ACERC
Abstracts - 1994 |
ACERC
Abstracts - 1994 |
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Thrust Area 3: Pollutant Formation/Control and Waste Incineration |
Anderson-Altmann, K.L.
Investigation of Solid State Nitrogen-15 Nuclear Magnetic Resonance,
Ph.D./U of U, August 1994. Advisor: Grant
Keyes, B.R. and Silcox,
G.D.
Environmental Science Technology, 28:840, 1994. Funded by ACERC and Gas
Research Institute.
Nonisothermal desorption of toluene from individual montmorillonite clay particles was measured experimentally and modeled mathematically to elucidate details of the overall thermal desorption process. A single-particle reactor was used. It consisted of a porous, 2-6mm clay pellet formed around a 0.05-mm diameter thermocouple in a 6- or 9-mm o.d. glass tube. The tube was surrounded by a supplementary heater and placed in a GC oven. Desorption rates were obtained as a function of heating rate, clay type, particle size, and purge gas flow rate. In addition, the absorption isotherms for two toluene/clay systems and one n-dodecane/clay system were measured and correlated using the Freundlich isotherm. At the conditions examined, the rate-controlling mechanism is associated with intraparticle diffusion. Isothermal desorption experiments using clay pellets of different sizes demonstrate that local desorption kinetics are not rate controlling. Toluene shows a slower desorption rate than n-dodecane at low concentrations. This is attributed to the hindered removal of toluene from interlamellar regions of the clay. Comparisons of single-particle reactor and pilot-scale rotary kiln results show that mass transport resistances associated with a bed of particles dominate the desorption process at rotary kiln conditions.
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.
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.
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.
McClennen, W.H.; Arnold,
N.S. and Meuzelaar, H.L.C.
Trends in Analytical Chemistry, 13(7):286-293, 1994. Funded by Hewlett
Packard and US Army.
The "tricorder," the tiny universal sensor of "Star Trek" science fiction fame, might be the ultimate objective for developers of field-portable instrumentation. The advantages of multi-dimensional ("hyphenated") analytical methods over one-dimensional techniques in working toward such a goal are based upon the degree of correlation of the information from the combined analytical techniques. With appropriately selected techniques that yield complementary (orthogonal) information, the actual resolution of the hyphenated technique is the product of the resolution of the two techniques. In effect, the whole of a suitable hyphenated system is greater than the sum of its parts.
The most widely used hyphenated method, combined gas chromatography-mass spectrometry (GC-MS), is regarded as the definitive method for certain applications and has become the officially required procedure for numerous environmental, clinical and occupational health or safety related tests. In fact, in most laboratories GC-MS has all but replaced the use of one-dimensional GC and MS techniques. Consequently, results based on characterization of complex environmental samples by GC or MS alone would tend to be disregarded or seen as tentative, at best. Yet, the use of one-dimensional GC and MS techniques represents the present state-of-the-art in field screening methods. The demonstration of hyphenated analytical techniques in field application via the use of mobile laboratories has been established in the last 10 years by a number of researchers using MS-MS or GC-MS techniques. However, it is appropriate to consider whether a field laboratory constitutes a truly field-portable analytical technique.
In-situ applications are an area of field portability where the use of hyphenated methods is a recent phenomenon that can be expected to continue due to the considerable power of these approaches. However, the large-scale acceptance of these techniques in the field will depend upon overcoming the constraints of inherent higher cost, complexity, size, weight and power requirements.
On the other hand, hyphenated techniques should certainly not be seen as a panacea for every analytical problem, whether in the laboratory or in the field. Although the information provided by a multi-dimensional method is often much greater than the summed information obtainable from the component techniques, a poorly designed hyphenated experiment may end up amplifying the characteristic weaknesses and shortcomings of the component methods and provide little or no useful information. In effect, the use of sophisticated hyphenated methods is certainly not a satisfactory way to compensate for a poor analytical technique!
Pershing, D.W.
Rock Products, Cement Edition, 19-23, April 1994. (Also presented at
the Waste Combustion in Boilers and Industrial Furnaces, Kansas City,
MO, April 1994.) Funded by Industrial Consortium.
A recent report by objective experts studying the emissions of cement kilns using waste-derived fuel (WDF) shows that under proper operating conditions that use of the fuel in cement kilns can provide a safe and cost effective disposal method for combustible wastes, as well as a net reduction of CO2 emissions.
The study, conducted by a Scientific Advisory Board (SAB) for the Cement Kiln Recycling Coalition (CKRC), was in response to inquiries about the effectiveness of cement kilns for waste disposal. The study also found this reduction in CO2 emissions is relative to incineration since the WDF is replacing a fossil fuel in the cement kilns using raw materials with inherently high hydrocarbon levels, the emission of organics can be controlled by applying well established, good combustion practices. Because of the high alkali content of the raw materials and the scrubbing action of the cement caused by its abrasiveness, metals emissions are generally below 1% of the input, except in the case of volatile metals such as mercury.
The SAB report, entitled "Evaluation of the Origin, Emissions, and Control of Organic and Metal Compounds from Cement Kilns Cofired With Hazardous Wastes," focused on organic and metal emissions from cement kilns using WDF. The following subsections of this article, which is an examination of the findings of the study, briefly discuss the findings of the SAB regarding the fate of metals and organics in these systems.
Bartholomew, C.H.
Catalyst Deactivation 1994, 88, 1994. Funded by ACERC.
