ACERC
Abstracts - 1986-1988 |
ACERC
Abstracts - 1986-1988 |
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Thrust Area 3: Pollutant Formation/Control and Waste Incineration |
Smith, P.J.; Smoot, L.D.
and Hill, S.C.
AIChE Journal, 32, (11), 1917-1919, 1986. 3 pgs. Funded by US Department
of Energy.
Nitrogen-containing pollutants from pulverized coal conversion processes have been of concern for several years, and reviews of this subject have been published (Wendt, 1980; Chen et al., 1981). Swirl of the secondary stream is one technique of fuel-air contacting that causes significant changes in NO concentrations. In some cases, increased swirl increases NO emissions (Heap et al., 1973b; Brown et al., 1977; Pershing and Wendt, 1979). In other cases, increased swirl initially decreases NO emissions (Harding et al., 1982; Asay et al., 1983). Thus, the observed effects of swirl are varied, and indicate that additional parameters influence the NO emissions. In this note a model, described in detail elsewhere (Smith and Smoot, 1981; Smith et al., 1981, 1982; Hill et al., 1984), was used for interpreting effects of inlet stream swirl and velocity on NO emissions during combustion of pulverized coal.
Boardman, R.D. and Smoot,
L.D.
AlChE J., 1987. 14 pgs. Funded by ACERC Consortium: Babcock & Wilcox,
Combustion Engineering, Consol, Electric Power Research Institute, Empire State
Electrical Energy Research Corp., Foster Wheeler, Pittsburgh Energy Technology
Center, Tennessee Valley Authority, and Utah Power & Light.
A computer model to predict nitric oxide (NO) concentrations has been applied to advanced-concept, pulverized-coal systems and evaluated by comparing model predictions with experimental data. Specifically, the effects of pressure, stoichiometric ratio, coal moisture content, particle size, and swirling and non-swirling diffusion flames (Hill et al., 1984; Smith et al., 1986).
The NO model is a subcomponent of a general combustion code that provides theoretical predictions for the temperature, velocity, major species, and other properties at local points throughout turbulent, combusting flow fields (Smoot and Smith, 1985). In the NO model, fuel nitrogen release from the coal is assumed to occur at a rate proportional to total coal weight loss. The volatile nitrogen is assumed to be instantaneously converted to HCN. NO is formed by oxidation of the HCN and is competitively reduced to N2 by reaction with HCN. Global rate expressions for these reactions were measured by the Soete (1985). The model also accounts for the destruction of NO by heterogeneous interaction with char using a rate expression from Levy et al., (1981). All rate parameters are used as reported except for the information of HO. For this rate equation, the pre-exponential factor was increased by a factor of ten. This value is still in within the range of experimental error and was used because it yielded better results. Effects of turbulence on the gaseous reactions are accounted for through use of a joint probability calculation of fluctuating gaseous and coal off-gas mixture fractions. These two progress variables are sufficient to track turbulent temperature and gas concentration variations (Smith et al., 1982). Experimental data sources for model comparisons were selected for axi-symmetric combustion exponents that investigated the variation of key test variables (e.g., pressure or stoichiometric ratio).
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.
Nichols, K.M.; Hedman, P.O.
and Smoot, L.D.
Fuel, 66, 1257-1263, 1987. 7 pgs. Funded by Morgantown Energy Technology
Center.
Effects of pressure, flame type and coal feed rate on fuel-nitrogen release and nitrogen pollutant formation were examined in a laboratory scale, entrained-coal gasifier. A Utah, high-volatile bituminous coal was used. With a water-quenched probe, gas-particulate samples were collected for oxygen-coal mass ratios from 0.6 to 1.1, pressures of 1, 4.9 and 10.4 atm and coal feed rates of 25 and 35 kg·h-1. Two injector types were utilized; one produced a diffusion flame, the other a premixed flame. Fuel-nitrogen release from the coal showed little dependence on oxygen-coal ratio, pressure or coal feed rate. Values at the gasifier exit averaged 83% for the diffusion flame and 92% for the premixed flame.
