Steadman, EN
1994
Coal Ash Behavior and Management Tools
Erickson, T.A.; O'Leary, E.M.; Folkedahl, B.C.; Ramanathan, M.; Zygarlicke, C.J.; Steadman, E.N.; Hurley, J.P. and Benson, S.A.
The Impact of Ash Deposition on Coal-Fired Plants, Taylor & Francis, Inc., 1994. Funded by US Department of Energy, Electric Power Research Institute, Tow, Texaco, Shell, Union Electric, Kansas City Power and Light, Minnesota Power and Northern States Power.
Over the past five years, computer-based research tools have been increasingly applied in making important economic and operational decisions in the utility power industry. These tools-which include models, indices, databases, and data manipulation programs-are used by researchers, operators, and managers in the evaluation of coal utilization as an efficient and environmentally acceptable source of energy. Applicable tools that have been developed at, and are currently used by, the Energy & Environmental Research Center (EERC) include Partchar©, MINCLASS©, VISCAL©, MANAGER©, ATRAN, LEADER©, PHOEBE©, and PCQUEST©. These software applications range from databases for retrieving coal and coal product analysis, to computer codes to process coal and coal product analysis, to advanced models and indices to evaluate the operational impacts of specific systems.
Inorganic Phase Characterization of Coal Combustion Products Using Advanced SEM Techniques
Folkedahl, B.C.; Steadman, E.N.; Brekke, D.W. and Zygarlicke, C.J.
The Impact of Ash Deposition on Coal-Fired Plants, Taylor & Francis, Inc., 1994. Funded by US Department of Energy, Brigham Young University, Electric Power Research Institute, Dow, Texaco and Shell.
Scanning electron microscopy/electron microprobe analysis (SEM/EMPA) techniques can quantify the inorganic phases present in complex coal combustion materials, as well as provide information on the morphology of the sample. Recent advancements in SEM instrumentation, data manipulation, and automated image analysis techniques have made the routine analysis of a large number of samples and data points possible. The scanning electron microscopy point count (SEMPC) routine, developed at the Energy & Environmental Research Center (EERC), randomly selects a statistically valid number of points and analyzes them for chemistry. This routine also allows for the concurrent storage of digitized images and the measurement of sample porosity. A mineral classification of the chemical point data is determined using a new data manipulation program, MINCLASS©. This new program uses carbon and oxygen region of interest (ROI) x-ray counts to differentiate between oxides and metals as well as sulfates and sulfides. A user-friendly graphical user interface (GUI) to execute under Windows© has been implemented, which makes the application very easy to learn and use. The GUI allows the user to easily select data sets that may be used to define and classify the chemistries of raw data. Mineral definition data sets have been developed for several types of samples, including coal combustion and gasification. Users may also enter their own mineral definitions for the program to use in the classification of Materials into mineral phases. In conjunction with this new program. MINCLASS©, a viscosity calculation program, VISCALC©, can be used to determine viscosity of silicate materials. This viscosity model will produce visual displays of viscosity distributions. The viscosity calculation also associates a viscosity value with each analysis point in a file. The user can retrieve a stored image and inspect the morphology of the area surrounding each point and relate it to the calculated viscosity. The measurement of porosity, calculation of viscosity, and determination of mineral-phase distribution for a sample are great assets in the characterization and determination of strength development in coal combustion deposits and by-products. The association of chemistry, mineralogy, and morphology is realized, utilizing the SEMPC technique developed at the EERC.
New Analysis Techniques Help Control Boiler Fouling
Karner, F.R.; Zygarlicke, C.J.; Brekke, D.W.; Steadman, E.N. and Benson, S.A.
Power Engineering, 98:35-38, 1994. Funded by US Department of Energy, Brigham Young University and Electric Power Research Institute.
Severe boiler fouling can be controlled. But, it demands a thorough understanding of how minor changes in the chemical and physical properties of coal and ash and operating conditions can cause hardened deposits. Traditional analytical techniques have helped reveal some of these mechanisms in the past, but limitations inherent to the analysis left many questions unanswered.