Studies of sintering kinetics of conventional supported metal catalysts are reviewed. Available kinetic data for sintering have been reanalyzed using the new General Power Law Expression (GPLE), which provides the capability of treating these data in a consistent, unifying fashion such that quantitative comparisons regarding effects of reaction conditions and catalyst properties are possible for the first time. It is shown that all available dispersion versus time data can be fitted to second order GPL kinetics. From the analysis of these data new conclusions arise regarding the effects of atmosphere, time, temperature, support, promoters, and metal on the thermal stability of supported metals.
Hydrotreating involves a number of catalytic steps. For example, reaction steps in HDS include: (i) adsorptions of H2 and the organic sulfide, (ii) hydrogenolysis of the carbon-sulfur bond, (iii) hydrogenation of unsaturates, (iv) hydrocracking, and (v) desorptions of hydrocarbons and H2S. An important objective in hydrotreating is to maximize the rates of S, N, and metal removal, while minimizing the rates of hydrogenation and hydrocracking and therewith hydrogen consumption.
Sulfided resid hydrotreating catalysts are deactivated over a period of months by coke, metals and nitrogen compounds. The deactivation process involves a combination of uniform poisoning, pore mouth poisoning and pore blockage by (i) decomposition of organometallic compounds and (ii) buildup of soft coke and its transformation over a period of time to hard, crystalline coke. These problems are minimized by careful selection of guard beds, reactor design, and catalyst design; moreover, it is possible to regenerate coked catalysts with an oxygen burn.
Deactivation of hydrotreating catalysts has been fairly extensively studied. Several previous reviews of the literature and an international symposium have covered in some depth most aspects of this subject. Nevertheless, an updated overview of the key aspects of residua hydrotreating deactivation, including coke formation chemistry, metals deposition chemistry, catalyst and reactor design, and the use of mathematical models to simulate the deactivation process may be timely.
This review focuses on the deactivation of sulfided Mo, CoMo, and NiMo catalysts in hydrotreating of heavy residuum feedstocks. Coke formation, metals deposition, the roles of catalyst and reactor design in minimizing catalyst decline, and the application of modeling to design and prediction of deactivation rates are discussed in this review in the sections which follow.
Dworzanski, J.P.; Kim, M.-G.;
Snyder, A.P.; Arnold, N.S. and Meuzelaar, H.L.C.
Anal. Chimica Acta, 293:219-235, 1994. Funded by US Army Chemical Research
Development and Engineering Center and Battelle.
Rugged, low weight, hand-held ion mobility spectrometry devices, initially developed for chemical warfare detection purposes, possess attractive characteristics as field-portable instruments for paramilitary (treaty verification, chemical demilitarization, drug interdiction, counterterrorism operations) and civilian (environmental monitoring, forensic characterization, process control) applications. Generally, however, such devices tend to exhibit limited resolution, narrow dynamic range, nonlinear response and long clearance times which severely limit their usefulness for qualitative and quantitative analysis of mixtures. To overcome these restrictions a prototype combined gas chromatography/ion mobility spectrometry (GC/IMS) unit was constructed by replacing the membrane inlet of a military IMS device known as the CAM (Chemical Agent Monitor) with suitable front-end modules. These modules enable high speed automated vapor sampling (AVS), microvolume preconcentration/thermal desorption, and isothermal GC preseparation of analytes using a short capillary column while operating the IMS source and cell at subambient pressures as low as 0.5 atm. The AVS-GC/IMS methodology sharply reduces competitive ionization and facilitates identification of mixture components, thereby enabling quantification of volatile and semivolatile compounds over a broad range of concentrations in air. At higher concentral levels (e.g.>1 ppm) using the AVS inlet in automatic attenuation control (AAC) mode maintains excellent linear response. At ultralow concentration levels, e.g. < 10 ppb, a microvolume, trap-and-desorb type preconcentration module, maintains adequate signal to noise levels, thereby expanding the effective dynamic range of the method to appox. 6 orders to magnitude (100 pp 5-100 ppm). The resulting "hyphenated" GC/IMS technique has the potential of evolving into the first hand-portable combined chromatography/spectroscopy instruments for field screening applications.
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.
Gopalakrishnan, R.; Davidson,
J.E.; Stafford, P.R.; Hecker, W.C. and Bartholomew, C.H.
ACS Symposium Series, 552:74-88, 1994. Funded by Westinghouse Idaho Nuclear
Company, Brigham Young University and ACERC.
Performance of Cu-ZSM-5, Pt/Al2O3 and Cu-ZSM-5 + Pt/Al2)3 for NH3 (425-750 ppm) and CO (~1%) oxidation in the presence of NO (250 ppm), O2 (14-15%) and H2O (~20%) was studied as a function of temperature. Pt/Al2O3 is more active for NH3 and CO oxidation, while Cu-ZSM-5 is more selective for conversion of NO and NH3 to N2. NH3 and CO are completely oxidized above 300°C on Pt/Al2O3, while on Cu-ZSM-5 about 99% of NH3 and NO are converted to N2 at 450-500°C, although only about 50% of CO is converted to CO2. The selectivity of Cu-ZSM-5 for conversion of NH3 and NO to N2 is about 100%, while selectivities of Pt/Al2O3 for N2 and N2O are 35-40% and 20-40% respectively. However, the activity and selectivity of a Cu-ZSM-5 + Pt/Al2O3 dual catalytic systems are very high, converting 99% of NH3, 94% of NO, and 100% of CO simultaneously at 485°C with a 100% selectivity to N2.
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