Blackham, AU
1994
Rates of Oxidation of Millimeter-Sized Char Particles: Simple Experiments
Blackham, A.U.; Smoot, L.D. and Yousefi, P.
Fuel, 73:602-612, 1994. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research Co. and ACERC.
Rates of oxidation of 5-10 mm particles of chars from six coals at various temperatures were measured in air at ambient pressure in simple devices: a muffle furnace, a Meker burner, and a heated ceramic tube. The chars were first prepared from the coals in the Meker burner at comparable temperatures. As well as coal type and oxidation temperature, initial char particle steps of several minutes for periods up to 1 h. The cube root of particles mass decreased linearly with increasing time in all tests. Ash layers formed and usually remained in place around the particle. Average mass reactivities increased with decreasing initial particle mass. With decreasing furnace temperature, char reactivity decreased at the lower temperatures. Two or four closely spaced char particles burned much more slowly than single particles of the same size. Correlative equations are consistent with the data, elucidating the roles of kinetic reaction and oxygen diffusion.
Effect of Pressure on Oxidation Rates of MM-Sized Char
Bateman, K.J.; Smoot, L.D.; Germane, G.J.; Blackham, A.U. and Eatough, C.N.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
Mass loss and burnout ties of large (five and eight millimeter diameter) char particles at pressures between 101 to 760 kPa have been measured in a newly designed and constructed high-pressure reactor. A cantilever balance attachment was fitted to the reactor to measure instantaneous particle mass while an optical pyrometer measured particle temperature continuously. The process was also videotaped at 1/30 s frame speed. Sixty-two combustion experiments produced burning and oxidation times for two sizes of Utah bituminous (HVBB) coal and North Dakota Lignite (L) at 101, 507, 760 kPa total pressure. The reactor air temperatures were about 900 or 1200 K while the airflow Reynolds Number was varied by a factor of two. Coal particles were placed in a platinum-wire basket inside the reactor at the end of the balance beam. The oxidation process was recorded by computer and on videotape, while continuous char oxidation rates were measured to burnout. An ash layer accumulated around the particles, and receded as the char was consumed. In all of the tests, including the elevated pressure tests, a linear decrease in the cube root of char mass with time was observed during char oxidation until near the end of burnout. Changes in air velocity had little effect on oxidation times while either increasing gas temperature or increasing pressure from 101 kPa to 507 kPa reduced oxidation times by about one-quarter. Further increase in pressure caused no further reduction in burn time. Pairs of nearly equally sized particles of coal had oxidation times similar to single particles that had a mass equal to the sum of the pairs
1993
Rates of Millimeter-Sized Char Particle Oxidation: Simple Experiments
Blackham, A.U.; Smoot, L.D. and Yousefi, P.
Fuel, 1993 (in press). Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
Oxidation rates of large (5-10 mm) coal particles are required in the description of fixed- and fluidized-bed combustion, gasification and mild gasification processes. Yet, very little has been published regarding these rates. In this study, rates of oxidation of chars for six coals at various temperatures were measured in simple devices in air at ambient pressure: in a muffle furnace, a Meker burner, and a heated ceramic tube. Chars were first prepared from the coals in the Meker burner at comparable temperatures. Test variables were coal type, oxidation temperature, initial char particle mass and number of particles. Char particles were oxidized in incremental steps, each over several minutes for time periods up to one hour. The cube root of particle mass declined linearly with time in all tests. Ash layers formed and usually remained in place around the coal particle. Average mass reactivities increased with decreasing initial char particle mass. Decreasing furnace temperature decreased char reactivity at the lower temperatures. Two or four char particles, closely spaced, burned at much slower rates than single particles of the same size. Correlative methods are consistent with the data, which elucidate the roles of kinetic reaction and oxygen diffusion.
1992
Char Oxidation at Elevated Pressures
Monson, C.R.; Germane, G.J.; Blackham, A.U. and Smoot, L.D.
Fall Meeting of Western States Section/The Combustion Institute, Berkely, CA, October 1992. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research and ACERC.
