ACERC
Abstracts - 1992 |
ACERC
Abstracts - 1992 |
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Thrust Area 3: Pollutant Formation/Control and Waste Incineration |
Eddings, E.G.
Behavior of Metal Contaminants during the Incineration of Solid Wastes,
Ph.D./U of U, June 1992. Advisor: Lighty
Keyes, B.R.
A Fundamental Study of the Thermal Desorption of Organic Wastes from Montmorillonite
Clay Particles, Ph.D./U of U, August 1992, Advisor: Silcox
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.
Gopalakrishnan, R.; Stafford,
P.R.; Davidson, J.E.; Hecker, W.C. and Bartholomew, C.H.
Applied Catalysis, 1992 (in press). (Also presented at the Seventh
Annual Symposium of the Western States Catalysis Club, Albuquerque, NM,
March 1992 and at the American Institute of Chemical Engineers Annual Meeting,
Miami Beach, FL, November 1992). Funded by Shell and Brigham Young University.
Selective catalytic reduction of NO with propane and oxygen was investigated on Cu-exchanged ZSM-5, mordenite, X-type and Y-type zeolites at temperatures in the range of 200 to 600ºC. Catalytic activities of Cu-X and Cu-Y are negligible, activity of Cu-mordenite moderate, and that of Cu-ZSM-5 very high, converting >90% of NO to N2 at 400ºC and at a space velocity of 102,300/hr. Effects of space velocity, NO concentration, C3H8/NO ratio, oxygen concentration, and water vapor on the activities of Cu-ZSM-5 and Cu-mordenite were investigated. NO conversion decreases with increasing space velocity, decreasing propane and NO concentrations, and decreasing propane/NO ratio. Water vapor decreases the activity significantly at all temperatures. At temperatures above 400ºC, propane oxidation by oxygen is a significant competing reaction in decreasing the selectivity for NO reduction. The results indicate that Cu-ZSM-5 is a promising catalyst for SCR of NO by hydrocarbons.
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.
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.
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.
Snyder, A.P.; Harden, C.S.;
Brittain, A.H.; Kim, M.-G.; Arnold, N.S. and Meuzelaar, H.L.C
Analytical Chemistry, 1992 (in press). (Also included in American Laboratory,
October:32B, 1992). Funded by US Army/Chemical Research Development and Engineering
Center.
The general applicability of gas chromatography (GC) in combination with its reliability, to more complex chemical mixtures has made this technology particularly valuable in environmental and medical applications. Such monitoring are conducted in laboratory settings, in mobile field laboratories, and increasingly, in the field with hand-held portable analyzers. Hand-held systems have made significant technical gains in recent years to complement existing logistical attractions of coat and speed of analysis.
Ion mobility spectrometry (IMS) is an attractive technique in conjunction with GC for the determination of constituents in a mixture. The analyses of mixtures of amines, alcohols, and, in particular, the drug solvents performed in this study illustrate the effectiveness of IMS as a true additional dimension of detection for a GC system. Significant advantages to rapid screening, detection, and identification of both indoor and outdoor scenarios can be realized with the GC-IMS concept as a hand-held portable device.
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.
Dworzanski, J.P.; Chapman,
J.; Meuzelaar, H.L.C. and Lander, H.R.
ACS National Meeting, San Francisco, CA, April 1992). Funded by Rocketdyne
and ACERC.
Detailed knowledge of the thermal stability and pyrolytic degradation of jet fuels will play an important role in the design of advanced hypersonic (mach 5-8) aircraft systems making use of an endothermic reaction of the fuel prior to combustion (1). However, after decades of study fundamental processes leading to deposition of solid materials on fuel system components and thermal decomposition of fuels are not fully understood, largely due to the complexity of the processes involved which include fuel degradation chemistry, heat transfer and fluid mechanics.
Therefore, in our laboratory, new systems for pyrolytic degradation studies of jet fuels have been developed based on microscale laboratory reactors for the gas phase and liquid phase pyrolysis coupled directly to a doubly "hyphenated" analytical system consisting of a Hewlett-Packard has chromatograph/mass spectrometer/infrared spectrometer (GC/MS/IR) combination.
Dworzanski, J.P.; Huai,
H.; Arnold, N.S. and Meuzelaar, H.L.C.
Proceedings of the Fortieth ASMS Conference on Mass Spectrometry and Allied
Topics, 762-767, Washington, DC, 1992. Funded by Consortium for Fossil Fuel
Liquefaction, Rocketdyne and ACERC.