Now, however, scanning electron microscopy and electron microprobe analysis (SEM/EMPA) provide researchers with the analytical tools necessary to truly understand deposit formation mechanisms. These new techniques are exposing the size, shape, and chemistry of the myriad individual ash particles formed when coal burns. This and other data can be used to predict combustion behavior and its impact on ash deposition, waterwall slagging, and other steam tube deposits.
Microanalysis is capable of helping operators to identify more efficient and cost effective corrective measures as well. Recognized control methods (i.e., soot-blowing or plant capacity reductions) are often expensive and ineffective. The same is true for trial and error operating changes. Logic dictates analyzing coal and ash deposits first and then modifying operating procedures accordingly; SEM/EMPA facilitates the process.
1993
Predicting Ash Behavior in Utility Boilers
Benson, S.A.; Hurley, J.P.; Zygarlicke, C.J.; Steadman, E.N. and Erickson, T.A.
Energy & Fuels, 7 (6):746, 1993. Funded by US Department of Energy and ACERC.
In recent years, significant advances have been made in the development of methods to predict ash behavior in utility boilers. This paper provides an overview of methods used to assess and predict ash formation and deposition. These prediction methods are based on a detailed knowledge of ash formation and deposition mechanisms that has been obtained through bench, pilot, and field-testing and detailed coal and ash characterization. The paper describes advanced methods of coal and ash analyses and the advantages of these methods over conventional methods. The advanced coal characterization methods provide sufficient data to predict size and composition distribution of fly ash. The composition and size data are used as inputs to mechanistic models that ultimately predict deposition propensities in various locations of utility boilers. Advanced indices based on advanced coal analysis data have also been developed and are being applied to predict convective pass fouling tendencies.
1992
Predicting Ash Behavior in Utility Boilers: Assessment of Current Status
Benson, S.A.; Erickson, T.A.; Hurley, J.P.; Zygarlicke, C.J. and Steadman, E.N.
Electric Power Research Institute Conference on Coal Quality, San Diego, CA, August 1992, Funded by US Department of Energy, ABB-Combustion Engineering, Electric Power Research Institute and ACERC.
The development of effective methods to predict ash behavior in utility boilers requires detailed information on ash-forming constituents in the coal, ash formation mechanisms, and behavior of the ash species in combustion systems. This paper described the application of advanced methods to characterize coal and provides examples of two methods to predict ash behavior. The advanced methods of coal analysis provide quantitative information on the size, association, and abundance of ash-forming species in the coal. The methodologies include computer-controlled scanning electron microscopy (CCSEM) and chemical fractionation. The CCSEM technique determines the size, abundance, and composition of 2000 to 3000 mineral grains in coal. The chemical fractionation technique is used to determine the abundance of organically associated inorganic components in lignite and subbituminous coals. The information obtained from the advanced methods of analyses is used as input into computer codes to predict ash behavior. The two methods to predict ash behavior include a fouling index and a phenomenological/mechanistic model. The fouling index provides the ability to rank coals based on their potential to produce convective pass deposits and was developed using data obtained from advanced methods of analyses, a knowledge base of ash behavior, and full-scale utility boiler operational data. The phenomenological or mechanistic models are used to predict the particle-size and composition distribution of ash and deposition potential of the ash as a function of boiler geometry and operational conditions. These predictive techniques have been developed through the use of full-scale utility boiler experience and have been verified for selected systems; however, these techniques are limited to certain types of coals and to certain regions of the boiler.
1990
Advanced SEM Techniques to Characterize Coal Minerals
Zygarlicke, C.J. and Steadman, E.N.
Scanning Microse. Int., 4:579-590, 1990. Funded by US Department of Energy and ACERC.
