Method and apparatus for treating wood with superheated steam to improve wood stability

Abstract

The invention relates to a method for treating wood by using superheated steam in an evaporation drying furnace to improve the stability of the wood, which comprises the following steps: 1) a primary heating procedure: heating the wood to be treated to 100-106 DEG C by using a steam atmosphere generated by microwaves in the furnace, and preserving heat; 2) a primary cooling procedure: the temperature of the steam atmosphere in the furnace is reduced to 97-103 DEG C by 3 DEG C after 20-70 minutes; 3) a circulating heating procedure: the temperature of the steam atmosphere is increased to 100-106 DEG C again after 12-50 minutes; 4) a circulating cooling procedure: reducing the temperature of the steam atmosphere in the furnace to 97-103 DEG C by 3 DEG C after 20-70 minutes; the step (3) and the step (4) are circulated alternately, the humidity in the furnace is gradually reduced, and circulation is carried out for 8-10 days; and (5) after the circulation program is finished, further cooling to the environment temperature. Under the synergistic effect of the metering water adding device (5) and the water and steam discharging device (3), the proper humidity required by wood treatment is formed in the drying furnace. And the treated wood has long-term storage stability.

Description

Technical Field

[0001] The present invention relates to a method for treating wood with superheated steam to improve the stability of wood and a steam drying furnace device, and particularly relates to a method for drying wet wood by microwave heating, belonging to the technical field of wood steam drying. Background Art

[0002] Wood contains a certain amount of moisture. Common artificial wood drying methods include conventional drying, high-temperature drying, dehumidifying drying, solar drying, vacuum drying, high-frequency drying, microwave drying, flue gas drying, etc.

[0003] The currently adopted drying devices and processes have the following disadvantages: (1) Improve the stability of the use of wood and wood products. Wood will undergo swelling and shrinkage when exposed to air for a long time, and the uneven swelling and shrinkage of wood often cause wood cracking and deformation, affecting the use and causing waste. Before use, drying the wood to the moisture content required for use can ensure the structural stability of wood products, making them beautiful in appearance and durable. (2) Improve the strength of wood and wooden parts. When the moisture content of wood is lower than the fiber saturation point, the strength of wood will increase as the moisture content of wood decreases. After drying, the wood can improve the cutting processing conditions, increase the strength of wood structure parts, the bonding strength, and the surface decoration quality of wood products. (3) Prevent the deterioration and decay of wood. If wet wood is stacked in the open air for a long time and no appropriate measures are taken, it often decays or is damaged by pests. When the moisture content of wood is reduced to less than 20%, the damage and destruction by fungi and pests can be greatly reduced. Generally, during use, the wood is dried to a moisture content of about 8 - 15%. This not only ensures the inherent properties and strength of the wood but also improves the corrosion resistance of the wood. (4) Reduce the weight of wood. In short, dried wood can ensure the quality of wood products, improve the use performance of wood, extend the service life, and thus save wood. Years of practice have proved that wood drying is an indispensable process in production.

[0004] The main components of raw wood include wood fibers, resins, minerals, and moisture. Among them, wood fibers provide the strength of the wood, and resins provide nutrients for the wood fibers. The best way to dry wood is to minimize the moisture in the raw wood while reducing the loss of resins in the wood. Currently, there are mainly the following problems in wood drying: 1. After the raw wood goes through the drying process, although the moisture decreases, the wood fibers inside the wood are still unstable; 2. The component contents of different varieties of wood are different, and there are about 50% of wood species that cannot be dried by direct hot air drying; 3. When directly using hot air drying, the drying speed is fast, but it is easy to cause surface cracks (the moisture on the wood surface loses quickly, while the moisture inside loses slowly, resulting in cracks on the wood surface) and internal cracks (for wood with a high resin content, due to the rapid loss of moisture, the resins inside the wood approach and solidify, blocking the channels for moisture volatilization in the wood, resulting in internal cracks in the wood).

[0005] CN110094712A discloses a method for drying wood using an evaporation furnace, where the heat treatment temperature of the wood is between 70 - 120 °C and the moisture of the wood can be controlled at 10 - 12 wt%. However, due to the inaccurate control of the heat treatment process conditions, the long-term stability of the processed or treated wood is still not very good.

[0006] CN109682172A discloses a method for drying wood by humid heat and microwave, where the temperature inside the furnace is raised by microwave, from room temperature to 105 - 115 °C in 10 - 16 hours; during this process, the microwave heats the water to generate steam, and the microwave further heats the steam; then it is kept warm at 105 - 115 °C until the weight of the wood is reduced to the set weight, and the microwave heating is turned off.

[0007] CN109780843A discloses a multi-layer microwave drying method, where by turning on the microwave generator, the conveyor belt motor, and the suction fan, the microwave starts to heat the material to be dried. The conveyor belt motor drives the multi-layer conveyor belt to move horizontally, and the material flows through the conveyor belts with staggered distribution on different layers in turn, and the microwave can heat the material multiple times; the evaporated moisture in the material is discharged from the furnace duct under the action of the suction fan; the dried material is conveyed by the conveyor belt and falls into the receiving hopper.

[0008] The patent CN109708430A of the inventors of the present application relates to a humid-heat microwave wood drying device, in which microwave is used to heat water to obtain high-temperature steam, and the wood is dried by the high-temperature steam. It is found in the production process that the temperature and pressure in the drying furnace are not only determined by the microwave components that generate steam. Precise control of the process conditions in the furnace is required to control the drying speed of the wood, ensure the quality of the dried wood, and also control the discharge of the drying medium in the furnace. Currently, in the prior art, for wood drying equipment, only the control of the input end of the drying medium is considered, and the output end of the drying medium is not involved (patent CN109708430A also directly discharges through a water tank, and the drying furnace body is directly connected to the water tank), resulting in the inability to precisely control the temperature and pressure in the drying furnace body, the unevenness of the atmosphere in the drying furnace body, and further the inability to precisely control the wood drying process. The raw wood is dried unevenly in the drying furnace body, and the overall quality of the dried wood is poor.

[0009] After research and observation, the inventors of the present application found that the dry shrinkage and wet swelling of natural wood are attributed to the peristalsis, expansion and contraction of fiber tubes in the wood, the generation of micropores and microcracks in brittle resin crystals, and the volatilization of oils in brittle resin crystals also leads to the generation of micropores (microchannels). The existence of these micropores and microcracks enables the moisture in the wood to enter and exit, and the lignin and cellulose in the wood shrink and swell due to water loss or water absorption. This phenomenon reduces the stability of the wood.

[0010] The inventors of the present application also found that the long-term storage instability of natural wood is caused by the instability of the resin and the instability of the fibers in natural wood, or rather, is caused by the activity of the resin and the activity of the fibers in natural wood.

[0011] The resin present in natural wood is a crystalline and brittle substance and it does not have long-term storage stability. The (natural) resin in natural wood usually contains oils (saturated or unsaturated low-molecular-weight hydrocarbons) and other volatile components (aromatic substances), and the oils and other volatile components described here are collectively referred to as "oils" hereinafter. Since the natural resin in wood contains oils, the crystal structure of the natural resin in wood is not dense or perfect and shows brittleness (similar to the brittleness of rosin). Therefore, micropores and microcracks will gradually form in the brittle resin (crystals) during the long-term storage process of wood. In addition, the small molecules of oils in wood resin may contain unsaturated bonds and active functional groups (such as aldehyde groups or carboxylic acid groups), and oxidation and aging occur during the long-term storage process. Therefore, the brittleness of the crystalline resin in wood and its own long-term storage instability will result in the inability to protect the fiber tubes (substances such as lignin and cellulose) of the wood for a long time. That is to say, the resin itself has no toughness and stability.

[0012] The content of resin and the fineness of fibers determine the density of wood. The density of wood is generally 200 - 1200 kg per cubic meter. For example, the density of paulownia wood is as low as 200 - 250 kg / m 3 . The higher the resin content or resin density (compactness) in the wood, the greater the resistance to water release or absorption by the wood.

[0013] The instability of the resin in wood is manifested as oil seepage and expansion / contraction of the wood with temperature changes.

[0014] Oily wood is not suitable for making furniture because the oil does not combine with the adhesive, resulting in debonding and cracking of the glued wood.

[0015] Wood with dense and crystalline resin is high-quality wood. Because the oil present in the resin of wood dilutes the resin, and when the oil content is relatively high, the resin in the wood is not easily crystallized. The deoiling of the resin in wood is beneficial to the full or dense crystallization of the resin. The crystalline components in the resin have a protective effect on the wood.

[0016] When the resin in the wood is deoiled of oil molecules and the deoiled resin undergoes sufficient crystallization, the resin in the wood exhibits moderate toughness (similar to plastic or synthetic resin).

[0017] In addition, the activity of the fibers in the wood is another factor affecting the long-term storage stability of the wood. The inventors of the present application found that in the prior art, heat treatment of wood at a relatively high temperature was carried out to eliminate the activity of the fibers in natural wood (eliminating unstable active groups and destroying unstable local microstructures), but this led to the denaturation, degradation, and carbonization of the fibers in the wood, destroying the structure of natural wood and seriously affecting the appearance, density, and feel of the wood.

[0018] In some early wood treatment methods of the prior art, in order to prevent internal and surface cracks in the wood, only low-temperature drying (50 - 80 degrees) could be carried out. In this regard, we believe that below 80 degrees, the activity of cellulose in the wood cannot be eliminated. In addition, in some early wood carbonization methods of the prior art, in fact, wet wood cannot be carbonized because as the wet wood is heated, the surface water of the wood is removed. At this time, the surface of the wood is water-free and has poor heat transfer, and the water content of the wood is lower than 12 wt%. If further heated for carbonization, it will cause the wood to not carbonize evenly at the same temperature inside and outside.

[0019] After years of research and observation, the inventors of the present application have found that the resins in most types of wood are intolerant to a temperature of 120°C during a short-term heat treatment process (e.g., 5 - 50 minutes), and are intolerant to a temperature of 110°C during a long-term heat treatment process (e.g., 3 - 7 days, such as 5 days). When the heat treatment temperature of the wood is higher than 120°C, after the wood has undergone a short-term heat treatment process (e.g., 5 - 50 minutes), or when the heat treatment temperature of the wood is higher than 110°C, after the wood has undergone a long-term heat treatment process (e.g., 3 - 7 days, such as 5 days), the resins in the wood degrade, the resins become coked or embrittled, and at the same time, the fibers in the wood also denature and embrittle, causing the fibers in the wood to lose their toughness. This is the reason, which actually exists in the existing wood heat treatment methods and has not been discovered for a long time, that leads to poor stability of the processed wood. Summary of the Invention

[0020] Aiming at the problems in the prior art that the drying furnace body of the hot and humid wood drying system has uneven atmosphere, and the system cannot control the discharge of the medium, resulting in the inability to achieve precise control of the drying process, the present invention provides a method for improving the stability of wood. This method can better process wood, significantly improving the long-term stability (or long-term storage stability) of the wood.

[0021] The evaporation furnace and the drying furnace refer to the same equipment and can be used interchangeably. Moisture content and water content can be used interchangeably.

[0022] In the present application, the stability of wood refers to: the shape stability of wood, the stability of water absorption rate, and the stability of appearance.

[0023] The (natural) wood to be processed in the present application refers to the (raw) wood segments sawn after peeling the natural log segments, or sawn wood boards or wood strips, etc. In the present application, the room temperature refers to the ambient temperature at the wood processing factory (or workshop) site (e.g., 15 - 35°C, such as 20 or 22°C).

[0024] The wood processed by the method of the present invention, when touched by hand, is obviously felt to be comfortable and smooth, and the appearance of the wood has gloss or brightness. In the present application, "superheated steam" refers to water vapor with a temperature (T0) exceeding 100°C (under 1 standard atmospheric pressure), for example, 101 - 107°C, more preferably 102 - 106°C, and particularly preferably 103 - 105°C.

[0025] In the present application, humidity refers to relative humidity (%), RH (%).

