A method of insecticidal treatment of wood

Abstract

The application discloses a kind of wood insecticidal treatment method, including wood heating treatment, until wood center temperature reaches and keeps temperature higher than 71.1 ℃, continue to process at least 75 min.The method of the application is based on finite element analysis to solve temperature change in wood heat treatment process, select the position point of large temperature gradient in wood interior as the temperature characteristic point of insecticidal treatment, and detect the temperature difference near the characteristic point, accurately and efficiently regulate and control wood temperature in wood insecticidal treatment process, reduce temperature difference at the place where temperature gradient is larger, reduce the generation of processing defects.The method improves wood pest control efficiency, insecticidal treatment cycle is short, energy consumption is low, insecticidal effect is good, the quality of wood after insecticidal treatment is high, defect is few, wood utilization rate is high;And the method of the application is simple to operate, control method is reliable, can accurately control heat treatment process, and effectively improve insecticidal, heat treatment effect and efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a wood heat treatment method, and belongs to the technical field of wood protection and quarantine treatment, in particular to a heat-treated wood insecticidal method for determining treatment process and regulating treatment process through finite element analysis. BACKGROUND

[0002] With the continuous increase of wood import in China, the risk of wood being invaded by foreign forest pests is increasing, which poses a very serious threat to the ecological environment of China. Therefore, doing a good job in wood quarantine and insecticidal control is an important means to ensure the quality, health and safety of imported and exported wood, and plays an important role in preventing the transmission of dangerous harmful organisms and ensuring the normal process of domestic and foreign trade.

[0003] The existing plant quarantine and pest control treatment methods can be divided into two categories. One is a chemical method based on chemical agents, which achieves the purpose of killing insects through fumigation and other application methods. The other is a physical method based on physics, which achieves the purpose of pest control by using the killing effect of various harmful organisms on the environment. Among the many treatment methods, fumigation with bromomethane as a fumigant is the most commonly used method for log pest control for a long time. However, bromomethane is a toxic and harmful gas, which not only causes harm to the human body and the surrounding nervous system, but also is an ozone-depleting substance, which can cause irreversible damage to the environment. Other fumigants, such as sulfuric fluoride, aluminum phosphide, ethylene oxide, methylthioisocyanate, and cyanide, also have problems such as poor low-temperature drug resistance, low penetration, unstable performance, and harm to the human body. Moreover, practice shows that the use of a single agent can greatly increase the insecticide resistance of many insects, affecting the insecticidal effect.

[0004] In contrast, heat treatment of wood for pest control offers advantages such as being green, efficient, and environmentally friendly. It requires no toxic or harmful agents and has a shorter treatment cycle, making it an ideal method for controlling wood pests. The theoretical basis of heat treatment for wood pest control is that heat rapidly dehydrates pests in the wood, causing cell wall damage and protein coagulation, leading to suffocation and death. Studies have shown that treatment at 56℃ for 30 minutes can effectively kill pests such as bark beetles, longhorn beetles, jewel beetles, longhorn beetles, weevils, termites, powdery beetles, false longhorn beetles, bark beetles, wood beetles, and pine wood nematodes. When the wood temperature reaches above 70℃, comprehensive pest control, including fungi, can be achieved. Furthermore, heat treatment usually results in a decrease in wood moisture content; if the moisture content of the treated wood is below 20%, it can effectively prevent reinfection by fungi. my country's "Methods and Technical Requirements for Quarantine and Pest Control Treatment of Imported Logs" stipulates that when treating logs with heat, the core temperature of the logs must reach at least 71.1℃ and be maintained for at least 75 minutes. Therefore, in order to reduce the cost of heat treatment while ensuring the effectiveness of pest control, experimental conditions with shorter heater start-up times and shorter times required to reach the core temperature of 71.1℃ should be selected as reference conditions for actual production.

[0005] However, the current wood heat treatment process and equipment for pest control are still imperfect. In particular, when the treatment process is not designed properly, the heat is unevenly transferred inside the wood, which leads to defects such as cracking and deformation of the wood. Pests inside the wood are not completely killed, and the treatment cycle and energy consumption may be greatly increased, resulting in reduced wood utilization and waste of resources. Summary of the Invention

[0006] The purpose of this invention is to address the technical shortcomings of existing wood heat treatment methods for pest control, and to provide a wood pest control method. This invention provides precise and efficient control of wood temperature during the pest control process, improving pest control efficiency, shortening the treatment cycle, reducing energy consumption, enhancing pest control effects, resulting in high-quality wood with fewer defects and higher wood utilization. In this method, the internal temperature of the wood is raised, and the high temperature destroys the physiological functions of insects, denatures proteins, and kills them. Furthermore, the wood temperature is uniform throughout the treatment process, ensuring even heat transfer and thorough pest control with high efficiency. Precise control of the pest control and heat treatment temperatures ensures uniform internal temperature, resulting in high-quality wood with fewer defects and superior overall quality.

[0007] To achieve the objectives of this invention, one aspect of this invention provides a method for treating wood with insecticides, comprising heating the wood until the core temperature of the wood reaches 71.1°C or higher, and continuing the treatment for at least 75 minutes while maintaining the temperature above 71.1°C.

[0008] The preferred temperature at the center of the wood is ≥71.5℃.

[0009] In particular, continue treatment for 75-90 minutes at a temperature of ≥71.5℃.

[0010] Another aspect of the present invention provides a method for treating wood with insecticides, comprising the following steps performed in sequence:

[0011] 1) The wood heat treatment process was analyzed (simulated) using finite element software. The temperature of various points inside the wood at different heat treatment time points was recorded during the simulated heat treatment. Furthermore, the time T required for the wood heat treatment to reach a temperature of 71.1℃ at the wood's center point was determined. 71.1 ;

[0012] 2) During duration T 71.1 Set n time points and record the duration T. 71.1 Divide into (n+1) segments; then find the temperature gradient distribution of each point inside the wood at the corresponding n time points from the simulation analysis results of the finite element software, and obtain the temperature gradient distribution results of each point inside the wood at n time points corresponding to the finite element analysis solution of the wood heat treatment process, where n is a natural number, n=1,2,3,…;

[0013] 3) Find the maximum temperature gradient inside the wood at each time point from the temperature gradient distribution results corresponding to each of the n time points, and obtain the spatial coordinates of the maximum temperature gradient inside the wood at each time point from the finite element software. Define the location of the maximum temperature gradient as a temperature feature point Kn, where n is a natural number, n = 1, 2, 3, ..., and obtain n temperature feature points.

[0014] 4) Set n temperature feature points on the wood to be treated with insecticide, where the location of the temperature feature points is the spatial location of the maximum temperature gradient corresponding to the n time points obtained in step 3) inside the wood.

[0015] 5) In the interior of the wood to be treated, at each temperature feature point, a temperature monitoring point is arranged at a position 0.1-1 cm away from each temperature feature point along the direction of the temperature gradient; that is, each temperature feature point corresponds to a pair of temperature monitoring points, and the distance between each temperature feature point and the corresponding temperature monitoring point is 0.1-1 cm in the direction of the temperature gradient (heat transfer direction);

[0016] 6) The wood is heated, and the temperature of each pair of temperature monitoring points corresponding to each temperature feature point on the wood is measured, and the temperature difference Δt between each pair of temperature monitoring points corresponding to each temperature feature point is calculated, wherein:

[0017] When the temperature difference Δt between any pair of temperature monitoring points corresponding to a temperature feature point on the wood to be treated is ≥10℃, heating is stopped; until the temperature difference Δt between each pair of temperature monitoring points corresponding to a temperature feature point on the wood to be treated is ≤2℃, heating is continued; the temperature difference between each pair of temperature monitoring points corresponding to each temperature feature point is continuously monitored during heating, and heating and stopping heating are repeated until the center temperature of the wood reaches and remains at 71.1℃; then the treatment is maintained for at least 75 min, and the heating and insecticidal treatment of the wood is completed.

[0018] In step 1), the finite element software can be selected from OpenFOAM, Code Aster, Salome-Meca, ABAQUS, ANSYS, etc., and Salome-Meca finite element software is preferred.

[0019] In particular, Salome-Meca finite element software is used to simulate and analyze the wood heat treatment process.

[0020] The finite element software is used to analyze the temperature distribution and temperature gradient distribution of each point in the wood during the treatment process at a heat treatment temperature of t f for T time.

[0021] In particular, before performing finite element software analysis of the heat treatment process, the initial moisture content and density of the wood to be treated are measured; then the tangential thermal conductivity λ 径 and the specific heat capacity c of the wood to be treated are calculated; and the properties of the density, thermal conductivity, and specific heat capacity of the wood to be treated are input into the finite element software.

[0022] In particular, the specific heat capacity c of the wood is calculated according to formula (1)

[0023]

[0024] In formula (1), c is the specific heat capacity, J·kg -1 ·k -1; t0 is the initial temperature of wood for heat treatment (usually room temperature, usually 15-30°C), °C; W is the initial moisture content of wood, %;

[0025] In particular, the chordwise thermal conductivity coefficient λ 弦

[0026]

[0027] In formula (2) : ε is the porosity of wood, wherein ε is calculated according to formula (3) :

[0028] ε = 1 - p (0.6536 + 0.3464W) (3)

[0029] Wherein, W is the initial moisture content of wood to be treated, %; p is the initial density of wood to be treated, g / cm 3 .

