ACERC
Abstracts - 1993 |
ACERC
Abstracts - 1993 |
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Thrust Area 1: Fuel Structure and Reaction Mechanisms |
Smith, L.K.; Smoot, L.D.;
Fletcher, T.H. and Pugmire, R.J.
Chapter 3, Fundamentals of Coal Combustion: For Clean and Efficient Use,
(L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded
by ACERC.
The purposes of this chapter are to document, correlate, synthesize, integrate and relate the structural characterization and reaction rates of the suite of ACERC coals. The focus has been on research projects sponsored by ACERC. However, related research work outside of ACERC has also been considered. This chapter (1) reviews the selection of the suite of research coals, (2) reviews the origin of coal which gives rise to the various structural moieties in coal, (3) reviews coal characterization programs and documents the structure and characteristics of the research coals, (4) reviews coal reaction mechanisms, (5) explores the relationships of coal structure to devolatilization and char oxidation reaction rates, and (6) considers the models being developed which predict reaction characteristics based on structurally dependent parameters. Research programs in the field are still very active, the models are still in the formative states, reaction rates for the selected research coals are being measured, and the reaction processes for these coals have yet to be fully explored using the structurally dependent models. Further results will undoubtedly be forthcoming. This chapter is a condensed version of a larger work to characterize the structure and conversion processes of the research coals.
Smith, L.K.; Smoot, L.D.;
Fletcher, T.H. and Pugmire, R.J.
Plenum Publishing Corp., The Netherlands, 1993 (in press). Funded by ACERC.
This new ACERC book documents and integrates the current understanding of the organic and inorganic structure of coal and its reaction processes. Work in ACERC forms the foundation while the book attempts to include pertinent worldwide results. The book cites more than eight hundred references, almost all within the past decade, while the large majority are from various researchers around the world.
Eleven U.S. coals of various rank are emphasized in the book. These commonly used and highly characterized eleven coals form the research coals for ACERC and include all eight coals of the Argonne National Laboratory's Premium Coal Sample Bank. Altogether, the book contains six chapters. After an introduction, Chapter 2 documents the selection and characteristics of the suite of eleven coals, and relates them to various national databases. Chapter 3 deals with the geochemical history of coal and its macromolecular structure. Chapter 4 describes advanced analytical methods for measuring organic and inorganic structure of coal and documents results for the eleven coals. Chapters 5 and 6 treat the reaction processes of coals and chars. Recent model developments that relate fuel structure to yields and reaction rates are presented and compared to rate and yield data. Important measurements from the coal suite and other coals are reported and related to coal structure.
Laying a foundation for the future, this book has been written at a time when progress in this area is dramatic. The authors acknowledge that new results will be published at a rapid rate. What we have sought to accomplish through the writing of this manuscript is to promote increasing cooperative focus regarding the understanding of coal structure and its reaction and conversion processes. From this perspective, the book is thought to be the first of its kind.
Smith, L.K.; Smoot, L.D.;
Fletcher, T.H. and Pugmire, R.J.
Plenum Press Co., New York, 1993 (in press). Funded by ACERC.
This book characterizes the properties and reaction rates of the eleven US coals selected for emphasis by ACERC. Eight of the eleven comprise the Argonne National Laboratory's Premium Coal Sample Bank. The book features the comprehensive measurement of organic and inorganic components of the coal structure by advanced methods (SEM, NMR, GC, porosimetry, pycnometry, X-ray, and MS). The book features the measurement of coal devolatilization and char oxidation rates by advanced, optical methods and correlative relationships between the structure and reaction processes.
Kramer, S.K.
Ignition, Explosion, and Flame Propagation Characteristics of a Low-Rank
Coal, Ph.D./BYU, April 1993. Advisor: Smoot
Ma, K.-L.
Interactive Volume Visualization, Ph.D./U of U, July 1993. Advisor: Sikorski
Pugmire, R.J. and Fletcher,
T.H.
Energy & Fuels, 7 (6):700-703, 1993. Funded by ACERC.
A major objective of the Advanced Combustion Engineering Research Center is the development and verification of data on fuel characterization and reaction mechanisms and rates that can be incorporated into submodels for use in the comprehensive combustion codes. As Technology has advanced, the levels of analytical sophistication has also advanced, making it possible to augment the existing body of information with new data. From this new data it is possible to draw new insights regarding the complex nature of coal and the various processes associated with combustion. The ACERC program has made it possible to bring different disciplines together to work on an integrated research program that is targeted at a few key strategic issues. The overall program has been divided into six areas of research, designated as Thrust Areas. The principal areas of focus in Thrust Area 1 have been in delineation of coal structure and those key factors that are important in developing fundamental knowledge of devolatilization and char oxidation processes. This article discusses the objectives, accomplishments, and plans of ACERC-sponsored research in these areas.
Hu, J.Z.; Alderman, D.W.;
Orendt, A.M.; Ye, C.; Pugmire, R.J. and Grant, D.M.
