Deng, XX
1992
The Desorption of Toluene from a Montmorillonite Clay Adsorbent in a Rotary Kiln Environment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing, D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Journal of Air Waste Management Assoc., 42:681-690, 1992. Funded by US Environmental Protection Agency, Gas Research Institute and ACERC.
The vaporization of toluene from pre-dried, 6mm montmorillonite clay particles was studied in a 130 kW pilot-scale rotary kiln with inside dimensions of 0.61 by 0.61 meters. Vaporization rates were obtained with a toluene weight fraction of 0.25 percent as a function of kiln fill fractions from 3 to 8 percent, rotation rates from 0.1 to 0.9 rpm, and kiln wall temperatures from 189 to 793ºC. Toluene desorption rates were obtained from gas-phase measurements and interpreted using a desorption model that incorporates the slumping frequency of the solids. Fill fraction of the kiln, binary gas diffusion in the bed, and particle desorption using an Arrhenius-type expression that is a function of bed temperature and average bed concentration. The model included three adjustable desorption parameters which were obtained by fitting the experimental data with a least squares technique. Solid and kiln-wall temperatures were continuously recorded and used by the model to perform toluene desorption predictions. The model was successful at predicting the effects of fill fraction and rotation rate over a range of temperatures. It was shown that an increase in kiln temperature and rotation rate increased toluene desorption rates. A decrease in kiln fill fraction showed an increase n desorption rate. Desorption predictions were performed using both predicted and measured temperature profiles. In addition, the model was used to perform sensitivity tests examine the relative importance of bed diffusion and particle desorption resistances. A methodology for predicting full-scale performance was developed. A full-scale, rotary-kiln heat-transfer model was used to estimate the bed thermal profile. This profile was then utilized by the model tp predict toluene desorption at full-scale.
Hydrocarbon and Formaldehyde Emissions from the Combustion of Pulverized Wood Waste
Larsen, F.S.; McClennen, W.H.; Deng, X.-X.; Silcox, G.D.and Allison, K.
Combustion Science and Technology, 1992 (in press). (Also presented at The Second International Congress on Toxic By-Products: Formation and Control, Salt Lake City, UT, March 1992). Funded by Weyerhaeuser Corp. and ACERC.
Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste were measured in 100 kW, cylindrical combustion chamber measuring 0.61 by 0.61 m. The wood was pneumatically conveyed to the burner and natural gas was used as an auxiliary fuel. The wood was screened prior to feeding so that its size distribution was representative of the suspension phase of a stoker boiler. Chamber wall and gas temperatures ranged from 920 to 1200 K and oxygen concentrations ranged from 2 to 9 percent, dry. Two types of waste were studied, plain wood and wood that was impregnated with a phenol-formaldehyde resin. The latter was a by-product of particleboard production. In general, the emissions of products of incomplete combustion (PICs) from the resinated waste were higher than those produced by plain wood. This may have been due to three factors: 1) the resinated wood was slightly wetter than the plain wood (6-9 percent by weight vs. 3 percent), 2) there was a difference in particle size distribution between the two materials as received, the resinated wood being larger, and 3) the resin may have had an effect on the emissions. Ultimate analyses of the two wastes showed no significant differences, other than moisture, in composition. At temperatures above 1200 K, total hydrocarbon emissions were roughly 10 to 29 ppm and formaldehyde emissions were less than the detection limit of 1 ppm. Typical waste wood boiler temperatures are roughly 1600 K. Hence, unless there are cool, poorly mixed regions in the full-scale facility, hydrocarbon and formaldehyde emissions should not be significant. However, the emissions from burning the two different types of wood would probably be different if all operating parameters in the wood-fired boiler are held constant.
1991
Hydrocarbon and Formaldehyde Emissions from the Combustion of Pulverized Wood Waste
Larsen, F.S.; McClennen, W.H.; Deng, X.-X.; Silcox, G.D. and Allison, K.
Combustion Science and Technology, 1991 (in press). Funded by Weyerhaeuser Corp. and ACERC.
Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste were measured in 100 kW, cylindrical combustion chamber measuring 0.61 by 0.61 m. The wood was pneumatically conveyed to the burner and natural gas was used as an auxiliary fuel. The wood was screened prior to feeding so that its size distribution was representative of the suspension phase of a stoker boiler. Chamber wall and gas temperatures ranged from 920 to 1200 K and oxygen concentrations ranged from 2 to 9 percent, dry. Two types of waste were studied, plain wood and wood that was impregnated with a phenol-formaldehyde resin. The latter was a by-product of particleboard production. In general, the emissions of products of incomplete combustion (PICs) from the resinated waste were higher than those produced by plain wood. This may have been due to three factors: 1) the resinated wood was slightly wetter than the plain wood (6-9 percent by weight vs. 3 percent), 2) there was a difference in particle size distribution between the two materials as received, the resinated wood being larger, and 3) the resin may have had an effect on the emissions. Ultimate analyses of the two wastes showed no significant differences, other than moisture, in composition. At temperatures above 1200 K, total hydrocarbon emissions were roughly 10 to 29 ppm and formaldehyde emissions were less than the detection limit of 1 ppm. Typical waste wood boiler temperatures are roughly 1600 K. Hence, unless there are cool, poorly mixed regions in the full-scale facility, hydrocarbon and formaldehyde emissions should not be significant. However, the emissions from burning the two different types of wood would probably be different if all operating parameters in the wood-fired boiler are held constant.
On-Line Monitoring of Formaldehyde in Comubustion Gases Using Gas Chromatography/Mass Spectrometry
McClennen, W.H.; Sheya, S.A.N.; Arnold, N.S.; Meuzelaar, H.L.C.; Deng, X.-X.; Larsen, F.S. and Silcox, G.D.
Combustion Science and Technology, 1991 (in press). Funded by ACERC.
This paper describes a method for on-line gas chromatography/mass spectrometry (GC/MS) of formaldehyde in combustion gases. The method uses a recently developed vapor-sampling inlet to monitor the concentration of formaldehyde and other products of incomplete combustion (PICs) from the burning of plain and phenol-formaldehyde resin treated wood chips. Other PICs that were simultaneously monitored included ketene, propylene, propyne and acetaldehyde. The direct analysis method has detection limits of less than 1 ppm for the reactive formaldehyde and excellent selectivity for determinations in the complex mixtures of combustion products. The rapid sampling technique allows monitoring of transient events of only a few minutes or less duration. Examples of the technique include the detection of sample line problems and the comparison of PIC concentrations from different points in the combustion exhaust stream.
Thermal Analysis of Rotary Kiln Incineration: Comparison of Theory and Experiment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Combustion and Flame, 86:101-114, 1991. Funded by Gas Research Institute, ACERC and Louisiana State University/Hazardous Waste Research Center.
A comprehensive heat-transfer model and associated simplified scaling laws are developed and verified using a pilot-scale, directly fired rotary kiln with a slumping bed of dry or wet, 6-mm clay sorbent particles. The kiln operating conditions examined include: rotation rate (0.1 to 0.9 rpm), percent fill fraction (3-8), feed moisture content (0-20 wt.%), and inner-wall temperature (190º to 790ºC). The model is used to determine the relative importance of several heat-transfer mechanisms including radiation, gas-to-solid convection, and wall-to-solid convection. Simple scaling laws are also developed for water vaporization. Generally good agreement is obtained between theory and experiment without adjusting any model parameters. Further, the simplified scaling laws provide a reasonable estimate of the pilot scale performance. The key conclusions of this study for kilns at the conditions examined are (1) water exerts a profound effect on the solids thermal profile, (2) simple geometrical scaling is not sufficient, (3) the assumption of a well mixed (radially isothermal) solids bed for the heat transfer analysis is appropriate, (4) a dimensionless group, which is a function of temperature, can be defined giving the relative importance of radiative and convective modes of heat transfer, and (5) moisture vaporization rates can be roughly approximated by assuming that the water vaporizes at the boiling point at a rate controlled by the rate of heat transfer to the bed. The implications of the scaling laws for scale-up and kiln design are also examined.
1990
Rate Limiting Processes in the Rotary-Kiln Incineration of Contaminated Solids
Lighty, J.S.; Eddings, E.G.; Lindgren, E.R.; Deng, X.-X.; Pershing, D.W.; Winter, R.M. and McClennen, W.H.
Combustion Science and Technology, 1990 (In press). Funded by ACERC, Gas Research Institute and Remediation Technology.