Most of the coal currently being consumed is combusted at atmospheric pressure in utility furnaces, but several other processes are also being used and developed for either the direct combustion of coal or its conversion into other products. Many of these other processes, including coal gasification, operate at elevated pressure. While a great deal of research has been conducted on coal and char combustion at atmospheric pressure, elevated pressure char oxidation has largely been ignored. This paper describes the results obtained from char oxidation experiments at atmospheric and elevated pressures.
The experiments were carried out in a high-pressure, electrically heated drop tube reactor. A particle imaging system provided in situ, simultaneous measurement of individual particle temperature, size and velocity. Approximately 100 oxidation experiments were performed with two sizes (70 and 40 µm) of Utah and Pittsburgh bituminous coal chars at 1, 5, 10, and 15 atm total pressure. Reactor temperatures were varied between 1000 and 1500K with 5 to 21% oxygen in the bulk gas, resulting in average particle temperatures ranging from 1400 to 2100K and burnouts from 15 to 96%. Independently determined particle temperature and overall reaction rate allowed an internal check of the data consistency and provided insight into the products of combustion. Results from atmospheric pressure tests were shown to be consistent with results obtained by other researchers using the same coal. The chars burned in a reducing density and diameter mode in an intermediate regime between the kinetic and pore diffusion zones, irrespective to total pressure. Significant CO2 formation occurred at the particle surface at particle temperatures below about 1800K over the entire pressure range. Particle temperatures were strongly dependent on the oxygen and total pressures; increasing oxygen pressure at constant total pressure resulted in substantial increases in particle temperature, while increasing the total pressure at constant oxygen pressure led to substantial decreases in particle temperature. Increasing total pressure from 1 to 5 atm in an environment of constant gas composition led to modest increases in the reaction rate coefficients (based on the nth order rate equation) showed a large pressure dependence; both the activation energy and frequency factor decreased with increasing pressure. The results suggested that the empirical nth order rate equation is not valid at elevated pressures.
1990
Reduction of Fuel-NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier
Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
Fuel, 69, 1339-1344, 1990. Funded by US Department of Energy and Morgantown Energy Technology Center.
Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2 and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (stoichiometric ration SR=0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of total fuel nitrogen (TFN) decreased as pressure was increased. Also, concentrations of N2 increased and concentrations TFN decreased as residence time was increased at 1 atm pressure. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.
1989
Reduction of Fuel NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier
Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
1989 Joint Environmental Protection Agency/Electric Power Research Institute Symposium on Stationary Combustion NOx Control, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2, and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (SR = 0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of TFN decreased as pressure was increased. Neither TFN or N2 concentrations were affected by increasing residence time. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.
1988-86
Effects of Coal Quality on Utility Furnace Performance
Blackham, A.U.
Fuel, 67, 27-35, 1988. 9 pgs. Funded by Utah Power and Light Co.
Use of lower than design grade coals can cause problems in furnaces and boilers due to increased ash deposits. A single-zone model has been developed to relate coal quality to thermal performance of pulverized, coal-fired power-generating boilers. The model, based on algebraic mass and energy balances and necessary auxiliary equations, estimates some of the required chemical and physical coal/ash properties. Three wall ash deposit parameters, thermal conductivity, emittance and thickness, have been determined by a sensitivity analysis to be critical to furnace performance and have been obtained by experimental procedures described herein. Data for ash properties are reported for Utah, Illinois and Western Kentucky bituminous coals. With these measured properties, the model has been used to predict effects of coal quality on furnace performance and to interpret changes in ash property data from a small-scale combustor to a large-scale utility boiler.
Sulfur Pollutant Formation During Coal Combustion
Zaugg, S.D.; Blackham, A.U.; Hedman, P.O. and Smoot, L.D.
Submitted to Fuel, 1988. Funded by Electric Power Research Institute.