Solid State Nuclear Magnetic Resonance, 2:235-243, 1993. Funded by US
Department of Energy and Pittsburgh Energy Technology Center.
Several improvements to the magic angle hopping experiment first introduced by Bax et al. (J. Magn. Reason., 52 (1983) 147 are presented. A dc servo motor driven sample hopping mechanism which requires less than 60 ms to accomplish a 120º sample rotation is described. Modifications to the data acquisition process, including starting the acquisition period immediately after the second hop and acquiring a hypercomplex data set, are also presented. Principal values of the C-13 chemical shielding tensor are measured for 1,2,3-trimethoxybenzene and 2,6-dimethoxynaphthalene.
Fletcher, T.H.; Bia, S.;
Pugmire, R.J.; Solum, M.S.; Woods, S. and Grant, D.M.
Energy & Fuels, 7 (6):734-742, 1993. (Presented at the Spring Meeting
of the Western States Section of the Combustion Institute, Salt Lake City,
UT, March 1993.) Funded by ACERC.
Soxhlet extractions were performed on the eight Argonne Premium coals using pyridine purged with argon and followed by a novel washing procedure to remove the pyridine. Mass closure (extracts plus residues) on duplicate experiments accounted for 94-96% of the original coal, repeatable to within 2%. Chemical structural features determined from C-13 NMR analyses of the extracts and residues showed more attachments per aromatic cluster for the residues, indicating a greater degree of covalent bonding in the residue than in the extract. H-1 NMR analysis of the extracts showed a gradual increase in the hydrogen aromaticity with rank, along with a maximum in the percentage of a-hydrogen in the high-volatile bituminous coals. Composite chemical features constructed from weighted averages of the features of the residues and extracts agree with many of the features of the parent coal. Chemical structural features of the extracts determined from H-1 NMR analyses agree with similar data reported previously for early coal tars during devolatilization at rapid heating rates.
Solomon, P.R.; Fletcher,
T.H. and Pugmire, R.J.
Fuel, 72:587-597, 1993. Funded, in part, by ACERC.
The heterogeneous nature of coal and the complexity of the pyrolysis process has made it very difficult to perform unambiguous experiments to determine the rates and mechanisms in coal pyrolysis. However, recent years have seen a number of new experimental and theoretical approaches that shed new light on the subject. This paper considers the recent progress on kinetics, the formation of volatile products, network models, crosslinking, rank effects, and the 'two-component model of coal structure.' Recent experiments that measured coal particle temperatures at high heating rates provide reasonable agreement on kinetic rate constants. These rates also agree with those derived from experiments at low heating rates. In tar formation and transport, a consensus is being reached on the central role of the volatility of tar molecules in explaining the variation with operating conditions (pressure, heating rate, particle size, etc.) of the amounts and molecular weight distribution of tars. Progress in the quantitative prediction of tar and char yields is being made through recently developed models for the fragmentation of the macromolecular coal network. These models, which provide quantitative descriptions of the relations between the chemical structure of the coal and the physical and chemical properties of the pyrolysis products (gas, tar, soot, and char), are an exciting advance in the understanding of the pyrolysis process. Such models are linking the occurrence of the plastic phrase with the 'liquid' fragments formed during pyrolysis. On the subject of retrogressive cross-linking reactions, both solvent swelling and NMR measurements confirm important rank-dependent differences in reaction rates: these appear to be related to the oxygen functionalities. Reasonable agreement is also seen for variations with coal rank of kinetics rates derived from measurements at low heating rates. Experiments suggest that the recently revived 'two-component' hypothesis of coal structure has application to low-rank coals which are mixtures of two distinct components: polymethylenes and a more aromatic network. Bituminous coals, however, appear far more homogeneous. Although experiments can distinguish loosely and tightly bound fractions these fractions appear to consist of similar materials and are differentiated primarily in their molecular weight and degree of connection to the network. These coals appear to behave in a manner that is described by the network decomposition models.
Orendt, A.M.; Solum, M.S.;
Sethi, N.K.; Hughes, C.D.; Pugmire, R.J. and Grant, D.M.
Magnetic Resonance of Carbonaceous Solids, Advances in Chemistry Series
#229, 22:419-439, 1993. Funded by US Department of Energy, Basic Energy Services
and ACERC.
The methods of available in NMR spectroscopy to obtain the principal values of the chemical-shift tensor are discussed. Applications to coal and to compounds with model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical-shift powder patterns is compared to results obtained by cross-polarization with magic-angle spinning and dipolar dephasing.
Hu, J.Z.; Alderman, D.W.;
Ye, C.; Pugmire, R.J. and Grant, D.M.
Journal of Magnetic Resonance, 31: 472, 1993. Funded by US Department
of Energy and Pittsburgh Energy Technology Center.
