SPÖRL KG Hall 8 / B13

Due to their high chemical, thermal and mechanical resistance, woven wire meshes as metallic filter media can be used in demanding operating conditions, for example in the form of high process pressures and temperatures or sharp-edges particles which have to be deposited. With their narrow pore size distribution woven wire cloths guarantee an excellent separation and classifying accuracy. Depending on the combination of the warp wires and the weft wires during the weaving process, the production of different types of weave with different aperture sizes and filtration behaviors is possible. Betamesh-PLUS is a weaving type, with which highest separation efficiencies at lowest power consumptions can be realized. As in any filter medium, the smaller the pore size, the thinner the structures forming the filter medium must be selected. In the case of a wire mesh, this means that the finer the mesh the thinner the used wires must be chosen. However, this also reduces the mechanical stability of the wire mesh.

To avoid this difficulty and to use these fine Betamesh-PLUS also under harsh operating conditions, the Betamesh-PLUS can be used as a filter layer in so-called composite-cloths. In composite-cloths, the filter layer is bonded to one or more supporting, protection and drainage layers over the entire surface in a high-temperature sintering process. These further layers are woven wire meshes with a large aperture size made of relatively thick wires.

The paper systematically evaluates the filtration performance of the composite-cloths based on the initial pressure loss, absolute pore size, dirt-holding capacity, load-dependent separation efficiency and cleaning behavior. These quantitative parameters are determined experimentally using a flow-rate test rig, an air-solid test rig and a cleaning test rig in accordance with DIN ISO 11057. The obtained results are subsequently compared with the performance characteristics of single-layered Betamesh-PLUS.

Furthermore, the influence of incorporating one or two supporting layers into the composite-cloth is examined and illustrated. For the protection of the filtration layer, a coarse woven wire mesh can be sintered onto it as the outermost layer of the composite structure. The results demonstrate that the integration of such a protection layer leads to a substantial reduction in permeability and dirt-holding capacity and consequently to a decrease in the service life of the filter medium. Additionally, particles may become entrapped between the protection layer and the filtration layer. Pulse-jet cleaning experiments reveal that these retained particles contribute to an increase in the residual pressure loss.

Cartridge filters are a frequently used geometry of filter elements, often made out of composite-cloths. The cartridge filters are flown through from outside to inside. The maximum possible overpressure until the element buckles, the so-called buckling-pressure, depends on the geometry of the cartridge and on the mechanical properties of the filter material used. Within the paper, the buckling-pressure of different cartridges made of composite-cloths with different layer structures is determined experimentally. Using these results, it is now possible to build the cartridges using the composite-cloths with the lowest number of needed supporting layers to withstand the arising pressure forces and consequently to operate the filtration process in an energy-efficient manner.