In this article, textile consultant Robert Bell provides valuable background understanding and insights into the use of technical fibres and textiles to separate and purify industrial products and to clean air, gases, effluents, and a myriad of other filtering or separating applications.
Filtration is an ever-growing marketplace. Textiles used in filtration are termed “filter media”, or more simply “media”. The filtration industry is large, global, sophisticated, diverse, profitable and growing as industrial and environmental demands increase. The two distinct areas of filtration can be best categorised as:
· Separation of solids from liquids
· Separation of solids in gases.
It is a high-tech industrial industry with large volumes of product going directly from a manufacturer to an end user such as a food processing company. Processors may also be part of the supply chain as in the manufacture of Aluminium, where bauxite is first mined then refined into Alumina, through several stages of liquid filtration (wet). The Alumina is transported to a smelter where it is converted into Aluminium this process subsequently requires further filtration, which is generally categorised as (“dry”).
The science of fabric permeability or “flows through fabric” is the knowledge needed to engineer specific characteristics into a functional fabric depending on the desired outcome, and the specifications of the solids being filtered. For commercial and environmental motives, it is essential to maximise flows (either air or liquid) through the media whilst ensuring that the minimum amount of particulate passes through the cloth, or does not impede further filtration by plugging the cloth; which can occur if the particle size and shape is such that it embeds itself into the aperture developed between the weave structure and the mechanical finish applied to the cloth to achieve the desired release properties.
The choice of fibre and textile construction is critical to the performance of a given filter cloth and its processing capabilities with a given slurry composition, the characteristics of which have to be clearly identified and understood to minimise the above mentioned problems. The various chemical, thermal and pressure conditions that are encountered in the many and varied functionalities of filtration and separation have a profound influence on the type of polymer used, as well as the base product needed. When considering these conditions a sound knowledge of the different performance characteristics of the different polymers, as well as the performance capabilities of the base media have to be understood and considered.
The solids being filtered or separated also have a significant influence on the type of fabric/textile structure being employed. The different types of filter equipment also affect the media selection.
For all the above reasons, a sound knowledge of fibres and textiles is a prerequisite for the separation of solids from both liquids and gases.
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