High-speed magic-angle spinning has become a ubiquitous method for obtaining high-resolution spectra in polycrystalline and amorphous solids. MAS reduces a chemical-shift-anisotropy powder pattern to a single line at the isotropic shift when the sample spinning speed is larger than the anisotropy. While the isotropic chemical shift is useful in characterizing chemical structure, the three principal values of the tensor are even more valuable. These principal values are available in the powder pattern obtained from a stationary or slowly spinning sample provided the molecule has few enough unique nuclei that the spectrum can be interpreted. Unfortunately, overlap of several broad powder patterns often prevents the separation necessary for their individual identification and measurement.
Recognizing that an equivalent of the hopping experiment could be achieved without stopping the sample, Gan has recently demonstrated an elegant technique that employs pulses spaced at one-third of the rotor period to produce 2D spectra with an isotropic shift projection along the evolution dimension and an undistorted slow-spinning-sideband powder pattern in the acquisition dimension. The pulse sequence produces an isotropic shift dimension completely free of sidebands even in the slow-spinning regime. Because it requires only a slow continuous rotation of the sample, Gan's experiment is much easier to perform than the hopping experiment. However, in the process of projecting the magnetization onto the longitudinal axis twice during the rotor period, only one-fourth of the magnetization is retained and the sensitivity of the experiment is reduced accordingly. Described here is a technique which uses the same slow rotation of the sample about an axis at the magic angle, but instead applies five pi (180º) pulses to the magnetization Precessing in the transverse plane. The pulse sequence produces a result similar to that of Gan's experiment without the sacrifice of any magnetization to projections out of the transverse plane. This "5p" pulse method can be viewed simply as a constant-time version of Gan's experiment, with resultant advantages and disadvantages to be discussed.
Maswadeh, W.; Arnold, N.S.;
McClennen, W.H.; Tripathi, A.; DuBow, J. and Meuzelaar, H.L.C.
Energy & Fuels, 7 (6):1006-1012, 1993. Funded by ACERC.
A CO2 laser Py-GC/MS system capable of identifying substantial numbers of pyrolysis products from single coal particles in the 50-15-µm range is reported. Also, a specially designed two-wavelength radiation thermometer module with integral video microscope produces reliable temperature/time profiles of single coal particles during rapid laser heating. A novel microbeam footprint technique using thin quartz wafers in combination with videomicroscopy greatly facilitates laser beam focusing and alignment operations. Comparison of an EDB type particle levitator with an EM grid type particle support system reveals considerable advantages of the EM grid approach with regard to tar collection efficiency, particle position stability, particle visualization, and recoverability of residual char particles. However, possible cooling effects of the grid on highly thermoplastic particles require further study. The feasibility of simulating PCC conditions with regard to heating rates and final particle temperatures is demonstrated with complete devolatilization of 100 µm diameter particle being observed within 10 ms. The nature and relative abundance of major pyrolysis products observed at typical laser heating rates (>=105 K/s) are found to be closely similar to those observed with Curie-point pyrolysis techniques at heating rates in the 10²-10³ K/s range. Spherocarb particles of approximately 102-µm diameter, e.g., impregnated with suitable coal tar compounds are shown to provide useful model samples for system optimization and calibration purposes.
Maswadeh, W.; Tripathi,
A.; Arnold, N.S.; DuBow, J. and Meuzelaar, H.L.C.
Journal of Analytical and Appl. Pyrolysis, 1993 (in press). Funded by
ACERC.
A high speed, two-wavelength radiation thermometer that is capable of monitoring the surface temperature of 50-150 µm diameter particles in the 600-2000 K range at heating rates of up to 106 K/s, characteristic of pulverized coal combustion, was designed and constructed. To meet the above characteristics, special attention was paid to detector wavelength range and speed, detection electronics and optical system alignment. The thermometer was calibrated using an in-house constructed, black cavity radiation source. Spherocarb model particles, which have a more uniform size; physical properties and emissivity than coal particles, were used to demonstrate the level of short-term reproducibility attainable. Consistent, reproducible temperature-time profiles obtained for particles from different coals indicate that non-grey effects do not dominate these measurements.
Keogh, R.A.; Hardy, R.H.;
Taghizadeh, K.; Meuzelaar, H.L.C. and Davis, B.H.
Fuel Processing Technology, 1993 (in press). Funded by US Department
of Energy.
The mobile component of western Kentucky coals were extracted and analyzed by conventional methods and Curie-point mass spectroscopy. The liquefaction of the parent coals, extracted coals, and blends of the extracted coals plus mobile components indicated that the absence of the mobile component generally decreases the observed conversions obtained. The results also show that, in general, blending the mobile component and extracted coal also produces lower conversions than those obtained from the parent coal. These data suggest that the location of the mobile component in the pore structure of the coal is as important as the presence of the mobile component in coal conversion.
Dong, J.-Z.; Vorkink, W.P.
and Lee, M.L.
Geochimica et Cosmochimica Acta, 57:837-849, 1993. Funded by Gas Research
Institute.