[0026] According to the first embodiment of the present invention, there is provided a method for treating wood with superheated steam to improve the stability of the wood, that is, a method for treating wood with superheated steam in a drying furnace to improve the stability of the wood, the method comprising:

[0027] 1) Set the weight of the wood at shutdown: According to the initial total weight W1 (unit: kg) of the wood to be treated, its average moisture content Wa 含水率 (wt%), and the target moisture content Wb 目标含水率 (wt%, for example 8 - 12%) that it finally reaches after being treated, to (calculate) determine the target terminal total weight W2 (kg) that the wood to be treated finally reaches after being steam-treated, and then set W2 as the weight of the wood at shutdown.

[0028] 2) Initial heating procedure: Add water to the water tank (101) of the microwave steam generating device (2) arranged in the drying furnace box through a metering water feeder (5), turn on the microwave generator (201) to perform microwave radiation on the water in the water tank (101) below (inside) the microwave shielding cover (202) having a steam through hole (20201) to generate (superheated) steam, and the steam circulates in the box under the action of the air flow circulation device (6) (through the steam through hole 20201), so that the circulating steam atmosphere in the box (for example, at a heating rate of 3 - 30 °C per hour, preferably 5 - 25 °C, preferably 7 - 20 °C) gradually rises from room temperature or ambient temperature to the set temperature T1, forming a circulating superheated steam atmosphere with a temperature of T1 in the box and using the circulating superheated steam atmosphere to steam-heat the wood placed in the box, wherein the steam heating time (t1) at the temperature T1 is 2 - 15 hours, preferably 3 - 14 hours, preferably 4 - 13 hours, preferably 5 - 12 hours, preferably 6 - 11 hours, preferably 7 - 10 hours, preferably 8 - 9 hours, for example 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5 hours; preferably, adjust the water addition amount (W 加水量1 , by weight) of the metering water feeder (5) according to the humidity required for treating the wood, and more preferably, the water addition amount (W 加水量1 , by weight) of the metering water feeder (5) should make the humidity in the box of the drying furnace reach 90 - 98%, preferably 90.5 - 97.7%, preferably 91 - 97.5%, preferably 91.5 - 97.3%, preferably 92 - 97%, preferably 92.3 - 96.8%, more preferably 92.5 - 96.5%, more preferably 93 - 96%.

[0029] Among them, T1 is or set in the range of 100 - 106 °C, preferably 100.1 - 105.9 °C, preferably 100.2 - 105.8 °C, preferably 100.3 - 105.7 °C, preferably 100.4 - 105.6 °C, preferably 100.5 - 105.5 °C, preferably 100.6 - 105.3 °C, preferably 100.7 - 105.2 °C, preferably 101 - 105 °C, preferably 101.1 - 104.9 °C, such as 101.4 °C, 101.5 °C, 101.6 °C, 101.7 °C, 101.8 °C, 101.9 °C, 102 °C, 102.1 °C, 102.2 °C, 102.3 °C, 102.4 °C, 102.5 °C, 102.6 °C, 102.7 °C, 102.8 °C, 102.9 °C, 103 °C, 103.1 °C, 103.2 °C, 103.3 °C, 103.4 °C, 103.5 °C, 103.6 °C, 103.7 °C, 103.8 °C, 103.9 °C, 104 °C, 104.1 °C, 104.2 °C, 104.3 °C, 104.4 °C, 104.5 °C, 104.6 °C, 104.7 °C, 104.8 °C.

[0030] Preferably, the heating rate is 3.8 - 28 °C / hour, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or 27 °C / hour.

[0031] In the initial (first) heating program of the present invention, a suitable heating rate is adopted, and water vapor carries heat into the wood, enabling the external and internal parts of the wood to be heated almost synchronously as much as possible. This can gradually soften the resin from the wood surface to the core, and form through micro-channels or pores in the softened resin of the entire wood from the inside to the outside. In the subsequent cooling program, the oil volatile components and inorganic salts in the wood resin (and fibers) can be thoroughly extracted by water (i.e., steam), so that the resin in the wood can be purified to fully crystallize during the cooling process, forming airtight and tough resin crystals to better protect the wood fibers (tubes). If the heating rate is too fast, it is necessary to increase the power of the microwave steam generator to generate superheated steam at a higher temperature (such as above 108 °C). On the one hand, the external and internal parts of the wood cannot achieve an almost synchronous heating rate, and on the other hand, the wood surface is scalded, and the surface resin denatures and hardens. These two aspects result in the inability to gradually penetrate into the wood core to form micro-channels or pores in the wood resin, thus preventing the water (i.e., steam) from thoroughly extracting the oil volatile components and inorganic salts in the internal resin of the wood.

[0032] 3) Initial cooling procedure: By lowering (or adjusting) the (power supply) power or microwave frequency of the microwave generator of the microwave steam generating device, the temperature of the (circulating) superheated steam atmosphere inside the drying furnace is reduced from temperature T1 to temperature T2 over a period of time (t2), so as to allow the steam or moisture at a relatively high temperature inside the wood (which already contains the oil volatiles extracted from the wood resin) to gradually escape due to the temperature difference between the inside and outside of the wood. The time (t2) is 15 - 80 minutes, preferably 18 - 70 minutes, preferably 20 - 60 minutes, preferably 25 - 55 minutes, preferably 30 - 50 minutes, preferably 35 - 45 minutes, preferably 37 - 43 minutes, for example 40 minutes. Generally, the (saturated) steam or moisture escaping from the wood contains the (oil) volatiles extracted from the wood resin (such as oils and other small molecule organic compounds, hereinafter both are simply referred to or collectively referred to as "oils") and trace or trace amounts of inorganic salts; preferably, the water addition amount (W 加水量2 , by weight) of the metering water feeder (5) is adjusted according to the humidity required for wood treatment and the amount of water released from the wood, and more preferably, the water addition amount (W 加水量2 , by weight) of the metering water feeder (5) and the amount of water released from the wood should make the humidity inside the drying furnace reach 94 - 99.5%, preferably 94.3 - 99.3%, preferably 94.5 - 99%, preferably 94.7 - 98.7%, preferably 94.5 - 98.5%, preferably 94.7 - 98.3%, preferably 95 - 98.1%, preferably 95.5 - 98%, preferably 96 - 97.8%.

[0033] Among them, T2 is or set in the range of 97 - 103°C, preferably 97.1 - 102.9°C, preferably 97.2 - 102.8°C, preferably 97.3 - 102.7°C, preferably 97.4 - 102.6°C, preferably 97.5 - 102.5°C, preferably 97.6 - 102.3°C, preferably 97.7 - 102.2°C, preferably 98 - 102°C, preferably 98.1 - 101.9°C, such as 98.4°C, 98.5°C, 98.6°C, 98.7°C, 98.8°C, 98.9°C, 99°C, 99.1°C, 99.2°C, 99.3°C, 99.4°C, 99.5°C, 99.6°C, 99.7°C, 99.8°C, 99.9°C, 100°C, 100.1°C, 100.2°C, 100.3°C, 100.4°C, 100.5°C, 100.6°C, 100.7°C, 100.8°C, 100.9°C, 101°C, 101.1°C, 101.2°C, 101.3°C, 101.4°C, 101.5°C, 101.6°C, 101.7°C, 101.8°C.

[0034] Among them, the set temperature difference ΔT = T1 - T2 is 2 - 4 °C, preferably 2.2 - 3.8 °C, preferably 2.4 - 3.6 °C, preferably 2.5 - 3.5 °C, preferably 2.7 - 3.3 °C, preferably 2.8 - 3.2 °C, preferably 2.9 - 3.1 °C, and most preferably 3 °C.

[0035] 4) Circulating heating program: By increasing (or adjusting) the (power supply) power or microwave frequency of the microwave generator of the microwave steam generating device, the temperature of the (circulating) flowing steam atmosphere in the box of the drying furnace is increased from the temperature T2 to the temperature T1 after a period of time (t3) to steam-heat the wood in the box; where the time (t3) is 10 - 70 minutes, preferably 12 - 60 minutes, preferably 13 - 50 minutes, preferably 15 - 45 minutes, preferably 20 - 40 minutes, preferably 20 - 30 minutes or 25 - 35 minutes, such as 30 minutes. Preferably, the water addition amount (W 加水量3 , by weight) of the metering water feeder (5) is adjusted according to the humidity required to process the wood. More preferably, the water addition amount (W 加水量3 , by weight) of the metering water feeder (5) should make the humidity in the box of the drying furnace reach 90 - 98%, preferably 90.2 - 97.8%, preferably 90.5 - 97.7%, preferably 91 - 97.5%, preferably 91.5 - 97.3%, preferably 92 - 97%, preferably 92.3 - 96.8%, more preferably 92.5 - 96.5%, and more preferably 93 - 96%.

[0036] 5) Circulating cooling program: By decreasing (or adjusting) the (power supply) power or microwave frequency of the microwave generator of the microwave steam generating device, the temperature of the (circulating) flowing steam atmosphere in the box of the drying furnace is decreased from the temperature T1 to the temperature T2 after a period of time (t4); where the time (t4) is 15 - 80 minutes, preferably 18 - 70 minutes, preferably 20 - 60 minutes, preferably 25 - 55 minutes, preferably 30 - 50 minutes, preferably 35 - 45 minutes, preferably 37 - 43 minutes, such as 40 minutes. The time (t4) is the same as or different from the time (t2). Preferably, the water addition amount (W 加水量4 , by weight) of the metering water feeder (5) is adjusted according to the humidity required to process the wood and the amount of water released from the wood. More preferably, the water addition amount (W 加水量4 , by weight) of the metering water feeder (5) and the amount of water released from the wood should make the humidity in the box of the drying furnace reach 94 - 99.5%, preferably 94.2 - 99.4%, preferably 94.3 - 99.3%, preferably 94.5 - 99%, preferably 94.7 - 98.7%, preferably 94.5 - 98.5%, preferably 94.7 - 98.3%, preferably 95 - 98.1%, preferably 95.5 - 98%, preferably 96 - 97.8%.

[0037] The heating program 4) and the cooling program 5) of the above first-round cycle are carried out in an alternating manner for multiple rounds (i.e., n rounds), and the cumulative or total cycle time (t 循环 ) is 60 - 360 hours (2.5 - 15 days), preferably 66 - 348 hours, preferably 72 - 336 hours (3 - 14 days), preferably 84 - 324 hours, preferably 96 - 312 hours, preferably 108 - 300 hours, preferably 120 - 288 hours, preferably 132 - 276 hours (5.5 - 11.5 days), preferably 144 - 264 hours (6 - 11 days), such as 156, 168, 180, 192, 204, 216, 228, 240, 252 hours. Depending on the size and thickness of the wood, the cycle time (t 循环 ) is sufficient to thoroughly steam the wood.

[0038] Generally, in the 5) cycle cooling program, the water addition amount W of the metering water feeder (5) 加水量4 is 8 - 30 wt% of the water addition amount W of the metering water feeder (5) in the 4) cycle heating program 加水3 , preferably 9 - 27 wt%, preferably 10 - 25 wt%, preferably 11 - 22 wt%, more preferably 12 - 20 wt%, more preferably 13 - 18 wt%.

[0039] 6) When the (certain, i.e., the last round above) cycle cooling program proceeds to the point where the terminal total weight (W3) of the wood to be processed is less than or equal to W2 (kg), the cycle program ends (i.e., the drying furnace stops), and further cooling (i.e., natural cooling) is carried out, and the processed wood is discharged from the drying furnace. Among them, the terminal total weight (W3) is obtained by the weighing sensor and weighing transmitter installed on the support feet of the drying furnace. When the moisture content of the wood in the cooling program drops to 12 - 13 wt%, the metering water feeder stops, and the wood has entered a safe state.

[0040] Among them, from the start of the 4) cycle heating program and 5) cycle cooling program of the first round to the end of the 4) cycle heating program and 5) cycle cooling program of the last round, the water addition amount of the metering water feeder (5) in each program is gradually (i.e., in each round of the cycle) reduced, so that the humidity in the box body of the drying furnace reaches 74 - 84%, preferably 74.5 - 83.5%, preferably 75 - 83%, preferably 75.5 - 82.5% in the 4) cycle heating program of the last round, and the humidity in the box body of the drying furnace reaches 83 - 92%, preferably 83.5 - 91.5%, preferably 84 - 91%, preferably 84.5 - 90.5%, preferably 85 - 90%, preferably 85.5 - 89.5% in the 5) cycle cooling program of the last round.