The growing demand for real-time monitoring of industrial processes performed in reactors under conditions of high pressure and temperature indicates that MS technology, especially in combination with GC preseparation potential could fulfill many current requirements. To achieve these goals we have expanded the application of our valveless vapor sampling inlet for on-line analysis of atmospheric gases and vapors by "transfer line" GC/MS to monitor chemical processes at high pressures (1000-2000 psi) through the construction of a special capillary restrictor to reduce the pressure to near ambient conditions. The restrictor effluent is coupled to the automatic vapor-sampling inlet via a dilution chamber. This allows repetitive GC/MS analyses to be obtained at 1-15 minute intervals.
Kinetic parameters and yields of primary and secondary decomposition products of jet fuels as well as model compounds in coal liquefaction processes have been obtained in a fraction of time needed for conventional off-line measurements and indicate that the proposed approach may be easily applied to a broad range of existing reactor types and potential processing environments.
Huai, H.; Tsai, C.H.; Shabtai,
J.S. and Meuzelaar, H.L.C.
ACS Division of Fuel Chemistry Preprints, 37(2):925-932, 1992 (203rd
ACS National Meeting, San Francisco, CA, April 1992). Funded by Consortium
for Fossil Fuel Liquefaction.
Direct coal liquefaction involves complex and insufficiently defined chemical reactions. In order to improve direct coal liquefaction processes, it is necessary to improve our understanding of key chemical reactions. Unfortunately, due to the high pressure and high temperature requirements of most coal liquefaction processes, real-time on-line reaction monitoring by advanced spectroscopic and/or chromatographic techniques has generally been impossible until now. Thus, relatively little is known about the precise reaction pathways as well as the intermediate reaction products involved. This is particularly true for conversion reactions carried out in batch reactors such as autoclaves. Due to the relatively long residence times primary reaction products formed in batch type autoclaves are quite susceptible to secondary, or even tertiary reactions. Consequently, real-time on-line monitoring experiments are needed to elucidate reaction pathways in autoclaves.
Although several on-line systems have been developed for coal conversion at near-ambient pressure or high vacuum conditions, there are no repots of on-line chromatography/spectroscopy based systems built for monitoring high-pressure conversion reactions. Therefore, the development of a direct GC/MS interface for near-real time analysis of high-pressure reaction products, while minimally disturbing the reaction process, has been undertaken in our laboratory.
It is well established that coal contains fused aromatic and hydroaromatic ring clusters, composed of an average of two to tour condensed ring units, connected by various alkylene, ether, sulfide and direct (Ar)C-C(Ar) bridges. Liquefaction reactions are primarily thought to involve these connecting bridges, especially ether linkages and alkylene linkages. In recent years, a number of workers have subjected coal-model compounds to various coal conversion conditions in order to confirm that certain coal structures are reactive during coal conversion and to infer the conversion mechanisms of real coals from mechanisms determined for such compounds.
The present paper reports the design and testing of a newly developed on-line GC/MS monitoring system for high pressure reactions and its application to the investigation of hydrogenation and hydrodeoxygenation (HDO) of model compounds, such as diphenyl methane and dibenzyl ether, under both catalytic and thermal conditions.
Arnold, N.S.; Kim, M.-G.;
McClennen, W.H. and Dworzanski, J.P.
Workshop on Ion Mobility Spectrometry, Mescalaro, AZ, June 1992. Funded
by US Army/Chemical Research Development and Engineering Center.
An automated vapor sampling (AVS) device has proved powerful for atmospheric (and other) vapor sampling applications when coupled with the "preseparation" available via rapid transfer line gas chromatography (TLGC) prior to detection by a "smart" detector. Initial applications of AVS TLGC utilized mass spectrometric (MS) detection along with rapid repetitive sampling to monitor on-line test reactors and industrial processes. Subsequent work extended this technique to AVS TLGC/FTIR for the monitoring of evolution products from a thermogravimetric analyzer. Most recently this technique has been extended to ion mobility spectrometry (IMS).
Because the AVS device samples directly from the ambient environment at the inlet into the GC column without any intervening mechanical parts (e.g. syringes, pumps, etc.), the GC column itself must function as a pressure restrictor between the sampled environment and a detector operated at reduced pressure. This technique found its first application in AVS TLGC/MS where the merits of vacuum outlet GC and the requirement of capillary flow restriction are obvious. Yet, the extension to detectors that are ordinarily operated at atmospheric pressure (i.e., IMS and FTIR) by pulling up to ½ atmosphere of vacuum on the detector cell has also proved successful.
These successes have motivated a search for "optimal" performance based upon the selection of appropriate column parameters for both separation and flow restriction criteria. Specifically, this paper evaluated the performance for AVS TLGC/IMS separations from the perspective of resolution, speed of separation and sensitivity.
Boardman, R.D.; Eatough,
C.N.; Germane, G.J. and Smoot, L.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 Morgantown
Energy Technology Center through subcontract from Advanced Fuel Research and
ACERC.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
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