A coal-bed wax was fractionated and analyzed using capillary column GC and combined GC/MS. It was found that the major components in the wax were n-alkanes (55.6%), cyclic/branched alkanes (26.0%), and several homologous series of alkylbenzenes (5.7%). All alkylbenzene isomers (except 6-n-alky-m-xylene) were positively identified by comparison with the retention times and mass spectra of newly synthesized authenic standards. 5-n-Alkyl-m-xylene, 2-n-alkyl-p-xylene, 4-n-alkyl-m-xylene, 4-n-alkyl-o-xylene, 2-n-alkyl-m-xylene, and 3-n-alkyl-o-xylene were identified for the first time from geological sources. All of these long-chain alkyl compounds (e.g., n-alkylcyclohexanes, n-alkylbenzenes, n-alkyl-o-toluenes, n-alkyl-p-toluenes, and 5-n-alkyl-m-xylenes) have similar total carbon number distributions and maxima with a slight even over odd carbon number preference between C28-C30. Moreover, the carbon number distributions of these compounds resembled those of the n-alkanes found in the same wax with slight odd over even carbon preference between C-C27class="sub">31. This indicates that the alkylcyclohexanes and alkylbenzenes may have the same fatty acid precursors as the n-alkanes. The alkylcyclohexanes and alkylbenzenes could have been formed by direct cyclization and aromatization, while the n-alkanes could have been formed by decarboxylation of the straight chain fatty acids. This explanation is further supported by the identification of homologous series of tetramethyl-n-alkylbenzenes and pentamethyl-n-alkylbenzenes with relatively high abundances at C15, C16, and C18, and a fatty acid distribution with maxima at C16 and C18. Based on these findings, mechanisms for the conversion of fatty acids or alcohols to alkylcyclohexanes and alkylbenzenes are proposed.
Blackham, A.U.; Smoot, L.D.
and Yousefi, P.
Fuel, 1993 (in press). Funded by US Department of Energy, Morgantown
Energy Technology Center and ACERC.
Oxidation rates of large (5-10 mm) coal particles are required in the description of fixed- and fluidized-bed combustion, gasification and mild gasification processes. Yet, very little has been published regarding these rates. In this study, rates of oxidation of chars for six coals at various temperatures were measured in simple devices in air at ambient pressure: in a muffle furnace, a Meker burner, and a heated ceramic tube. Chars were first prepared from the coals in the Meker burner at comparable temperatures. Test variables were coal type, oxidation temperature, initial char particle mass and number of particles. Char particles were oxidized in incremental steps, each over several minutes for time periods up to one hour. The cube root of particle mass declined linearly with time in all tests. Ash layers formed and usually remained in place around the coal particle. Average mass reactivities increased with decreasing initial char particle mass. Decreasing furnace temperature decreased char reactivity at the lower temperatures. Two or four char particles, closely spaced, burned at much slower rates than single particles of the same size. Correlative methods are consistent with the data, which elucidate the roles of kinetic reaction and oxygen diffusion.
Hurt, R.H.; Fletcher, T.H.
and Sampaio, R.S.
ASME Journal of Heat Transfer, 115:717-723, 1993. Funded by Sandia Technology
Maturation Program.
In several development and commercial processes, coal particles come into direct contact with a high-temperature molten phase. These processes include molten carbonate coal gasification and bath smelting for the production of iron. Recently, real-time X-ray fluoroscopic images have been published that show volatile matter evolving rapidly from coal particles immersed in molten phases, displacing the surrounding melt and producing a periodic cycle of formation, rise, and detachment of gas cavities. The present work makes use of these observations to develop a model of heat transfer from the melt to particles undergoing gas evolution. The model is developed for the general case and applied to predict melt-particle heat transfer coefficients under conditions relevant to bath smelting processes. The model shows that the presence of the gas film can actually increase the overall heat transfer rate under certain conditions.
Fletcher, T.H.
Fuel, 72:1485-1495, 1993. Funded by Sandia National Laboratories and
ACERC.
Coal devolatilization experiments are commonly conducted at moderate temperatures (800 to 1300 K) and heating rates (10³ to 104 K/s) in inert environments in order to measure evolved species before secondary reaction in gas phase. However, chars from these experiments exhibit different physical characteristics than chars obtained under typical combustion conditions (1500 to 2000 K, 105 K/s, and 3 to 10 MOL% oxygen). Experiments were conducted in two laminar, entrained-flow reactors to determine characteristics of coal chars in inert and oxygen-rich environments. One flow reactor was heated electrically, with gas temperatures of 1250 K, and the mol% oxygen was varied from 0 to 10%. The other flow reactor used a flat flame burner as the heat source, with gas temperatures of 1600 K, and the post-flame oxygen content was varied from 0 to 12 mol%. In both reactors, sampling was limited to regions during and immediately following devolatilization. Five coals of different rank were examined; for a given coal, similar total volatile yields were obtained in both flow reactors, and similarities in chemical compositions of the resulting chars are discussed. For softening coals, the apparent densities of chars obtained in the electrically heated reactor are much lower than that of chars from the flat-flame reactor, regardless of the gas phase oxygen content. This implies that changes in particle swelling behavior between typical devolatilization experiments and char combustion experiments are not due to the pressure of oxygen, but to heating rate or post-flame gas species other than oxygen.