Fuel-nitrogen release, mostly during devolatilization, exceeded fuel-carbon release by . 10% for the premixed flame and . 30% for the diffusion flame, depending on oxygen-coal mass ratio. Over 50% of the released fuel-nitrogen formed N2, with significant amounts of NH3 and HCN, and smaller amounts of NO. Increased pressure at constant mass feed rates caused sharp decreases in effluent NO concentrations (to near zero) for both flame types which was explained by a combination of increased residence time and increased homogeneous NO decay rate. Elevated pressure also increased the effluent NH3 and decreased HCN concentrations for the diffusion flame whereas the more complete mixing of the premixed flame resulted in lower NH3 and HCN levels, and higher N2 levels. In general, nitrogen species concentrations were not largely affected by coal feed rate, though increased coal feed rate decreased NH3 levels somewhat. From these observations, together with observations from other investigators; possible explanations are postulated.
Silcox, G.D.; Kramlich,
J.C. and Pershing, D.W.
Submitted to I&EC/Research, 1987. 28 pgs. Funded by ACERC (National Science
Foundation and Associates and Affiliates).
A mathematical model for the flash calcination of Ca(OH)2 and CaCO3 is presented. The model describes the decomposition of the parent material at the reactant-product interface, the diffusion of CO2 or H2O through the growing CaO layer, and the sintering of the CaO layer. The model is qualitative, but it provides useful estimates of peak CO2 pressures in the CaO layer, relative rates of surface area development and loss for Ca(OH)2 and CaCO3, the effect of particle size, and the effects of time and temperature.
Lemieux, P.M. and Pershing,
D.W.
Submitted to Review of Scientific Instrument, 1987. Funded by Westinghouse
and National Science Foundation/Presidential Young Investigators.
Rotary kiln systems are widely used in industrial applications to transfer energy from high temperature flames to irregular solids. Recently these systems have been shown to be suitable for the incineration of hazardous solid waste materials and the thermal treatment of contaminated soils. Destruction and removal efficiencies in excess of 99.99% have been reported for hazardous species, but the rate controlling steps of the incineration process are not well understood.
This paper describes the design, construction and operation of a laboratory scale simulator that was developed to investigate the fundamentals of hazardous incineration in a rotary kiln environment. This 2 ft. x 2 ft. refractory-lined kiln allows time resolved characterization of contaminant evolution and destruction. Continuous thermal and exhaust concentration measurements are used to characterize the fate of the solid charge as a function of residence time within the kiln. Overall destruction efficiency can be measured by subsequent analysis of the solid phase.
The initial performance of this facility has been demonstrated by studying the combustion of waste zirconium metal and by characterizing the thermal clean up of solid sorbent contaminated with toluene. The rotary kiln simulator has been shown suitable for investigation of parameters such as amount of charge, contaminant loading, rotation speed, temperature, excess oxygen, and particle size.
Lemieux, P.M. and Pershing,
D.W.
Submitted to Metals, 1987. Funded by Westinghouse and National Science
Foundation/Presidential Young Investigators.
The combustion of off-grade zirconium sponge in a rotary kiln environment is described. The purpose of these experiments was to determine the suitability of rotary kiln incineration for the disposal of zirconium wastes, and to determine the design parameters and optimum operating conditions for a zirconium burning rotary kiln. In the rotary kiln simulator, the experiments are done in a batch mode, simulating a control volume of solids moving down the length of a full-scale rotary kiln, and exchanging time for distance as the independent variable. Parametric studies investigating the effect of oxygen concentration, charge size, rotational velocity, particle size and temperature on the burning rate have been completed. The burning rate appears to be controlled by intra- and interparticle diffusion, thus the rate at which the product layer is abraded off and the availability of O2 at the particle surface appear to strongly affect the burning rate. The burning rate is independent of charge size, weakly dependent on oxygen concentration, rotational velocity and particle size, and strongly dependent on temperature.
