Filtration is one of the most efficient and versatile methods of eliminating particulate mater from industrial gases. The process is made possible with the use of filter fabrics – also called baghouse filters, cartridge filters, sleeve filters and many other names – made of woven or felted material.
Filter fabrics are placed in a housing with a gas inlet and outlet connections, collection hopper, and a mechanism that periodically removes the collected dust from the fabric. As gas passes through the filter, dust may be trapped in the fabric through different mechanisms, such as diffusion, inertial impaction and direct interception.
Advantages of Fabric Filters
There are a number of advantages to using fabric filters, and here are the most important:
> Up to 99.9+% collection efficiency and with more variations in particle size and inlet grain loadings Compared to other types of single dust collectors, fabric filters can have consistent static pressure and efficiency for more particle sizes and concentrations within certain limits.
> Sulfur content of combustion fuel has no effect on collection efficiency, as in ESPs
> Minimal sensitivity to particle size distribution
> No voltage requirements
> Collects flammable dust
> Can eliminate smoke and fumes at sub-micron levels with the use of special fibers or filter aids
> Available in an entire variety of inlet and outlet locations, sizes and configurations
Types of Fabric Materials
There are two types of materials used to make fabric filters: tissue and felt. As a two-dimensional network woven in many possible ways, tissue offers varying degrees of permeability and pliability. Additionally, the properties of tissue are a product of the individual characteristics of the thread or fibre that was used to make it, along with the coating and surface treatment. The dust cake that accumulates on the filter dictates the filter qualities of tissue.
Because felt is a three-dimensional fiber network, it is more effective for filtration. Compared to tissue, felt has greater mechanical strength, allowing it to work with high fabric loading, while a smaller filter installation is enough.
Aromatic polyamide and glass fibre are two examples of basic materials used to make filter fabrics in gas applications, each having their own unique pros and cons in relation to chemical resistance, temperature, mechanical strength and cost.
Fabric filters can be used in a whole range of processes, and limitations can be overcome simply by using the most suitable filter material. This technique also allows the removal of acid components or the absorption of dioxins by injecting lime or carbon, respectively, into the fume channel. Through catalytic fabric filters, dioxins can be removed as well.
Fabric filters are currently used in various industries, such as chemicals, metal processing, food, waste processing and cattle-feed.