Research at the University of North Dakota Energy and Environmental Research Center (EER) has focused on methods to characterize the inorganic components in coals. Because the scanning electron microscope and electron probe microanalysis system (SEM/EPMA) provide both morphologic and chemical information, the SEM/EPMA system is well suited to the characterization of discrete minerals in coal. Computer-controlled scanning electron microscopy (CCSEM), along with simultaneous automated digital image collection, is one means of gaining more detailed insight into coal mineralogy. Computer-stored images of coal surfaces already analyzed for minerals using CCSEM can be reanalyzed to discern mineral morphologies and coal-to-mineral associations. Limitations may exist when using just CCSEM to characterize chemically and physically complex clay minerals without complimentary data on the association of the minerals to the coal organic matrix. Mineralogical investigations of San Miguel and Beulah lignites and Upper Freeport bituminous coal using CCSEM and automated digital image collection are given with a particular reference to the clay minerals present. Total mineral quantities generated for the three coals were in good agreement with total ash content, provided that organically bound constituents were taken into account for the lignites. Classification of the more complex aluminosilicate minerals was aided by the use of distribution plots of Si/A1 ratios and concentrations of ion exchangeable cations derived from the CCSEM analysis. Morphologic analysis of stored SEM images proved to be helpful in characterizing kaolinite group minerals.
A Microanalytical Approach to the Characterization of Coal, Ash, and Deposit
Steadman, E.N.; Zygarlicke, C.J.; Benson, S.A. and Jones, M.L.
Proceedings of Seminar on Fireside Fouling Problems, ASME, Washington, DC, 1990. Funded by US Department of Energy and ACERC.
Techniques have been developed that allow for the detailed chemical characterization of coal inorganics, ash, and deposited ash material. This paper focuses on microanalytical techniques that utilize an automated scanning electron microscope and electron microprobe (SEM/EMPA). This combination provides both chemical as well as morphological information, making it a valuable tool in studies of inorganic components associated with coal combustion.
Two techniques are discussed. Computer-controlled scanning electron microscopy (CCSEM) is a technique used to determine size, shape, and semiquantitative composition of mineral grains in coal or char/ash intermediates. Scanning electron microscopy point count (SEMPC) is used to quantify the various phases in fly ashes and deposits. This combination of techniques provides a valuable set of tools to follow the fate of coal inorganic materials in coal conversion processes. The techniques discussed are still in the development stage. Plans for future activities to improve both techniques are discussed.
1989
Deposition of Beulah Ash in a Drop-Tube Furnace Under Slagging Conditions
Kalmanovitch, D.P.; Zygarlicke, C.J.; Steadman, E.N. and Benson, S.A.
To be published in Prog. Energy Comb. Sci., Special Issue on Ash Deposition, Pergamon Press, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
Deposits formed during coal combustion in the UND EERC drop-tube furnace have been characterized. Pulverized lignite from Beulah, North Dakota, was combusted under carefully controlled conditions with gas temperatures ranging from 1100ºC to 1200ºC and deposit residence times ranging from 1 to 20 minutes. The deposits were characterized using X-ray diffraction and scanning electron microscopy techniques. The SEM techniques included morphological examination, back-scattered electron imaging, and a technique called scanning electron microscopy point count (SEMPC). SEMPC uses automated microprobe techniques to identify and quantify crystalline and amorphous phases present in a selected region of a deposit cross section. The SEMPC data was compared to the original mineralogical composition of the Beulah lignite, which was determined by a technique called computer controlled scanning electron microscopy (CCSEM). Comparisons of the deposit characteristics with coal mineralogy and fly ash characteristics led to insights into fundamental processes of ash deposit formation and growth.
Studies of Transformations of Inorganic Constituents in a Texas Lignite During Combustion
Zygarlicke, C.J.; Steadman, E.N.; Benson, S.A. and Kalmanovitch, D.P.
To be published in Prog. Energy Comb. Sci., Special Issue on Ash Deposition, Pergamon Press, 1989. (Also ACS Div. Fuel Chem. Preprints of Papers,, 34 (2), 355-366). Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
The mechanisms of coal ash formation were studied in relation to coal composition and combustion conditions. Monticello lignite, from Titus County, Texas, was analyzed to determine both mineralogical and organically bound components using computer controlled scanning electron microscopy (CCSEM) and chemical fractionation techniques, respectively. The coal was combusted in the EMRC drop-tube furnace at 1500ºC. Fly ash was collected and aerodynamically size-segregated into six stages. Scanning electron microscopy point count (SEMPC) was used to ascertain the bulk and surface chemistry of each fly ash size fraction. Fly ash composition and size distribution correlated well with the distribution of inorganics in the coal. Less than 3% of the coal mineral phases contained significant amount of Fe. Roughly 50% of the elemental iron was associated with acid-insoluble minerals. The remaining Fe was distributed in the finer fraction of the coal as organically bound species or soluble minerals. The smallest size fraction (<1.2 microns) had 26% Fe2O3 in bulk composition with less than 2% of the crystalline phases containing Fe.
