Lighty, JS

1998

Waste Incineration for Resource Recovery in Bioregenerative Life Support Systems

Fisher, J.; Pisharody, S.; Wignarajah, K.; Lighty, J.S.; Burton, B.; Edeen, M. and Davis, K.A.
28th International Conference on Environmental Systems, Danvers, Massachusetts, July 13-16, 1998

Over the last three years, the University of Utah (U of U), NASA Ames Research Center (ARC), and Reaction Engineering International (REI) have been developing an incineration system for the regeneration of components in waste materials for long-term life support systems. The system includes a fluidized bed combustor and a catalytic flue gas clean up system. An experimental version of the incinerator was built at the U of U. The incinerator was tested and modified at ARC and then operated during the Phase III human testing at NASA Johnson Space Center (JSC) during 1997. This paper presents the results of the work at the three locations: the design and testing at U of U, the testing and modification at ARC, and the integration and operation during the Phase III tests at JSC.

Trace Metals Behavior During the Thermal Treatment of Paper-Mill Sludge

Holbert, C. and Lighty, J.S.
Accepted for publication, Journal of Waste Mgt. (1998)

The objective of the present study is to investigate trace metals (Cd, Cr, and Pb) behavior during thermal treatment of sludge wastes. Paper mill sludge spiked with extraneous amounts of Cd, Cr, and Pb was subjected to different thermal regimes using two different bench-scale reactors. Metals retention in the resultant ash is discussed, as is the influence of structural modifying additives. Ash is characterized according to leachability tests to determine the environmental availability of the trace metals and provide insight as to the extent of metals immobilization within the ash matrix. The bulk of the ash appears to be supermicron particles composed of individual fragments with no evidence of localized sintering effects. Cadmium and chromium partitioning behavior is similar for both reactors, with metal retention by the ash strongly influenced by treatment temperature. Lead behavior exhibits significant differences between the two reactors. Under fully oxidizing conditions, 95 to 100% of the lead is retained by the ash and occurs as an immobilized form resistant to leaching using a strong mineral acid. Structural modifying additives did not increase metals retention or decrease metals leachability from the ash matrix. Alternatively, these additives appear to have a detrimental effect upon metals immobilization by the ash.

1997

Waste Incineration for Resource Recovery in a Regenerative Life Support System

Brouwer, J.; Kemp, G.; Heap, M.P.; Lighty, J.S.; Burton, B.; Sirdeshpande, A.; Inkley, D.; Pershing, D.W.; Fisher, J. and Pisharody, S.
Western States Section of the Combustion Institute, Spring 1997

For the last two years, the University of Utah and Reaction Engineering International, in cooperation with Ames Research Center, have been developing a waste incineration system for regenerative life support systems. The system is designed to burn inedible plant biomass and human waste. The exhaust gas is currently designed to recycle back to the plant growth chamber and will eventually be recycled to the human chamber after passing through a Trace Contaminant Control System. The incineration system, a fluidized bed reactor, has been designed for a 4-person mission. This paper will detail the design of the components of this system. In addition, results will be presented from testing at the University of Utah. Presently, the unit has been shipped to Ames Research Center for more tests prior to delivery to Johnson Space Center for testing in a 90-day, 4-person test.

Waste Incineration for Resource Recovery in a Bioregenerative Life Support System

Lighty, J.S.; Burton, B.; Sirdeshpande, A.; Inkley, D.; Pershing, D.W.; Brouwer, J.; Kemp, G.; Heap, M.P.; Fisher, J. and Pisharody, S.
27th International Conference on Environmental Systems, Lake Tahoe, Nevada, July 14-17, 1997

For the last two years, the University of Utah and Reaction Engineering International, in cooperation with NASA Ames Research Center (ARC), have been developing a waste incineration system for regenerative life support systems. The system is designed to burn inedible plant biomass and human waste. The goal is to obtain an exhaust gas clean enough to recycle to either the plant or human habitats. The incineration system, a fluidized bed reactor, has been designed for a 4-person mission. This paper will detail the design of the units. In addition, results will be presented from testing at the University of Utah. Presently, the unit has been shipped to Ames Research Center for more tests prior to delivery to Johnson Space Center for testing in a 90-day, 4-person test.

The Role of Research in Practical Incineration Systems-A Look at the Past and the Future

Lighty, J.S. and Veranth, J.M.
Twenty-Seventh Symposium (International) on Combustion, The Combustion Institute (1997)

The interaction between advances in combustion research, practical demonstrations of incineration technology, and changing regulations over the past 10 years is reviewed. The driving force behind changes in technologies for the incineration of hazardous and municipal waste is the changing regulatory climate. More stringent regulations create the need for better understanding of all aspects of the combustion process. In this review case studies are employed to demonstrate how recent advances in combustion have impacted the design and operation of memerators with special emphasis on pollutant minimization are methods for complying with proposed memerator emission standards for dioxins and furans the interaction of NOx and chlorine in incinerators and the environmental impact of solid residues from incinerators.

