Kozinski, JA
1994
Biosludge Incineration in FBCs: Behavior of Ash Particles
Rink, K.K.; Kozinski, J.A. and Lighty J.S.
Combustion and Flame, (in press). (Also presented at the 25th Symposium on Combustion, Irvine, CA, August 1994.) Funded by ACERC and National Science Foundation/Presidential Young Investigators.
The evolution of ash morphology and metals behavior during incineration of a biosludge and silica sand in a 300 kW fluidized bed facility have been studied. The reactor was operated in the bubbling mode. Analyses of ash particles were performed using a computer-controlled electron probe microanalyzer equipped with four wavelength-dispersive spectrometers. The paper presents data on ash particle structure formation, size/numbers density distribution and migration/distribution of metals inside a supermicron fly ash particle. A mechanistic model of the fly ash evolution process is proposed. The major trends in the suggested mechanism are (1) the massive formation of porous particles (45-110 µm) in the splash zone, (2) their extensive fragmentation/disintegration along the incineration pathway resulting in the particle size reduction and number density increase, (3) the presence of a phase transition in locally high-temperature regions (1650 K), and (4) the formation of smooth-surfaced compact-structured glassy fly ash submicron (<0.7 µm) and supermicron (3-30 µm) spheres. A physical of a compact/glassy supermicron fly ash particle is also developed. Light metal elements (Si, Al, Ca, K, Na) create a multiplayer external shell (4-6 µm in thickness) encapsulating heavy metals (Cd, Cu, Ni, Pb) distributed in discrete pockets toward the core of the particle. The distance 4-6 µm does not constitute any definite boundary between these two characteristic regions since no dependence is found between particle size and shell thickness. These data illustrate that heavy trace metals are partitioned inside a biosludge-originated supermicron fly ash particle rather than on the surface, and assumption previously accepted on the basis of fly ash data obtained during coal combustion.
Design and Construction of a Circulating Fluidized Bed Combustion Facility for Use in Studying the Thermal Remediation of Wastes
Rink, K.K.; Kozinski, J.A.; Lighty, J.S. and Lu, Q.
Rev. Sci. Instrum., 65(8):2704-2713, 1994. Funded by ACERC and National Science Foundation/Presidential Young Investigators.
Fluidized bed combustion systems have been widely applied in the combustion of solid fossil fuels, particularly by the power generation industry. Recently, attention has shifted from the conventional bubbling fluidized bed (BFB) to circulating fluidized bed (CFB) combustion systems. Inherent advantages of DFB combustion such as uniform temperatures, excellent mixing, high combustion efficiencies, and greater fuel flexibility have generated interest in the feasibility of CGB combustion systems applied to the thermal remediation of contaminated soils and sludges. Because it is often difficult to monitor and analyze the combustion phenomena that occurs within a full scale fluidized bed system, the need exists for smaller scale research facilities that permit detailed measurements of temperature, pressure, and chemical specie profiles. This article describes the design, construction, and operation of a pilot-scale fluidized bed facility developed to investigate the thermal remediation characteristics of contaminated soils and sludges. The refractory-lined reactor measures 8 m in height and has an external diameter of 0.6 m. The facility can be operated as a BFB or CFB using a variety of solid fuels including low calorific or high moisture content materials supplemented by natural gas introduced into the fluidized bed through auxiliary fuel injectors. Maximum firing rate of the fluidized bed is approximately 300 kW. Under normal operating conditions, internal wall temperatures are maintained between 1150 and 1350 K over superficial velocities ranging from 0.5 to 4 m/s. Contaminated material can be continuously fed into the fluidized bed or introduced as a single charge at three different locations. The facility is fully instrumented to allow time-resolved measurements of gaseous pollutant species, gas phase temperatures, and internal pressures. The facility has produced reproducible fluidization results that agree well with the work of other researchers. Minimum fluidization velocities (Umf) ranging from 0.4 to 2.3 m/s were experimentally determined for various sizes and types of material. Static wall pressure varied between 2.6 and 12.9 kPa along the length of the reactor over the range of superficial velocities. Superficial velocity was found to significantly influence the behavior of the axial pressure profiles, particularly in the slugging and turbulent regimes of operation. In addition to fluidization tests, initial combustion tests were performed while burning natural gas and operating with an inert silica sand bed. Results indicate that combustion of natural gas occurred to only a limited extent within the bed. The lowest CO2 and the highest CO concentrations (1.9% and 0.9%, respectively) were found 0.5 m above the expanded bed surface. Maximum measured gas temperatures (1400 K) were also observed in this region. These results indicate that ignition occurred immediately above the bed surface and combustion proceeded in the freeboard section. Although significant quantities of NOx (45.0 ppm) and CO2 (7.2%) were formed further downstream in the freeboard of the reactor, the combustion process was found to be essentially complete before the entrance to the cyclone.
