Particle from coal combustion

Coal-fired power plants release very large amounts of particulate material. The question Is, however, what fractions of the various elements In ambient air can be accounted for by particles from coal-fired plants A major fraction of an element can be contributed by coal combustion only If (1) coal accounts for an appreciable fraction of the A1 In the local atmosphere and (2) the EF value of the element on particles from coal combustion Is as great as for ambient particles. Only for those elements In Figure 1 for which there Is considerable overlap between the ranges for cities and for coal-fired plants can coal possibly be a major contributor. Even If there Is overlap, coal Is not necessarily a major source, as condition 1 above may not be met. On this basis, coal combustion could be a major source of many llthophlles plus Cr, N1, As, Se and, In cities where little residual oil Is used (Charleston and St. Louis), V. The very high EF values for As and Se and low values for V and Nl In Charleston, where little oil and a great deal of coal are burned, lends credence to this Interpretation. 

Enrichments of several elements on particles from coal combustion are too low for coal to be a major source Na, K, Mn, Cu, Zn, Cd, Sb and Pb. Except possibly for Cu, whose major source Is unknown, these results agree with the CEBs for Washington, which Indicate other principal sources for those elements. A possible weakness In the argument presented Is that It contains the Implicit assumption that there Is no fractionation of particles bearing... 

When sources are studied, several things should be done to provide data needed for receptor-model applications. First, particles should be collected In at least two different size fractions corresponding to the division at about 2.5-ym dlam now used In many studies of ambient aerosols. In some cases. It may be desirable to have more size cuts. As noted above, compositions of particles from coal combustion change dramatically below about 0.5-pm dlam (44, 46). Above we Identified a minimum of about twenty elements that should be measured. Also, In order to develop adequate markers for sources that emit carbonaceous particles, measurements of organic compounds and other properties related to carbonaceous particles should be made. 

Fine particles from coal combustion are a threat to human health and air quality. Numerous studies have reported higher concentrations of volatile trace elements in small particles... 

Flagan, R.C. Taylor, D.D. Laboratory Studies of Submicron Particles From Coal Combustion, Eighteenth Symposium (International) on Combustion, Waterloo, Ontario, Canada, August 1980 (in press). 

As fine particles arise from many sources, it would be desirable to replace the fine particle mass concentration in the equations by the concentration of an element borne by the fine particles from coal combustion and no other source. The best candidate for such an element is Se (2.4.17). If coal-fired power plants were the only significant source of Se (probably a good assumption in many areas), one could measure emission rates of SO2, SO4 and Se from the source and their concentrations at a downwind location and plug the values into the equations and solve them to obtain the conversion and deposition rates averaged over the travel time of the plume. The model is a useful first step towards the use of... 

The use of EF values allows us to set limits on possible sources of elements. In Figure 1, EF values for six cities are compared with the ranges for particles from nine coal-fired power plants. For llthophlle elements such as SI, Tl, Th, K, Mg, Fe and many others not shown, E values are close to unity as expected, as these elements have mainly crustal sources, l.e., entrained soil and the aluminosilicate portion of emissions from coal combustion (see Table I). Many other elements are strongly enriched In some or all cities, and, to account for them, we must find sources whose particles have large values for those elements. Some are fairly obvious from the above discussions Pb from motor vehicles, Na from sea salt In coastal cities, and V and, possibly, N1 from oil In cities where residual oil Is used In large amounts (Boston, Portland, Washington). 

Ondov, J. M. Blermann, A. H. "Elemental Composition of Atmospheric Fine Particle Emissions from Coal-Combustion In a Modern Utility Electric Power Plant", This Symposium. 

The principal source may be air pollution emissions from coal combustion, suggested by the fact that aerosol S levels are generally high and vary independently of Fe (Figure 1), Pb was found only in the most polluted air (16-17 March), and fine particle K and Cl show some temporal similarities presented in Figure 5. When pollution contributions to the total aerosol are very large, Zn and other elements with fine modes may also be enhanced by pollution additions to their natural levels. 

Atmospheric aerosols are complex mixtures of particles derived from diverse sources. Soot from diesel engines, fly ash from coal combustion, and sulfates, nitrates, and organic compounds produced by atmospheric reactions of gaseous pollutants all contribute to the aerosol. Particle size and composition depend upon the conditions of aerosol formation and growth and determine the effects of atmospheric aerosols on human health, ecosystems, materials degradation, and visibility. Much of the research on environmental aerosols has focused on fine particles ranging from a few micrometers in... 

Coal contains most of the elements of the periodic table, the majority of which are present in concentrations of 100 ppm or less. Many of these trace elements are toxic to plant and animal life, even at low levels. Because U.S. power plants consune on the order of 600 million tons of coal annually for the production of electricity (1), coal combustion can mobilize thousands of tons of potentially hazardous trace elements into the environment each year. Due to the large quantities of coal combusted, even trace amounts of toxic elements present in the coals can accumulate to hazardous levels. Also, potentially deleterious effects of particulate emissions from coal combustion may be enhanced since many trace elements are surface-enriched (2) and concentrate preferentially in the smaller, more respirable particle sizes (3). Substantial amounts of some elements, such as As, Hg, and Se, are in the vapor phase in flue gases from coal combustion and are essentially unaffected by most particle control devices. Aside from the potential detrimental environmental aspects, trace elements in coal can pose adverse technological... 

