Utility fly ash

Abstract Coal extraction and combustion produce a number of waste streams, some of which can be utilized. Fly ash from the combustion of pulverized coal is characterized it finds application as a partial replacement for Portland cement in concrete. Relatively few uses exist for other wastes, much of which is stockpiled, stored, or landfilled. These leave a legacy for future generations that must be managed to minimize geochemical impacts on air, soil, and groundwater quality. 

Torrey, W. 1978. Coal ash utilization fly ash, bottom ash and slag. Pollution Technology Review, 48, 136-145. 

ElDERMAN, B., VOSKOBOINIK, M., LEVY, H. Soskine, M. 2000. Operational and financial advantages of a new technology for fly ash separation. Proceedings 2000 Conference on Unbumed Carbon on Utility Fly Ash, US Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory, 51-55. 

Chromium occurs in three valence states 2 - -, 3 +, and 6 +. The 2 + state is formed in extreme reducing environments, but the bulk waste streams such as utility fly ash and... 

Miller, WP University of Georgia Study waste streams from the poultry production (manure/litter), pulp and paper (sludges and ashes), and electric utility (fly ash/bottom ash) industries in Georgia CRIS/USDA 2001... 

In summary, we have presented a simple approach to synthesize hollow SiC spheres. The size of the hollow spheres depending on the size of the template carbon spheres. The shell of the spheres consists of a lot of twisted SiC nanowires with length of 5 20 pm and diameter of 50-500 nm, which is formed through a gas phase reaction. This technique presents a convenient method to synthesize hollow SiC spheres and an effective way to utilize fly ash. 

Asbestos fiber presently used in cement matrix for the production of asbestos sheets leads to serious health hazards. AMPRI, Bhopal has developed a technology to effectively utilize fly ash along with organic fibers for the production of cormgated roofing sheets. 

In the earlier days of coal utilization, fly ash was not a major problem. What has changed that has resulted in much greater production of fly ash What modem mode of coal combustion significantly reduces the production of fly ash and acid gases from combustion ... 

Industrial by-products are becoming more widely used as raw materials for cement, eg, slags contain carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from utility boilers can often be a suitable feed component, because it is already finely dispersed and provides silica and alumina. Even vegetable wastes, such as rice hull ash, provide a source of silica. Probably 50% of all industrial by-products are potential raw materials for Pordand cement manufacture. 

A major market which has developed for fabric fillers is for the control ot flue-gas fly ash in the utility industry. This market is primarily at the expen.se of electrostatic precipitators. Fabric filters have the inherent advantage of operating at a high level of collection efficiency tor a wide range of dust and gas conditions. 

More than 90% of the coal used by electric utilities is burned in pulverized coal boilers. In these boilers, 65-80% of the ash produced is in the form of fly ash. This fly ash is carried out of the combustion chamber in the flue gases and is separated from these gases by electrostatic precipitators and/or mechanical collectors. The remainder of the ash drops to the bottom of the furnace as bottom ash. While most of the fly ash is collected, a small quantity may pass through the collectors and be discharged to the atmosphere. The vapor is that part of the coal material that is volatilized during combustion. Some of these vapors are discharged into the atmosphere others are condensed onto the surface of fly ash particles and may be collected in one of the fly ash collectors. 

The DustMASTER system is designed to limit dust from fly ash and other dust generating waste streams such as fly and bottom ash from waste-to-energy and utility plants, cement kiln dust, baghouse residue, iron-oxide, and other powder-type materials. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Ulrich, G.D., An Investigation of the Mechanism of Fly-Ash Formation in Coal-Fired Utility Boilers, Interim Report, US-ERDA FE-2205-1, May 28, 1976. 

Cahill, T.A. Ashbaugh, L.L. "Size/Composltlon Profiles of Resuspended Fly Ash" in Environmental and Climatic Impact of Coal Utilization, Jag J. Singh and Adarsh Deepak, Eds. Academic Press, New York, 1980, 569-573. 