Determination of Metal Behavior During the Incineration of a Contaminated Montmorillonite Clay
Eddings, E.G.; Lighty, J.S. and Kozinski, J.
Environmental Science and Technology, 28:1791, 1994. Funded by ACERC (different contract) and National Science Foundation/Presidential Young Investigators.
The goal of this study was to develop an understanding of metals behavior during thermal treatment. Clay samples, contaminated with metals to obtain a surrogate waste, were analyzed prior to and following thermal treatment using nitric acid and/or hydrogen fluoride digestion, followed by inductively coupled plasma emission spectrophotometry analysis. Techniques were used to examine particle surface and metal distribution within cross sections. Lead, cadmium, and chromium results are discussed. With hydrogen fluoride-digested samples, the results indicated that vaporization increased slightly with increasing temperature for cadmium and lead. Chromium did not show increased vaporization. At higher temperatures, the nitric acid digestions did not completely remove the metals. Scanning electron microscope pictures showed that, at higher temperatures, the particle structure became compact and glassy; the electron microprobe results indicated that lead and cadmium were located in regions with high silicon, suggesting reactions with the silicon. Chromium distribution remained uniform, suggesting that chromium was immobilized due to structural changes not reactions.
1993
Thermal Treatment of Hazardous Wastes: A Comparison of Fluidized Bed and Rotary Kiln Incineration
Rink, K.K.; Larsen, F.S.; Kozinski, J.A.; Lighty, J.S.; Silcox, G.D. and Pershing, D.W.
Energy & Fuels, 7 (6):803-814, 1993. Funded by ACERC.
Large volumes of sludge are produced by a wide variety of industrial processes and by municipal wastewater treatment. Interest in incinerating these sludges, either alone, or co-fired with other fuels, is increasing. The issues surrounding sludge incineration in rotary kilns and fluidized beds were identified through a series of pilot-scale tests using two slightly different paper mill sludges. The specific issues examined include hydrocarbon emissions, NOx emissions, and bottom and fly ash properties. A 61-cm i.d. X 61-cm long, 130-kW pilot-scale rotary kiln simulator (RKS) and a 23-cm i.d., 300-kW circulating fluidized bed combustor (CFB) were maintained at a nominal temperature of 1100 K and a stoichiometric ratio of 1.5. The rotary kiln was fed in a batch mode in order to simulate the passage of solids through a kiln. The fluidized bed was fed in both batch and continuous modes. Samples were removed from the kiln (bottom ash) and transition section (fly ash). Samples of the fluidized bed materials were removed from the bed (bottom ash) and after the cyclone (fly ash). The exhaust gases were analyzed continuous for hydrocarbons, CO, O2, NO, and CO2. This paper presents data on these analyses as well as NO conversion and ash properties. The production of NO in the RKS was dependent on the supply of nitrogen (in the sludge) and oxygen (in the gas phase), in the reactor. The availability of oxygen to the sludge was affected by the particle diameter of the sludge, the charge size, and whether a solids bed was present at the time of the incineration. In the CFB, the nitrogen-containing compounds were oxidized primarily downstream of the feedboard region, resulting in elevated levels of NO in the transition and cyclone regions. Carbon monoxide concentrations were high immediately above the bed, which led to the reduction of NO inside the freeboard zone. In both the CFB and RKS tests little unburned hydrocarbons were present in the exhaust gas streams. Formation of fly ash particles was dependent on types of incinerated material (sludge; mixture of sludge and silica sand). Bottom ash material resembled randomly organized skeletons (or cenospheric skeletons), the structure of which was independent of the type of sludge or reactor. Smaller fly ash and bottom ash particles were formed during CFB incineration experiments.
