Kalmanovitch, DP
1990
Sintering Behavior and Strength Development in Various Coal Ashes
Nowok, J.W.; Benson, S.A.; Jones, M.L. and Kalmanovitch, D.P.
Fuel, 1990 (In press). Funded by US Department of Energy.
Sintering, crystallization, and mechanical properties of six coal ashes are being studied to obtain an understanding of ash deposit and agglomerate formation in combustion and gasification systems. Results show that viscous sintering is accomplished by neck growth between particles, shrinkage of closed pores, and/or by diffusion of slag constituents in a liquid film along the grain surfaces. These processes are dependent on temperature, atmosphere, and ash composition. In addition, studies show that the strength of sintered pellets produced from crystallized Beulah lignite ash are weaker than those produced from the amorphous form of the ash. Further, the amorphous form sintered in a CO/CO2 atmosphere is not as strong as the amorphous form sintered in air. Criteria are given for the relationship between compressive strength of sintered coal fly ashes and their activity in the sintering process measured by means of viscosity and surface tension.
1989
New Techniques for Thermochemical Phase Equilibria Predictions in Coal Ash Systems - II
Ramanathan, M.; Kalmanovitch, D.P. and Ness, S.
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.
PHOEBE is a new computer code developed at UND-EMRC as part of a long-term study of coal ash deposition phenomena in coal combustion systems. The task of developing a new code was undertaken to eliminate the various problems encountered with existing phase equilibria calculation packages and to apply better techniques in the minimization of the Gibbs free energy of the system. The results from PHOEBE for a couple of thermodynamic systems are presented and compared with their corresponding experimental values.
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.
Studies of Ash Deposit Formation From Powder River Basin and Fort Union Coals
Benson, S.A.; Kalmanovitch, D.P.; Zygarlicke, C.J. and Steadman, E.N.
Presented at the Fifteenth Biennial Low-Rank Fuels Symposium, Sponsored by the University of North Dakota and the US Department of Energy, St. Paul, Minnesota, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
The mechanisms of formation of troublesome fireside deposits in utility boilers as a result of combusting coals from the Powder River Basin and Fort Union Region are being examined in detail at the Energy and Environmental Research Center. Fireside ash fouling resulting from the combustion of Fort Union lignites has been correlated with the formation of sodium-rich liquid phases in deposits. As a result of combusting some Powder River Basin coals, calcium sulfate rich deposits form in the convective passes of boilers causing serious fouling problems. Detailed characterization of fouling deposits from utility boilers firing Powder River Basin and Fort Union coals has shown that complex processes. Scanning electron microscope/microprobe analyses have shown sodium- or calcium-rich phases are the materials that bind the ash particles together resulting in formation of deposits. In some cases the problem-causing phase is sulfate-based and in others the phase is aluminosilicate-based. The process of consolidation to form a strong-bonded deposit depends on the type of phase present. In the case of the sulfate-based deposits the mechanism appears to be low-temperature sintering in the absence of an extensive liquid phase. In the case of the aluminosilicate-based deposits the consolidation process is that of viscous flow sintering of a reactive liquid phase. In both cases, the abundance and association of alkali and alkaline earth elements in the coal, and their transformations during combustion and deposition, will control the extent of formation of troublesome deposits in a boiler.
Evaluation of Coals Using a Drop Tube Furnace
Kalmanovitch, D.P. and Benson, S.A.
Proceedings of the Sixth Annual International Pittsburgh Coal Conference, 2, 939-948, Pittsburgh, Pennsylvania, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
A drop-tube furnace system was used to evaluate the ash deposition propensity of Illinois #6 bituminous coal. The coal, size classified fly ash, and deposits were characterized using automated scanning electron microscope/microprobe techniques. The information derived from the SEM techniques consists of quantitative determination of the size, composition, and abundance of minerals in the coal and a distribution of phases in the fly ash and deposits. Based on the analysis of the ash using the SEM techniques, important parameters can be determined that are related to the ability of ash to form a deposit. These include viscosity distribution profiles that provide insight into sintering (strength development) behavior and base-to-acid ratios for each ash particle. The combustion conditions of the drop-tube furnace were adjusted to simulate the time-temperature profiles of combustors. Ash was collected using a multicyclone to provide size classified ashes for detailed analysis. Results indicate the majority of quartz and pyrite derived particles were greater than 11 micrometers. The smaller particles consisted mainly of amorphous materials. A deposit was formed under conditions that simulate fouling in the drop-tube furnace and analyzed using the SEM. Results indicate that the initial mechanism of deposition was by ash particles greater than 11 micrometers. These particles have liquid phases present that do not facilitate sintering processes either via low viscosity phases or via liquid reaction mechanisms. These particles have liquid phases present that do not facilitate sintering processes either via low viscosity phases or via liquid reaction mechanisms. The bulk of the deposit was shown to have been formed by preferential deposition of particles with liquid phases of low viscosity (between log 2 and log 4 poise) and high relative reactivity (based on base/acid distribution).
