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Sodium transformation mechanisms during pulverized coal combustion were investigated as functions of combustion temperature and of the modes in which sodium occurred in the parent coal. The combustion experiments took place in a 17-kW... more
Sodium transformation mechanisms during pulverized coal combustion were investigated as functions of combustion temperature and of the modes in which sodium occurred in the parent coal. The combustion experiments took place in a 17-kW laboratory downflow combustor which was designed to form a link between bench-scale reactor studies and commercial-scale combustors. Three different coals were burned under excess air conditions, and size-segregated fly-ash samples were extracted far from the combustion zone. Atomic absorption on each ash sample yielded bulk composition data. Computer-controlled scanning electron spectroscopy (CCSEM) yielded composition data of individual ash particles and allowed inference of mechanisms governing the formation of these individual particles. It was demonstrated that partitioning of sodium in the vapor, and the subsequent fraction of sodium in the submicron fume, is greatly reduced by the presence of silicates and high temperatures. This was attributed to reaction, of sodium in the vapor with solid silicates. The CCSEM analysed showed that reaction to form sodium aluminum silicates was preferred over reactions forming sodium silicates, alone, although both are formed. Some physical condensation also occurs. Both included and excluded alumino-silicates are effective in reactively scavenging sodium. The maximum amount of sodium scavenged in any one particle was consistent with formation of Na 2 O·Al 2 O 3 ·2SiO 2 . It was demonstrated that sodium from coal reacted with kaolinite additives mixed with the coal, suggesting that this is a strategy to reactively scavenge vaporized sodium. Additional bench-scale experiments and equilibrium calculations suggest that the mechanism of sodium reaction with alumino-silicates involves sodium as sodium hydroxide.
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The physical and chemical characteristics that influence the conversion of fuel nitrogen to nitrogen oxides during coal char combustion were theoretically examined by using a simplified model in which nitric oxide is an intermediate... more
The physical and chemical characteristics that influence the conversion of fuel nitrogen to nitrogen oxides during coal char combustion were theoretically examined by using a simplified model in which nitric oxide is an intermediate product between fuel nitrogen and N2.It was found that diffusion‐reaction interactions were important in determining the selectivity of the char particle toward nitric oxide production. At low temperature fluidized bed combustion conditions, pore size is important, and low conversion of fuel nitrogen to nitric oxide is favored by long narrow pores. Under high temperature, pulverized coal combustion conditions, the model provided insight into mechanisms of nitric oxide formation and predicted the observed weak temperature dependence of fuel nitrogen conversion, as well as a significant effect of particle size.
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... In this case, the quartz sam-pling tube was followed by a diaphragm pump, which pushed the sample continuously through a cooler and knock-out ... SECONDARY FUEL INJECTION 901 2.8 2.4< 2.C 1.6 ~ 1.21 0.8 0.4 0.0 [] I0.7%w S IN FUEL,... more
... In this case, the quartz sam-pling tube was followed by a diaphragm pump, which pushed the sample continuously through a cooler and knock-out ... SECONDARY FUEL INJECTION 901 2.8 2.4< 2.C 1.6 ~ 1.21 0.8 0.4 0.0 [] I0.7%w S IN FUEL, CO AS SECONDARY FUEL )~ AA O ...
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Research Interests: Chemistry, Combustion, Waste Management, Incineration, Kiln, and 3 moreSorbent, Rotary Kiln, and Vaporization
Research Interests: Heat Transfer and Coal
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discomfort and pain in the mice can be obtained from M.L.W.) We found no significant differences in other pulmonary functions (pulmonary compliance or resistance). Increased lung permeability enhances access by a toxin to the lung... more
discomfort and pain in the mice can be obtained from M.L.W.) We found no significant differences in other pulmonary functions (pulmonary compliance or resistance). Increased lung permeability enhances access by a toxin to the lung interstitium and pulmonary circulation, correlating with the extent of pathological lung injury. We measured the distribution in particle sizes to which the mice were exposed by using a Berner low-pressure impactor, and recorded differences in mass and concentration of certain elements. Mass and size distributions for particles produced by coal/MSS ash mixtures and by coal ash on its own are quite similar, although the coal ash generates a slightly greater fraction of nanometresized particles. We conclude that the increased toxicity of the MSS/coal is not due to a difference in the size of the particles it produces on combustion. Instead, the toxic effects seem to be associated with the presence of zinc in the particles. Combustion of MSS together with coa...