Hecker, W.C and Breneman,
R.B.
Catalysis and Automotive Pollution Control, 30, 257-265, 1987. Funded
by Brigham Young University.
Rhodium catalysts with very low weight loadings (0.01 to 0.06%) are used to efficiently reduce the nitrogen oxides in automobile exhaust. Many academic studies, however, are done suing catalysts with high weight loadings (1 to 10%). The study reported herein explored differences in activity and surface properties between high and low weight-loaded Rh catalysts before and during NO reduction by CO. Initial and steady state turnover numbers were found to increase significantly (factor of 7) as weight loading was increased from 0.2% to 12%. At the same time the activation energy decreased form 36 to 24 kcal/more. Power rate laws determined by varying NO and CO partial pressures were found to be fairly similar for the high and low weight-loaded catalysts. These results seem to indicate that NO reduction is a structure sensitive reaction. The effect of varying the reduction temperature of the catalysts between 200 and 450ºC was also explored, but no significant effect was seen on hydrogen uptakes, infrared spectra, initial rates, or steady state rates.
Cundy, V.A.; Lester, T.W.;
Morse, J.S.; Montestruc, A.N.; Leger, C.B.; Acharya, S.; Sterling, A.M. and Pershing,
D.W.
Submitted to Journal of the Air Pollution Control Association, 1988.
39 pgs. Funded by Environmental Protection Agency.
A multifaceted experimental and theoretical program directed toward the understanding of rotary kiln performance is underway. Following a general overview of the program, we describe in more detail the program components including: In-situ measurements from an industrial-scale rotary kiln located at the Louisiana Division of Dow Chemical USA in Plaquemine, Louisiana; laboratory-scale desorption characterization and kiln-simulator studies; and incinerator modeling efforts. Using water-cooled probes, hot-zone samples have been obtained from both the full-scale rotary kiln and the afterburner and have been analyzed subsequently using GC and/or GC/MS techniques. We report on these preliminary measurements in some detail.
Cundy, V.A.; Lester, T.W.;
Morse, J.S.; Montestruc, A.N.; Leger, C.B.; Acharya, S.; Sterling, A.M. and
Pershing, D.W.
Submitted to Journal of the Air Pollution Control Association, 1988.
28 pgs. Funded by Gas Research Institute, ACERC (National Science Foundation
and Associates and Affiliates), and National Science Foundation/Presidential
Young Investigators.
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 four-fold approach is being 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. A pilot-scale rotary kiln was developed to study the evolution of contaminants from solids within a realistic temperature and rotation environment. Finally, in-situ measurements are being obtained from a full-scale rotary-kiln.
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.
Cundy, V.A.; Lester, T.W.;
Morse, J.S.; Montestruc, A.N.; Leger, C.B.; Acharya, S.; Sterling, A.M. and
Pershing, D.W.
Submitted to Journal of the Air Pollution Control Association, 1988.
31 pgs. Funded by Environmental Protection Agency.
Temperature and stable species concentration data are presented from various locations within a full-scale rotary kiln firing natural gas/carbon tetrachloride/air. The data are being collected as part of a cooperative program involving university, industrial and government participation. The overall goal of the program is to develop a rudimentary understanding of and a predictive capability for rotary kiln and afterburner performance as influenced by basic design and operation parameters. The data clearly demonstrates that severe non-uniformities exist at the kiln exit under certain operating conditions. Even so, the data further indicate that high destruction efficiencies were achieved through adequate secondary combustion processing. The data further show that flow perturbations from within the kiln can persist well into the afterburner section and even into the stack.
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.
Nichols, K.M.; Hedman, P.O.
and Smoot, L.D.
Western States Section, 1986, The Combustion Institute, Tucson, AZ. Also
published in Fuel, 1257-1263, 1987. 7 pgs. Funded by US Department of
Energy and Morgantown Energy Technology Center.
