Characterisation of woven filter media in solid-liquid filtration : the study of pore size distribution, air, and water permeability

Abstract

Currently, we cannot imagine our lives without filtration. Filtration, separation and recycling processes are the future if we want to live in a clean and sustainable world. Filtration processes can be found in various industries, starting with wastewater treatment and ending with the manufacturing of pharmaceuticals, food processing and so forth. The filtration process is based on high-quality technologies and equipment. Any filter, in turn, consists of a filter medium, which is sometimes called the heart of a filtration process. The primary purpose of a filter medium is to separate suspended particles from liquids or gases by allowing the solution to flow through its porous structure. Therefore, the filter medium’s characteristics can affect the success of any filtration process.

Nowadays, woven filter media characterisation, which is deemed one of the most crucial components in the media marketplace, is constrained by air permeability values. Cloth manufacturers mainly provide only information about this property to their customers. There are numerous studies on the significance of individual parameters, but clothes are never designed using only one parameter. Moreover, the key characteristics that dictate the performance of filter cloths in solid-liquid filtration, namely pore size (distribution) and water permeability, are poorly understood.

The objective of this study was to examine two attributes of woven filter media related to performance: water permeability and pore size distribution. Currently, there are no standardised techniques for assessing and quantifying the water permeability of woven filter media. Therefore, the development and implementation of new equipment are central. Furthermore, the characteristics of pore size distribution have not been extensively studied. Much criticism is associated with the capillary flow porometry technique utilised to determine pore size and pore size distribution. Therefore, a deep understanding and improvement of the existing technology and making it acceptable to the scientific community were the other goals of this work. The final step was to analyse and study three characteristics of woven filter media related to performance, including air and water permeability and pore size distribution, with the aim of identifying correlations among them.

During this study, new equipment was designed, developed and tested for measuring water permeability under both constant and declining pressure conditions. The results were subsequently compared with fluid flow simulations. The study demonstrated that the apparatus functioning at constant pressure yielded the most reliable and consistent results and could be recommended to form the standard in the future. In addition, a new improved approach for calculating pore size distribution was developed, tested and proposed as an alternative to the commonly used procedure. Moreover, the capillary constant parameter was investigated and explained, and its necessity in pore diameter calculations was evaluated.

It was concluded that a singular value of air permeability is insufficient for embracing and describing the performance of woven filter media in solid-liquid filtration. Two other characteristics—pore size distribution and water permeability—are valuable sources of information that can enrich the understanding of woven filter media and improve their properties. Gathering information on three different performance-related characteristics is essential for cloth manufacturers and those who work and use this filter media. Adequate state-of-the-art characterisation requires the incorporation of several parameters to comprehensively assess the filter media used in the processes of solid-liquid filtration. Moreover, finding correlations between air and water permeability along with pore size distribution and expressing them in the form of empirical equations are essential. This approach can help gather information about multiple characteristics simultaneously and save time and money spent on additional tests, equipment and labour.