A combined listing of all the compounds identified in the vapor and on particles emitted during the combustion of coal at the /toes power plant are listed in Table I. Similar compounds have been identified in the emissions from a second coal-fired power plant located at Iowa State University. Therefore, this list may be partially representative of coal combustion in semi-modern boilers. Certainly, many more organic compounds than the listed 78 are present in these effluents, but so far these have not been positively identified. Indeed, a 1980 review of organic compounds from coal combustion (1) taken from all the literature reports had only 106 compounds identified. 

If one is performing CMBs of an area in which particulate emissions from coal combustion are dominated by those from one to several plants, it is obviously desirable to use a coal component based on measurements of compositions of the particles released by those specific plants, preferably particles collected in their plumes. However, as those data are rarely available, we have placed data from as many multielement studies as possible in the library so the user can construct a component from results of the most appropriate studies that have been done. 

Emissions of sulfur oxides, nitrogen oxides, and particulates from coal combustion are problems of increasing concern and regulation. Coal combustion contributes about 25 percent of the particulate matter, 25 percent of the sulfur oxides, and 5 percent of the nitrogen oxides emitted to the atmosphere. Much of the particulates are derived from the mineral content of the coal, but some particulates also result from sulfur and nitrogen oxides that react to form various sulfate and nitrate salts. A major concern about particulate matter is that the smallest particles are respirable and may pose a health hazard. Particulate matter is recovered in most power plants by the use of electrostatic precipitators, which have been developed to very high efficiencies (>99%). Other methods of particulate removal include baghouses and cyclone collectors. 

Solid submicron particles may form from condensable molecules generated in a gas by chemical or physical processes. Thi.s method is used routinely for the commercial production of line particles and materials fabricated from them, as well as for pilot and laboratory scale production. Similar processes occur in fine particle formation in many other ca.ses ranging from coal combustion to meteor burn-up on entering Earth s atmosphere. The smallest individual particles composing such aerosols prittiary particles) range from less than 10 nm to about I jum, depending on the application. 

Figure 1. Large particle, derived from coal-combustion, detected on the thallus surface of in situ Ramalina lacera near the Oroth-Rabin coal-fired power plant near Hadera, Israel, in 1995. Scale bar, 10 p,m (Garty, Kunin, Delarea, unpublished).

Figure 4. SEM photograph of a spheroidal carbonaceous particle from (he combustion of coal, showing a convoluted surface texture, previously thought typical of oil combustion and used in fuel-type apportionment ofSCPs.

The deposition and accumulation of fly ash downwind from coal-combustion sites is a concern because it may be significantly enriched in potentially toxic trace elements, including lead (Pb) and arsenic (As), compared to the burned coal (Coles et al, 1979 Eary et al, 1990 Hower et al, 1999 Kaakinen et al, 1975). Other elements such as zinc (Zn) and germanium (Ge), of less environmental concern, may also be enriched in fly ash. The relatively high concentrations of As in fly ash reflect partly its presence in pyrite in coal from the Appalachian Basin (Goldhaber et al, 2002). More importantly, the concentration of these metals and metalloids occurs during the combustion process itself. A suite of elements including As, Ca, Cr, Cu, Ga, Mo, Ni, Pb, Sb, Se, V, and Zn is enriched in the fine fraction of coal fly ash (Coles et al, 1979), because of vaporization in the furnace and subsequent condensation or absorption onto ash particles (Kaakinen et al, 1975). 

It should be noted that audible sound (generated by cheap loudspeakers) can be used for related separation techniques, even on large scales (pilot plant). A reduction in particle emissions from coal combustion fumes has been achieved using an array of stepped-plate piezoelectric transducers, which produce a homogeneous distribution of high-intensity waves (145-165 dB), located along the waU of the chamber at that high-temperature environment [135]. 

A significant health concern with particles, especially those from combustion sources, is their ability to carry toxic metals. Of these, lead is of the greatest concern because it usually comes closest to being at a toxic level. Problems with particulate lead in the atmosphere have been greatly reduced by the elimination of tetraethyl lead as a gasoline additive, an application that used to spew tons of lead into the atmosphere every day. Another heavy metal that causes considerable concern is mercury, which can enter the atmosphere bound to particles or as vapor-phase atomic mercury. Airborne mercury from coal combustion can become a serious water pollution problem, leading to unhealthy accumulations of this toxic element in some fish. Other metals that can cause health problems in particulate matter are beryllium, cadmium, chromium, vanadium, nickel, and arsenic (a metalloid). 

The radiation from a flame is due to radiation from burning soot particles of microscopic andsubmicroscopic dimensions, from suspended larger particles of coal, coke, or ash, and from the water vapor and carbon dioxide in the hot gaseous combustion products. The contribution of radiation emitted by the combustion process itself, so-called chemiluminescence, is relatively neghgible. Common to these problems is the effect of the shape of the emitting volume on the radiative fliix this is considered first. 

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