[0041] In each cycle of the heating process 4) and the cooling process 5), since part of the steam expands due to heat in the heating process and is discharged from the drainage and exhaust device, and the wood releases steam or moisture in the cooling process, the humidity inside the box in the cooling process is actually higher than that in the heating process.

[0042] "Gradually (i.e., in each round of the cycle) reducing the water addition amount of the metering water feeder (5) in each process" means that in the cycle, the overall trend is to gradually reduce the water addition amount of the metering water feeder (5), but it does not exclude the situation of fluctuations in the water addition amount. For example, the water addition amount in individual or a small number of subsequent (heating or cooling) processes may be higher than that in the previous (heating or cooling) processes. Similarly, the humidity inside the box generally shows a decreasing trend, but there will also be fluctuations.

[0043] Preferably, the above step 1) is carried out as follows: 1) Measure the average moisture content Wa 含水率 (wt%) of the wood to be processed, weigh the wood to be processed to obtain the initial total weight W1 (unit: kg) of the wood to be processed, and then preset the target moisture content Wb 目标含水率 (wt%, such as 8 - 12wt% or 9 - 11wt%, e.g., 10%) that the wood to be processed will finally reach after being processed. Then, according to the formula W2 (kg) = [1 - (Wa 含水率 – (Wb 目标含水率 + D))] * W1 (kg), where D is the wood moisture content correction value, and the value range of D is 0.5 - 3.5wt%, preferably 1 - 3wt%, more preferably 1.5 - 2.5wt%, more preferably 1.8, 2.0, 2.2wt%, calculate the target terminal total weight W2 (kg) that the wood to be processed will finally reach after being steam-treated, and set W2 as the shutdown wood weight of the drying furnace. Generally, the target moisture content Wb 目标含水率 is the water content when the fiber activity of the wood after processing is inactivated and in a stable state, such as 8 - 12wt% or 9 - 11wt%, e.g., 10% (sandalwood).

[0044] Generally, (open the furnace door) put the (natural) wood to be processed (e.g., through the wood input side furnace door 103 of the drying furnace) into the box of the drying furnace and close the wood input side furnace door of the drying furnace. Weigh the wood in the box by the weighing sensor and weighing transmitter installed on the supporting feet of the drying furnace to obtain the initial total weight W1 (unit: kg) of the wood to be processed (i.e., subtract the weight of the drying furnace before the wood is input from the weight of the drying furnace after the wood is input), and then determine the target terminal total weight W2 (kg) according to the calculation method described above.

[0045] Load cells and load cell transmitters are installed on each support leg of the evaporation furnace. The latter transmits the data and / or signals of the load cells to a control system (such as a single-chip microcomputer) and a display. The weight of the wood being weighed is displayed on the display.

[0046] In the above 2) initial heating program and 4) cyclic heating program, the microwave generator (201) irradiates microwaves on the water in the water tank (101) to generate steam. Then, the rising steam generated from the water tank (101) and the steam that enters the microwave shielding cover (202) through the steam through-hole (20201) (at the lower part of the microwave shielding cover (202)) under the (suction) action of the air flow circulation device (6) (such as a blower or a fan) (located above the microwave shielding cover (202)) are further heated by microwave radiation and become (expanded) rising superheated steam. Then, the rising superheated steam diffuses outwards through the steam through-hole (20201) at the upper part of the microwave shielding cover (202) into the box body of the evaporation furnace, and then forms a (circulating) flowing steam atmosphere under the (suction and pushing) action of the air flow circulation device (6) (such as a blower or a fan) (located above the microwave shielding cover (202)).

[0047] After the cyclic program ends (i.e., after the last cooling program ends or the last heating program ends), it is further cooled (such as natural cooling after turning off the power of the microwave steam generating device of the evaporation furnace) or slowly cooled (from the T2 temperature, such as 102 °C, or from the T1 temperature, such as 105 °C), and the wood is discharged to obtain the processed wood. In the final step 6), through natural cooling or slow cooling, the purified resin in the wood is fully crystallized. For example, it is further cooled to the ambient temperature (such as 10 - 25 °C, such as 10 °C, 15 °C, 20 °C, 22 °C or 25 °C) to 40 °C, so that the purified resin in the wood is fully crystallized, and a dense resin crystal structure is formed in the fibers (fiber tubes) of the wood.

[0048] During the whole processing process, the condensed water and part of the steam in the evaporation furnace are discharged (such as discharged to the outside of the evaporation furnace) from the bottom of the box body of the evaporation furnace in a forced or restricted manner, so as to maintain a slightly positive pressure in the evaporation furnace (such as a gauge pressure of 1.002 - 1.4 atm, preferably 1.004 - 1.3 atm, such as a slightly positive pressure of 1.005, 1.01 atm, 1.03 atm, 1.05 atm, 1.07 atm, 1.08 atm, 1.1 atm, 1.12 atm, 1.15 atm, 1.2 atm, 1.25 atm).

[0049] The discharge (or emission) in the forced or restricted manner is generated or caused by the drainage and steam discharge device (3) located at the bottom of the evaporation furnace, which (to a certain extent) restricts the discharge or emission of condensed water and steam in the box body.

[0050] Generally, the temperature (T0) of the superheated steam generated by the microwave steam generating device in the microwave shielding cover (202) is 100.5 - 107 °C, preferably 101 - 106.5 °C, preferably 101.5 - 106 °C, preferably 102 - 105.5 °C, particularly preferably 102 - 105 °C, such as 101.5, 102.5, 103 or 104 °C. The superheated steam with temperature (T0) diffuses outward through the steam through-hole (20201) in the upper part of the microwave shielding cover (202) into the box body of the evaporation furnace.

[0051] In the present invention, by precisely controlling the water addition amount (or water addition flow rate) of the metering water feeder (5) in different cyclic heating and cooling procedures, especially by precisely controlling the water addition amount (or water addition flow rate) of the metering water feeder (5) and utilizing the restricting effect of the drainage and steam discharge device (3) located at the bottom of the evaporation furnace (to a certain extent) on the discharge or emission of condensed water and steam in the box body, the appropriate humidity and slightly positive pressure of the steam atmosphere in the box body are precisely controlled. That is, a humidity suitable for wood is maintained in the box body, thereby protecting the safety and stability of the wood (shape stability, preventing internal cracks and external cracking, deformation, etc.) of the wood. At the same time, the time of 4) the cyclic heating procedure and 5) the cyclic cooling procedure is shortened respectively (for example, 30 minutes and 40 minutes), thereby greatly shortening the total time of the entire process (shortened by about 60 - 70%), and greatly saving electric energy. Both the quality and stability of the treated wood are improved, and at the same time, a large amount of energy conservation is achieved.

[0052] Generally, the superheated steam is unsaturated steam with a temperature higher than 100 °C.

[0053] In the cooling procedure, the wood releases heat, and the moisture in the wood runs out in the form of steam. As the heating procedure and the cooling procedure are alternately carried out, the steam in the box body is discharged wave by wave outside the box body of the evaporation furnace.

[0054] Generally, the total time of the initial heating procedure is 6 - 12 hours, preferably 7 - 11 hours, preferably 8 - 10 hours.

[0055] Generally, depending on the thickness and diameter of the wood, the total time of the heating and cooling procedures is 5 days - 10 days. For example, for a wooden board with a thickness of 4 - 5 cm, the total time is 7 - 10 days, and for a wooden board with a thickness of 7 - 8 cm, the time is 10 - 15 days. While the total time of the traditional method is about 40 days.

[0056] The change in humidity inside the box causes the drying of the wood. The wooden boards on the charging car can be spaced apart with spacers, for example, 2 - 3 cm thick.

[0057] During the whole treatment process, the operation of the microwave equipment is uninterrupted and can vary between 1 - 100% of the rated power to extend the service life of the microwave equipment. In addition, the water addition by the metering water feeder is also uninterrupted to ensure that the humidity inside the box is always appropriate, the speed of the wood releasing moisture is more uniform, prevent the wood from dehydrating too fast, and protect the safety and stability of the wood.

[0058] Adjust the water addition amount according to the humidity required by the wood in the furnace body. Continuously add water to protect the safety of the wood (the surface of the wood is always not dry), avoid internal cracks, surface cracks and distortion, and improve the efficiency of wood treatment.

[0059] Regarding the stability of the wood: The wood evenly absorbs heat, the water molecules transfer heat, the wood is heated evenly, the ripening of the fibers is uniform, and the stability of the fibers is improved.

[0060] Preferably, the above-mentioned evaporation furnace (or evaporation furnace system) includes an evaporation furnace box body (1), a microwave steam generating device (2) arranged on one side (such as the right side or the left side) of the box body (1) as the operation side, an air flow circulation device (6) arranged above the inner wall of the box body (1) on the operation side of the box body (1), and a (strip-shaped) drainage and exhaust device (3) arranged on the bottom plate of the box body (1); the microwave generating device (2) includes a microwave through hole (102) opened on the operation side of the box body (1), a microwave generator (201) arranged on the outer wall of the box body (1) outside the microwave through hole (102), an inclined (such as a downward inclination angle of 30-60 degrees, such as 35-55 degrees, or about 40, 45 or 50 degrees) (metal) waveguide plate (203) arranged on the inner wall of the box body (1) above the inner side of the microwave through hole (102), a water tank (101) arranged at the bottom of the inner wall of the operation side of the box body, and a porous microwave shielding cover (202) covering the water tank (101) and the waveguide plate (203) and having a steam through hole (20201); wherein on the inner wall of the operation side of the box body (1), the microwave through hole (102), the microwave generator (201) and the inclined (metal) waveguide plate (203) are divided into a lower first layer (A) and an upper second layer (B). The inclined (metal) waveguide plate (203) of the lower first layer (A) reflects the microwave from the microwave through hole (102), and the microwave radiates downward to vaporize the water in the water tank. The inclined (metal) waveguide plate (203) of the upper second layer (B) is used to further heat (expand) the water vapor rising in the shielding cover (202) into superheated steam. The rising superheated steam diffuses outward through the steam through hole (20201) of the microwave shielding cover (202) under the (suction) action of the air flow circulation device (6) and reaches the atmosphere in the box body for circulation, so as to form a circulating steam flow (in the inner cavity or internal space of the box body) and be used for heating wood.

[0061] The air flow circulation device (6) is located above the porous microwave shielding cover (202).

[0062] One end of the evaporation furnace box body 1) is provided with a feeding and discharging door (103).

[0063] Among them, the volume inside the box body (1) is 3-60 m 3 , preferably 4-55 m 3 , preferably 5-50 m 3 , preferably 6-45 m 3 , preferably 7-40 m 3 , preferably 8-35 m 3 , more preferably 9-30 m 3 . For example, 4, 6, 8, 10, 12, 14, 15, 16, 18 m 3 .

[0064] The length of the box body (1) is 1 - 20 meters, preferably 1.5 - 18 meters, preferably 2 - 15 meters, preferably 2.5 - 12 meters, preferably 3 - 10 meters. The width of the box body (1) is 1.5 - 3.5 meters, preferably 1.8 - 3 meters. The height of the box body (1) is 1.6 - 3.5 meters, preferably 1.7 - 3.2 meters, preferably 1.8 - 3 meters.

[0065] The above-mentioned evaporation furnace further includes (or is equipped with) a water inlet pipe (4) for adding water to the water tank (101) and a metering water adder (5) communicated with the water inlet pipe (4). Preferably, the water adding level point of the water tank is close to the feeding and discharging door (103). Preferably, the metering water adder (5) is a metering pump, such as a medical metering pump.

[0066] The above-mentioned evaporation furnace further includes a plurality of (such as at least 4 or 6) feet (8) equipped with weighing sensors (and weighing transmitters). Preferably, the lower first layer (A) and the upper second layer (B) each further include 2 or 3 or 4 sub-layers of microwave through-holes (102), microwave generators (201) and downwardly inclined (metal) waveguide plates (203). Each sub-layer includes a plurality of microwave through-holes (102) arranged at approximately equal intervals along the horizontal direction or substantially along the horizontal direction, and one microwave generator (201) and one downwardly inclined (metal) waveguide plate (203) corresponding to or matching each microwave through-hole (102). Preferably, the microwave through-holes (102) in one sub-layer are arranged staggeredly in the vertical direction with the microwave through-holes (102) in the adjacent sub-layer. This setting method is beneficial to the flow of air, and at the same time better covers the range or area of microwave radiation. The number of microwave through-holes (102) in each sub-layer is generally 5 - 30, such as 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29.