A laboratory-scale pulverized coal combustor was used to determine the effects of secondary air swirl, stoichiometric ratio (O2/fuel), and coal type on the formation and reaction of sulfur pollutants (SO2, H2S, COs and CS2). Detailed local measurements within the reactor were obtained by analyzing solid-liquid-gas samples collected with a water-quenched probe. Increasing the stoichiometric ratio increased sulfur conversion and SO2 levels, and decreased H2S, COs, and CS2 levels. Swirl of secondary combustion air had a pronounced effect on the distribution of sulfur species formed at an O2-coal stoichiometric ratio of 0.87, but had very little effect at stoichiometric ratios of 0.57 and 1.17. Combustion of a bituminous coal produced more SO2 and less H2S, COs, and CS2 compared to a subbituminous coal.
The Behavior of Chlorine in Kentucky and Illinois Coals During Combustion and Its Effects on Ash Deposits
Sowa, W.A.; Hedman, P.O.; Smoot, L.D. and Blackham, A.U.
Western States Section, 1986, The Combustion Institute, Tucson, AZ. Also accepted for publication in Fuel, 1988. 34 pgs. Funded by Tennessee Valley Authority.
Ash deposition tests were performed in a modified pulverized coal combustor with four different coals: low chlorine Kentucky No. 9, and Kentucky No. 11, and high chlorine Illinois No. 5 and Illinois No. 6. The amount of coal available for testing differed markedly between coal types ranging from 100-1000 kg. per coal type. Several repeated one-hour combustion tests were performed for all four coals. Each firing consumed 15-25 kg. of coal. Ash deposition tests provided samples from simulated waterwall and superheater probes, and from an exhaust cyclone and a water-quenched char sample probe. Measured physical properties included, ash chemical analyses, proximate and elemental analyses of both raw coal and ash deposits, ash fusion temperature tests, ash sintering temperature tests, ash shear and compressive strength analyses, and ash thermal conductivity and emittance. Chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine condensed and concentrated on the waterwall collection surfaces. The amount of chlorine that condensed onto the ash collection surfaces was dependent on the temperature of the collection surface. The colder surfaces had the highest chlorine concentrations. Corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The carbon and chlorine conversion rate from the char appeared to be equal for carbon conversion levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements which were performed on samples from the waterwall and superheater probes showed no observable differences between the four coal types tested. The one-hour firings were probably too short for the ash deposits to reflect the influence of metal corrosion on the measured physical properties. Emittance, ash sintering temperature, compressive strength and shear strength were dependent on sample location.
Sulfur Species Formation in a High-pressure Entrained-Coal Gasifier
Nichols, K.M.; Hedman, P.O.; Smoot, L.D. and Blackham, A.U.
Western States Section, 1987, The Combustion Institute, Provo, UT. 16 pgs. Funded by Morgantown Energy Technology Center.
This work summarizes several observations concerning the effects of pressure and oxygen-to-coal mass ratio on the fate of coal-sulfur during entrained gasification. A high-volatile bituminous coal was pulverized to a mass mean of near 50 mm. The coal was gasified with oxygen in a laboratory-scale entrained-flow gasifier. Test pressures were atmospheric (1.0 ATM, 101 kPa), 4.9 ATM (500 kPa), and 10.4 ATM (1050 kPa). Oxygen-to-coal mass ratios between 0.6 and 1.1 were investigated. Gas-particulate samples were collected with a water-quenched probe from the gasifier chamber effluent stream. Measurements were made of the sulfur retained in the char particles and of the concentrations of H2S, SO2, COS and CS2 in the product gas. Conversion of sulfur to the gas phase was observed to decrease with increasing pressure, possibly through sulfur captured by char. Changing pressure caused a change in the distribution of gas phase sulfur species. At higher pressure, the proportions of SO2 and CS2 decreased, and the proportion of H2S increased. This redistribution with increasing pressure is not predicted by equilibrium calculations, nor was it observed in learner (less particle laden) combustion environments. This suggests the importance of char in determining the fate of the coal-sulfur during gasification. Increasing oxygen-to-coal mass ratio increased sulfur conversion, SO2 concentration, and COs concentration, while it decreased H2S and CS2 concentrations.
Blackham, AU
1994
Rates of Oxidation of Millimeter-Sized Char Particles: Simple Experiments
Blackham, A.U.; Smoot, L.D. and Yousefi, P.
