Monson, CR
1994
Improved Diameter, Velocity, and Temperature Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Monson, C.R.; Germane, G.J. and Hecker, W.C.
Energy & Fuels, 8(4):925-931, 1994. Funded by ACERC, Advanced Fuel Research and US Department of Energy.
Coal combustion researchers have typically used the average temperature and residence time of a burning particle cloud to determine the high-temperature reactivity of coals and chars. These average values, however, cannot account for particle-to-particle variations or their possible causes. Researchers at Sandia National Laboratories developed a pyrometry technique to simultaneously measure the temperature, velocity, and diameter of individual char particles burning in a transparent-wall flat-flame facility. This work reports two significant advances relative to the optical pyrometry technique. First, pyrometer modifications together with a new analysis technique now permit the particle properties to be measured for smaller/cooler particles. Second, the modified pyrometer has been implemented in two heated-wall drop-tube reactors, rather than transparent-wall, flat-flame burners. This is significant because drop-tube reactors allow greater flexibility/control of gas environments and operating pressures during char oxidation. Glowing reactor walls, however, present some unique challenges for these optical measurements. Means of overcoming these challenges are discussed, and reliable in situ measurement of particle temperatures, velocities, and diameters is verified. The results of measurements made in these drop-tube reactors, both for calibration tests and actual oxidation tests with Spherocarb and a Utah bituminous coal char, are also presented.
1993
A High-Pressure Drop-Tube Facility for Coal Combustion Studies
Monson, C.R. and Germane, G.J.
Energy & Fuels, 7 (6):928-936, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
A number of processes, including coal gasification, combined cycles and heat engines, are being used or developed that combust coal at elevated pressures. While practical research is being conducted on the use of coal in these applications, little is known about the basic nature of high-pressure coal combustion. The few studies that have examined the effect of pressure on these reactions during the past 25 years have been limited by experimental apparatus (shock tubes) and have produced conflicting results. A need clearly exists for well-characterized facilities that can be used for high-pressure coal combustion research. This paper describes the design and characterization of an elevated pressure drop-tube facility. This unique facility consists of a high-pressure drop-tube reactor, a tar/char/gas separation and collection system, an optical pyrometer and support equipment. The electrically heated, computer controlled reactor was shown to provide the following capabilities: pressure from 1 to 5 atm, wall and gas temperatures from 1000 to 1700 K, controllable temperature profile along the reaction tube length, particle residence times from 30 to 1000 ms, variable gas compositions of inert and oxidizing gases, and optical access ports for in situ diagnostics. Characterization of the reactor over the range of design operating conditions verified the suitability of the reactor for coal combustion experiments. Results from a series of char oxidation tests are also presented, demonstrating the wide range of possible experimental conditions; these oxidation experiments spanned a broader range of conditions than other known work.
1992
Char Oxidation at Elevated Pressure
Monson, C.R.
Char Oxidation at Elevated Pressure, Ph.D./BYU, December 1992. Advisor: Germane
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.
1991
Improved Temperature, Velocity and Diameter Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Hecker, W.C.; Monson, C.R. and Germane, G.J.
Western States Section/The Combustion Institute, Los Angeles, CA, October 1991. Funded by Advanced Fuel Research, Morgantown Energy Research Center and ACERC.
Early attempts to determine the high-temperature reactivity of coals and chars were hampered by the inability to measure a burning particle's temperature and residence time. Researchers have typically approximated these values with the average temperature and residence time of a cloud of burning particles. Average values, however, do not account for particle-to-particle variations or their possible causes. In 1984 researchers at Sandia National Laboratories developed an optical technique to simultaneously measure the temperature, velocity and diameter of individual particles burning in a flat flame facility. This work reports modifications to the Sandia technique that allow measurement of smaller particles (ca. 30-200 µm) and its application to particles burning in atmospheric and elevated pressure drop-tube reactors.
The modified pyrometer is applied to drop-tube reactors, rather than flat flame burners, to allow a broad range of well-controlled gas environments and operating pressures for char oxidation experiments. Electrical wall heating allows good control of particle temperature histories, however glowing reactor walls present some unique challenges. Diffuse radiation emitted from the reactor walls enters the pyrometer's optical path, producing excess noise in the particle signal. This noise has been minimized by optimizing the design of the reactors' optical ports and the alignment of the pyrometer. The possibility of temperature measurement error caused by wall emissions reflecting off of the particle is shown to be minimal by Maxwell's electromagnetic equations.
Particle properties are obtained by focusing the burning particle's image onto a coded aperture that, as re-designed at Brigham Young University, contains a series of carefully sized blackouts and windows. Temperature is measured by conventional 2-color pyrometry, while velocity is obtained from the particle's transit time. Particle size is extracted from the signal by means of a unique geometric/statistical fitting technique developed during this work. Proper operation of the modified pyrometer has been verified during oxidation of both Spherocarb and coal char in the drop-tube reactors.