Abstract The future use of coal as a fuel for power generation in the US depends on the availability of financially viable technologies for capture and storage of CO2 emissions from power plants. Key second-generation candidates for CO2... more
Abstract The future use of coal as a fuel for power generation in the US depends on the availability of financially viable technologies for capture and storage of CO2 emissions from power plants. Key second-generation candidates for CO2 capture include high temperature and pressurized oxy-firing of coal, which has the potential to increase efficiency, lower capital costs, avoid air ingress and reduce oxygen requirements. However, unquantified challenges, such as flame behavior, heat transfer, ash transformation, ash deposition and char oxidation, still exist for those technologies. This study specifically focuses on the formation of submicron particles and initial layer ash deposition during high temperature oxy-coal combustion. Previous work has shown that the initial layer deposits are mainly formed of submicron size ash aerosols transported by thermophoresis. Unfortunately, the importance of submicron particle deposition has not received much attention, probably due to the insignificant deposit mass and difficulty in prediction of the submicron particles formation. In this work, models including mineral matter vaporization model, scavenging model and deposition model are developed and applied into a three-dimensional CFD framework to predict the submicron particles formation and subsequent initial layer deposits formation. The model results are comparable to experimental data. The merits of this work are that it has led to the development of a novel approach to predict both submicron particle formation and initial layer ash deposition during oxy-coal combustion.
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... kW load 16-kW load Natural gas 1.4 m3/h ... and16-kWloads,hasbeendescribedinapreviouspaper[ 6].Naturalgas,primaryair,andaqueousmetalsaltswereintroducedviaavariableswirlburnerwitha centerlineplainjet ... 3 (above the semivolatile... more
... kW load 16-kW load Natural gas 1.4 m3/h ... and16-kWloads,hasbeendescribedinapreviouspaper[ 6].Naturalgas,primaryair,andaqueousmetalsaltswereintroducedviaavariableswirlburnerwitha centerlineplainjet ... 3 (above the semivolatile cadmium dew point), instantaneously diluted ...
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Research Interests: Mechanical Engineering, Chemical Engineering, Environmental Science, Materials Science, Combustion, and 15 moreCoal, Pyrolysis, Automotive Engineering, Inflammatory Immune Response, Alkali Metals, Iron Oxide, Iron, The, Fly Ash, Particle Size, Coal Fly Ash, Health Effect, Inflammatory response, Total Carbon, and Elemental composition
Research Interests: Mechanical Engineering, Chemical Engineering, Materials Science, Combustion, Coal, and 14 moreTransmission Electron Microscopy, Automotive Engineering, Transition-Metal Oxides, Interdisciplinary research, Chromium, Fly Ash, Wavelength Dispersive X-Ray Fluorescence, Particulate Matter, Lung Injury, Coal Fly Ash, Mossbauer Spectroscopy, Health Effect, extended x-ray absorption fine structure (EXAFS), and Transition metal oxides
JD_description.
