Measurement of wood fibre slurry distributions in a laboratory wood refiner using high-resolution gamma-ray tomography

At present, wood fibres for the production of medium density fibreboards (MDF) are produced in acceptable quality, but with high energy consumption. The adjustment of defined fibre properties is quite difficult, because the defibration process in refiners is a very complex one. Currently, its effectiveness as well as physical correlations can only be described to a minor degree. Existing knowledge is based on experiences and empirically retrieved coherences. For this reason, there is still a great demand for optimisation regarding efficiency and defined wood fibre quality. Recently our research group developed a high-resolution gamma-ray computed tomography (CT) measurement system for industrial applications, which has been successfully used in many foregoing projects. It consists of a collimated 137Cs isotopic source, a detector arc, a signal processing unit and a cooling unit. The detector arc contains 320 single detectors based on scintillation technology and the complete measurement system is non-sensitive to electromagnetic fields as well as ambient temperature changes. In a joined project, the CT measurement system of the FZD (Forschungszentrum Dresden - Rossendorf) was applied onto the downscaled refiner of the IHD gemeinnützige GmbH (Institut für Holztechnologie Dresden, Germany). The main objective is to measure wood fibre slurry density differences in the so called ring slit as well as in the refiner gap for the fully working machine. Therefore, classical radiation tomography as well as angular resolved tomography is applied. Results of first experiments will be presented, which were carried out in 2010.