Fuel, 73:602-612, 1994. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research Co. and ACERC.
Rates of oxidation of 5-10 mm particles of chars from six coals at various temperatures were measured in air at ambient pressure in simple devices: a muffle furnace, a Meker burner, and a heated ceramic tube. The chars were first prepared from the coals in the Meker burner at comparable temperatures. As well as coal type and oxidation temperature, initial char particle steps of several minutes for periods up to 1 h. The cube root of particles mass decreased linearly with increasing time in all tests. Ash layers formed and usually remained in place around the particle. Average mass reactivities increased with decreasing initial particle mass. With decreasing furnace temperature, char reactivity decreased at the lower temperatures. Two or four closely spaced char particles burned much more slowly than single particles of the same size. Correlative equations are consistent with the data, elucidating the roles of kinetic reaction and oxygen diffusion.
Effect of Pressure on Oxidation Rates of MM-Sized Char
Bateman, K.J.; Smoot, L.D.; Germane, G.J.; Blackham, A.U. and Eatough, C.N.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
Mass loss and burnout ties of large (five and eight millimeter diameter) char particles at pressures between 101 to 760 kPa have been measured in a newly designed and constructed high-pressure reactor. A cantilever balance attachment was fitted to the reactor to measure instantaneous particle mass while an optical pyrometer measured particle temperature continuously. The process was also videotaped at 1/30 s frame speed. Sixty-two combustion experiments produced burning and oxidation times for two sizes of Utah bituminous (HVBB) coal and North Dakota Lignite (L) at 101, 507, 760 kPa total pressure. The reactor air temperatures were about 900 or 1200 K while the airflow Reynolds Number was varied by a factor of two. Coal particles were placed in a platinum-wire basket inside the reactor at the end of the balance beam. The oxidation process was recorded by computer and on videotape, while continuous char oxidation rates were measured to burnout. An ash layer accumulated around the particles, and receded as the char was consumed. In all of the tests, including the elevated pressure tests, a linear decrease in the cube root of char mass with time was observed during char oxidation until near the end of burnout. Changes in air velocity had little effect on oxidation times while either increasing gas temperature or increasing pressure from 101 kPa to 507 kPa reduced oxidation times by about one-quarter. Further increase in pressure caused no further reduction in burn time. Pairs of nearly equally sized particles of coal had oxidation times similar to single particles that had a mass equal to the sum of the pairs
1993
Rates of Millimeter-Sized Char Particle Oxidation: Simple Experiments
Blackham, A.U.; Smoot, L.D. and Yousefi, P.
Fuel, 1993 (in press). Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
Oxidation rates of large (5-10 mm) coal particles are required in the description of fixed- and fluidized-bed combustion, gasification and mild gasification processes. Yet, very little has been published regarding these rates. In this study, rates of oxidation of chars for six coals at various temperatures were measured in simple devices in air at ambient pressure: in a muffle furnace, a Meker burner, and a heated ceramic tube. Chars were first prepared from the coals in the Meker burner at comparable temperatures. Test variables were coal type, oxidation temperature, initial char particle mass and number of particles. Char particles were oxidized in incremental steps, each over several minutes for time periods up to one hour. The cube root of particle mass declined linearly with time in all tests. Ash layers formed and usually remained in place around the coal particle. Average mass reactivities increased with decreasing initial char particle mass. Decreasing furnace temperature decreased char reactivity at the lower temperatures. Two or four char particles, closely spaced, burned at much slower rates than single particles of the same size. Correlative methods are consistent with the data, which elucidate the roles of kinetic reaction and oxygen diffusion.
1992
Char Oxidation at Elevated Pressures
Monson, C.R.; Germane, G.J.; Blackham, A.U. and Smoot, L.D.
Fall Meeting of Western States Section/The Combustion Institute, Berkely, CA, October 1992. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research and ACERC.