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ABSTRACT Certain designs of hazardous waste incinerator systems include emergency safety vents (ESVs). ESVs (also called dump stacks, vent stacks, emergency by-pass stacks, thermal relief valves, and pressure relief valves) are regarded... more
ABSTRACT Certain designs of hazardous waste incinerator systems include emergency safety vents (ESVs). ESVs (also called dump stacks, vent stacks, emergency by-pass stacks, thermal relief valves, and pressure relief valves) are regarded as true emergency devices. Their purpose is to vent combustion gases directly from the combustion chambers to the atmosphere in the event of a failure of other system components. This is done for operator safety as well as to protect the incinerator and other downstream equipment from damage. ESVs are typically required for rotary kiln and hearth incinerators which process a portion of their waste load as bulk solids or contained liquids introduced continuously or in batch charges. Research has been performed at the U.S. EPA on a 73 kW (250,000 Btu/hr) rotary kiln incinerator simulator examining optimum settings of kiln operating parameters so as to minimize emissions during an ESV opening event. Experimental results are interpreted in the light of previous research results on transient &#39;&#39;puffs.&#39;&#39; Mechanisms governing both the release of volatile matter during an ESV event and the subsequent pyrolysis and oxidation in the residual sorbent bed are identified. From a practical point of view, results indicate that alteration of operator-controllable kiln parameters during the onset of certain ESV opening events can have a significant effect on emissions of both organics and hydrogen chloride (HCI). A low air flow rate results in lower emissions of both organics and HCI. This hypothetical low air flow rate could possibly be equal to the flow rate induced by the natural draft coupled with air in-leakage. Rotational speed (RPM) appears to have slightly different effects on organics and HCl. Whereas emissions of HCI are minimized at a very low or non-existent RPM, emissions of organics exhibit a minimum at a low (but non-zero) RPM, with increasing emissions at both zero and high RPM. The use of a small afterburner to simulate an in-stack flare during an ESV event dramatically reduced organic emissions.
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Combustion is a significant source of fine particulate matter (PM) emissions, and heavy oil combustion is suspected of producing particulate emissions with potentially significant toxicity. This paper is concerned with the... more
Combustion is a significant source of fine particulate matter (PM) emissions, and heavy oil combustion is suspected of producing particulate emissions with potentially significant toxicity. This paper is concerned with the characterization of particulate emissions from a practical boiler burning heavy fuel oils, The purpose of the study was to identify possible mechanisms that might relate both the combustion process
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ABSTRACT When “containerized” liquid wastes, bound on sorbents, are introduced into a rotary kiln in batch mode, transient phenomena involving heat transfer into, and waste mass transfer out of, the sorbent can promote the rapid release... more
ABSTRACT When “containerized” liquid wastes, bound on sorbents, are introduced into a rotary kiln in batch mode, transient phenomena involving heat transfer into, and waste mass transfer out of, the sorbent can promote the rapid release of waste vapor into the kiln. This rapid vapor release can cause depletion of available oxygen, and the formation of a “puff” which can result in a temporary failure of the incinerator system. A systematic study has been completed examining the effect of waste and sorbent properties on the magnitudes of transient puffs in a laboratory scale rotary kiln simulator. Of primary importance were waste boiling point and waste stoichiometric oxygen requirement. Of secondary importance were sorbent parameters such as bulk void fraction, and the fraction of the adsorbed waste that was contained within the individual sorbent particles. A theoretical model that utilizes a vaporization/surface renewal approach can be used as a guide to explain experimental results for several wastes on sawdust and corncob sorbents. Resin sorbents, on the other hand, are extremely effective at controlling puffs because they appear to be able to bind the liquid waste tightly to the sorbent in such a way that it is not released by a vaporization process. This non-physical waste release process is not described by the current model. In general, the results suggest that the practice of limiting containerized waste feed rates based on the heat of combustion of a given container be modified to provide feed rate limitations based on the stoichiometric oxygen requirements and boiling point of waste in a given container. This modified practice may enable containerized waste feed rates to be optimized, with a view to minimizing both the transient load on the afterburner and the transient emissions from the stack.
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Page 1. Combust. Sci. and Tech., 1996, Yols.1I6-117, pp.479-498 Reprints available directly from the publisher Photocopying permitted by license only © 1996 OPA (Overseas Publishers Association) Amsterdam BY Published ...
