Patent FR-2801241-A1 (FR)
Title: Treatment of wood for timber preservation uses a succession of hot and cold baths with transfer in a shrouded environment to give the required impregnation more rapidly and with low energy consumption
Inventor: VITRAC OLIVIER
IPC: B27K5/00
Filed: 1999-11-22
Abstract: The process to treat wood, or similar material, uses heat and impregnation. The wood (4) is initially made wet to give a water content of \-25 mass%. The heating stage gives a strong evaporation of the contained water within the wood structure, followed by a dwell time in a controlled ambient environment for cooling. When cool, the wood is given a rapid chilling action by immersion in a bath of a preserving medium.  The wood is heated to a level of at least 10 kW/m<2> or 2 MW/m<3>, for the surface or the vol. The moisture content of the wood (4) is raised to 40-80 mass% of the dry mass. The heating and cooling is effected by successive immersion in two baths of oil (3,6), with a min. transfer time of 30 secs. from the first bath to the second, and pref. min. 10 secs. The first bath is held at a temp. of 110-250 deg C, and the temp. of the second bath is 10-70 deg C. Before the heating stage, the ends of the wood (4) are covered or treated to make them liquid-proof, or the longitudinal wood fibers are shrouded to give an inner pressure within the wood material during heating and reduce the scope for some of the wood to be untreated. The wood processing time is from 30 mins. to 4 hrs., with a cooling phase which is longer than the heating stage. The heat is applied to the wood surface with a flow density of 10-300 kW/m<2> by contact with a hot liquid, infra red rays or superheated steam (at 140-300 deg C) or air at a high temp. of 150-300 deg C, by high frequency or very high frequency waves at a density of 2-20 MW/m<3>. The cooling phase is by water where the wood has a dry mass content of 60% to 20%. An Independent claim is included for a wood processing assembly with a heating stage (7) to raise the temp. of the wood (4) with a flow of at least 10 kW/m<2> or 2 MW/m<3>, to give a strong evaporation of any moisture within the wood material. A cooling stage (8) reduces the temp. of the wood by immersion in a liquid (6). A transfer system (9) moves the wood (4) between the stages (7,8), which prevents any significant dwell time in a non-processing environment such as ambient air, to give the best impregnation during the rapid cooling action. Preferred Features: The assembly has a basin (2) for a bath (3) with a heater (7) such as a heat exchanger, and a mechanism (10) to ensure that the wood (4) is immersed within the bath (3). There is relative movement between the wood (4) and the bath (3) liquid by a recirculation pump or a wood agitator. A second basin (5) holds a bath (6) with a cooling unit (8) such as a heat exchanger, and a system (12) to keep the wood (4) immersed together with a recirculation pump and/or a conveyor to give a relative movement between the wood (4) and the bath (6) liquid. The transfer unit (9) between the two baths has a conveyor (14) or a traversing unit with a sieve or a lock. A hood (16) shrouds the two basins (2,5) at least partially and the transfer system (9) between them. Non-contact heat for the wood is provided by a microwave generator or an infra red radiator. A hot gas is fed (18) into the shrouding around the processing stages (2,5). The assembly can contain at least two alternating heating (2) and cooling (5) basins, with transfer units for the wood between them. A further Independent claim is included for the wood where at least a part is impregnated with a used preservation oil at a rate of 0.05-2.0 kg per kg of dry non-oily material. The oil is a composition of used or contaminated oil and pref. a vegetable oil. Preferred Features: The wood has an outer roasted layer with a thickness of 0.5-2.0 cm. The layer of impregnated wood has a thickness of 10-100% of its dia., with a water content of  <= 0.4 kg per kg of dry material.