AirPollutionControl..doc

Air Pollution Control Particulate Collectors and Separators Some of the more common collectors and separators are identified below. These have application in mechanical operations for dust control such as in pulverizing, grinding, blending, woodworking, and in handling flour, also at power stations, incinerators, cement plants, heavy metallurgical operations, and other dusty operations. In general, collector efficiencies increase with particle size and from a low efficiency with baffled settling chambers, increasing with cyclones, electrostatic precipitators, spray towers, scrubbers, and baghouses, depending also on design and operation. Settling chambers cause velocity reduction, usually to lower than 10 fps, and the settling of particles larger than 40μm in diameter in trays that can be removed for cleaning. Special designs can intercept particles as small as 10μm. Cyclones impose a spiraling downward movement on the tangentially directed incoming dust-laden gas, causing separation of particles by centrifugal force and collection at the bottom of the cone. Particle sizes collected range from 5 to 200μm at gas flows of 30 to 25,000 ft3/min. Removal efficiency below 10μm particle size is low. Cyclones can be placed in series or combined with other devices to increase removal efficiency. Fig.1 Simplified diagram of a baghouse Sonic collectors can be used to facilitate separation of liquid or solid particles in settling chambers or cyclones. High-frequency sound-pressure waves cause particles to vigorously vibrate, collide, and coalesce. Collectors can be designed to remove particles smaller than 10μm. Filters are of two general types: the hag-house and cloth-screen. The filter medium governs the temperature of the gas to be filtered, particle size removed, capacity and loading, and durability of the filter. Filter operating temperatures vary from about 200°F for wool or cotton to 450 to 500°F for glass fiber. A bag-house filter is shown in Figure1. The tubular ba