JPS6157993B2 - - Google Patents

Description

Detailed Description of the Invention: In order to eliminate the drawback of the vacuum drying method in which the water content decreases only when the pressure is reduced, the present invention uses pressurized heated gas in a pressure vessel without using a mechanically generated air flow such as a fan. This relates to pressure-fluidized and reduced-pressure drying of wood in which the moisture content is reduced even during pressurized heating by fluidizing the wood.

In the conventional SV method, the high-temperature gas during pressurization and heating does not flow, and the water content does not decrease at that time. Even if heating is carried out in the most rational manner using saturated steam, it will take approximately 70 minutes to heat a 45 mm diameter softwood, during which time the moisture content will not decrease but rather increase. After pressurized heating, the saturated steam is released from the pressure vessel, the pressure is reduced, and the water contained can be boiled for about 30 minutes at the longest.
The moisture content is reduced only during that period. Therefore, the SV method, which involves repeated pressurization and depressurization, lowers the moisture content by repeatedly increasing and decreasing the moisture content at a ratio of 2:1 in the case of 45 mm coniferous wood. In the case of hardwoods, this ratio is even lower. Furthermore, in the SV method, which uses steam heating, it is difficult to reduce the moisture content to below 20%, so even if you try to lower the moisture content by installing a fan inside the pressure vessel, the walls of the pressure vessel are round. Because of this, normal pressure wind moves along the wall and does not pass smoothly between stacked timbers, making it very difficult to achieve a uniform moisture content distribution, and equipment needs to be increased due to the processing volume. Unprofitable due to deterioration in efficiency.

In addition, various drying methods have been implemented in the past that use a sealed dryer and create air flow using an electric fan, but one of them is a regular hot air dryer. A method of high temperature drying has been conventionally used. According to it, the hot bulb temperature is 120
℃, when wood is dried at a wet bulb temperature of 100℃,
Since the equilibrium moisture content is 4%, it has the advantage of being faster drying than normal wood drying methods, but on the other hand, this method does not take any means to artificially transfer the water content from the center of the wood to the surface layer. However, even if the wood is dried in high humidity, a large moisture gradient occurs, resulting in a large amount of cracking and distortion in the dried wood. Furthermore, due to operation in high humidity, the fan, door, and wall structure were severely corroded.
It becomes difficult to use the dryer for a long period of time.

The present invention was developed to eliminate the drawbacks of the above-mentioned SV method and high temperature drying, and the present invention will be explained based on Examples.

The wood 22 to be dried is piled up and put into the pressurized fluidized decompression dryer (hereinafter referred to as this device) 1 which is a pressure vessel, the door is closed, and the valves 13, 16, 1 are closed.
7, 18, 19, close valves 12, 14, 1
5 and 20, the saturated steam that has passed through the pressure reducing valve 11 from the boiler 2 is injected into the apparatus 1 from the injection pipes 4 and 5 to heat the wood 22 to be dried with fluctuating steam pressure, and the drain valve 20 is opened. control and
The internal temperature of the wood is 0.9Kg/ which is the pressure of saturated steam.
The temperature is proportional to cm ² (gauge pressure and below)
The temperature is varied between 118°C and 112°C, which is proportional to 0.7Kg/cm ² , and then the valve 12 is closed and the drain valve 20 is fully opened to release saturated steam from the device 1. Close the vacuum pump 2
1, open the valve 18, reduce the pressure inside the device 1 only while all the water contained in the wood is uniformly boiling, then close the valve 18 and stop the operation of the vacuum pump 21. When the valve 19 is turned on and the inside of the apparatus 1 is returned to atmospheric pressure, the wood to be dried will have cavities in which a portion of the contained water is evenly dispersed in all the cell cavities of the wood to be dried. Wood that has become like this has cavities that allow the water contained in the wood to move to adjacent cell cavities, making it easier for the water contained within the wood to move to the surface layer.