Alderman, D.W.; Sherwood,
M.H. and Grant, D.M.
Journal of Magnetic Resonance, 101:188-197, 1993. Funded by US Department
of Energy, Division of Chemical Sciences and Office of Basic Energy Sciences.
A measure of the difference between two chemical-shift tensors is developed by defining the scalar distance between them. Chemical-shift tensors are treated as functions whose domain is the surface of a sphere and the mathematical definition of the quadratic distance between two functions is invoked. Expressions for the distance between two chemical-shift tensors are developed in the Cartesian and irreducible spherical representations and in a new icosahedral representation. A representation wherein the chemical-shift tensor is specified by the shifts when the magnetic field is along six directions defined by the vertices of an icosahedron is developed and its properties are discussed. The expression for the distance between two tensors is found to be particularly attractive and useful in this icosahedral representation. The distance between tensors computed in the icosahedral representation is useful in fitting linear models to tensor data. It is shown how such fitting can contribute to the assignment of tensors obtained from single-crystal studies. A quantitative figure of merit useful for comparing multiple assignment possibilities is developed. The results derived are applicable to any physical phenomenon described by real zero-rank and second-rank tensors.
Hughes, C.D.; Sherwood,
M.H.; Alderman, D.W. and Grant, D.M.
Journal of Magnetic Resonance, 102:58-72, 1993. Funded by US Department
of Energy.
Sample reorientation during the mixing time of a two-dimensional NMR exchange experiment allows the measurement of chemical-shift tensors in powdered samples whose one-dimensional powder patterns are too complex to reliably analyze. This technique has the advantages that the chemical-shift anisotropy has an unscaled representation, the artifacts caused by cross polarization, spin relaxation, and partial sample orientation can be accounted for, the experiment is relatively easy to perform, and no spinning sidebands interfere. The method is useful for sorting out the principal values of overlapping chemical-shift tensors.
Facelli, J.C. and Grant,
D.M.
Nature, 365:325-327, 1993. Funded by US Department of Energy, National
Institutes of Health, Utah Supercomputing Institute and the State of Utah.
Diffraction techniques have shown that the crystal structure of naphthalene has a unit cell with Ci symmetry. These studies were unable, however to resolve any departure of the molecular structure from the D2h symmetry observed in the gaseous state. We found recently that the solid-state C-13-nuclear magnetic resonance (NMR) chemical shifts for naphthalene exhibit the Ci symmetry of the unit cell. If these chemical-shift data reflect structural distortions of the molecule, rather than simply intermolecular effects on the shifts owing to the Ci symmetry of the environment of each molecule, one could assert that the NMR data are able to reveal structural information beyond the limits of the diffraction methods. Here we show that this is the case by performing ab initio quantum-mechanical calculations of the C-13 chemical shifts for naphthalene, and their derivatives, with respect to structural parameters. We find that intermolecular shift terms (which of necessity exhibit Ci symmetry) can account for only 30% of the maximum deviations from D2h symmetry; the remainder must therefore result from structural distortions of the molecules below D2h symmetry. This sensitivity of NMR chemical shifts to very small changes in molecular structure opens up the possibility of using solid-state NMR along with quantum-chemical methods to refine structural parameters obtained from diffraction methods.
Rasband, P.B. and Hecker,
W.C.
Journal of Catalysis, 139:55l, 1993. Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data from IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (+/-2) and an Ab value of 42 (+/-6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR. Rh dispersions were determined for Rh/SiO2 samples of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in nitrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
Fletcher, T.H.; Solum, M.S.;
Pugmire, R.J.; Grant, D.M.; Bai, S.; Ma, J. and Woods, S.
7th International Conference on Coal Science, Banff, Alberta, Canada,
September 1993 (in press). Funded by ACERC.
Structural characteristics have been determined for parent coals and for chars collected at different stages of pyrolysis. Recent work has focused on trying to understand the relationship between chemical structural features of the unreacted coal and the devolatilization and char oxidation phenomena. Models of coal devolatilization have recently related devolatilization behavior to the structure of the parent coal and the initial amount of pyridine extracts. Fong et al. used pyridine extraction methods to quantify the amount of metaplast formed during pyrolysis of a Pittsburgh #8 coal. These experiments demonstrated that under moderate heating conditions (~500 K/s to 873 K), as much as 80% of the initial coal was transformed into a combination of extractable material and volatiles. The work presented here is an examination of the pyridine extraction procedure of the Argonne Premium coal samples and the detailed study of the carbon skeletal structure of the extracts and the extraction residues from these coals. This is the first stage of an experimental program to examine the yield and chemical features of extracts of coal chars collected as a function of time during pyrolysis.
