Coal ashes

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). 

Normally ca 50% of the coal ash is removed from the bottom of the gasifier as a quenched slag. The balance is carried overhead in the gas as droplets which are solidified when the gas is cooled with a water spray. A fluxing agent is added, if required, to the coal to lower the ash fusion temperature and increase the molten slag viscosity. 

The potassium combines with the sulfur to form potassium sulfate, which condenses as a soHd primarily in the electrostatic precipitator (ESP) or baghouse. The recovered potassium sulfate is then deUvered to a seed regeneration unit where the ash and sulfur are removed, and the potassium, in a sulfur-free form such as formate or carbonate, is recycled to the MHD combustor. It is necessary also to remove anions such as Cf and E which reduce the electrical conductivity of the generator gas flow. These are present in the coal ash in very small and therefore relatively harmless concentrations. As the seed is recycled, however, the concentrations, particularly of CF, tend to build up and to become a serious contaminant unless removed. 

PermeOx is also used to improve the bioremediation of soils contaminated with creosote or kerosene (see Bioremediation (Supplement)), to deodori2e sewage sludges and wastewater (see Odormodification), and to dechloriaate wastewater and effluents. A special formulation of calcium peroxide, made by FMC and sold ia the United States under the trademark Trap2ene, is used for removing metal ions from acidic waste streams such as coal ash leachate and acid mine drainage (see Wastes, industrial). 

In the United States, the largest concentration of atmospheric vanadium occurs over Eastern seaboard cities where residual fuels of high vanadium content from Venezuela are burned ia utility boilers. Coal ash ia the atmosphere also coataias vanadium (36). Ambient air samples from New York and Boston contain as much as 600—1300 ng V/m, whereas air samples from Los Angeles and Honolulu contained 1—12 ng V/m. Adverse pubHc health effects attributable to vanadium ia the ambieat air have aot beea deteroiiaed. lacreased emphasis by iadustry oa controlling all plant emissions may have resulted ia more internal reclamation and recycle of vanadium catalysts. An apparent drop ia consumption of vanadium chemicals ia the United States since 1974 may be attributed, in part, to such reclamation activities. 

A related property is the viscosity of coal ash. Ash viscosity affects the rate at which ash deposits may flow from the walls, and thus the requirements for ash removal equipment such as wall blowers and soot blowers. The preferred coal ash has a narrow temperature range through which it passes the plastic range, ca 25, 000-1,000, 000 mPa-s (=cP) (62). 

Phosphoms determination involves the conversion of phosphoms to soluble phosphate by digesting the coal ash with a mixture of sulfuric, nitric, and hydrofluoric acids (18). Phosphate is precipitated as ammonium phosphomolybdate, which may be reduced to give a blue solution that is determined colorimetricaHy or volumetricaHy (D2795) (18). 

Coal ash is derived from the mineral content of coal upon combustion or utilization. The minerals are present as discrete particles, cavity fillings, and aggregates of sulfides, sulfates, chlorides, carbonates, hydrates, and/or oxides. The key ash-forming elements and compounds are (4,5) ... 

Pig. 4. Viscosity—temperature profiles of coal ash samples, where A represents Buckskin B, Pyro No. 9 C, Blacksvike (Appalachia) No. 2 and D, Drayton. 

J. A. Salter and co-workers, "Shell Coal Gasification Process By-Product Utili2ation," Ninth Jntemational Coal Ash Etilicyation Symposium, Orlando, Fla.,Jan. 1991. 

The main stages of coal combustion have different characteristic times in fluidized beds than in pulverized coal combustion. Approximate times are a few seconds for coal devolatilization, a few minutes for char burnout, several minutes for the calcination of limestone, and a few hours for the reaction of the calcined limestone with SO2. Hence, the carbon content of the bed is very low (up to 1% by weight) and the bed is 90% CaO in various stages of reaction to CaSO. About 10% of the bed s weight is made up of coal ash (91). This distribution of 90/10 limestone/coal ash is not a fixed ratio and is dependent on the ash content of the coal and its sulfur content. 

The composition of coal ash varies widely. Calculated as oxides, the composition (percent by weight) varies as follows ... 

Knowledge of the composition of coal ash is usehil for estimating and predicting coal performance in coke making and, to a hmited extent, the folding and corrosion of heat-exchange surfaces in pidverized-coal-fired furnaces. 

The mean specific heat of coal ash and slag, which is used for calculating heat balances on furnaces, gasifiers, and other coal-consuming systems, follows. 

Germanium minerals are extremely rare but the element is widely distributed in trace amounts (like its neighbour Ga). Recovery has been achieved from coal ash but is now normally from the flue dusts of smelters processing Zn ores. 

Bock. m. buck (Brewing) bock beer (Twk.) trestle, jack, horse, stand, stool blunder, -asche, /. coal ashes. -hoLz, n. guaiacum wood, lignum vitae,... 

Fireclay bricks are used in kilns, malleable-iron furnaces, incinerators, and many portions of metallurgical furnaces. They are resistant to spalling and stand up well under many slag conditions but are not generally suitable for use with high-lime slags or fluid-coal-ash slags or under severe load conditions. 

Coal ash, coal fly ash, power station fly ash, incinerator ash, vehicle exhaust particulates, urban dust, atmospheric dust, metal smelter dust, welding dust, diesel particulates, particulates on filter media Sewage sludge, wastewater... 

Ambroise, J., Amoura, A., and Pera, J., Development of flowable high volume - fly ash mortars, in Proceedings of the 11th International Symposium on the Use and Management of Coal Combustion Byproducts (CCBs), Vol. 2, American Coal Ash Association, 1995. 

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