After that, valves 12, 16, 17, 18, 19
Close the valves 13, 14, 15, and 20, and immediately reduce the pressure of the saturated steam from the boiler 2 to approximately 3 kg/cm 2 with the pressure reducing valve 10, and then reduce the pressure of the saturated steam from the boiler 2 to approximately 3 kg/cm ² in the heating furnace 3.
Super steam heated to 300℃ is injected into the device 1 from the injection pipes 4 and 5, and when the pressure inside the device reaches 0.5Kg/cm ² , the drain valve 20 is opened. Injecting is carried out only through the injection pipe attached to one side wall of the device 1, and at the same time the discharge pipe attached to the opposite side wall is opened. When the valves 14 and 17 and the valves 15 and 16 are used as a pair and super steam is injected from the injection pipe 4, the injection from the injection pipe 5 is stopped and the super steam is passed from the discharge pipe 7 to the central pipe 9 outside the device 1. Release super steam to the outside. When super steam is to be injected from the injection pipe 5, the injection from the injection pipe 4 is stopped, and the super steam is released from the discharge pipe 6 to the outside via the concentration pipe 8 outside the device 1. The pressure in the space surrounded by the wall of the pressure vessel with the injection pipe that injects super steam and the wood to be dried 22 is greater than the pressure in the space surrounded by the wall of the pressure vessel with the discharge pipe and the wood to be dried 22. , because the super steam is higher,
It passes almost evenly between the piles of timber,
In the pressurized state within the pressure vessel, a stream of super-steam pressurized gas will averagely flow over the surface of the wood. By appropriately alternating the above combinations of injection pipes and discharge pipes, the direction of the air flow of the pressurized gas of super steam can be changed, and the heating temperature applied to the wood 22 to be dried can be made uniform. can be measured. Super steam is a dry, colorless steam with no moisture, but the steam released from the discharge pipe is a normal white saturated steam with a lot of moisture. When the super steam pressurized gas stream first started flowing, it is thought that the temperature of the wood was low, so the super steam dropped in temperature and became normal saturated steam. As the exchange continues, the temperature of the wood to be dried becomes higher than the saturated steam temperature, which is proportional to the pressure, but even after that, the steam coming out of the discharge pipe is white saturated steam, so the temperature of the wood to be dried becomes higher than that of the wood to be dried. This means that the released steam mixed with super steam and became saturated steam. After alternating the super steam pressurized gas stream,
If colorless super steam is released from the tip of the concentration pipe in steps 8 and 9 instead of white saturated steam, the moisture content of the wood to be dried has decreased to near the equilibrium moisture content. This was confirmed experimentally.

Even if this device is used to continue operating with high-pressure saturated steam from the boiler, it will not be possible to reduce the moisture content of the wood to be dried. However, by replacing high-pressure saturated steam with super steam, Under the circumstances, it was found that the moisture content decreased even without the use of an electric fan, unlike the hot air drying method, so a method that utilizes the pressurized state to further accelerate the moisture content decrease was proposed. Some things are easy to understand. This will be described below.

If the amount of super steam injected is slightly larger than the amount released, the pressure inside the device 1 will gradually rise.
In the case of a combination of the injection pipe 4 and the discharge pipe 7, when the pressure increases and the pressure inside the device 1 reaches 1.5Kg/cm ² , the valve 14 will automatically close by electromagnetic operation and stop the injection. Then, the pressure inside the device 1 gradually decreases, and when it drops to 0.5Kg/cm ² , the valve 17 is automatically closed and the valves 15 and 16 are opened by electromagnetic operation, and the injection pipe 5 and discharge pipe 6 are combined. Instead, the direction of the super steam pressurized gas flow is reversed.
The pressure of pressurized gas inside this device 1 is 1.5Kg/cm ² and 0.5
By going back and forth between kg/ ^cm2 , the temperature inside the wood will also rise and fall. When the pressure increases,
When the temperature of the water contained in the wood 22 to be dried approaches 126°C, which is a temperature proportional to the pressure of saturated steam of 1.5 kg/cm ² , and the pressure decreases, the temperature of the water contained in the wood 22 to be dried approaches, The temperature will drop to 110℃, which is proportional to the pressure of saturated steam of 0.5Kg/ ^cm2 , so the rise and fall of this temperature will cause temperature changes above and below the boiling point of the contained water, and when the pressure decreases, the contained water will rise. A boil occurs;
The movement of contained water from the center of the wood to the surface layer is promoted. In the flow of super steam pressurized gas airflow,
By increasing and lowering the pressure of the airflow, it is possible to achieve a phenomenon that causes boiling to evaporate on the surface of the water contained in the wood to be dried in a short period of time, which cannot be achieved with hot air drying or other drying methods. I started to be able to do it.