[0030] In the art, when the wood to be treated is a board, the chordwise thermal conductivity coefficient λ 弦 is the thermal conductivity coefficient in the width direction of the board. The width direction of the board is the chordwise direction; the length direction is the axial direction; and the thickness direction is the radial direction.

[0031] In particular, due to the anisotropy of wood, when the test sample is a board, the axial thermal conductivity coefficient λ 径 , the radial thermal conductivity coefficient λ 弦 , and the chordwise thermal conductivity coefficient λ 径 of wood are respectively input in the finite element software; when the test sample is a log, the axial thermal conductivity coefficient λ 弦 , the radial thermal conductivity coefficient λ 径 are respectively input in the finite element software. Wherein, the radial thermal conductivity coefficient and the chordwise thermal conductivity coefficient are close, and are usually taken as the same, i.e. λ 弦 = λ .

[0032] In particular, it also includes setting the geometric model and size of the wood to be treated in the finite element software.

[0033] In particular, the geometric model of the wood to be treated is set as a cuboid or a cylinder in the finite element software analysis process; if the geometric model is a cuboid, then the values of 1 / 2 of the length, width, and thickness of the board are respectively input in the software in the X, Y, Z three directions of the Cartesian coordinate system; if the geometric model is a cylinder, then the values of 1 / 2 of the radius size, the angle of 90°, and the length of the wood are respectively input in the software in the r, φ, Z three directions of the cylindrical coordinate system.

[0034] In particular, the software analysis further comprises meshing the set-up geometric model of the wood to be treated to obtain basic elements for finite element calculation.

[0035] In particular, the meshing is divided into 1-6 levels according to the meshing accuracy, wherein the meshing accuracy is from high to low in the order of 1 to 6. Level 1 is the most accurate, and level 6 is the most rough.

[0036] In particular, the software further comprises setting up loads and constraints for the set-up geometric model of the wood to be treated.

[0037] In particular, the setting up of the loads is setting up temperature loads of the heat treatment medium on the heat treated wood in the heat treatment process by the finite element method analysis, wherein the temperature load is the heat treatment temperature t f . Generally, the heat treatment temperature t f is 90-200℃.

[0038] In particular, the setting up of the constraints is setting up the convective heat transfer coefficient between the heat treatment medium and the heat treated wood in the heat treatment process by the finite element method analysis, wherein the gas forced convective heat transfer coefficient is 5-100 W / (m 2 ·K), preferably 90 W / (m 2 ·K).

[0039] When setting up the loads and constraints in the finite element method analysis (i.e. simulation) of the heat treatment process, the temperature load of the heat treatment medium on the heat treated wood and the convective heat transfer coefficient between the heat treatment medium and the heat treated wood in the heat treatment process are mainly considered. The temperature load is the heat treatment temperature t f , and the gas forced convective heat transfer coefficient is 5-100 W / (m 2 ·K), preferably 20-100 W / (m 2 ·K), and further preferably 90 W / (m 2 ·K).

[0040] In particular, in the finite element method analysis of the heat treatment process, the simulation time T of the insecticidal treatment is set up, wherein if the wood to be treated is a board, the time T' required for the center temperature of the wood to reach 71.1℃ is estimated according to formula (4), and then the time length of 15-25% (preferably 20%) more than the time (i.e. T') is taken as the simulation time T of the insecticidal treatment (i.e. T / T' = 1.15-1.25, preferably 1.12), formula (4) is as follows:

[0041]

[0042] In formula (4), t fT is the temperature of wood heat treatment, °C; t0 is the initial temperature of wood (usually room temperature, 15-30 °C), °C; b is the width of wood, mm; h is the thickness of wood, mm; a is the thermal conductivity of wood, wherein the thermal conductivity of wood can be found in "Wood Drying Science", Gao Jianmin, Beijing: Science Press, 2008.1, P49, the table of thermal conductivity of wood.

[0043] In particular, in the finite element method analysis of the heat treatment process, the simulation time T of the insecticidal treatment is set, wherein if the wood to be treated is a log, the time T' required for the temperature at the center of the wood to reach 71.1 °C is estimated according to formula (4'), and then a time period of 15-25% (preferably 20%) longer than the time (i.e. T') is taken as the simulation time T of the insecticidal treatment (i.e. T / T' = 1.15-1.25, preferably 1.12), formula (4') is as follows:

[0044]

[0045] t0 is the initial temperature of wood (usually room temperature, 15-30 °C), °C; b is the width of wood, mm; h is the thickness of wood, mm; a is the thermal conductivity of wood, wherein the thermal conductivity of wood can be found in "Wood Drying Science", Gao Jianmin, Beijing: Science Press, 2008.1, P49, the table of thermal conductivity of wood. f T is the temperature of wood heat treatment, °C; t0 is the initial temperature of wood (usually room temperature, 15-30 °C), °C; b is the width of wood, mm; h is the thickness of wood, mm; a is the thermal conductivity of wood, wherein the thermal conductivity of wood can be found in "Wood Drying Science", Gao Jianmin, Beijing: Science Press, 2008.1, P49, the table of thermal conductivity of wood.

[0046] In particular, it also includes setting the simulation time step and the output frequency of the results in the software during the analysis of the heat treatment process.

[0047] In particular, the simulation time step is 5-60 s, preferably 30 s, and the simulation state is written into the result file after each sub-step is completed.

[0048] If the size of the wood is small, T is short, and if the size of the wood is large, T is long, and usually T is 0.1-8 h (preferably 0.2-5 h, and further preferably 0.5-3).

[0049] In particular, it also includes post-processing of the finite element analysis, i.e. visualizing the results of the finite element analysis, to check, analyze and output the results of the analysis calculation.

[0050] Especially, the general postprocessor and the time-history postprocessor are provided in the software. The general postprocessor is used to view the corresponding results of the whole model at a load step and substep, the temperature distribution cloud at a certain time, the temperature gradient cloud, etc. In addition to the intuitive display of the results in the form of graphics, the corresponding information of each node and element can also be introduced in detail in the form of a list. The time-history postprocessor is used to view the change of a certain result of a specified node with respect to time. Through the time-history postprocessor, the curve of the temperature of the center point of the wood with respect to time can be obtained, and the time T required for the temperature of the center point of the wood to reach the insecticidal temperature 71.1℃ can be obtained 71.1 .

[0051] In step 2), n time points are set within the total heat treatment time T 71.1 , which are denoted as T1, T2, …, T n , respectively. The time T 71.1 is divided into (n+1) segments. The finite element analysis of the heat treatment process is carried out at the heat treatment times T1, T2, …, T n , respectively, and the temperature and temperature gradient of the whole model after the corresponding heat treatment time are obtained through the software, and the results are read in the form of a list. The node number of the point with the maximum temperature gradient and the spatial position coordinates in the wood are obtained.

[0052] In particular, in step 2), n≥3, preferably 5-20, further preferably 5-10, and more preferably 9-10.

[0053] In particular, the n time points divide the time T 71.1 into (n+1) segments.

[0054] In step 3), n≥3, preferably 5-20, further preferably 5-10, and more preferably 9-10; in step 5), the distance between the pair of temperature monitoring points corresponding to each temperature feature point and the temperature feature point is 0.2-1.0 cm, preferably 0.3 cm; that is, the distance between the pair of temperature monitoring points is 0.4-2 cm, preferably 0.6 cm; in step 6), when the temperature difference Δt is ≥3℃ (preferably 3-10℃, and further preferably 3℃), heating is stopped; and when the temperature difference Δt is ≤1℃ (preferably 1-2℃, and further preferably 1℃), heating is continued.

[0055] In particular, in the process of obtaining temperature characteristic points from the temperature gradient distribution results, if the positions of the maximum temperature gradient in the wood at different processing time points are the same, these same characteristic points are combined; the temperature characteristic point of the previous processing time (i.e. the previous processing time point) is selected as the position of the maximum temperature gradient at this time point; the position of the second largest temperature gradient value is selected as the temperature characteristic point of the subsequent processing time point; the position of the third temperature gradient value is selected as the temperature characteristic point of the subsequent processing time point; and the temperature characteristic points of other processing time points are selected in the same way. If there are multiple maximum temperature gradients in the temperature gradient distribution cloud map of a processing time point, one of them is selected as the temperature characteristic point.

[0056] The temperature gradient refers to the rate of change of temperature along the direction of heat transfer in the wood. The direction of the temperature gradient in step 5) refers to the direction of heat transfer in the wood.

[0057] When the distance between the pair of temperature monitoring points corresponding to the temperature characteristic point is 2.0 cm, the temperature difference is greater than 10℃, and the wood is prone to defects due to heat treatment; when the distance between the pair of temperature monitoring points is 0.6 cm, the temperature difference is greater than 3℃, and the wood produces heat treatment defects.

[0058] In particular, when the distance between the pair of temperature monitoring points corresponding to any one temperature characteristic point is 2 cm, the temperature difference Δt≥5℃ (preferably Δt≥3℃, and further preferably 3℃), heating is stopped; until the temperature difference Δt≤2℃ (preferably Δt≤1℃, and further preferably 1℃) between the pair of temperature monitoring points corresponding to all temperature characteristic points in the wood or pile, heating is continued. When the distance between the pair of temperature monitoring points corresponding to any one temperature characteristic point is 0.6 cm, the temperature difference Δt≥3℃ (preferably 3℃), heating is stopped; until the temperature difference Δt≤1℃ (preferably 1℃) between the pair of temperature monitoring points corresponding to all temperature characteristic points in the wood or pile, heating is continued.

