ACERC
Abstracts - 1990 |
ACERC
Abstracts - 1990 |
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Thrust Area 3: Pollutant Formation/Control and Waste Incineration |
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.
Silcox, G.D.; Larsen, F.S.
and Pershing, D.W.
Combustion Science and Technology, 1990 (In press). Funded by ACERC and
Gas Research Institute.
The heat and mass transfer in an indirectly fired rotary kiln are examined using a combination of physical and mathematical modeling. The physical modeling is used to determine characteristic mixing times in a slumping kiln bed. These times are compared with characteristic times for diffusion of heat and mass through the bed in order to justify a lumped capacitance analysis of heat and mass transfer.
Mathematical models of heat and mass transfer are used to examine the effects of design and operating parameters on bed temperature and desorption rates. Limited comparisons with temperature measurements are presented. The design and operating parameters studied include kiln length, solid residence time, solid feed rate, and feed moisture content. The effects of moisture are particularly important to both heat and mass transfer. Scaling considerations are examined and it is shown that maintaining equivalent wall temperature profiles, fill fractions, moisture levels, and burden residence times does not necessarily result in equivalent bed thermal profiles.
Silcox, G.D. and Pershing,
D. W.
J. Air Waste Management Association, 40, 1990. Funded by ACERC.
A mathematical model of heat transfer in a directly-fired rotary kiln is developed and used to examine the effects of operating and design parameters on burden temperature. The model includes a mean beam length radiation model and axial zoning. Conductive and convective heat transfer are also included. Radiation between immediately adjacent zones is permitted. Calculation of heat transfer rates is facilitated by the use of an electric circuit analogue. An iterative solution procedure is adopted to solve the energy balance equations.
At the conditions examined, the model predicts that coflowing gas and solid streams result in higher average burden temperatures than do counter flowing streams. The moisture level of the feed is predicted to be a key operating parameter. The effects of kiln length, burden residence time, firing rate, and flame length are also examined.
Milne, C.R.; Silcox, G.D.
and Pershing, D.W.
I & EC Research, 29, 2192, 1990. Funded by Environmental Protection Agency
and ACERC.
A mathematical model for the sulfation of CaO is developed around the overlapping grain concept employed in the calcination and sintering models of Milne et al. (1988). The potential influence of high mass-transfer rates from simultaneous calcination of CaCO3 or Ca(OH)2 is incorporated in the mass-transfer coefficient for SO2 diffusion to the particle. A solution scheme for the nonlinear differential equation governing pore diffusion with changing particle structure is developed. The influence of grain overlap on product-layer diffusion is quantified. The model predictions show good agreement with the differential reactor data of Borgwardt and Bruce (1986) that include the influences of surface area, temperature, and SO2 partial pressure.
Milne, C.R.; Silcox, G.D.
and Pershing, D.W.
I & EC Research, 29, 2202, 1990. Funded by Environmental Protection Agency
and ACERC.
The fundamental processes for injection of CaCO3 and Ca(OH)2 for the removal of SO2 from combustion gases of coal-fired boilers are analyzed on the basis of experimental data and a comprehensive theoretical model. Sulfation data were obtained in a 30-KW isothermal dispersed-phase reactor at conditions simulating those of upper-furnace injection. The theoretical model accounts for particle structure, calcination, sintering, sulfation, and heat and mass transfer. Pore diffusion, product-layer diffusion, and sintering appear to be the principle processes that govern the rate of SO2 capture for the hydrate particles of interest for commercial dry sorbent injection.
Milne, C.R.; Silcox, G.D.
and Pershing, D.W.
I & EC Research, 29, 139, 1990. Funded by Environmental Protection Agency
and ACERC.
To simulate the staged availability of transient high surface area CaO observed in high-temperature flow-reactor data, the rate of calcination of CaCO3 of Ca(OH)2 is described by an empirical modification of the shrinking-core model. The physical model depicts particle decomposition by the shrinking-core mechanism. The subsequent time dependent decrease in CaO reactivity (surface area and porosity) due to sintering is simulated by reducing the grain-center spacing for the matrix of overlapping CaO grains. Information from SEM micrographs and from other physical property measurements of the porous particles is incorporated. This submodel simulates the time dependent availability and reactivity of CaO for a comprehensive model used to study sulfation of CaCO3 and Ca(OH)2 particles at upper-furnace injection conditions.