Application of SEM Techniques to the Characterization of Coal and Coal Ash Products
Jones, M.L.; Kalmanovitch, D.P.; Steadman, E.N.; Zygarlicke, C.J. and Benson, S.A.
Presented at the First Symposium on Advances in Coal Spectroscopy, Salt Lake City, Utah, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
Techniques developed at Energy & Environmental Research Cetner (EERC) for the characterization of coal and coal ash by scanning electron microscopy (SEM) and electron microprobe analysis are detailed along with the application of these techniques. A description of the overall EERC approach to understanding coal ash formation and behavior in combustion systems and commentary on the significance of inorganic components in combustion systems are also presented.
The EERC approach to understanding inorganic components in combustion systems involves the detailed characterization of each component in the process by SEM techniques. Characterization of the minerals present in coal and in intermediate components (such as chars and fly ashed) is accomplished using a technique called CCSEM. The CCSEM technique uses a backscattered electron image to locate and determine the size, shape, and association of the minerals. A computer program then collects an energy dispersive spectra (EDS) from each particle in order to classify it according to mineral type. Since the CCSEM program is automated, data is collected from a large number of particles allowing for a statistical quantification of the minerals present.
The SEMPC technique is used to quantify the various phases in fly ashes and deposits. An automated program is used to raster the electron beam across the sample and an EDS analysis is collected from selected intervals until about 250 spectra are collected. These spectra are then subjected to the ZAF correction procedure that converts the data into chemical composition. The composition of each point is then classified into various crystalline and amorphous phases according to weight and molar ratios. In this manner, the overall chemistry of the sample is determined along with the quantities of the individual phases present. Thus, the SEM is used for the detailed characterization of mineral grains in the coal and materials produced from the various stages of coal combustion, intermediate formation, and finally, fly ash and deposit formation. This detailed characterization provides the data needed to elucidate the mechanisms of ash transformations during combustion and deposition.
CCSEM analysis of a North Dakota lignite revealed major amounts of quartz and aluminosilicate and minor amounts of pyrite, barite, gypsum and Ca-clay. CCSEM analysis of partially burned coal showed in increase in Ca-aluminosilicates indicating a reaction between the organically associated Ca and the clay minerals. SEMPC analysis of the fly ash corroborated this reaction, as it indicated the presence of mililite and anorthite in the larger sized fractions. Calcium silicate, anorthite, and melilite were also observed in the base of a deposit by the SEMPC technique. Predictions concerning the relative reactivity (base/acid ratio distribution) and physical properties (viscosity distribution) of the deposit were also made using the SEMPC technique.
Characterization of Mineral Matter in ACERC Coals
Zygarlicke, C.J.; Jones, M.L.; Steadman, E.N. and Benson, S.A.
Advanced Combustion Engineering Research Center Report, 1989. Funded by ACERC.
To assist with the overall goals of ACERC, especially Thrust Area 2, mineral behavior, a detailed characterization of the inorganic material in eight ACERC coals was completed. These analyses are essential to understanding the role inorganic components play in the behavior of coal in combustion systems. Of particular interest are the amount, size, and type of inorganic constituents found in coal. Without this information, it is not possible to predict the behavior of various coals in combustion systems. With this information, a coal's mineral behavior can be predicted (its fouling and slagging tendencies), as well as the impact of its inorganic components on the combustion process. The analysis of the ACERC coals included the following: 1) computer controlled SEM - to determine the size, quantity, juxtaposition, and association of mineral phases; 2) chemical fractionation - to determine organically bound inorganics (used with low-rank coals only); and 3) XRFA, XRD - used to verify inorganic constituents found with techniques noted above.
