Flyash

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). 

Formation of Airborne Emissions. Airborne emissions are formed from combustion of waste fuels as a function of certain physical and chemical reactions and mechanisms. In grate-fired systems, particulate emissions result from particles being swept through the furnace and boiler in the gaseous combustion products, and from incomplete oxidation of the soHd particles, with consequent char carryover. If pile burning is used, eg, the mass bum units employed for unprocessed MSW, typically only 20—25% of the unbumed soHds and inerts exit the combustion system as flyash. If spreader-stoker technologies are employed, between 75 and 90% of the unbumed soHds and inerts may exit the combustion system in the form of flyash. 

Formation of emissions from fluidised-bed combustion is considerably different from that associated with grate-fired systems. Flyash generation is a design parameter, and typically >90% of all soHds are removed from the system as flyash. SO2 and HCl are controlled by reactions with calcium in the bed, where the lime-stone fed to the bed first calcines to CaO and CO2, and then the lime reacts with sulfur dioxide and oxygen, or with hydrogen chloride, to form calcium sulfate and calcium chloride, respectively. SO2 and HCl capture rates of 70—90% are readily achieved with fluidi2ed beds. The limestone in the bed plus the very low combustion temperatures inhibit conversion of fuel N to NO. ... 

D. A. Tillman and C. Leone, "Control of Trace Metals in Flyash at the Tacoma, Washington Multifiiels Incinerator," Proceedings of the Mmerican Flame Research Committee Fall International Symposium, San Francisco, 1990. 

Combinations of lignite flyash from North Dakota and hydrated lime can increase the strength and durabiHty of soils. The lime content varies from 2—7% and 1ime flyash ratio from 1 1 to 1 7 (61). Lignite flyash can also be used as a partial replacement for Portland cement to produce strong, durable concrete (62). 

E. Y. Murad, L. V. HiUier, md E. R. Kilpatrick, Boiler Flue Gas Desulfurisyation by Flyash Mlkali, Morgmtown Energy Research Center Report, Morgmtown, W. Va., 1976, pp. 450—460. 

T. R. Dobie md N. E. Henning, Eignite Flyash as a Partial Replacementfor Portland Cement in Concrete, final report PB 247414, Twin City Testing md Engineering Lab., Inc., St. Paul, Minn., 1975. 

Hydrated lime is also used to stabilize the calcium sulfite—sulfate sludge derived from thickeners at SO2 scmbbing plants that use limestone—lime. Hydrated lime (2—3%) is added to react with the gypsum sludge and flyash or other added siHceous material. Under ambient conditions the lime and siHca serve as a binder by reacting as calcium siHcates so that the material hardens into a safe, nonleaching, stable, sanitary landfill or embankment fill. 

The wide range of types of paper products results in a variety of sludges. SoHd wastes result from several sources within the mill, eg, bark, sawdust, dirt, knots, pulpwood rejects, flyash, cinders, slag, and sludges. Sludges often are disposed of in combination with residuals from other sources. Approximately 300 kg of soHd waste per ton of finished product is generated by the pulp and paper industry. 

Similar to oil-fired plants, either low NO burners, SCR, or SNCR can be appHed for NO control at PC-fired plants. Likewise, fabric filter baghouses or electrostatic precipitators can be used to capture flyash (see Airpollution controlmethods). The collection and removal of significant levels of bottom ash, unbumed matter that drops to the bottom of the furnace, is a unique challenge associated with coal-fired faciUties. Once removed, significant levels of both bottom ash and flyash may require transport for landfilling. Some beneficial reuses of this ash have been identified, such as in the manufacture of Pordand cement. 

At the roofing plant, coating asphalts ate blended with mineral stabiHzet such as finely ground limestone, slate, flyash, or traprock. The stabiHzet increases the coating asphalt s resistance to fire and foot-traffic and adds durabiHty. 

Other problems that can be associated with the high dust plant can include alkaH deterioration from sodium or potassium in the stack gas deposition on the bed, calcium deposition, when calcium in the flue gas reacts with sulfur trioxide, or formation and deposition of ammonium bisulfate. In addition, plugging of the air preheater as weU as contamination of flyash and EGD wastewater discharges by ammonia are avoided if the SCR system is located after the FGD (23). 

Creosote PIC are comprised of PCDD/PCDF, flyash and soot, NO, SOj, COj, HCl, and various PAHs ... 

Flyash is assumed to settle out of the atmosphere close to the source ... 

Of the fuel blend portion resulting in PIC, 15% is attributed to large particulate flyash ... 

Available Fuel, Lbs Lbs Fuel Tor Energy Lbs Flyash Total Lbs Gaseous + PM Lbs NO., SO, CO, Other Lbs PCDD/ PCDF... 

Flyash - Flyashes are finely divided matter generally entrained in flue gases that arise from combustion. Particles range from 1 /im in size on down. This is not within the operational range of gravity settling chambers. Wet... 

Figure 19. Variable venturi scrubber for flyash and sulfur dioxide removal.

Moisture removal through the use of adsorbents such as ground clay, flyash, or powdered lime... 

Furnace areas require baffles to deflect the gases back and forth between the tubes. Correct baffle arrangements are necessary to maintain combustion gas velocity, ensure correct temperature differentials, prevent short circuiting of the gas path, and minimize dead spots, which encourage the deposition of flyash. 

Human activities have resulted in exposure of Antarctic fishes to petroleum-derived PAHs (McDonald et al. 1992). Fish captured near Palmer station on the Antarctic peninsula had induced EROD activities and elevated concentrations of biliary PAH metabolites of phenanthrene and naphthalene when compared to conspecifics from reference sites (McDonald et al. 1995). Artificial reefs consisting of oil and coal flyash stabilized with cement and lime in Florida waters near Vero Beach contained elevated PAH levels ranging from as high as 1.2 mg fluoranthene/kg and 0.25 mg naphthalene/kg. But there is negligible leaching because seawater is not an effective medium for removing PAHs from reef bricks or the ash (Frease and Windsor 1991). 

ARTIFICIAL REEF COMPONENTS (mg/kg FW) Bricks made from oil ash vs. bricks made of flyash ... 

In North Dakota in 1968 from flyash from a lignite burning plant... 

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