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Author : Joseph John Helble
Publisher :
ISBN 13 :
Total Pages : 540 pages
Book Rating : 4.:/5 (178 download)
Download or read book Mechanisms of Ash Particle Formation and Growth During Pulverized Coal Combustion written by Joseph John Helble and published by . This book was released on 1987 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : J J. Helble
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (12 download)
Download or read book Mechanisms of Ash Particle Formation Growth Pulverised Coal Combustion written by J J. Helble and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Aura Cecilia Davila Latorre
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)
Download or read book Ash Formation Under Pressurized Pulverized Coal Combustion Conditions written by Aura Cecilia Davila Latorre and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Coal combustion is a source of inorganic particulate matter (ash), which can deposit in boilers and also be emitted into the atmosphere becoming part of ambient fine particulate matter (PM 2.5). In order to decrease coal combustion emissions per unit of power produced, higher efficiency systems have been proposed, including systems operating at elevated pressures. These new operating conditions will affect pollutant formation mechanisms, particularly those associated with the conversion of mineral matter to ash. Ash particle formation mechanisms are particularly sensitive to changes in pressure as they are related to the structure of coal char particles at early stages of combustion. To assess the importance of pressure on ash particle formation, pyrolyzed chars and ash particles from pressurized pulverized combustion of two bituminous and one subbituminous U.S. coals at operating pressures up to 30 atm were studied. Pressure changes the distribution of char particle types, changing the spatial distribution of the minerals during the combustion process and therefore affecting particle formation mechanisms. Chars were examined by Scanning Electron Microscopy (SEM) and classified into two different types (cenospheric and solid) depending on porosity and wall thickness. A correlation for estimating the amount of these cenospheric char particles was then proposed for bituminous coals based on the operating conditions and coal maceral analysis. The ash particle size distribution of the coals combusted at different operating pressures was measured using Computer Controlled Scanning Electron Microscopy (CCSEM). The results of the char characterization and ash particle size distribution measurements were then incorporated into an ash particle formation algorithm that was proposed and implemented. The model predicts ash particle size and composition distributions at elevated pressures under conditions of complete char burnout. Ash predictions were calculated by first developing char structure distribution functions based on coal characteristics. To obtain an ash particle size distribution, carbon is then allowed to react away while following coalescence, fragmentation and other transformation processes as combustion proceeds. Particle size distributions calculated with this model showed qualitative agreement with the trends identified in the experimental portion of this research.
Author :
Publisher :
ISBN 13 :
Total Pages : 7 pages
Book Rating : 4.:/5 (683 download)
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames. Quarterly Technical Progress Report No. 10, January 1, 1995--March 31, 1995 written by and published by . This book was released on 1995 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The production of ash particles from coal combustion limits it's use as a fuel. On mechanism by which small ash particles are formed is the generation of submicron aerosols through a vaporization/condensation mechanism. Previous work has shown that coal cleaning can lead to increased emissions of aerosols. This research will investigate the means or aerosol formation in coals and the effects that various methods of coal cleaning have on aerosol production, and whether or not cleaning can be performed in a manner that will not lend itself to aerosol formation.