Steadman, EN
1994
Coal Ash Behavior and Management Tools
Erickson, T.A.; O'Leary, E.M.; Folkedahl, B.C.; Ramanathan, M.; Zygarlicke, C.J.; Steadman, E.N.; Hurley, J.P. and Benson, S.A.
The Impact of Ash Deposition on Coal-Fired Plants, Taylor & Francis, Inc., 1994. Funded by US Department of Energy, Electric Power Research Institute, Tow, Texaco, Shell, Union Electric, Kansas City Power and Light, Minnesota Power and Northern States Power.
Over the past five years, computer-based research tools have been increasingly applied in making important economic and operational decisions in the utility power industry. These tools-which include models, indices, databases, and data manipulation programs-are used by researchers, operators, and managers in the evaluation of coal utilization as an efficient and environmentally acceptable source of energy. Applicable tools that have been developed at, and are currently used by, the Energy & Environmental Research Center (EERC) include Partchar©, MINCLASS©, VISCAL©, MANAGER©, ATRAN, LEADER©, PHOEBE©, and PCQUEST©. These software applications range from databases for retrieving coal and coal product analysis, to computer codes to process coal and coal product analysis, to advanced models and indices to evaluate the operational impacts of specific systems.
Inorganic Phase Characterization of Coal Combustion Products Using Advanced SEM Techniques
Folkedahl, B.C.; Steadman, E.N.; Brekke, D.W. and Zygarlicke, C.J.
The Impact of Ash Deposition on Coal-Fired Plants, Taylor & Francis, Inc., 1994. Funded by US Department of Energy, Brigham Young University, Electric Power Research Institute, Dow, Texaco and Shell.
Scanning electron microscopy/electron microprobe analysis (SEM/EMPA) techniques can quantify the inorganic phases present in complex coal combustion materials, as well as provide information on the morphology of the sample. Recent advancements in SEM instrumentation, data manipulation, and automated image analysis techniques have made the routine analysis of a large number of samples and data points possible. The scanning electron microscopy point count (SEMPC) routine, developed at the Energy & Environmental Research Center (EERC), randomly selects a statistically valid number of points and analyzes them for chemistry. This routine also allows for the concurrent storage of digitized images and the measurement of sample porosity. A mineral classification of the chemical point data is determined using a new data manipulation program, MINCLASS©. This new program uses carbon and oxygen region of interest (ROI) x-ray counts to differentiate between oxides and metals as well as sulfates and sulfides. A user-friendly graphical user interface (GUI) to execute under Windows© has been implemented, which makes the application very easy to learn and use. The GUI allows the user to easily select data sets that may be used to define and classify the chemistries of raw data. Mineral definition data sets have been developed for several types of samples, including coal combustion and gasification. Users may also enter their own mineral definitions for the program to use in the classification of Materials into mineral phases. In conjunction with this new program. MINCLASS©, a viscosity calculation program, VISCALC©, can be used to determine viscosity of silicate materials. This viscosity model will produce visual displays of viscosity distributions. The viscosity calculation also associates a viscosity value with each analysis point in a file. The user can retrieve a stored image and inspect the morphology of the area surrounding each point and relate it to the calculated viscosity. The measurement of porosity, calculation of viscosity, and determination of mineral-phase distribution for a sample are great assets in the characterization and determination of strength development in coal combustion deposits and by-products. The association of chemistry, mineralogy, and morphology is realized, utilizing the SEMPC technique developed at the EERC.
New Analysis Techniques Help Control Boiler Fouling
Karner, F.R.; Zygarlicke, C.J.; Brekke, D.W.; Steadman, E.N. and Benson, S.A.
Power Engineering, 98:35-38, 1994. Funded by US Department of Energy, Brigham Young University and Electric Power Research Institute.
Severe boiler fouling can be controlled. But, it demands a thorough understanding of how minor changes in the chemical and physical properties of coal and ash and operating conditions can cause hardened deposits. Traditional analytical techniques have helped reveal some of these mechanisms in the past, but limitations inherent to the analysis left many questions unanswered.