A study of transport processes during the desorption of organic and metallic contaminants from solids is being conducted using several fundamental experiments. This paper presents results from three experimental systems, a Particle-Characterization Reactor, Bed-Characterization Reactor, and Metals Reactor.
The organic experiments attempt to identify the controlling transports processes within a particle of soil and through a bed of particles, as well as quantify the necessary parameters to model these processes. Gas and solid-phase speciation data for field samples, soils contaminated with a variety of organics (boiling points from 220ºC to 495ºC), are discussed. The data suggest that local temperature and gas/solid contacting are important in the desorption process. As expected, lighter components desorb faster than the heavier hydrocarbons. Moisture content was also important in the desorption of contaminant.
The metals reactor has been used to determine the fate of metals, specifically the partitioning between the gas and solid, for a metal species on an inert solid matrix. Data from a parametric characterization study of partitioning of lead, in the form of lead oxide on an inert matrix, in different gas environments are presented. The results indicate that lead is most volatile in a dilute hydrogen chloride/nitrogen environment.
Thermal Analysis of Rotary Kiln Incineration: Comparison of Theory and Experiment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Combustion and Flame, 1990. Funded by Gas Research Institute, ACERC and Louisiana State University Hazardous Waste Research Center.
A comprehensive heat-transfer model and associated simplified scaling laws are developed and verified using a pilot-scale, directly-fired rotary kiln with a slumping bed of dry or wet, 2 mm clay sorbent particles. The kiln operating conditions examined include: rotation rate (0.1 to 0.9 rpm), percent fill fraction (3 to 8), feed moisture content (0 to 20 wt. percent), and inner-wall temperature (190 to 790º). The model is used to determine the relative importance of several heat-transfer mechanisms including radiation, gas-to-solid convection, and wall-to-solid convection. Simple scaling laws are also developed for water vaporization. Generally good agreement is obtained between theory and experiment without adjusting any model parameters. Further, the simplified scaling laws provide a reasonable estimate of the pilot scale performance.
The key conclusions of this study for kilns at the conditions examined are: (1) water exerts a profound effect on the solids thermal profile, (2) simple geometrical scaling is not sufficient, (3) the assumption of a well mixed (radially isothermal) solids bed for the heat transfer analysis is appropriate, (4) a dimensionless group, which is a function of temperature, can be defined giving the relative importance of radiative and convective modes of heat transfer, and (5) moisture vaporization rates can be roughly approximated by assuming that the water vaporized at the boiling point at a rate controlled by the rate of heat transfer to the bed. The implications of the scaling laws for scale-up and kiln design are also examined.
On-Line GC/MS Sampling of Exhaust Gas from a Rotary Kiln Simulator
Lighty, J.S.; Wagner, D.; Deng, X.-X.; Pershing, D.W.; McClennen, W.H.; Sheya, S.A.N.; Arnold, N.S. and Meuzelaar, H.L.C.
AWMA Specialty Conference on Waste Combustion in Boilers and Industrial Furnaces, Kansas City, MO, 1990. Funded by ACERC.
An on-line, short-column gas chromatography/mass spectrometry (GC/MS) system has been used to monitor the evolution of trace amounts of hydrocarbons evolving from a material which has been combusted in a rotary-kiln simulator. The system uses the isothermally heated, 1-m long transfer line of an Ion Trap Detector (ITD) as the gas chromatograph. The fused silica capillary normally used in the transfer line is replaced by a 1 m, 0 .15-mm inside diameter, 1.2 micron thick methyl silicone stationary phase (DB-1) GC column. Given the short column length and using a direct vapor sampling inlet, the exhaust gas can be sampled quickly, approximately every 10 s in these experiments. Since the column is isothermal, only a limited range of compounds can be analyzed for any given experiment.
1989
A Fundamental Study of the Rate of Thermal Desorption of Contaminants from Soil Beds
Lighty, J.S.; Eddings, E.G.; Deng, X.-X.; VanOs, L.M. and Pershing, D.W.
82nd Annual Air and Waste Management Association Annual Meeting, Anaheim, California, 1989. Funded by the Gas Research Institute, Dave Linz, Project Manager, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.