Author : Xiaofei Wang
Publisher :
ISBN 13 :
Total Pages : 260 pages
Book Rating : 4.:/5 (897 download)
Download or read book Fine Particle and Mercury Formation and Control During Coal Combustion written by Xiaofei Wang and published by . This book was released on 2014 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pulverized coal combustion is widely used worldwide for the production of electricity. However, it is one of the primary emission sources of air pollutants, including particulate matter (fly ash) and mercury (Hg), into the atmosphere. This dissertation investigated three aspects of pollutant formation and control from the coal combustion process: (1) organic aerosol formation during coal combustion, (2) mercury removal during coal combustion by injection of Vanadium Pentoxide (V2O5), and (3) submicrometer particle formation during oxy-coal combustion. Part. 1. While the characterization and formation of the mineral matter component of aerosol during coal combustion has been well studied and understood, the characterization and fate of corresponding organic matter content was not examined in detail earlier. The first part of this dissertation studies the formation mechanism of organic aerosols during coal combustion. Pilot-scale experiments were conducted in a 1 MW coal combustor, and showed that black carbon aerosol formation was greatly enhanced by increasing the fuel-air equivalence ratio. However, organic carbon aerosol formation was lowered by increasing the fuel-air equivalence ratio, which was opposite to the trend of black carbon aerosol formation. This phenomenon indicates that the formation mechanism of organic carbon aerosol is different from black carbon (soot) aerosol. Detailed organic aerosol formation mechanisms have been studied in a laboratory-scale system. Aerosol mass spectrometry techniques were applied to characterize both coal combustion aerosols from a drop-tube coal combustor and coal pyrolysis products from a flat-flame coal pyrolyzer. The chemical composition of major species for both combustion organic aerosols and pyrolysis products are hydrocarbons, carboxylic acids and aromatic compounds. The similarities of the chemical compositions demonstrate that the products from coal pyrolysis, (the initial step of coal combustion), are the precursors of organic aerosols. More carboxylic acids and oxygenated organic compounds were found in the combustion aerosols, indicating that many pyrolysis products are oxidized before they are converting to organic aerosols. A strong correlation between inorganic and organic aerosol formation mechanisms has been found in this work, demonstrating that inorganic particles play a critical role as carriers of organic species. Sulfate species in inorganic aerosols play a particularly important role in organic aerosol formation. Enhanced organic aerosol formation during the combustion of high sulfur content coal has been observed for the first time. High resolution mass spectra analysis shows the presence of amine-like organics in the aerosols. The correlation between particulate sulfate and organics suggests that acidic sulfate particles may absorb basic amine-like organics, a major coal pyrolysis product, from the gas phase into the particle phase via acid-base neutralization reactions. Part. 2. Coal combustion is a major source of atmospheric mercury. High-temperature sorbent injection is an efficient method to capture metallic species during combustion. This part of the study examines the performance on Hg capture from pulverized coal combustion in a drop-tube furnace. V2O5 was tested as a sorbent and demonstrated good performance on elemental mercury capture, which results from the formation of ultrafine V2O5 particles during the combustion process. It is proposed that the ultrafine V2O5 particles catalyzed Hg0 oxidation on their large surfaces. Hg2+, the oxidation product, may condense on fly ash particle surfaces or on tubing surfaces, thereby being removed from the flue gas. Part. 3. Coal combustion is the largest single contributor to global anthropogenic CO2 emissions. Oxy-coal combustion replaces the air with oxygen and uses recycled flue gas (RFG) as a diluent, resulting in a higher concentration (>98%) of CO2 in the exhaust, which promotes more effective control, capture, and possible conversion of CO2. This part of the dissertation investigates the effects of recycling (up to recycle ratios of 60%) on submicrometer particle formation in a drop-tube furnace system. The recycled exhaust gas containing lower O2 concentration and higher CO2 concentration suppressed submicrometer particle formation. However, it was found that water vapor in recycled exhaust gas greatly enhanced the formation of submicrometer particles. The gas composition changes that result from exhaust-gas recycling significantly affected the size distribution of submicrometer particles at the exit of the combustor. Differences in the particle size distribution with and without the filtration of recycled exhaust gas were insignificant. The composition of the resultant particles in oxy-coal combustion and conventional coal-air combustion as determined by X-ray diffraction was similar.