Now, however, scanning electron microscopy and electron microprobe analysis (SEM/EMPA) provide researchers with the analytical tools necessary to truly understand deposit formation mechanisms. These new techniques are exposing the size, shape, and chemistry of the myriad individual ash particles formed when coal burns. This and other data can be used to predict combustion behavior and its impact on ash deposition, waterwall slagging, and other steam tube deposits.
Microanalysis is capable of helping operators to identify more efficient and cost effective corrective measures as well. Recognized control methods (i.e., soot-blowing or plant capacity reductions) are often expensive and ineffective. The same is true for trial and error operating changes. Logic dictates analyzing coal and ash deposits first and then modifying operating procedures accordingly; SEM/EMPA facilitates the process.
1993
Predicting Ash Behavior in Utility Boilers
Benson, S.A.; Hurley, J.P.; Zygarlicke, C.J.; Steadman, E.N. and Erickson, T.A.
Energy & Fuels, 7 (6):746, 1993. Funded by US Department of Energy and ACERC.
In recent years, significant advances have been made in the development of methods to predict ash behavior in utility boilers. This paper provides an overview of methods used to assess and predict ash formation and deposition. These prediction methods are based on a detailed knowledge of ash formation and deposition mechanisms that has been obtained through bench, pilot, and field-testing and detailed coal and ash characterization. The paper describes advanced methods of coal and ash analyses and the advantages of these methods over conventional methods. The advanced coal characterization methods provide sufficient data to predict size and composition distribution of fly ash. The composition and size data are used as inputs to mechanistic models that ultimately predict deposition propensities in various locations of utility boilers. Advanced indices based on advanced coal analysis data have also been developed and are being applied to predict convective pass fouling tendencies.
1992
Predicting Ash Behavior in Utility Boilers: Assessment of Current Status
Benson, S.A.; Erickson, T.A.; Hurley, J.P.; Zygarlicke, C.J. and Steadman, E.N.
Electric Power Research Institute Conference on Coal Quality, San Diego, CA, August 1992, Funded by US Department of Energy, ABB-Combustion Engineering, Electric Power Research Institute and ACERC.
The development of effective methods to predict ash behavior in utility boilers requires detailed information on ash-forming constituents in the coal, ash formation mechanisms, and behavior of the ash species in combustion systems. This paper described the application of advanced methods to characterize coal and provides examples of two methods to predict ash behavior. The advanced methods of coal analysis provide quantitative information on the size, association, and abundance of ash-forming species in the coal. The methodologies include computer-controlled scanning electron microscopy (CCSEM) and chemical fractionation. The CCSEM technique determines the size, abundance, and composition of 2000 to 3000 mineral grains in coal. The chemical fractionation technique is used to determine the abundance of organically associated inorganic components in lignite and subbituminous coals. The information obtained from the advanced methods of analyses is used as input into computer codes to predict ash behavior. The two methods to predict ash behavior include a fouling index and a phenomenological/mechanistic model. The fouling index provides the ability to rank coals based on their potential to produce convective pass deposits and was developed using data obtained from advanced methods of analyses, a knowledge base of ash behavior, and full-scale utility boiler operational data. The phenomenological or mechanistic models are used to predict the particle-size and composition distribution of ash and deposition potential of the ash as a function of boiler geometry and operational conditions. These predictive techniques have been developed through the use of full-scale utility boiler experience and have been verified for selected systems; however, these techniques are limited to certain types of coals and to certain regions of the boiler.
1990
Advanced SEM Techniques to Characterize Coal Minerals
Zygarlicke, C.J. and Steadman, E.N.
Scanning Microse. Int., 4:579-590, 1990. Funded by US Department of Energy and ACERC.