Effects of pressure, flame type and coal feed rate on fuel-nitrogen release and nitrogen pollutant formation were examined in a laboratory scale, entrained-coal gasifier. A Utah, high-volatile bituminous coal was used. With a water-quenched probe, gas-particulate samples were collected for oxygen-coal mass ratios from 0.6 to 1.1, pressures of 1, 4.9 and 10.4 ATM and coal feed rates of 25 and 35 kg·h-1. Two injector types were utilized; one produced a diffusion flame, the other a premixed flame. Fuel-nitrogen release from the coal showed little dependence on oxygen-coal ratio, pressure or coal feed rate. Values at the gasifier exit averaged 83% for the diffusion flame and 92% for the premixed flame. Fuel-nitrogen release, mostly during devolatilization, exceeded fuel-carbon released by ~10% for the premixed flame and ~30% for the diffusion flame, depending on oxygen-coal mass ratio. Over 50% of the released fuel-nitrogen formed N2, with significant amounts of NH3 and HCN, and smaller amounts of NO. Increased pressure at constant mass feed rates caused sharp decreases in effluent NO concentrations (to near zero) for both flame types which was explained by a combination of increased residence time and increased homogeneous NO decay rate. Elevated pressure also increased the effluent NH3 and decreased HCN concentrations for the diffusion flame whereas the more complete mixing of the premixed flame resulted in lower NH3 and HCN levels, and higher N2 levels. In general, nitrogen species concentrations were not largely affected by coal feed rate, though increased coal feed rate decreased NH3 levels somewhat.
Boardman, R.D. and Smoot,
L.D.
Western States Section, 1987, The Combustion Institute, Provo, UT. 25
pgs. Funded by Morgantown Energy Technology Center through subcontract from
Advanced Fuel Research Co.
Further verification of a predictive model for nitric oxide formation during turbulent combustion of coal containing fuels has been conducted. Computations for pulverized coal combustion in CO2-02 mixtures of various percents have been completed. The predicted NO concentrations compare favorably with experimental measurements. Simulations were also completed for entrained-flow gasification in a laboratory-scale combustor. Again, reasonable agreement is demonstrated by comparing laboratory NO maps to predicted NO concentrations. The effects of pressure on NO concentrations were reliably predicted. Calculations were also completed for air-staged combustion in a one-dimensional, laboratory-scale reactor. In general, the trend of decreasing primary zone stoichiometric ratio and variation in staging air location were correctly predicted. The simplified global mechanism expressions of the NO model appear to sufficiently account for the formation and competing destruction of NO in both fuel-lean and fuel-rich environments for different reactor systems and conditions.
Nichols, K.M.; Hedman, P.O.;
Smoot, L.D. and Blackham, A.U.
Western States Section, 1987, The Combustion Institute, Provo, UT. 16
pgs. Funded by Morgantown Energy Technology Center.
This work summarizes several observations concerning the effects of pressure and oxygen-to-coal mass ratio on the fate of coal-sulfur during entrained gasification. A high-volatile bituminous coal was pulverized to a mass mean of near 50 mm. The coal was gasified with oxygen in a laboratory-scale entrained-flow gasifier. Test pressures were atmospheric (1.0 ATM, 101 kPa), 4.9 ATM (500 kPa), and 10.4 ATM (1050 kPa). Oxygen-to-coal mass ratios between 0.6 and 1.1 were investigated. Gas-particulate samples were collected with a water-quenched probe from the gasifier chamber effluent stream. Measurements were made of the sulfur retained in the char particles and of the concentrations of H2S, SO2, COS and CS2 in the product gas. Conversion of sulfur to the gas phase was observed to decrease with increasing pressure, possibly through sulfur captured by char. Changing pressure caused a change in the distribution of gas phase sulfur species. At higher pressure, the proportions of SO2 and CS2 decreased, and the proportion of H2S increased. This redistribution with increasing pressure is not predicted by equilibrium calculations, nor was it observed in learner (less particle laden) combustion environments. This suggests the importance of char in determining the fate of the coal-sulfur during gasification. Increasing oxygen-to-coal mass ratio increased sulfur conversion, SO2 concentration, and COs concentration, while it decreased H2S and CS2 concentrations.