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.
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.
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.
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.
Arnold, N.S.; McClennen,
W.H. and Meuzelaar, H.L.C.
Analytical Chemistry, 1990 (In press). Funded by ACERC.
A number of methods are currently used for atmospheric vapor and gas sampling with mass spectrometric detection and identification. Direct mass spectrometry (MS) sample introduction methods include fixed molecular tasks (1), atmospheric pressure ionization (2,3), trap and desorb (4), and membrane separation (5), while gas chromatography/mass spectrometry (GC/MS) methods employ trap and desorb (6), direct bubbler solvent injection (7,8), sample loops (9), and pressurized gas plug introduction (10). Approaches vary depending upon whether MS, tandem MS, or GC/MS analyses are desired. Direct MS and tandem MS analyses typically give quick response times and high repetition rates but are often sensitive to interference, including atmospheric constituents, while GC/MS analyses offer greater specificity but with typically lower results.
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.
Meuzelaar, H.L.C.; Kim,
M.-G.; Arnold, N.S.; Urban, D.T. ; Kalousek, P.; Snyder, A.P. and Eiceman, G.A.
US Army Chemical Research Development and Engineering Center Scientific Conference
on Chemical Defense Research, Aberdeen Proving Grounds, Maryland, 1990.
Funded by US Army Chemical Research Development and Engineering Center.
Currently there is widespread interest in extending the capabilities of ion mobility spectrometry (IMS) to various military as well as nonmilitary fields of application, including chemical demilitarization, treaty verification, drug enforcement, explosives detection and environmental monitoring. Characteristic features of IMS are high sensitivity, fast response, low weight, small size, low power requirements, and relatively low cost. An attractive approach is to add a front-end module capable of performing "transfer line gas chromatography" (TLGC). In its present form the TLGC/IMS system consists of a special automated air sampling valve, a short (1-2 m long) capillary GC column with isothermal oven, a Chemical Agent Monitor (CAM) and a small laptop PC. The IMS system is operated below ambient pressures.
Meuzelaar, H.L.C.; Urban,
D.T. and Arnold, N.S.
Proceedings of the 1990 US Army Chemical Research Development and Engineering
Center Scientific Conference on Chemical Defense, Aberdeen Proving Grounds,
Maryland, 1990. Funded by Hewlett Packard Corp. and ACERC.
In situations involving special military or law enforcement operations, as well as industrial accidents or natural disaster, mobile laboratories may be of little use because of limited site access restrictions due to contamination or terrain constraints. Under such conditions man-portable analytical instruments may offer the only acceptable means of carrying out on-site analyses. The current prototype weighs approx 70-75 lbs and uses 150-200 W of battery power. The mass spectrometer and computer are carried in front of the operator by means of a shoulder harness whereas battery pack, carrier gas supply and roughing vacuum system are carried as a backpack. Air samples can be analyzed using a special automated air-sampling inlet. The man-portable GC/MS system is supported by a vehicle transportation "docking station."
Meuzelaar, H.L.C.; Arnold,
N.S.; McClennen, W.H. and Snyder, A.P.
Proceedings of the 1989 US Army Chemical Research Development and Engineering
Center Scientific Conference on Chemical Defense, 373-379, 1990. Funded
by ACERC, US Army Chemical Research Development and Engineering Center, and
Finnigan Corp.
A novel direct vapor-sampling inlet has been tested in combination with Transfer Line Gas Chromatography/Mass Spectrometry (TLGC/MS) using the MINITMASS (Miniaturized Ion Trap Mass Spectrometer) system developed at the University of Utah. Typically, 0.2-0.5 s wide air pulses are injected into the 1 m long transfer line at 15-60 s intervals. Even with relatively complex mixtures of vapors, e.g., produced by desorption and combustion of model compounds in a laboratory-scale fixed bed reactor, sufficient GC separation may be obtained to allow positive identification of minor reaction products by direct library search and matching procedures. Moreover, the high sensitivity of the MINITMASS allows tandem MS analysis of subpicogram quantities of selected model compounds.
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