Research at the University of North Dakota Energy and Environmental Research Center (EER) has focused on methods to characterize the inorganic components in coals. Because the scanning electron microscope and electron probe microanalysis system (SEM/EPMA) provide both morphologic and chemical information, the SEM/EPMA system is well suited to the characterization of discrete minerals in coal. Computer-controlled scanning electron microscopy (CCSEM), along with simultaneous automated digital image collection, is one means of gaining more detailed insight into coal mineralogy. Computer-stored images of coal surfaces already analyzed for minerals using CCSEM can be reanalyzed to discern mineral morphologies and coal-to-mineral associations. Limitations may exist when using just CCSEM to characterize chemically and physically complex clay minerals without complimentary data on the association of the minerals to the coal organic matrix. Mineralogical investigations of San Miguel and Beulah lignites and Upper Freeport bituminous coal using CCSEM and automated digital image collection are given with a particular reference to the clay minerals present. Total mineral quantities generated for the three coals were in good agreement with total ash content, provided that organically bound constituents were taken into account for the lignites. Classification of the more complex aluminosilicate minerals was aided by the use of distribution plots of Si/A1 ratios and concentrations of ion exchangeable cations derived from the CCSEM analysis. Morphologic analysis of stored SEM images proved to be helpful in characterizing kaolinite group minerals.
A Microanalytical Approach to the Characterization of Coal, Ash, and Deposit
Steadman, E.N.; Zygarlicke, C.J.; Benson, S.A. and Jones, M.L.
Proceedings of Seminar on Fireside Fouling Problems, ASME, Washington, DC, 1990. Funded by US Department of Energy and ACERC.
Techniques have been developed that allow for the detailed chemical characterization of coal inorganics, ash, and deposited ash material. This paper focuses on microanalytical techniques that utilize an automated scanning electron microscope and electron microprobe (SEM/EMPA). This combination provides both chemical as well as morphological information, making it a valuable tool in studies of inorganic components associated with coal combustion.
Two techniques are discussed. Computer-controlled scanning electron microscopy (CCSEM) is a technique used to determine size, shape, and semiquantitative composition of mineral grains in coal or char/ash intermediates. Scanning electron microscopy point count (SEMPC) is used to quantify the various phases in fly ashes and deposits. This combination of techniques provides a valuable set of tools to follow the fate of coal inorganic materials in coal conversion processes. The techniques discussed are still in the development stage. Plans for future activities to improve both techniques are discussed.
1989
Deposition of Beulah Ash in a Drop-Tube Furnace Under Slagging Conditions
Kalmanovitch, D.P.; Zygarlicke, C.J.; Steadman, E.N. and Benson, S.A.
To be published in Prog. Energy Comb. Sci., Special Issue on Ash Deposition, Pergamon Press, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
Deposits formed during coal combustion in the UND EERC drop-tube furnace have been characterized. Pulverized lignite from Beulah, North Dakota, was combusted under carefully controlled conditions with gas temperatures ranging from 1100ºC to 1200ºC and deposit residence times ranging from 1 to 20 minutes. The deposits were characterized using X-ray diffraction and scanning electron microscopy techniques. The SEM techniques included morphological examination, back-scattered electron imaging, and a technique called scanning electron microscopy point count (SEMPC). SEMPC uses automated microprobe techniques to identify and quantify crystalline and amorphous phases present in a selected region of a deposit cross section. The SEMPC data was compared to the original mineralogical composition of the Beulah lignite, which was determined by a technique called computer controlled scanning electron microscopy (CCSEM). Comparisons of the deposit characteristics with coal mineralogy and fly ash characteristics led to insights into fundamental processes of ash deposit formation and growth.
Studies of Transformations of Inorganic Constituents in a Texas Lignite During Combustion
Zygarlicke, C.J.; Steadman, E.N.; Benson, S.A. and Kalmanovitch, D.P.
To be published in Prog. Energy Comb. Sci., Special Issue on Ash Deposition, Pergamon Press, 1989. (Also ACS Div. Fuel Chem. Preprints of Papers,, 34 (2), 355-366). Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
The mechanisms of coal ash formation were studied in relation to coal composition and combustion conditions. Monticello lignite, from Titus County, Texas, was analyzed to determine both mineralogical and organically bound components using computer controlled scanning electron microscopy (CCSEM) and chemical fractionation techniques, respectively. The coal was combusted in the EMRC drop-tube furnace at 1500ºC. Fly ash was collected and aerodynamically size-segregated into six stages. Scanning electron microscopy point count (SEMPC) was used to ascertain the bulk and surface chemistry of each fly ash size fraction. Fly ash composition and size distribution correlated well with the distribution of inorganics in the coal. Less than 3% of the coal mineral phases contained significant amount of Fe. Roughly 50% of the elemental iron was associated with acid-insoluble minerals. The remaining Fe was distributed in the finer fraction of the coal as organically bound species or soluble minerals. The smallest size fraction (<1.2 microns) had 26% Fe2O3 in bulk composition with less than 2% of the crystalline phases containing Fe.