Pugmire, R.J.; Hu, J.Z.;
Alderman, D.W.; Orendt, A.M.; Ye, C. and Grant, D.M.
7th International Conference on Coal Science, Banff, Alberta, Canada,
September 1993 (in press). Funded by US Department of Energy and Pittsburgh
Energy Technology Center.
The chemical shift of a C-13 spin in a solid sample varies with the change of the relative orientation of the nuclei (or molecule) to the external magnetic field. This orientational dependence produces the well-known chemical shift anisotropy (CSA). The tensor values of the CSA provides a wealth of information about subtle differences in the electronic environment of the nuclei, such as the type of bond, the effects of electron devolatilization and the bond conformation as well as the dynamics of the nuclei. The principal values of the CSA can be obtained in a straightforward way when the molecule has only a few, e.g., 2-3 unique nuclei. In most substances, unfortunately, the overlap of the several broad powder patterns prevents the spectral separation necessary for individual carbon resolution and identification.
Pugmire, R.J.; Solum, M.S.;
Bai, S.; Fletcher, T.H.; Woods, S. and Grant, D.M.
Proceedings of the 205th ACS National Meeting, 38, no. 2, Denver, CO,
March 1993. Funded by ACERC.
The relationship between coal structure and combustion behavior is a matter of on-going research in our laboratories. A great deal of effort has gone into obtaining data that is used for modeling studies of devolatilization behavior. We have also carefully studied the process of char formation. Our past work has focused on trying to understand the relationship between coal/char/tar formation as they relate to the devolatilization and char oxidation phenomena. The formation of metaplast during pyrolysis was studied by Fong and Howard in terms of extractable material obtained at different stages of the devolatilization process. We have recently turned our attention to metaplast formation in devolatilization and plan to conduct a series of experiments that will help define the formation and chemical structure of metaplast in coals of different rank.
Pugmire, R.J.; Hu, J.Z.;
Alderman, D.W.; Orendt, A.M.; Ye, C. and Grant, D.M.
10th Annual International Pittsburgh Coal Conference, Pittsburgh, PA,
September 1993. Funded by US Department of Energy and ACERC.
The C-13 CP/MAS experiment has proven to be a powerful technique for obtaining high resolution spectra in complex solids such as coal. MAS narrows the chemical shift anistropy (CSA) to its isotropic shift when the sample spinning speed is greater than the anistropy. While the isotropic chemical shift is useful in characterizing chemical structure, the principal values of the chemical shift tensor provide even more information. These principal values are available from the powder pattern obtained from a stationary or slowly spinning sample. Unfortunately, the overlap of many broad powder patterns in a complex solid often prevents the measurement of the individual principal values.
Meuzelaar, H.L.C.
Proceedings of American Chemical Society Conference Fuel Division, ACS
Preprints, Fuel Chem. Div., 1993 (in press). Funded by ACERC.
Less than two decades ago a typical mass spectrometer was an extremely expensive and delicate instrument that would completely take up a moderately sized laboratory room. Few coal scientists or engineers had access to such an instrument and even fewer mass spectrometrists were willing to "contaminate" their instrument with something as complex and dirty as coal and its tar. Against this historic background it is nothing less than amazing that as early as 1966 Vastola et al. at Penn State University, using a finely focused ruby laser and a time of flight (TOF) mass spectrometer, already carried out laser pyrolysis experiments on coal samples inside the ion source. Joy et al soon followed their example. However, since Vastola's experiment was too far ahead of the state-of-the-art in signal processing electronics it would take more than 15 years before his group was able to obtain reproducible pyrolysis mass spectrometry (Py-MS) patterns from a series of PSOC coal samples.
Nie, X.; Lui, K.; Maswadeh,
W.; Tripathi, A. and Meuzelaar, H.L.C.
Proceedings ACS Conference Fuel Chem. Division, ACS Preprints, Fuel Chem.
Div., 1993 (in press). Funded by ACERC.
During the past decade marked progress has been made with regard to our understanding of the chemical processes occurring during the thermal degradation ("devolatilization," "desorption + pyrolysis") of coal and several advanced mechanistic models offering a qualitative and quantitative description of these processes, e.g., FG-DVC and CPD models, are now available. By contrast, there appears to be a comparative lack of progress in the description and understanding of the physical processes involved. It is becoming increasingly clear that the frequent lack of interlaboratory reproducibility almost invariably originates within the physical parameters of the experiment. Although heating rate, particle size and reactor pressure have long been recognized as the dominant physical parameters influencing the rates and product yields of coal devolatilization processes, current models pay little or no attention to heat and mass transport limitations. In fact, particle size is not an input parameter in these models. Furthermore, although most industrial scale coal devolatilization processes occur at near ambient pressures, current renewed interest in high pressure coal conversion processes would seem to dictate a more detailed look at the effects of pressure. The objective of the research reported here is to exploit the capabilities of two novel experimental techniques, based on the on-line coupling of microscale, TG-type reactors to mass spectrometry and combined gas chromatography/mass spectrometry systems. The TG/GC/MS technique has high-pressure TG capabilities and will be described separately at this meeting. The direct TG/MS instrument is characterized by a heated, all quartz interface and will be discussed here. The complementary nature of both systems enables us to investigate the nature and extent of physical control mechanisms over a broad range of experimental conditions.