Download or read book Investigation of Mechanisms of Ash Deposit Formation from Low-rank Coal Combustion written by and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This project was undertaken to determine the chemical behavior of alkali metal and other species implicated in the ash fouling which can occur during the combustion of low rank coals. The coal combustion was studied in unaugmented premixed pulverized coal flames. Vapor species were measured by molecular beam mass spectrometry. Temperatures were also measured, and time-resolved coal/ash particulate samples were collected and analyzed. A major part of the research on this project was devoted to: (1) the development and refinement of techniques for the MBMS analysis of trace quantities of unstable and reactive high temperature vapor species from the pulverized coal flames; and (2) the time-resolved sampling and collection of particulates. The equipment is now operating very satisfactorily. Inorganic species, some of which were present at parts-per-million levels, were quantitatively sampled and measured in the pulverized coal flames. Time-resolved particulate samples which were free of vapor deposited contaminants were collected without the use of an interfering substrate. Profiles of the alkali metal species in Beulah lignite and Decker subbituminous coal flames were obtained. It was found in both flames that sodium is volatilized as the atomic species early (milliseconds) in the combustion process. The gaseous Na reacts, also in milliseconds, to form an unknown species which is probably an oxide fume, but which is not NaOH or Na2SO4. This is probably the mechanism for the formation of the alkali ''fumes'' observed in other systems. Measurements were also made of a number of other gaseous species, and time-resolved coal/ash samples were obtained and analyzed. 27 refs., 23 figs., 8 tabs.
Author :
Publisher :
ISBN 13 :
Total Pages : 105 pages
Book Rating : 4.:/5 (893 download)
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames. Final Technical Report, September 30, 1992--January 31, 1996 written by and published by . This book was released on 1996 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coal ash, and particularly fine fly ash, remain one of the principal practical and environmental problems in coal-based power generation. In particular, submicron aerosols are identified with direct inhalation risk. Submicron ash is thought to arise from mineral vaporization during char combustion, followed by nucleation, condensation and coagulation to yield an aerosol. While aerosols are predominantly made out of volatile alkali minerals, they also can include refractory oxides that are chemically reduced to more volatile forms within the char particle and vaporized. Most of the ash of size greater than 1 [mu]m is generated by agglomeration of mineral as the char particle bums out. These two principal mechanisms are thought to account for most of the ash generated in coal combustion. Previous research has shown that various forms of coal treatment can influence the yields of fine ash from combustion. The research reported here investigates various forms of treatment, including physical coal cleaning, aerodynamic sizing, degree of grinding, and combinations of these on both aerosol yields and on yields of fine residual ash (1-4 [mu]m). The work also includes results from the combustion of artificial chars that include individual mineral elements. This research shows that these various forms of coal treatment can significantly change ash characteristics. While none of the treatments affected the bulk of the residual ash size distribution significantly, the yield of the ash aerosol mode (d
Author : T. Shimohara
Publisher :
ISBN 13 :
Total Pages : 25 pages
Book Rating : 4.:/5 (465 download)
Download or read book A Study of the Mechanism of Forming Submicron Fly Ash by Pulverized Coal Combustion written by T. Shimohara and published by . This book was released on 1987 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :
Publisher :
ISBN 13 :
Total Pages : 9 pages
Book Rating : 4.:/5 (727 download)
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames written by and published by . This book was released on 1993 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second major ash producing mechanism is the generation of a submicron aerosol through a vaporization/condensation mechanism. When the ash size distribution is plotted in terms of number density, the submicron mode generally peaks at about 0. 1 [mu]m. When plotted in terms of mass, this mode is sometimes distinct from the residual ash mode, and sometimes merged into it. During diffusion-limited char combustion, the interior of the particle becomes hot and fuel-rich. The non-volatile oxides (e.g., Al[sub 2]O[sub 3], SiO[sub 2], MgO, CaO, Fe[sub 2]O[sub 3]) can be reduced to more volatile suboxides and elements, and partially vaporized. These reoxidize while passing through the boundary layer surrounding the char particle, thus becoming so highly supersaturated that rapid homogeneous nucleation occurs. This high nuclei concentration in the boundary layer promotes more extensive coagulation than would occur if the nuclei were uniformly distributed across the flow field. The vaporization can be accelerated by the overshoot of the char temperature beyond the local gas temperature. Although these particles represent a relatively small fraction of the mass, they can present a large fraction of the surface area. Thus, they are a preferred site for the condensation of the more volatile oxides later in the furnace. This leads to a layering effect in which the refractory oxides are concentrated at the particle core and the more volatile oxides resideat the surface. This also explains the enrichment of the aerosol by volatile oxides that has been noted in samples from practical furnaces. These volatile metal oxides include the majority of the toxic metal contaminants, e.g., mercury, arsenic, selenium and nickel. Risk assessment studies suggest that toxic metal emissions represent a significant portion of the health risk associated with combustion systems.