[0067] The microwave emitted from the microwave generator (201) passes through the microwave through-hole (102) and is reflected by the downwardly inclined (such as an inclination angle of 30 - 60 degrees, such as 35 - 55 degrees, or about 40, 45 or 50 degrees) (metal) waveguide plate and radiates downward to the water and the rising steam in the water tank.

[0068] Of course, due to the loss of moisture caused by the (continuous) discharge of condensate and a part of steam through the drainage and exhaust device (3), water is continuously supplied to the water tank through the water inlet pipe, and the water in the water tank is vaporized by microwave radiation to make up for it.

[0069] Although the steam flow in the drying furnace chamber is a closed cycle, the loss of moisture caused by the continuous discharge of condensate water and a part of the steam in the drying furnace is replenished by continuously supplying water to the water tank and vaporizing the water in the water tank by microwave. Therefore, the steam circulation in the drying furnace is a partial circulation.

[0070] The size or aperture of the steam through-holes of the porous microwave shielding cover (202) should be such that steam can pass through but microwaves cannot. The porous microwave shielding cover (202) is made of metal or alloy, such as a stainless steel cover with mesh holes.

[0071] If microwaves act directly on the wood, relatively serious consequences will occur. Because the internal water molecules and minerals are heated, and the surface is airtight, causing internal cracks in the wood. When there is almost no water vapor in the chamber, the microwaves continue to heat the wood, and the resin inside the wood denatures.

[0072] The present invention uses a drainage and exhaust device (3) to continuously discharge (to the outside of the drying furnace) the condensate water and a part of the steam in the drying furnace from the bottom of the chamber of the drying furnace in a forced or restricted manner.

[0073] The drainage and exhaust device (3) includes a drainage tank (301), a cover plate (or hood plate) (302) on the drainage tank (301), and a drainage and exhaust pipe (303). The drainage tank (301) is arranged on the bottom plate of the drying furnace chamber 1; one side or both sides of the (elongated) cover plate (or hood plate) (302) are respectively provided with a plurality of (slender) through-holes (30201), that is, n, n = 6 - 40, preferably n = 8 - 35, preferably n = 10 - 30, preferably n = 12 - 25, such as 18, 28 or 32. The drainage tank (301) communicates with the internal space of the drying furnace chamber (1) through the through-holes (30201).

[0074] One end (i.e., the front) of the drying furnace chamber (1) is provided with a loading and unloading door (103).

[0075] Preferably, the water inlet pipe (4), the metering water feeder (5), and the drainage and exhaust pipe (303) of the drainage and exhaust device (3) are arranged at the other end (i.e., the back) of the drying furnace chamber (1) opposite to the loading and unloading door (103). Preferably, the (elongated) cover plate (or hood plate) (302) has a Π-shaped cross-section.

[0076] The hole size of the through-holes (30201) on the cover plate (302) and the spacing between adjacent through-holes (30201) (designed) should be such that a slightly positive pressure steam atmosphere is formed in the drying furnace chamber during the process of treating wood with superheated steam in the drying furnace.

[0077] (Micro) through-holes (30201) are rectangular or elongated; in the order away from the drain pipe (303), the hole length of the first through-hole is L1, the hole length of the second through-hole is L2, the hole length of the third through-hole is L3, ……, the hole length of the (n - 2)th through-hole is L(n - 2), the hole length of the (n - 1)th through-hole is L(n - 1), and the hole length of the nth through-hole is Ln; as the distance between the positions of the through-holes on the cover plate (302) and the drain pipe (303) increases, the hole lengths of these through-holes gradually increase; that is; L2 > L1, L3 > L2, ……, L(n - 1) > L(n - 2), Ln > L(n - 1); preferably, L2 is 101% - 150% of L1 (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), L3 is 101% - 150% of L2 (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), and so on, L(n - 1) is 101% - 150% of L(n - 2) (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), and Ln is 101% - 150% of L(n - 1) (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%).

[0078] In the order away from the drain pipe (303), the center distance between the second through-hole and the first through-hole is D1, the center distance between the third through-hole and the second through-hole is D2, ……, the center distance between the (n - 1)th through-hole and the (n - 2)th through-hole is D(n - 2), and the center distance between the nth through-hole and the (n - 1)th through-hole is D(n - 1); as the distance between the positions of the through-holes on the cover plate (302) and the drain pipe (303) increases, the center distance between adjacent through-holes gradually decreases; that is; D2 < D1, ……, D(n - 1) < D(n - 2); preferably, D2 is 60% - 98% of D1 (preferably 70% - 95%, further preferably 80% - 92%), and so on, D(n - 1) is 60% - 95% of D(n - 2) (preferably 70% - 90%, further preferably 80% - 92%).

[0079] The hole length L1 of the first through-hole is 0.5 - 10 cm, preferably 1 - 8 cm, more preferably 1.5 - 5 cm.

[0080] The center distance D1 between the second through-hole and the first through-hole is 20 - 100 cm, preferably 25 - 90 cm, more preferably 30 - 80 cm. For example, 22 cm, 27 cm, 32 cm, 35 cm, 37 cm, 40 cm, 45 cm, 50 cm, 55 cm, 60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 90 cm.

[0081] Generally, the width of the through hole (30201) is 0.5 - 2 cm, preferably 0.7 - 1.5 cm, such as 1 or 1.2 cm. The number n of through holes (30201) on either one or both sides of the cover plate (or the cover board) (302) is respectively, for example, 6 - 35, preferably n = 8 - 30, preferably n = 10 - 25, preferably n = 12 - 20, such as 15, 25 or 32.

[0082] Since steam and condensed water are discharged from a single drain and steam exhaust pipe (303), the drainage and steam exhaust device with the specific structure of the present invention (the gradually changing length of the through hole 30201 and the gradually changing center distance between adjacent holes) is conducive to the uniform distribution of humidity and temperature inside the furnace body. The specific size and spacing of the through holes (30201) are also conducive to controlling the steam discharge rate.

[0083] When closing the loading and unloading door (103) through the hydraulic control system, the sealing effect between the loading and unloading door (103) and the door frame on the box body is achieved through a rubber sealing strip (such as a silicone rubber sealing strip) attached to the door frame.

[0084] In this application, preferably, the outer shape of the drying furnace presents a cuboid box structure, similar to the outer shape of a container or an elongated container. The cuboid drying furnace has a front side (front), a left side, a right side, and a back side (rear side). Generally, the (loading / unloading) furnace door is located on the front side of the box body of the drying furnace (i.e., the wood input side). The microwave steam generating device is arranged on the left or right side of the drying furnace, which is the operating side.

[0085] Generally, the length of the microwave steam generating device (i.e., the length of the porous microwave shielding cover) is approximately 50 - 99% of the (horizontal direction) length of the inner wall on the left or right side, preferably 60 - 97%, preferably 70 - 95%.

[0086] The gas circulation equipment can be multiple blowers or fans (such as moisture - resistant and heat - resistant fans) arranged at approximately the same height or substantially along the horizontal direction (above the upper part of the inner wall of the box body or above the microwave shielding cover).

[0087] The moisture content of the wood to be processed before entering the drying furnace is about 30%. After the above - mentioned drying treatment, the moisture content of the wood is stabilized at about 12%, such as 11 - 13% or 11.5 - 12.5%. Therefore, the drying described in the present invention is not absolute drying to prevent internal and external cracking and distortion of the wood. Additionally, the resin softens, the fibers fully stretch, and at the same time, the fiber activity is eliminated while ensuring the fiber toughness. The stable moisture content is called the moisture content origin (critical point).

[0088] In the heating-up process (i.e., the step of heating), superheated steam infiltrates the fibers and resins inside the wood, improving the thermal conductivity of the wood (facilitating the entry of heat into the interior of the wood) and softening the resins, and forming micro-channels or micropores in the softened resins of the wood, so that during the cooling process, the oil volatiles and inorganic salts contained in the resins of the wood can be extracted by the steam through the micropores (the oil forms an azeotrope with water). Then, as the steam gradually penetrates into the core of the wood, (through-type) micro-channels or micropores are formed throughout the interior of the wood. Through the extraction action of the steam, the oils and inorganic salts are removed, and finally all the resins in the wood are purified, and a dense crystalline and somewhat ductile resin component is formed in the wood. The fully crystallized resin can produce good (gas or moisture) barrier properties in the wood fibers. At the same time, for the wood treated by the drying process, the activity of its fibers has been eliminated, and the water absorption of the wood has decreased significantly (almost to zero). Therefore, the good (gas or moisture) barrier properties of the fully crystallized resin and the elimination of the fiber activity enable the water absorption rate of the wood after treatment to remain stable for a long time (for example, the moisture content remains at 10 - 12%, and most often stably remains at 10%).

[0089] The full crystallization of the purified resin in the wood and the ripening of the fibers (elimination of activity) enable the wood treated by the method of the present invention to have a moisture content change of only about 1% and only surface moisture absorption when experiencing the four seasons. Moreover, in different humidity environments in the south and the north, a moisture content change of about 1% can be maintained when experiencing the four seasons.

[0090] Generally, the power of the microwave steam generator in the heating-up process is set to 80 - 95% of the rated power of the microwave steam generator (for example, 40 - 60 KWa, preferably 45 - 55 KWa, such as 50 KWa), preferably 85 - 92%, preferably 87 - 90%. The power of the microwave steam generator in the cooling process is set to 18 - 32% of the rated power of the microwave steam generator, preferably 20 - 30%, preferably 23 - 27%, such as 25%.

[0091] In 1) the initial heating-up process, the time (t 升 ) required from starting the initial heating-up process by turning on the power of the microwave steam generator until a (circulating) flowing superheated steam atmosphere with a temperature of T1 (not exceeding 106 °C) is formed in the box depends on the weight of the wood placed in the drying furnace. For example, when 3 tons of wood is loaded in the drying furnace, the time (t 升 ) is generally 6 - 8 hours, and when 5 tons of wood is loaded in the drying furnace, the time (t 升 ) is generally 10 - 15 hours.

[0092] Preferably, in the temperature reduction process, it takes 35 - 45 minutes to reduce the temperature by 3 degrees. In the temperature increase process, it takes 25 - 35 minutes to increase the temperature by 3 degrees again.

[0093] In the temperature increase and temperature reduction processes, there is an alternation between the unsaturated steam generated by the expansion of superheated steam and the saturated steam released by the wood.

[0094] The moisture content of the wood to be processed is generally 30%. After one temperature increase and temperature reduction cycle, the moisture content of the wood can be reduced by 2 - 5%. When the moisture content of the wood is reduced to about 15%, it becomes increasingly difficult to remove water from the wood in subsequent temperature increase and temperature reduction cycle processes.

[0095] In the temperature increase process, the water vapor in the microwave shielding cover inside the drying furnace box is heated by the microwave radiation of the second layer and expands (becomes unsaturated steam, that is, superheated steam), so that the condensed water and a part of the steam are discharged from the bottom drainage and exhaust device in a restricted or limited manner, and a slightly positive pressure is formed in the internal space of the box.

[0096] The saturated steam released in the temperature reduction process becomes unsaturated steam in the drying furnace box. The slightly positive pressure atmosphere in the box forces the excess steam to be discharged. At the same time, the wood absorbs a part of the unsaturated steam.

[0097] In the temperature increase process, under humid and hot conditions, water molecules enter the interior of the wood. Due to the heat conduction of the moisture, heat is introduced into the interior of the wood, and it is easy for the wood to penetrate, so that the temperature inside and outside the wood is the same (the temperature inside and outside is consistent). In the temperature reduction process, when the ambient temperature in the box is reduced by about 3 degrees, heat is released from the wood and water molecules evaporate. In addition, in the sealed space in the box, a part of the water vapor condenses into water droplets and is discharged from the drainage and exhaust device on the bottom plate of the box.

[0098] The stability of the wood shape can be judged by sawing the processed wood into boards, sawing the board samples into a comb shape, and observing whether the comb teeth are distorted and whether the spacing between the comb teeth is uniform after being placed in a room temperature environment for 1 year and experiencing four seasons of changes.