1996

The Formation and Control of NOx Emissions from Biomass Combustion

Pershing, D.W.; Lighty, J.S.; Harding, S.N.; Brouwer, J.; Heap, M.P.; Munro, J.M. and Winter, R.M.
Proceedings from the Finnish-Swedish Flame Days, Naantali, Finland, September, 1996. Funded by Environmental Protection Agency, US Department of Energy and National Science Foundation.

Biomass fuels account for a significant fraction of the worldwide energy usage. In 1990 consumption is believed to have exceeded 13 quads according to Tillman (1991). This does not include the combustion of peat that is known to be widely used in some northern European countries and in parts of the former Soviet Union. Biomass energy consumption is also a significant fraction of total energy usage in many developing nations. Hence, emissions from combustion of biofuels are of interest to the environmental community.

Most biomass materials generally produce lower NOx emissions when they are burned than their fossil fuel counterparts, but under certain conditions NOx emissions can be significant. Biomass fuels usually contain relatively limited amounts of organic nitrogen (often 0.1 ± 0.1%) so NOx formation from fuel nitrogen is generally small (except in the case of peat and some plant wastes). Biofuels also tend to burn at cooler combustion temperatures (due to higher moisture contents and the presence of oxygen in the fuel structure), which tends to minimize the formation of NOx by the thermal mechanism (the high temperature fixation of N2 in the combustion air).

The purpose of this paper is review the available information on the formation and the control of NOx emissions during the combustion of biofuels alone and in combination with fossil fuels and/or wastes. Both laboratory and pilot scale studies have been included, as well as full scale field test results where they are generally available.

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.

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.

Interactions of Toxic and Radioactive Metals During Thermal Treatment of Mixed Wastes

Barton, R.G.; Lighty, J.S. and Hillary, J.M.
Proceedings of the 13th International Incineration Conference, Houston, TX, May 1994.

The Idaho National Engineering Laboratory has many wastes that are candidates for thermal treatment. Some of these wastes are soils contaminated with toxic and radioactive metals. The objective of this effort was to learn more about the behavior of the metals present in wastes during thermal treatment processes. All tests were conducted using a bench-scale rotary reactor system. The system minimizes the impact of external mass and heat transfer processes and allows the study of processes intrinsic to the waste. Thus, the data generated are not specific to any single treatment device and can be easily scaled. Three groups of metals can be identified based on the behavior observed in this test program: Group 1 Lead, cadmium, and cesium; Group 2 Gadolinium, samarium, neodymium, and cerium; and Group 3 Zinc.

Group 1 metals vaporize slightly at 925ºC when no chlorine is present. Vaporization increases dramatically in the presence of chlorine. Group 2 metals also appear to vaporize slightly at 925ºC. However, their behavior did not change with the addition of chlorine. The Group 3 metal was not affected by any of the test conditions.

1993

Investigation of Incineration Characteistics of Waste Water Treatment Plant Sludge

McClennen, W.H.; Lighty, J.S.; Summit, G.D.; Gallagher, B. and Hillary, J.M.
Combustion Science & Technology, 1993 (in press). (Presented at the Third International Congress on Toxic Combustion Byproducts, Cambridge, MA, June 1993.) Funded by Kodak, Presidential Young Investigators and ACERC.

Incineration is an important disposal method for the large volumes of sludge produced by industrial and municipal wastewater treatment. This paper describes analytical methods developed for examining industrial sludge incineration processes and the dependence of potential products of incomplete combustion (PICs) on the sludge composition. A surrogate sludge was developed from peat, calcium and iron salts, and a waste water-treatment polymer suspension to simulate incineration characteristics of the real sludge while allowing for controlled variation of its composition. Experiments were conduced under both oxidative and pyrolysis conditions, in reactor systems ranging from microscale up to bench scale with on-line analytical instrumentation. The organic products emitted from the surrogate were quite similar to those of the sludge, with the exception of products from certain synthetic polymers. Significant quantities of aromatic hydrocarbons were emitted from the combustion of cellulosic and lignin fractions of the material even without the presence of those specific compounds in the original waste. The presence of the metal salts and the additional water they retained significantly affected the peak hydrocarbon concentration by delaying the onset of emissions and lengthening their duration. The amount of polystyrene and polymethylmethacrylate in the real sludge made their decomposition products important potential PICs, which would need further combustion.

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.

1992

Solid Waste Incineration in Rotary Kilns

Pershing, D.W.; Lighty, J.S.; Silcox, G.D.; Heap, M.P. and Owens, W.D.
Combustion Science and Technology, 1992 (in press). (Previously presented at the First International Conference on Combustion Technologies for a Clean Environment, Vilamoura, Portugal, September 1991.) Funded by the National Science Foundation, Environmental Protection Agency, Gas Research Institute and ACERC.