Liu, K.; Jakab, E.; McClennen,
W.H. and Meuzelaar, H.L.C.
Proceedings of the 206th American Chemical Society National Meeting,
ACS Preprints, Fuel Chem. Div., 38 (3): 823-830, Chicago, IL, August 1993. Funded
by US Department of Energy.
Over 279 million automotive tires are discarded in the United States each year. These used tires cause serious environmental problems since they are non-biodegradable, occupy considerable landfill space, and emit noxious fumes when burned. One of the promising approaches to deal with used rubber is the co-processing of it with coal to produce hydrocarbon liquids for use as fuels and specialty chemicals. Recently there have been numerous studies on co-processing of tire rubber and coal since depolymerized rubber has good solvent properties and the carbon black which constitutes of about 20-30% of the rubber is a good catalyst for depolymerization and possibly enhanced coal liquefaction. Monitoring sample weight loss as a function of temperature with on-line analysis of the evolved products during the co-processing reactions is necessary to elucidate mechanisms and kinetics of the key conversion reactions. Due to the high pressure and high temperature required by some of the most interesting processes, it is difficult to continuously monitor the weight loss and reaction intermediates without interrupting the reactions.
On-line analysis techniques for high-pressure conversion reactions have been reported previously, but these systems did not monitor total weight loss vs reaction temperature. They also were not applied directly to coal conversion studies because of the strong potential for plugging of sample orifices with pulverized coal. Microscale simulation of coal conversion reactions has been performed by high-pressure thermogravimetry with on-line combined gas chromatography and mass spectrometry (TG/GC/MS). It requires only a small sample size and can be operated at high temperature and pressure. The weight loss and low molecular weight products can be monitored vs reaction temperature. Analysis of pyrolysis and hydropyrolysis of coal, rubber and coal with tire rubber, with our without catalyst, by high pressure TG/GC/MS are reported here.
Nie, X.; McClennen, W.H.;
Liu, K. and Meuzelaar, H.L.C.
Proceedings of the 206th American Chemical Society National Meeting,
ACS Preprints, Fuel Chem. Div., 38 (4), Chicago, IL, August 1993. Funded by
US Department of Energy.
It is well known that on-line analytical methods offer considerable advantages over conventional off-line procedures for fuel conversion processes. Although many on-line spectroscopic detection systems for thermal process reactors have been reported, they have had only very little application to high-pressure reactors. Therefore, relatively little is known about the precise pathways and intermediate products involved in high-pressure reactions. The application of real time, on-line chromatographic and/or spectroscopic techniques capable of throwing light on these processes is hampered by the high temperatures and pressures inside the reactor which complicate direct interfacing to standard analytical instruments.
Thermogravimetry (TG) can provide detailed information on thermally driven conversion reactions, especially when combined with on-line detection and identification techniques such as Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). However, high pressure TG systems have only recently become available for studying the basic pyrolysis and especially hydropyrolysis reactions involved in coal liquefaction, thus, the combined chromatographic/spectroscopic interfaces for such high pressure systems are only now producing results. Other high-pressure reactors of interest include those used to study the thermal processes in liquid fuels or in solvent-based coal conversion. Thus there have been recent reports of on-line GC/MS monitoring of a high pressure recirculating autoclave used to study coal derived liquid model compounds. Other work in our laboratory has examined the supercritical pyrolytic degradation of jet fuels with on-line GC/IR/MS. Several of these systems have involved the use of a patented automated vapor sampling (AVS) inlet with short column or so-called "transfer line" gas chromatography (TLGC) with MS or FTIR.
This paper presents the experimental descriptions and results from three high-pressure systems using a variety of components. The first is a high pressure TG/GC/MS system used to study coal hydropyrolysis. The other two use quartz-tubing reactors to examine the liquid and gaseous products from the thermal decomposition of jet fuels.
Hars, G.; Arnold, N.S. and
Meuzelaar H.L.C.
Proceedings of the 41st ASMS Conference on Mass Spectrometry and Allied Topics,
San Francisco, CA, May 1993. Funded by US Army Research Office.