[0059] When calculating the temperature difference (Δt) of the pair of temperature monitoring points corresponding to each temperature characteristic point, it is generally considered that when the distance between the pair of temperature monitoring points corresponding to any one temperature characteristic point is 0.6 cm (usually 0.4-2 cm), the temperature difference is less than 3℃, and the wood is not prone to defects due to heat treatment, i.e. when the temperature difference between the two monitoring points corresponding to the same characteristic point is greater than 3℃, the heat treatment process needs to be adjusted.

[0060] In another aspect, the present application provides a method for killing insects in wood, comprising the following steps in sequence:

[0061] 1) using finite element software to analyze the wood heat treatment process, record the temperature of each point in the wood at different time points in the simulation heat treatment process; and find the wood center point temperature reaches 71.1℃, the wood heat treatment time T 71.1 ;

[0062] 2) in the length T 71.1 n time points, the length T 71.1 is divided into (n+1) segments; then find the temperature gradient distribution of each point in the wood at the corresponding n time points from the analysis results of the finite element software, respectively, obtain the temperature gradient distribution of each point in the wood at the corresponding n time points in the finite element analysis of the wood heat treatment process, wherein n is a natural number, n=1, 2, 3, …;

[0063] 3) find the maximum temperature gradient of each time point in the wood from the temperature gradient distribution of each point in the wood at the corresponding n time points, and obtain the spatial position coordinates of the maximum temperature gradient at each time point in the wood from the finite element software, and define the position of the maximum temperature gradient as the temperature characteristic point Kn, wherein n is a natural number, n=1, 2, 3, …, obtain n temperature characteristic points;

[0064] 4) select at least one piece of wood from the wood to be treated as a test plate for wood heat treatment, and set n temperature characteristic points on each test plate, wherein the temperature characteristic point is set at the spatial position of the maximum temperature gradient in the wood corresponding to each time point in step 3);

[0065] 5) In the wood to be treated, set one temperature monitoring point at a position 0.1-1cm in front of and behind each temperature characteristic point along the direction of the temperature gradient;

[0066] 6) After the wood to be treated and the test plate are stacked to form a pile, heat treatment is carried out, and the temperature of each temperature characteristic point on each test plate is measured, and the temperature difference Δt between each temperature characteristic point is calculated; measure the center temperature of the center wood of the pile, wherein:

[0067] When the temperature difference Δt between a pair of temperature monitoring points corresponding to any temperature characteristic point on the inspection board in the stack of wood to be treated by insecticidal treatment is ≥10°C, stop heating; continue heating until the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points in the stack of wood to be treated is ≤2°C; during the heating process, continue to monitor the temperature difference between a pair of temperature monitoring points corresponding to each temperature characteristic point on the inspection board in the stack, repeat heating and stopping heating until the central temperature of all inspection boards in the stacked wood reaches and remains at 71.1°C; then maintain the treatment for at least 75 minutes, and the wood heating insecticidal treatment ends.

[0068] Among them, the number of inspection boards in the stack in step 4) is preferably 3 - 9 pieces, and more preferably 5 - 9 pieces.

[0069] In particular, during the stacking process, the inspection boards are evenly distributed in the stack of wood.

[0070] Especially, during the stacking process, one inspection board is set at the central position of the stack of wood.

[0071] Especially, if 9 inspection boards are set in the stack of wood to be treated during stacking, the 9 inspection boards in the stack are respectively located at the upper end, middle, and lower end of the stack, evenly distributed in a "field" shape, and the inspection boards extend along the longitudinal direction of the stack; if 5 inspection boards are set in the stack, the 5 inspection boards in the stack are respectively located at the upper end, middle, and lower end of the stack, evenly distributed in a "×" shape, and the inspection boards extend along the longitudinal direction of the stack; if 3 inspection boards are set in the stack, the 3 inspection boards in the stack are respectively located at the upper end, middle, and lower end of the cross-section passing through the center of the stack and along the longitudinal direction of the stack, evenly distributed in a "1" shape, and the inspection boards extend along the longitudinal direction of the stack; if 1 inspection board is set in the stack, the 1 inspection board in the stack is located at the center of the stack, and the inspection board extends along the longitudinal direction of the stack.

[0072] The stacking of the wood to be treated by insecticidal treatment is carried out by using the existing known methods in the field; the setting of the inspection boards during the stacking process is set in the existing known manner in the field.

[0073] In particular, it also includes measuring the central temperature of the wood at the center of the wood or the stack until the temperature at the central position of the wood or the stack reaches the insecticidal temperature, and the insecticidal temperature ≥71.1°C.

[0074] Among them, the distance between a pair of temperature monitoring points corresponding to each temperature characteristic point in step 5) from the temperature characteristic point is 1.0 cm; preferably 0.6 cm. In step 6), when the temperature difference Δt is preferably ≥3°C (more preferably 3°C), stop heating; when the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points is ≤1°C (preferably 1°C), continue heating.

[0075] Especially, the wood pile in step 6) is cuboid, and the length square of the wood pile is consistent with the longitudinal direction of the heat treatment equipment.

[0076] Compared with the prior art, the present application has the following advantages and benefits:

[0077] 1. In the wood heating and insect killing process, the main reason for incomplete insect killing and heat treatment defects is that the local temperature distribution of wood is uneven during the heat treatment process, resulting in different water movement and evaporation speeds, different wood shrinkage degrees, and defects. The migration of water in wood is related to the heat transfer in wood. In order to make the heat and moisture content in wood change uniformly and smoothly, the temperature gradient in wood needs to be controlled.

[0078] It is difficult to accurately measure and control the temperature and temperature gradient of each point in wood. The present application uses finite element software to analyze and solve the prediction of the temperature field in wood and the required temperature and time for heat treatment. According to the simulation analysis of the temperature gradient change at different times during the wood heat treatment process, the positions of the maximum points of the temperature gradient in wood at multiple heat treatment time points during the heat treatment process are selected as the temperature characteristic points of the wood heat treatment. The monitoring positions with larger temperature changes are determined for temperature monitoring during the wood heat treatment process. Then, the temperature difference of the temperature monitoring points set before and after the temperature characteristic points is monitored in real time. By controlling the temperature difference of the temperature monitoring points corresponding to the position with larger temperature gradient in wood, the wood heat treatment process is regulated and controlled, the temperature uniformity of the wood heat treatment process is regulated and controlled, the heat treatment defects of wood during the wood heating and insect killing process are reduced, and the quality of the heat treated wood is ensured.

[0079] 2. The wood heating and insect killing method of the present application can accurately and efficiently control the progress of wood heat treatment during the heat treatment process. The quality of the heat treated wood prepared is high. In the case of ensuring the quality of wood heat treatment, the purpose of wood insect killing and harm removal can be achieved in a shorter time. The wood is effectively insect killed and removed, and the problem of wood treatment defects during the wood heating and insect killing process is solved, improving the quality of heat treated wood and the utilization rate of wood.

[0080] 3. In the wood heat treatment and insect killing method of the present application, the temperature in wood increases uniformly, the heat is uniformly transferred in wood, the insect killing is complete, and the heat treated wood has no defects such as cracking and deformation. The quality of the heat treated wood is high, and the utilization rate of wood is improved.

[0081] 4. The wood treated by the method of the present application has high insect killing and harm removal efficiency, and can kill most pests and fungi. After treatment, the moisture content of the test sample is low, effectively preventing the re-invasion of pests and fungi.

[0082] 5. The method of the present invention has high heat treatment efficiency, shortens the heat treatment and insecticidal cycle, and reduces the energy consumption of heat treatment and insecticidal. Attached Figure Description

[0083] Figures 1A-1E Example 1 uses the finite element method to analyze and solve the internal temperature gradient distribution cloud map of eucalyptus wood during heat treatment at processing times of 141s, 423s, 705s, 987s, and 1269s.

[0084] Figure 2 This is a schematic diagram of the first placement method for inspection boards in a timber stack.

[0085] Figure 3 This is a schematic diagram of the second placement method for inspection boards in a timber stack.

[0086] Figure 4 This is a schematic diagram of the third placement method for inspection boards in a timber stack.

[0087] Figure 5A , 5B Example 2 uses the finite element method to analyze and solve the internal temperature gradient distribution cloud map of eucalyptus logs during heat treatment at processing times of 465s and 2325s. Detailed Implementation

[0088] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0089] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, equipment, and instruments used in the following examples are commercially available.

[0090] This invention uses heat treatment of wood to kill pests within it. During the heat treatment process, the internal temperature of the wood rises, and the high temperature damages the physiological functions of the insects, causing protein denaturation and ultimately killing them.