Rotary kilns are used to dispose of many solid wastes and sludges and to thermally treat contaminated soils. In this communication the fates of hydrocarbon and metal species are examined with a view toward optimization of new kiln designs and maximizing existing unit throughout while minimizing pollutant emissions. Initially, process fundamentals are considered to characterize the controlling phenomena. Pilot- and large-scale data are then examined to define practical system complexities. Finally, techniques for data scale-up and performance prediction are summarized. Temperature is clearly the most important parameter with respect to the fate of both metal and hydrocarbon species; hence, heat transfer is often rate limiting. High temperatures favor hydrocarbon evolution, but can also enhance the formation of toxic metal fumes. Both the solid composition and the moisture content can significantly influence the time at temperature required for hydrocarbon destruction and metal vaporization.

Improving bed mixing helps contaminant release but can also aggravate puffing tendencies with batch charging. Full-scale performance predictions currently require a combination of small-scale data and computer modeling. Future work needs to focus on verification of large-scale predictions for complex mixtures and sludges so that expensive trial burns can be minimized.

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.

Fundamental Studies of Metal Behavior During Solids Incineration

Eddings, E.G. and Lighty, J.S.
Combustion Science and Technology, 85:375-390, 1992. Funded by National Science Foundation, Gas Research Institute and ACERC.

An experimental apparatus was constructed which allows investigation of the vaporization behavior of metal contaminants during incineration of their host substrate. Comparisons were made between equilibrium predictions and experimental observations for a number of different metals in chlorinated, inert, and reducing environments between 150ºC and 650ºC.

The equilibrium predictions for Pb vaporization were found to show the greatest deviation from experimental observations. Comparisons showed that a knowledge of elements associated with the initial metal species, as well as omission of PbCl4 from the calculations, can be important for the equilibrium predictions. Experimental results showed that the formation of volatile PbCl4 predicted by equilibrium was not kinetically favorable under the conditions studied. Subsequent vaporization studies involving PbCl2 deposited on a silica substrate demonstrated an influence of initial concentration on the amount of Pb vaporization observed. The extent of vaporization appeared to be independent of a moderate increase in temperature and an increase in the time allowed for vaporization.

Evolution of Metal Contaminants from Incinerated Solids

Eddings, E.G. and Lighty, J.S.
Air Toxic Reduction and Combustion Modeling, 15:69-78, 1992. (Also presented at the ASME International Joint Power Generation Conference, Atlanta, GA, 1992). Funded by National Science Foundation-Presidential Young Investigators, Gas Research Institute and ACERC.

The vaporization behavior of metal contaminants was studied in both a bench-scale and pilot-scale reactor. The results of bench-scale experiments indicated that the behavior of metal contaminants at low concentrations on solid substrates can be very different from the pure component behavior of the metal contaminant.

Pilot-scale studies focused on characterizing the behavior of metal contaminants at low concentrations in a batch rotary kiln environment. Solid samples of the contaminated clay bed material were removed from the kiln at various intervals providing data for the concentration of chromium, cadmium, copper, barium, lead, zinc, and strontium in the clay material over time. The resulting evolution plots indicated that after an initial drop in concentration, a temperature dependent, pseudo-equilibrium concentration was maintained in the batch rotary kiln simulator. Further processing for time up to 2 hours did not result in additional vaporization. In addition, different initial metal contamination solutions were used in the pilot-scale experiment including nitrate, chloride, and sulfate solutions of the contaminant metals and the results indicated essentially the same vaporization behavior for most all of the metals regardless of the initial spiking solution.

1991

Rotary Kiln Incineration: Comparison and Scaling of Field-Scale Contaminant Evolution Rates from Sorbent Beds

Lester, T.W.; Cundy, V.A.; Sterling, A.M.; Montestruc, A.N.; Jakway, A.J.; Lu, C.; Leger, C.B.; Pershing D.W.; Lighty, J.S.; Silcox, G.D. and Owens, W.D.
Environmental Science Technology, 25:1142-1152, 1991. Funded by Environmental Protection Agency, Louisiana State University/Hazardous Waste Research Center and ACERC.

A comparison is made, for the first time, between the evolution of hydrocarbons from clay sorbent beds in a field-scale rotary kiln incinerator and in a pilot-scale rotary kiln simulator. To relate the data from the different sized units, due allowance is made for bed dynamical similitude, bed geometrical factors, and bed heat-up. To minimize the effects of disturbances caused by foreign matter in the field scale bed and differences in loading techniques, the rate of evolution is characterized by an "evolution interval" defined as the time required for the middle 80% of the ultimate containment evolution to occur. A comparison of evolution intervals with reciprocal bed temperature reveals that the data are consistent with an analysis that assumes a uniform bed temperature (at any instant of time) and desorption controlled evolution rate. Furthermore, the evolution intervals scale inversely with a modified Froude Number, which characterizes bed dynamics. The success in comparing field and simulator results indicates that pilot scale rotary kilns may be used to simulate certain features of industrial-scale units if dynamical, geometrical and thermal parameters are matched appropriately.

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.