Monson, CR
1994
Improved Diameter, Velocity, and Temperature Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Monson, C.R.; Germane, G.J. and Hecker, W.C.
Energy & Fuels, 8(4):925-931, 1994. Funded by ACERC, Advanced Fuel Research and US Department of Energy.
Coal combustion researchers have typically used the average temperature and residence time of a burning particle cloud to determine the high-temperature reactivity of coals and chars. These average values, however, cannot account for particle-to-particle variations or their possible causes. Researchers at Sandia National Laboratories developed a pyrometry technique to simultaneously measure the temperature, velocity, and diameter of individual char particles burning in a transparent-wall flat-flame facility. This work reports two significant advances relative to the optical pyrometry technique. First, pyrometer modifications together with a new analysis technique now permit the particle properties to be measured for smaller/cooler particles. Second, the modified pyrometer has been implemented in two heated-wall drop-tube reactors, rather than transparent-wall, flat-flame burners. This is significant because drop-tube reactors allow greater flexibility/control of gas environments and operating pressures during char oxidation. Glowing reactor walls, however, present some unique challenges for these optical measurements. Means of overcoming these challenges are discussed, and reliable in situ measurement of particle temperatures, velocities, and diameters is verified. The results of measurements made in these drop-tube reactors, both for calibration tests and actual oxidation tests with Spherocarb and a Utah bituminous coal char, are also presented.
1993
A High-Pressure Drop-Tube Facility for Coal Combustion Studies
Monson, C.R. and Germane, G.J.
Energy & Fuels, 7 (6):928-936, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
A number of processes, including coal gasification, combined cycles and heat engines, are being used or developed that combust coal at elevated pressures. While practical research is being conducted on the use of coal in these applications, little is known about the basic nature of high-pressure coal combustion. The few studies that have examined the effect of pressure on these reactions during the past 25 years have been limited by experimental apparatus (shock tubes) and have produced conflicting results. A need clearly exists for well-characterized facilities that can be used for high-pressure coal combustion research. This paper describes the design and characterization of an elevated pressure drop-tube facility. This unique facility consists of a high-pressure drop-tube reactor, a tar/char/gas separation and collection system, an optical pyrometer and support equipment. The electrically heated, computer controlled reactor was shown to provide the following capabilities: pressure from 1 to 5 atm, wall and gas temperatures from 1000 to 1700 K, controllable temperature profile along the reaction tube length, particle residence times from 30 to 1000 ms, variable gas compositions of inert and oxidizing gases, and optical access ports for in situ diagnostics. Characterization of the reactor over the range of design operating conditions verified the suitability of the reactor for coal combustion experiments. Results from a series of char oxidation tests are also presented, demonstrating the wide range of possible experimental conditions; these oxidation experiments spanned a broader range of conditions than other known work.
1992
Char Oxidation at Elevated Pressure
Monson, C.R.
Char Oxidation at Elevated Pressure, Ph.D./BYU, December 1992. Advisor: Germane
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.
1991
Improved Temperature, Velocity and Diameter Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Hecker, W.C.; Monson, C.R. and Germane, G.J.
Western States Section/The Combustion Institute, Los Angeles, CA, October 1991. Funded by Advanced Fuel Research, Morgantown Energy Research Center and ACERC.
Early attempts to determine the high-temperature reactivity of coals and chars were hampered by the inability to measure a burning particle's temperature and residence time. Researchers have typically approximated these values with the average temperature and residence time of a cloud of burning particles. Average values, however, do not account for particle-to-particle variations or their possible causes. In 1984 researchers at Sandia National Laboratories developed an optical technique to simultaneously measure the temperature, velocity and diameter of individual particles burning in a flat flame facility. This work reports modifications to the Sandia technique that allow measurement of smaller particles (ca. 30-200 µm) and its application to particles burning in atmospheric and elevated pressure drop-tube reactors.
The modified pyrometer is applied to drop-tube reactors, rather than flat flame burners, to allow a broad range of well-controlled gas environments and operating pressures for char oxidation experiments. Electrical wall heating allows good control of particle temperature histories, however glowing reactor walls present some unique challenges. Diffuse radiation emitted from the reactor walls enters the pyrometer's optical path, producing excess noise in the particle signal. This noise has been minimized by optimizing the design of the reactors' optical ports and the alignment of the pyrometer. The possibility of temperature measurement error caused by wall emissions reflecting off of the particle is shown to be minimal by Maxwell's electromagnetic equations.
Particle properties are obtained by focusing the burning particle's image onto a coded aperture that, as re-designed at Brigham Young University, contains a series of carefully sized blackouts and windows. Temperature is measured by conventional 2-color pyrometry, while velocity is obtained from the particle's transit time. Particle size is extracted from the signal by means of a unique geometric/statistical fitting technique developed during this work. Proper operation of the modified pyrometer has been verified during oxidation of both Spherocarb and coal char in the drop-tube reactors.