Author :
Publisher :
ISBN 13 :
Total Pages : 5 pages
Book Rating : 4.:/5 (873 download)
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames. Quarterly Technical Progress Report No. 3, April 1, 1993--June 30, 1993 written by and published by . This book was released on 1993 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the major obstacles to the economical use of coal is managing the behavior of its mineral matter. Ash size and composition are of critical importance for a variety of reasons. Fly ash size and emissivity affect radiant furnace heat transfer. Heat transfer is also affected by the tendency of ash to adhere to heat transfer surfaces, and the properties of these deposits. Removal of ash from flue gas by electrostatic precipitators is influenced by both particle size and particle resistivity. The efficiency of fabric filter-based cleaning devices is also influenced by ash size. Both types of devices have reduced collection efficiencies for smaller-sized particles, which corresponds to the size most efficiently retained in the alveolar region of the human lung. Laboratory work and studies of full-scale coal-fired boilers have identified two general mechanisms for ash production. The vast majority of the ash is formed from mineral matter that coalesces as the char burns, yielding particles that are normally larger than 0.5 [mu]m. The second major mechanism is the generation of a submicron aerosol through a vaporization/condensation mechanism. Although these particles represent a relatively small fraction of the mass, they can present a large fraction of the surface area. Thus, they are a preferred site for the condensation of the more volatile oxides later in the furnace. This leads to a layering effect in which the refractory oxides are concentrated at the particle core and the more volatile oxides reside at the surface. This also explains the enrichment of the aerosol by volatile oxides that has been noted in samples from practical furnaces. These volatile metal oxides include the majority of the toxic metal contaminants, e.g., mercury, arsenic, selenium and nickel. Risk assessment studies suggest that toxic metal emissions represent a significant portion of the health risk associated with combustion.
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames. Quarterly Technical Progress Report No. 5, October 1, 1993--December 31, 1993 written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Laboratory work and studies of full-scale coal-fired boilers have identified two general mechanisms for ash production. The vast majority of the ash is formed from mineral matter that coalesces as the char burns, yielding particles that are normally larger than 0.5[mu]m. Flagen and Friedlander proposed a simple model for this residual ash, called the breakup model. The second major mechanism is the generation of a submicron aerosol through a vaporization/condensation mechanism. When the ash size distribution is plotted in terms of number density, the submicron mode generally peaks at about 0.1 [mu]/m. When plotted in terms of mass, this mode is sometimes distinct from the residual ash mode, [sup 13] and sometimes merged into it. Although these particles represent a relatively small fraction of the mass, they can present a large fraction of the surface area. Thus, they are a preferred site for the condensation of the more volatile oxides later in the furnace. This leads to a layering effect in which the refractory oxides are concentrated at the particle core and the more volatile oxides reside at the surface. This also explains the enrichment of the aerosol by volatile oxides that has been noted in samples from practical furnaces. These volatile metal oxides include the majority of the toxic metal contaminants, e.g., mercury, arsenic, selenium and nickel. Risk assessment studies suggest that toxic metal emissions represent a significant portion of the health risk associated with combustion.