Solid Waste Incineration in Rotary Kilns

Pershing, D.W.; Lighty, J.S.; Silcox, G.D.; Heap, M.P. and Owens, W.D.
First International Conference on Combustion Technologies for a Clean Environment, Vilamoura, Portugal, September 1991. Funded by the National Science Foundation, Environmental Protection Agency, Gas Research Institute and ACERC.

Rotary kilns are used to dispose of many solid wastes and sludges and to thermally treat contaminated soils. In this communication the fates of hydrocarbon and metal species are examined with a view toward optimization of new kiln designs and maximizing existing unit throughout while minimizing pollutant emissions. Initially, process fundamentals are considered to characterize the controlling phenomena. Pilot- and large-scale data are then examined to define practical system complexities. Finally, techniques for data scale-up and performance prediction are summarized. Temperature is clearly the most important parameter with respect to the fate of both metal and hydrocarbon species; hence, heat transfer is often rate limiting. High temperatures favor hydrocarbon evolution, but can also enhance the formation of toxic metal fumes. Both the solid composition and the moisture content can significantly influence the time at temperature required for hydrocarbon destruction and metal vaporization.

Improving bed mixing helps contaminant release but can also aggravate puffing tendencies with batch charging. Full-scale performance predictions currently require a combination of small-scale data and computer modeling. Future work needs to focus on verification of large-scale predictions for complex mixtures and sludges so that expensive trial burns can be minimized.

The Application of a Mobile Ion Trap Mass Spectrometer System to Environmental Screening and Monitoring

McClennen, W.H.; Arnold, N.S.; Meuzelaar, H.L.C.; Ludwig, E. and Lighty, J.S.
2nd International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, Las Vegas, NV, February 1991. Funded by ACERC, Environmental Protection Agency, Finnigan MAT Corp., US Army Chemical Research Development and Engineering Center and Utah Power and Light.

This paper presents examples of the use of a mobile Ion Trap Mass Spectrometer (ITMS, Finnigan MAT) for on-site environmental screening and monitoring of vapors by gas chromatography/mass spectrometry (GC/MS). The instrument is built around a miniaturized ITMS system, with a novel direct vapor-sampling inlet and coupled to a high-speed transfer line GC column (short capillary column with fixed pressure drop). The column is temperature controlled inside the standard ion trap transfer line housing. This provides for high-speed analyses at 10-60 s intervals using an automated sampling system constructed with only inert materials in the sample path.

Specific laboratory and field applications exemplify key characteristics of the system including sensitivity, specificity for a broad range of compounds, ruggedness for field-testing in harsh environments, and general speed for field-testing in harsh environments, and general speed and versatility of the analytical technique. The system has been calibrated for alkylbenzenes at concentrations as low as 4 ppb in air and used to monitor these compounds in an office space. Both the MINITMASS and a simpler Ion Trap Detector (ITD) based system have been used to monitor organic vapors from acetone through 5 ring polycyclic aromatic hydrocarbons produced in laboratory scale reactors for studying the thermal desorption and incinerations of hazardous wastes. The ruggedness of the MINITMASS system has been demonstrated by vapor sampling in the Utah summer desert and at a 600 MW coal fired power plant. Finally, the analysis speed and versatility are described for vapor monitoring of volatile organic compounds at an EPA national priority list waste site.

Behavior of Metals During Incineration of Solids

Eddings, E.G. and Lighty, J.S.
Western States Section/The Combustion Institute, Los Angeles, CA, October 1991. Funded by National Science Foundation.

Metal vaporization experiments were carried out in a bench-scale, Differential-Bed Reactor to identify possible inconsistencies between experimental behavior and predictions based on equilibrium considerations. It was found that, under the conditions investigated, the equilibrium model accurately reflected the behavior of Cr, Ni, and Zn, but there was disagreement between the model and the experimental behavior of Pb and Cu. Pb predictions were improved by including information about elements associated with the particular species of Pb present on the waste and by omitting volatile PbCl4 from the calculations.

Detailed experiments of Pb behavior exhibited a strong binding effect of the solid substrate at low concentrations of PbCl2 preventing volatile behavior at temperatures expected to promote vaporization. A surface effect was also noted with experiments involving Cu; however, the effect was to actually enhance the vaporization of CuSO4 at low concentrations in the solid substrate relative to its behavior at high concentrations. The combined effects resulted in overprediction of Pb volatility and underprediction of Cu volatility by the equilibrium model.

1990

Development of Novel, Mass Spectrometric Combustion Monitoring Techniques

McClennen, W.H.; Arnold, N.S.; Sheya, S.A.N.; Lighty, J.S. and Meuzelaar, H.L.C.
Preprints for Papers Presented at the 200th ACS National Meeting, 35 (3), 713-720, Washington, D.C., 1990. Funded by ACERC.