Milne, C.R. and Pershing,
D.W.
Proc. 4th Annual Pittsburgh Coal Conf., 1987. 14 pgs. Funded by ACERC
(National Science Foundation and Associates and Affiliates).
The sulfation of raw and sized calcium-based sorbents under high-temperature, short time conditions typical of injection in pulverized coal fired boilers was studied. A 100,000 Btu/hr refractory walled flow reactor was used to obtain isothermal SO2 capture which occurs in the first 30 ms after injection and results from inherent particle size difference between the two sorbent types. In this instance, the hydrate particle size is one-tenth that of the carbonate, and the hydrate capture at Ca/S = 2 is 30% versus 5% for the carbonate.
Beyond approximately 200 ms the sulfation rate was insensitive to particle size, but the rate of SO2 capture increase with the hydrated sorbent was larger than that measured with the carbonate sorbent. This suggests that the ultimate extent of sulfation is also influenced by structural parameters. Ultimate calcium utilization does not appear to be significantly influenced by the calcination rate differences between hydrates and carbonates for particles smaller than 5 um. For large carbonate particles, the calcination delay slightly retards the initial sulfur capture and reduces the ultimate calcium utilization.
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.
Lindgren, E.R. and Pershing,
D.W.
Western States Section, Combustion, Combustion Institute,
1987. Funded by Environmental Protection Agency.
A major concern associated with the combustion of coal for heat and electricity is the emission of acid rain precursors, NOx and SO2. Dry calcium based sorbent injection is a potential method for reducing SO2 emissions from existing coal-fired boilers. A great deal of study has been devoted to the fuel lean SO2 reaction:
CaO + SO2 ==> CaSO4
The fuel rich analogies:
CaO + H2S ==> CaS + H2O
CaO + COs ==> CaS + CO2
are kinetically faster than the SO2 reaction. Thermodynamics plays an important role in the rich capture reactions because the gaseous products are also products of combustion. These fuel rich reactions have not been extensively studied, particularly under combustion conditions.
In this study a refractory lined, down fired natural gas furnace was used to study fuel rich sulfur capture as a function of sulfur concentration (750-3000 ppm), molar ratio of calcium to sulfur (Ca/S = 1 to 4), residence time (0.30 to 0.65 sec), quench rate (450 to 900ºF/sec), stoichiometric ratio in the rich zone (SR=0.65, 0.75), and sorbent type (Marblehead hydrate and Fredonia carbonate). The fuel rich sulfur species H2S and COs were monitored in a near continuous fashion using a gas chromatograph equipped with a flame photometric detector (GC-FPD) and an automatic sampling system which sampled every 30 seconds. Below the fuel rich zone, 25% excess air was added and the ultimate fuel lean capture was measured using a continuous SO2 monitor.
Under fuel rich conditions, calcium utilization increases with increasing sulfur concentration and decreasing Ca/S. At low concentrations, fuel rich sulfur capture may be thermodynamically limited. The ultimate lean capture was found to be independent of the sulfur capture level obtained in the fuel rich zone, thus the high capture realized in the rich zone was lost. The results on the lean side are very typical of lean capture data reported by others; i.e. the calcium utilization is weakly dependent on Ca/S and sulfur concentration. These results suggest that the rate-limiting step under fuel rich conditions is different than under fuel lean conditions.
Lindgren, E.R. and Pershing,
D.W.
Western States Section, Combustion Institute, 1987, Honolulu, Hawaii.
Funded by Environmental Protection Agency.