Kozinski, JA
1994
Biosludge Incineration in FBCs: Behavior of Ash Particles
Rink, K.K.; Kozinski, J.A. and Lighty J.S.
Combustion and Flame, (in press). (Also presented at the 25th Symposium on Combustion, Irvine, CA, August 1994.) Funded by ACERC and National Science Foundation/Presidential Young Investigators.
The evolution of ash morphology and metals behavior during incineration of a biosludge and silica sand in a 300 kW fluidized bed facility have been studied. The reactor was operated in the bubbling mode. Analyses of ash particles were performed using a computer-controlled electron probe microanalyzer equipped with four wavelength-dispersive spectrometers. The paper presents data on ash particle structure formation, size/numbers density distribution and migration/distribution of metals inside a supermicron fly ash particle. A mechanistic model of the fly ash evolution process is proposed. The major trends in the suggested mechanism are (1) the massive formation of porous particles (45-110 µm) in the splash zone, (2) their extensive fragmentation/disintegration along the incineration pathway resulting in the particle size reduction and number density increase, (3) the presence of a phase transition in locally high-temperature regions (1650 K), and (4) the formation of smooth-surfaced compact-structured glassy fly ash submicron (<0.7 µm) and supermicron (3-30 µm) spheres. A physical of a compact/glassy supermicron fly ash particle is also developed. Light metal elements (Si, Al, Ca, K, Na) create a multiplayer external shell (4-6 µm in thickness) encapsulating heavy metals (Cd, Cu, Ni, Pb) distributed in discrete pockets toward the core of the particle. The distance 4-6 µm does not constitute any definite boundary between these two characteristic regions since no dependence is found between particle size and shell thickness. These data illustrate that heavy trace metals are partitioned inside a biosludge-originated supermicron fly ash particle rather than on the surface, and assumption previously accepted on the basis of fly ash data obtained during coal combustion.
Design and Construction of a Circulating Fluidized Bed Combustion Facility for Use in Studying the Thermal Remediation of Wastes
Rink, K.K.; Kozinski, J.A.; Lighty, J.S. and Lu, Q.
Rev. Sci. Instrum., 65(8):2704-2713, 1994. Funded by ACERC and National Science Foundation/Presidential Young Investigators.
Fluidized bed combustion systems have been widely applied in the combustion of solid fossil fuels, particularly by the power generation industry. Recently, attention has shifted from the conventional bubbling fluidized bed (BFB) to circulating fluidized bed (CFB) combustion systems. Inherent advantages of DFB combustion such as uniform temperatures, excellent mixing, high combustion efficiencies, and greater fuel flexibility have generated interest in the feasibility of CGB combustion systems applied to the thermal remediation of contaminated soils and sludges. Because it is often difficult to monitor and analyze the combustion phenomena that occurs within a full scale fluidized bed system, the need exists for smaller scale research facilities that permit detailed measurements of temperature, pressure, and chemical specie profiles. This article describes the design, construction, and operation of a pilot-scale fluidized bed facility developed to investigate the thermal remediation characteristics of contaminated soils and sludges. The refractory-lined reactor measures 8 m in height and has an external diameter of 0.6 m. The facility can be operated as a BFB or CFB using a variety of solid fuels including low calorific or high moisture content materials supplemented by natural gas introduced into the fluidized bed through auxiliary fuel injectors. Maximum firing rate of the fluidized bed is approximately 300 kW. Under normal operating conditions, internal wall temperatures are maintained between 1150 and 1350 K over superficial velocities ranging from 0.5 to 4 m/s. Contaminated material can be continuously fed into the fluidized bed or introduced as a single charge at three different locations. The facility is fully instrumented to allow time-resolved measurements of gaseous pollutant species, gas phase temperatures, and internal pressures. The facility has produced reproducible fluidization results that agree well with the work of other researchers. Minimum fluidization velocities (Umf) ranging from 0.4 to 2.3 m/s were experimentally determined for various sizes and types of material. Static wall pressure varied between 2.6 and 12.9 kPa along the length of the reactor over the range of superficial velocities. Superficial velocity was found to significantly influence the behavior of the axial pressure profiles, particularly in the slugging and turbulent regimes of operation. In addition to fluidization tests, initial combustion tests were performed while burning natural gas and operating with an inert silica sand bed. Results indicate that combustion of natural gas occurred to only a limited extent within the bed. The lowest CO2 and the highest CO concentrations (1.9% and 0.9%, respectively) were found 0.5 m above the expanded bed surface. Maximum measured gas temperatures (1400 K) were also observed in this region. These results indicate that ignition occurred immediately above the bed surface and combustion proceeded in the freeboard section. Although significant quantities of NOx (45.0 ppm) and CO2 (7.2%) were formed further downstream in the freeboard of the reactor, the combustion process was found to be essentially complete before the entrance to the cyclone.