The description of the workings of the control technologies is beyond the scope of this article. However, it is worth noting that many of these technologies create substantial amounts of solid or liquid waste that needs to be disposed of properly. For example, in the USA the total amount of fly ash produced from coal combustion alone is about 57 Mt/y (Kalyoncu 2000). About one-third is utilized as secondary raw material (e.g., for aggregate and asphalt), but the rest is usually disposed of in landfills. The wet and dry scrubbers for S02 control produce a sludge or dry waste that finds little secondary use, and a large amount is disposed in landfills. 

Clean coal production will undoubtedly help reduce combustion waste, especially if reject material is returned to the coal extraction site. Some ash, especially fly ash, finds useful application, but scope exists for innovative research to improve utilization of coal combustion products. For example, tailoring ash properties to specific applications offers scope for increased utilization, provided tailoring can be done economically. 

The compounds that result from FGD technologies have very different bulk chemical and mineralogical characteristics than those from conventional combustion. They still contain Si, Al, and Fe, but they contain as much as 50-60 wt% Ca and S, much of which is soluble in water. Although many types of FGD products have been used successfully as engineered fill, they may also be utilized as soil amendments, particularly when combined with organic byproducts. Use of FBC ash in structural fill is limited compared to fly ash, bottom ash, and FGD products due to the expansion problems that occur when FBC ash first comes into contact with water. 

Adriano, D. C., Page, A. L., Elseewi, A. A., Chang, A. C. Straughan, I. 1980. Utilization and disposal of fly ash and other coal residues in terrestrial ecosystems A review. Journal of Environmental Quality, 9, 333-344. 

McCarthy, G. J. 1988. X-ray powder diffraction for studying the mineralogy of fly ash. In Fly Ash and Coal Conversion By-Products Characterization, Utilization and Disposal. Materials Research Society Symposium Proceedings, 113, 75-86. 

McCarthy, G. J., Solem, J. K., Manz, O. E. Hassett, D. J. 1990. Use of a database of chemical, mineralogical and physical properties of North American fly ash to study the nature of fly ash and its utilization as a mineral admixture in concrete. Materials Research Society Symposium Proceedings, 178, 3-34. 

One of the most significant uses of fly ash is as a mineral admixture in Portland cement concrete. This use alone accounted for over 56 wt% of the fly ash utilized in the USA in 2001 (American Coal Ash Association 2002). Fly ash is particularly well suited to this application because of its... 

Perhaps the most significant advantage of using froth flotation to beneficiate fly ash is the ability to process ash that has been impounded in disposal ponds and landfills. This is advantageous for several reasons. First, it effectively de-couples ash beneficiation from ash production. There is no need for the utility to alter disposal practices or install additional ash handling equipment in order to accommodate ash processing since the feed to the processing plant... 

Utilities using post-combustion SCR-supported ammonia injection for NOx control as well as those using ammonia conditioning to improve electrostatic precipitator performance will produce fly ash that contains ammonia compounds. The ammonia is primarily physically adsorbed onto the fly ash particles as sulphate and bisulphate species. In many cases, the residual ammonia levels are quite low (<50ppm) however, elevated concentrations can occur as the catalyst ages or due to mechanical problems with the ammonia injection system. While elevated ammonia concentrations in fly ash do not negatively impact pozzolanic properties, it can reduce ash marketability due to odour concerns. For this reason, several processes have been developed to remove or reduce the amount of ammonia in fly ash. 

Meij, R. van den Berg, J. 2001. Coal Fly Ash Management in Europe Trends, Regulations and Health Safety Aspects. Keynote Address, 2001 International Ash Utilization Symposium, 20-24 October 2001, Lexington, KY. 

Despite the emphasis on waste minimization and recycling, society will continue to generate waste requiring incineration or landfill disposal in the foreseeable future. Owing to the formation of bottom and fly ash through MSW incineration, it is important to find criteria for their utilization in an environmentally sound manner. This is in line with the policies adopted by several EU countries, such as Italy, where the utilization of... 

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