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Fabric Filter Collectors
Published in Kenneth Schifftner, Air Pollution Control Equipment Selection Guide, 2021
Sizing fabric filters starts with an air-to-cloth ratio that field experience has shown will work on a certain application. The air (cubic feet per minute) to cloth (medium area) calculation gives us the face or impact velocity of dirty air as it hits the filter medium. Let us assume we have a ventilation process requiring 7200 acfm and the suggested ratio is 6/1; therefore, 7200/6 = 1200 ft cloth required in the dust collector (nominally), and 7200/1200 = 6 cfm/ft2 or 6 ft/min face velocity. As you can see, this provides us with a relative value for the volume and velocity of dirt and air flowing through the surface of the medium. The higher the gas velocity, the harder it is to push the dust off because you are pushing the dust back into the oncoming gas stream.
Control of Particulate Emissions
Published in Jeff Kuo, Air Pollution Control Engineering for Environmental Engineers, 2018
For a filter system, there is a threshold air-to-cloth ratio. Below this threshold value, the particulate emission rates are relatively constant. Above this threshold, the emissions can increase sharply (Figure 6.28). The shaker fabric filters often use woven fabrics and operate with an air-to-cloth ratio of 2 to 4 ft/min (0.6 to 1.2 m/min). Reverse-air collectors usually use woven fabrics (membrane bags and felted bags are used in some applications) and operate with an air-to-cloth ratio of 1.5 to 3.5 ft/min (0.45 to 1.1 m/min). Pulse jet collectors use felted fabrics and operate with an air-to-cloth ratio of 3 to 10 ft/min (0.9 to 3.1 m/min) (EPA, 2012).
Gas Scrubbing Systems
Published in David A. Lewandowski, Design of Thermal Oxidation Systems for Volatile Organic Compounds, 2017
One of the most important design parameters of the fabric filter is the air-to-cloth ratio. This is the volumetric flowrate of the flue gas (ft3/min) divided by the surface area of the fabric (ft2). The higher this ratio, the smaller the fabric filter, but the higher the pressure drop. Reverse-air (flue gas) and shaker baghouses with woven fabric bags generally have air-to-cloth ratios ranging from 2.0 to 3.5. Baghouses utilizing the pulse-jet (compressed air) cleaning technique usually use felted fabric bags and have air-to-cloth ratios from 5 to 12.
Evaluation of a self-cleaning portable dust collector for reducing worker exposures to silica at hydraulic-fracturing sites
Published in Journal of the Air & Waste Management Association, 2023
Grant King, Arthur Miller, Carl Schneider, Greg Feagan, Darby Gain
Rapid filter overloading is normally prevented by balancing the available filter surface area with the expected airflow, i.e., ensuring that the air to cloth ratio (A/C) would be in an acceptable range during operation. The A/C is defined as the ratio of airflow to filter surface area i.e., cfm per square foot of filter area. The term A/C thus has units of velocity, and in fact is sometimes considered synonymous with the term “face velocity” which will be used here. Acceptable face velocity is determined by a number of factors: material factor, application factor, temperature, inlet dust loading, and mass mean diameter of particles (Schousboe 2017; Turner et al. 1998). If the face velocity of air (and particles) is too high at the filter interface, the particles will tend to penetrate the filter media and “blind” (plug) the filter. This is typically avoided by designing the system such that the face velocity is in the range of 3–10 feet per minute (ft/min) (depending on the factors noted above) (Schousboe 2017; Turner et al. 1998). When velocity is in this range, or lower, the particles do not penetrate, but instead collect on the outer surface of the filter media forming a surface layer of “cake”. The cake provides two advantages: 1) it is itself an excellent filter media and 2) after sufficient filter cake buildup is achieved, it is more easily removed by a jet pulse.