Thermal treatment is a proven, permanent destruction technology for most organic wastes and is presently available commercially. Rotary kiln incineration is one of the most common systems for thermal remediation of solids; however, new thermal technologies are being sought. The EPA Superfund Innovative Technology Evaluation (SITE) Program, which focuses on the use of innovative technologies for permanent remediation purposes, has identified seven thermal technologies that have been or will be demonstrated this has identified seven thermal technologies that have been or will be demonstrated this year. These technologies include infrared thermal destruction, circulating fluidized bed combustion, and in situ steam/air stripping. In each of these technologies important transport phenomena, specifically mass and heat transfer, must be understood to enable performance prediction, through modeling, for these technologies as full-scale processes.
The program at the University of Utah attempts to identify the fundamental transport rates in the decontamination of solids using thermal treatment. Once these phenomena are understood, the thermal treatment system can then be optimized. The experimental approach involves three fundamental rate reactors and two reactors designed specifically to address incineration in a rotary kiln environment. The fundamental experiments attempt to address incineration in a rotary kiln environment. The fundamental experiments attempt to identify the controlling processes at a particle level in a Particle-Characterization Reactor (PCR) and the resistances within a bed of solid in two Bed-Characterization Reactors (BCR). The fundamental insights gained from these reactors can be applied to any thermal treatment system, since the systems differ only in the mechanisms of heat transfer and mass treatment system, since the systems differ only in the mechanisms of heat transfer and mass transfer. For example, in infrared thermal destruction the transport limitations within the bed and radiation from the top of the bed are important processes that need to be understood. In a circulating fluidized bed combustor, an understanding of gas/solid contacting and convection needs to be gained. In situ steam/air stripping requires knowledge of the interactions between the water, contaminant, and soil matrix.
Two other experimental systems focus specifically on the unique features of rotary-kiln incineration technology. An ambient temperature mixing reactor and a rotary kiln simulator are used to evaluate mixing and combustion characteristics typical of a large-scale rotary kiln.
The paper focuses on results obtained in the Bed-Characterization Reactors. Mass transfer and heat transfer resistances have been found to be extremely important. The effects of packing density, moisture, and particle size on these resistances will be discussed.
Deng, XX
1992
The Desorption of Toluene from a Montmorillonite Clay Adsorbent in a Rotary Kiln Environment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing, D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Journal of Air Waste Management Assoc., 42:681-690, 1992. Funded by US Environmental Protection Agency, Gas Research Institute and ACERC.
The vaporization of toluene from pre-dried, 6mm montmorillonite clay particles was studied in a 130 kW pilot-scale rotary kiln with inside dimensions of 0.61 by 0.61 meters. Vaporization rates were obtained with a toluene weight fraction of 0.25 percent as a function of kiln fill fractions from 3 to 8 percent, rotation rates from 0.1 to 0.9 rpm, and kiln wall temperatures from 189 to 793ºC. Toluene desorption rates were obtained from gas-phase measurements and interpreted using a desorption model that incorporates the slumping frequency of the solids. Fill fraction of the kiln, binary gas diffusion in the bed, and particle desorption using an Arrhenius-type expression that is a function of bed temperature and average bed concentration. The model included three adjustable desorption parameters which were obtained by fitting the experimental data with a least squares technique. Solid and kiln-wall temperatures were continuously recorded and used by the model to perform toluene desorption predictions. The model was successful at predicting the effects of fill fraction and rotation rate over a range of temperatures. It was shown that an increase in kiln temperature and rotation rate increased toluene desorption rates. A decrease in kiln fill fraction showed an increase n desorption rate. Desorption predictions were performed using both predicted and measured temperature profiles. In addition, the model was used to perform sensitivity tests examine the relative importance of bed diffusion and particle desorption resistances. A methodology for predicting full-scale performance was developed. A full-scale, rotary-kiln heat-transfer model was used to estimate the bed thermal profile. This profile was then utilized by the model tp predict toluene desorption at full-scale.
Hydrocarbon and Formaldehyde Emissions from the Combustion of Pulverized Wood Waste
Larsen, F.S.; McClennen, W.H.; Deng, X.-X.; Silcox, G.D.and Allison, K.
Combustion Science and Technology, 1992 (in press). (Also presented at The Second International Congress on Toxic By-Products: Formation and Control, Salt Lake City, UT, March 1992). Funded by Weyerhaeuser Corp. and ACERC.
Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste were measured in 100 kW, cylindrical combustion chamber measuring 0.61 by 0.61 m. The wood was pneumatically conveyed to the burner and natural gas was used as an auxiliary fuel. The wood was screened prior to feeding so that its size distribution was representative of the suspension phase of a stoker boiler. Chamber wall and gas temperatures ranged from 920 to 1200 K and oxygen concentrations ranged from 2 to 9 percent, dry. Two types of waste were studied, plain wood and wood that was impregnated with a phenol-formaldehyde resin. The latter was a by-product of particleboard production. In general, the emissions of products of incomplete combustion (PICs) from the resinated waste were higher than those produced by plain wood. This may have been due to three factors: 1) the resinated wood was slightly wetter than the plain wood (6-9 percent by weight vs. 3 percent), 2) there was a difference in particle size distribution between the two materials as received, the resinated wood being larger, and 3) the resin may have had an effect on the emissions. Ultimate analyses of the two wastes showed no significant differences, other than moisture, in composition. At temperatures above 1200 K, total hydrocarbon emissions were roughly 10 to 29 ppm and formaldehyde emissions were less than the detection limit of 1 ppm. Typical waste wood boiler temperatures are roughly 1600 K. Hence, unless there are cool, poorly mixed regions in the full-scale facility, hydrocarbon and formaldehyde emissions should not be significant. However, the emissions from burning the two different types of wood would probably be different if all operating parameters in the wood-fired boiler are held constant.
1991
Hydrocarbon and Formaldehyde Emissions from the Combustion of Pulverized Wood Waste
Larsen, F.S.; McClennen, W.H.; Deng, X.-X.; Silcox, G.D. and Allison, K.
Combustion Science and Technology, 1991 (in press). Funded by Weyerhaeuser Corp. and ACERC.
Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste were measured in 100 kW, cylindrical combustion chamber measuring 0.61 by 0.61 m. The wood was pneumatically conveyed to the burner and natural gas was used as an auxiliary fuel. The wood was screened prior to feeding so that its size distribution was representative of the suspension phase of a stoker boiler. Chamber wall and gas temperatures ranged from 920 to 1200 K and oxygen concentrations ranged from 2 to 9 percent, dry. Two types of waste were studied, plain wood and wood that was impregnated with a phenol-formaldehyde resin. The latter was a by-product of particleboard production. In general, the emissions of products of incomplete combustion (PICs) from the resinated waste were higher than those produced by plain wood. This may have been due to three factors: 1) the resinated wood was slightly wetter than the plain wood (6-9 percent by weight vs. 3 percent), 2) there was a difference in particle size distribution between the two materials as received, the resinated wood being larger, and 3) the resin may have had an effect on the emissions. Ultimate analyses of the two wastes showed no significant differences, other than moisture, in composition. At temperatures above 1200 K, total hydrocarbon emissions were roughly 10 to 29 ppm and formaldehyde emissions were less than the detection limit of 1 ppm. Typical waste wood boiler temperatures are roughly 1600 K. Hence, unless there are cool, poorly mixed regions in the full-scale facility, hydrocarbon and formaldehyde emissions should not be significant. However, the emissions from burning the two different types of wood would probably be different if all operating parameters in the wood-fired boiler are held constant.
On-Line Monitoring of Formaldehyde in Comubustion Gases Using Gas Chromatography/Mass Spectrometry
McClennen, W.H.; Sheya, S.A.N.; Arnold, N.S.; Meuzelaar, H.L.C.; Deng, X.-X.; Larsen, F.S. and Silcox, G.D.
Combustion Science and Technology, 1991 (in press). Funded by ACERC.
This paper describes a method for on-line gas chromatography/mass spectrometry (GC/MS) of formaldehyde in combustion gases. The method uses a recently developed vapor-sampling inlet to monitor the concentration of formaldehyde and other products of incomplete combustion (PICs) from the burning of plain and phenol-formaldehyde resin treated wood chips. Other PICs that were simultaneously monitored included ketene, propylene, propyne and acetaldehyde. The direct analysis method has detection limits of less than 1 ppm for the reactive formaldehyde and excellent selectivity for determinations in the complex mixtures of combustion products. The rapid sampling technique allows monitoring of transient events of only a few minutes or less duration. Examples of the technique include the detection of sample line problems and the comparison of PIC concentrations from different points in the combustion exhaust stream.
