Dust Control Handbook for Industrial Minerals Mining and Processing

may be related to specific applications or the fabrics may simply provide a more efficient way of4optimizing the collector's potential. A wider variety of filter fabrics are now available, givingthe design engineer more options to address the problem.One of the most critical aspects to any dust collector device is the filter fabric's ability to removethe dust particles from the airstream as the dust-laden air passes through the filter fabric materialin the collector. The term "filter fabric" can be used interchangeably with the term "filtermedia." For use in dust collector devices, there are numerous types of filter fabrics with a widevariety of properties and characteristics produced by different manufacturers. Regardless of thisvariability, filter fabric effectiveness is fundamentally dependent on the ability to capture orremove dust particles from the airstream. A filter fabric's ability to let air pass through themedia (i.e., its permeability) is usually defined as the volume of air that can pass through onesquare foot of filter fabric each minute, at a pressure drop of 0.5 inches wg.Along with permeability, another measure of a filter fabric's effectiveness is its efficiency atremoving dust particles. For instance, a HEPA quality filter is one that is 99.97 percent efficientat removing 0.3-μm particles. A practice that is becoming more prevalent in the industry is torefer to a fabric's dust removal efficiency by its minimum efficiency reporting value (MERV)rating (see Table 1.3). As Table 1.3 illustrates, the higher the MERV rating, the more efficientthe filter is at capturing the various size ranges of dust particles.GroupTable 1.3. Minimum Efficiency Reporting Values (MERV) according toASHRAE Standard 52MERV RatingAverage ParticleSize Efficiency(PSE) 0.3–1.0μmAverage ParticleSize Efficiency(PSE) 1.0–3.0μmAverage ParticleSize Efficiency(PSE) 3.0–10.0μm1 < 20%1 2 < 20%3 < 20%4 < 20%5 20–34.9%2 6 35–49.9%7 50–69.9%8 70–84.9%9 < 50% ≥ 85%3 10 50–64.9% ≥ 85%11 65–79.9% ≥ 85%12 80–89.9% ≥ 90%13 < 75% ≥ 90% ≥ 90%4 14 75–84.9% ≥ 90% ≥ 90%15 85–94.9% ≥ 90% ≥ 90%16 ≥ 95% ≥ 95% ≥ 95%4For instance, many applications that involve temperature and corrosive dust or gases had been previously handledby using wet scrubbers. However, as emission requirements become more stringent, the use of scrubbers mustdiminish.Fundamentals of Dust Collection Systems 45