[0091] Install finite element software (for example, ABAQUS, ANSYS or OpenFOAM, Code Aster, Salome-Meca, etc.) in the computer, analyze and solve the change of the temperature field inside the wood before the wood heat treatment for killing insects through the finite element analysis (simulation) technology, since the main reason for the wood defect generated in the heat treatment for killing insects is the uneven heat transfer, which leads to the different moisture content changes in different parts of the wood, therefore, through the finite element analysis and solution, the position with the larger temperature gradient inside the wood is determined, and the temperature difference between the two position points along the temperature gradient direction (i.e. the heat transfer direction) and located at a certain distance before and after the position point is taken as the regulation index in the heat treatment for killing insects, according to the temperature difference, the heating or stopping heating (opening or closing the heater) of the heat treatment process is regulated in real time, so as to realize the accurate and efficient control of the heat treatment process and the wood treatment quality, and the purpose of killing insects and removing pests is achieved in a shorter time under the condition of ensuring the quality of the wood.

[0092] The working principle and working process of the wood insect killing treatment system are as follows:

[0093] 1) The wood heat treatment process is simulated (i.e. analyzed and solved) through the finite element analysis software, a series of heat transfer and temperature distribution of the wood inside at different heat treatment for killing insects temperatures t f (usually t f is 90-200℃, for example, 90, 100, 110, 120, 150, 180, 200℃, etc.) and different treatment time points are obtained;

[0094] 2) The actual treatment conditions (i.e. heat treatment for killing insects temperature and time) of the wood heat treatment for killing insects are selected by combining the analysis of the wood heat treatment for killing insects time, treatment equipment, environmental conditions, treatment efficiency and economic cost, etc.

[0095] 3) According to the selected temperature of the wood heat treatment for killing insects, the time T 71.1 required for the wood center point temperature to reach 71.1℃ at the heat treatment for killing insects temperature is found in the finite element software;

[0096] 4) n time points are selected within the time T 71.1 , and the temperature gradient distribution of the wood inside at the selected n time points is found from the analysis results of the finite element software;

[0097] 5) The n maximum temperature gradients of the wood inside at the n time points and the spatial positions of the maximum temperature gradients in the wood are found and obtained from the temperature gradient distribution of the wood inside at the n time points, wherein the position of the maximum temperature gradient in the wood is taken as a temperature characteristic point, and n temperature characteristic points are obtained in total;

[0098] 6) In the wood, along the direction of temperature gradient (i.e. the direction of heat transfer), one temperature monitoring point is arranged before and after each of the n temperature characteristic points, i.e. each temperature characteristic point corresponds to a pair of temperature monitoring points, and a temperature sensor for measuring temperature is arranged at each temperature monitoring point;

[0099] 7) In the process of wood heating and insect killing treatment, the temperature difference (Δt) of the pair of temperature monitoring points corresponding to each temperature characteristic point is monitored, if the temperature difference of the pair of temperature monitoring points corresponding to any one temperature characteristic point is ≥10℃ (preferably ≥5℃, further preferably ≥3℃, and more preferably 3℃), the heating is stopped; until the temperature difference of the pair of temperature monitoring points corresponding to all temperature characteristic points is ≤2℃ (preferably ≤1℃, and further preferably 1℃), the heating is continued; the heating and stopping are repeated until the temperature of the center point of the wood reaches or exceeds the heating and insect killing treatment temperature 71.1℃;

[0100] 8) Under the condition that the temperature of the center of the wood is ≥71.1℃, the heat preservation treatment is carried out for at least 75 min, the process of wood heating and insect killing treatment is completed, and the wood treated by heating and insect killing treatment is obtained, which is completely insect-killed, has high quality, and has few heat treatment defects.

[0101] If the wood is subjected to heating and insect killing treatment after being stacked into a wood pile, the corresponding n temperature characteristic points and the pair of temperature monitoring points corresponding to each temperature characteristic point are arranged on the inspection plate of the wood pile, and the temperature sensor is arranged at each temperature monitoring point to measure the temperature of the temperature monitoring point and calculate the temperature difference of the corresponding temperature monitoring point; in the process of wood heating and insect killing treatment, the temperature sensor arranged on the inspection plate records the temperature values of the pair of temperature monitoring points corresponding to each temperature characteristic point on the inspection plate, and calculates the temperature difference (Δt) between the pair of temperature monitoring points corresponding to each temperature characteristic point, if the temperature difference Δt between the pair of temperature monitoring points corresponding to any one temperature characteristic point is ≥10℃, the heating is stopped (i.e. the heater in the wood heat treatment equipment is turned off, wherein the wood heat treatment equipment is usually a drying kiln), until the temperature difference Δt between the pair of temperature monitoring points corresponding to all temperature characteristic points in the pile is ≤2℃, the heating is continued, the temperature in the wood continues to rise, the temperature difference between the pair of temperature monitoring points corresponding to each temperature characteristic point is continuously monitored, the process of stopping and continuing heating is repeated, until the temperature of the center of the center wood in the pile is ≥71.1℃, then under the condition that the temperature is ≥71.1℃, the treatment is carried out for at least 75 min, and the process of insect killing and heat treatment is completed, wherein:

[0102] When the distance between the pair of temperature monitoring points corresponding to any one temperature feature point is 2 cm, and the temperature difference Δt is greater than or equal to 5℃ (preferably greater than or equal to 3℃, and more preferably 3℃), heating is stopped; and when the temperature difference Δt between the pair of temperature monitoring points corresponding to any one temperature feature point in the wood or the timber pile is less than or equal to 2℃ (preferably less than or equal to 1℃, and more preferably 1℃), heating is continued.

[0103] When the distance between the pair of temperature monitoring points corresponding to any one temperature feature point is 0.6 cm, and the temperature difference Δt is greater than or equal to 3℃ (preferably 3℃), heating is stopped; and when the temperature difference Δt between the pair of temperature monitoring points corresponding to any one temperature feature point in the wood or the timber pile is less than or equal to 1℃ (preferably 1℃), heating is continued.

[0104] In the embodiment of the present application, eucalyptus wood is used as an example for illustration, which is produced in Guangxi, China, and has no defects and an initial moisture content of 50%-90%. Any other wood can be used in the present application, such as poplar, pine, beech, rubber wood, and especially high-grade imported wood, such as walnut, acacia, rosewood, etc.

[0105] In Example 1, sawn eucalyptus wood boards are used as an example for heating and insect killing treatment, wherein the size of the eucalyptus wood is 1000 mm x 100 mm x 40 mm (length x width x thickness), the thickness of the board is the radial height of the eucalyptus wood, the length is the axial length of the wood, and the width is the chord direction of the eucalyptus wood. Other boards and boards made by other cutting methods can also be used in the present application.

[0106] In Example 2, eucalyptus logs are used as an example for heating and insect killing treatment, wherein the size of the eucalyptus wood is 1000 mm x 60 mm (length x radius). Any other tree species of uncut or cut logs can also be used in the present application.

[0107] The boards are sawn according to the national standard GB1928-91, and boards with sizes of 200-2000 mm (length) x 100-300 mm (width) x 20-60 mm (thickness) in addition to 1000 mm x 100 mm x 40 mm (length x width x thickness) can also be used in the present application.

[0108] Insect killing treatment of eucalyptus wood boards in Example 1

[0109] I. Finite element analysis solution

[0110] First, the open-source Salome-Meca finite element software is used to simulate the temperature field and temperature gradient distribution in the wood, i.e. to simulate the temperature field in the wood during the insect killing treatment of the wood under a series of different heat treatment temperatures and heat treatment times. According to the treatment equipment, environmental conditions, treatment efficiency, and treatment cost, the required treatment temperature and treatment time for the wood to achieve the purpose of insect killing are determined.

[0111] The finite element simulation software in the present application is exemplified by Salome-Meca finite element software, and other finite element simulation software such as ABAQUS, ANSY or OpenFOAM, Code Aster, finite element software are all applicable to the present application. The specific steps are as follows:

[0112] 1. Determine the initial moisture content W and density p of the wood to be treated; then calculate the properties of the wood to be treated (thermal conductivity λ, specific heat capacity c) according to formulas (1), (2), (3); wherein:

[0113] The specific heat capacity c of the wood is calculated according to formula (1)

[0114]

[0115] In formula (1), c is the specific heat capacity, J·kg -1 ·k -1 ; t0 is the initial temperature of the wood for heat treatment (usually room temperature, usually 15-30℃), ℃; W is the initial moisture content of the wood, %;

[0116] The chordwise thermal conductivity λ of the wood is calculated according to formula (2) 弦

[0117]

[0118] In formula (2), ε is the porosity of the wood, wherein ε is calculated according to formula (3):

[0119] ε = 1 - p (0.6536 + 0.3464W) (3)

[0120] In formula (3), W is the initial moisture content of the wood to be treated, %; p is the initial density of the wood to be treated, g / cm 3 .

[0121] In the art, it is generally considered that the length direction of the board is the axial direction, the thickness direction is the radial direction, and the width direction is the chordwise direction. For a round log, only the radial direction and the axial direction are considered.

[0122] Due to the anisotropy of wood, the axial thermal conductivity (λaxial) of the wood is about 1.5-2.75 times (usually 2 times) the radial thermal conductivity (λradial) or the chordwise thermal conductivity (λchord) according to the difference in moisture content, and the radial and chordwise thermal conductivities are relatively close (usually considered as the same) ; the specific heat capacity of the wood is the same in the radial, axial and chordwise directions.

[0123] The initial moisture content, density and initial temperature of the wood are determined according to the existing known methods in the art.