This can be demonstrated by the following. If the pressure changes between 1.5Kg/cm ² and 0.5Kg/cm ² using saturated steam from the boiler, the thermometer attached to this device will
It goes back and forth between 126℃ and 110℃, but when using super steam, while the moisture content of the wood to be dried is high,
The temperature fluctuates between 118°C and 110°C and does not show a temperature increase approaching 126°C. This means that each time boiling occurs, the temperature rise of the wood is prevented by the heat of vaporization caused by boiling, and as the moisture content of the wood to be dried approaches the equilibrium moisture content, the maximum temperature exceeds 126℃. As a result, the temperature is much higher than 126℃, and even the lowest temperature is higher than 126℃. It can be understood that due to the temperature change different from this saturated steam heating, the contained water is boiled by the pressurized gas flow of super steam.

Due to the process of altering the flow of the supersteam pressurized gas stream, a moisture gradient is created since the boiling that occurs does not necessarily originate from the center of the wood to be dried. In the hot air drying method, in order to correct the moisture gradient during the drying process, the process of steaming to increase the moisture content is repeated many times during the drying process. Then, perform the following process. When the temperature of the thermometer attached to this device 1 becomes higher than the saturated steam temperature of 1.5Kg/cm ² at the maximum pressure even at the minimum pressure, the valve is automatically opened electromagnetically when the maximum pressure is reached. The process of opening and closing is stopped, and the valves 16, 17 and drain valve 20 are manually opened to release super steam from the device 1 at once.Then, the inside of the device 1 is reduced in pressure, and the The moisture gradient can be corrected by promoting boiling of the water contained in the center of the wood to lower the overall moisture content. Thereafter, the process returns to the process of alternately flowing the pressurized gas of super steam. The process is
If you do this twice during the entire process, you can prevent moisture gradient from occurring during the drying process.

In the case of the normal SV method, that is, a method that combines pressurized heating with saturated steam and depressurization to promote a reduction in moisture content, when wood is heated with saturated steam, the boiling amount of water contained during depressurization increases. If the temperature of the wood is raised to 140-150℃, the pressure of saturated steam will be 4-5Kg/ ^cm2 , so the compression of the wood will be large and collapse of cell cavities will occur. When heated using the method of the invention, as the moisture content in the wood decreases, it is easy to raise the temperature of the wood to 140 to 150°C even at a pressure of 1.5 kg/cm ² , so that the inside of the wood is crushed. This phenomenon never occurs. Furthermore, when heating using saturated steam such as the SV method, the moisture content does not decrease during heating, but with the method of the present invention, the moisture content decreases by 1.5 to 0.5.
The lowest pressure during the process of pressure change of Kg/ ^cm2 is 0.5
Even when the temperature is Kg/cm ² , the temperature of the saturated steam becomes higher than 1.5 Kg/cm ² , so even when the pressure is reduced during the pressure change process, the moisture content shows a significant decrease. Furthermore, by adding the step of reducing the pressure to below atmospheric pressure, the pressure is reduced to below atmospheric pressure, which is higher than the heating temperature that cannot be obtained with saturated steam heating, resulting in an increased amount of dehydration compared to the amount of dehydration during depressurization in the SV method. It was decided that the amount could be obtained.

