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Characterization of porosity via secondary reactions

Description: During the course of recent work applying temperature programmed desorption (TPD) to the determination of energetic distributions of oxygen complexes on the surfaces of oxidized coal chars, we discovered that secondary interactions occurring within the char structure during TPD produce characteristic features in the resultant spectra that appear to be quite sensitive to char porosity. The relative and absolute extents of these secondary interactions from the basis of a potential characterization technique. The use of such a method to characterize coal char porosity is potentially attractive because the requisite spectra can be obtained in a single TPD experiment -- a very facile experimental procedure. However, the unambiguous and quantitative interpretation of such data in terms of parameters that can be used to characterize coal char porosity still requires development and an improved understanding of the controlling phenomena. These issues define the primary focus of the current proposal.
Date: January 1, 1991
Creator: Calo, J.M. & Lilly, W.D.
Partner: UNT Libraries Government Documents Department

A new model of coal-water interaction and relevance for dewatering

Description: This project is concerned with a basic scientific question concerning the properties of coal--to what extent is the ability of coal to hold moisture a manifestation of the well-known ability of coal to swell, when exposed to good solvents The question implies that the long-held belief that coal holds a significant portion of its moisture by classical capillary condensation processes, is possibly in error. It is likely that a sound approach to permanent drying would involve highly crosslinking the coal at mild drying conditions. The crosslinked coal could not swell sufficiently to hold much water. It is identifying processes to achieve this goal, that constitute the objective of the second phase of this work. 25 refs., 4 figs., 1 tab.
Date: January 1, 1991
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, 1 January 1996--31 March 1996

Description: The vapor pressure correlations that exist at present for coal tars are very crude and they are not considered reliable to even an order of magnitude. Sophisticated general correlative approaches are slowly being developed, based upon group contribution methods, or based upon some key functional features of the molecules. These are as yet difficult to apply to coal tars. The detailed group contribution methods, in which fairly precise structural information is needed, do not lend themselves well for application to very complex, poorly characterized coal tars. The methods based upon more global types of characterizations have not yet dealt much with the question of oxygenated functional groups. In short, only very limited correlations exist, and these are not considered reliable to even an order of magnitude when applied to tars. The present project seeks to address this important gap in the near term by direct measurement of vapor pressures of coal tar fractions, by application of well- established techniques and modifications thereof. The principal objectives of the program are to: (1) obtain data on the vapor pressures and heats of vaporization of tars from a range of ranks of coal, (2) develop correlations based on a minimum set of conveniently measurable characteristics of the tars, (3) develop equipment that would allow performing such measurements in a reliable, straightforward fashion. A significant amount of time has been devoted during this quarter to developing techniques for measurements of vapor pressures of coal tar related compounds, and mixtures, in a ``continuous`` mode, using the effusion technique.
Date: September 1, 1996
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, July 1--September 30, 1995

Description: There is significant current interest in general area of coal pyrolysis, particularly because of the central role of pyrolysis in all thermally driven coal conversion processes-gasification, combustion, liquefaction, mild gasification, or thermal beneficiation. There remain several key data needs in these application areas. Among them is a need for more reliable correlation for prediction of vapor pressure of heavy, primary coal tars. The vapor pressure correlations that exist at present for coal tars are very crude and they are not considered reliable to even an order of magnitude when applied to tars. The present project seeks to address this important gap in the near term by direct measurement of vapor pressures of coal tar fractions, by application of well-established techniques and modifications thereof. The principal objectives of the program are to: (1) obtain data on the vapor pressures and heats of vaporization of tars from a range of ranks of coal, (2) develop correlations based on a minimum set of conveniently measurable characteristics of the tars, (3) develop equipment that would allow performing such measurements in a reliable, straightforward fashion. A significant amount of time has been devoted during this quarter to extending the work on measurements of vapor pressures of tars. For this purpose, cellulose tar and cellulose tar related compounds have been selected as model systems. Cellulose tar has a much narrower distribution of molecular weight than does coal tar, and it is much more homogeneous. Thus it is better to develop the methods to be used for coal tars on this simpler model system first.
Date: December 31, 1995
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Reactivity of young chars via energetic distribution measurements. Final report, 1 September 1990--31 December 1994