An on-line gas and vapor analysis method has been developed to monitor combustion products by short column ("transfer line") Gas Chromatography/Mass Spectrometry. An automated vapor-sampling inlet with only inert materials (quartz and fused silica) in the sample path is utilized to introduce flue gases into a 1 m long "transfer line" capillary GC column for rapid, repetitive chromatographic separation of products. The column effluent is introduced directly into the source of an ion trap type mass spectrometer. Combustion products from a gas fired rotary kiln were monitored by this method using a standard Ion Trap Detector (ITD). Detection limits of 20 to 50 ppb were obtained for various substituted benzenes. Monitoring of polycyclic aromatic hydrocarbons (PAHs) from the thermal desorption of contaminated soils in a fixed bed reactor utilized a modified Ion Trap Mass Spectrometer (ITMS). Varying isothermal column temperature allowed analysis of PAHs from naphthalene through 6 ring PAHs. The ITMS system provides higher sensitivity (~4 ppb for benzene) in addition to tandem MS and chemical ionization capabilities for unambiguous identification of combustion products incompletely resolved by the transfer line GC approach.

Fundamentals for the Thermal Remediation of Contaminated Soils - Particle and Bed Desorption Models

Lighty, J.S.; Silcox, G.D.; Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Environmental Science & Technology, 24 (5), 750-757, 1990. Funded by the Gas Research Institute, Dave Linz, Project Manager, NSF - Presidential Young Investigator Program, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.

A major research effort has been initiated to characterize the rate-controlling processes associated with the evolution of hazardous materials from soils. A threefold experimental approach is being used in conjunction with computer modeling to analyze thermal desorption of contaminants. Phenomena occurring both inside particles (intraparticle) and with a bed of particles (interparticle) were studied.

The results obtained suggest that the most important process variable are local thermal environment and gas-phase contaminant concentration because the adsorption equilibrium characteristics of the contaminant/soil pair control the desorption of contaminant from a particle at a given temperature. A mass-transfer/desorption model, which assumes gas/solid equilibrium at all points and time, is proposed and the model was found to predict the measured temperature dependence.

Fast, Repetitive GC/MS Analysis of Thermally Desorbed Polycyclic Aromatic Hydrocarbons (PAHs) from Contaminated Soils

McClennen, W.H.; Arnold, N.S.; Roberts, K.A.; Meuzelaar, H.L.C.; Lighty, J.S. and Lindgren, E.R.
Combustion Science and Technology, 1990 (In press). Sponsored by Remediation Technology, Gas Research Institute, ACERC, Finnigan Corp. and IT Corporation.

A system for on-line analysis of organic vapors by short column gas chromatography/mass spectrometry (GC/MS) has been used to monitor products from a thermal soil desorption reactor. The system consists of a unique air-sampling inlet with a 1-meter long capillary column coupled directly to a modified Ion Trap Mass Spectrometer (Finnigan MAT) with demonstrated detection limits for alkylbenzenes in the low ppb range. In this work the mobile instrument is used for repetitive GC/MS and GC/MS (tandem MS) analysis at 30 to 60 sec intervals of PAH products from coal tar contaminated soils in a bed characterization reactor.

Results for napthalene through dibenzanthracenes are compared to conventional, more detailed GC/MS analyses of extracts from the soil before and after thermal treatment.

A combustion map of burnout values was made using the laboratory nozzle at an A/S of 0.7, swirl number of 1.5 and SR of 1.1.

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.

Rotary Kiln Incineration: Comparison of Field and Pilot Scale Measurements of Contaminant Evolution Rates from Sorbent Beds

Lester, T.W.; Cundy, V.A.; Sterling, A.M.; Montestruc, A.N.; Jakway, A.J.; Leger, C.B.; Pershing D.W.; Lighty, J.S.; Silcox, G.D. and Owens, W.D.
Environmental Science Technology, 1990. Funded by Environmental Protection Agency and Louisiana State University Hazardous Waste Research Center.

A comparison is made, for the first time, between the evolution of hydrocarbons from sorbent beds in an industrial rotary kiln incinerator and in a laboratory scale rotary kiln simulator. To relate the data from the different sized units, due allowance is made for bed dynamical similitude, bed geometrical factors, and bed heat-up. To minimize the effects of disturbances caused by foreign matter in the full scale bed and differences in loading techniques, the rate of evolution is characterized by an "evolution interval," that is defined as the time required for total hydrocarbon evolution at the maximum evolution rate. A comparison of evolution intervals with reciprocal bed temperature reveals that the data are consistent with an analysis that assumes a uniform bed temperature (at any instant of time) and desorption control of the evolution rate. Furthermore, the evolution intervals scale inversely with modified Froude Number, which characterizes bed dynamics. The success in comparing field and simulator results indicates that pilot scale rotary kilns may be used to simulate certain features of industrial scale units if appropriate care is taken in matching dynamical, geometrical and thermal parameters.

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

Fundamental Experiments on Thermal Desorption of Contaminants from Soils

Lighty, J.S.; Silcox, G.D.; Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Environmental Progress, 8 (1), 1989. Funded by the Gas Research Institute, Dave Linz, Project Manager, National Science Foundation - Presidential Young Investigator Program, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.