[0099] The drying furnace also includes a material cart. Guide rails are laid on the bottom plate inside the drying furnace box. Rollers are provided at the bottom of the material cart. The rollers are arranged in cooperation with the guide rails. The wood to be processed is stacked into a wood stack on the material cart or the wood bracket by using gaskets (such as gaskets with a thickness of 2 - 3 cm).

[0100] Preferably, the drying furnace also includes a weighing system (which includes a weighing sensor and a weighing transmitter). The weighing system (weighing sensor and weighing transmitter) is arranged on the support feet of the drying furnace. Or, the weighing system is arranged at the bottom of the entire drying furnace box.

[0101] Preferably, a humidity detection device, a temperature detection device, and / or a (gas) pressure detection device are provided inside the evaporation furnace box.

[0102] As a preference, the evaporation furnace further includes a drive and control system (9) (arranged on one side outside the box). The drive and control system is connected to the humidity detection device, the temperature detection device, the pressure detection device, the microwave generating device (2), the air flow circulation device (6), the hydraulic control system (10) of the inlet and outlet doors, the first control valve provided on the water inlet pipe (4), the second control valve provided on the drain pipe (303), and the weighing sensor and weighing transmitter installed on the support feet (8). The control system controls the start and stop of the microwave generating device and the air flow circulation device. The control system controls the opening and closing of the inlet and outlet doors. The control system (9) is used to control the opening, closing, and respective opening degrees of the first control valve provided on the water inlet pipe (4) and the second control valve provided on the drain pipe (303).

[0103] Compared with the prior art, the wood drying system of the present invention has the following beneficial technical effects:

[0104] 1. The present invention adjusts the water addition amount of the metering water feeder according to the humidity required by the wood during the heating and cooling processes. In particular, the drainage and steam discharge device (3) located at the bottom of the evaporation furnace is also used to restrict the discharge or expulsion of condensed water and steam in the box to a certain extent, so as to accurately control the appropriate humidity and slightly positive pressure of the steam atmosphere in the box, that is, maintain a humidity suitable for the wood in the box and thus protect the safety and stability of the wood (stable shape, prevent internal cracks and external cracking, deformation, etc.) of the wood. At the same time, when accurately controlling the appropriate humidity of each process, the time of the 4) cyclic heating process and the 5) cyclic cooling process is shortened respectively (for example, 30 minutes and 40 minutes respectively), thereby greatly shortening the total time of the whole process (shortened by about 60 - 70%), saving electric energy. It not only improves the quality and stability of the treated wood, but also achieves a large amount of energy saving.

[0105] 2. Through the synergistic effect of the metering water feeder (5) and the drainage and steam discharge device (3), the water addition amount of the metering water feeder is adjusted according to the humidity required by the wood during the steam treatment process, forming a suitable humidity required for wood treatment in the evaporation furnace and avoiding waste of steam. When there is a lack of water in some places of the water tank, the microwave radiation above these places heats the steam entering the porous microwave shielding cover 202.

[0106] 3. By subjecting natural wood to multi-cycle steam heating by the method of the present invention, it is possible to utilize the heat of steam in the cyclic operation of multiple heating and cooling procedures to soften the resin in the wood successively from the outside to the inside without causing the denaturation of wood fibers (degradation occurs, or the fiber tube structure is damaged) and the degradation and denaturation of the resin in the wood, and form channels and pores that continuously penetrate deep into the wood in the resin, allowing the steam to continuously penetrate deep into the wood. In the cooling procedure, due to the temperature difference between the inside and the outside environment of the wood, the steam inside the wood runs out, and oils and inorganic salts are extracted from the resin, so that the resin of the wood is purified. Then, during the final cooling process, the purified resin is allowed to fully crystallize, thereby forming dense and tough resin crystals in the wood.

[0107] 4. After being treated by the method of the present invention, the activity of the fibers in the wood is eliminated (active groups such as carboxyl and aldehyde groups decompose, and active hydroxyl groups undergo etherification, esterification, etc.), and the fibers are matured.

[0108] 5. Due to the full crystallization of the purified resin in the wood, dense resin crystals are formed in the fibers. At the same time, the activity of the fibers in the wood is eliminated. Therefore, the treated wood has good gloss and very excellent long-term storage stability. Whether placed in different humidity environments in the south or the north and experiencing seasonal changes, its water absorption rate only fluctuates by about 1%. This shows that mainly the surface of the wood absorbs moisture, and the shape of the treated wood does not deform or twist, and the color of the wood hardly changes. The stability of the wood during long-term storage is almost the same in the south and the north of China. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] Figure 1 is a schematic structural diagram of the drying furnace of the present invention;

[0110] Figure 2 is a front view (in the direction of the inlet and outlet door) of the drying furnace of the present invention;

[0111] Figure 3 is a schematic internal structural diagram of the drying furnace of the present invention;

[0112] Figure 4 is a schematic structural diagram of the drainage and steam exhaust device in the drying furnace of the present invention;

[0113] Figure 5 is a schematic structural diagram of the drying furnace of the present invention with microwave through holes and waveguide plates provided on the side wall;

[0114] Figure 6 is a rear view of the drying furnace of the present invention;

[0115] Figure 7 、 8, 9, 10, 11, 12, 13, 14, 15, 16 are the assembly photos of the evaporation furnace.

[0116] Figure 17 are the photos of the samples of Example 1 and Comparative Example 1.

[0117] Figure 18 are the photos of the samples of Example 6 and Comparative Example 4

[0118] Reference numerals:

[0119] 1: Evaporation furnace body; 101: Water tank; 102: Microwave through-hole; 103: Inlet and outlet door; 104: Guide rail; 2: Microwave generating device; 201: Microwave generator; 202: Microwave shielding cover; 20201: Steam through-hole; 203: Waveguide plate; 3: Drainage and exhaust device; 301: Drainage tank; 302: Cover plate; 30201: Through-hole; 303: Drainage and exhaust pipe (abbreviation, drain pipe); 4: Water inlet pipe; 5: Metering water adding device (or metering water replenishing device); 6: Air flow circulation device; 601: Mounting bracket; 602: Steering device; 603: Fan; 7: Material cart; 701: Roller; 8: Legs equipped with load cells and load cell transmitters; 9: Driving and control system; 10: Hydraulic control system (for opening or closing the inlet and outlet door 103). Detailed implementation manners

[0120] The technical solutions of the present invention will be illustrated by way of examples below. The scope claimed by the present invention includes but is not limited to the following examples.

[0121] The structure of the evaporation furnace used is as Figures 1-16 shown. A wood evaporation furnace using a structure similar to an elongated container structure has a wood capacity of 5 cubic meters (5 tons). The moisture content of the wood is measured with a moisture detector and the average value is taken.

[0122] The evaporation furnace includes an evaporation furnace body 1, a microwave steam generating device 2 provided on the right side of the body 1 as the operation side, a drainage and exhaust device 3 provided on the bottom plate of the body 1, and an air flow circulation device 6 provided above the inner wall of the body 1 on the operation side of the body 1; and an inlet and outlet door 103 is provided at one end of the evaporation furnace body 1.

[0123] The microwave steam generating device 2 includes a microwave through-hole 102 opened on the operating side (right side) of the box body 1, a microwave generator 201 provided on the outer wall of the box body 1 outside the microwave through-hole 102, a downwardly inclined waveguide plate 203 provided on the inner wall of the box body 1 above the inner side of the microwave through-hole 102, a water tank 101 provided at the bottom of the inner wall on the operating side, and a porous microwave shielding cover 202 (i.e., a stainless steel cover with mesh holes through which steam can pass but microwaves cannot) covering the water tank 101 and the waveguide plate 203 and having steam through-holes 20201.

[0124] The drainage and exhaust device 3 includes a drainage tank 301 and a cover plate 302 on the drainage tank 301. The drainage tank 301 is provided on the bottom plate of the drying furnace box body 1; the cover plate 302 is provided with a plurality of through-holes 30201; the drainage tank 301 communicates with the internal space of the drying furnace box body 1 through the plurality of through-holes 30201.

[0125] The emission source of the microwave generator 201 communicates with the internal space of the drying furnace box body 1 through the microwave through-hole 102.

[0126] On the inner wall of the operating side of the box body 1, the microwave through-hole 102, the microwave generator 201, and the inclined waveguide plate 203 are divided into a lower first level A and an upper second level B. The inclined waveguide plate 203 at the lower first level A reflects the microwaves entering through the microwave through-hole 102, so that the microwaves change direction and radiate downward to vaporize the water in the water tank. The inclined waveguide plate 203 at the upper second level B reflects the microwaves entering through the microwave through-hole 102, so that the microwaves change direction and radiate downward to further heat and expand the water vapor rising in the shielding cover 202 into superheated steam. The rising superheated steam enters the atmosphere in the box body through the steam through-holes 20201 of the microwave shielding cover 202 under the suction of the air flow circulation device 6 for circulation, so as to form a circulating steam flow in the internal space of the box body and be used for heating wood.

[0127] The lower first level A and the upper second level B each further include 3 sub-levels of microwave through-holes 102, microwave generators 201, and downwardly inclined stainless steel waveguide plates 203. Each sub-level includes a plurality of microwave through-holes 102 arranged at approximately equal intervals substantially along the horizontal direction and a microwave generator 201 and a downwardly inclined stainless steel waveguide plate 203 corresponding to or matching each microwave through-hole 102. The microwave through-holes 102 in one sub-level are staggered from the microwave through-holes 102 in the adjacent sub-level in the vertical direction. This setting method is beneficial to the flow of air, and at the same time better covers the range or area of microwave radiation. The number of microwave through-holes 102 in each sub-level is 18.

[0128] The drainage and exhaust device 3 includes a drainage tank 301 and a cover plate 302 on the drainage tank 301. The drainage tank 301 is arranged on the bottom plate of the drying furnace body 1; a cover plate 302 is provided at the top of the drainage tank 301, and a plurality of through holes 30201 are provided on the cover plate 302; the drainage tank 301 is communicated with the internal space of the drying furnace body 1 through the through holes 30201. The hole size of the through holes 30201 on the cover plate 302 and the distance between adjacent through holes 30201 are designed in the following described manner, so as to form a slightly positive pressure steam atmosphere in the drying furnace body during the process of treating wood with superheated steam in the drying furnace.

[0129] The above-mentioned drainage and exhaust device 3 can enable the condensed water and a part of the steam in the drying furnace to be discharged from the bottom of the drying furnace body (continuously, in waves) to the outside of the drying furnace in a forced or restricted manner.

[0130] The air flow circulation device 6 is located above the porous microwave shielding cover 202.

[0131] The number (m) of the air flow circulation devices 6 (fans) in the drying furnace body 1 is 4. The power of a single microwave unit can vary between 250W and 1KW. Correspondingly, the power of 10 microwave units can vary between 2.5KW and 10KW.

[0132] The above-mentioned drying furnace further includes a water inlet pipe 4 for adding water to the water tank 101 and a metering water feeder 5 communicated with the water inlet pipe 4. Preferably, the water adding position of the water tank is close to the feeding and discharging door 103. Preferably, the metering water feeder 5 is a metering pump, such as a medical metering pump.

[0133] The above-mentioned drying furnace further includes a plurality of (such as at least 4 or 6) feet 8 equipped with weighing sensors (and weighing transmitters).

[0134] The drying furnace further includes a water inlet pipe 4 and a drainage and exhaust pipe (abbreviated as drainage pipe) 303; the water inlet pipe 4 is communicated with the water tank 101; a first control valve is provided on the water inlet pipe; the drainage pipe 303 is communicated with one end of the drainage tank 301; a second control valve is provided on the drainage pipe 303.

[0135] There are 12 through holes 30201 respectively on both sides of the cover plate 302. The through holes 30201 are of rectangular structure or long strip structure. The through hole on the cover plate 302 close to the drainage pipe 303 is the first through hole (the end of the drying furnace close to the drainage pipe), and as the distance from the drainage pipe 303 increases (that is, gradually away from the direction of the drainage pipe), the through holes on the cover plate 302 are successively the second through hole, the third through hole,..., the tenth through hole, the eleventh through hole, and the twelfth through hole (the end close to the feeding and discharging door 103 of the drying furnace).

