A bag filter, also called the bag house, or the fabric filter is the air pollution control device that eliminates particulates out of the gas or air released from the commercial processes or electricity production combustion. Steel mills, power plants, food manufacturers, pharmaceutical, chemical and other industries often use bag filters in order to control the air pollutants’ emission. The bag filters come into a number of uses, started in 19070s, after the higher temperature fabric was invented, for the use in filter media and was able to bear temperature beyond 350 F.
As opposed to electrostatic precipitators, where the performance might differ significantly on the basis of electrical conditions and process, functioning bag filters usually have a specific collection efficiency of around 99 percent, even when the particle size is quite tiny. It is to be noted that most of the bag filters use a long and cylindrical bags or even tubes that are made up of felted or woven fabrics as a filter medium. This is specifically for the specifications where there is quite low dust loading and gas temperature of 250 F or less, pleated, non-woven cartridges are often used like filtering media instead of bags.
Dust-laden air or gas enters the bag filter via hoppers which are big funnel like containers used for storing and filtering the particulate, and is then moved into bag filter compartment. The gas is drawn through the bags, either on the inside or the outside depending on cleaning method, and a layer of dust accumulates on the filter media surface until air can no longer move through it. When sufficient pressure drop (delta P) occurs, the cleaning process begins. Cleaning can take place while the bag filter is online (filtering) or is offline (in isolation). When the compartment is clean, normal filtering resumes.