FWF - KR - Filter Clean - KR-Filter Cake Dislodgement in Gas Cleaning

In process engineering, filtration is often applied to separate small particles from gases. While the gas flows through a flexible, porous filter media, the particles are collected on the filter surface where they form a filter cake. While particles accumulate on the filter surface, flow resistance increases and intermittent filter cleaning is required to continue operation. Cleaning is often accomplished by initiating short termed high pressure air pulses in the opposite gas flow direction. Thereby the filter media is accelerated together with the deposited filter cake. At some point the filter cake is dislodged from the filter media and it breaks. Overall filter cleaning is, however, ineffective, when these filter cake patches or particles are not withdrawn from the filter but are re-deposited on the filter media once particle separation continues right after the air cleaning pulse. (Particle removal from the filter unit is generally accomplished by gravitational sedimentation of the filter cake patches and their withdrawal at the bottom of the filter unit.) Filter cake sedimentation is enhanced when cake patches settle like a curtain, i.e., when the filter cake patches are rather large and aligned vertically. Filter cleaning is investigated to understand filter cake dislodgement and its breakage, dependent upon duration and pressure of the cleaning pulse and the properties of the filter cake. Special attention is paid to the velocity of these cake patches and their positions after the cleaning pulse was initiated. Experiments are performed where filter cakes are produced from different gas-solid mixtures and under different conditions. These filter cakes are exposed to reverse air jet pulses and the resulting filter cake patches are measured optically in terms of size and location. Patterns are impressed locally on filter media by e.g. annealing to change cake formation locally. During subsequent cleaning cake breakage is likely to occur along these patterns where the filter cake interconnectivity is weaker. Existing mathematical models are applied and expanded, and simulations are performed to mimic the experimental situation and verify the models. Triggered by model simulations, experiments are performed with parameters where cake dislodgement is ensured, and the resulting cake patches are expected to have a rather uniform and large size and the distance from the filter media is constant. This information is used to visualize the optimization potential in filter design and operation.