Thermal Analysis of Rotary Kiln Incineration: Comparison of Theory and Experiment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Combustion and Flame, 86:101-114, 1991. Funded by Gas Research Institute, ACERC and Louisiana State University/Hazardous Waste Research Center.
A comprehensive heat-transfer model and associated simplified scaling laws are developed and verified using a pilot-scale, directly fired rotary kiln with a slumping bed of dry or wet, 6-mm clay sorbent particles. The kiln operating conditions examined include: rotation rate (0.1 to 0.9 rpm), percent fill fraction (3-8), feed moisture content (0-20 wt.%), and inner-wall temperature (190º to 790ºC). The model is used to determine the relative importance of several heat-transfer mechanisms including radiation, gas-to-solid convection, and wall-to-solid convection. Simple scaling laws are also developed for water vaporization. Generally good agreement is obtained between theory and experiment without adjusting any model parameters. Further, the simplified scaling laws provide a reasonable estimate of the pilot scale performance. The key conclusions of this study for kilns at the conditions examined are (1) water exerts a profound effect on the solids thermal profile, (2) simple geometrical scaling is not sufficient, (3) the assumption of a well mixed (radially isothermal) solids bed for the heat transfer analysis is appropriate, (4) a dimensionless group, which is a function of temperature, can be defined giving the relative importance of radiative and convective modes of heat transfer, and (5) moisture vaporization rates can be roughly approximated by assuming that the water vaporizes at the boiling point at a rate controlled by the rate of heat transfer to the bed. The implications of the scaling laws for scale-up and kiln design are also examined.
1990
Rate Limiting Processes in the Rotary-Kiln Incineration of Contaminated Solids
Lighty, J.S.; Eddings, E.G.; Lindgren, E.R.; Deng, X.-X.; Pershing, D.W.; Winter, R.M. and McClennen, W.H.
Combustion Science and Technology, 1990 (In press). Funded by ACERC, Gas Research Institute and Remediation Technology.
A study of transport processes during the desorption of organic and metallic contaminants from solids is being conducted using several fundamental experiments. This paper presents results from three experimental systems, a Particle-Characterization Reactor, Bed-Characterization Reactor, and Metals Reactor.
The organic experiments attempt to identify the controlling transports processes within a particle of soil and through a bed of particles, as well as quantify the necessary parameters to model these processes. Gas and solid-phase speciation data for field samples, soils contaminated with a variety of organics (boiling points from 220ºC to 495ºC), are discussed. The data suggest that local temperature and gas/solid contacting are important in the desorption process. As expected, lighter components desorb faster than the heavier hydrocarbons. Moisture content was also important in the desorption of contaminant.
The metals reactor has been used to determine the fate of metals, specifically the partitioning between the gas and solid, for a metal species on an inert solid matrix. Data from a parametric characterization study of partitioning of lead, in the form of lead oxide on an inert matrix, in different gas environments are presented. The results indicate that lead is most volatile in a dilute hydrogen chloride/nitrogen environment.
Thermal Analysis of Rotary Kiln Incineration: Comparison of Theory and Experiment
Owens, W.D.; Silcox, G.D.; Lighty, J.S.; Deng, X.-X.; Pershing D.W.; Cundy, V.A.; Leger, C.B. and Jakway, A.J.
Combustion and Flame, 1990. Funded by Gas Research Institute, ACERC and Louisiana State University Hazardous Waste Research Center.
A comprehensive heat-transfer model and associated simplified scaling laws are developed and verified using a pilot-scale, directly-fired rotary kiln with a slumping bed of dry or wet, 2 mm clay sorbent particles. The kiln operating conditions examined include: rotation rate (0.1 to 0.9 rpm), percent fill fraction (3 to 8), feed moisture content (0 to 20 wt. percent), and inner-wall temperature (190 to 790º). The model is used to determine the relative importance of several heat-transfer mechanisms including radiation, gas-to-solid convection, and wall-to-solid convection. Simple scaling laws are also developed for water vaporization. Generally good agreement is obtained between theory and experiment without adjusting any model parameters. Further, the simplified scaling laws provide a reasonable estimate of the pilot scale performance.