Author : Zhonghua Zhan
Publisher :
ISBN 13 :
Total Pages : 161 pages
Book Rating : 4.:/5 (952 download)
Download or read book Ash Deposition and Ash Aerosol Formation Mechanisms During Oxy-coal Combustion written by Zhonghua Zhan and published by . This book was released on 2015 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Alan N. Sayre
Publisher :
ISBN 13 :
Total Pages : 22 pages
Book Rating : 4.:/5 (196 download)
Download or read book Properties of Ash Particles Generated During Pulverized Coal Combustion written by Alan N. Sayre and published by . This book was released on 1988 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Suppression of Fine Ash Formation in Pulverized Coal Flames. Quarterly Technical Progress Report No. 4, July 1, 1993--September 30, 1993 written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Laboratory work and studies of full-scale coal-fired boilers have identified two general mechanisms for ash production. The vast majority of the ash is formed from mineral matter that coalesces as the char burns, yielding particles that are normally larger than 0.5 [mu]m. The second major mechanism is the generation of a submicron aerosol through a vaporization/condensation mechanism. Previous work has shown that pulverized bituminous coals that were treated by coal cleaning (via froth flotation) or aerodynamic sizing exhibited altered aerosol emission characteristics. Specifically, the emissions of aerosol for the cleaned and sized coals increased by as much as one order of magnitude. The goals of the present progress are to: (1) perform measurements on carefully characterized coals to identify the means by which the coal treatment increases aerosol yields; (2) investigate means by which coal cleaning can be done in a way that will not increase aerosol yields; (3) identify whether this mechanism can be used to reduce aerosol yields from systems burning straight coal. This paper discusses model description and model formulation, and reports on the progress of furnace design and construction, and coal selection.
Author :
Publisher :
ISBN 13 :
Total Pages : 252 pages
Book Rating : 4.:/5 (873 download)
Download or read book Mechanisms Governing Fine Particulate Emissions from Coal Flames. Final Report written by and published by . This book was released on 1990 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary objective of this program was to provide a basic understanding of the principal processes that govern the formation of particulate matter in the 0.5--10 [mu]m size range in pulverized coal flames. The mechanism that produces ash particles in this size range is not clear. Particle sizes smaller than the 0.5--10 [mu]m size range are generally accepted to result from a vaporization/condensation mechanism while particles larger than this size result from the coalescence of ash in coal particles which may breakup as they burn. This program combined experimental and theoretical studies to understand the mechanisms which control the production of ash in the 0.5--10 [mu]m size range. (VC).
Author : Jim Williamson
Publisher : Taylor & Francis
ISBN 13 : 1351410261
Total Pages : 1103 pages
Book Rating : 4.3/5 (514 download)
Download or read book The Impact Of Ash Deposition On Coal Fired Plants written by Jim Williamson and published by Taylor & Francis. This book was released on 2022-10-12 with total page 1103 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coal provides almost 40% of the world's electricity, and despite the understandable concern with respect to the environmental impact associated with coal use, forecasts from the International Energy Agency predict, that worldwide coal use will increase by up to 2% per annum until the year 2OlO. Faced with this increase, it is clearly important that the most efficient and environmentally acceptable clean coal technologies are available. This book is comprised of the proceedings of the Engineering Foundation Conference held in June 1993 in England. The objective of the conference was to present ideas on methods of predicting and reducing the effects of ash deposition in coal conversion systems, highlighting the problems experienced in industry, considering both utilities and industrial plants, and providing a view of the technology of coal ash deposition and its impact. Better techniques are needed to reduce the impact of ash deposition in coal fired plants, and these proceedings should form a reference document for anyone either experiencing slagging or actively engaged in trying to understand or eliminate the phenomenon.
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Publisher :
ISBN 13 :
Total Pages : 252 pages
Book Rating : 4.:/5 (16 download)
Download or read book Mechanisms Governing Fine Particulate Emissions from Coal Flames written by and published by . This book was released on 1990 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary objective of this program was to provide a basic understanding of the principal processes that govern the formation of particulate matter in the 0.5--10?m size range in pulverized coal flames. The mechanism that produces ash particles in this size range is not clear. Particle sizes smaller than the 0.5--10?m size range are generally accepted to result from a vaporization/condensation mechanism while particles larger than this size result from the coalescence of ash in coal particles which may breakup as they burn. This program combined experimental and theoretical studies to understand the mechanisms which control the production of ash in the 0.5--10?m size range. (VC).
