26. Apr 2019

Optimized dutch weaves: Key role in backwashing

Patrick Morsch, postgraduate student at the Institute for Mechanical Process Engineering and Mechanics from the Karlsruhe Institute of Technology (KIT), is investigating process parameters for perfect cake discharge with use of as little filtrate as possible. Particularly in the case of thin filter cakes, which are created during filtration of suspensions with a low concentration of fine-grained particles, this is often a challenge in practical application. Optimized dutch weaves made of stainless steel from GKD – GEBR. KUFFERATH AG performed most impressively in terms of backwashing rate and quality of cleaning in a test of five meshes.

Cake-forming solid-liquid separation is an established standard in many industrial processes. Examples include the production of biodiesel or cleaning of process streams in the petrochemical industry. Residue-free filter cake discharge is of particular importance for these processes. Small particles form very small pore diameters in the filter cake, leading to high flow resistance even at minimal cake thicknesses. The cake is then removed by reversing the flow. If fragments stick in place, they lead to increased flow resistance, which results in the backwashing having no effect. The required backwashing rate needs to be increased and the process performance drops. In order to determine process-relevant improvement parameters, Patrick Morsch investigated various plastic and metal mesh types used in industry. Among the metal meshes, he tested optimized dutch weaves (ODW 10 and ODW 20) and a 25 µm Porometric mesh from GKD. The results of his experiments at KIT showed that the weave type and stability of the materials play a decisive role. Plus, high porosity of the media is essential for efficient backwashing. Plain dutch weaves made from plastic and metal offer the required porosity. However, there were significant differences between plastic and metal mesh in terms of the stability of the material. The apertures of plastic dutch weaves are limited by the production process: pore openings ˂ 10 µm can only be achieved here through calendering. The thinner and less stable mesh this produces bulges out during backwashing. As such, there is increased risk of the cake breaking or only being partially removed. In addition to this, the bulging increases the required backwashing rate by more than double. Thanks to their material-specific stability, optimized dutch weaves made from metal meshes with comparable separation rates do not suffer bulging. Thanks to the higher stability of the wires, they enable a finer mesh with greater porosity. With the ODW 10 from GKD made from stainless steel, the backwashing rate was 2.5 l/m² and in the variant ODW 20 it was only 0.8 l/m². This also means that optimized dutch weaves require a thinner filter cake for complete cake discharge. In consequence, the use of optimized dutch weaves during cleaning leads to shorter cleaning cycles and further improved process efficiency.