Determination of the heat energy for hydrothermal treatment of ashwood (Fraxinus excelsior) by log soaking

Abstract

The treatment of logs by soaking is a complex technological and thermal procedure, in which logs and prisms are used as raw material for the production of peeled and sliced veneers. Such treatment of logs is carried out in pools or pits constructed in the ground. By log soaking two significant changes to the wood are achieved, its coloring and the inevitable plastification of the wood fibers. During this procedure, the time required for air drying is significantly reduced. The soaking medium is fresh water or previously used water at an elevated temperature. This soaking treatment is particularly suitable for logs for the production of peeled and sliced veneer, from which resin must be removed. Soaking is also used when treating wood species that are sensitive to steaming. This paper provides an analysis of the thermal energy required for hydrothermal treatment by log soaking of ashwood (Fraxinus excelsior). The logs were intended for the production of peeled veneer. The log treatment was done in a reinforced concrete pool built in the ground. The total amount of heat for log soaking (Q) consists of effective heat (Qpv) and heat loss (Qzv). The procedure was conducted by the strong treatment mode, with a temperature interval in the range of 70 to 90 °C. The treated logs had a minimum mean diameter of 35,0 cm and a minimum length of 1,8 m. Log soaking was used as a method for defrosting of the logs, due to their low initial temperature, which was– 15 °C.