[0136] In the order away from the drain pipe 303, on either side of the cover plate 302, the aperture length of the first through-hole is L1, the aperture length of the second through-hole is L2, the aperture length of the third through-hole is L3, ……, the aperture length of the tenth through-hole is L10, the aperture length of the eleventh through-hole is L11, and the aperture length of the twelfth through-hole is L12. As the distance between the through-hole position on the cover plate 302 and the drain pipe 303 increases (i.e., in the order away from the drain pipe 303), the aperture length of the through-hole gradually increases; that is, L2 > L1, L3 > L2, ……, L11 > L10, L12 > L11. The aperture length (hole length) L1 of the first through-hole is 2 cm, and the aperture length (hole length) L12 of the twelfth through-hole is 3 cm. The width of all through-holes is 1.2 cm.

[0137] In the order away from the drain pipe 303, the center distance between the second through-hole and the first through-hole is D1, the center distance between the third through-hole and the second through-hole is D2, ……, the center distance between the eleventh through-hole and the tenth through-hole is D10, and the center distance between the twelfth through-hole and the eleventh through-hole is D11; as the distance between the through-hole position on the cover plate 302 and the drain pipe 303 increases (i.e., in the order away from the drain pipe 303), the center distance length between adjacent through-holes gradually decreases; that is, D2 < D1, ……, D11 < D10. The center distance D1 between the second through-hole and the first through-hole is 52 cm, and the center distance D11 between the twelfth through-hole and the eleventh through-hole is 18 cm.

[0138] Figure 7 and Figure 8 are on-site assembly photos of the microwave through-holes 102 and the waveguide plate (203) for microwave reflection on the inner wall of the operation side (right side) of the evaporation furnace box body (1).

[0139] Figure 9 is a panoramic photo of the wood drying system (evaporation furnace) being assembled. The furnace door of the evaporation furnace has not been installed yet, and the far end is the water inlet and outlet (drainage) end.

[0140] Figure 10It is a photo of the inner wall of the box on the right side of the evaporation furnace. The bottom of the inner wall is a water tank 101. On the inner wall of the operation side (right side) of the box 1, the microwave through-holes 102 (the corresponding or matching microwave generator 201 and the inclined metal waveguide plate 203) are divided into the lower first layer A and the upper second layer B. The lower first layer A and the upper second layer B each further include 3 sub-layers of microwave through-holes 102, microwave generators 201, and downward-inclined (metal) waveguide plates 203. Each sub-layer includes a plurality of microwave through-holes 102 arranged at approximately equal intervals along the horizontal direction or substantially along the horizontal direction, and one microwave generator 201 and one downward-inclined (metal) waveguide plate 203 corresponding to or matching each microwave through-hole 102. The microwave through-holes 102 in one sub-layer are staggered from the microwave through-holes 102 in the adjacent (upper or lower) sub-layer in the vertical direction. This setting method is beneficial to the flow of air, and at the same time better covers the range or area of microwave radiation.

[0141] Figures 11-16 It is a photo of the installed evaporation furnace device.

[0142] In this application, the water addition amount of the metering water adder refers to the water addition amount per unit time, or the water addition flow rate, kg water / hour.

[0143] For example, control the humidity in the box according to the moisture content of the wood, as shown in the following table:

[0144] Wood moisture content % Range of humidity inside the box 45％ 97-99％ 40％ 96-98％ 35％ 95-97％ 30％ 93-96％ 25％ 90-95％ 20％ 85-92％ 15％ 80-90％ 10％ 75-87％

[0145] Generally, the higher the moisture content of the wood, the higher the humidity in the box. The humidity in the box mainly comes from: 1) the water output rate of the wood. The higher the moisture content (wood density) of the wood, the higher the water output rate; 2) adjust the water addition amount (i.e., the water addition flow rate) of the metering water adder according to the change of the required humidity in the box.

[0146] Example 1

[0147] The process of treating wood with superheated steam in the evaporation furnace includes:

[0148] 1) Weigh the evaporation furnace without loaded wood by the load cells and load cell transmitters installed on the 4 feet at the bottom of the box, and adjust the zero point (adjust the weight of the obtained evaporation furnace to zero). Use a moisture monitor to measure the moisture content (i.e., water content) of the boards of about 4.5 tons of East African rosewood with a thickness of 4.5 cm and a length of 6 m to be treated, and take the average value to obtain the average moisture content Wa of the wood 含水率 It is 33.1 wt%.

[0149] Open the stainless-steel furnace door (i.e., the loading and unloading door) 103 of the drying furnace 1, put about 4.5 tons of East African rosewood boards to be processed, whose moisture content has been detected, into the material cart 7 in the stainless-steel box body 1 of the drying furnace through the wood input side furnace door opening 103 of the drying furnace, and close the wood input side furnace door 103 of the drying furnace. Weigh the drying furnace with the loaded wood by the load cells and weighing transmitters installed on the 4 feet at the bottom of the box body, and obtain the initial total weight W1 of the boards to be processed as 4549.3 kg. Set the target moisture content Wb that the wood to be processed finally reaches after being processed. 目标含水量 is 10 wt%. The wood moisture content correction value D is taken as 2 wt%. According to the formula W2 (kg) = [1 - (Wa 含水率 – (Wb 目标含水率 + D))] * W1 (kg), calculate the target terminal total weight W2 (kg) that the wood to be processed finally reaches after being steam-treated as 3589.4 kg, and set this W2 as the shutdown wood weight of the drying furnace.

[0150] 2) Initial heating-up procedure: Water is added to the water tank (101) of the microwave steam generating device (2) disposed within the drying furnace chamber through the metering water feeder (5). The water addition (flow) rate of the metering water feeder 5 is adjusted at any time according to the target humidity range of 92 - 96% within the chamber (for example, at a water addition flow rate of approximately 7 - 8 kg of water per hour, aiming to obtain a humidity of 92 - 96%). The power supply of the microwave generator 201 of the microwave steam generating device 2 is turned on and its power range is set to 36 KWa (kilowatts) (rated power is 52 KWa, with a total of 52 microwave units) before reaching the target humidity, and the power varies around 24 KW (for example, 20 - 28 KW) after reaching the target humidity. The microwave generator (201) performs microwave radiation on the water in the water tank (101) below the microwave shield (202) having steam through holes (20201) to generate steam. The steam further expands into superheated steam (temperature T0 is approximately 105.5 - 106.5 °C) under microwave radiation during its upward movement within the microwave shield (202). The superheated steam diffuses into the chamber and circulates under the suction and pushing action of the fan (airflow circulation device 6) through the steam through holes 20201. Starting from room temperature of 21 °C, with a heating-up rate of 30 °C per hour (after a heating-up time of approximately 2.8 hours), a circulating superheated steam atmosphere with a temperature of T1 (105 °C) is gradually formed within the chamber, and the wood within the chamber is steam-heated using the circulating superheated steam atmosphere. Among them, the steam heating time (t1) (holding time) at temperature T1 (105 °C) is 6 hours. During the circulation process, the steam entering the microwave shield (202) from the environment within the chamber through the steam through holes (20201) at the lower part of the microwave shield (202) mixes with the rising steam generated from the water tank 101, is heated again by microwave radiation (reaching temperature T0), expands and rises, and diffuses into the atmosphere within the chamber through the steam through holes (20201) at the upper part of the microwave shield (202) to continue circulating.

[0151] 3) Initial cooling-down procedure: The power of the microwave generator 201 of the microwave steam generating device 2 is adjusted down to 6 KWa, and the water addition (flow) rate of the metering water feeder is adjusted at any time according to the target humidity range of 95 - 98% within the chamber (for example, at a water addition flow rate of approximately 1 - 1.5 kg of water per hour). The temperature of the circulating superheated steam atmosphere within the drying furnace chamber is reduced from temperature T1 to temperature T2 of 102 °C over 40 minutes, so as to allow the higher-temperature steam or moisture (which already contains the oil volatiles extracted from the wood resin) inside the wood to gradually escape due to the temperature difference between the inside and outside of the wood. The saturated steam or moisture escaping from the inside of the wood contains the oil volatiles extracted from the wood resin and trace or trace amounts of inorganic salts.

[0152] 4) Circulation heating program in the first round: By increasing the (power supply) power or microwave frequency of the microwave generator 201 of the microwave steam generating device 2, adjust the water addition (flow) rate of the metering water feeder according to the target humidity range of 92 - 96% inside the box (for example, adjust the water addition flow rate to approximately 7 - 8 kg of water per hour, aiming to obtain a humidity of 92 - 96%). After 25 minutes, increase the temperature of the circulating superheated steam atmosphere inside the drying furnace box from temperature T2 (102 °C) to temperature T1 (105 °C) to steam-heat the wood inside the box.

[0153] 5) Circulation cooling program: By reducing the (power supply) power of the microwave generator 201 of the microwave steam generating device 2 to 10 KWa (20% of the rated power), adjust the water addition (flow) rate of the metering water feeder according to the target humidity range of 95 - 98% inside the box (for example, adjust the water addition flow rate to approximately 1 - 1.5 kg of water per hour) to add water. After 40 minutes, reduce the temperature of the circulating superheated steam atmosphere inside the drying furnace box from temperature T1 (105 °C) to temperature T2 (102 °C).

[0154] The above heating program 4) and cooling program 5) of the first round are carried out in an alternating manner for multiple rounds of circulation, and the cumulative or total circulation time (t 循环 ) is 144 hours (6 days). Gradually reduce the water addition amount of the metering water feeder (5) in each program for each round, so that the humidity inside the drying furnace box reaches 75.5 - 82.5% in the 4) circulation heating program of the last round, and the humidity inside the drying furnace box reaches 85.5 - 89% in the 5) circulation cooling program of the last round.

[0155] 6) In the above last 5) circulation cooling program, the terminal total weight (W3) of the wood to be processed measured by the support leg weighing system is less than W2 (kg) (i.e., 3589.4 kg), the drying furnace stops, and further natural cooling occurs, and the processed wood is discharged from the drying furnace. After being cooled to room temperature in the workshop environment, the moisture content of the wooden board is measured to be 10.02%, reaching the target value.

[0156] During the entire processing process, the condensate water and a part of the steam inside the drying furnace (especially in the heating program) are discharged from the drainage and exhaust device 3 on the bottom plate of the drying furnace box in waves to the outside of the drying furnace. In the heating program, the air pressure inside the drying furnace is slightly positive pressure (1.011 atm).

[0157] Take a wooden board sample and measure the weight of the sample. Place it indoors for 3 years and measure the weight of the sample every month. It is found that the maximum change in the weight of the wooden board sample between the humid and hot summer and the dry spring is only 0.8%, that is, only surface moisture absorption occurs. After 3 years of long-term storage, wet the sample with water and observe the color of the wooden board. As Figure 17 shown in A (right side) of Figure 17 , the surface of the wooden board has good gloss (bright red). The sufficient crystallization of wood resin is beneficial to improving the gloss of wood.

[0158] Comparative Example 1

[0159] Repeat Example 1, except that in 1) the initial heating program, by further slightly increasing the (power supply) power of the microwave generator 201 of the microwave steam generating device 2 to 50 KWa (rated power is 52 KWa), starting from room temperature 21 °C, at a heating rate of 56 °C / hour (after a heating time of about 1.5 hours), gradually form a circulating flow of superheated steam atmosphere with a temperature of T1 (105 °C) in the box.

[0160] Take a wooden board sample. After placing it indoors for 3 years, wet the sample with water and observe the color of the wooden board. As Figure 17 shown in B (left side) of Figure 17 , the gloss of the surface of the wooden board is poor and the color is dull (biased towards black). This shows that in 1) the initial heating program, due to the overly rapid heating rate, the outer resin of the wood hardens prematurely, so that a large number of through micro-channels or pores cannot be formed in the wood resin from the core of the wood to the surface layer of the wood, and then the oil volatiles and inorganic salts in the resin are not completely extracted, and the resin is not fully purified and thus not fully crystallized. After placing it indoors for a long time, the long-term storage stability of the wood is observed to be poor.