Description: We have developed what we believe to be the very first, a priori, correlation/prediction technique for the gasification reactivity of coal char. With this method the gasification reactivity of a coal char as a function of temperature can be correlated using the data from a temperature programmed desorption (TPD) experiment following gasification under conditions where the reactivity is controlled by the thermal desorption of oxygen surface complexes formed during gasification. The current project was directed at extending and developing related techniques for the characterization and prediction/correlation of the reactivity of the ``young`` chars to CO{sub 2} and steam. Of particular interest was mapping of the reactivity behavior of the resultant chars, as revealed by the energetic heterogeneity of the complexes with char preparation conditions.
Date: January 1, 1996
Creator: Calo, J.M.; Zhang, L.; Lu, W. & Lilly, W.D.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NO{sub x}: Char reduction

Description: This report conveys recent progress on two issues. The first concerns the prediction on char-NO reactivity in general. The work has been performed upon a literature review, supplemented by our own recent results. The second part has to do with more detailed issues related to the mechanism of the reaction. Specifically, it is concerned with how oxide desorption can affect the observed kinetics. The report is divided into two stand-alone sections, on each of the above two topics. This material recently served as a basis for two manuscripts prepared for presentation at an American Chemical Society National meeting.
Date: September 1, 1996
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, April 1, 1996--June 30, 1996

Description: As the world continues to deplete its petroleum reserves, then heavy crude oil, coal liquids, and other heavy fossil fuels may be required to meet the world energy needs. Heavy fossil fuels contain molecules that are large and more aromatic and that contain more heteroatoms than those found in liquid crude oil. There is also significant current interest in general area of coal pyrolysis, particularly with respect to comprehensive models of this complicated phenomenon. This interest derives from central role of pyrolysis in all thermally driven coal conversion processes - gasification, combustion, liquefaction, mild gasification, or thermal beneficiation. There remain several key data needs in these application areas. Among them is a need for a more reliable correlation for prediction of the vapor pressures of heavy, primary coal tars. Such information is important in design of all coal conversion processes, in which the volatility of tarry products is of major concern. This paper presents work on the vapor pressures of coal tars using the continuous knudsen effusion technique.
Date: December 31, 1997
Creator: Suuberg, E.M.; Oja, V. & Lilly, W.D.
Partner: UNT Libraries Government Documents Department

Char crystalline transformations during coal combustion and their implications for carbon burnout. Semiannual technical progress report, July 1, 1996--January 1, 1997

Description: This paper reports on research concerned with coal combustion and the crystal transformations of coal chars. Goals were to: determine transient high-temperature deactivation kinetics as a function of parent coal; and to characterize the effect of thermal treatments on the carbon crystal structure.
Date: June 1, 1997
Creator: Hurt, R.H.
Partner: UNT Libraries Government Documents Department

Characterizadtion of porosity via secondary reactions. Quarterly technical progress report, 1 July 1994--30 September 1994

Description: The following was accomplished during the reporting period: Comparisons between porosity characterization data obtained from nitrogen adsorption isotherms, and that revealed by CO and CO{sub 2} temperature programmed desorption (TPD) spectra were performed for Pittsburgh {number_sign}8 coal char samples prepared at various degrees of burn-off, ranging from 0--72% burn-off, in 0.1 MPa oxygen at 470{degrees}C. Conclusions derived from these analyses include: The CO TPD spectra correlate the development of the microporosity; and the CO{sub 2} spectra correlate the development of the larger, external porosity. This behavior is the same as we have observed for Wyodak coal char. This behavior is currently attributed to the restriction of formation of the larger C0{sub 2}-liberating oxygen surface complexes (e.g., lactones, carboxylic acid anhydrides) to the larger, external porosity, while the smaller CO{sub 2}-liberating complexes (e.g., carbonyls, semi-quinones) form on the surfaces of all they porosity, but since the microporosity accounts for the bulk of the surface area, the latter correlates the microporosity quite well. Together with the Wyodak coal char results, these data represent the first time that this particular connection has been made between porosity development and TPD spectra.
Date: December 31, 1994
Creator: Calo, J.M. & Zhang, L.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NOx - char reduction. Quarterly technical progress report, 1 August, 1996--31 October, 1996

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or {open_quotes}greenhouse{close_quotes} gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2}, in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons.
Date: May 1, 1997
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, 1 October--31 December 1994

Description: The vapor pressure correlations that exist at present for coal tars are very crude and they are not considered reliable to even an order of magnitude when applied to tars. The present project seeks to address this important gap in the near term by direct measurement of vapor pressures of coal tar fractions, by application of well-established techniques and modifications thereof. The principal objectives of the program are to: (1) obtain data on the vapor pressures and heats of vaporization of tars from a range of ranks of coal, (2) develop correlations based on a minimum set of conveniently measurable characteristics of the tars, and (3) develop equipment that would allow performing such measurements in a reliable, straightforward fashion. A significant amount of time has been devoted during this quarter to testing the equipment for measurements by the gas saturation method and the Knudsen effusion method. These techniques are beginning to yield reliable results. Some key features of the methods are summarized, and sample results presented.
Date: April 1, 1995
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NO{sub x} - char reduction. Quarterly technical progress report, 1 May, 1996--31 July, 1996

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or {open_quotes}greenhouse{close_quotes} gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2}, in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons.
Date: December 31, 1997
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Kinetics and Mechanisms of NO(x) - Char Reduction.

