Coal combustion wastes formation

Donahoe, R. J. (2004). Secondary Mineral Formation in Coal Combustion Byproduct Disposal Facilities Implications for Trace Element Sequestration. In Giere, R. Stille, P. (eds) Energy, Waste, and the Environment a Geochemical Perspective. Geological Society, London, Special Publications, 236, 641-658. 

On cooling the gas phase some gas components condense and thus lead to the formation of deposits in the boiler. Table 7.9 shows the composition of the condensed phases and the residual waste gas. The change in concentration of the main gas components is low on rapid cooling from 1600 to 700 °C. The condensed phases mainly consist of compounds of K and Na with Cl, P, and S. The low-melting sulfates, phosphates, and chlorides form first a liquid layer where solid dust particles can be deposited by sticking. The composition of the input fuel (coal, and waste material) besides the temperature and O2 partial pressure in the combustion chamber, determine... 

Energy recovery from packaging waste is discussed, with particular reference to the co-combustion of mixed plastics with other conventional fuels such as wood, coal and peat. Experimental work is described in which a project was established to evaluate the possibility of energy recovery from a circulating fluidised bed boiler using packaging from different sources as fuel. The role of sulphur in the formation of PCDD/F in the combustion process was also studied. 

Mercury is one of a number of toxic heavy metals that occur in trace amounts in fossil fuels, particularly coal, and are also present in waste materials. During the combustion of fuels or wastes in power plants and utility boilers, these metals can be released to the atmosphere unless remedial action is taken. Emissions from municipal waste incinerators can substantially add to the environmental audit of heavy metals, since domestic and industrial waste often contains many sources of heavy metals. Mercury vapor is particularly difficult to capture from combustion gas streams due to its volatility. Some processes under study for the removal of mercury from flue gas streams are based upon the injection of finely ground activated carbon. The efficiency of mercury sorption depends upon the mercury speciation and the gas temperature. The capture of elemental mercury can be enhanced by impregnating the activated carbon with sulfur, with the formation of less volatile mercuric sulfide [37] this technique has been applied to the removal of mercury from natural gas streams. One of the principal difficulties in removing Hg from flue gas streams is that the extent of adsorption is very low at the temperatures typically encountered, and it is often impractical to consider cooling these large volumes of gas. 

This priority order ensures that co-combustion of waste is only possible in case the waste cannot be re-used or when formation cannot be avoided. Each plan for cocombustion of waste in coal-fired power plants is therefore tested on its order in priority. An Environmental Impact Study is often mandated or desired by the national administration and/or regional authorities, who discuss and compare the possibilities for reutilization and alternative processing routes (for exanqile by means of a Life Cycle Analysis) (KEMA, 1999). 

The clear implication from the data in Figure 4-9 is that sawdust is the preferred woody biomass fuel in terms of combustion while minimizing NOx formation. Urban wood waste exhibits a slight lag between the evolution of volatile nitrogen and volatile carbon in the low temperature (e.g., <600 C) region, and then performs favorably with respect to NOx management. Urban wood waste is somewhat less favorable than Black Thunder as a representative PRB coal it is more favorable than the Pittsburgh 8 bituminous coal. 

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