Research Interests: Mechanical Engineering, Chemical Engineering, Chemistry, Combustion Science, Combustion, and 11 moreNatural Gas, Chromium, Chemical Analysis, High Temperature, Experimental Study, Chemical equilibrium, Aerosol Dynamics, Hexavalent Chromium, Experimental Data, Particle Size Distribution, and Waste Incineration
Page 1. ENVIRONMENTAL AND ENERGY ENGINEERING Hybrid SNCR-SCR Technologies for NO Control: x Modeling and Experiment Jost OL Wendt Dept. of Chemical and Environmental Engineering, University of Arizona ...
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Page 1. Combust. Sci. and Tech., 1994, Vol. 101, pp. 7-27 Reprints available directly from the publisher Photocopying permitted by license only ?? 1994 OPA (Overseas Publishers Association) Amsterdam BV Published under ...
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To this end experiments were completed on a (nominally rated) 100kW down flow combustor, with special deposit coupons inserted. Results are presented from two groups of experiments. In the first group of experiments, once through CO2 was... more
To this end experiments were completed on a (nominally rated) 100kW down flow combustor, with special deposit coupons inserted. Results are presented from two groups of experiments. In the first group of experiments, once through CO2 was used to simulate flue gas recycle with all contaminants removed, and the coupons consisted of un-cooled ceramic inserts attached to a cooled probe. In the second group of experiments, a specially designed deposit probe was constructed and experiments were conducted on the system with actual flue gas recycle of varying composition.
a Department of Chemical Engineering and Institute for Clean and Secure Energy, University of Utah, 50 South Central Campus Drive, Salt Lake City, UT 84112, USA b Praxair Inc., 175 East Park Drive, Tonawanda, NY 14150, USA c Reaction... more
a Department of Chemical Engineering and Institute for Clean and Secure Energy, University of Utah, 50 South Central Campus Drive, Salt Lake City, UT 84112, USA b Praxair Inc., 175 East Park Drive, Tonawanda, NY 14150, USA c Reaction Engineering International, 77 West 200 South, Suite 210, Salt Lake City, Utah 84101, USA d School of Mechanical Engineering, Shanghai Jiaotong University, NO.800 Dongchuan Road, Minhang, Shanghai, 200240, China e State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, China * Corresponding author: Jost O.L. Wendt (TEL: +1-801-585-9291, E-mail: Jost.Wendt@utah.edu) Abstract
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The purpose of this project was to advance the fundamental understanding of fuel nitrogen conversion in coal combustion towards the ultimate end of providing for the rational design of coal combustors with acceptably low NO/sub x/... more
The purpose of this project was to advance the fundamental understanding of fuel nitrogen conversion in coal combustion towards the ultimate end of providing for the rational design of coal combustors with acceptably low NO/sub x/ outputs. In pursuit of this objective the program attached the problem both experimentally and theoretically. Experimental work concentrated upon the pyrolysis stage of coal combustion. It investigated the loss of mass, nitrogen, and sulfur from the solid phase and the distribution of important chemical species in the pyrolyzate under simulated combustion heating conditions. Experimental variables included temperature, heating rate, atmospheric reactivity, thermal history (preheating, reheating) and coal type. These experiments were performed upon twenty coals of widely varying types, two chars, and one petroleum coke. The results of the work suggest that the conditions of coal nitrogen conversion can be controlled by adjusting external variables
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A 2Kg/h pulverized-fuel, plane-flame combustor was used to determine time-resolved NO profiles under fuel-rich and staged combustion conditions. Seven solid fuels, including two coal chars, were investigated. Results show that at all... more
A 2Kg/h pulverized-fuel, plane-flame combustor was used to determine time-resolved NO profiles under fuel-rich and staged combustion conditions. Seven solid fuels, including two coal chars, were investigated. Results show that at all fuel-rich conditions NO is formed rapidly and then is slowly destroyed. The peak NO value and the rate of destruction are strong functions of coal composition and stoichiometry. Under staged combustion conditions, NO may increase or decrease at the staging point depending on the fuel and on the quantity of NO formed in the first stage. Use of artificial oxidants confirmed that the NO formed in the first and second stages consisted of fuel NO. Heterogeneous formation and reduction of NO during char combustion was modeled by a two-reaction scheme. Heterogeneous reduction was less than first order in NO and had an activation energy of 47 kcal/mole. The roles of devolatilization and homogeneous reactions are discussed in the light of the data presented.