As the flow of pressurized super steam gas is repeated alternately, the moisture content of the wood to be dried approaches the equilibrium moisture content, and the super steam is released from the tip of the concentration pipes 8 and 9. It's starting to look like this. If this continues, the temperature inside the device 1 will rise more and more, so if air that has passed through the compressor is put between the boiler 2 and the pressure reducing valve 10 to create a mixture of super steam and air, Since the temperature of the heated air stream is lowered and the humidity of the air stream is also lowered, it becomes easier to reduce the moisture content below the equilibrium moisture content, improving the drying quality and increasing the drying speed.

When the drying method of the present invention is carried out using the pressurized fluidized vacuum dryer of the present invention, the commonly used lauan and agathis species can be processed into 45 mm lumber with a moisture content of 70 to 80% immediately after sawing. The board becomes a dry material with a moisture content of 8% in 12 to 13 hours, with extremely little cracking and distortion.
There was no unevenness in the moisture content distribution, resulting in a dry plate with good results.

As shown in the above embodiments, the present invention creates a pair of injection pipes and discharge pipes that face each other across the piled wood in the pressure vessel, and by changing the pair at the appropriate time. A pressurized fluidized vacuum dryer that is used by changing the flow direction of pressurized gas, a pressurized fluidized vacuum dryer for wood that creates a flow of high-temperature gas during pressurization, and reduces the moisture content while pressurizing and heating; A pressurized flow decompression drying method for wood in which the pressurized gas is changed in a predetermined pressure range at regular intervals to periodically cause changes in pressure and depressurization in the pressurized and heated gas, and The injection pipe in the container and the discharge pipe facing each other are activated in pairs, and the pressurized heated gas is changed at the appropriate time to equalize the heating temperature to the wood. Since this is a pressurized fluidized vacuum drying method for wood that reduces pressure, even with the vacuum drying method, which is said to be the fastest way to dry lumber among conventional drying methods for lumber products, the drying period is 2 to 4 days. Compared to the days required, the present invention
Since drying can now be done in 12 to 13 hours, the number of drying days has been greatly shortened, and by improving the rotation rate of the dryer, the burden of depreciation costs, which represent the highest cost of drying, has been reduced. The presence of raw materials can also be reduced, which is of great benefit to the industry.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for implementing the present invention, and FIG. 2 is a sectional view inside the pressure vessel. 1... Pressure vessel (this device), 2... Boiler,
3... Heating furnace, 4, 5... Injection pipe, 6, 7... Discharge pipe, 8, 9... Concentration pipe, 21... Vacuum pipe,
22... Wood to be dried.

Claims (1)

[Claims] 1. An injection pipe for injecting a gas such as super steam and a pipe (discharge pipe) connected to a discharge port for discharging the pressurized gas in the container are attached to both sides of the pressure vessel, and the injection pipes are connected to the opposite sides of the pressure vessel. A pressure vessel is used in which the direction of flow of pressurized gas is changed in a pressurized state within the vessel by forming a pair of a pipe and a discharge port and changing the pair at a timely manner. Pressurized fluidized vacuum dryer. 2 While pressurizing the wood in the pressure vessel with a gas such as steam, a gas such as super steam is injected from the injection pipe in the container, passing between the wood stacked on the stacks, and releasing it on the opposite side. It is characterized by performing a step of releasing gas such as steam from the outlet to create a flow of high-temperature gas while pressurizing the inside of the container, thereby reducing the moisture content of the wood to be dried while pressurizing and heating it. Then, the amount of gas such as super steam injected into the pressure vessel enclosing the stacked wood is greater than the amount of gas such as steam flowing out of the container, and the inside of the container is By changing the pressure at regular intervals within a predetermined pressure range, changes in pressurization and depressurization are periodically caused in the pressurized heated gas flowing in the container. , and a pair of pipes (discharge pipes) that connect the injection pipe of the pressure vessel containing the stacked wood to the opposite discharge port are operated in a timely manner, and the super A pressurized fluidized reduced pressure drying method for wood, which comprises changing the direction of passage of gas such as steam to equalize the heating temperature of the wood, and then reducing the pressure inside the pressure vessel.