JPS6158748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wood drying method that extends the time when the moisture content can be reduced due to boiling only to the time of depressurization in the vacuum drying method of wood, and extends it to the time of pressurization and heating. It is.

In the vacuum drying method, it is necessary to heat the internal temperature of the wood to above the boiling point at the time of depressurization before depressurizing, which is the time when the moisture content can decrease, and the heating time is longer than the time during depressurization. Because the moisture content does not decrease during heating, the moisture content decreases in less than one-third of the cycle time in the time period of one cycle that combines heating and depressurization in the vacuum drying method. . If the S/V method is used to prevent damage to the wood during heating, the moisture content increases during heating, so the time required to dry the wood according to the vacuum drying method is 2 or more was not a time when the moisture content was decreasing, but rather a time when the moisture content was increasing. Therefore, when drying wood using a vacuum drying method, it has been considered more advantageous to take the wood out of the vacuum dryer after one cycle and dry it using another drying method. This idea is based on the premise that the boiling phenomenon of contained water cannot occur when wood is heated. It is faster to use boiling than to use evaporation to evaporate the water contained in wood, so if there is a method that can boil the water contained in wood even when heating the wood, the evaluation of vacuum drying methods will fundamentally change. It turns out.

Therefore, let's reconsider the vacuum drying method. Naturally, the higher the internal temperature of the wood during heating, the greater the difference between the boiling point and the boiling point at reduced pressure, and therefore the amount of boiling will increase. If saturated steam is used to heat wood, the steam pressure and temperature will increase proportionally, so there is a limit to the pressure during steaming due to the strength of the wood, and generally the pressure is 1 kg/cm ² or more. It is dangerous to steam the food over water, so the heating temperature should be 120℃.
cannot be exceeded. Therefore, in order to heat above 120°C, a heating source other than saturated steam must be used. This separate heating source must be a pressurized gas to provide a uniform heating method for each piece of wood in the load, and a humid heating source to avoid damaging the wood. That is the premise.

If you look for a high-humidity heating source, putting the risk of damage to the wood as a secondary consideration, first of all, if it is heating steam, the pressure inside pressure vessel A will be 1 kg/kg.
^cm2 , it is possible to heat the wood above its boiling point, but due to the nature of heating steam, the temperature that can be used for heating wood is low, making temperature control difficult, and it is difficult to directly heat wood. It is dangerous to inject into pressure vessel A containing. If a gas mixture of high-pressure saturated steam and heated air is introduced, it is possible to heat the steam above its saturation temperature, but the mixing ratio is unstable due to fluctuations in the steam pressure of the boiler, resulting in excessive humidification. It is dangerous to directly inject into the pressure vessel A, as this may lead to water leakage or lack of humidity. Therefore, in addition to the pressure vessel A that performs vacuum drying, a pressure vessel B is installed to supply high-pressure steam from the boiler and air pressurized by the compressor according to the instructions from the thermometer and pressure gauge of pressure vessel B. The wood in the pressure vessel A is mixed at a predetermined ratio and continuously injected into the pressure vessel B while being heated. Depending on the situation, if high-pressure boiler steam can be sprayed and humidified to create high-pressure, high-temperature, and high-humidity air, pressure vessel B can be used to pressurize and heat the wood in pressure vessel A.
Therefore, high pressure, high temperature, and high humidity air can be continuously injected into the pressure vessel A under safe conditions.

Even if you suddenly inject high-pressure, high-temperature, and high-humidity air into pressure vessel A and pressurize the wood to be dried loaded in pressure vessel A without pre-treating it, the surface of the wood will be heated. As the temperature of the wood increases, evaporation occurs only from near the surface layer of the wood, and the contained water does not boil, increasing the moisture gradient and making the wood more likely to crack. It is unsuitable for use in heating methods.

Therefore, the high-temperature vacuum drying method of the present invention will be explained based on an example in which a 45 mm thick board of commonly used South Sea wood and rice wood was dried.