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A laminar, counterflow, premixed flame configuration was utilized to investigate coal pyrolysis under both reducing and oxidizing environments, and at superficial heating rates between 20,000 and 70,000 K/s. Whether the unique attributes... more
A laminar, counterflow, premixed flame configuration was utilized to investigate coal pyrolysis under both reducing and oxidizing environments, and at superficial heating rates between 20,000 and 70,000 K/s. Whether the unique attributes of this system can be exploited to yield quantitatively interpretable data, depends first on the adequacy of mathematical models of the entire heterogeneous flow system, and second, on
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ABSTRACT Diesel exhaust and especially diesel exhaust particles (DEP) are a health concern because of their complex chemistry, small size, and ubiquitous presence in urban environments. As part of a research program designed to relate... more
ABSTRACT Diesel exhaust and especially diesel exhaust particles (DEP) are a health concern because of their complex chemistry, small size, and ubiquitous presence in urban environments. As part of a research program designed to relate diesel exhaust properties to adverse health effects, a series of inhalation exposure studies were conducted to investigate the propensity of diesel exhaust to promote cardiopulmonary diseases, immune polarization, and trans-generational effects in mice. Three diesel engines were utilized to generate diesel exhaust for whole animal exposures. These include a four cylinder 31 kW non-catalyst equipped engine and air compressor (CDEP), an eight cylinder 134 kW mid-1990s vintage pickup truck engine equipped with an oxidation catalyst and eddy current dynamometer (TDEP), and a one cylinder 4.8 kW non-catalyst equipped engine and generator (GDEP). The CDEP and TDEP engines were operated at approximately 25% of their maximum engine loads at speeds of 1700 and 2500 rpm, respectively. These operating conditions were chosen to be representative of typical equipment operation, and for TDEP, to imitate steady-state highway driving. The GDEP engine was operated at approximately 80% of its maximum load at 3600 rpm. This also was intended to be representative of how a small generator might be used. During the exposures, gas/particle concentrations and particle size distributions were monitored in real-time. DEP was collected at engine exhaust and inhalation chamber locations using filters, baghouses, and/or an electrostatic precipitator, and analyzed for particle mass concentration, organic and elemental carbon (OC-EC), inorganic (non-EC) elements, and organic components. Dichloromethane-extracted organic material (EOM) was sequentially sub-fractionated through a silica column using four organic solvents of increasing polarity: hexane, 50:50 hexane:dichloromethane, dichloromethane, and methanol. The EOMs and the sub-fractions were also determined gravimetrically. The exhaust particle mass concentration of the CDEP was approximately 11 times greater than either the TDEP or GDEP. This also corresponded to higher amounts of quantifiable polycyclic aromatic hydrocarbons (PAHs) in the CDEP samples (&gt;400 μg/g) compared to the TDEP and GDEP samples (&lt;100 μg/g). Geometric mean number diameters of the CDEP was slightly larger (84-102 nm) than the TDEP and GDEP (48-74 nm). However, with the exception of PAH species, other organic chemical components were similar for all three engines. Sulfur, chlorine, zinc, calcium, and iron were the most abundant inorganic elements, comprising &lt;5% of the mass. OC/EC mass ratios ranged from 0.2-2.0. EOM comprised 10-40% of the DEP mass, and partitioned at 54-77% and 8-13% between the least-polar (hexane) and most-polar (methanol) solvents, respectively. Less than 2.5% of mass of all DEP samples was identified and quantified as specific organic compounds, and 84-98% of the organics identified were alkanes or organic acids. The overall characteristics placed the three EPA-generated DEP samples between the NIST SRM2975 and Japanese (Sagai) samples, which are commonly used as reference samples but have drastically different properties from each other (This abstract does not reflect EPA policy.).