Description: Most industrially important carbons are produced from naturally occurring materials such as coal, oil, peat or wood by some form of thermal process. Chars are obtained from those natural materials as a residue after removal of the volatile matter. Chars (prepared from coal or other organic precursors) are non-graphitizable carbons, meaning that they cannot be transformed into graphitic carbon. Chars are comprised of elementary crystallites in parallel layers which are randomly oriented with respect to each other and are crosslinked together through weak bonds. Voids between crystallites determine the porosity of the char, and this plays an important role in char gasification behavior. Chars usually contain a pore size distribution, in which the larger macro- and mesopores play an important role in transport of reactants into the much smaller micropores, in which most gasification and combustion take place. Therefore, the effectiveness of micropores in gasification depends heavily on the numbers of meso- and macropores.
Date: December 31, 1997
Creator: Suurerg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Characterization of porosity via secondary reactions: Quarterly technical progress report, 1 October 1994--31 December 1994

Description: Specific surface area, as well as its accessibility to gaseous reactants, are of paramount importance for all heterogeneous interactions occurring at coal char surfaces. Accessibility of this surface area is governed by the pore structure morphology of the char; i.e., pore size distribution, tortuosity, intersections, shape, etc. The porosity morphology of coal chars varies over a considerable range and is determined by a large number of factors including the nature of the porosity of the precursor material prior to carbonization, the carbonization process, and extent and method of any subsequent activation or gasification. A persistent problem in this area has been the reliable, quantitative measurement and characterization of the resultant porosity, especially the micropores. The following was accomplished during the reporting period: use of the random pore model as a method of rationalizing the data obtained from CO and CO{sub 2} TPD spectra has been initiated; and {alpha}-plot data obtained for Wyodak coal char samples prepared at various degrees of burn-off, ranging from 0--75% burn-off, in 0.1 MPa oxygen at 470 C, were used to compare with random pore model predictions. Conclusions derived from this analysis include: the random pore model predictions are consistent with the evolution of sample surface area and porosity with burn-off as determined for the Wyodak coal char samples; and the parameters obtained from the random pore model provide a reasonably good comparison with the {alpha}-plot data.
Date: May 1, 1995
Creator: Calo, J.M. & Zhang, L.
Partner: UNT Libraries Government Documents Department

Kinetics and Mechanisms of NO(x) - Char Reduction

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or greenhouse gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent N0{sub 2} (since it is mainly a secondary product of combustion, e.g. see ref. 1), in recent years the emissions of N{sub 2}0 have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}0 problem. This is in part because earlier estimates of the importance of N{sub 2}0 in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}0 by carbons. It was recognized some years ago that NO formed during fluidized bed coal combustion can be heterogeneously reduced in-situ by the carbonaceous solid intermediates of combustion. This has been recently supplemented by the knowledge that heterogeneous reaction with carbon can also play an important role in reducing emissions of N{sub 2}0{sub 2}, but that the NO-carbon reactions might also contribute to formation of N{sub 2}0{sub 2}. The precise role of carbon in N{sub 2}0 reduction and formation has yet to be established, since in one case the authors of a recent study were compelled to comment that the basic knowledge of N{sub 2}0 formation and reduction still has to be improved. The same can be said of the NO-carbon system. Interest in the NO- and N{sub 2}0-char reactions has been significant in connection with both combustor modeling, as well as in design of post-combustion NO{sub x} control strategies.
Date: September 1, 1997
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Char crystalline transformations during coal combustion and their implications for carbon burnout. Semiannual technical progress report, 1 January 1996--1 July 1996