The stacked wood to be dried is put into pressure vessel A, the door is closed, and pressure vessel A is filled with saturated steam, and the pressure of this saturated steam is frequently varied in the range of 0.1 to 0.5 kg/ ^cm2 . As a result, high-temperature drain water of saturated steam generated on the surface of the wood and inside the wood is forced into the wood, and the high-temperature drain water is spread inside the wood. Further increasing the saturated vapor pressure,
By frequently varying the steam pressure in the range of 0.6 to 0.9 Kg/cm ² , the temperature inside the wood becomes uniform through the high-temperature drain water forced into the wood. After that, by releasing saturated steam and creating a reduced pressure atmosphere, all the water contained in the wood will boil uniformly, and the resin that was an obstacle to the movement of the contained water will be removed by steam distillation, and the inside of all cell cavities will be uniform. This creates a diluted state in which some of the water contained in the wood evaporates, creating a condition in which high-pressure, high-temperature, and high-humidity air can easily enter the wood.

After that, the operation of the vacuum pump is stopped, and the high-pressure, high-temperature, and high-humidity air of about 180℃ and around 5 kg/cm ² produced in pressure vessel B is injected into pressure vessel A from the injection pipe of pressure vessel A. When this happens, air at a temperature of approximately 180°C enters the wood. When the vacuum pump stopped operating, the temperature of the wood to be dried was 75 to 80℃, but immediately after boiling stopped, all the water contained below the boiling point was evaporating rapidly, so there was a temperature difference of 100℃. Even if high-temperature gas enters the wood, it will not damage the wood. The high-temperature air of about 180°C that enters the wood penetrates into all the cell cavities, and the water remaining in all the cell cavities boils uniformly, raising the temperature of the wood. This injection of high-pressure, high-temperature, and high-humidity air is continued until the pressure inside the pressure vessel A reaches 0.9 kg/cm ² , and once that pressure is reached, the injection is stopped once. When the injection is stopped, the pressure inside the pressure vessel A decreases, and when the pressure drops to 0.6 kg/cm ² , the injection is started again. By frequently repeating the start and stop of injection at a range of 0.6 to 0.9 Kg/cm ² , the pressure is increased and reduced within the range of 0.6 to 0.9 Kg/cm ² , and each time, the inside of the cell cavity is increased. The phenomenon in which the contained water boils, forms bubbles, and leaves the wood, and then the high-temperature air enters, is repeated. Although high-temperature air of about 180°C is constantly injected into the high-pressure vessel A, the temperature inside the pressure vessel A never exceeds 140°C, except at the end of drying. From this, it can be inferred that the water contained in the wood boils while the wood is pressurized and heated, and the resulting heat of vaporization continues to consume calories. This 0.6
If pressure and heating in the range of ~0.9Kg/ ^cm2 are continued, the internal temperature of the wood will reach 130~135℃, but if this process is prolonged too much, a moisture gradient will occur and increase as in normal drying. A phenomenon appears. When this process is stopped and the pressurized and heated air is released from the pressure vessel A and the pressure is reduced to below atmospheric pressure, the moisture content decreases further due to boiling of the contained water, and at the same time,
The result is that the occurrence of moisture gradient is corrected. For this reason, better drying quality was obtained by repeating pressurization, heating, and depressurization using high-pressure, high-temperature, and high-humidity air two or more times. After placing the wood to be dried in a pressure vessel, it took about 16 hours to dry the wood with a moisture content of 8%.

As seen in the above examples, the present invention is a high-temperature vacuum drying method in which the water contained in the vacuum drying method is boiled and released even during the pressurization and heating of the vacuum drying method.
The limit of the S/V method, where it was impossible to reduce the moisture content to 20% or less, has been eliminated, and the vacuum drying method will eventually eliminate the inconvenience of having to use other drying methods. There is no need to move the wood during the drying process, and the wood is dried in the same vacuum dryer.
It became possible to dry the product within a few days, which greatly benefited the industry.

Claims (1)

[Claims] 1. A pressure vessel B that produces high-pressure, high-temperature, and high-humidity air is attached to the pressure vessel A capable of vacuum drying wood, and the air is injected from the pressure vessel B into the pressure vessel A. The wood to be dried inside is heated with saturated steam and reduced pressure to boil and evaporate some of the water contained in all the cell cavities of the wood. High-temperature, high-humidity air with a pressure of around cm ² is injected, and while it is pressurized and heated to a predetermined pressure above atmospheric pressure, the contained water is brought to a boiling phenomenon to lower the water content, and it is boiled while heating. A high-temperature vacuum drying method for wood, which is characterized in that the wood to be dried that has caused the phenomenon is placed directly in a reduced pressure atmosphere to further boil off the water contained therein and reduce the water content.