Extensive analytical interest in characterization of particulate matter extends in many applications to evaluation of individual micro-particles. For complete chemical characterization of individual microparticles adequate measurements of both particle physical characteristics (e.g., size, mass) and chemical constituents are required. Like molecular species, particles may also be readily ionized and manipulated by electrical techniques based on mass to charge ratios. An approach favored by the authors would provide an accurate mass determination that could be followed by laser pyrolysis (ionization) mass spectrometry to determine the chemical composition. Both measurements can be carried out in the same ion trap but they require different electrical operating conditions. For particle mass determination the ion trap operates as an Electrodynamic Balance (EDB) while the compositional analysis is performed in the Ion Trap Mass Spectrometer (ITMS) mode. For macro-ions and submicron particles the distinction between ions and charged particles may become blurred making it profitable to consider the ability to make mass measurements of individual submicroparticles based on optical detection techniques.
Cope, R.F.; Swensen, M.R.
and Hecker, W.C.
Proceedings of 7th Annual International Conference on Coal Science, Banff,
Alberta, Canada, September 1993. Funded by US Department of Energy and ACERC.
Many researchers have studied the impact of mineral catalysis, particularly by CaO, on the low-temperature (<=750 K) oxidation rates of synthetic and low rank coal-derived chars. Fewer have studied Ca effects during high-temperature (>=1300 K) char oxidation. The objectives of this ongoing study are to determine (1) the significant of CaO catalysis during the oxidation of a lignite char at both high and low particle temperatures, and (2) the effect of high-temperature burnout level on oxidation rates and CaO catalysis. Three char series, with and without potentially catalytic metal ions, were prepared. High-temperature rates and particle temperatures were measured for each in a drop-tube reactor. Low-temperature (intrinsic) rates and activation energies were determined using isothermal TGA. Changes in char densities and surface areas (N2, CO2, and CaO) were also measured and related to changes in the observed oxidation rates.
Gale, T.K.; Bartholomew,
C.H. and Fletcher, T.H.
Proceedings of the International Conference on Coal Science, Banff, Canada,
September 1993. Funded by ACERC.
Coal combustion consists of basically two main steps: 1) pyrolysis and oxidation of the liquid and volatile matter, and 2) subsequent oxidation of the residual porous char matrix. Char oxidation is the slower of these two steps and is difficult to bring to completion. Pyrolysis significantly affects the resulting char structure, porosity, internal surface area and chemical composition (e.g. H/C ratios) and hence the char oxidation rate. A highly porous char particle is more accessible to reactant molecules and will, therefore, have a higher reactivity in the reaction zone influenced by pore diffusion. Under surface reaction controlled conditions, reactivity increases with increasing internal surface area and H/C ratio.
A number of different experimental methods and reactor types are currently used to produce chars for laboratory study. These different reactors typically operate under conditions that are quite reproducible from one run to another. However, variations in pyrolysis conditions from one method to another and from one reactor type to another may be large. Comparisons of data obtained in different laboratories are often rationalized by matching experimental conditions thought to be most critical such as temperature and residence time, or temperature and total volatiles yield. However, comparing chars at the same residence time or the same mass loss may not be valid, because at different heating rates and/or gas-phase oxygen concentrations, the chemical and physical nature of the pyrolysis will vary.
The objective of this research was to determine effects of variations in pyrolysis conditions on char structure and reactivity for a group of chars prepared from coals of low to high rank. Heating rate, temperature, residence time, and gas atmosphere during pyrolysis were the main variables in the study.
Pugmire, R.J.; Solum, M.S.;
Fletcher, T.H. and Grant, D.M.
The 5th Australian Coal Science Conference, Melbourne, Australia, March
1993. (Also presented at the 5th Australian Coal Science Conference,
Melbourne, Australia, November, 1992.) Funded by ACERC.
In contrast to previous efforts where coal-general devolatilization model input parameters describing chemical structure are adjusted to force agreement between predicted and measured tar and total volatiles yields, coal-dependent chemical structure coefficients for the Chemical Percolation Devolatilization (CPD) model developed by the authors and others are taken directly from C-13 NMR analyses of parent coals. This procedure, outlined in the paper eliminates most adjustable parameters from the model, and predictions of tar and total volatiles yields become true tests of the model and the NMR data, rather than mere results of curve fitting. Resulting model predictions of tar and total volatiles yields as a function of coal type, temperature, heating rate, and pressure comparable with available experimental data, showing the value of both the model and the NMR chemical structure data.
Mohr, J.W.
Gas Phase Velocity Measurements in an Industrial Scale Coal-Fired Boiler,
M.S./BYU, August 1993. Advisor: Cannon
Oettli, M.C.
Analysis of Gas and Particle Composition in a Full-Scale Utility Power Station,
M.S./BYU, April 1993. Advisor: Cannon
Pyper, D.K.
The Study of Non-Swirl and Swirl Non-Premixed Flame Stability Near Lean Blow
Out and the Design of a Research Combustion Facility, M.S./BYU, December
1993. Advisor: Hedman
Sanderson, D.K.
Composition of Combustion Gases and Particles in a Pulverized Coal-Fired
Reactor, M.S./BYU, April 1993. Advisor: Germane
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