[0124] For example, the initial moisture content W of the eucalyptus board in the embodiment is 12%, the density p is 700 kg / m 3 , the initial temperature t0 is 25℃; c = 1696.15 J / (kg·K); λ 弦 = 0.17 W / (m·K); λ 径 = 0.17 W / (m·K).

[0125] 2. Establishing a finite element analysis model in software

[0126] According to the shape of the wood to be treated, set the geometric model of the wood to be treated in the finite element analysis software, and input the corresponding geometric dimensions of the wood to be treated in the finite element software;

[0127] Set the initial density (p), thermal conductivity (λ), and specific heat capacity (c) of the wood to be treated in the finite element simulation software;

[0128] 2A) Determining the geometric model of the wood to be treated

[0129] The eucalyptus board to be treated is a cuboid, and the simulation geometric model of the wood to be treated is set as a cuboid in the finite element software; and in the software, the X, Y, and Z directions correspond to inputting the length, width, and thickness values of the board by 1 / 2 respectively;

[0130] 2B) Setting the properties of the wood to be treated

[0131] According to the anisotropic characteristics of wood, set the thermal conductivity, specific heat capacity, and density of the wood to be treated along the X, Y, and Z directions in the finite element analysis software respectively;

[0132] In the software, X, Y, and Z correspond to the length, width, and thickness of the wood to be treated respectively, so the X direction is the axial direction, the Y direction is the chordal direction, and the Z direction is the radial direction.

[0133] In the embodiment, the wood to be treated is eucalyptus board with a size of 1000 mm x 100 mm x 40 mm (length x width x thickness), and the simulation geometric model of the wood to be treated is set as a cuboid in the finite element software. In the finite element software, the wood to be treated is selected as "Thermal Solid and 8NODE 70, i.e. eight-node hexahedral thermal unit"; in the software, half of the length, width, and thickness of the wood to be treated are inputted, for example, in the embodiment, the size of the wood to be treated is 1000 mm x 100 mm x 40 mm (length x width x thickness), so in the software, X1 = 0, X2 = 0.500; Y1 = 0, Y2 = 0.050; Z1 = 0, Z2 = 0.020;

[0134] In the software, the specific heat capacity was set to 1696.15 J / (kg·K), and the density was set to 0.7 g / cm³. 3 The specific heat capacity and density are the same in the X, Y, and Z axes; the axial, chordal, and radial thermal conductivity are 0.34 W / (m·K), 0.17 W / (m·K), and 0.17 W / (m·K), respectively, in the X, Y, and Z axes.

[0135] 3. Finite element analysis solution of the heat treatment process (i.e., simulated heat treatment)

[0136] 3A) Grid generation process for the wood to be treated

[0137] The established model is meshed. In the finite element software, six meshing levels, from Fine to Coarse, are selected, with meshing precision decreasing from 1 to 6, where level 1 is the most precise and level 6 is the coarsest. The meshing parameters for the six levels in the software are selected based on the required simulation accuracy. In this embodiment, level 3 is selected for meshing the model of the wood to be processed; precision levels 1-6 are all applicable.

[0138] 3B) Set convective heat transfer boundary conditions (i.e., set the convective heat transfer coefficient and the insecticidal heat treatment temperature).

[0139] In the process of wood heating for pest control, the heat exchange between the heat treatment environment medium and the wood is mainly accomplished through convection heat transfer. Therefore, in the finite element method (FEM) analysis, only the surfaces in contact with the environment in the model are selected to be subjected to convective heat transfer loads, and the convective heat transfer coefficient and the ambient medium temperature (t) are set. f This refers to the temperature at which the insecticide is heated.

[0140] In this embodiment of the invention, the convective heat transfer coefficient is 90 W / (m²). 2 Taking K as an example, other convective heat transfer coefficients are 5-100 W / (m²). 2 ·K) are all applicable to this invention; the ambient medium temperature in the heat treatment process is 100℃ as an example, and other medium temperatures in the heat treatment process of 90-200℃ are also applicable to this invention.

[0141] During the finite element analysis process, the ambient medium temperature is first raised to the heat treatment temperature t for insecticidal treatment. f (e.g., 90, 100, 110, 120, 150, 180, 200℃), then place the test material in and maintain the temperature to heat and kill insects in the wood.

[0142] 3C) Set the initial temperature of the wood t0, and set the simulation heating and insecticidal treatment time T.

[0143] In the process of heat treatment for killing insects, the initial temperature of wood is usually the same as the ambient temperature, i.e. t0 is room temperature; the simulation time T of heat treatment for killing insects is set according to the size of wood to be treated, and is usually estimated according to the time T' required for the temperature at the center of wood to reach 71.1°C according to formula (4), and the simulation time T of heat treatment for killing insects is 15%-25% longer than T' (in this embodiment, 24.5% longer than T'), wherein formula (4) is as follows:

[0144]

[0145] In formula (4), t f is the temperature of heat treatment for killing insects, t f =(90-200), °C; t0 is the initial temperature of wood (usually room temperature, 15-30°C), °C; b is the width of wood, mm; h is the thickness of wood, mm; and a is the thermal conductivity coefficient of wood, which can be found in Wood Drying Science, Gao Jianmin, Beijing: Science Press, 2008.1, P49.

[0146] If the size of wood is small, T is short, and if the size of wood is large, T is long, and usually T is 0.1-8h (preferably 0.2-5h, and further preferably 0.5-3h). In this embodiment, the temperature t f of the ambient medium during heat treatment for killing insects is 100°C, and T' is calculated to be 1445.7s, and the simulation time T of heat treatment for killing insects is about 1800s.

[0147] 3D) by software analysis to obtain a series of temperatures t f (t f =90-200°C) of heat treatment for killing insects and the temperature and temperature gradient of each point inside wood at different heat treatment time, to obtain the corresponding temperature distribution cloud picture and temperature gradient (Thermal Gradient) distribution cloud picture of each point inside wood at different temperatures and different treatment time, and to obtain the curve of the temperature at the center of wood varying with time at different heat treatment temperatures for killing insects from the beginning of heat treatment for killing insects to the end of simulation, and thus to obtain the treatment time T of the center of wood reaching 71.1°C at different heat treatment temperatures for killing insects. 71.1 .

[0148] By analyzing and solving the heat treatment for killing insects at different temperatures t f , the temperature t f of heat treatment for killing insects at which the temperature at the center of wood reaches 71.1°C and the treatment time T 71.1 at which the temperature at the center of wood reaches 71.1°C at the corresponding temperature are obtained.The combination of the temperature t and the time T is used to select a reasonable heat treatment condition in the production process according to the actual situation.

[0149] According to the actual situation of the wood heat treatment production, the suitable heat treatment condition for heat treatment is selected, that is, the heat treatment temperature t f , the time T 71.1 for the wood center temperature to reach 71.1°C is selected.

[0150] 4. Determine the temperature feature point and its position in the wood

[0151] 4A) Select the temperature t of heat treatment f , the time T 71.1 for the wood center temperature to reach 71.1°C, and set n time points (T1, T2, …, Tn) within the time T 71.1 , that is, divide the selected time T 71.1 into (n+1) time periods (wherein n≥3, preferably 5-20, further preferably 5-10, and further preferably 9-10), that is, select n time points within the time T 71.1 for the wood center temperature to reach 71.1°C in the simulation of heat treatment, divide T 71.1 into (n+1) periods, and obtain the temperature gradient in the wood at the selected n time points during the heat treatment, that is, obtain n temperature gradient distribution maps of the wood at the n time points.

[0152] Generally, T 71.1 is divided into (n+1) time periods (wherein n≥3, preferably 5-20, further preferably 5-10, and further preferably 9-10), that is, within the selected time T 71.1 , n time points are selected at equal intervals except the starting point and the ending point, that is, the time from the starting point (0) to the ending point (T 71.1 ) is divided into (n+1) equal parts, and the interval between adjacent time points is the same, that is, the lengths of the (n+1) time periods are the same; or T 71.1 may not be divided equally to form (n+1) time periods with different intervals, that is, the time from the starting point (0) to the ending point (T 71.1 ) is divided into (n+1) time periods with different intervals, and the interval between adjacent time points is different.

[0153] In the temperature gradient distribution cloud picture, different color areas respectively represent the high and low of the temperature gradient, wherein the red color represents the area with higher temperature gradient, and the blue color represents the area with lower temperature gradient, so that the relative relationship of the temperature gradient at different positions in the wood under the same heat treatment time and the change of the temperature gradient in the wood between different heat treatment times can be observed more intuitively.

[0154] The "temperature gradient" refers to that in an object with a continuous temperature field, the direction with the maximum temperature change rate through any point P is located on the normal direction of the isotherm, and the maximum temperature change rate through the point P is referred to as the temperature gradient, which is denoted by gradt.

[0155] 4B) According to the temperature gradient distribution results of n different set time points in the time length T 71.1 , the maximum value of the temperature gradient in the wood at n different time points and the spatial position coordinates of the maximum value of the temperature gradient in the wood are determined, and the position where the maximum value of the temperature gradient is located is defined as the temperature characteristic point Kn; that is, n temperature characteristic points corresponding to different time points are obtained, the spatial position coordinates of the temperature characteristic points on the wood are recorded, the maximum point of the temperature gradient is the temperature characteristic point at the corresponding processing time point, and the position of the maximum point of the temperature gradient in the wood is the position of the temperature characteristic point in the wood at the corresponding processing time point; the selected time point n corresponds to the temperature characteristic point Kn; the temperature characteristic point is denoted as K1, K2,..., Kn;

[0156] The temperature gradient distribution results of the selected time points obtained by the finite element analysis are read in the software in the form of a list, so that the maximum value of the temperature gradient at each time point and the spatial position coordinates of the temperature characteristic point in the wood are determined.