Most of the coal currently being consumed is combusted at atmospheric pressure in utility furnaces, but several other processes are also being used and developed for either the direct combustion of coal or its conversion into other products. Many of these other processes, including coal gasification, operate at elevated pressure. While a great deal of research has been conducted on coal and char combustion at atmospheric pressure, elevated pressure char oxidation has largely been ignored. This paper describes the results obtained from char oxidation experiments at atmospheric and elevated pressures.
The experiments were carried out in a high-pressure, electrically heated drop tube reactor. A particle imaging system provided in situ, simultaneous measurement of individual particle temperature, size and velocity. Approximately 100 oxidation experiments were performed with two sizes (70 and 40 µm) of Utah and Pittsburgh bituminous coal chars at 1, 5, 10, and 15 atm total pressure. Reactor temperatures were varied between 1000 and 1500K with 5 to 21% oxygen in the bulk gas, resulting in average particle temperatures ranging from 1400 to 2100K and burnouts from 15 to 96%. Independently determined particle temperature and overall reaction rate allowed an internal check of the data consistency and provided insight into the products of combustion. Results from atmospheric pressure tests were shown to be consistent with results obtained by other researchers using the same coal. The chars burned in a reducing density and diameter mode in an intermediate regime between the kinetic and pore diffusion zones, irrespective to total pressure. Significant CO2 formation occurred at the particle surface at particle temperatures below about 1800K over the entire pressure range. Particle temperatures were strongly dependent on the oxygen and total pressures; increasing oxygen pressure at constant total pressure resulted in substantial increases in particle temperature, while increasing the total pressure at constant oxygen pressure led to substantial decreases in particle temperature. Increasing total pressure from 1 to 5 atm in an environment of constant gas composition led to modest increases in the reaction rate coefficients (based on the nth order rate equation) showed a large pressure dependence; both the activation energy and frequency factor decreased with increasing pressure. The results suggested that the empirical nth order rate equation is not valid at elevated pressures.
1990
Reduction of Fuel-NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier
Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
Fuel, 69, 1339-1344, 1990. Funded by US Department of Energy and Morgantown Energy Technology Center.
Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2 and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (stoichiometric ration SR=0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of total fuel nitrogen (TFN) decreased as pressure was increased. Also, concentrations of N2 increased and concentrations TFN decreased as residence time was increased at 1 atm pressure. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.
1989
Reduction of Fuel NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier
Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
1989 Joint Environmental Protection Agency/Electric Power Research Institute Symposium on Stationary Combustion NOx Control, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2, and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (SR = 0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of TFN decreased as pressure was increased. Neither TFN or N2 concentrations were affected by increasing residence time. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.
1988-86
Effects of Coal Quality on Utility Furnace Performance
Blackham, A.U.
Fuel, 67, 27-35, 1988. 9 pgs. Funded by Utah Power and Light Co.
Use of lower than design grade coals can cause problems in furnaces and boilers due to increased ash deposits. A single-zone model has been developed to relate coal quality to thermal performance of pulverized, coal-fired power-generating boilers. The model, based on algebraic mass and energy balances and necessary auxiliary equations, estimates some of the required chemical and physical coal/ash properties. Three wall ash deposit parameters, thermal conductivity, emittance and thickness, have been determined by a sensitivity analysis to be critical to furnace performance and have been obtained by experimental procedures described herein. Data for ash properties are reported for Utah, Illinois and Western Kentucky bituminous coals. With these measured properties, the model has been used to predict effects of coal quality on furnace performance and to interpret changes in ash property data from a small-scale combustor to a large-scale utility boiler.
Sulfur Pollutant Formation During Coal Combustion
Zaugg, S.D.; Blackham, A.U.; Hedman, P.O. and Smoot, L.D.
Submitted to Fuel, 1988. Funded by Electric Power Research Institute.
A laboratory-scale pulverized coal combustor was used to determine the effects of secondary air swirl, stoichiometric ratio (O2/fuel), and coal type on the formation and reaction of sulfur pollutants (SO2, H2S, COs and CS2). Detailed local measurements within the reactor were obtained by analyzing solid-liquid-gas samples collected with a water-quenched probe. Increasing the stoichiometric ratio increased sulfur conversion and SO2 levels, and decreased H2S, COs, and CS2 levels. Swirl of secondary combustion air had a pronounced effect on the distribution of sulfur species formed at an O2-coal stoichiometric ratio of 0.87, but had very little effect at stoichiometric ratios of 0.57 and 1.17. Combustion of a bituminous coal produced more SO2 and less H2S, COs, and CS2 compared to a subbituminous coal.
