Enrichment coal combustion

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). 

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... 

Although the data presented here are limited to a single coal burned in two combustor operating modes, several important observations can be made about the fine particles generated by pulverized coal combustion. The major constituents of the very small nucleation generated particles vary with combustion conditions. High flame temperatures lead to the volatilization of refractory ash species such as silica and alumina, probably by means of reactions which produce volatile reduced species such as SiO or Al. At lower flame temperatures which minimize these reactions other ash species dominate the fine particles. Because the major constitutents of the fine particles are relatively refractory, nucleation is expected to occur early in the combustion process. More volatile species which condense at lower temperatures may also form new particles or may condense on the surfaces of the existing particles. Both mechanisms will lead to substantial enrichment of the very small particles with the volatile species, as was observed for zinc. 

Studies of fresh ash produced by coal combustion have shown that many trace elements (As, B, Bi, Cd, Cr, Cu, Ge, Hg, Mo, Pb, Ni, Se, Sr, Tl, V, W, Zn) are enriched in the fly ash compared to the bottom ash (Hansen Fisher 1980 Eary et al. 1990 Mukhopadhyay et al. 1996 Karayigit et al. 2001). For example, Mukhopadhyay et al. (1996) reported 10-20 times enrichment of most trace elements in the fly ash compared to the feed coal and association of As with crystalline Fe-0 and Fe-S phases in the bottom ash from a power plant in Nova Scotia fed by eastern Canadian coal. Elements enriched in fly ash are typically those more easily volatilized. Because fly ash particles also have smaller sizes and therefore greater reactivity than bottom ash, the probability of metal leaching is correspondingly greater. Ainsworth Rai (1987) and Rai et al. (1988) found that most of the Cu, Mo, Se, Sr, and V in fly ash was readily soluble. 

Research indicates that a significant fraction (50-90% ) of mercury is volatilized and lost during coal combustion (10, 11, 12) and that many of the potentially hazardous trace elements appear concentrated upon finer particulate emissions (13, 14). Several investigators have observed enrichment of these hazardous elements upon particulates in urban areas... 

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... 

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. 

Real MHD Channel Slag (Ki). Detailed TMS and KMS studies were made of vapor transport over a high liquidus temperature (a. 1700 K) potassium-enriched coal slag with initial composition as indicated in Table II. This slag sample was obtained by combustion of Illinois No. 6 coal with additional potassium added to the combustor [see ( )[. Note that this slag composition lies between those of the "Eastern" and "Western" coal-types. 

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). 

Perhaps the most obvious trend in the data from the Hinkel cores is that maxima in elements known to be associated with coal-combustion products e.g. Zn, Pb, As, Ge, and Hg) occur at a depth corresponding to deposition just subsequent to the enactment of the Clean Air Act in 1970 (Fig. 4). Sulfur dioxide emissions from power plants are known to have peaked near 1970 (Husar et al, 1991), although S peaks at a slightly shallower depth (younger age) than do the trace elements. The overall suite of elements plotted in Fig. 4 is commonly enriched in coal fly ash as noted above, or in the case of Hg and S, vapor phase output from coal combustion (Kaakinen et al, 1975). The timing of the decrease in these elements suggested to us decreased... 

As was the case for Hinkel Reservoir, the Ti-normalized data help us distinguish weathering from coal-combustion input. When compared to the youngest reservoir sediments, patterns in the Ti-normalized data from MTR are only slightly different from those previously discussed for Hinkel Reservoir (Fig. 12). Zn and S resemble the Hinkel core data in that they are enriched in reservoir sediments relative to sods. Similarly, Pb and magnetite (IRM) are relatively enriched in soil (although there is scatter in the IRM data). However, in contrast to the Hinkel data, Ti-normalized Fe and As in MTR soil samples tend to be depleted compared to reservoir sediments. 

Reaction kinetics of coal combustion in oxygen-enriched environment is investigated by non-iso-thermal method in this work. The reaction kinetic equation of coal combustion can be expressed as (Liu et al. 2005, Li 2007, Shan et al. 2005, QI et al. 2010) ... 

Zhuang et al. 1999, Yao et al. 2003). As a consequence, the particulate matter is enriched in sodium. In Fig. 2.29, the measured ratio Rmeas = [Na]/[C1] is given for different chlorine reservoirs in sea water Rseawater = 0.86 (molar ratio mass ratio amount 0.56). Thus, deviations to higher values indicate Cl loss. However over continents and in polluted air masses, so-called excess chloride may occur, which is mainly caused by human activity (coal combustion, waste incineration, salt industries). This excess chloride can be calculated according to Eq. (2.83) however, there are two preconditions (a) that there are no sodium sources other than sea salt, and (b) that the local reference value of Rseasait is known. In older literature, instead of Rseasait, authors used the seawater bulk value Rseawater = 0.86. 

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... 

Overall, the Kentucky and Purdue studies show similar trends. The most important change resulting from the addition of TDF to coal is the increase in the Zn content of the fly ash. In contrast, most other trace elements have lower concentrations in the fly ash resulting from the combustion of the blend. Despite many similarities, two notable differences between the two test bums are observed. S03 and Pb showed opposite trends in the Purdue fly ash compared to the Kentucky fly ash. In both studies, enrichments of many trace elements... 

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