The goals of this research are to develop an understanding of the transport phenomena that occur during the desorption of contaminants from soil and to obtain rate information. This information can then be used to develop a model to predict the performance of full-scale thermal treatment systems for optimization and cost reduction.

Rotary Kiln Incineration--Combustion Chamber Dynamics

Cundy, V.A.; Lester, T.W.; Leger, C.B.; Miller, G.; Montestruc, A.N.; Acharya, S.; Sterling, A.M.; Pershing, D.W.; Lighty, J.S.; Silcox, G.D. and Owens, W.D.
Journal of Hazardous Materials, 22, 195-219,1989. Funded by US Environmental Proctection Agency and ACERC (National Science Foundation and Associates and Affiliates).

A multifaceted experimental and theoretical program aimed at understanding rotary kiln performance is underway. The overall program involves university, industry, and government participation and is broken into distinct sub-programs. This paper discusses in some detail the research effort performed to date in two of the sub-programs: Full-scale in situ sampling and kiln-simulator experimentation. Full-scale in situ measurements are obtained from the Louisiana Division rotary kiln facility of Dow Chemical USA, located in Plaquemine, Louisiana. Summary results obtained from controlled experiments that were performed during continuous processing of carbon tetrachloride and preliminary results obtained during batch mode processing of toluene-laden sorbent packs are presented. Kiln-simulator data are obtained by using the facilities of the Chemical Engineering Department at the University of Utah. Recent kiln-simulator work, conducted in support of the full-scale measurements sub-program, has aided in providing an understanding of the results that have been obtained at the full-scale. Modeling efforts, conducted at Louisiana State University and the University of Utah, have concentrated on the development of realistic, fluid-flow and heat-transfer models, near-term chlorinated kinetic models and bed mass-transfer models to be incorporated into a global three-dimensional kiln-simulator model. The paper concludes with an overview of these modeling efforts.

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.

Monitoring the Evolution of Organic Compounds from the Thermal Treatment of Contaminated Soil Samples Using Short Column GC/MS

McClennen, W.H.; Arnold, N.S.; Lighty, J.S.; Eddings, E.G.; Lindgren, E.R.; Roberts, K.A. and Meuzelaar, H.L.C.
Preprints of Papers Presented at the 198th ACS National Meeting, 34 (3), Miami Beach, Florida, 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.

Incineration is an effective technology for the remediation of organic chemical contaminated wastes. For solid wastes, such as contaminated soils, processes involving separate stages of a primary desorber and secondary afterburner are particularly useful. The desorption stage is currently being modeled using a particle-characterization reactor (PCR, 0-500 g capacity), a bed-characterization reactor (BCR, 0.5-5 kg), and a rotary kiln simulator (2-15 kg) to study fundamental processes such as mass transfer, heat transfer, and volatilization of contaminants. This paper describes the analytical methods and preliminary results from monitoring the evolution of organic compounds in these and smaller reactors.

The samples are soil contaminated with a broad range of polynuclear aromatic (PNA) hydrocarbons such as those derived from coal tars. The analytical methods primarily involve mass spectrometry (MS) with a variety of sample introduction techniques. The on-going analyses include solvent and thermal extractions of soil before and after various thermal treatments as well as on-line monitoring of vapors during desorption.

Fast, Repetitive GC/MS Analysis of Thermally Desorbed Polycyclic Aromatic Hydrocarbons (PAHs) from Contaminated Soils

McClennen, W.H.; Arnold, N.S.; Roberts, K.A.; Meuzelaar, H.L.C.; Lighty, J.S. and Lindgren, E.R.
1st International Congress on Toxic Combustion, 1989. Funded by Remediation Technologies, the Gas Research Institute, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.

A system for on-line analysis of organic vapors by short column gas chromatography/mass spectrometry (CG/MS) has been used to monitor products from a thermal soil desorption reactor. The system consists of a unique air-sampling inlet with a 1 meter long capillary column coupled directly to a modified Ion Trap Mass Spectrometer (Finnigan MAT) with demonstrated detection limits for alkylbenzenes in the low ppb range. In this work the mobile instrument is used for repetitive GC/MS and GC/MSn (tandem MS) analysis at 30 to 60 sec intervals of PAH products from coal tar contaminated soils in a bed characterization reactor.

Results for naphthalene through dibenzanthracenes are compared to conventional, more detailed GC/MS analyses of extracts from the soil before and after thermal treatment.

An In-Depth Study of Incineration - Rotary Kiln Performance Characterization

Cundy, V.A.; Lester, T.W.; Conway, L.R.; Jakway, A.J.; Leger, C.B.; Montestruc, A.N.; Acharya, S.; Sterling, A.M.; Owens, W.D.; Lighty, J.S.; Pershing, D.W. and Silcox, G.D.
Louisiana State University/Hazardous Waste Research Center SAC Review Meeting, Baton Rouge, Louisiana, 1989. Funded by Louisiana State University/Hazardous Waste Research Center (Supported by US Environmental Protection Agency).