[0157] In the specific embodiment of the present application, nine points are selected at equal intervals as an example, and the time length T 71.1 is divided into 10 equal time intervals, that is, 9 points are selected in the time length T 71.1 except the starting point and the end point.

[0158] In the present embodiment, the heating and insecticidal heat treatment temperature t f is taken as 100℃ as an example, the finite element software analysis solves the time T 71.1 when the center temperature of the wood reaches 71.1℃ during the heat treatment process, and T 71.1 = 1410s is divided into 10 time intervals, each time interval is 141s, and the selected 9 points are 141s, 282, 423, 564, 705, 846, 987, 1128, and 1269.

[0159] Nine temperature gradient distribution cloud maps of the wood interior were generated at nine selected time points during the heat treatment process for insecticide application. Five of these maps were selected, as shown below. Figures 1A-1E As shown, the temperature gradient distribution cloud map inside the wood under different treatment times is shown. The treatment times for 1A, 1B, 1C, 1D, and 1E are 141s, 423s, 705s, 987s, and 1269s, respectively.

[0160] Combining the temperature gradient distribution cloud maps (a total of 9), the finite element analysis results are displayed in a list format. The maximum temperature gradient at each corresponding time point and its location within the wood to be treated are then identified. This location is recorded as the temperature feature point location, resulting in 9 temperature feature points (denoted as K1, K2, K3, K4, K5, K6, K7, K8, K9), and the spatial locations of the 9 maximum temperature gradients within the wood. The positions of the 9 temperature feature points corresponding to the 9 time points within the wood are as follows: K1(0 .455, 0.045, 0.015); K2 (0.370, 0.005, 0.015); K3 (0.420, 0.005, 0.015); K4 (0.410, 0.010, 0.015); K5 (0.445, 0.00 5, 0.015); K6 (0.440, 0.010, 0.015); K7 (0.395, 0.015, 0.015); K8 (0.445, 0.010, 0.015); K9 (0.435, 0.015, 0.015).

[0161] In the process of obtaining corresponding temperature feature points from the temperature gradient distribution cloud map, the location of the maximum temperature gradient value in the wood may be the same at different treatment time points. These identical feature points are then merged, with the maximum temperature gradient value used as the feature point for the previous treatment time, and the next largest temperature gradient value selected as the feature point for the next treatment time. This process continues when the maximum temperature gradient values ​​overlap across multiple treatment times. At the same treatment time point, if there are multiple identical maximum temperature gradient values, one of them is selected as the temperature feature point for that treatment time point. For example, if two treatment time points have the same maximum temperature gradient value in the wood, the maximum temperature gradient value is selected as the feature point for the earlier of these two treatment time points, and the second largest temperature gradient value is selected as the feature point for the next treatment time point. Similarly, if three treatment time points have the same maximum temperature gradient value in the wood, the maximum temperature gradient value is selected as the feature point for the earlier of these three treatment time points, the second largest temperature gradient value is selected as the feature point for the next treatment time point, and the next largest temperature gradient value (i.e., the third temperature gradient value) is selected as the feature point for the subsequent treatment time point.

[0162] During the heat treatment process, heat is continuously transferred to the interior of the wood, causing the temperature of the wood to gradually increase from the surface to the inside. From the temperature gradient distribution cloud chart and the coordinates of the temperature characteristic points, it can be known that the temperature gradient of the surface layer of the wood gradually decreases, while the temperature gradient of the core layer gradually increases. However, in combination with the treatment results at different time periods, it is found that before the temperature at the center of the wood reaches the heat treatment insecticidal temperature, the maximum temperature gradient region of the whole wood is always in the middle and shallow layer in the thickness direction of the wood, and with the extension of the treatment temperature, the region continuously shrinks towards the Z axis.

[0163] II. Heat insecticidal treatment

[0164] 1. Determining temperature monitoring points on the wood to be subjected to heat insecticidal treatment, installing temperature sensors at the temperature monitoring points, and installing temperature sensors at the center of the wood

[0165] 1. Determining the positions of temperature monitoring points inside the wood on the wood to be subjected to heat insecticidal treatment, installing temperature sensors at the temperature monitoring points, and installing temperature sensors at the center of the wood

[0166] 1A) According to the results of the finite element software analysis solution, the positions of the corresponding temperature characteristic points Kn in the wood to be treated or the test plate of the wood pile are determined according to the selected spatial position coordinates of the n temperature characteristic points Kn in the wood;

[0167] 1B) In the interior of the wood or the test plate of the wood pile, 1 temperature monitoring point is respectively set at a distance of 0.3 cm (usually 0.1-1 cm) before and after each selected temperature characteristic point along the temperature gradient direction (i.e. along the direction of heat transfer in the wood), and a temperature sensor (Pt100) is arranged at each temperature monitoring point for measuring the temperature of each temperature monitoring point during the heat insecticidal treatment. One temperature monitoring point is respectively set before and after each temperature characteristic point along the temperature gradient direction, i.e. each temperature characteristic point corresponds to a pair of temperature monitoring points;

[0168] In the embodiment of the present application, 9 temperature characteristic points are selected, which are respectively denoted as K1, K2, K3, K4, K5, K6, K7, K8 and K9. One temperature monitoring point is respectively set before and after each temperature characteristic point, and the temperature of each temperature monitoring point is monitored. There are 18 temperature monitoring points in the test plate of the wood or the wood pile. The temperature monitoring points corresponding to the 9 temperature characteristic points before and after are denoted as: K 1,1 , K 1,2 ; K 2,1 , K 2,2 ; …; Kn ,1 , Kn ,2 ; …, K 9,1 , K 9,2 .

[0169] 1C) A sensor is arranged at the central position of the wood or at the central position of the wood in the center of the wood stack for monitoring the temperature (tx) at the central position of the wood.

[0170] 2. Wood stacking

[0171] Stack the wood to be treated by heating for insect killing, that is, stack the boards in any form of wood stacking disclosed in the field of wood drying to form a wood stack; there is a spacer with a certain thickness between adjacent two layers of boards, and there is a certain distance between adjacent two spacers within the same spacer layer;

[0172] Inspection boards provided with temperature monitoring points and temperature sensors are evenly placed in the wood stack. The ways, methods and quantities of setting inspection boards in the wood drying process in the art are applicable to the present invention. In the present invention, 3 - 9 inspection boards are provided.

[0173] The 9 inspection boards arranged in the wood stack are respectively located at the upper end, middle and lower end of the wood stack, and are evenly distributed in a "field" shape, and the inspection boards extend along the longitudinal direction of the wood stack, as Figure 2 , that is, along the 4 edges of the cuboid-shaped wood stack; the left and right sides of the cross-section passing through the center line of the wood stack and parallel to the bottom surface of the wood stack along the longitudinal direction of the wood stack; the upper and lower sides of the cross-section passing through the center line of the wood stack and perpendicular to the bottom surface of the wood stack along the longitudinal direction of the wood stack and the center line along the longitudinal direction of the wood stack are respectively provided with inspection boards, a total of 9; the 5 inspection boards arranged in the wood stack are respectively located at the upper end, middle and lower end of the wood stack, and are evenly distributed in a "×" shape, and the inspection boards extend along the longitudinal direction of the wood stack, as Figure 3 , that is, along the 4 edges of the cuboid-shaped wood stack and the center line along the longitudinal direction of the wood stack are respectively provided with inspection boards, a total of 5; the 3 inspection boards arranged in the wood stack are respectively located at the upper end, middle and lower end of the cross-section passing through the center line of the wood stack and parallel to the bottom surface of the wood stack along the longitudinal direction of the wood stack, or at the left end, middle and right end of the cross-section perpendicular to the bottom surface of the wood stack, and are evenly distributed in a "1" shape, and the inspection boards extend along the longitudinal direction of the wood stack, as Figure 4 , and the inspection boards are shown in black in the figure.

[0174] A temperature sensor is arranged at the central position of the wood in the center of the wood stack to measure the central temperature of the wood stack in real time. If an inspection board is placed at the center of the wood stack, a temperature sensor is arranged at the central position of the inspection board for monitoring the central temperature of the wood stack in real time.

[0175] In the embodiment of the present application, five test plates are arranged in the material pile, one test plate is arranged at the center of the material pile, and one test plate is arranged at each of the four corners of the cross section of the material pile perpendicular to the longitudinal direction of the heat treatment chamber, that is, one test plate is arranged at each of the four positions where the upper and lower bottom surfaces and the left and right side surfaces of the material pile along the longitudinal direction of the heat treatment chamber intersect, that is, the four edges of the material pile are respectively arranged as test plates. Each test plate is arranged with temperature monitoring points, temperature monitoring point temperature sensors, and wood center position temperature sensors according to the method of step 1.

[0176] The placement position and placement method of the test plate known in the art are suitable for the present application.