Sized 3 to 10 µm calcium based sorbent particles (one hydrate and one carbonate) were precalcined to calcium oxide (CaO) and injected into a refractory lined, natural gas fueled furnace operated under fuel rich conditions (SR=0.75). Fuel rich sulfur species, H2S and COs react with CaO to form calcium sulfide (CaS). Gas phase sulfur capture measurements were made at a residence time of 0.44 seconds as a function of sulfur concentration (800 to 3200 PPM) and calcium availability (Ca/S = 1 to 4). For selected runs, solid samples were collected simultaneously at a residence time of 0.65 seconds and N2 porosimetry measurements were made to determine the effect of conversion on the pore size distribution (PSD).
The data are compared to the predictions of a computer model which views a sorbent particle as a sphere made up of a distribution of randomly oriented, highly interconnected, cylindrical pores, (attributed to Christman and Edgar). Both precalcined sorbents exhibit a strong positive dependence on sulfur concentration that the model predicts well for the hydrate but not for the carbonate. These results parallel those found for the same raw sorbents (not precalcined) in an earlier study. The effect of conversion on the PSD was predicted better for the hydrate sorbent than for the carbonate sorbent.
Milne, C.R. and Pershing,
D.W.
Proc. 4th Annual Pittsburgh Coal Conf., 1987. 6 pgs. Funding source ACERC
(National Science Foundation and Associates and Affiliates).
The sulfation of raw and sized calcium-based sorbents under high-temperature, short time conditions typical of injection in pulverized coal fired boilers was studied. A 100,000 Btu/hr refractory walled flow reactor was used to obtain isothermal SO2 capture data for a carbonate and a hydrate derived from the carbonate as a function of reactor residence time and particle size.
Experimental results confirmed the importance of sorbent type and particle size. The hydrated sorbent was clearly superior to the carbonate. This difference is primarily attributable to a dramatic difference in prompt SO2 capture which occurs in the first 30 ms after injection and results from inherent particle size difference between the two sorbent types. In this instance, the hydrate particle size is one-tenth that of the carbonate, and the hydrate capture at Ca/S = 2 is 30% versus 5% for the carbonate.
Beyond approximately 200 ms the sulfation rate was insensitive to particle size, but the rate of SO2 capture increase with the hydrated sorbent was larger than that measured with the carbonate sorbent. This suggests that the ultimate extent of sulfation is also influenced by structural parameters. Ultimate calcium utilization does not appear to be significantly influenced by the calcination rate differences between hydrates and carbonates for particles smaller than 5 µm. For large carbonate particles, the calcination delay slightly retards the initial sulfur capture and reduces the ultimate calcium utilization.
Hecker, W.C.; Wardinsky,
M.D.; Clemmer, P.C. and Breneman, R.B.
Proc. of 9th Inter. Congress on Catalysts, 1988. Funded by Brigham Young
University.
The effects of molybdena and ceria addition on the catalytic activity of silica-support rhodium for the reduction of NO by CO have been measured. FTIR spectroscopy was used as a qualitative and quantitative probe of the catalyst surface to determine the type and number of Rh surface sites present under reaction conditions. The addition of Mo was seen to have only a small effect on the bulk rate, but had a significant effect on transient behavior, turnover frequency, Rh oxidation state, and power rate law. A 1% Rh / 4% MO catalyst which was prepared by consecutive impregnation with intermediate calcination exhibited no transient decay and had a steady-state turnover frequency 2.5 times that observed for 1% Rh/silica. Infrared spectra of this catalyst showed a new dicarbonyl species with bands at 2110 cm-1 that indicate that the Rh is in a more oxidized state in the Rh/MO catalyst than in straight Rh. The NO partial pressure dependency was seen to be much more negative on Rh/MO than on Rh, probably due to MO-assisted NO adsorption. The addition of CE was seen to give opposite behavior to MO addition in terms of Rh dispersion, turnover frequency, and NO partial pressure dependency. While MO addition decreased the Rh dispersion, the addition of CE was seen to increase it; however, it decreased turnover frequency. The NO partial pressure dependency became less negative than that for straight Rh.
