Dust separator, applications

Dowtherm(R) pressure drop, charts, 94,113 Draft tubes, mixing, 309, 313 Dust clouds, 517 Dust explosions, 513 Calculations, 513 Dust separator, applications, 278 Characteristics, 234 Table, 232... 

The Sylvan Chart [2] of Figure 4-3 is useful in preliminary equipment selection, although arranged primarily for dust separations, it is applicable in the appropriate parts to liquid separations. Perry [23] presents a somewhat similar chart that is of different form but contains much of the same information as Figure 4-1 and 4-lA. 

Scrubbers are pollution control devices, which remove pollutants from gas streams, particularly from the combustion gases produced by facilities such as coal-fired power plants. Scrubbers may use absorbents in slurry or solution form (wet scrubbers), or in powder form (dry scrubbers), with wet scrubbers being more often used. Modern scrubbers can consist of several cleaning steps such as dust separation, sulfur removal, capture of mercury, lead, or other heavy metals, and breakdown of nitrogen oxides. Scrubbers of the future will also need to capture and sequester carbon dioxide. Currently, the most common application of scrubbers is still the removal of sulfur, frequently combined with capture of fly-ash. 

The high speed of the easy phase, which are carrying away in direct-flow motion a liquid, and reliable separation of phases after interacting in a vortex flow allow to intensify sharply a mass transfer and in 3-8 times to increase carrying capacity of the apparatus. Application of whirlwind apparatuses for a dust separation (Ershov, 1973 Prihodko, 1979 and Diarov, 1979) is presented. 

Comparison of opportunities dust separation the equipment of various types also testifies to prefer ability of application of vortical devices at clearing great volumes of gas emissions. All above-stated has... 

The Optimum mode of clearing of gas emissions can be reached achieved at application of the developed design bubbling— the vortical device providing a mode evaporation—condensation cooling and centrifugal wet dust-separation[4-7]. 

Dust entrained in the exit-gas stream is customarily removed in cyclone cohectors. This dust may be discharged back into the process or separately cohected. For expensive materials or extremely fine particles, bag collectors may follow a cyclone collector, provided fabric temperature stability is not hmiting. When toxic gases or solids are present, the exit gas is at a high temperature, the gas is close to saturation as from a steam-tube diyer, or gas recirculation in a sealed system is involved, wet scrubbers may be used independently or following a cyclone. Cyclones and bag collec tors in diying applications frequently require insulation and steam tracing. The exhaust fan should be located downstream from the cohection system. 

The basic operations in dust collection by any device are (1) separation of the gas-borne particles from the gas stream by deposition on a collecting surface (2) retention of the deposit on the surface and (3) removal of the deposit from the surface for recovery or disposal. The separation step requires (1) application of a force that produces a differential motion of a particle relative to the gas and (2) a gas retention time sufficient for the particle to migrate to the coUecting surface. The principal mechanisms of aerosol deposition that are apphed in dust collectors are (1) gravitational deposition, (2) flow-line interception, (3) inertial deposition, (4) diffusional deposition, and (5) electrostatic deposition. Thermal deposition is only a minor factor in practical dust-collectiou equipment because the thermophoretic force is small. Table 17-2 lists these six mechanisms and presents the characteristic... 

The cast grids are made into battery anode and cathode plates by the application of a lead oxide paste of 70 percent lead oxide (PbO) and 30 percent metallic lead. Lead ingots are tumbled in a ball mill with airproducing lead oxide and fine lead dust (referred to as leady oxide ). Leady oxide particulates are entrained in the mill exhaust air, which is treated sequentially by a cyclone separator and fabric filter. The used fabric filter bags are shipped to a RCRA-permitled commercially operated ha2ardous waste landfill located in Colorado. The leady oxide production process does not produce wastewater. 

The two-stage electrostatic precipitators used in light-industry applications are compact devices which can be fitted into the ventilation system. These air cleaners are normally used to clean air from dusts, smokes, and fumes in industrial workplaces. The basic features of these devices are the separate sections for particle charging and collection. The charging section consists of thin metal wires installed between grounded metal plates. The distance... 

Table 4-5 [10] summarizes dry dust particle separators as to general application in industry, and Table 4-6 and Figures 4-4 and 4-5 [42] compare basic collector characteristics. Figure 4-5 presents a typical summary of dust collection equipment efficiencies which have not changed significantly for many years except for specialized equipment to specialized applications. 

Figures 4-65, 4-66, and 4-67 show several units of the bag. The bags may be of cotton, wool, synthetic fiber, and glass or asbestos with temperature limits on such use as 180°F, 200°F, 275°F, 650°F respectively, except for unusual rnaterials. (See Table 4-12A and B.) These units are used exclusively on dry solid particles in a gas stream, not being suitable for wet or moist applications. The gases pass through the woven filter cloth, depositing the dust on the surface. At intervals the unit is subject to a de-dust-ing action such as mechanical scraping, shaking or back-flow of clean air or gas to remove the dust from the cloth. The dust settles to the lower section of the unit and is removed. The separation efficiency may be 99%-i-, but is dependent upon the system and nature of the particles. For extremely fine particles a precoat of dry dust similar to that used in some wet filtrations may be required before re-establishing the pi ocess gas-dust flow.

The separation step requires (1) application of a force that produces a differential motion of the particles relative to the gas, and (2) sufficient gas-retention time for the particles to migrate to the collecting surface. Most dust-collections systems are comprised of a pneumatic-conveying system and some device that separates suspended particulate matter from the conveyed air stream. The more common systems use either filter media (e.g., fabric bags) or cyclonic separators to separate the particulate matter from air. 

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