[0177] 3. Heating and insecticidal treatment

[0178] After the heat treatment chamber (usually a drying kiln or drying chamber) is heated to the treatment temperature, the heater is kept on and the temperature is maintained, the material pile is pushed into the heat treatment chamber, the door of the chamber is closed, and the wood is subjected to heating and insecticidal treatment, and the temperature of the material pile is monitored in real time by the temperature sensors installed in the test plates.

[0179] When the temperature difference (Δt) between a pair of temperature monitoring points corresponding to any temperature feature point on the test plate in the material pile reaches 3°C (usually Δt≥3°C), the heater in the wood heat treatment equipment (usually a wood drying kiln) is turned off and heating is stopped; until the temperature difference (Δt) between a pair of temperature monitoring points corresponding to all temperature feature points in all test plates in the material pile reaches 1°C (usually Δt≤1°C), the heater in the wood heat treatment equipment is turned on and heating is continued, and the temperature difference between a pair of temperature monitoring points corresponding to each temperature feature point is continuously monitored during the heating process. Once the temperature difference (Δt) between a pair of temperature monitoring points corresponding to any temperature feature point on the test plate in the material pile is monitored to reach 3°C (usually Δt≥3°C), heating is stopped, and until the temperature difference (Δt) between a pair of temperature monitoring points corresponding to all temperature feature points on all test plates in the material pile reaches 1°C (usually Δt≤1°C), the heater is turned on again for heating, and the heating and stopping of the heater (turning off and turning on of the heater) is repeated until the center temperature of the wood in the center of the material pile reaches or exceeds 71.1°C (usually the center temperature is 71.1°C); then the temperature is maintained at 71.1°C for at least 75 minutes, and the wood heating and insecticidal treatment is completed.

[0180] When calculating the temperature difference (Δt) between a pair of temperature monitoring points corresponding to each temperature feature point, it is generally considered that when the distance between a pair of temperature monitoring points corresponding to any temperature feature point is 0.6 cm (usually 0.4-2 cm), the temperature difference is less than 3°C, and the wood is not prone to defects due to heat treatment, that is, when the temperature difference between the two monitoring points corresponding to the same feature point is greater than 3°C, the heat treatment process needs to be adjusted.

[0181] Example 2 Heat treatment of eucalyptus logs for killing insects

[0182] I. Finite element analysis solution

[0183] 1. Determine the initial moisture content W and density p of the wood to be treated;

[0184] Calculate the properties of the wood to be treated (thermal conductivity λ, specific heat capacity c) according to formula (1), (2), (3); wherein:

[0185] Calculate the specific heat capacity c of the wood according to formula (1)

[0186]

[0187] In formula (1), c is the specific heat capacity, J·kg -1 ·k -1 ; t0 is the initial temperature of the wood heat treatment for killing insects (usually room temperature, usually 15-30℃), ℃; W is the initial moisture content of the wood, %;

[0188] Calculate the chordwise thermal conductivity λ of the wood according to formula (2) 弦

[0189]

[0190] In formula (2), ε is the porosity of the wood, wherein ε is calculated according to formula (3):

[0191] ε = 1 - p (0.6536 + 0.3464W) (3)

[0192] Wherein, W is the initial moisture content of the wood to be treated, %; p is the initial density of the wood to be treated, g / cm 3 .

[0193] Due to the anisotropy of wood, the axial thermal conductivity (λ 径 ) of the wood is about 1.5-2.75 times (usually 2 times) the radial thermal conductivity (λ 弦 ) or chordwise thermal conductivity (λ 3 ) according to the difference in moisture content, while the radial and chordwise thermal conductivities are relatively close (usually the same) ; The specific heat capacity of the wood is the same in the radial, axial and chordwise directions.

[0194] In the present application, the initial moisture content, density and initial temperature of the wood are determined according to the conventional methods known in the art.

[0195] For example: In this example, the initial moisture content W of the eucalyptus log wood is 12%, and the density p is 700 kg / m 3Specific heat c = 1696.15 J / (kg·K); axial thermal conductivity λ 轴 = 0.34 W / (m·K); radial thermal conductivity λ 径 = 0.17 W / (m·K); initial temperature t0 is 25℃.

[0196] 2. Establishing a finite element analysis model in software

[0197] According to the shape of the wood to be treated, the geometric model of the wood to be treated is determined in the finite element software, and the corresponding geometric size of the wood to be treated is input in the finite element software;

[0198] 2A) Determining the geometric model of the wood to be treated

[0199] The eucalyptus roundwood to be treated is in the shape of a cylinder, and the geometric model of the wood to be treated is set to 1 / 8 of a cylinder in the finite element software; and a cylindrical model is established in the software with (0, 0, 0) as the coordinate origin and according to the size of the test piece. In the cylindrical coordinate, 1 / 2 of the length of the test piece, the radius of the roundwood, and 90° are input;

[0200] 2B) Setting the properties of the wood to be treated

[0201] The same as example 1

[0202] In this example, the wood to be treated is eucalyptus roundwood with a size of 1000 mm x 60 mm (length x radius), and the geometric model of the wood to be treated is set to a cylindrical shape in the finite element software. The wood to be treated is selected as "Thermal Solid and 8NODE 70, i.e. eight-node hexahedral thermal element" in the finite element software; and half of the length of the wood to be treated, the radius, and 90° are input in the software. For example, in the example of the present application, the size of the wood to be treated is 1000 mm x 60 mm (length x radius), and Z = 0.500, r = 0.060, and φ (Angle) = 90 are input in the software;

[0203] 3. Finite element analysis solution of the heat treatment process

[0204] The same as example 1

[0205] During the heat treatment process, the initial temperature of the wood is usually the same as the ambient temperature, i.e. t0 is room temperature; and the heat treatment time T for simulation and simulation is set according to the size of the wood to be treated. Due to the difference in shape between the board and the roundwood, the temperature change process of the center point inside the board is also different, and the time T' required for the center temperature of the roundwood to be treated to reach 71.1℃ is estimated according to formula (4') to exceed the time by 15%-25% (preferably 20%), which is the simulation and simulation heat treatment time T, wherein formula (4') is as follows:

[0206]

[0207] t0 is the initial temperature of wood (usually room temperature, 15-30℃), ℃; R is the radius of the round wood, mm; a is the wood thermal conductivity coefficient, and the wood thermal conductivity coefficient table can be found in Wood Drying Science, Gao Jianmin, Beijing: Science Press, 2008.1, P49.

[0208] In this embodiment, the temperature t of the environmental medium in the heating and insecticidal treatment process is 100℃ f Taking 100℃ as an example, T' is 4655.15s, and the simulated heating and insecticidal treatment time is 5500s, that is, the simulated heating and insecticidal treatment time T is about 5500s.

[0209] 4. Determining the temperature characteristic points and their positions in the wood

[0210] The same as in Example 1

[0211] In this embodiment, the temperature t of the environmental medium in the heating and insecticidal treatment process is 100℃ f Taking 100℃ as an example, T' is 4655.15s, and the simulated heating and insecticidal treatment time is 5500s, that is, the simulated heating and insecticidal treatment time T is about 5500s. 71.1 71.1 is 4650s. T = 4650s is divided into 10 time intervals, each interval is 465s, and the selected 9 time points are 465s, 930s, 1395s, 1860s, 2325s, 2790s, 3255s, 3720s and 4185s.

[0212] At the selected 9 time points, the wood has 9 corresponding temperature gradient distribution clouds in the heating and insecticidal treatment process, and the wood internal temperature gradient distribution clouds at the treatment time of 465s and 2325s are as shown in Figure 5A 5B ​​Then, the maximum temperature gradient and the position of the maximum temperature gradient in the wood at each time point are found and obtained from the finite element analysis results in the form of a list by combining each temperature gradient distribution nephogram. The position of the maximum temperature gradient in the wood is recorded as the position of a temperature characteristic point. The positions of nine temperature characteristic points in the wood at nine time points are as follows: K1 (0.008, 0.053, 0.440); K2 (0.006, 0.006, 0.490); K3 (0.006, 0.012, 0.490); K4 (0.012, 0.006, 0.490); K5 (0.011, 0.011, 0.490); K6 (0.017, 0.005, 0.490); K7 (0.007, 0.047, 0.020); K8 (0.053, 0.008, 0.330); and K9 (0.051, 0.017, 0.200).

[0213] In the process of obtaining the corresponding temperature characteristic points from the temperature gradient distribution nephogram, the positions of the maximum temperature gradients at different treatment time points in the wood can be the same. In this case, the same characteristic points are combined, the characteristic point at the previous time point is retained, and the point with the second largest temperature gradient at the next time point is selected as the temperature characteristic point at the time point. If the maximum temperature gradients at multiple time points overlap, the same applies. If there are multiple same maximum temperature gradients in the temperature gradient distribution nephogram at a treatment time point, one of them is selected as the temperature characteristic point.

[0214] As shown in the temperature gradient distribution nephograms of the logs at different time points, the temperature gradient of the surface and the end of the log is large in the initial stage of the log heat treatment process. With the extension of the treatment time, the extreme value of the temperature gradient is mainly concentrated in the central region of the end of the wood. In the later stage of the heat treatment, when the temperature in the center of the wood approaches 71.1°C, the maximum temperature gradient mainly appears in the middle and shallow layers in the radial direction of the wood. Overall, with the progress of the heat treatment, the maximum temperature gradient in the wood gradually decreases, and the uniformity of the internal temperature gradually increases.