Determination of Metal Behavior During the Incineration of a Contaminated Montmorillonite Clay
Eddings, E.G.; Lighty, J.S. and Kozinski, J.
Environmental Science and Technology, 28:1791, 1994. Funded by ACERC (different contract) and National Science Foundation/Presidential Young Investigators.
The goal of this study was to develop an understanding of metals behavior during thermal treatment. Clay samples, contaminated with metals to obtain a surrogate waste, were analyzed prior to and following thermal treatment using nitric acid and/or hydrogen fluoride digestion, followed by inductively coupled plasma emission spectrophotometry analysis. Techniques were used to examine particle surface and metal distribution within cross sections. Lead, cadmium, and chromium results are discussed. With hydrogen fluoride-digested samples, the results indicated that vaporization increased slightly with increasing temperature for cadmium and lead. Chromium did not show increased vaporization. At higher temperatures, the nitric acid digestions did not completely remove the metals. Scanning electron microscope pictures showed that, at higher temperatures, the particle structure became compact and glassy; the electron microprobe results indicated that lead and cadmium were located in regions with high silicon, suggesting reactions with the silicon. Chromium distribution remained uniform, suggesting that chromium was immobilized due to structural changes not reactions.
1993
Thermal Treatment of Hazardous Wastes: A Comparison of Fluidized Bed and Rotary Kiln Incineration
Rink, K.K.; Larsen, F.S.; Kozinski, J.A.; Lighty, J.S.; Silcox, G.D. and Pershing, D.W.
Energy & Fuels, 7 (6):803-814, 1993. Funded by ACERC.
Large volumes of sludge are produced by a wide variety of industrial processes and by municipal wastewater treatment. Interest in incinerating these sludges, either alone, or co-fired with other fuels, is increasing. The issues surrounding sludge incineration in rotary kilns and fluidized beds were identified through a series of pilot-scale tests using two slightly different paper mill sludges. The specific issues examined include hydrocarbon emissions, NOx emissions, and bottom and fly ash properties. A 61-cm i.d. X 61-cm long, 130-kW pilot-scale rotary kiln simulator (RKS) and a 23-cm i.d., 300-kW circulating fluidized bed combustor (CFB) were maintained at a nominal temperature of 1100 K and a stoichiometric ratio of 1.5. The rotary kiln was fed in a batch mode in order to simulate the passage of solids through a kiln. The fluidized bed was fed in both batch and continuous modes. Samples were removed from the kiln (bottom ash) and transition section (fly ash). Samples of the fluidized bed materials were removed from the bed (bottom ash) and after the cyclone (fly ash). The exhaust gases were analyzed continuous for hydrocarbons, CO, O2, NO, and CO2. This paper presents data on these analyses as well as NO conversion and ash properties. The production of NO in the RKS was dependent on the supply of nitrogen (in the sludge) and oxygen (in the gas phase), in the reactor. The availability of oxygen to the sludge was affected by the particle diameter of the sludge, the charge size, and whether a solids bed was present at the time of the incineration. In the CFB, the nitrogen-containing compounds were oxidized primarily downstream of the feedboard region, resulting in elevated levels of NO in the transition and cyclone regions. Carbon monoxide concentrations were high immediately above the bed, which led to the reduction of NO inside the freeboard zone. In both the CFB and RKS tests little unburned hydrocarbons were present in the exhaust gas streams. Formation of fly ash particles was dependent on types of incinerated material (sludge; mixture of sludge and silica sand). Bottom ash material resembled randomly organized skeletons (or cenospheric skeletons), the structure of which was independent of the type of sludge or reactor. Smaller fly ash and bottom ash particles were formed during CFB incineration experiments.