Fabric filters reverse-pulse cleaned

Fabric-filter designs fall into three types, depending on the method of cleaning used (1) shaker-cleaned, (2) reverse-flow-cleaned, and (3) reverse-pulse-cleaned. 

In the reverse-pulse-cleaned filter, the bag forms a sleeve drawn over a cylindrical wire cage, which supports the fabric on the clean-gas side (i.e., inside) of the bag. The dust collects on the outside of the bag. 

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally reinforced with a woven insert. The physical properties and air permeabilities of some typical woven and felt filter fabrics are presented in Tables 17-6 and 17-7. The air permeability of a filter fabric is defined as the flow rate of air in cubic feet per minute (at 70°F, 1 atm) that will pass through 1 ft2 of clean fabric under an applied differential pressure of Vt in water. The resistance coefficient KF of the clean fabric is defined by the equation in Table 17-6, which may be used to calculate the value of KF from the air permeability. If Ap, is taken as 0.5 in water, t as 0.0181 cP (the viscosity of air at 70°F and 1 atm), and Vj as the air permeability, then //, = 27.8/air permeability. 

Bag filter batch load cycle and clean intermittent shaking, reverse pulse, reverse blow ring or sonic cleaifing. Load filter until the gas pressure drop across the filter is >1.5 kPa, then clean. Choice of fabric is critical static charge on fabric, operating temperature, potential for fumes to absorb with moisture to deteriorate bag, and need to select dust removal option to keep the Ap across the bag of 0.5 to 1.5 kPa. Felted material gives higher gas flow rate per unit area than woven, costs 3 to 4 times more, and cannot be cleaned by... 

Fabric Filters. Fabric filters normally use either woven or felt type cloth in the common bag-filter configuration. The fabric is made into bags 6-10 in. in diameter and 6- ft long. The air flow can be in either direction through the bag wall. The dust is periodically removed from the bag either by a shaking mechanism or by a reverse flow pulse-jet. Means are provided in either style so that only a fracrion of the total number of bags are being cleaned at any one time. 

Cleaning by reverse-flow pulses of high pressure air is normally applied to fabric filters and to pleated cartridge collectors alike. The high pressure pulses may be created by a pressure blower or come directly from a compressed air supply. In the latter case the type is normally called a pulse-jet filter. 

In a filter, the dusty gases are passed through a filter medium, which retains the particles to the extent provided by the medium chosen. Media include sand gravel beds natural, synthetic, or glass fiber woven mats woven fabrics or felts. The most cotmnon are woven fabrics, which are cleaned by shaking, intermittent reverse flow, continuous reverse flow, or air pulses. 

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