The dust cake falls into a hopper for disposal or reuse in the industrial process. Filter bags hang in a sturdy house. Sometimes the house is insulated when cleaning hot gases to prevent corrosive moisture or acid mists from condensing and harming the equipment. Sometimes dozens, even hundreds of cylindrical filters, each eight to 40 feet long may hang in a series of houses at one location. Filters are made of woven cotton, wool or synthetic materials.
Some synthetic materials can withstand high temperatures or are resistant to chemical reaction.
Each baghouse must meet the needs of the particular industry process. Gas temperature, moisture content and chemical reactivity decide what filter material is used. When an industry applies for an air quality permit to install a baghouse, DNR air quality engineers must determine if the baghouse has enough filters and surface area to remove an adequate amount of pollutants before issuing the permit. The DNR also reviews the design to ensure the proposed fan size is adequate to pull or push air through the series of filters. This can be learned from similar baghouses or calculated using mathematical equations and laws of physics.