Particle coal-fired power plant

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

There are 720 coal-fired power plants in the USA. When coal is burned in these power plants, two types of ash are produced coal fly ash and bottom ash. Coal fly ash is the very fine particulate matter carried in the flue gas bottom ash (or slag) is the larger, heavier particles that fall to the bottom of the hopper after combustion [261-264]. The physical and chemical characteristics of these ashes vary depending on the type of coal burned. These ashes are characterized by the following ... 

From a public health point of view, the concentration of nickel associated with small particles that can be inhaled into the lungs is of greatest concern. The nickel content of aerosols from power plant emissions is not strongly correlated with particle size (Hansen and Fisher 1980). In one modem coal plant, 53% and 32% of nickel in emissions were associated with particles <3 and <1.5 pm in diameter, respectively (Sabbioni et al. 1984). Other studies found that only 17-22% of nickel emissions from coal-fired power plants were associated with particles of >2 pm, and that the mass medium diameter (MMD) of nickel-containing particles from a plant with pollution control devices was 5. 4 pm (Gladney et al. 1978 Lee et al. 1975). In one study, 40% of the nickel in coal fly ash was adsorbed on the surface of the particles rather than being embedded in the aluminosilicate matrix (Hansen and Fisher 1980). Surface-adsorbed nickel would be more available than embedded nickel. 

In both component and factor analysis, the properties of the system being observed are assumed to be linearly additive functions of the contribution from each of the m causalities that actually govern the system. For example, for airborne particles, the amount of particulate lead in the air could be considered to be a sum of contributions from several sources including automobiles, incinerators and coal-fired power plants, etc. 

Coal-Fired Power Plants. Detailed studies of compositions of particles collected from stacks of about ten coal-fired power plants have been performed (, 27-36). In a few cases, the composition has been determined for particles In several size groups. Some measurements on suspended particles have been aug-... 

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). 

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. 

Comparisons with Ambient Fine Particles. Above we noted a potential problem of using EFj.j-ust values to determine possible coal contributions to ambient levels of various elements, namely that large, aluminosilicate particles might preferentially settle out of the atmosphere between the source and receptor. Here we have tried to avoid that problem by calculating values only for fine particles from several cities and from coal-fired power plants as shown In Table V. Again, fine particles are those with dlam <2.5 ym. The EFs for coal In Table V are taken from Col. 4 of Table IV. 

In summary, coal-fired power plants appear not to be the major source of most enriched elements on particles In urban areas, despite the great attention devoted to mechanisms by which those elements become preferentially attached to fine particles (e.g.. Refs. 18, 34). However, the detailed studies of processes In coal-fired plants are of considerable value, as the fundamentals should be applicable to other kinds of combustion sources. Furthermore, It may be necessary to use this fundamental approach to develop methods for predicting the source compositions for coal-fired power plants that have not been measured. Selenium Is much... 

As discussed above, many detailed studies of sources are needed to establish compositions of source components for receptor-model use. Coal-fired power plants have been studied more than other sources, but even In that case, there are not nearly enough data to establish trends for predicting components for plants that have not been studied. The situation Is much worse for most other sources, except possibly refuse Incinerators, of which the three studied release particles of very similar compositions (9, 10). 

It is now well documented that large numbers of particles are emitted from coal-fired power plants in distinct distributions with modal diameters less than 1 pm (1-5). 

The relative concentrations of rare earth elements in fine particles have also been suggested as being indicative of emissions from oil-fired power plants and from refineries. For example, the ratio of lanthanum to samarium is much higher in emissions from these sources than found in particles formed from the earth s crust (Olmez and Gordon, 1985). Thus the La Sm ratio was measured to be about 20 for refinery emissions and 28 for emissions from an oil-fired power plant compared to 5 from a coal-fired power plant and 9 from the earth s crust (Olmez and Gordon, 1985 Kitto et al., 1992). 

Application of a combination of all of these approaches can be particularly powerful when the requisite input data are available. For example, Malm and Gebhart (1997) used a combination of these source apportionment techniques to show that in the Grand Canyon area, about 50% of the sulfur in particles was associated with sources that also emitted Se and hence was attributed to coal-fired power plants in the region. A strong association with bromine was also found, suggesting that wood smoke was also a significant source of sulfur in this region. 