A comprehensive study aimed at understanding rotary kiln performance is underway. The program is led by personnel from Louisiana State University. Bench and pilot-scale facilities at the University of Utah are available for use in solids desorption studies. Full-scale in situ measurements are obtained from the Louisiana Division rotary kiln facility of Dow Chemical USA, located in Plaquemine, Louisiana. This paper presents a summary of the project providing some detail of the work that has been accomplished from 1 January through 31 August 1989.

Fast, Repetitive GC/MS Analysis of Thermally Desorbed Polycyclic Aromatic Hydrocarbons (PAHs) from Contaminated Soils

McClennen, W.H.; Arnold, N.S.; Roberts, K.A.; Meuzelaar, H.L.C.; Lighty, J.S. and Lindgren, E.R.
1st International Congress on Toxic Combustion, 1989. Funded by Remediation Technologies, the Gas Research Institute, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.

A system for on-line analysis of organic vapors by short column gas chromatography/mass spectrometry (CG/MS) has been used to monitor products from a thermal soil desorption reactor. The system consists of a unique air-sampling inlet with a 1 meter long capillary column coupled directly to a modified Ion Trap Mass Spectrometer (Finnigan MAT) with demonstrated detection limits for alkylbenzenes in the low ppb range. In this work the mobile instrument is used for repetitive GC/MS and GC/MSn (tandem MS) analysis at 30 to 60 sec intervals of PAH products from coal tar contaminated soils in a bed characterization reactor.

Results for naphthalene through dibenzanthracenes are compared to conventional, more detailed GC/MS analyses of extracts from the soil before and after thermal treatment.

Fundamentals for the Thermal Remediation of Contaminated Soils - Particle and Bed Desorption Models

Lighty, J.S.; Silcox, G.D.; Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Accepted for publication in Environ. Science Tech., 1989. Funded by the Gas Research Institute, Dave Linz, Project Manager, National Science Foundation/Presidential Young Investigators, ACERC (National Science Foundation and Associates and Affiliates), the State of Utah, and US Department of Energy.

A major research effort has been initiated to characterize the rate-controlling processes associated with the evolution of hazardous materials from soils. A threefold experimental approach is being used in conjunction with computer modeling to analyze thermal desorption of contaminants. Phenomena occurring both inside particles (intraparticle) and with a bed of particles (interparticle) were studied.

The results obtained suggest that the most important process variables are local thermal environment and gas-phase contaminant concentration because the adsorption equilibrium characteristics of the contaminant/soil pair control the desorption of contaminant from a particle at a given temperature. A mass-transfer/desorption model, which assumes gas/solid equilibrium at all points and time, is proposed and the model was found to predict the measured temperature dependence.

1988-1987

Transport Fundamentals for the Thermal Remediation of Contaminated Soils

Lighty, J.S.; Silcox, G.D.; Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Submitted for Review to AIChE Journal, 1988. 23 pgs. Funded by Gas Research Institute, ACERC (National Science Foundation and Associates and Affiliates), and National Science Foundation/Presidential Young Investigators.

A major research effort has been initiated to characterize the transport phenomena associated with the evolution of hazardous materials from contaminated soils. A threefold experimental approach is being used in conjunction with computer modeling to analyze thermal desorption of contaminants from soils under a variety of experimental conditions. First, a particle-characterization reactor (PCR) is being employed to characterize intraparticle transport under conditions where the bulk concentration and temperature at the particle surface are known. Secondly, a packed-bed reactor is being used to examine interparticle transport within a bed of particles. In the third portion of the work, a 73 kW pilot-scale rotary kiln is providing time-resolved measurements of the species evolution. The results from the PCR experiments and modeling are reported in this manuscript.

The PCR experimental results obtained suggest that the most important process variable is local thermal environment and that the absorption characteristics of the contaminant/soil pair are important in the desorption process. The adsorption characteristics are a function of local temperature, thus accounting for the steep dependence of the cleanup efficiency of a soil on temperature. In addition, the adsorption characteristics are influenced by soil type and moisture; it has been found that these parameters also effect desorption of contaminants. A mass-transfer model, which assumes gas/solid equilibrium at all points and times, is proposed and the model predictions were found to exhibit temperature dependence similar to the data.

Characterization of Thermal Desorption Phenomena for the Clean-Up of Contaminated Soil

Lighty, J.S.; Pershing, D.W.; Cundy, V.A. and Linz, D.G.
Accepted for Nuclear & Chemical Waste Management, 1987. 32 pgs. Funded by ACERC (National Science Foundation and Associates and Affiliates).

The overall goal of this research is to develop an understanding of the fundamental transport phenomena associated with the evolution of hazardous materials from solids, in particular contaminated soils. At the present time, incineration is a relatively costly alternative for the clean up of contaminated soils. An understanding of the mass transfer and heat transfer limitations might lead to a more economical option, where the contaminants are desorbed from the soil at lower temperatures in a primary combustor and then a secondary, high temperature combustor (afterburner) decomposes the hazardous off-gases. This work is aimed at providing fundamental rate information which will be used to model thermal desorption of contaminants from soils under a variety of thermal conditions, soil properties and contaminants.