Eatough, C.N.; Rawlins,
D.C.; Germane, G.J. and Smoot, L.D.
Western States Section, The Combustion Institute, Dana Point, California,
1988. Funded by US Department of Energy (Morgantown Energy Technology Center)
and ACERC (National Science Foundation Associates and Affiliates).
Lignite slurry atomization and combustion characteristics were studied using two atomizers, one developed at Brigham Young University (laboratory nozzle) and the other a Parker-Hannifin Model 6840610 M3 atomizer (commercial nozzle). These nozzles were used because of the significantly different spray patterns produced by each. In these cold-flow studies, it was found that the laboratory nozzle produced a solid cone type spray pattern with the highest mass flux near the spray center line. The commercial nozzle has a hollow cone spray pattern with a larger spray angle. Atomization studies were performed with these nozzles to determine the effect of atomizing air to slurry mass flow ratio (A/S) on particle/droplet size and velocity, and slurry spray mass distribution. These measurements were then used to study the effect of particle/droplet size and velocity, and spray mass distribution on carbon burnout in a laboratory scale reactor using hot-water dried lignite slurry as a fuel. Both the laboratory and commercial nozzles follow the same trends for mean droplet size and droplet velocity with variation in A/S. As expected, mean droplet size decreased with A/S and velocity increased with A/S. Spray angle decreased for the laboratory nozzle but increased for the commercial nozzle with increase in A/S.
Analysis of combustion data indicates an expected strong dependence of burnout on particle/droplet size. Burnout increased markedly as particle/droplet size decreased. Burnout was also affected by the mass distribution of the slurry spray. Large spray angles directed slurry to the relatively cool reactor walls resulting in lower burnout values. Burnout values from both nozzles followed the same trends with regard to droplet size. Burnout increased with decreasing mean droplet size to about 50 mm, which corresponded closely with the coal particle size in the slurry which has a mean diameter of about 40 mm. A mean droplet diameter larger than about 80 mm with a 300 mm top size could not sustain combustion in the laboratory reactor.
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.; 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.
Chen, S.L.; Cole, J.A.;
Heap, M.P.; Kramlich, J.C.; McCarthy, J.M. and Pershing, D.W.
Twenty-Second Symposium (International) on Combustion/The Combustion Institute,
1135-1145, 1988. Funded by Pittsburgh Energy Technology Center.
The effectiveness of combustion modifications for the control of nitrogen oxide emissions from coal fired combustors is most often limited by problems due to carbon burnout or flame impingement. This paper presents new data on the use of selective reducing agents suggesting that a hybrid control scheme is possible which uses combustion modification to provide those conditions that optimize the selective reduction process. Very low emission levels appear possible that can presently only be achieved by catalytic reduction. The experimental studies were conducted in a tunnel furnace that simulated the thermal environment within a pulverized coal boiler. Application of each of the agents (ammonia, urea, cyanuric acid, and ammonium sulfate) to an overall fuel lean environment produced NO reduction behavior very similar to that of thermal deNOx. However, if the agent was added to the fuel rich zone of a rich/lean staged combustor, very high NO reductions were obtained after the leanout point. The result of the staging was to extend the effectiveness of the agent to lower temperatures relative to overall lean injection. Parametric variations indicated that in addition to temperature, the most important variable was the rich zone stoichiometry. Kinetic modeling suggests that the rich zone acts primarily as a source of CO. At the rich/lean transition the CO is oxidized and excess OH is produced by the usual chain branching reactions. For low initial CO concentrations the excess radicals are consumed by:
NH3 + OH = NH2 + H2O
HNCO + H = NH2 + CO
The NH2 is then available for reaction with NO to eventually yield N2. The strong rich zone stoichiometry dependence is exerted mainly through the amount of CO supplied to the lean zone. Insufficient CO will limit the extent of the initial NH3 or HNCO reaction.
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