Coal-fired power plants particulates

Hazardous air pollutants (HAPs) are substances that may cause immediate or long-term adverse effects on human health. HAPs can be gases, particulates, trace metals such as mercui y, and vapors such as benzene. For coal-fired power plants, the HAPs of most concern are metals such as mercury, arsenic, and vanadium. 

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 ... 

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 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. 

A series of mercury mass balances was obtained at a coal-fired power plant by comparing the volatile and particulate mercury in the stack gas stream to the mercury initially in the coal, corrected for the mercury adsorbed and retained by the various ashes. These data were used to determine the fate of the mercury in the combustion process and to check the accuracy of the volatile mercury sampling procedure (gold amalgamation). The bottom ash had the lowest mercury concentration of the ash samples collected, and the mercury concentration increased as one proceeded through the ash collection system from the initial mechanical ash to the electrostatic ash. The mercury recovered in the various ashes represented about 10% of the total mercury introduced in the raw coal. 

NGCC/GTCC, Natural gas combined cycle (often termed gas-turbine combined cycle) PC, Pulverized-coal-fired power plant IGCC, Integrated gasification combined cycle, Oxy-fuel (PC boiler) plant. Flue-gas desulfurization and air particulate control is included in the total cost, but not in the separation unit cost. 

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. 

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 both a hybrid receptor model, developed by Lewis and Stevens ( 2) and modified by Gordon and Olmez (3), and a simple model of emission from the Ohio River Valley, we compare the results of the College Park (CP) samples as well as those of another continuous set of samples taken from July 3-29, 1983 at Wallops Island, VA (WI), to predicted results. Single-source differential equations (2) are used to describe the time-varying concentrations of SO2, SO and a particulate element characteristic of coal-fired power plant emissions (chosen here as Se). An additional equation (3) can be added to describe the concentration variation of B(0H)3 The following rate constants apply to the concentrations of the four species in question ... 

A power plant generates 2.76 x 10 megawatt hours (MWh) of electricity per year by burning 1.66 x 10 tons of a low-grade coal containing 3.2% sulfur and 15.4% ash. The ratio of fly ash to bottom ash is 0.65 and the plant s particulate collection efficiency is 85%. Determine the amount of each pollutant (particulates, NO4 and SO2) emitted per year in pounds/kilowatt-hour for the coal-fired power plant. 

A baghouse is needed at a coal-fired power plant for a design operating period of 20 years. If the unit fails at anytime (bag meltdown), a 45% (of the initial cost) reinvestment cost will result. Two companies submit bids for this particulate control device with the following cost and operating characteristics data ... 

Of the elements listed in Table 1.3, Zn, As, Se, Ag, Cd, Tl, Pb, and Bi are accumulated to high levels in the finest fraction of particulate aerosols which leave the stacks of coal firing power plants, whereas Hg is the only metal which is predominantly emitted as a gas during coal firing (Brumsack et al. 

Source Apportionment Assume that for a rural site the measured PM 0 concentration is 32jig m-3 containing 2.58 pgm-3 Si and 3.84pgm 3Fe. The two major sources contributing to the location s particulate concentration are a coal-fired power plant and soil-related dust. Analysis of the emissions of these sources indicates that the soil contains 200 mg(Si) g (20% of the total emissions) and 32 mg(Fe) g 1 (3.2% of the total emissions), while the particles emitted by the power plant contain IOmg(Si)g (1%) and 150mg(Fe)g (15%). Neglecting Si and Ft contributions from other sources... 

The characteristics of several QCM instruments for aerosol measurement have been reviewed (ll). Particles are collected by impaction, electrostatic precipitation or both. The mass sensitivity is reported to be affected by the location of deposited particles on the crystal, the size of the particles, and the type of coating. In addition, the sensitivity changes as the crystal becomes loaded. Despite some limitations, most of the studies Indicated that QCMs can be successfully used for aerosol measurement with good correlation coefficient with the reference filtration method. Applications included measurement of aerosol in ambient air, particulate emission from automobiles and diesel engines, smoke plume from a coal-fired power plant, solid fueled rocket plvune, and particulate matter in the effluents in combustion sources. 

A more effective approach to clean air policy, and one example of a sensible program being implemented by the federal government, is the Clean Air Interstate Rule or CAIR, intended to reduce emissions of particulate matter and NO in the eastern United States. EPA finalized the CAIR rules on March 10, 2005 in response to a finding of non-attainment of National Ambient Air Quality Standards (NAAQS) for fine particulate matter and ozone formation. CAIR requires reductions in SOj and NOj emissions from coal-fired power plants the emissions limits spelled out in the CAIR plan affect electric utilities in 28 eastern states and the District of Columbia. Emissions reductions are to be achieved through a market-based cap-and-trade system similar to other air pollution programs EPA has put into practice over the last few decades. 

A major industrial source of particulate matter in the environment is coal-fired combustion for electricity generation. Source performance standards in the US restrict total particulate emissions from new coal-fired power plants to 6.4 ng... 

Sulfur and nitrogen oxides are not the only output from coal combustion that may leave a detectible environmental impact. Particulate matter (fly ash) is also released during coal combustion and can be detected near coal-fired power plants (Flanders, 1999 Godbeer and Swain, 1995 Kapicka et al, 1999). The focus of the present study was to test whether these particulate emissions have produced a detectible impact on the geochemical landscape downwind from power plants. It is already known that atmospheric inputs can be detected in lake and reservoir sediments (Locke and Bertine, 1986 Norton, 1986), and we sought to further test whether atmospheric coal fly ash inputs could be identified and quantified. 

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