Description: Recent work at Sandia National Laboratories, Imperial College, and the U.K. utility PowerGen, has identified an important mechanism believed to have a large influence on unburned carbon levels from pulverized coal fired boilers. That mechanism is char carbon crystalline rearrangements on subsecond times scales at temperatures of 1800 - 2500 K, which lead to char deactivation in the flame zones of furnaces. The so-called thermal annealing of carbons is a well known phenomenon, but its key role in carbon burnout has only recently been appreciated, and there is a lack of quantitative data in this time/temperature range. In addition, a new fundamental tool has recently become available to study crystalline transformations, namely high resolution transmission electron microscopy (HRTEM) fringe imaging, which provides a wealth of information on the nature and degree of crystallinity in carbon materials such as coal chars. Motivated by these new developments, this University Coal Research project has been initiated with the following three goals: to determine transient, high-temperature thermal deactivation kinetics as a function of parent coal and temperature history; and to characterize the effect of this thermal treatment on carbon crystalline structure through high-resolution transmission electron microscopy and specialized, quantitative image analysis. Work is currently underway on the following three tasks: (1) experimental technique development; (2) thermal deactivation kinetics; and (3) crystal structure characterization. In this second project period, progress was made on subtasks 1 and 3, in both cases in the areas of equipment and technique development. These activities are discussed in detail in this report.
Date: November 1, 1996
Creator: Hurt, R.H.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NO{sub x}: Char reduction

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or greenhouse gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2} (since it is mainly a secondary product of combustion), in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processed were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons.
Date: September 1, 1996
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, April 1--June 30, 1995

Description: The vapor pressure correlations that exist at present for coal tars are very crude and they are not considered reliable to even an order of magnitude when applied to tars. The present project seeks to address this important gap in the near term by direct measurement of vapor pressures of coal tar fractions, by application of well-established techniques and modifications thereof. The principal objectives of the program are to: (1) obtain data on the vapor pressures and heats of vaporization of tars from a range of ranks of coal, (2) develop correlations based on a minimum set of conveniently measurable characteristics of the tars, (3) develop equipment that would allow performing such measurements in a reliable, straightforward fashion. Both the gas saturation method and the Knudsen effusion method are being used. Results are presented for anthracene, naphthacene, pentacene, and a mixture of anthracene and perylene obtained using the effusion method.
Date: October 1, 1995
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NOx - char reduction. Quarterly technical progress report, August 1, 1995--October 31, 1995

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or {open_quotes}greenhouse{close_quotes} gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2} (since it is mainly a secondary product of combustion), in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons. It was recognized some years ago that NO formed during fluidized bed coal combustion can be heterogeneously reduced in-situ by the carbonaceous solid intermediates of combustions. This has been recently supplemented by the knowledge that heterogeneous reaction with carbon can also play an important role in reducing emissions of N{sub 2}O, but that the NO-carbon reactions might also contribute to formation of N{sub 2}O. The precise role of carbon in N{sub 2}O reduction and formation has yet to be established, since in one case the authors of a recent study were compelled to comment that the basic knowledge of N{sub 2}O formation and reduction still has to be improved. The same can be said of the NO-carbon system.
Date: May 1, 1996
Creator: Suuberg, E.M.; Lilly, W.D. & Aarna, I.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NO{sub x} - char reduction. Quarterly technical progress report, November 1, 1994--January 31, 1995

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or {open_quotes}greenhouse{close_quotes} gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2} (since it is mainly a secondary product of combustion), in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons.
Date: March 1, 1995
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Vapor pressures and heats of vaporization of primary coal tars. Quarterly technical progress report, October 1, 1995--December 31, 1995

Description: As the world continues to deplete its petroleum reserves, lower quality fossil fuels will play an increasingly important role in energy production. Heavy crude oil, coal liquids, and other heavy fossil fuels may be required to meet world energy needs. Heavy fossil fuels are generally higher in molecular weight, more aromatic, and contain more heteroatoms than higher quality petroleum. There will be an increasing need to deal with such low quality feedstocks, and therefore, an incentive to learn more about their properties. There is also significant current interest in the general area of coal pyrolysis, particularly with respect to comprehensive models of this complicated phenomenon. This interest derives from the central role of pyrolysis in all thermally driven coal conversion processes - gasification, combustion, liquefaction, mild gasification, or thermal beneficiation. There remain several key data needs in these application areas. Among them is a need for more reliable correlations for predicting vapor pressures of heavy, primary coal tars. Such information is important in design of all coal conversion processes, in which the volatility of tarry products is of major concern. This work presents results on vapor pressures and vaporization heat of polycyclic aromatic hydrocarbons and mixtures found in coal tar.
Date: June 1, 1996
Creator: Suuberg, E.M.; Oja, V. & Lilly, W.D.
Partner: UNT Libraries Government Documents Department

