Study On The Characteristics Of Impinging Stream Drying Of Wood Particulate

Impinging stream drying technology is a new drying technology with, high drying capacity. Many studies have been made on its theory and application on food and chemical industries. However, few have been reported on its study and application in wood industry. Drying of wood particle is the most energy consuming process in whole production of wood-based panel, and impinging stream drying technology will play an important role in energy saving and benefit improvement in the process of drying wood particle. Therefore, the study of this project is of important theoretical value and practical significance.To study the applicability of impinging stream drying technology in drying wood particulate, the Vertical-inclined semi-circular Impinging Stream Drying System was built to dry wood particulate materials, and drying trials were done for wood fiber and wood particle respectively. Also effects of various factors on drying process and drying efficiency were examined. These factors include: initial moisture content, airflow temperature and flux, and load. The experience results indicate that there is little effects of the initial moisture content of wood fiber on the final moisture content, i.e., fiber meeting the required final moisture content can be obtained even if materials contain different initial moisture content. However, the initial moisture content of wood particle has greater effect on the final content, and wood particle with high initial moisture content could not reach the required final moisture content through one dryingprocess, so that more drying processes may be needed. The results also suggest that only wood particle with moisture content near fiber saturation point can reach the required final moisture content after one drying process, and ail'flow temperature and flux can improve the drying capacity significantly. With the load increasing, the final moisture content goes up slightly, and the ability of system removing moisture rises linearly with the increasing of load. Therefore, raising load is an effective way to improve system throughput.As a new high speed drying technology, the wood particulate quality through impinging stream drying system is the most concern. In the thesis, both microscopic inspection and product properties were analyzed. The results indicate that no scathes are found in microscopic structure of material dried under impinging stream drying system. F-test shows that there are no significant differences between the properties of products produced under same conditions but materials dried under different systems, i.e., impinging stream drying system and conventional drying system. Therefore, we may draw conclusion that impinging stream drying technology may be employed to effectively dry wood particulate with less energy consummation and no negative effects on product quality.Also tested were temperature distribution, changes of moisture content along the direction of material movement, pressure drops of system, drying effects of various parameter combinations. Test outcomes demonstrate that drying capacity of impinging stream drying system is considerably higher than that of conventional airflow drying system.Impinging drying of wood is a process of moisture removal with high speed and efficiency, so that moisture diffusion and movement, heat transfer from drying media tomaterial are very prompt. As a result, the coupling effect of heat and moisture might affect drying process. The thesis testified the existence of such a coupling effect theoretically and nearly experimentally, and revised the description of the heat transfer and mass diffusion in related textbooks, and educed the relationship formula about relationship of heat transfer and mass diffusion during the wood being dried. In order to examine the characteristics of heat transfer in wood particle, an analogy approach of computing resistance of electro-circuit was employed in deriving transversal heat conductivity of wood particulate. The correction coefficients for uneven material distrib...