The Basic Technology of Steaming and Drying of Wood

Abstract

Drying is a complex heat and mass transfer process which is affected by operating parameters environment and thermophysical properties of wood. Basis for classification of methods of drying is a method of transmission of heat to material. The basic method of drying is convective, but it is accompanied by a conductivity of wood (from the material surface to its center) and thermal radiation. The research investigates the processes of initial heating and steaming of beech wood in the form of profile pieces, which describes the dynamics of change in temperature of wood in general and particularly of surface and inner layers of wood, as well as changing the thermal properties (coefficients of heat-conducting, diffusivity and specific heat capacity) of wood. The change of thermal properties of wood causes the change of heat-exchange criteria of Fourier and Nusselt. So the use of differential equalization of heat-conducting of Fourier is possible only for the certain period of process of heating. Firstly, experimental studies of process of drying of profile workpiece (firewoods) are undertaken with a previous steaming and without a previous steaming; the corresponding sizes of speed of drying, coefficients of moisture conductivity and output of moisture are found. Consequently, taking into account the criterion of Reynolds the coefficient of drying and mass transfer coefficient of Fourier and Nusselt it is possible to synthesize the physical-mathematical model of process of drying. In the course of the study we have elaborated the structure of technological process of drying of firewoods. It is proved to include such successive technological operations as the initial heating, steaming, drying, that allows considerably to intensify mass transfer processes and, to the eventual result, shorten duration of process of drying on 25 % and accordingly to economize the charges of thermal energy. As a conclusion the author proposes structure of the technological process of drying wood that involves the use of environmentally-friendly drying agent for heating and steaming, and drying process steam-air mixture received from the combustion of waste wood. In general, the structure provides an energy saving of realization of technological process and reduces its overall duration.