A.D. Schwarz, J. Meyer, A. Dittler

Separation and Purification Technology, 2021, https://doi.org/10.1016/j.seppur.2020.118128

In surface filtration processes, particles are collected on the upstream face side of the filter and form a filter cake. In commonly studied processes for the removal of particles from dust-laden gas streams, this cake remains on the filter surface until it is removed from the filter for example by pulse-jet cleaning. However, soluble particles are present in our ambient air as well as a common component of aerosols in various gas cleaning processes. When soluble particles are present in the filter cake and are exposed to fine water droplets throughout the process, the soluble particles dissolve. This can lead to a restructuring of the filter cake and the penetration of particles into the filter medium. This behavior in gas cleaning systems and its possible influence on the structure of the cake and pressure drop across the filter has not yet been systematically investigated.

The experiments presented in this work show how soluble filter cakes restructure on hydrophobic glass fiber media after being exposed to water droplets at a filtration velocity of 3.5 cm s⁻¹. Sodium chloride, potassium chloride and potassium sulfate particulate matter is separated from a dry air stream and subsequently exposed to different amounts of water droplets or a relative humidity above 85% with no liquid droplets present. The effect soluble species have on the operational behavior are observed by recording the pressure drop over the filter medium. Additionally, micrographs with a scanning electron microscope visualize the structural changes of the filter cakes. In combination with the pressure drop recordings, the images are used to analyze the restructuring of the particles on the filter when the salt is exposed to the liquid or high relative humidity only.