Kalmanovitch, DP
1990
Sintering Behavior and Strength Development in Various Coal Ashes
Nowok, J.W.; Benson, S.A.; Jones, M.L. and Kalmanovitch, D.P.
Fuel, 1990 (In press). Funded by US Department of Energy.
Sintering, crystallization, and mechanical properties of six coal ashes are being studied to obtain an understanding of ash deposit and agglomerate formation in combustion and gasification systems. Results show that viscous sintering is accomplished by neck growth between particles, shrinkage of closed pores, and/or by diffusion of slag constituents in a liquid film along the grain surfaces. These processes are dependent on temperature, atmosphere, and ash composition. In addition, studies show that the strength of sintered pellets produced from crystallized Beulah lignite ash are weaker than those produced from the amorphous form of the ash. Further, the amorphous form sintered in a CO/CO2 atmosphere is not as strong as the amorphous form sintered in air. Criteria are given for the relationship between compressive strength of sintered coal fly ashes and their activity in the sintering process measured by means of viscosity and surface tension.
1989
New Techniques for Thermochemical Phase Equilibria Predictions in Coal Ash Systems - II
Ramanathan, M.; Kalmanovitch, D.P. and Ness, S.
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.
PHOEBE is a new computer code developed at UND-EMRC as part of a long-term study of coal ash deposition phenomena in coal combustion systems. The task of developing a new code was undertaken to eliminate the various problems encountered with existing phase equilibria calculation packages and to apply better techniques in the minimization of the Gibbs free energy of the system. The results from PHOEBE for a couple of thermodynamic systems are presented and compared with their corresponding experimental values.
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.
Studies of Ash Deposit Formation From Powder River Basin and Fort Union Coals
Benson, S.A.; Kalmanovitch, D.P.; Zygarlicke, C.J. and Steadman, E.N.
Presented at the Fifteenth Biennial Low-Rank Fuels Symposium, Sponsored by the University of North Dakota and the US Department of Energy, St. Paul, Minnesota, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
The mechanisms of formation of troublesome fireside deposits in utility boilers as a result of combusting coals from the Powder River Basin and Fort Union Region are being examined in detail at the Energy and Environmental Research Center. Fireside ash fouling resulting from the combustion of Fort Union lignites has been correlated with the formation of sodium-rich liquid phases in deposits. As a result of combusting some Powder River Basin coals, calcium sulfate rich deposits form in the convective passes of boilers causing serious fouling problems. Detailed characterization of fouling deposits from utility boilers firing Powder River Basin and Fort Union coals has shown that complex processes. Scanning electron microscope/microprobe analyses have shown sodium- or calcium-rich phases are the materials that bind the ash particles together resulting in formation of deposits. In some cases the problem-causing phase is sulfate-based and in others the phase is aluminosilicate-based. The process of consolidation to form a strong-bonded deposit depends on the type of phase present. In the case of the sulfate-based deposits the mechanism appears to be low-temperature sintering in the absence of an extensive liquid phase. In the case of the aluminosilicate-based deposits the consolidation process is that of viscous flow sintering of a reactive liquid phase. In both cases, the abundance and association of alkali and alkaline earth elements in the coal, and their transformations during combustion and deposition, will control the extent of formation of troublesome deposits in a boiler.
Evaluation of Coals Using a Drop Tube Furnace
Kalmanovitch, D.P. and Benson, S.A.
Proceedings of the Sixth Annual International Pittsburgh Coal Conference, 2, 939-948, Pittsburgh, Pennsylvania, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and US Department of Energy.
A drop-tube furnace system was used to evaluate the ash deposition propensity of Illinois #6 bituminous coal. The coal, size classified fly ash, and deposits were characterized using automated scanning electron microscope/microprobe techniques. The information derived from the SEM techniques consists of quantitative determination of the size, composition, and abundance of minerals in the coal and a distribution of phases in the fly ash and deposits. Based on the analysis of the ash using the SEM techniques, important parameters can be determined that are related to the ability of ash to form a deposit. These include viscosity distribution profiles that provide insight into sintering (strength development) behavior and base-to-acid ratios for each ash particle. The combustion conditions of the drop-tube furnace were adjusted to simulate the time-temperature profiles of combustors. Ash was collected using a multicyclone to provide size classified ashes for detailed analysis. Results indicate the majority of quartz and pyrite derived particles were greater than 11 micrometers. The smaller particles consisted mainly of amorphous materials. A deposit was formed under conditions that simulate fouling in the drop-tube furnace and analyzed using the SEM. Results indicate that the initial mechanism of deposition was by ash particles greater than 11 micrometers. These particles have liquid phases present that do not facilitate sintering processes either via low viscosity phases or via liquid reaction mechanisms. These particles have liquid phases present that do not facilitate sintering processes either via low viscosity phases or via liquid reaction mechanisms. The bulk of the deposit was shown to have been formed by preferential deposition of particles with liquid phases of low viscosity (between log 2 and log 4 poise) and high relative reactivity (based on base/acid distribution).