Application of SEM Techniques to the Characterization of Coal and Coal Ash Products
Jones, M.L.; Kalmanovitch, D.P.; Steadman, E.N.; Zygarlicke, C.J. and Benson, S.A.
Presented at the First Symposium on Advances in Coal Spectroscopy, Salt Lake City, Utah, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
Techniques developed at Energy & Environmental Research Cetner (EERC) for the characterization of coal and coal ash by scanning electron microscopy (SEM) and electron microprobe analysis are detailed along with the application of these techniques. A description of the overall EERC approach to understanding coal ash formation and behavior in combustion systems and commentary on the significance of inorganic components in combustion systems are also presented.
The EERC approach to understanding inorganic components in combustion systems involves the detailed characterization of each component in the process by SEM techniques. Characterization of the minerals present in coal and in intermediate components (such as chars and fly ashed) is accomplished using a technique called CCSEM. The CCSEM technique uses a backscattered electron image to locate and determine the size, shape, and association of the minerals. A computer program then collects an energy dispersive spectra (EDS) from each particle in order to classify it according to mineral type. Since the CCSEM program is automated, data is collected from a large number of particles allowing for a statistical quantification of the minerals present.
The SEMPC technique is used to quantify the various phases in fly ashes and deposits. An automated program is used to raster the electron beam across the sample and an EDS analysis is collected from selected intervals until about 250 spectra are collected. These spectra are then subjected to the ZAF correction procedure that converts the data into chemical composition. The composition of each point is then classified into various crystalline and amorphous phases according to weight and molar ratios. In this manner, the overall chemistry of the sample is determined along with the quantities of the individual phases present. Thus, the SEM is used for the detailed characterization of mineral grains in the coal and materials produced from the various stages of coal combustion, intermediate formation, and finally, fly ash and deposit formation. This detailed characterization provides the data needed to elucidate the mechanisms of ash transformations during combustion and deposition.
CCSEM analysis of a North Dakota lignite revealed major amounts of quartz and aluminosilicate and minor amounts of pyrite, barite, gypsum and Ca-clay. CCSEM analysis of partially burned coal showed in increase in Ca-aluminosilicates indicating a reaction between the organically associated Ca and the clay minerals. SEMPC analysis of the fly ash corroborated this reaction, as it indicated the presence of mililite and anorthite in the larger sized fractions. Calcium silicate, anorthite, and melilite were also observed in the base of a deposit by the SEMPC technique. Predictions concerning the relative reactivity (base/acid ratio distribution) and physical properties (viscosity distribution) of the deposit were also made using the SEMPC technique.
Characterization of Mineral Matter in ACERC Coals
Zygarlicke, C.J.; Jones, M.L.; Steadman, E.N. and Benson, S.A.
Advanced Combustion Engineering Research Center Report, 1989. Funded by ACERC.
To assist with the overall goals of ACERC, especially Thrust Area 2, mineral behavior, a detailed characterization of the inorganic material in eight ACERC coals was completed. These analyses are essential to understanding the role inorganic components play in the behavior of coal in combustion systems. Of particular interest are the amount, size, and type of inorganic constituents found in coal. Without this information, it is not possible to predict the behavior of various coals in combustion systems. With this information, a coal's mineral behavior can be predicted (its fouling and slagging tendencies), as well as the impact of its inorganic components on the combustion process. The analysis of the ACERC coals included the following: 1) computer controlled SEM - to determine the size, quantity, juxtaposition, and association of mineral phases; 2) chemical fractionation - to determine organically bound inorganics (used with low-rank coals only); and 3) XRFA, XRD - used to verify inorganic constituents found with techniques noted above.