Particulate collection

Settling chambers, low-pressure-drop cyclones, and dynamic precipitators are among the most common and important devices applied in end-of-pipe control applications for dust and particulate matter. 

Before selecting or sizing a specific control device, a careful evaluation of all aspects of the process and contaminants must be made. Improper terminology can lead to poor design and/or operation of any type of device. A list of contaminant definitions in accordance with the USA Standards Institute includes the following. 

Physical dimensions are characterized by the ductwork above the collection 

The primary section of the chamber is characterized by its cross-sectional area (W X H) and by its length (L). The cross-sectional area is designed to be larger than the inlet and exit ducts in order to reduce substantially the gas stream s inlet linear velocity. The length of the chamber determines the amount of time the particles remain at the redueed rate. This starving of the gas s forward motion allows the partieles sufficient time to settle out into the hoppers. 

For dilute systems, Stoke s law is applicable to particle settling. References cited at the end of this chapter provide design and sizing information. 

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Pulverized lime or limestone injected into flue gas (often through burner). SO2 absorbed on soHd particles. High excess alkah required for fairly low SO2 absorption. Finer grindings lime preheat, flue gas humidification benefit removal. Particulate collected in baghouse. 

Parquet, The E/ectroscrubber Filter Applications and Particulate Collection Performance, EPA-600/9-82-005c, p. 363,1982. 

W. Strauss, "Particulate Collection by Liquid Sembbing," in Industrial Gas Cleaning 2nd ed., Pergamon Press, Oxford, 1975, Chapt. 9, pp. 367—408. 

W. Licht, Air Pollution Control Engineering. Basic Calculationsfor Particulate Collection, Marcel Dekker, Inc., New York, 1980. 

Cement plants in the United States are now carehiUy monitored for compliance with Environmental Protection Agency (EPA) standards for emissions of particulates, SO, NO, and hydrocarbons. AH plants incorporate particulate collection devices such as baghouses and electrostatic precipitators (see Air POLLUTION CONTROL methods). The particulates removed from stack emissions are called cement kiln dust (CKD). It has been shown that CKD is characterized by low concentrations of metals which leach from the CKD at levels far below regulatory limits (63,64). Environmental issues continue to be of concern as the use of waste fuel in cement kilns becomes more widespread. 

The various venturi-scrubber models embody a variety of assumptions and approximations. The solutions of the equations for particulate collection must in general be determined numerically, although... 

Relatively low overall particulate collection efficiencies, especially on particulates below 10 im in size... 

The selection of the optimum type of particulate collection device (i.e., ESP or fabric filter oaghouse) is often not obvious without conducting a site-specific economic evaluation. This situation has been brought about by both the recent reductions in the allowable emissions levels and advancements with fabric filter and ESP technologies. Such technoeconomic evaluations can result in application and even site-specific differences in the final optimum choice (see Piecip New.sLetter, 220, June, 1994 and Fabric Filter Newsletter, 223, June, 1994). 

Three of the disadvantages of ESPs are as follows (1) the initial cost is the highest of any particulate collection system, (2) a large amount of space is required for the installation, and (3) ESPs are not suitable for combustible particles such as grain or wood dust. 

List the advantages and disadvantages of using a baghouse, wet scrubber, or LSI tor particulate collection from an asphalt plant drying kiln. The gases are at 250 X and contain 450 mg m of rock dust in the 0.1-10 /rm size range. Gas flow is 2000 min. Consider initial and operation cost, space requirement, ultimate disposal, etc,... 

Several separating systems are used for particulate sampling. All rely on some principle of separating the aerosol from the gas stream. Many of the actual systems use more than one type of particulate collection device in series. If a size analysis is to be made on the collected material, it must be remembered that multiple collection devices in series will collect different size fractions. Therefore, size analyses must be made at each device and mathematically combined to obtain the size of the actual particulate in the effluent stream. In any system the probe itself removes some particulate before the carrying gas reaches the first separating device, so the probe must be cleaned and the weight of material added to that collected in the remainder of the train. 

Transfers to Other Off-S(te Locations. Yourfacility returns the lead particulate collected by the fabric filters to the off-site smelter for recovery and reuse. You are not required to report releases of listed substances to off-site recovery facilities therefore, no information concerning the off-site smelter should be entered in Part III, Section 6 of Form R. 

Decontamination factor A logarithmic scale used to measure the collection efficiency of a particulate collection device. 

Tackifier A substance applied to a particulate collection device to increase its efficiency in dust retention. 

Unit collector A particulate-collection device that is self-contained with fans, filters, etc. 

Wet centrifugal A dust collector that uses water or other fluid in a centrifugal action in order to improve the particulate collection efficiency. 

Where low-grade coal is burned, electrostatic precipitators or fabric filters may be required for flue-gas particulate collection and a wet desulfurization system (gas scrubbers) to remove sulfur from the flue gas. 

Querying the adequacy of chimneys and stacks, scrubbers and particulates collection equipment (e.g. filters, cyclones). 

The various venturi-scrubber models embody a variety of assumptions and approximations. The solutions of the equations for particulate collection must in general be determined numerically, although Calvert et al. [J. Air Pottut. Control Assoc., 22, 529 (1972)] obtained an explicit equation by making some simplifying assumptions and incorporating an empirical constant that must be evaluated experimentally the constant may absorb some of the deficiencies in the model. Although other models avoid direct incorporation of empirical constants, use of empirical relationships is necessary to obtain specific estimates of scrubber collection efficiency. One of the areas of greatest uncertainty is the estimation of droplet size. 

A thin film of oil-like material was visible after 28 d on the exterior surfaces of the SPMD membrane. Analysis of this film indicated that the triolein impurities, oleic acid and methyl oleate, were the major constituents. This external lipid film (Petty et al., 1993) appeared to contain imbibed particulates. Although the film was removed from the SPMDs by solvent rinsing and analyzed separately, some lipid-mediated desorption of particle-associated PCBs and subsequent diffusion into the SPMD may have occurred prior to solvent-removal of the film. This observation suggests the potential for SPMD concentrations to reflect both vapor phase concentrations and to a lesser extent, lipid-extracted particulate-associated residues (see Section 3.9.2.). Unfortunately, concentrations of more chlorinated congeners in particulates collected on GFFs from the NIOSH method were often below quantitation limits, because only a small volume of air was sampled (1 m ) using this active method. 

The determination of the levels of drugs of abuse in atmospheric particulates collected at regular air quality monitoring sites could constitute a useful pubhc health tool with a range of potential applications... 

Simoneit BRT, Biogenic Hpids in eolian particulates collected over the ocean, in NovakovT ed), Proceedings Carbonaceous Particles in the Atmosphere NSF-LBL, pp. 233-244, 1979. 

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