[0215] II. Heat treatment for killing insects

[0216] 1. Determine the position of the temperature monitoring point in the wood in the test plate of the wood heat treatment for killing insects, install a temperature sensor at the temperature monitoring point, and set a temperature sensor in the center of the test plate

[0217] The same as in Example 1

[0218] 2. Stack the wood to be heat treated for killing insects

[0219] The same as in Example 1

[0220] 3. Heat treatment for killing insects

[0221] The same as example 1.

[0222] The temperature distribution of each position of the wood in the heat treatment process, the temperature change of each position inside the wood and the overall temperature distribution of the wood are obtained by analyzing and solving the heat treatment process by the finite element software. The position with a large temperature gradient is recorded as a temperature characteristic point inside the wood in the wood heat treatment process, and one temperature monitoring point is arranged before and after each temperature characteristic point to form a pair of temperature monitoring points corresponding to each temperature characteristic point. The temperature difference of a pair of temperature monitoring points corresponding to a temperature characteristic point is usually more than 3 DEG C when the distance between the two temperature monitoring points is 0.6 cm, and the wood defect is prone to occur, so the heater needs to be closed and the heating needs to be stopped. After the temperature difference between a pair of temperature monitoring points corresponding to all temperature characteristic points in the wood is less than 1 DEG C, it is indicated that the temperature inside the wood tends to be consistent, and the heating is continued. The above process is repeated until the temperature of the center point of the wood reaches the insecticidal treatment temperature 71.1 DEG C, and then the heat preservation is performed for at least 75 min to complete the wood heat insecticidal treatment process.

[0223] When the temperature difference between a pair of temperature monitoring points is more than 3 DEG C, the heater is closed and the heating is stopped, and the temperature difference between the two monitoring points decreases and the temperature tends to be consistent. In the process, heat is also transferred in other parts of the wood, and the temperature difference also gradually decreases, and the temperature of each part tends to be consistent but not equal. When the temperature difference between the two points falls below 1 DEG C, the heating is performed again.

[0224] The temperature difference between adjacent positions in the wood heat treatment process is taken as the basis to control the heat treatment process, so as to ensure the treatment quality of the heat treatment test material and avoid the generation of heat treatment defects.

[0225] In the application, the temperature gradient distribution cloud diagram obtained by analyzing and solving by the finite element software can accurately obtain the position with a large temperature gradient difference in the wood heat treatment process. In the wood heat treatment process, the temperature of the region with a large temperature gradient is controlled to prevent the drying defects caused by the large temperature gradient. That is, the temperature of the wood heat insecticidal treatment is controlled by measuring the temperature difference between a pair of temperature monitoring points corresponding to a temperature characteristic point, so that the wood can be uniformly heated, the temperature difference between each part of the test material is reduced, and the treatment defects are reduced.

Claims

1. A method for controlling insects in wood, characterized in that, The steps are performed in the following order: 1) The wood heat treatment process was analyzed using finite element analysis software. The temperature of various points inside the wood at different heat treatment time points was recorded during the heat treatment process. Furthermore, the time T required for heat treatment was determined when the temperature at the center of the wood reached 71.1℃. 71.1 ; 2) During duration T 71.1 Set n time points and record the duration T. 71.1 Divide into (n+1) segments; then find the temperature gradient distribution of each point inside the wood at the corresponding n time points from the analysis results of the finite element software, and obtain the temperature gradient distribution results of each point inside the wood at n time points during the finite element analysis of wood heat treatment, where n is a natural number, n=1, 2, 3, ...; 3) Find the maximum temperature gradient inside the wood at each time point from the temperature gradient distribution results corresponding to each of the n time points, and obtain the spatial coordinates of the maximum temperature gradient inside the wood at each time point from the finite element software. Define the location of the maximum temperature gradient as a temperature feature point Kn, where n is a natural number, n=1, 2, 3, ..., and obtain n temperature feature points. 4) Set n temperature feature points on the wood to be treated with insecticide, where the location of the temperature feature points is the spatial location of the maximum temperature gradient corresponding to the n time points obtained in step 3) inside the wood. 5) Inside the wood to be treated for pest control, set up one temperature monitoring point 0.1-1 cm before and after each temperature feature point along the direction of the temperature gradient. 6) The wood undergoes heat treatment, and the temperature of a pair of temperature monitoring points corresponding to each temperature characteristic point on the wood is measured simultaneously. The temperature difference Δt between the pair of temperature monitoring points corresponding to each temperature characteristic point is calculated. The temperature at the center of the wood is also measured, where: When the temperature difference Δt between a pair of temperature monitoring points corresponding to any temperature characteristic point on the wood to be treated is ≥10℃, heating is stopped; heating continues until the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points on the wood to be treated is ≤2℃; during the heating process, the temperature difference between a pair of temperature monitoring points corresponding to each temperature characteristic point is continuously monitored, and heating and stopping are repeated until the core temperature of the wood reaches and is maintained at 71.1℃; then the treatment is maintained for at least 75 minutes, and the wood heating and insecticidal treatment is completed.

2. The method as described in claim 1, characterized in that, It also includes step 1A): Before using finite element software to analyze the heat treatment process, the initial moisture content and density of the wood to be treated are determined; then the chordal thermal conductivity λ of the wood to be treated is calculated. 弦 Specific heat capacity c Then, the density, thermal conductivity, and specific heat capacity of the wood to be treated are input into the finite element software.

3. The method as described in claim 1 or 2, characterized in that, The n time points mentioned in step 2), where n≥3.

4. The method as described in claim 1 or 2, characterized in that, The n time points mentioned in step 2) are between 5 and 20.

5. The method as described in claim 1 or 2, characterized in that, The n time points mentioned in step 2) are 5-10.

6. The method as described in claim 1 or 2, characterized in that, The n time points mentioned in step 2) are 9-10.

7. The method as described in claim 1 or 2, characterized in that, In step 5), inside the wood to be treated for pest control, a temperature monitoring point is set at a distance of 0.3 cm before and after each temperature feature point along the direction of the temperature gradient.

8. The method as described in claim 1 or 2, characterized in that, In step 6), when the temperature difference Δt between a pair of temperature monitoring points corresponding to any temperature characteristic point on the wood is ≥3℃, heating is stopped; heating continues until the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points on the wood to be treated is ≤1℃.

9. A method for controlling insects in wood, characterized in that, The steps are performed in the following order: 1) The wood heat treatment process was analyzed using finite element method (FEM) software. The temperature of various points inside the wood was recorded at different heat treatment time points during the simulated heat treatment process. Furthermore, the time T required for heat treatment was determined when the temperature at the wood's center point reached 71.1℃. 71.1 ; 2) During duration T 71.1 Set n time points and record the duration T. 71.1 Divide into (n+1) segments; then find the temperature gradient distribution of each point inside the wood at the corresponding n time points from the analysis results of the finite element software, and obtain the temperature gradient distribution results of each point inside the wood at the corresponding n time points during the finite element analysis of wood heat treatment, where n is a natural number, n=1, 2, 3, ... 3) Find the maximum temperature gradient inside the wood at each time point from the temperature gradient distribution results corresponding to each of the n time points, and obtain the spatial coordinates of the maximum temperature gradient inside the wood at each time point from the finite element software. Define the location of the maximum temperature gradient as a temperature feature point Kn, where n is a natural number, n=1, 2, 3, ..., and obtain n temperature feature points. 4) Select at least one piece of wood from the wood to be treated as an inspection board for stacking into timber piles during wood heat treatment, and set n temperature feature points on each inspection board, wherein the location of the temperature feature points is the spatial location of the maximum temperature gradient corresponding to the n time points obtained in step 3) within the wood. 5) Inside the wood to be treated for pest control, set up one temperature monitoring point 0.1-1 cm before and after each temperature feature point along the direction of the temperature gradient. 6) Stack the timber to be treated and the inspection boards to form a timber pile. Then, perform heat treatment. Simultaneously, measure the temperature of a pair of temperature monitoring points corresponding to each temperature characteristic point on each inspection board, and calculate the temperature difference Δt between the pair of temperature monitoring points corresponding to each temperature characteristic point. Measure the center temperature of the timber at the center of the pile, where: When the temperature difference Δt between a pair of temperature monitoring points corresponding to any temperature characteristic point on the inspection board in the timber pile to be treated is ≥10℃, heating is stopped; heating continues until the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points in the timber pile is ≤2℃; during the heating process, the temperature difference between a pair of temperature monitoring points corresponding to each temperature characteristic point on the inspection board in the timber pile is continuously monitored, and heating and stopping are repeated until the center of all inspection boards in the stacked timber pile reaches and is maintained at 71.1℃; then the treatment is maintained for at least 75 minutes, and the timber heating and insecticidal treatment is completed.

10. The method of claim 9, characterized in that, The number of inspection plates mentioned in step 4) is 3-9.

11. The method of claim 9, characterized in that, The number of inspection plates mentioned in step 4) is 5-9.

12. The method of claim 9, characterized in that, In step 6), heating is stopped when the temperature difference Δt between a pair of temperature monitoring points corresponding to any temperature characteristic point on the inspection board in the stacked timber pile is ≥3℃; heating continues until the temperature difference Δt between a pair of temperature monitoring points corresponding to all temperature characteristic points on the inspection board in the stacked timber pile is ≤1℃.

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