Wight, S. A., J. M. Ondov, and Z.-C. Lin, Tagging In-Stack Suspended Particles from a Coal-Fired Power Plant with an Enriched Isotopic Tracer, Aerosol Sci. Technol., 15, 191-200 (1991). 

Wadge, A., Hutton, M. Peterson, P. J. 1986. The concentration and particle size relationships of selected trace elements in fly ashes from U.K coal-fired power plants and a refuse incinerator. Science of the Total Environment, 54, 13-27. 

CDDs are released into the air in emissions from municipal solid waste and industrial incinerators. Exhaust from vehicles powered with leaded and unleaded gasoline and diesel fuel also release CDDs to the air. Other sources of CDDs in air include emissions from oil- or coal-fired power plants, burning of chlorinated compounds such as PCBs, and cigarette smoke. CDDs formed during combustion processes are associated with small particles in the air, such as ash. The larger particles will be deposited close to the emission source, while very small particles may be... 

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. 

Tetrachlorodibenzo-p-d1oxin (TCDD). At the detection limit of ten parts per trillion, no TCDD was found in the effluents from the combustion of coal in three different boilers at the Ames power plant (see summary table in reference 16 for description of boilers). This observation was confirmed at a second smaller coal-fired power plant located at Iowa State University. Even when the coal fuel was supplemented with RDF, which should contain the precursor compounds, no dioxins were observed in the vapor and particle samples taken from the effluents. Thus no de novo synthesis occurred during the combustion of coal alone and if dioxins were formed from precursor compounds in the co-combustion of coal and RDF, they were destroyed in the efficient combustion as explained above for the thermal destruction of the PCBs present in the RDF. 

Introduction and Statement of Problem. Current techniques to remove particulates in coal fired power plant flues are based on electrostatic precipitators, bag houses, cyclones and wet scrubbers. Typical collection efficiencies of such devices and the far less efficient cyclones are shown in Figure 1 (J,). Of interest is the fact that below 1 micrometer the efficiencies drop off rather precipitously. Work presented by Davies ( ), Figure 2, has shown that the human lower pulmonary system is unfortunately most efficient in absorbing and retaining particles in the 1 micrometer range. These particles are the primary cause of such respiratory ailments as bronchitis, emphysema and lung cancer. 

Variability of Compositions of Particles Released by Coal-Fired Power Plants... 

Particulate emissions data for 21 studies of coal-fired power plants were compiled for use in receptor models. Enrichment factors were calculated (relative to Al) with respect to the earth s crust (EFcrust) and to the input coal (EFcoai). Enrichment factors for input coals relative to crustal material were also calculated. Enrichment factors for some elements that are most useful as tracers of coal emissions (e.g., As, Se) vary by more than ten-fold. The variability can be reduced by considering only the types of plants used in a given area, e.g., plants with electrostatic precipitators (ESPs) burning bituminous coal. For many elements (e.g., S, Se, As, V), EFcrust values are higher for plants with scrubbers than for plants with ESPs. For most lithophiles, EFcrust values are similar for the coarse (>2.5 ym) and fine (<2.5 ym) particle fractions. 

Using a source-composition library containing data from 21 studies of coal-fired power plants, we have investigated the effects of particle size, coal type, and pollution control device on the composition of particles emitted from coal-fired power plants. 

In an earlier study (15) we addressed some of the problems in obtaining accurate concentration-vs-particle-size distributions for elements in stack aerosols collected downstream of an electrostatic precipitator and a Venturi wet scrubber at a coal-fired power plant. The problems investigated were error associated with the use of the... 

Ondov JM, Choquette CE, Zoller WH, et al. 1989. Atmospheric behavior of trace elements on particles emitted from a coal-fired power plant. Atmos Environ 23(10) 2193-1104. 

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... 

M. E. Kitto and D. L. Anderson, "Simultaneous collection of particles and acidic gases for tracing emissions from coal-fired power plants," presented at the Amer. Chem. Soc. National Meeting, New York, April, 1986. 

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