Basic Theory Of The Equipment Of Wood Carbonization And Optimal Control Of Temperature Field

Wood carbonization is a frontier problem in wood drying science,and its theory and technology is attracting increasingly more attention in academia.Wood carbonization is achieved mainly through the high-temperature heating treatment on wood at 160-250?,leading to the production of heat conduction function of moisture,oily substances,and inert gas in wood,the thermal decomposition effect in a short-term high temperature state could be produced by the specific substances,of which process will not produce any pollution to the atmosphere and environment,hence the physical environmental protection treatment of wood could be implemented.Wood treatment at high temperature can significantly change the physical and chemical properties of wood,significantly improve the stability of wood molecular structure,corrosion resistance and water resistance,and significantly change the color of wood.The change of wood properties after carbonization largely depends on the difference of technological conditions.Wood carbonization temperature is an important process parameter in the wood carbonization process.The temperature difference is higher than 10?,wood carbonization quality will produce certain deviation within a certain carbonization time.For example,carbonization color,carbonization depth,mechanical properties will produce differences,and even lead to the carbonized wood grade inconsistency.At present,there are few studies on the control of temperature uniformity in the wood carbonization process.It is of great significance for the wood carbonization industry to study the control of temperature uniformity in the carbonization process of the equipment of the wood carbonization,to further enhance the robustness of the wood carbonization process,and to improve the intelligence of the equipment.By analyzing the typical carbonization process,this paper discusses the influence of carbonization process parameters(e.g.,temperature and time)on the color physical and mechanical properties of carbonized wood,summarizes the best selection method of process parameters such as temperature and time.The specific research is carried out from the following aspects.(1)Referring to and analyzing the design and existing problems of the original carbonization equipment,aiming at the uniformity of the temperature field,the carbonization equipment is improved.Combined with the carbonization equipment,the three-dimensional structure model of the equipment is constructed.According to the structural characteristics of the carbonization equipment,the sensor group is optimized to improve the detection efficiency,and reduce the number of sensors from 28 to 8.It provides effective feedback parameters for uniform control of temperature field.(2)Based on the equations of heat transfer and turbulent kinetic energy,according to the process of wood carbonization,the characteristics of heat and mass transfer are discussed in stages,the boundary conditions are defined,and the heat and mass coupling equations are solved by FLUENT software,forming multi physical field coupling model of wood carbonization temperature.By using the model,temperature field of the empty equipment,carbonization temperature rising of the equipment and carbonization stage of it are simulated.According to the experimental results,the Pearson correlation coefficients of simulated and real temperature monitoring values are greater than 0.95,and the simulated and real values have a good positive correlation.The results show that the mathematical model of wood carbonization can effectively represent the temperature gradient in the tank during the carbonization process.(3)According to the multi physical field coupling model of carbonization temperature of the equipment of the wood carbonization,the changes of heat distribution in wood carbonization,field distribution of calculation model of wood carbonization,control parameters of wood carbonization and factory distribution of calculation model are analyzed.The overall changes of field and temperature uniformity in horizontal and vertical aspects of the equipment under different conditions are concluded.By analyzing the influence factors of temperature field uniformity of the equipment,six control parameters are selected,including heat transfer oil inlet temperature,fan speed,air pressure,humidity,fan horizontal angle and fan vertical angle response surface experiment scheme is designed,54 groups of crossover tests are conducted,the relationship model between six control parameters and temperature field uniformity of the equipment are established.According to the test results,the Pearson correlation coefficient between the calculated value and the measured value of the spatial temperature variance is greater than 0.95,and the p value of t test is greater than 0.05,which shows that there is no significant difference between the calculated value and the measured value,and there is a good positive correlation.The results show that the model can effectively reflect the relationship between the control parameters and the temperature field uniformity of the carbonization tank.(4)Combined with the temperature uniformity model design of carbonization equipment,the temperature uniformity control method fitting the requirements of carbonization process is established;Anti fuzzification of the equipment are used based on the compound fuzzy+PID.Through the cloud PC calculation based on the uniform model of temperature field,the temperature,air pressure,humidity,fan speed,fan vertical angle and fan horizontal angle of the heat transfer oil are controlled.The control system based on cloud end mode is realized.By controlling the inlet air temperature,inlet air volume,inlet angle and other parameters of the fan,the temperature uniformity in the furnace is achieved in the shortest time,and the temperature uniformity of the equipment in the carbonization stage is guaranteed.The experimental results show that 90%homogeneous carbonized wood can be produced by the control system.The experiment shows that the calculation model of the wood carbonization process and the control method of temperature field uniformity in carbonization stage of the equipment of wood carbonization established in this thesis can significantly increase the quality evaluation indexes of carbonized wood.They can provide theoretical basis and technical guidance for enterprises to improve the quality and yield of high-quality carbonized wood.At the same time,they also provide a meaningful reference for the drying direction of wood science,especially for the optimization of wood carbonization process.