The key conclusions of this study for kilns at the conditions examined are: (1) water exerts a profound effect on the solids thermal profile, (2) simple geometrical scaling is not sufficient, (3) the assumption of a well mixed (radially isothermal) solids bed for the heat transfer analysis is appropriate, (4) a dimensionless group, which is a function of temperature, can be defined giving the relative importance of radiative and convective modes of heat transfer, and (5) moisture vaporization rates can be roughly approximated by assuming that the water vaporized at the boiling point at a rate controlled by the rate of heat transfer to the bed. The implications of the scaling laws for scale-up and kiln design are also examined.
On-Line GC/MS Sampling of Exhaust Gas from a Rotary Kiln Simulator
Lighty, J.S.; Wagner, D.; Deng, X.-X.; Pershing, D.W.; McClennen, W.H.; Sheya, S.A.N.; Arnold, N.S. and Meuzelaar, H.L.C.
AWMA Specialty Conference on Waste Combustion in Boilers and Industrial Furnaces, Kansas City, MO, 1990. Funded by ACERC.
An on-line, short-column gas chromatography/mass spectrometry (GC/MS) system has been used to monitor the evolution of trace amounts of hydrocarbons evolving from a material which has been combusted in a rotary-kiln simulator. The system uses the isothermally heated, 1-m long transfer line of an Ion Trap Detector (ITD) as the gas chromatograph. The fused silica capillary normally used in the transfer line is replaced by a 1 m, 0 .15-mm inside diameter, 1.2 micron thick methyl silicone stationary phase (DB-1) GC column. Given the short column length and using a direct vapor sampling inlet, the exhaust gas can be sampled quickly, approximately every 10 s in these experiments. Since the column is isothermal, only a limited range of compounds can be analyzed for any given experiment.
1989
A Fundamental Study of the Rate of Thermal Desorption of Contaminants from Soil Beds
Lighty, J.S.; Eddings, E.G.; Deng, X.-X.; VanOs, L.M. and Pershing, D.W.
82nd Annual Air and Waste Management Association Annual Meeting, Anaheim, California, 1989. Funded by the Gas Research Institute, Dave Linz, Project Manager, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.
Thermal treatment is a proven, permanent destruction technology for most organic wastes and is presently available commercially. Rotary kiln incineration is one of the most common systems for thermal remediation of solids; however, new thermal technologies are being sought. The EPA Superfund Innovative Technology Evaluation (SITE) Program, which focuses on the use of innovative technologies for permanent remediation purposes, has identified seven thermal technologies that have been or will be demonstrated this has identified seven thermal technologies that have been or will be demonstrated this year. These technologies include infrared thermal destruction, circulating fluidized bed combustion, and in situ steam/air stripping. In each of these technologies important transport phenomena, specifically mass and heat transfer, must be understood to enable performance prediction, through modeling, for these technologies as full-scale processes.
The program at the University of Utah attempts to identify the fundamental transport rates in the decontamination of solids using thermal treatment. Once these phenomena are understood, the thermal treatment system can then be optimized. The experimental approach involves three fundamental rate reactors and two reactors designed specifically to address incineration in a rotary kiln environment. The fundamental experiments attempt to address incineration in a rotary kiln environment. The fundamental experiments attempt to identify the controlling processes at a particle level in a Particle-Characterization Reactor (PCR) and the resistances within a bed of solid in two Bed-Characterization Reactors (BCR). The fundamental insights gained from these reactors can be applied to any thermal treatment system, since the systems differ only in the mechanisms of heat transfer and mass treatment system, since the systems differ only in the mechanisms of heat transfer and mass transfer. For example, in infrared thermal destruction the transport limitations within the bed and radiation from the top of the bed are important processes that need to be understood. In a circulating fluidized bed combustor, an understanding of gas/solid contacting and convection needs to be gained. In situ steam/air stripping requires knowledge of the interactions between the water, contaminant, and soil matrix.
Two other experimental systems focus specifically on the unique features of rotary-kiln incineration technology. An ambient temperature mixing reactor and a rotary kiln simulator are used to evaluate mixing and combustion characteristics typical of a large-scale rotary kiln.
The paper focuses on results obtained in the Bed-Characterization Reactors. Mass transfer and heat transfer resistances have been found to be extremely important. The effects of packing density, moisture, and particle size on these resistances will be discussed.