[0161] Comparative Example 2

[0162] Repeat Example 1, except that T1 is set to 108 °C and T2 is set to 105 °C. Starting from room temperature 21 °C, at a heating rate of 6 °C / hour, gradually form a circulating flow of superheated steam atmosphere with a temperature of T1 (108 °C) in the box.

[0163] Take a wooden board sample. After placing it indoors for 3 years, wet the sample with water and observe the color of the wooden board sample. It is found that the gloss of the surface of the wooden board is poor and the color is dull (biased towards black).

[0164] This shows that the temperature of steam heating is too high (108 °C), resulting in the denaturation of the resin and fibers in the wood, and the long-term storage stability is poor.

[0165] Comparative Example 3

[0166] Repeat Example 1, except that in 1) the initial temperature increase procedure, after the temperature of the steam atmosphere in the box is gradually increased to 105°C, the steam heating time (t1) (holding time) at temperature T1 (105°C) is 40 minutes.

[0167] After taking a wooden board sample and placing it indoors for 3 years, wet the sample with water and observe the color of the wooden board sample. It is found that the glossiness is poor and the color is slightly darker (showing black) in the area of the core of the round wood on the surface of the wooden board. Additionally, the glossiness is good in the area other than the core on the surface of the wooden board.

[0168] This shows that in 1) the initial temperature increase procedure, a short holding time at temperature T1 (105°C) is not sufficient for the resin in the core of the round wood to reach (almost) the same degree of being wetted by steam as the resin in the outer layer of the round wood. Therefore, when the resin in the core of the wood is not sufficiently wetted by steam, a through-channel microchannel cannot be established between the resin in the core of the wood and the resin in the outer layer of the wood, and the resin in the core of the wood is not sufficiently purified.

[0169] Example 2

[0170] Repeat Example 1, except that T1 is set to 106°C and T2 is set to 103°C. In 1) the initial temperature increase procedure, after the temperature of the steam atmosphere in the box is gradually increased to 106°C, the steam heating time (t1) (holding time) at temperature T1 (106°C) is 3 hours.

[0171] After taking a wooden board sample and placing it indoors for 3 years, wet the sample with water and observe that the surface of the wooden board sample has good glossiness (bright red).

[0172] Example 3

[0173] Repeat Example 1, except that T1 is set to 104°C and T2 is set to 101°C. In 1) the initial temperature increase procedure, after the temperature of the steam atmosphere in the box is gradually increased to 104°C, the steam heating time (t1) (holding time) at temperature T1 (104°C) is 12 hours.

[0174] After taking a wooden board sample and placing it indoors for 3 years, wet the sample with water and observe that the surface of the wooden board sample has good glossiness (bright red).

[0175] Example 4

[0176] Repeat Example 1, except that T1 is set to 103°C and T2 is set to 100°C.

[0177] The surface of the wooden board sample has good glossiness (bright red).

[0178] Example 5

[0179] Repeat Example 1, except that T1 is set to 102 °C and T2 is set to 99 °C.

[0180] The surface of the wooden board sample has good gloss (bright red).

[0181] Example 6

[0182] Repeat Example 1, except that the wood to be treated is a wooden board of Abelia biflora about 4 tons, with a thickness of 4.5 cm and a length of 6 m.

[0183] Take a wooden board sample and measure the sample weight. Place it indoors for 3 years and measure the weight of the sample every month. It is found that the maximum change in the weight of the wooden board sample between the humid and hot summer and the dry spring is only 1.0%, that is, only surface moisture absorption occurs. After 3 years of long-term storage, observe the color of the wooden board. As Figure 18 shown in C (right side), the surface of the wooden board has good gloss (bright red) and no cracks. This shows that after treatment, the oils and inorganic salts in the wood are fully removed, the resin is purified, fully crystallized to form dense resin crystals, the purified resin has a certain toughness, and in addition, the fibers are fully extended, and at the same time, the activity of the fibers is eliminated, all of which are beneficial to improving the long-term storage stability (no deformation) of the treated wood.

[0184] Comparative Example 4

[0185] Repeat Example 4, except that T1 is set to 99.8 °C and T2 is set to 96.8 °C.

[0186] Take a wooden board sample and measure the sample weight. Place it indoors for 3 years and measure the weight of the sample every month. It is found that the maximum change in the weight of the wooden board sample between the humid and hot summer and the dry spring is 4.1%, and the water absorption rate of the wooden board is still relatively high. After 3 years of long-term storage, observe the color of the wooden board. As Figure 18 shown in D (left side), the color of the surface of the wooden board turns white and cracks appear. This shows that after treatment, the oils and inorganic salts in the wood are not fully removed, the resin inside the wood may be brittle, the fibers are not fully extended (there is internal stress), and the internal stress and the brittleness of the resin cause cracks to occur in the wood during long-term storage.

[0187] Comparative Example 5

[0188] Repeat Example 1, except that instead of using a metering water feeder (metering pump), sufficient water is supplied to the water tank 101 through the water inlet pipe 4 by tap water, and the water tank 101 is kept full of water throughout the process. However, it is found that in order to maintain the normal progress of the whole process, a microwave generator with a power of 45 KW is required during the heating process, and a microwave generator with a power of 9 KW is required during the cooling process. This shows that if the water addition is not accurately metered according to the humidity required by the wood during the treatment process, even if there is surplus steam generated in the box, the surplus steam is discharged from the drainage and exhaust device, resulting in steam waste and thus waste of electric energy.

[0189] In addition, since the humidity required by the wood during the heating and cooling processes is not accurately controlled, the quality and stability of the treated wood are still affected.

Claims

1. A method for treating wood with superheated steam in a drying furnace to improve the stability of the wood, the method comprising: 1) Set the weight of the wood at shutdown: Based on the initial total weight W1 (unit: kg) of the wood to be processed, its average moisture content Wa 含水率 (wt%), and the target moisture content Wb 目标含水率 that it finally reaches after being processed, to determine the target terminal total weight W2 (unit: kg) that the wood to be processed finally reaches after being steam-treated, and then set W2 as the weight of the wood at shutdown; 2) Initial heating procedure: Water is added to the water tank (101) of the microwave steam generating device (2) disposed in the box body of the drying furnace through a metering water feeder (5). The microwave generator (201) is turned on to perform microwave radiation on the water in the water tank (101) below the microwave shielding cover (202) having steam through holes (20201) to generate steam. The steam circulates in the box body under the action of the air flow circulation device (6), so that the temperature of the circulating steam atmosphere in the box body gradually rises to the set temperature T1, and a circulating superheated steam atmosphere with a temperature of T1 is formed in the box body, and the wood placed in the box body is steam-heated by using the circulating superheated steam atmosphere; Wherein the steam heating time (t1) at the temperature T1 is 2 - 15 hours, preferably 3 - 14 hours, preferably 4 - 13 hours, preferably 5 - 12 hours, preferably 6 - 11 hours, preferably 7 - 10 hours, preferably 8 - 9 hours, such as 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5 hours; Preferably, the amount of water added by the metering water feeder (5) (W 加水1 , by weight) should be such that the humidity in the chamber of the drying furnace reaches 90 - 98%, preferably 90.5 - 97.7%, preferably 91 - 97.5%, preferably 91.5 - 97.3%, preferably 92 - 97%, preferably 92.3 - 96.8%, more preferably 92.5 - 96.5%; Wherein T1 is or is set in the range of 100 - 106 °C, preferably 100.1 - 105.9 °C, preferably 100.2 - 105.8 °C, preferably 100.3 - 105.7 °C, preferably 100.4 - 105.6 °C, preferably 100.5 - 105.5 °C, preferably 100.6 - 105.3 °C, preferably 100.7 - 105.2 °C, preferably 101 - 105 °C, preferably 101.1 - 104.9 °C, such as 101.4 °C, 101.5 °C, 101.6 °C, 101.7 °C, 101.8 °C, 101.9 °C, 102 °C, 102.1 °C, 102.2 °C, 102.3 °C, 102.4 °C, 102.5 °C, 102.6 °C, 102.7 °C, 102.8 °C, 102.9 °C, 103 °C, 103.1 °C, 103.2 °C, 103.3 °C, 103.4 °C, 103.5 °C, 103.6 °C, 103.7 °C, 103.8 °C, 103.9 °C, 104 °C, 104.1 °C, 104.2 °C, 104.3 °C, 104.4 °C, 104.5 °C, 104.6 °C, 104.7 °C, 104.8 °C; 3) Initial cooling procedure: By reducing the power or microwave frequency of the microwave generator (201) of the microwave steam generating device (2), the temperature of the circulating superheated steam atmosphere in the box body of the drying furnace is reduced from the temperature T1 to the temperature T2 after a period of time (t2), so as to allow the higher temperature steam or moisture inside the wood to gradually escape by utilizing the temperature difference between the inside and the outside environment of the wood; Among them, the time (t2) is 15 - 80 minutes, preferably 18 - 70 minutes, preferably 20 - 60 minutes, preferably 25 - 55 minutes, preferably 30 - 50 minutes, preferably 35 - 45 minutes, preferably 37 - 43 minutes, for example 40 minutes; Preferably, the amount of water added by the metering water adder (5) (W 加水量2 , by weight) and the amount of water released from the wood should be such that the humidity in the chamber of the drying furnace reaches 94 - 99.5%, preferably 94.3 - 99.3%, preferably 94.5 - 99%, preferably 94.7 - 98.7%, preferably 94.5 - 98.5%, preferably 94.7 - 98.3%, preferably 95 - 98.1%, preferably 95.5 - 98%; Among them, T2 is or is set in the range of 97 - 103 °C, preferably 97.1 - 102.9 °C, preferably 97.2 - 102.8 °C, preferably 97.3 - 102.7 °C, preferably 97.4 - 102.6 °C, preferably 97.5 - 102.5 °C, preferably 97.6 - 102.3 °C, preferably 97.7 - 102.2 °C, preferably 98 - 102 °C, preferably 98.1 - 101.9 °C, for example 98.4 °C, 98.5 °C, 98.6 °C, 98.7 °C, 98.8 °C, 98.9 °C, 99 °C, 99.1 °C, 99.2 °C, 99.3 °C, 99.4 °C, 99.5 °C, 99.6 °C, 99.7 °C, 99.8 °C, 99.9 °C, 100 °C, 100.1 °C, 100.2 °C, 100.3 °C, 100.4 °C, 100.5 °C, 100.6 °C, 100.7 °C, 100.8 °C, 100.9 °C, 101 °C, 101.1 °C, 101.2 °C, 101.3 °C, 101.4 °C, 101.5 °C, 101.6 °C, 101.7 °C, 101.8 °C; Among them, the set temperature difference ΔT = T1 - T2 is 2 - 4 °C, preferably 2.2 - 3.8 °C, preferably 2.4 - 3.6 °C, preferably 2.5 - 3.5 °C, preferably 2.7 - 3.3 °C, preferably 2.8 - 3.2 °C, preferably 2.9 - 3.1 °C, most preferably 3 °C; 4) The cyclic temperature increase program in the first round: By increasing the power or microwave frequency of the microwave generator (201) of the microwave steam generating device (2), after a period of time (t3), the temperature of the circulating steam atmosphere in the box of the drying furnace is increased from the T2 temperature to the T1 temperature, so as to perform steam heating on the wood in the box; Among them, the time (t3) is 10 - 70 minutes, preferably 12 - 60 minutes, preferably 13 - 50 minutes, preferably 15 - 45 minutes, preferably 20 - 40 minutes, preferably 20 - 30 minutes or 25 - 35 minutes, for example 30 minutes; Preferably, the amount of water added by the metering water feeder (5) (W 加水3 , by weight) should be such that the humidity in the box body of the drying furnace reaches 90 - 98%, preferably 90.2 - 97.8%, preferably 90.5 - 97.7%, preferably 91 - 97.5%, preferably 91.5 - 97.3%, preferably 92 - 97%, preferably 92.3 - 96.8%, more preferably 92.5 - 96.5%; 5) The cyclic temperature decrease program in the first round: By decreasing the power or microwave frequency of the microwave generator (201) of the microwave steam generating device (2), after a period of time (t4), the temperature of the circulating steam atmosphere in the box of the drying furnace is decreased from the T1 temperature to the T2 temperature; Among them, the time (t4) is 15 - 90 minutes, preferably 18 - 80 minutes, 20 - 70 minutes, preferably 25 - 65 minutes, preferably 30 - 60 minutes, preferably 35 - 55 minutes, preferably 40 - 50 minutes; Preferably, the amount of water added by the metering water adder (5) (W 加水量2 , by weight) and the amount of water released from the wood should be such that the humidity in the chamber of the evaporation furnace reaches 94-99.5%, preferably 94.2-99.4%, preferably 94.3-99.3%, preferably 94.5-99%, preferably 94.7-98.7%, preferably 94.5-98.5%, preferably 94.7-98.3%, preferably 95-98.1%, preferably 95.5-98%; The heating process 4) and the cooling process 5) of the above first-round cycle are carried out in multiple rounds in an alternating manner, and the cumulative cycle time (t 循环 ) is 60 - 360 hours (2.5 - 15 days), preferably 66 - 348 hours, preferably 72 - 336 hours (3 - 14 days), preferably 84 - 324 hours, preferably 96 - 312 hours, preferably 108 - 300 hours, preferably 120 - 288 hours, preferably 132 - 276 hours (5.5 - 11.5 days), preferably 144 - 264 hours (6 - 11 days), such as 156, 168, 180, 192, 204, 216, 228, 240, 252 hours; 6) When the last cyclic temperature decrease program above reaches that the terminal total weight (W3) of the wood to be processed is less than or equal to W2 (kg), the cyclic program ends, and further cooling is carried out, and the processed wood is discharged from the drying furnace; Among them, starting from the 4) cycle heating program and 5) cycle cooling program in the first round of cycles to the end of the 4) cycle heating program and 5) cycle cooling program in the last round of cycles, the water addition amount of the metering water feeder (5) in each program is gradually reduced, so that the humidity in the box body of the drying furnace reaches 74-84%, preferably 74.5-83.5%, preferably 75-83%, preferably 75.5-82.5% in the 4) cycle heating program of the last round of cycles, and the humidity in the box body of the drying furnace reaches 83-92%, preferably 83.5-91.5%, preferably 84-91%, preferably 84.5-90.5%, preferably 85-90%, preferably 85.5-89.5% in the 5) cycle cooling program of the last round of cycles.

