Particulate control

Most commonly used particulate control technologies are  

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Sampling of Particulates. Ambient air suspended particulate concentration was traditionaUy measured gravimetricaUy over a 24-h period with a "Hi-Vol" sampler. However, in 1987 the EPA changed ambient particulate control to the PM q reference method (24). In the PM q method, a... 

V. Reyes, Comparison between TraditionalandModem Automatic Controllers on Eull-scale Precipitators, Seventh Symposium on Transfer and Utilization of Particulate Control Technology, Nashville, Term., March 1988, F. L. Smidth Co., Valby, Denmark. 

V. E. Schoeck ia B. E. Kester, ed.. Proceedings, Specialty Conference on Design, Operation, and Maintenance of High Efficiemy Particulate Control Equipment, Air Pollution Control Association, Pittsburgh, Pa., 1973, pp. 103—117. 

These references do not iaclude electrostatic augmentation which are iacluded under "Particulate Control, Electrostatic Attraction."L. E. Sparks... 

The principal technological changes in the engineering control of air pollution were the perfection of the motor-driven fan, which allowed large-scale gas-treating systems to be built the invention of the electrostatic precipitator, which made particulate control in many processes feasible and the development of a chemical engineering capability for the design of process equipment, which made the control of gas and vapor effluents feasible. 

Since mist and droplets differ significantly from the carrying gas stream, just as dry parhculates do, the removal mechanisms are similar to those employed for the removal of dry particulates. Control devices developed particularly for condensing mists will be discussed separately. Mist collcc-hon is further simplified because the parhcles are spherical and tend to resist reentrainment, and they agglomerate after coming in contact with the surface of the collechng device. 

Calcined limestone or Ume reacts with sulfur oxides. They are then removed with a dry particulate control system. 

Oxides of sulfur react with copper oxide to form copper sulfate. Removal with a dry particulate control system follows. 

Szabo, M. F., and Gerstle, R. W., "Operation and Maintenance of Particulate Control Devices on Coal-Fired Utility Boilers," EPA-600/2-77-129. U.S. Environmental Protection Agency, Research Triangle Park, NC, 1977. 

Figure 30-lB is similar to Fig. 30-1A except that an ESP is used for particulate control. This represents the most common approach for compliance when configured without a catalytic NO urrit. 

Figure 30-lD represents the simplest, least expensive, and lowest water consumer of all the alternatives. There is a single solid waste product. The key element is the integrated S02/particulate control process. Using sodium-based sorbants, compliance may be achievable for western United States coals. 

A very important analytical tool that is overlooked by many sourcetesting personnel is the microscope. Microscopic analysis of a particulate sample can tell a great deal about the type of material collected as well as its size distribution. This analysis is necessary if the sample was collected to aid in the selechon of a piece of control equipment. All of the efficiency curves for particulate control devices are based on fractional sizes. One would not try to remove a submicron-size aerosol with a cyclone collector, but unless a size analysis is made on the sampled material, one is merely guessing at the actual size range. Figure 32-8 is a photomicrograph of material collected during a source test. 

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

An ESP is a particulate control device that uses electrical forces to move particles entrained within an exhaust stream onto collection surfaces. The basic theory has already been described under dry ESPs, but a brief summary here is included, with... 

Applicability/Limitations Liquid injection incineration can be applied to all pumpable organic wastes including wastes with high moisture content. Care must be taken in matching waste (especially viscosity and solids content) to specific nozzle design. Particle size is a relevant consideration so that the wastes do not clog the nozzle. Emission control systems will probably be required for wastes with ash content above 0.5 percent (particulate control) or for halogenated wastes (acid gas scrubbers). 

Electrostatic precipitators are satisfactory devices for removing small particles from moving gas streams at high collection efficiencies. They have been used almost universally in power plants for removing fly ash from the gases prior to discharge. Electrostatic precipitators have the capability of fine particulate control. Resistivity plays an important role in determining whether a particle can be readily collected in this device. 

Wet scrubbers have found widespread use in cleaning contaminated gas streams because of their ability to effeetively remove both particulate and gaseous pollutants. Specifically, wet scrubbing describes the technique of bringing a contaminated gas stream into intimate contact with a liquid. The types most widely used for particulate control are spray towers, packed-bed units, ionizing wet scrubbers, and venturi scrubbers. 

It is important to note tlmt tlic deposition rate is a strong function of particle dimneter tluough the term v, wliich appears twice in tlic deposition flux equation. Equation (9.7.10) must be modified to treat process gas streams discliarging particles of a given size distribution. The suggested procedure is somewhat simihu to tlial for calculating overall collection efficiencies for particulate control equipment (12). For this condition, the overall rale is given by... 

FIGURE 16.7 Filtering module for fine particulate control and droplet separators. (With... 

Core, J.E. Hanrahan, P.L. Cooper, J.A. "Air Particulate Control Strategy Development A New Approach Using Chemical Mass Balance Methods." This symposium. 

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