood that the present invention also realizes the drying schedule based on the theory of drying based on the water content. A method of inputting with a personal computer instead of the signal converter is also included.

Third step: Drying is started, the water content is measured, the difference between the measured water content and the optimum water content change curve is determined, and the temperature, humidity and air flow rate of the dry atmosphere are calculated accordingly. It is a step of changing at least one condition.
Such condition changes are sequentially repeated along the optimum moisture content change curve, that is, the dry-bulb and wet-bulb temperature change curves.

Based on the selected drying schedule, a signal converter for converting an input signal from the moisture content sensor into an input signal of the temperature controller is incorporated, and the entire drying process corresponds to the moisture content change. Is set by the digital setter. The set number shall be up to 2 ° C.

The function of controlling the dry-bulb temperature and the wet-bulb temperature corresponding to the moisture content at a certain drying point is to send a temperature signal to the temperature controller via an arithmetic circuit at an arbitrary position between the two moisture contents. By activating the temperature control function.
Unlike the conventional time control method that can be operated unattended at night,
It is completely unmanned, and the finished water content can be controlled without waste and the end operation can be performed automatically.

That is, the temperature and humidity of the drying atmosphere are adjusted so that the difference between the water content measured continuously after the start of drying and the water content determined from the above-mentioned optimum water content change curve becomes zero. Then, at least one of the air volumes is changed. At this time, if the temperature is abnormally high, the drying from only the surface of the desiccant will proceed abnormally, which will lead to cracking of the desiccant.Therefore, the instrument is instructed to quickly lower the temperature and the function is activated. The same function is repeated for humidity and air volume.

The measurement of the water content, the calculation of the deviation, and the change of the conditions are sequentially repeated until the target water content is reached.
That is, when the difference between the measured water content and the conditions on the optimum water content change curve exceeds 1% at a certain time point, the dry-bulb temperature and the wet-bulb temperature are close to those on the optimum water content change curve. It is advanced (moving forward).

Fourth step: a step of ending the drying operation after confirming that the target water content has been reached. FIG. 1 is a schematic explanatory view of an apparatus for carrying out the automatic drying method according to the present invention.

In the figure, a water content measuring sensor 12 is attached to a wood material 10 as a material to be dried, which is appropriately placed in a drying oven, and its signal is sent to a water content meter 14 to continuously contain water. The rate is being measured. On the other hand, a dry-bulb temperature sensor 15 and a wet-bulb temperature sensor 16 are provided in the furnace, and respective signals are sent to a dry-bulb temperature controller 20 and a wet-bulb temperature controller 22.

The optimum temperature and humidity conditions according to the drying schedule determined from the initial moisture content and the final moisture content are input by the implanter 26, and the dry bulb temperature controller 20, the wet bulb and the wet bulb are passed through the converters 28, 30. A signal is sent to the temperature controller 22, and the optimum drying schedule represented by the optimum moisture content change curve, that is, the dry-bulb and wet-bulb temperature change curve is set.

After the start of drying, the water content measured every moment is converted from the water content meter 14 through the converters 28 and 30 into the corresponding dry-bulb temperature and wet-bulb temperature, and compared with each set value. Find the difference. A signal is output to each of the controllers 20, 22 according to the calculated difference. Reference numeral 32 is a heater electric valve, and 34 is a damper motor.

In the preferred embodiment of the present invention, the dry state is converted into the dry-bulb temperature and the wet-bulb temperature, which are correlated with the water content characteristic, and processed. You can do it.

Therefore, the control operation of the present invention is remarkably simple and easy, and more closely adheres to the actual condition of drying. Next, the operation and effect will be described in more detail with reference to Examples.

[0035]

EXAMPLES In this example, the apparatus shown in FIG. 1 was used to dry birch and pine pine according to the present invention. In the optimum moisture content change curve in the case of this example, an initial moisture content of 60% was obtained by using an average value of moisture content measured at the time of the crossing. An optimum moisture content change curve was assumed, assuming that this was dried to a final moisture content of 10% with an even reduction rate.

On the other hand, the dry-bulb temperature and the wet-bulb temperature corresponding to each water content are obtained based on the empirical formulas,
Drying operation was started using it as a control index. The water content was measured almost every hour, the dry-bulb temperature and the wet-bulb temperature at that time were obtained by the same empirical formula as above, and the dry-bulb temperature and the wet-bulb temperature corresponding to the optimum water content change curve were respectively compared. , The temperature, humidity, and air volume were changed so that the difference was calculated and then set to zero.

When the difference between the dry-bulb temperature and the wet-bulb temperature exceeds the optimum drying gradient value, it is regarded as a dangerous atmosphere condition and humidification control is performed to follow the optimum moisture content change curve so as to obtain an appropriate atmosphere. The operation was performed. FIG. 2 is a graph showing the results of the drying test of this example conducted on birch wood, showing the relationship between the water content and the dry-bulb temperature and the wet-bulb temperature.

In this example, control was performed along the predetermined optimum moisture content change curve and the change curves of the dry-bulb temperature and the wet-bulb temperature determined based on the optimum curve, and the drying was performed almost according to the schedule. FIG. 3 is a graph showing the drying schedule of the bay pine shown in Table 1. Also in this example,
The control was performed along the illustrated change curves of the dry-bulb temperature and the wet-bulb temperature, and the drying was performed almost according to the schedule.

[0039]

[Table 1]

[0040]

According to the present invention, the water content itself is continuously measured and the dry-bulb temperature and the wet-bulb temperature are measured based on the measured values, instead of the indirect method of measuring the change in the weight of wood as in the past. Is a method that automatically changes according to a preset optimum moisture content change curve, that is, a drying schedule represented by a dry-bulb and wet-bulb temperature change curve, so operation is simple and easy, and always in an optimal state. Since it is dried, energy saving is also realized, and its practical effects are remarkable. As described above, the present invention automatically adopts a method in which the dry-bulb temperature and the wet-bulb temperature are automatically switched by the decrease of the water content, which is particularly epoch-making as a method for drying wood. It can be said that it is automatic control.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an apparatus for carrying out the present invention.

FIG. 2 is a graph showing the results of Example 1 of the present invention.

FIG. 3 is a graph showing a drying schedule used in another example of the present invention.

[Explanation of symbols]

10: Wood 12: Moisture content measuring sensor 14: Moisture content meter 15: Dry-bulb temperature sensor 16: Wet-bulb temperature sensor 20: Dry-bulb temperature controller 22: Wet-bulb temperature controller 26: 28: Transducer 30: Transducer 32: Heater electric valve 34: Damper motor

Claims (2)

[Claims] 1. An optimum moisture content change curve that defines a stage of measuring an initial moisture content of a material to be dried and a drying process up to the measured initial moisture content and a final target moisture content is a dry bulb temperature, a drying gradient, and a material. And the step of obtaining considering the morphology, start drying, measure the water content at every moment, find the difference between the measured water content and the optimum water content change curve, and respond to the degree of the difference Then, at least one of the conditions of the temperature, humidity and air volume of the drying atmosphere is sequentially repeated along the optimum moisture content change curve, and the step of terminating the drying operation after confirming that the target moisture content has been reached A method for automatically drying a material to be dried, which comprises 2. The optimum moisture content change curve is replaced with respective change curves of dry-bulb temperature and wet-bulb temperature, while the measured water content is also converted into corresponding dry-bulb temperature and wet-bulb temperature, respectively. The method according to claim 1, characterized in that