2. The method according to claim 1, characterized in that: Among them, During the whole treatment process, the condensed water and a part of the steam in the drying furnace are discharged from the drain and steam discharge device (2) at the bottom of the box body of the drying furnace in a forced or restricted manner; for example, in order to maintain a slightly positive pressure in the drying furnace, preferably, the gauge pressure is 1.001-1.4 atm, preferably 1.004-1.3 atm, such as a slightly positive pressure of 1.005, 1.01 atm, 1.03 atm, 1.05 atm, 1.07 atm, 1.08 atm, 1.1 atm, 1.12 atm, 1.15 atm, 1.2 atm, 1.25 atm; and / or The above step 1) is carried out as follows: 1) Measure the average moisture content Wa 含水率 (wt%) of the wood to be processed, weigh the wood to be processed to obtain the initial total weight W1 (unit: kg) of the wood to be processed, and then preset the target moisture content Wb 目标含水率 (wt%) that the wood to be processed will finally reach after being processed. Then, according to the formula W2 (kg) = [1 - (Wa 含水率 – (Wb 目标含水率 + D))]*W1 (kg), where D is the wood moisture content correction value, and the value range of D is 0.5 - 3.5 wt%, preferably 1 - 3 wt%, more preferably 1.5 - 2.5 wt%, and more preferably 1.8, 2.0, 2.2 wt%, calculate the target terminal total weight W2 (kg) that the wood to be processed will finally reach after being steam-treated, and set W2 as the shutdown wood weight of the drying furnace; where the target moisture content Wb 目标含水率 is 8 - 12 wt% or 9 - 11 wt%, such as 10%; and / or A weighing sensor and a weighing transmitter are installed on each support leg of the drying furnace, and the weighing transmitter transmits the data and / or signals of the weighing sensor to the control system and the display, and the weighed wood weight is displayed on the display; and / or In the above 2) initial heating program and 4) cycle heating program, the microwave generator (201) performs microwave radiation on the water in the water tank (101) to generate steam. Then, the rising steam generated from the water tank and the steam that enters the microwave shielding cover (202) through the steam through hole (20201) at the lower part of the microwave shielding cover (202) under the action of the air flow circulation device (6) (such as a blower or a fan) in the box body are further heated by microwave radiation to become rising superheated steam. Then, the rising superheated steam diffuses outwards through the steam through hole (20201) at the upper part of the microwave shielding cover (202) into the box body of the drying furnace, and then a circulating steam atmosphere is formed under the action of the air flow circulation device (6) (such as a blower or a fan).

3. The method according to claim 1 or 2, wherein, The microwave emitted from the microwave generator (201) passes through the microwave through hole (102) and enters the box body and is reflected by the waveguide plate inclined downward (for example, the inclination angle is 30-60 degrees, such as 35-55 degrees, or about 40, 45 or 50 degrees), and the microwave changes direction and radiates downward to the water and the rising steam in the water tank (101); and / or The loss of moisture caused by the discharge of condensate and a part of the steam through the drainage and exhaust device (3) is replenished by supplying water to the water tank through the water inlet pipe and vaporizing the water in the water tank by microwave radiation of the water in the water tank; and / or Measure the water addition amount W of the water addition device (5) in the 5) cyclic cooling program 加水量4 It is to measure the water addition amount W of the water addition device (5) in the 4) cyclic heating program 加水量3 is 8-30 wt%, preferably 9-27 wt%, preferably 10-25 wt%, preferably 11-22 wt%, more preferably 12-20 wt%, and even more preferably 13-18 wt%.

4. A wood drying furnace or a drying furnace for the method according to any one of claims 1-3, the drying furnace comprising: A drying furnace body (1), a microwave steam generating device (2) provided on one side of the body (1) as the operation side, an air flow circulation device (6) provided above the inner wall of the body (1) on the operation side of the body (1), and a drainage and exhaust device (3) provided on the bottom plate of the body (1); The microwave generating device (2) includes a microwave through hole (102) opened on the operation side of the body (1), a microwave generator (201) provided on the outer wall of the body (1) outside the microwave through hole (102), a waveguide plate (203) inclined downward (for example, with a downward inclination angle of 30-60 degrees, such as 35-55 degrees, or about 40, 45 or 50 degrees) provided on the inner wall of the body (1) above the inner side of the microwave through hole (102), a water tank (101) provided at the bottom of the inner wall on the operation side, and a porous microwave shielding cover (202) covering the water tank (101) and the waveguide plate (203) and having a steam through hole (20201); Wherein the drying furnace is further equipped with a water inlet pipe (4) for adding water to the water tank (101) and a metering water feeder (5) communicated with the water inlet pipe (4); One end of the drying furnace body (1) is provided with a loading and unloading door (103); Wherein on the inner wall of the operation side of the body (1), the microwave through hole (102), the microwave generator (201) and the inclined (metal) waveguide plate (203) are divided into a lower first level (A) and an upper second level (B).

5. The evaporative drying furnace according to claim 4, wherein, The lower first level (A) and the upper second level (B) each further include 2 or 3 or 4 sub-levels of microwave through holes (102), microwave generators (201) and downward inclined (metal) waveguide plates (203); each sub-level includes a plurality of microwave through holes (102) arranged at approximately equal intervals along the horizontal direction or substantially along the horizontal direction, and one microwave generator (201) and one downward inclined waveguide plate (203) corresponding to or matching each microwave through hole (102); wherein, the number of microwave through holes (102) in each sub-level is 5-30, such as 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29; Preferably, the microwave through holes (102) in one sub-level are staggered from the microwave through holes (102) in the adjacent sub-level in the vertical direction, and this setting method is beneficial to the flow of air, and at the same time better covers the range or area of microwave radiation; and / or The above drying furnace further includes a plurality of feet (8) equipped with weighing sensors and weighing transmitters; and / or The size or aperture of the steam through-holes of the porous microwave shielding cover (202) should be such that steam can pass through but microwaves cannot; preferably, the porous microwave shielding cover (202) is made of metal or alloy, for example, a stainless steel cover with mesh holes; and / or The downwardly inclined waveguide plate (203) of the first lower layer (A) reflects the microwaves from the microwave through-hole (102), and the microwaves change direction and radiate downward to vaporize the water in the water tank. The downwardly inclined waveguide plate (203) of the second upper layer (B) is used to further heat and expand the water vapor rising in the shielding cover (202) into superheated steam. The rising superheated steam diffuses outwards through the steam through-holes (20201) of the microwave shielding cover (202) under the action of the air flow circulation device (6) and reaches the atmosphere in the box body for circulation, so as to form a circulating steam flow in the internal space of the box body and be used to heat the wood.

6. The evaporation furnace according to any one of claims 4 or 5, wherein The drainage and exhaust device (3) includes a drainage tank (301) and a cover plate (302) on the drainage tank (301). The drainage tank (301) is arranged on the bottom plate of the drying furnace box body (1); a plurality of through-holes (30201) are provided on the cover plate (302); the drainage tank (301) is communicated with the internal space of the drying furnace box body (1) through the through-holes (30201).

7. The evaporation furnace according to any one of claims 4-6, wherein, The through-holes (30201) are rectangular or strip-shaped; the hole length of the first through-hole is L1, the hole length of the second through-hole is L2, the hole length of the third through-hole is L3,..., the hole length of the (n - 2)th through-hole is L(n - 2), the hole length of the (n - 1)th through-hole is L(n - 1), and the hole length of the nth through-hole is Ln; as the distance between the positions of the through-holes on the cover plate (302) and the drain pipe (303) increases, the hole lengths of these through-holes gradually increase; that is, L2 > L1, L3 > L2,..., L(n - 1) > L(n - 2), Ln > L(n - 1); Preferably, L2 is 101% - 150% of L1 (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), L3 is 101% - 150% of L2 (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), and so on, L(n - 1) is 101% - 150% of L(n - 2) (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%), and Ln is 101% - 150% of L(n - 1) (preferably 102% - 140%, further preferably 103% - 120%, more preferably 104% - 110%); and / or The center distance between the second through-hole and the first through-hole is D1, the center distance between the third through-hole and the second through-hole is D2, ……, the center distance between the (n - 1)th through-hole and the (n - 2)th through-hole is D(n - 2), and the center distance between the nth through-hole and the (n - 1)th through-hole is D(n - 1); as the distance between the positions of the through-holes on the cover plate (302) and the drain pipe (303) increases, the center distance between adjacent through-holes gradually decreases; that is, D2 < D1, ……, D(n - 1) < D(n - 2); Preferably, D2 is 60% - 98% of D1 (preferably 70% - 95%, more preferably 80% - 92%), and so on, D(n - 1) is 60% - 95% of D(n - 2) (preferably 70% - 90%, more preferably 80% - 92%).

8. The drying furnace according to claim 7, wherein: The hole length L1 of the first through-hole is 0.5 - 10 cm, preferably 1 - 8 cm, more preferably 1.5 - 5 cm; and / or The center distance D1 between the second through-hole and the first through-hole is 20 - 100 cm, preferably 25 - 90 cm, more preferably 30 - 80 cm; and / or The width of the through-hole (30201) is 0.5 - 2 cm, preferably 0.7 - 1.5 cm, such as 1 or 1.2 cm.

9. The evaporation furnace according to claim 4, wherein the metering water adding device (5) is a metering pump; and / or A humidity detection device, a temperature detection device and / or a (gas) pressure detection device are provided inside the evaporation furnace body; and / or The evaporation furnace further includes a material cart, a guide rail is laid on the bottom plate inside the evaporation furnace body, and rollers are provided at the bottom of the material cart, and the rollers are arranged in cooperation with the guide rail; and / or A humidity detection device, a temperature detection device and a pressure detection device are provided inside the evaporation furnace body.

10. The evaporation furnace according to claim 9, the evaporation furnace further includes a drive and control system (9), and the drive and control system is connected to the humidity detection device, the temperature detection device, the pressure detection device, the microwave generating device (2), the air flow circulation device (6), the hydraulic control system (10) of the inlet and outlet door, the first control valve provided on the water inlet pipe (4), the second control valve provided on the drain pipe (303), and the weighing sensor and weighing transmitter installed on the support feet (8).

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