Coal, combustion emissions, source

Environmental considerations also were reflected in coal production and consumption statistics, including regional production patterns and economic sector utilization characteristics. Average coal sulfur content, as produced, declined from 2.3% in 1973 to 1.6% in 1980 and 1.3% in 1990. Coal ash content declined similarly, from 13.1% in 1973 to 11.1% in 1980 and 9.9% in 1990. These numbers clearly reflect a trend toward utilization of coal that produces less SO2 and less flyash to capture. Emissions from coal in the 1990s were 14 x 10 t /yr of SO2 and 450 x 10 t /yr of particulates generated by coal combustion at electric utiUties. The total coal combustion emissions from all sources were only slightly higher than the emissions from electric utiUty coal utilization (6). 

Trace element data can shed some light on the source of this SO -episode oil-combustion emissions are enriched in vanadium and coal-combustion emissions, on the other hand, are enriched in selenium. 

For the other metals, Hg correlates with Zn, Pb and Cd at SC but not at CBL. Similarly, Hg did not correlate with other metals in Florida (30). The metals Cu, Ni and Cr are strongly correlated at both sites. Mercury, which is transported globally, also likely has a two component signal from local sources -coal combustion emissions and waste (medical and municipal) incineration while Pb and Cd have their primary sources as waste incineration (P, II). The overall inter-relationships of Pb, Cd and Hg suggest that overall, in the city, Pb and Cd do have different sources. The metals Pb, Cd, Cu and Zn are well correlated at CBL (Table III). This suggests that the correlations found for Hg at SC reflect the urban sources and not the regional picture. 

Diverse techniques have been employed to identify the sources of elements in atmospheric dust (and surface dust) (Table V). Some involve considering trends in concentration and others use various statistical methods. The degree of sophistication and detail obtained from the analyses increases from top left to bottom right of the Table. The sources identified as contributing the elements in rural and urban atmospheric dusts are detailed in Table VI. The principal sources are crustal material, soil, coal and oil combustion emissions, incinerated refuse emissions, motor vehicle emissions, marine spray, cement and concrete weathering, mining and metal working emissions. Many elements occur in more than one source, and they are classified in the... 

The use of plastics as an energy source was demonstrated on a commercial scale at ICl Materials plastics manufacturing site in Dumfries, UK. This paper covers the preparation and use of pre- and post-consumer plastics as supplementary fuels in a circulating fluidised bed boiler specially designed for co-combustion with coal. Full emissions data on the 15% mixtures of individual plastics with coal are given, together with calculations of thermal efficiencies. Measurements by an independent body (British Coal Research Establishment) confirmed that the co-combustion of coal and plastic reduces some emissions compared with coal alone. Thermal efficiencies of around 80% were achieved and this heat was used effectively during the production of plastics. 7 refs. 

Anthropogenic sources of fluoride include fossil fuel combustion and industrial waste. Hydrogen fluoride is water soluble and emissions are readily controlled by acid gas scrubbers. HF emission from coal combustion, that is considered to be the main anthropogenic source of HF, was estimated to be 0.18 Tg annually emission of HF from the combustion of petroleum and natural gas is almost certainly negligible [24]. Apparently only limited data are available concerning total annual emissions of HF from industrial operations however, there is evidence that emissions of fluorides have been declining [24,25]. 

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). 

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. 

It should be noted that Pb concentrations in this polluted air are about 100 times lower than the aerosol S levels, or are only a few tens of ng Pb/m. In the Beijing area the contribution of automotive emissions to atmospheric Pb at Xinglong is expected to be minor owing to the small amounts of leaded gasoline used privately owned automobiles, trucks, and other gasoline powered vehicles are nonexistent in China. Instead, coal combustion may be the principal source of fine particle Pb as well as K and S. 

Ash from pulverized coal combustion is a strategic material that has many critical applications from a source of aggregate to the most important source of pozzolan for addition to Portland cement concrete. Environmental control measures on the emissions of coal combustion have resulted in a loss of quality for these materials. In response we have seen the advent of beneficiation processes applying both proven and new technologies to produce high-quality consistent products from these materials. Currently we estimate that about one-fifth of all ash products marketed are processed through some form of beneficiation method. We expect that the demand for quality and consistency will continue and the relative amount of process ash products will increase in the future. 

The composition of trace element emissions during coal combustion is described by Bolton et al. in Chapter 13. The actual quantities are somewhat variable depending upon the coal source, the combustion process, the pollution abatement equipment, and the assay itself. Much less is known about important local concentrations of emissions in and around the source, their chemical and physical characteristics, and their fate in the environment. 

The seasonal distribution of particle-associated PAHs is controlled by a combination of emission factors (EFs), dispersion conditions and chemical mechanisms (Caricchia et al., 1999 Menichini et al., 1999). This balance depends on the relative importance of degradation processes and emission sources (Guo et al., 2003b). The highest PAH concentrations of a sampling site were usually obtained from winter samples, and the differences were far higher in northern cities than southern ones, suggesting that coal combustion for space heating contributes the most PAHs in winter in Northern China. 

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