Particulates, fly ash

A source of fly ash particulates is the mineral matter in the biomass feedstock. As material is gasified, the inorganic matter from the feedstock may be either retained in the gasifier bed or entrained in the product gas and swept out from the reactor. The mineral concentrations in clean wood are typically 1 to 2%, and herbaceous crops may contain up to 10% or more. Crop residues such as straw or rice hulls typically contain 15 to 20% inorganic material. Mineral matter... 

Fly ash particulate matter produced from mineral matter in coal that is converted during combustion to finely divided inorganic material which emerges from the combustor in the gases. 

Pollution control devices for particulates do not depend upon new technology whereas SO2 control does. Since the first decade of this century, as a result of Cottrell s original work (9j, the electrostatic precipitator had been used to collect fly ash particulates. These devices were used on many of the older coal burning plants which had converted to oil. On the reconversion to coal, they were put back in operation or else new ESP units were put in the place occupied by the older ones. The performance of these systems, when designed for a specific coal, was... 

Figure 3. Scanning electron photomicrographs of fly ash particulates collected on alundum thimbles used to sample the precipitator inlet and outlet and the stack...

The electrostatic precipitator was very efficient (— 98% ) for most trace elements based on analyses of the fly ash particulate specimens collected from the precipitator inlet and outlet. An exception was selenium. Although a reasonable mass balance was obtained for this element (see NAA results, Table III), it was not removed efficiently by the precipitator. This may indicate that a significant fraction of the material is in the vapor phase in the flue gas and that it is being adsorbed in... 

Particulate-bound CDDs are removed by wet or dry deposition with an atmospheric lifetime 10 days (Atkinson 1991) and, to a lesser extent, by photolysis. Miller et al. (1987) measured photolysis of 2,3,7,8-TCDD sorbed onto small-diameter fly ash particulates suspended in air. The results indicated that fly ash confers photostability to the adsorbed 2,3,7,8-TCDD. The authors reported little (8%) to no loss of 2,3,7,8-TCDD on the fly ash samples after 40 hours of illumination in simulated sunlight. 

Background. A commercially common soda-lime-silica glass has been considered as an absorbing medium for removing fly ash particulates in combustion gas streams ( ). However, a possible limitation with this application is the release of alkali from the glass into the gas stream. Glass also has some common features... 

The objective of this paper aims to present recent studies on the ecological and human health impacts resulting from the deposition of coal fly-ash particulates from emissions due to fossil fuel combustion within the Pechora Basin. Problems exist when monitoring airborne particulate deposition around urban centers, as air and precipitation chemistries show high temporal and spatial variation (e.g. Reimann et al. 1999). Elemental concentrations are usually low and sample contamination is a significant problem. Approaches include the analysis of ecological materials that accumulate contaminants (e.g. snow, soils and lichens) which become modified by exposure to pollution from airborne particulate deposition. 

Fly-ash Particulate matter emitted to the atmosphere with flue gases. 

Metals in Fly Ash Particulates from waste incinerators typically contain oxides of silicon, iron, calcium, and aluminum. The other trace metals of importance are antimony, arsenic, barium, beryllium, cadmium, chromium, lead, mercury, silver, and thallium. Carcinogenic toxic metals include arsenic, cadmium, chromium, and beryllium. Arsenic is only present in samples 7 (100% plastic) and 6 (50% nonplastic/50% plastic C) and not present in other samples. 

Soxhlet extraction is the most commonly used technique to quantitatively remove PCDDs and PCDFs from solid environmental matrices (such as sediments, fly ash, particulate matter) and solid sorbents employed in air or water sampling. A Dean-Stark apparatus is often used in combination with the Soxhlet extractor to remove traces of water [13]. Besides the classical Soxhlet apparatus, other innovative techniques have been developed for the extraction of organic substances from solid matrices. Among these techniques, the pressurized fluid extraction (PEE) found wide acceptance in the scientific community. 

Differential pulse polarography and stripping voltammetry have been applied to the analysis of trace metals in airborne particulates, incinerator fly ash, rocks. 