The Behavior of Chlorine in Kentucky and Illinois Coals During Combustion and Its Effects on Ash Deposits
Sowa, W.A.; Hedman, P.O.; Smoot, L.D. and Blackham, A.U.
Western States Section, 1986, The Combustion Institute, Tucson, AZ. Also accepted for publication in Fuel, 1988. 34 pgs. Funded by Tennessee Valley Authority.
Ash deposition tests were performed in a modified pulverized coal combustor with four different coals: low chlorine Kentucky No. 9, and Kentucky No. 11, and high chlorine Illinois No. 5 and Illinois No. 6. The amount of coal available for testing differed markedly between coal types ranging from 100-1000 kg. per coal type. Several repeated one-hour combustion tests were performed for all four coals. Each firing consumed 15-25 kg. of coal. Ash deposition tests provided samples from simulated waterwall and superheater probes, and from an exhaust cyclone and a water-quenched char sample probe. Measured physical properties included, ash chemical analyses, proximate and elemental analyses of both raw coal and ash deposits, ash fusion temperature tests, ash sintering temperature tests, ash shear and compressive strength analyses, and ash thermal conductivity and emittance. Chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine was found to release quickly from the coal to the gas phase. Gas phase chlorine condensed and concentrated on the waterwall collection surfaces. The amount of chlorine that condensed onto the ash collection surfaces was dependent on the temperature of the collection surface. The colder surfaces had the highest chlorine concentrations. Corrosion of the stainless steel test surfaces was observed during the combustion tests with the Illinois coals. The carbon and chlorine conversion rate from the char appeared to be equal for carbon conversion levels above 65%. Ash fusion temperature, ash sintering temperature, emittance, thermal conductivity, shear strength and compressive strength measurements which were performed on samples from the waterwall and superheater probes showed no observable differences between the four coal types tested. The one-hour firings were probably too short for the ash deposits to reflect the influence of metal corrosion on the measured physical properties. Emittance, ash sintering temperature, compressive strength and shear strength were dependent on sample location.
Sulfur Species Formation in a High-pressure Entrained-Coal Gasifier
Nichols, K.M.; Hedman, P.O.; Smoot, L.D. and Blackham, A.U.
Western States Section, 1987, The Combustion Institute, Provo, UT. 16 pgs. Funded by Morgantown Energy Technology Center.
This work summarizes several observations concerning the effects of pressure and oxygen-to-coal mass ratio on the fate of coal-sulfur during entrained gasification. A high-volatile bituminous coal was pulverized to a mass mean of near 50 mm. The coal was gasified with oxygen in a laboratory-scale entrained-flow gasifier. Test pressures were atmospheric (1.0 ATM, 101 kPa), 4.9 ATM (500 kPa), and 10.4 ATM (1050 kPa). Oxygen-to-coal mass ratios between 0.6 and 1.1 were investigated. Gas-particulate samples were collected with a water-quenched probe from the gasifier chamber effluent stream. Measurements were made of the sulfur retained in the char particles and of the concentrations of H2S, SO2, COS and CS2 in the product gas. Conversion of sulfur to the gas phase was observed to decrease with increasing pressure, possibly through sulfur captured by char. Changing pressure caused a change in the distribution of gas phase sulfur species. At higher pressure, the proportions of SO2 and CS2 decreased, and the proportion of H2S increased. This redistribution with increasing pressure is not predicted by equilibrium calculations, nor was it observed in learner (less particle laden) combustion environments. This suggests the importance of char in determining the fate of the coal-sulfur during gasification. Increasing oxygen-to-coal mass ratio increased sulfur conversion, SO2 concentration, and COs concentration, while it decreased H2S and CS2 concentrations.