PROJECT DESCRIPTION
BACKGROUND
Wood is an environmentally attractive building material, but it has to be preserved by impregnation with fungicides and pesticides to prolong its service life. Conventional impregnation methods are based on heavy metals and organic solvents, both undesirable pollutants. Instead of end-of-pipe treatment of these pollutants, they could be avoided by super critical wood impregnation. The super critical technique would allow the replacing of organic solvents with safe medias, such as CO2 (carbon dioxide). This would reduce the environmental strain and the pureness and quality of the product would be enhanced. Super critical technique are based on the fact that certain gases, when they are close to and in the super critical region, act as solvents. The solubility increases rapidly when the pressure is close to and above the critical point. In the super critical region, the solubility and the selectivity of a super critical fluid is changed with pressure and temperature, and small changes in these parameters can dramatically change the solvent properties. The estimated world and European market for pressure impregnated wood is in the order of 25,000,000 and 7,000,000 m3 per year, respectively. A preliminary marketing study has shown that the potential end-users of super critical impregnation recognise its advantages, from both a product and a process point-of-view. However, super crtical impregnation does present significant challenges. A major risk associated with the implementation of this project is the potential for resin diffusion to the surface of difficult to impregnate wood, like spruce. This would make the super critical technique unsuitable for such applications. Other concerns are changing wood quality and the relatively high capital cost of high pressure equipment.
OBJECTIVES
The aim of the project was to demonstrate the impregnation of wood with organic fungicides using the super critical CO2 technique. The demonstration was to be conducted in a full scale installation with a capacity of 30,000 m3 of wood per shift, per year. The technique was developed using laboratory scale equipment at FLS miljoe, where wood that is difficult to impregnate by conventional techniques was treated with organic fungicides (tebuconazole and propiconazole) using super critical CO2. The tests showed in-depth impregnation and high retention of active compounds. The impregnation technique was subsequently optimized and patented. The demonstrated outstanding penetration properties and attractive environment friendly profile of super critical CO2 encouraged the promoters to conduct a full scale demonstration of the technique. This had never been demonstrated previously. The full scale installation was to be build near Kolding, Denmark and would consist of the following major components: 4 reactors, CO2 supply system, N2 supply system (optional), warm water loop, fungicide system, gas cleaning system, pressure regulation system and piping system. The operation of the full scale unit was to proceed in two pressurisation steps, following impregnation, and then in three pressure reduction steps. The selection of operating paramenters, such as pressure, duration, and temperature would depend on the type of wood, its quality, the formulation of impregnation agents, and the quality requirements of the end product. The selection of a proper pressure reduction regime was critical to minimise diffusion of resin to the surface. The super critical wood impregnation demonstration project was to be executed, using ISO 9000 procedures, within 36 months, through the following tasks: * Process design and engineering * Procurement and installation * Start-up and process optimization * Monitoring and dissemination
RESULTS
The results of the project demonstrated the success of this super-critical impregnation technique. Tis technique is now being used commercially at the factory "Supertr " (Superwood) in Denmark. This constitutes the worlds first environmentally neutral production plant for impregnation of wood. The special high-pressure treatment method allows impregnation of wood without use of heavy metals, and without leaving traces of organic solvents in the wood. The only agent which is applied to the wood is a fungicide, which now penetrates right into the wood as a result of the innovative technology. Therefore it is possible to treat the surface of the wood, without destroying the impregnation effect. This method also allows treatment of all sorts of wood, not only pine, as is the case with conventional treatment techniques. In 2002 Supertr was awarded the EU environmental award for Denmark, within the category "clean-technologies", as an aknowledgement of the results achieved in reducing the environmental impact of economic activities. . Acccording to latest information from the LIFE external monitoring team in 2005, the new impregnation plant, based on the technology developed, is operational and in commercially productive use in Jutland.(See: www.supertrae.dk). The results of the project demonstrated the success of this super-critical impregnation technique. Tis technique is now being used commercially at the factory "Supertr " (Superwood) in Denmark. This constitutes the worlds first environmentally neutral production plant for impregnation of wood. The special high-pressure treatment method allows impregnation of wood without use of heavy metals, and without leaving traces of organic solvents in the wood. The only agent which is applied to the wood is a fungicide, which now penetrates right into the wood as a result of the innovative technology. Therefore it is possible to treat the surface of the wood, without destroying the impregnation effect. This method also allows treatment of all sorts of wood, not only pine, as is the case with conventional treatment techniques. In 2002 Supertr was awarded the EU environmental award for Denmark, within the category "clean-technologies", as an aknowledgement of the results achieved in reducing the environmental impact of economic activities. . Acccording to latest information from the LIFE external monitoring team in 2005, the new impregnation plant, based on the technology developed, is operational and in commercially productive use in Jutland.(See: www.supertrae.dk).