The monoalkyl derivatives in salt form appear to have low toxicity. The monomethyl sulfate sodium salt has an approximate oral lethal dose greater than 5000 mg/kg of body weight for rats (129). Monododecyl sulfate sodium salt is widely marketed as a detergent and shampoo ingredient (oral LD q 1268 mg/kg for rats) (126). Both dimethyl sulfate and monomethyl sulfate occur in the environment in coal fly-ash and in airborne particulate matter (130). 

ITie major component of atmospheric haze is sulfate particulate matter (particularly ammonium sulfate), along with varying amounts of nitrate particulate matter, which in some areas can equal the sulfate. Other components include graphitic material, fine fly ash, and organic aerosols. 

In the past, for many air pollution control situations, a change to a less polluting fuel offered the ideal solution to the problem. If a power plant was emitting large quantities of SO2 and fly ash, conversion to natural gas was cheaper than instaUing the necessary control equipment to reduce the pollutant emissions to the permitted values. If the drier at an asphalt plant was emitting 350 mg of particulate matter per standard cubic meter of effluent when fired with heavy oil of 4% ash, it was probable that a switch to either oil of a lower ash content or natural gas would allow the operation to meet an emission standard of 250 mg per standard cubic meter. 

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Figure 30-lE includes a hot ESP for fly ash collection prior to a catalytic NO , unit. Having a hot ESP dictates the use of a conventional wet scrubber and perhaps the need for a second particulate matter control device at the end of the system. Fly ash and scrubber sludge would be separate byproducts, but sludge could be contaminated with NH4 from the catalytic NO process. 

Fly ash Fine ash particulate matter found in flue gases. 

Electrostatic precipitators are satisfactory devices for removing small particles from moving gas streams at high collection efficiencies. They have been used almost universally in power plants for removing fly ash from the gases prior to discharge. Electrostatic precipitators have the capability of fine particulate control. Resistivity plays an important role in determining whether a particle can be readily collected in this device. 

Similarly, when burning low grade, high-ash fuels, the particulate fly ash is also carried through the flue gas system and into the atmosphere unless precautionary measures are taken. Dust control and desulfurization equipment employed today includes ... 

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... 

The management or disposal of metals and ash, other by-products of the combustion process, also causes concern. Ash is an inert solid material composed primarily of carbon, salts, and metals. During combustion, most ash collects at the bottom of the combustion chamber (bottom ash). When this ash is removed from the combustion chamber, it may be considered hazardous waste via the derived-from rule or because it exhibits a characteristic. Small particles of ash (particulate matter that may also have metals attached), however, may be carried up the stack with the gases (fly ash). These particles and associated metals are also regulated by the combustion regulations, as they may carry hazardous constituents out of the unit and into the atmosphere. Since combustion will not destroy inorganic compounds present in hazardous waste, such as metals, it is possible that such... 

Nitro polycyclic aromatic hydrocarbons are environmental contaminants which have been detected in airborne particulates, coal fly ash, diesel emission and carbon black photocopier toners. These compounds are metabolized Tn vitro to genotoxic agents through ring oxidation and/or nitroreduction. The details of these metabolic pathways are considered using 4-nitrobiphenyl, 1- and 2-nitronaphthalene, 5-nitro-acenaphthene, 7-nitrobenz[a]anthracene, 6-nitro-chrysene, 1-nitropyrene, 1,3-, 1,6- and 1,8-dinitro-pyrene, and 1-, 3- and 6-nitrobenzo[a] pyrene as examples ... 

A wide variety of nitro PAHs have been isolated from different environmental sources including airborne particulates (27-34), coal fly ash (35-37), diesel emission particulates (38-41) and carbon black photocopier toners (42-43). Their presence has also been suggested in the smoke from nitrate-fortified cigarettes (44). The structures of the most commonly detected nitro PAHs are shown in Figure 1 and in each instance it is the kinetically-favored isomer that is found. 

I,, = 0.7 h on silica gel, tA = 2.2 h on alumina and tA = 44 h on fly ash for different atmospheric particulate substrates determined in the rotary photoreactor (appr. 25 pg/g on substrate) (Behymer Hites 1985) direct photolysis tA = 9.08 h (predicted-QSPR) in atmospheric aerosol (Chen et al. 2001). Photodegradation k = 3 x 10-5 s in surface water during the summertime at mid-latitude (Fasnacht Blough 2002)... 

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