Characterization of porosity via secondary reactions. Quarterly technical progress report, 1 April 1995--30 June 1995

Description: In the previous quarterly report (DE-FG22-91PC91305-14), we presented an analysis of small angle neutron scattering (SANS) data obtained for Pittsburgh {number_sign}8 coal char. These samples exhibited considerable scattering. However, when the voids between the particles were filled with a liquid that had the same neutron scattering density as the carbon, the amount of scattering was reduced by more than two orders of magnitude. Analysis of the scattering invariant in terms of surface area showed that the char had very little porosity. To date this has been the only contrast matching SANS study of carbon and the first recognition that interparticle scattering effects are important. In this report, we focus on SANS data obtained for a very different char--a phenolic resin char (PRC). The following was accomplished during the reporting period: contrast matching, SANS data obtained for resin char has been analyzed in detail. Conclusions derived from this analysis include: contrast matching SANS has been demonstrated to be a useful technique for monitoring the activation/gasification process. It is demonstrated how this technique can be used to address such important issues as the role of ``closed`` vs ``open`` porosity, and interparticle scattering. It has been used here to establish that the development of porosity in phenolic resin char upon gasification in air proceeds primarily by ``opening `` or originally ``closed`` porosity. This is quite different than the behavior of Pittsburgh {number_sign}8 coal char. for example, as presented in the previous quarterly report.
Date: December 31, 1995
Creator: Calo, J.M.; Hall, P.J.; Antxustegi, M.M. & Zhang, L.
Partner: UNT Libraries Government Documents Department

Kinetics and mechanisms of NO{sub x} - char reduction. Quarterly technical progress report, May 1, 1995--July 31, 1995

Description: The emission of nitrogen oxides from combustion of coal remains a problem of considerable interest, whether the concern is with acid rain, stratospheric ozone chemistry, or {open_quotes}greenhouse{close_quotes} gases. Whereas earlier the concern was focused mainly on NO (as a primary combustion product) and to a lesser extent NO{sub 2} (since it is mainly a secondary product of combustion), in recent years the emissions of N{sub 2}O have also captured considerable attention, particularly in the context of fluidized bed combustion, in which the problem appears to be most acute. The research community has only recently begun to take solid hold on the N{sub 2}O problem. This is in part because earlier estimates of the importance of N{sub 2}O in combustion processes were clouded by artifacts in sampling which have now been resolved. This project is concerned with the mechanism of reduction of both NO and N{sub 2}O by carbons. It was recognized some years ago that NO formed during fluidized bed coal combustion can be heterogeneously reduced in-situ by the carbonaceous solid intermediates of combustion. This has been recently supplemented by the knowledge that heterogeneous reaction with carbon can also play an important role in reducing emissions of N{sub 2}O, but that the NO-carbon reactions might also contribute to formation of N{sub 2}O. The precise role of carbon in N{sub 2}O reduction and formation has yet to be established, since in one case the authors of a recent study were compelled to comment that {open_quotes}the basic knowledge of N{sub 2}O formation and reduction still has to be improved{close_quotes}. The same can be said of the NO-carbon system. In this program, carbons studied include graphite, resin char, coconut char, and a Wyodak coal char.
Date: December 1, 1995
Creator: Suuberg, E.M.
Partner: UNT Libraries Government Documents Department

Characterization of porosity via secondary reactions. Quarterly technical progress report, 1 July 1995--1 October 1995

Description: The following was accomplished during the reporting period: The random pore model was extended to correlate the development of microporosity in resin and Wyodak coal char. Conclusions derived from this analysis include: the random pore model can be extended to microporosity development for chars which are initially (i.e., at zero burn-off) microporous, assuming a normal micropore volume distribution. The resultant mean pore radius and variance prior to oxidation were, respectively, 1.04 nm and 0.24 nm for Wyodak coal char, and 0.64 nm and 0.18 nm for resin char. Consequently, the pore size is larger, and the pore distribution is broader for Wyodak coal char than for resin char prior to activation. The rate of mean micropore radius decrease with burn-off at high conversion is slower for resin char than for Wyodak coal char. This result suggests that the percentage of micropores converted to larger pores is smaller for resin char than for Wyodak coal char; i.e., resin char remains more microporous with burn-off. The nonmicroporous surface area was estimated by difference from the total surface area as determined from nitrogen adsorption data. These values correlate reasonably well with nonmicroporous surface areas determined from the {alpha}{sub s}-plot method.
Date: December 31, 1995
Creator: Calo, J.M. & Zhang, L.
Partner: UNT Libraries Government Documents Department