Coal combustion effluents

As an aid in establishing the analytical problems, published data were compiled and reviewed for coal combustion and waste incineration (1 ). Important conclusions drawn from this review were 1) only a limited number of organic components had been identified in the effluents 2) the identified components reflected analytical capabilities and interests rather than a true distribution 3) reliable quantitative data were not available and 4) the data base was insufficient for predicting the probable environmental effects associated with the combustion of coal. 

A combined listing of all the compounds identified in the vapor and on particles emitted during the combustion of coal at the /toes power plant are listed in Table I. Similar compounds have been identified in the emissions from a second coal-fired power plant located at Iowa State University. Therefore, this list may be partially representative of coal combustion in semi-modern boilers. Certainly, many more organic compounds than the listed 78 are present in these effluents, but so far these have not been positively identified. Indeed, a 1980 review of organic compounds from coal combustion (1) taken from all the literature reports had only 106 compounds identified. 

Table I. List of Organic Compounds Present in Effluents From Coal Combustion...

Polycyclic Aromatic Hydrocarbons (PAHs). The most highly studied class of compounds in combustion effluents 1s the PAHs. However, very little information about the amounts present in the vapor phase and on particles in the effluents from the efficient combustion of coal is available. The data in Table II partially fills this informational gap. The amounts in the vapor phase varied according to the firing conditions and the stack temperature that was 170 C. Even 1f all these PAHs were to condense on the particles, the amounts are well below the multiple ng/g quantities present on ambient air particles. 

None of these known components were detected in the water at the conservative limit of one ppB. Indeed, this pond water did not contain any gas chromatographable organic compounds at the detection limit of 0.1 ppB even though the well water used for sluicing contained multiple ppB levels of aromatic compounds indicative of the coal tar that had contaminated the aquifer (20). Thus, the ash effluents from coal combustion appear to adsorb rather than release organic compounds into the water. 

Emissions Sampling of Combustion Effluents from a Stationary Diesel Engine That Bums a Coal-Derived Liquid Fuel... 

Increased reliance on coal combustion can give rise to significant fly ash storage or disposal problems. Most fly ash is presently used as a low cost material for construction purposes and also as cover material for landfills. Other, more economically advantegeous, uses for this inexpensive material would be desirable. One such use for fly ash could be to treat ash pond effluent for reuse by power plants as cooling tower makeup water. Another application could be as... 

Acenaphthene is a component of crude oil and a product of combustion, which may be produced and released to the environment during natural fires. Emissions from petroleum refining, coal tar distillation, coal combustion, and diesel fueled engines are the major contributors of acenaphthene to the environment. Acenaphthene is used as a chemical intermediate and may be released to the environment via manufacturing effluents and the disposal of manufacturing waste by-products. Because of the widespread use of acenaphthene in a variety of products, acenaphthene may also be released to the environment through landfills, municipal waste... 

EXPOSURE ROUTES airborne coal tar emissions combustion of oil, gasoline, wood and refuse detected in rain, snow, and fog smoking tobacco inhalation of polluted air ingestion of food and water contaminated by combustion effluents... 

The environmental aspects of coal combustion have been a major factor in the various processes, and the movement of the fossil fuel base away from petroleum and natural gas to coal has increased the need for effluent/pollutant control for large, fossil-fueled power plants (Argonne, 1990). Very large amounts of coal are consumed in generating electricity and the emissions from power stations and similar industrial sources represent a potential, and considerable, environmental hazard. These power plants and the accompanying flue gas desulfurization processes emit effluents, which often are pollutants, and which by mere contact with the external environment or by (generally) simple atmospheric chemical transformations, may form secondary pollutants that are more harmful than the initial effluent/pollutant. 

Water effluents are not a problem in coal gasification plants. In fact, water effluents may create fewer problems for IGCC than for direct combustion-based power generation because the steam cycle in an IGCC plant produces less than 40% of the power plant s power. Therefore, the water effluents from boiler feedwater preparation and cooling-water blowdown are significantly less than those for steam < cle-based power generation with direct coal combustion. 

The second source is process water blowdown, where the water has scrubbed coal-derived gases to remove coal ash and trace components. The raw process water in coal gasification processes contains various organic and inorganic compounds. Purification of this water removes most of the organic compounds, and the plant then recycles much of the water. The net amount of this wastewater effluent reflects the water-soluble inorganics in the feed coal (such as chlorides) and the amount of coal feed. Coal gasification (and direct coal combustion) with dry gas cleanup systems can reduce process water effluents. Coal plants also often use water effluents to control the dust and bulk density of the solid waste. 

An IGCC plant generally produces fewer water effluents than a conventional coal-fired power plant does. The amount of process water blowdown is about the same for both gasification and direct coal combustion. However, the steam cycle in IGCC power plants produces much smaller amounts of wastewater blowdown because less than 40% of the total power generated comes from the steam cycle. 

Designing a zero water effluent for IGCC is easier than designing for direct coal combustion power plants because IGCC plants usually produce fewer water effluents. The 250 MW IGCC power plant under construction in The Netherlands is designed as a zero water effluent discharge plant. 

Resorcinol may be released to the environment in waste effluents associated with coal gasification and conversion, coal-tar production and shale oil processing and from the combustion of wood and tobacco. It has been detected in low levels in groundwater samples (United States National Library of Medicine, 1997). 

How does a scrubber remove noxious gaseous effluents created in the combustion of coal ... 

Fig. 7. Overview of coal preparation, conversion, combustion, and effluent treatment technologies that are designed to markedly reduce deleterious emissions and thus protect the environment. The line at the bottom, indicating traditional practices, now fully applies only to the very oldest coat-energized electric power plants. The Clean Air Act (U.S.) and the Clean Coal program call for progressive upgrading or modernization for achieving major goals by 1995. as described in the text. It should be mentioned that traditional practices have been improved over the years, but these have not been sufficient to meet environmental goals. Better results can be achieved only by way of marked advances in technology...

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