The experimental approach is threefold. First, a bench scale particle characterization reactor (PCR) has been developed and is being used to characterize intraparticle transport under conditions where the bulk concentration and temperature at the particle surface are known. Following these studies, a packed-bed reactor will be used to examine interparticle transport within a well-characterized bed of particles. In the third portion of the work, a 73 kW pilot-scale rotary kiln will be used to obtain time resolved measurements of trace species evolution. This paper reports recent PCR results that indicate that soil properties, type of contaminant, and temperature are important in desorption of contaminants from soil particles.

The overall goal of this research is to develop an understanding of the fundamental transport phenomena associated with the evolution of hazardous materials from solids, in particular contaminated soils. At the present time, incineration is a relatively costly alternative for the clean up of contaminated soils and it may render the soil inert. A more economical option is to desorb the contaminants from the soil at lower temperatures and then use high temperature incineration to decompose the hazardous off-gases. This work is aimed at providing fundamental rate information which may be used to model the thermal desorption of contaminants from soils under a wide variety of thermal conditions.

The experimental approach is three-fold. First, a bench-scale particle characterization reactor (PCR) has been developed and is being used to characterize intraparticle transport under conditions where the bulk concentration and temperature at the particle surface are known. Following these studies, a packed bed reactor will be used to examine interparticle transport within a well-characterized bed of particles. In the third portion of the work, a 73,000 Watt pilot-scale rotary kiln will be used to reports recent PCR and kiln results; it does not address the packed bed reactor studies since they are just being initiated. The PCR results indicate that soil pore structure is important in desorption of contaminants from soil particles and that the desorption/diffusion step is probably a controlling mechanism.

The Clean Up of Contaminated Soil By Thermal Desorption

Lighty, J.S.; Pershing, D.W.; Cundy, V.A.; Groves, F.R. Jr. and Linz, D.G.
Proc. 2nd Int. Conf. on New Frontiers in Hazardous Waste Management, 1987, NUS, Pittsburgh, PA. 10 pgs. Funded by Gas Research Institute, National Science Foundation, and ACERC (National Science Foundation and Associates and Affiliates).

The overall goal of this research is to develop an understanding of the fundamental transport phenomena associated with the evolution of hazardous materials from solids, in particular, contaminated soils. At the present time, incineration is a relatively costly alternative for the clean up of contaminated soils and it may render the soil inert. A more economical option is to desorb the contaminants from the soil at lower temperatures and then use high temperature incineration to decompose the hazardous off-gases. This work is aimed at providing fundamental rate information which may be used to model the thermal desorption of contaminants from soils under a wide variety of thermal conditions.

The experimental approach is threefold First, a bench-scale particle characterization reactor (PCR) has been developed and is being used to characterize intraparticle transport under conditions where the bulk concentration and temperature at the particle surface are known. Following these studies, a packed bed reactor will be used to examine interparticle transport within a well-characterized bed of particles. In the third portion of the work, a 73,000 Watt pilot-scale rotary kiln will be used to obtain time resolved measurements of trace species evolution. This paper reports recent PCR and kiln results; it does not address the packed bed reactor studies since they are just being initiated. The PCR results indicate that soil pore structure is important in desorption of contaminants from soil particles and that the desorption/diffusion step is probably a controlling mechanism.

Fundamentals of Hazardous Solid Waste Incineration in a Rotary Kiln Environment

Lighty, J.S.; Silcox, G.D.; Britt, R.; Owens, W.D.; Pershing, D.W. and Cundy, V.A.
Proc. AFRC Int'l. Symposium on Waste Incineration, 1987, Palm Springs. Funded by Environmental Protection Agency.

With landfill costs increasing and regulations on landfilling becoming more stringent, alternatives to conventional hazardous waste treatment strategies are becoming more desirable. Incineration is presently a permanent, proven solution for the disposal of most organic contaminants, but also a costly one, especially in the case of solids that require some auxiliary fuel. The goal of this research is to develop an understanding of the phenomena associated with the evolution of contaminants from solids in the primary combustor of an incineration system. A threefold approach has been used. First, a bench-scale Particle Characterization Reactor was developed to study the transport phenomena on a particle basis, where the controlling processes are mainly intraparticle. Second, a Bed Characterization Reactor was built to examine the controlling transport phenomena within a bed of particles, where the processes are primarily interparticle. The results of these studies can be applied to any primary combustor. Finally a pilot-scale rotary kiln was developed to study the evolution of contaminants from solids within a realistic temperature and rotation environment.

This paper describes results obtained in a study using a commercial sorbent contaminated with toluene. The data are from the Particle Characterization Reactor and the Rotary-Kiln Simulator. The results show that the method of contamination and charge size does not have a large effect on desorption, while temperature and contaminant concentration are important parameters in the evolution of contaminants in a rotary kiln. Preliminary modeling efforts for the kiln are also discussed.